LIFE PROCESSES - Weebly · movements are a major criterion which distinguishes living beings from the non-living ones. Movements are taking place all the time. Movements. Changes

DEEPAK SIR 981129104 X LIFE PROCESSES

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LIFE PROCESSES

It is very difficult to define life and living beings. Life is a self regulated complex system of molecules where chemical reactions are

going on all the time that lead to its maintenance, growth, responsiveness and reproduction. Living beings are organised self regulated

discrete entities which exhibit the various characteristics of life like movements, growth, responsiveness and reproduction. Self sustained

movements are a major criterion which distinguishes living beings from the non-living ones. Movements are taking place all the time.

Movements. Changes in position are called movements. Living beings show both visible and invisible movements.

Visible movements are changes in position of body parts which can be detected by human eyes. Animals show two types of visible

movements, locomotion and movement of body parts. In locomotion an organism moves from one place to another. Running of dog,

flying of a bird and swimming of fish are movements of locomotion. They are performed by animals for obtaining food, shelter and mate.

Cud chewing by cow* shouting and gesturing by a man in street are movements of body parts. They are carried out in connection with a

particular function. Some of these continue even in sleep, e.g., breathing, heart beat.

Plants do not show locomotion. They are fixed. Visible movements are slow with the exception of plants like Mimosa pudica (Sensitive

Plant, "Touch-me-not") which show folding of leaves on being touched. Breathing movements are absent in plants. They show bending

movements towards light and water. Sunflower head moves from east to west alongwith the sun. Leaves orientate to receive optimum

light.

Invisible movements are those changes in position which cannot be observed by human senses because they occur at the molecular level,

e.g., entry of nutrients into cells or release of wastes from tliem. Molecular movements are basic to living. They are essential as all

protoplasmic structures are made of molecules. They take part in biosynthetic activity for repair and replacement. Energy required for

functioning of protoplasmic structures is also obtained horn molecules. Wastes are also molecular in nature. Organisation of cells into

tissues, tissues into organs and organs into organ systems is dependent upon the movement or molecules. Thcrcfore , molecules must

move into and out of them all the time. Viruses are also made of molecules. However, they show molecular movements only inside their

host cells. Outside the host cells, molecular movements are absent in viruses. Therefore, viruses are considered to lie at the border-line

between the living and the non-living.

WHAT ARE LIFE PROCESSES Life processes are those basic functions of living beings which are essential for their survival. They are the same in all types of living

forms whether unicellular or multicellular, plants or animals. Energy is required by all of them.

1. Maintenance of Protoplasmic Structures. All living beings are made of protoplasmic structures. They have to be kept in functional

state whether an organism is active or inactive. Functional state of protoplasmic structures is maintained only if they are kept in dynamic

state with breakdown and buildup processes going on simultaneously.

2. Metabolism. It is the sum total of all chemical reactions which occur in a living being due to interaction amongst its molecules. All

functions of organisms are due to metabolism. Metabolism has two components, anabolism and catabolism. Anabolism or constructive

metabolism consists of build-up reactions where complex molecules are formed from simpler ones, e.g., formation of glycogen from

glucose or proteins from amino acids. Energy is required for anabolic reactions. Catabolism or destructive metabolism consists of

breakdown reactions where complex substances are broken down into simpler substances, e.g., respiration (breaks glucose into carbon

dioxide and water).

3. Nutrition. It is the process by which living beings procure food for obtaining energy and body building materials. Body building

materials are usually carbon-based so that food sources are also carbon based. They are, of course, varied. Plants manufacture their own

food in the process of photosynthesis. Animals obtain food from outside. Food obtained from outside is first broken down into simpler

soluble substances for absorption. Inside the cells, the simple substances are converted into various complex biochemicals to form

components of protoplasm. Some biochemicals function as respiratory substrates.

4. Respiration. Every living being requires energy for working of body machinery, its maintenance, repair, replacement and biosynthesis.

Energy is obtained by breakdown of carbon based molecules in the process of respiration. Oxidation-reduction reactions are common

chemical reactions involved in respiratory breakdown of molecules. Most organisms use oxygen obtained from outside for the process of

respiration.

5. Growth. It is irreversible increase in body size that occurs in young organisms prior to reaching maturity. Plants have the ability to

continuously grow. Growth is possible if build-up reactions (anabolism) are more abundant than breakdown reactions (catabolic

reactions). For this, the organisms must prepare or obtain food materials more than their requirement for maintenance.

6. Exchange ol Materials. There is a regular exchange of materials between the living organisms and their environment. Living beings

obtain nutrients, water and oxygen from their environment. They give out undigested materials, carbon dioxide and waste products.

Single-celled organisms have the entiresurface in direct contact with the environment. They do not possess any specific structures for

intake and expulsion of materials. Diffusion, facilitated transport and active transport are involved in movement of substances across the

cell membrane.

In multicellular organisms specialised structures have been formed for different functions, e.g., ingestion, egestion, exchange of gases.

7. Transportation. In multicellular organisms, all the cells are not in direct contact with the environment. They have specific structures

for exchange of gases, ingestion and digestion of food materials. However, every cell of the body has to be provided with food, water and

oxygen. Similarly, carbon dioxide and wastes have to be taken away from every cell. Therefore, a mechanism of transportation is found.

It is circulatory system in animals and vascular tissues in plants.


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8. Excretion. A number of waste products are formed as by-products of metabolism. They are usually toxic and are removed from the

body. The process of removal of waste products from the body is called excretion.

NUTRITION Nutrition is the process of procuring and utilisation of food. Food is the material substance which is used by living organisms for

obtaining energy and-raw materials to produce biochemicals required for body building, repair, growth, development and regulation. The

different components of food that have distinct functions like providing energy, materials for body building, maintenance and regulation

of metabolism are called nutrients.

They are of three main types — energy foods (e.g., carbohydrates, fats), body building foods (e.g., proteins, some minerals and

carbohydrates) and protective or regulatory foods (e.g., vitamins and minerals).

Importance of Nutrition/Food

1. Energy. Food provides energy. Energy is required by the body all the time, whether asleep, taking rest or doing work. It is because

biosynthetic activities must continue for replacing materials being consumed or degraded, j A number of other activities are going on all

the time. Heart is always beating. Breathing movements never stop. Food eaten by a person has to be digested and absorbed. Excretory

products are being produced.

2. Body Structure. All body components are built up of materials obtained from food.

3. Growth. Food is used in building protoplasm required for formation and enlargement of cells that take part in growth of the organism.

4. Repair. Food provides materials for replacement and repair of worn out or damaged structures.

5. Regulators. Hormones and enzymes are formed from ingredients of food. They regulate metabolism and body functions.

6. Resistance. Defence system of the body is formed from raw materials got from food.

7. Reproduction. Food provides materials to form reproductive structures.

Types of Nutrition

There are two main types of nutrition, autotrophic and heterotrophic. Green plants, some protists and bacteria are able to manufacture

their own food from inorganic raw materials with the help of energy obtained from outside. They are autotrophs and nutrition performed

by them is called autotrophic or holophytic nutrition. Animals, fungi, protozoans and many prokaryotes obtain food readymade from

outside sources as they cannot synthesise their own food. They are called heterotrophs and the mode of nutrition carried out by them is

termed as heterotrophic nutrition.

Autotrophic or Holophytic Nutrition

It is a mode of nutrition in which organisms are able to build up their own organic food from inorganic raw materials with the help of

energy. The organisms performing autotrophic nutrition are called autotrophs. Autotrophic nutrition is of two types, chemosynthesis and

photosynthesis. In chemosynthesis the energy used in synthesis of organic food is obtained by oxidation of substances present in the

surrounding medium, e.g., Nitrobacter (nitrifyingbacterium), Ferrobacillus (iron bacterium). In photosynthesis the energy is got from

solar radiations trapped with the help of pigments like chlorophyll.

Importance

1. Organic Food. Photosynthesis is the only process which produces organic food from inorganic raw materials. All organisms of the

world are dependent upon this organic food. Plants, which manufacture food, are called producers. Others, which are directly or indirectly

dependent upon plants for food, are known as consumers.

2. Energy. Photosynthesis converts solar energy into chemical energy. The whole living world uses this chemical energy for all the

functions.

3. Fuels. Wood, coal, petroleum and natural gas are all products of photosynthesis.

4. Carbon Dioxide. Respiration and combustion add carbon dioxide into environment. By using carbon dioxide, photosynthesis helps in

maintaining the concentration of the gas in the environment.

5. Oxygen. It supports life and combustion on earth and is, therefore, being continuously consumed. Photosynthesis is the only process

known to release oxygen into the atmosphere.

6. Useful Articles. A number of plant products produced as a result of photosynthetic activity are used in our daily life, e.g., timber, oil,

fibres, drugs, resins, rubber, etc.

Photosynthesis (Gk. photos- synthesis-putting together)

Photosynthesis is a biochemical process of manufacture of organic food from carbon dioxide and water

with the help of solar energy inside chlorophyll containing cells. Oxygen is liberated. Simple

carbohydrate or sugar (e.g., glucose) is the main product from which other organic substances are

formed . Excess of glucose is stored as starch to function as internal energy reserve to be used as and

when required. It is similar to storage of glycogen as energy reserve in our body. Most of the

photosynthesis occurs in leaves which are green in colour due to chlorophyll. Small amount of

photosynthesis also takes place in young green stems.


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chloroplasts are found as green dots in the palisade and spongy cells of mesophyll. Epidermis is devoid of chloroplasts except for guard

cells of stomata. A chloroplast has a double membrane envelope, a crystallo-colloid matrix or stroma and a number of membrane covered

flattened sacs called thylakoids. Thylakoids are small and stacked at places to form grana (singular granum). They are connected to one another by intergranal or stroma thylakoids. Thalakoids are centres of light reaction as photosynthetic pigments are located in their membranes. Dark

reaction occurs in the stroma region.

Leaf is most suitable for photosynthesis as it has a large surface area for harvesting sunlight, numerous stomata for exchange of gases and abundant

vascular supply for bringing in water and taking out manufactured food materials.

Most of the experiments of photosynthesis are based on the fact that starch is the end product of photosynthesis. It develops a blue-black colour with

iodine solution (I + KI solution). Starch is, however, only temporarily stored in leaves. It is converted ultimately into sucrose and transported to various

parts of the plant for use and storage. Leaves become completely destarched within 2-3 days after the stoppage of photosynthesis.

2. Carbon Dioxide. Land plants obtain it from atmosphere while aquatic plants absorb the same from water. Atmosphere contains about 0-036% carbon

dioxide. It enters the leaves through stomata. Stomata function as turgor-operated valves. Their guard cells are thicker on the inner side and thinner on

the outer side. K+ ion influx causes them to swell up and get curved out and produce a pore in between. Efflux of K+ ions causes closure of stomata.

Stomata generally remain open during the daytime. As carbon dioxide is used internally in photosynthesis, more of it diffuses from outside. During day

time the leaves can also use a small quantity of carbon dioxide produced internally through respiration. Requirement of carbon dioxide is only for the day

when photosynthesis is occurring. At night the carbon dioxide evolved in respiration remains unutilised.

During evening and early morning, when light intensity is low, the rate of photosynthetic utilisation of carbon dioxide may just balance respiratory

release of the gas. At this time the leaves neither obtain carbon dioxide from outside nor release the gas. The light intensity wherein the

photosynthesizing organ neither absorbs carbon dioxide nor releases the same is called compensation point. During night when carbon dioxide is not

required for photosynthesis, the stomata get closed (l:ig. 1.5). This prevents loss of water through transpiration.

Oxygen is Evolved During Photosynthesis.

Apparatus. A larger beaker (1 litre capacity), Short stemmed small funnel, Test tube, Soda bicarb (NaHC03), Fresh aquatic plant like Hydrilla.

Procedure. Pour small quantity of water in a large sized beaker. Place a few fresh shoots of aquatic plant Hydrilla at the bottom of the beaker with cut

ends of the shoots kept upwardly. Invert a short stemmed small funnel over it. Pour water into the beaker well above the stem end of the funnel. Add a

pinch of soda bicarb. Invert a test tube full of water over the funnel. Check that water does not fall down in the test tube. Place the apparatus in sun light.

Observation. Bubbles of gas will be seen to come out of the cut ends of the shoots of the aquatic plant and collect in the test tube. As a result

water level begins to come down. When sufficient gas has been collected, take out the test tube, covering its mouth by thumb. Introduce a glowing

splinter in the test tube. It will burn brightly.

Inference. Bright burning of glowing splinter indicates that the gas evolved during photosynthesis of the plant is oxygen.

4. Light. It is the source of energy for photosynthesis. Light is visible part of the electromagnetic radiations. It has a wavelength of 390-760 nm.

Photosynthetically active radiations or PAR are 400-700 nm. Natural source of light is sun but artificial light can also provide energy to plants for their

photosynthesis. Plants absorb light mostly in violet-blue and red parts of visible light. Violet-blue light carries more energy as compared to red light.

Plants growing under shade of others receive mostly green and some violet light. They have lower rates of photosynthesis.

Light has two functions, photolysis of water and excitation of chlorophyll to emit electrons. Photolysis of water produces oxygen, protons and electrons.

Electrons and protons (Hydrogen ions) help in producing ATP and NADPH2, popularly called assimilatory power.

Mechanism of Photosynthesis

Basic Requirements of Photosynthesis

Photosynthesis has four basic requirements — chlorophyll, carbon dioxide, water and light. They are

also called raw materials of photosynthesis.

1. Chlorophyll. Plants possess pigment molecules for absorption of light energy. There are

three types of photosynthetic pigments

green chlorophylls, orange coloured carotenes and yellowish xanthophylls. Carotenes and

xanthophylls are collectively called carotenoids. Chlorophylls are of two main types, chlorophyll a

and chlorophyll b. Chlorophyll a is called primary photosynthetic pigment as it takes part in

conversion of light energy into chemical energy. Other pigments absorb light energy of various

wavelengths and hand over the energy to chlorophyll a molecules through resonance. Photosynthetic

pigments occur in green coloured cell organelles called chloroplasts. In a cross-section of a leaf,

Chloroplast.


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Photosynthesis is formation of organic food from carbon dioxide and water with the help of sunlight inside chlorophyll containing cells. Oxygen is

produced as by-product.

Oxygen comes from water. Hydrogen of water is used to reduce carbon dioxide to form carbohydrate.

1. Photochemical Phase (Light or Hill Reaction). The reactions of this phase are driven by light energy. They are of two types— photolysis of water and

formation of assimilatory power.

(a) Photolysis of Water. Light energy splits up water into two components. The step requires an oxygen evolving complex (formerly called Z-complex)

having manganese ions. Calcium and chlorine are also required.

(b) Formation of Assimilatory Power. Electrons released by photolysis of water are picked up by chlorophyll a molecules. On absorption of light energy,

each chlorophyll a molecule throws out an electron with gain of energy. This is primary reaction of photosynthesis which converts light energy into

chemical energy. Electrons travel along an electron transport system, releasing energy in the process. The energy is used in the formation of ATP

(adenosine triphosphate) from ADP and inorganic phosphate. Synthesis of ATP from ADP and inorganic phosphate (Pi) with the help of light energy is

called photophosphorylation.

ADP + Pi + energy -» ATP

The electrons ultimately activate NADP (nicotinamide dinucleotide phosphate) and make it combine with hydrogen to form NADPH2

Both ATP and NADPH2 together form assimilatory power.

2. Biosynthetic Phase (Dark or Blackman's Reaction). It is actually light independent reaction which can occur both in light as well as in dark. It requires

the energy and reducing power contained in assimilatory power of light reaction. Common pathway of biosynthetic phase is Calvin cycle. Carbon

dioxide combines with ribulose biphosphate in the presence of enzyme ribulose biphosphate carboxylase or rubisco. It produces two molecules of

phosphoglyceric acid (PGA).

In the presence of ATP, phosphoglyceric acid is reduced by NADPH2 to form glyceraldehydc phosphate (GAP).

A part of glyceraldehydc phosphate is changed into dihydroxyacctonc phosphate. The two condense and form glucose. Ribulose biphosphate is

regenerated to combine with carbon dioxide again. Glucose undergoes condensation to form starch. Synthesis of carbohydrates during photosynthesis is

a mechanism to form food materials for body building and meet energy requirements. Plants also require a number of other inorganic raw materials or

minerals from soil for building other biomolecules, e.g., nitrogen, phosphorus, iron, magnesium etc. Nitrogen is required for building proteins and many

other compounds. Phosphorus is required for synthesis of nucleotides.Minerals are absorbed in the form of ions, e.g., for nitrogen. Some bacteria convert

atmospheric nitrogen into organic compounds. Part of them can also be picked up by plants.

Differences between Light and Dark Reactions

■ Answers

1. It is a cyclic series of reactions that occur in stroma of chloroplasts in which ATP and NADPH2 produced during photochemical phase provide energy

and reducing power respectively for endergonic reduction of carbon dioxide to carbohydrate. ,

2. Nutrition is the process of taking in of food and its utilisation inside the body.

3. Food is material substance that is used by living beings in obtaining energy and biochemicals for body building, maintenance and regulation.

4. Nutrients are components of food having distinct functions like providing energy, forming regulators, repair and body building.

Light Reaction 1. Light. It is required for the reaction. 2. Conversion. The reaction converts light energy into chemical energy. 3. Chlorophyll .It is essential for the reaction. 4. Occurrence. It occurs in thylakoids of chloroplasts. 5. Products. Its products are ATP and NADPH2. 6. Oxygen. Oxygen is liberated as a by-product. 7. Electron Transport. Light reaction involves movement * of

electrons along a transport chain.

Dark Reaction It is light independent. The reaction uses chemical energy in building organic substances. Chlorophyll is not required directly. It occurs in stroma part of chloroplasts. Its main product is starch. It does not produce oxygen.

There is no involvement of an electron transport chain.

Very Short Answer Questions 1. What is Calvin cycle ?

2. Define nutrition.

3. What is food ?

4. Define nutrients.

5. Name two life processes.

6. Name the two types of nutrition.

7. What is autotrophic nutrition ?

8. What is autotroph ?

9. Name two types of autotrophic nutrition.

10. What is chemosynthesis ?

11. Define photosynthesis.

12. Name the raw materials of photosynthesis.

13. Name the primary photosynthetic pigment.

14. Which cell organelle is the seat of photosynthesis ?

15. Name the various types of photosynthetic pigments.

Short Answer Questions

16. Describe importance of nutrition.

17. How is photosynthesis important ?

18. Describe photochemical/light phase of photosynthesis.

19. What happens in biosynthetic or dark phase of photosynthesis ?

20. Differentiate light reaction from dark reaction.


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5. Nutrition, respiration.

6. Autotrophic nutrition and heterotrophic nutrition.

7. Autotrophic nutrition is one in which an organism is able to build up its own organic food from inorganic raw materials with the help of energy.

8. Autotroph is an organism which builds up its own organic food from inorganic raw materials with the help of energy.

9. Chemosynthesis and photosynthesis.

10. Chemosynthesis is a mode of autotrophic nutrition in which external energy required for synthesis of

organic food is obtained from chemical reactions.

1 1. Photosynthesis is the synthesis of organic food from inorganic raw materials with the help of light energy inside chlorophyll containing cells.

12. Raw materials of photosynthesis are carbon dioxide, water (hydrogen donor), light and chlorophyll (photosynthetic pigment).

13. Chlorophyll a as it converts light energy into chemical energy.

14. Chloroplast.

15. Chlorophylls (two main types, a and b), carotenes and xanthophylls.

1.2.2. Heterotrophic Nutrition

It is a mode of nutrition in which the organisms obtain ready-made organic food from outside sources. The organisms that depend upon outside sources

for obtaining organic nutrients are called heterotrophs (Gk. hetero or heteros— other, troph or trophe— nourishment). As the organic nutrients are

complex and insoluble, they are first broken down into simpler soluble substances with the help of digestive enzymes. The process is called digestion.

Heterotrophs are also called consumers (as they consume food prepared by others) in contrast to autotrophs which are known as producers (as they

prepare organic food from inorganic sources).

Differences between Autotrophic and Heterotrophic

Types of Heterotrophic Nutrition

Heterotrophic nutrition is of three types — saprophytic, parasitic and holozoic.

1. Saprophytic or Saprotrophic Nutrition. It is a mode of heterotrophic nutrition in which food is obtained from organic remains like dead organisms,

excreta, fallen leaves, broken twigs, food articles, etc. Organisms performing

saprophytic nutrition are called saprophytes (Gk. sopro or sopros— rotten, phyte or phyton— plant) or saprotrophs (Gk. sapros-toiten, trophe-

nouiishment).

Saprophytes pour digestive enzymes over Sporanglophore the external organic substrate. The enzymes cause breakdown of complex organic compounds

into simpler and soluble substances which can be absorbed by the saprophytes. Saprophytes perform external digestion (digestion outside the body).

Most of the saprophytes are fungi (e.g., Mushrooms, Morels, Bread Moulds, Yeast), several bacteria, a few animals (e.g., Chilomonas) and plants (e.g.,

Neottia, Monotropa). Saprotrophic nutrition of animals is called saprozoic nutrition.

importance

(i) Scavenging. Saprophytes function as scavengers as they remove the organic remains and create space for the newer generations of organisms. In the

absence of saprophytes the whole earth would have been littered with organic remains with no space left for the newer generations.

(ii) Biogeochemicals. Saprophytes bring about circulation of biogeochemicals. Biogeochemicals are inorganic raw materials which are absorbed from the

environment by producers to synthesise food. They are limited in supply. Unless and until biogeochemicals are made available to producers, further

manufacturing of organic food will stop. Saprophytes act on organic remains and release a major portion of biogeochemicals back into environment

during their external digestion.

(iii) Spoilage of Food. Saprophytes attack all types of exposed food articles (e.g., bread, jam, pickle, milk, vegetables, fruits) and spoil the same.

(iiO Food Poisoning. Some saprophytes secrete toxins over the food. It results in food poisoning, e.g., bacterium Staphylococcus aureus.

2. Parasitic Nutrition. It is a mode of heterotrophic nutrition in which a living organism flourishes by obtaining food from another living organism. The

living organism which obtains food and shelter from another organism is called parasite (Gk. para-other, site or sitos-food). The organism which

provides food and shelter to a parasite is known as host. The parasites which cause diseases are known as pathogens. They are of two types, ectoparasites

and endoparasites. Endoparasites or internal parasites live inside the body of the host. They belong to all groups of organisms. Plasmodium (Malaria),

Trypanosoma (Sleeping Sickness)

3. Holozoic Nutrition. It is a mode of heterotrophic nutrition which involves intake of solid pieces of food. Since solid food is taken in, holozoic nutrition

is also called ingestive nutrition. Holozoic nutrition (Gk. holo-who\e, zoon-amma\) is found in animals and protozoan protists. The food may consist of

another animal, plant or its parts. Depending upon the source of food, holozoic organisms are of three types — herbivores, carnivores, omnivores.

Herbivores (L. herba-p\am, vorare-to eat). They are holozoic organisms which feed on plants or plant parts, e.g., Cow, Buffalo, Deer, Goat, Rabbit,

Grasshopper, Elephant, Squirrel, Hippopotamus.

Nutrition Autotrophic

1. Food. It is self manufactured. 2. External Energy. An external source of energy is required for synthesis of food. 3. Inorganic Substances. They constitute the raw materials for manufacturing food. 4. Digestion. It is absent. 5. Chlorophyll. It is present for trapping light energy. 6. Status. Organisms performing autotrophic nutrition function as producers. Examples. Green plants, some bacteria, some protists.

Nutrition Heterotrophic Nutrition

Food is obtained ready-made from outside. An external source of' energy is not required. The required energy is present in the food obtained fjrom outside. Inorganic substances are not much required. An external or internal digestion is required for conversion of complex organic materials into simpler and soluble ones. Chlorophyll is absent. Organisms performing heterotrophic nutrition function as consumers. Animals, many protists and monerans.


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Carnivores (L. carne-flesh, vorare-to eat). They are animals which feed on other animals. Carnivores are also called predators as they hunt, kill and feed

on their preys, e.g., Lion, Tiger, Leopard, Snake, Hawk.

Differences Between Herbivores and Carnivores

Herbivores Carnivores

1. Food. Herbivores feed on plant parts. 1. They feed on other animals.

2. Predation. There is no predation as the plants are 2. Predation is involved as the prey trees to escape, defenceless and stationary.

Ex. Cow, Buffalo, Deer. Ex. Leopard, Tiger, Lion.

Omnivores (L. omnis—all, vorare-to eat). They are holozoic organisms which feed on both plant and animal materials, e.g., Cockroach, Ant, Pig, Crow,

Rat, Bear, Dog, Humans.

A fourth category of holozoic organisms is detrivores. Detrivores (L, detritus— dead, vorare-to eat) are animals which feed on dead bodies of other

animals. They are also called carrion feeders or scavengers, e.g., Vulture, Hyaena, Kite.

Holozoic Nutrition That type of nutrition in solid food is taken in.

Steps in Holozoic Nutrition

There are five steps in holozoic nutrition — ingestion, digestion, absorption, assimilation and egestion.

1. Ingestion (L. ingestus — taken in). It is taking in of solid food with the help of temporary or permanent mouth. Different animals use different organs

for catching, holding and putting the food into mouth. Gutting and tearing the solid food into small pieces is common for ingestion.

2. Digestion. The ingested food is solid. It consists of complex insoluble organic ; ' substances. The conversion of complex insoluble food ingredients

into simple absorbable form is called digestion. It has two components, physical and chemical. The physical process consists of breaking food into finer

particles through chewing and grinding by means of teeth. It is meant for providing larger surface area for chemical action. The chemical process

involves actual conversion of insoluble food materials into soluble form with the help of digestive enzymes. It is a catabolic process. Digestion can be

intracellular or intercellular. Intracellular digestion is found in protozoan protists {e.g., ^Amoeba, Paramecium), simple animals and certain cells of

higher animals {e.g., macrophages, monocytes). Here the ingested food particle is digested in a food vacuole. In higher animals the ingested food is taken

to a digestive tract where digestive enzymes arc poured over it. As it occurs outside the cells, the digestion is intercellular or extracellular, e.g., fish, frog,

lizard, lion, human.

3. Absorption. The digested food is absorbed from the digestive tract and transported to all body parts. It is picked up by all the living cells.

4. Assimilation. It is conversion of absorbed food into protoplasmic constituents for repair, growth and storage. Assimilation is an anabolic process as it

takes part in synthesis of proteins, polysaccharides, fats and other macromolecules.

5. Egestion (L. egestus-discharge). The whole of ingested food is seldom digested. The undigested components of food are thrown out of the body as

faecal matter. The process is called egestion.

How Do Unicellular Organisms Carry out the Process of Holozoic Nutrition

Protozoan protists carry out holozoic nutrition through intracellular digestion. They are generally omnivores as they feed on microscopic algae, bacteria,

other protozoa and particles of decaying organic matter.

(i) Ingestion. Some protists can ingest food particle from any point on the surface {e.g., Amoeba) while others have fixed points for the same (e.g.,

Paramoecium). Protozoans like Amoeba capture food with the help of temporary finger-like processes called pseudopodia. Protozoans

like Paramoecium have small hair-like processes called cilia. Beating of cilia creates current in water that pushes food particle through cytostome or cell

mouth. The process of ingestion of solid food particle by a cell or unicellular organism is called phagocytosis.

As soon as Amoeba comes in contact with a food particle or prey, it throws pseudopodia all around the same. The tips of encircling pseudopodia fuse and

the prey comes to lie in a vesicle or phagosome . This method of intake of food is called circuiuvallation . Amoeba can also ingest food by other methods

like-import, circumfluencc and invagination.

(ii) Digestion. A lysosomc fuses with phagosome to produce a food vacuole, also callcd gestriole or stomach. food vacuole does not remain stationary.

It circulates in cytoplasm due to cyclosis or streaming movement of cytoplasm. Reaction ol lood vacuole is acidic at first and alkaline later on. Digestion

ol tood occurs with the help of digestive enzymes brought by lysosomc. It changes complex insoluble substances of lood into simpler absorbable

substances.

(iii) Absorption. The digested simple and soluble substances pass out of food vacuole into the surrounding cytoplasm.

(iv) Assimilation. The absorbed food materials are converted into various constituents of protoplasm including food reserve.

(v) Egestion. The old food vacuole with heavier undigested material reaches the rear end, passes to the surface, fuses with surface membrane and throws

out the undigested materials. The process is called egestion. Paramoecium has a definite cytopyge or cell anus.


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Nutrition in Human Beings

Human beings are omnivorous in nutrition. Like other multicellular animals, humans have a digestive system for nutrition. Digestive system is a group of

organs and associated digestive glands that take part in ingestion of food, its crushing digestion, absorption of digested materials and egestion of

indigestible matter. The digestive organs form a continuous canal called alimentary canal. It contains a number of digestive glands of its own. Three

types of external glands also pour their secretion into alimentary canal. They are salivary glands, liver and pancreas. Digestion is extracellular, i.e.,

outside the individual cells in the lumen of alimentary canal.

Alimentary canal (L. alere-w nourish) is a tubular passage extending from mouth to anus through which food passes during its digestion and absorption.

It is about 9 metres in length. Alimentary canal consists of mouth, buccal cavity, oesophagus, stomach, small intestine, large intestine and anus.

1. Mouth. It is a transverse slit or aperture that occurs in between the nose and the chin. Mouth is bounded by two soft, movable sensitive lips, upper and

lower. Lips are covered by skin on the outside and mucous membrane on the inner side. They help in holding the food. Lips also aid in phonation

(speech).

2. Buccal or Oral Cavity (L rWw-chcck). It is anterior part of alimentary canal that extends from mouth to pharynx and lies between two jaws, upper

(fixed) and lower (movable). It has palate on upper side, throat and tongue on the lower side and checks on the sides. Both the jaws contain teeth in

semicircular rows or arches.

(i) Tongue. It is a muscular, sensory, movable and protrusible flat structure which is attached posteriorly over the lower jaw. Tongue bears taste buds for

tasting the quality of food—sweet anteriorly, salt anterio-laterally, sour postcro-laterally and bitter posteriorly. It moves food in the buccal cavity lor

crushing under teeth, mixing with saliva and pushing the food during swallowing. Tongue cleans the teeth. It also aids in phonation (speech). It functions

as a movable spoon during drinking.

(ii) Teeth. They are hard structures which are used for cutting, chewing and crushing the food (physical digestion). They are partially embedded

insockets of jaw bones (thecodont). Teeth are made of ivory like substance called dentine. The exposed parts of teeth or crowns are covered by a shining substance called enamel . The type of teet are Incisors Canines Pre-molars Molars . ( Humans have two sets of teeth (diphyodont), deciduous and permanent. Deciduous or milk teeth occur in infants.) iii) Salivary Glands. Three pairs of salivary glands (saliva secreting glands) open into buccal cavity. They are parotid (below ears), sub-maxillary (at the angles of lower jaw) and sublingual (below tongue). About 1.0-1.5 litres of near neutral saliva is poured into buccal cavity every day. Saliva consists of mucus, water, lysozyme and enzyme ptyalin. (i) Due to presence of mucus and water, saliva makes the food soft and slippery for easy crushing and formation of bolus. Watering of mouth at the sight of a delicious dish or during eating a favourite dish is due to excessive secretion of saliva, (ii) Lysozyme is antimicrobial enzyme which kills bacteria by cleaving their walls (Withers et al, 2001). (Hi) The digestive enzyme ptyalin or salivary amylase acts on starch and glycogen of cooked food and changes the same into sweet sugar called maltose. Bread tastes sweeter if chewed for longer period because of this conversion. Normally 30-40% of starch is converted into dextrins and maltose by the action of salivary amylase.

Starch -----pitaylin- Maltose + Dextrins (iv) Saliva cleans the teeth, (v) It provides solvent for dissolving chemicals present in the food for knowing the taste of food, (vi) It keeps the buccal cavity, lips and tongue moist for proper phonation (speech).

Action on Food in Buccal Cavity. Food is moistened, crushed and partially digested in buccal cavity due to action of salivary amylase on starch. At the end it is rolled into a small ball or bolus. 2. Pharynx. It is a funnel-shaped common passage of respiratory and digestive tracts which is also connected with middle ear. At the end of mastication, nasal chambers are closed by the raising of uvula while glottis or opening of trachea is closed by the raising of larynx to come in contact with epiglottis. Masticated food enters pharynx in the form of bolus. Soon the muscles of pharynx contract to push the food into oesophagus. The act of pushing food into oesophagus is called swallowing (deglutition). 3. Oesophagus (Food Pipe). It is a narrow muscular distensible tubular part of alimentary canal that connects pharynx with stomach. It passes through neck, thorax and diaphragm. Length is about 25 cm. Oesophagus does not contain digestive glands. However, its wall secretes mucus for lubrication of passing food. Action of salivary amylase (ptyalin) over starch continues in oesophagus. In oesophagus the food is pushed towards stomach by a wave of alternate contraction and expansion called peristalsis. Peristalsis occurs all along the rest of the alimentary canal and helps in pushing the food forward. 4. Stomach. It has j-shapcd, widest, thick walled but distensible and muscular organ of the alimentary canal which lies in

the lelt upper part ol abdomen below diaphragm. It has a large number of branched and tubular gastric glands. The

secretion of gastric glands is called gestric juices it is secreated, by the presence of food, the sight, smell or even touch

ol favourite food can initiate secretion of gastric juice. Wall of the stomach undergoes periodic contraction. It churns the contained food and mixes it thoroughly with gastric juice. Gastric juice contains HCl, mucus, pepsin, gastric lipase and rennin. Pepsin and rennin are secreted in their inactive states of pepsinogen and prorennin. HCl (hydrochloric acid) has five functions (i) It softens the food (ii) HC1 makes the food acidic (pH 1-2) for proper functioning of pepsin. (iii) HCl stops the action of salivary amylase, (iv) It kills germs and bacteria so as to disinfect food, (v) HCl converts inactive pepsinogen and prorennin into active pepsin and rennin. Pepsinogen – HCl-- Pepsin Prorennin --- HCl---> Rennin Pepsin is a major enzyme of gastric juice which functions in acidic medium (pH 2-0-3-5). It hydrolyses proteins into soluble fragments called proteoses and peptones. The enzyme gastric lipase is active in infants. It partially breaks down fat into its components. Rennin is also active only in infants. It curdles the milk by converting soluble milk protein casein into insoluble protein called paracasein. As a result milk stays in stomach for longer period for the pepsin to act on it.


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Excessive secretion of gastric juice, especially HCl causes corrosions in the wall of stomach to form open depressions called peptic ulcers. Bacterium Helicobacter pylori resides in these ulcers. Peptic ulcers are highly painful. 5. Small Intestine. It is the longest part of the alimentary canal. The length depends upon the feeding habit, being longer in herbivores (due to higher bulk of vegetal matter) and comparatively shorter in carnivores (due to smaller bulk of animal food). In human beings, it is about 6 metres in length and 2-5-3-5 cm in diameter. It is extensively coiled to get accommodated in small space. Small intestine is known so because it is narrower as compared to large intestine. It is the scat of major digestion and absorption. For this it possesses a number of intestinal glands. The secretion of intestinal glands is called succus cnteiicus. The first part of small intestine also receives secretion of liver and pancreas. Intestinal wall is thrown up into numerous folds having finger-like projections called villi. Villi increase the surface area for absorption of digested food. Intestinal glands are mostly present at the bases of villi. Small intestine is differentiated into three parts — duodenum, jejunum and ileum. (i) Duodenum. It is proximal part of small intestine which receives partially digested acidified food from stomach. Duodenum forms a U-shaped loop with stomach. It is about 25 cm in length. Duodenal glands secrete an alkaline, mucus containing juice that helps in neutralising the chyme and protect the wall from corrosion. A common hepatopancreatic duct opens into duodenum. It is formed of a common bile duct from liver and gall bladder and a pancreatic duct from pancreas. Common bile duct brings a yellowish green bitter liquid or bile from gall bladder (5 times more concentrated) and liver. Bile is alkaline due to presence of alkaline inorganic salts (mostly bicarbonates of Sodium and Potassium). Other components of bile are bile pigments (green biliverdin and yellowish bilirubin) and bile salts (sodium glycocholate and sodium taurocholate). A digestive enzyme is absent, (i) Bile neutralises the acidity of chyme and protects duodenal wall from corrosion, (ii) It makes the food alkaline for action of pancreatic juice. (Hi) It prevents putrefaction of food, (iv) A major function of bile is to break fat into fine globules for action of lipase of pancreatic juice. Breaking of fat into fine globules is called em unification. Pancreatic juice is the major digestive juice of the body. It is slightly alkaline. The juice contains three main enzymes — trypsin, amylase and lipase. Trypsin is proteolytic enzyme which functions in alkaline medium. It is secreted in inactive form of trypsinogen. Trypsin breaks down proteins, proteoses and peptones to form peptides. Pancreatic lipase (steapsin) is the main fat digesting enzyme. It acts on emulsified fat to form fatty acids and glycerol. Pancreatic amylase (amylopsin) acts on starch, glycogen, dextrins and other complex carbohydrates to form maltose and other similar sugars. Amylase lipase trypsin

Starch + Dextrins -» Maltose Fat -> Fatty acids + Glycerol Protein + Proteoses + Peptones-» Peptides

Liver. It is the largest gland of the body which weighs about 1-5 kg or 1/40 weight of the body. Liver lies in right upper side of abdomen. It is soft and

reddish brown in colour. Liver has two lobes, larger right lobe and smaller left lobe. A pear shaped yellowish green sac or gall bladder is attached on the

inferior surface of right lobe. Gall bladder concentrates and stores bile. Bile is secreted by liver. Liver has some 500 functions. The most important ones

are (i) Storage of glycogen, (ii) Removal of amino group (—NH2) group from surplus amino acids and combining it with CO2 to form urea. (Hi)

Formation of glucose from excess organic acids, (iv) Storage of iron. (v) Storage of vitamins— A, D, E, B12. (vi) Synthesis of vitamin A from carotene,

(vii) Secretion of blood anticoagulant named heparin, (viii) Synthesis of blood or plasma proteins, fibrinogen and prothrombin. (ix) Destruction of some

worn out blood carpuscles (major destruction by spleen.) (x) Decomposition of haemoglobin released from broken down red blood carpusches. (xi)

Secretion of bile, (xii) Detoxification of harmful chemicals.

Pancreas. It is the second largest gland of the body which is heterocrine in nature. Pancreas is a diffused gland of 12-15 cm length that lies in the loop of

duodenum and below the stomach. Pancreas secretes a digestive fluid called pancreatic juice. The secretion is major digestive juice of the body as it has

enzymes for hydrolysing all types of food ingredients. The enzymes are trypsin, chymotrypsin, carboxypeptidases, nucleases, pancreatic lipase and

pancreatic amylase. Pancreas also produces two types of hormones, insulin and glucagon. Insulin is essential for utilisation of glucose by cells and its

conversion into glycogen for storage. Glucagon is required for conversion of glycogen into glucose. (ii) Jejunum. It is middle coiled part of small intestine which is 1-5-2-0 metres in length. It has abundant digestive glands producing major part of intestinal juice or succus entericus. Jejunum is the seat of maximum digestion. Enzymes of intestinal juice complete the process of digestion, e.g., erepsin or peptidases (peptides -> amino acids), invertase or sucrase (sucrose -> glucose + fructose), maltase (maltose -> glucose), lactase (lactose or milk sugar-> glucose + galactose).erepsin Peptides * Amino acids invertase Sucrose-> Glucose + Fructose maltase Maltose -> Glucose + Glucose Lactose

In stomach the food stays for 1-6 hours depending upon type of food — carbohydrate rich (1-2 hrs), protein rich (2-3 hrs), fat rich (3-6 hrs). During this period it is changed into partially digested pulpy mass called chyme. Chyme passes in small amounts into duodenum part of small intestine through a pyloric valve (at the end of stomach) guarded by sphincter (circular muscle). Water, glucose, alcohol, drugs and some minerals are absorbed in stomach. Functions of Stomach. (i) Temporary Storage. Stomach functions as a chamber for temporary storage of upto 2-3 It of ingested food, {it} Softening of Food. HCl of gastric juice softens the food. (iii) Disinfection. The germs are killed and the food is disinfected (iv) Churning. Stomach undergoes churning movements. This mixes the food with gastric juice. It also breaks the larger pieces of food into smaller particles, (v) Partial Digestion. Food is partially digested by enzymes contained in gastric juice, (vt) Absorption. Some soluble components of food are absorbed in stomach, e.g., glucose, alcohol, drugs, minerals (vii) Regulation of Passage into Intestine. Only finely broken partially digested pulpy food is allowed to pass into small intestine by pyloric valve of the stomach.


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lactase ->

Glucose + Galactose (iii) Ileum. It is the distal coiled part of small intestine. The length is about 4.0 metres. Digestive glands are fewer. However, villi are most abundant. Major function of ileum is absorption of digested food. Villi are suited for this function. A villus has one lymph vessel or lacteal, a number of blood capillaries and a covering of epithelial cells specialised for absorption. Absorption occurs by passive transport, active transport and cotransport. The absorbed fat is taken away by lacteal while other materials are taken up by blood capillaries for transport to the regions of storage and use. Glucose is stored as glycogen in liver and muscles. It also reaches every cell for absorption. Amino acids are absorbed by individual cells for assimilation. Excess amino acids are deaminated by liver. Fat is stored in adipose tissue. It is also absorbed by individual cells in small quantity. (6). large Intestine. It is a distal region of alimentary canal which is 1-5-1-8 metres long and 4-6 cm in diameter. It receives a semifluid mixture of undigested matter, mucus and water. Large intestine does not contain digestive glands. It is specialised to absorb water from slurry of the undigested matter to form semisolid faecal matter. Some heavy and toxic chemicals are poured over this faecal matter by wall of large intestine. Bacteria present in large intestine produce vitamins K and B which are also absorbed here. Large intestine has three parts— caecum, colon and rectum. (i) Caecum. It is a small pouch of about 6 cm diameter that lies at the junction of small and large intestine. Caecum gives out a narrow blind tubular lymphoid outgrowth of 8-9 cm length. It is called vermiform appendix. Both caecum and vermiform appendix are vestigial organs* in humans. Infection of vermiform appendix causes acute pain in the lower right part of abdomen. It is called appendicitis. Infected appendix is removed surgically without much delay. The practice is called appendectomy. (ii) Colon. It is longest, inverted U-shaped part of large intestine. Colon bears alternate sac-like swellings called haustra. There are four parts— ascending, transverse, descending and sigmoid. Colon absorbs water from undigested food and converts it into faecal matter. A number of bacteria reside in colon and feed on undigested matter. Some of them secrete B- and K-vitamins. Gas formation of alimentary canal is mostly due to these bacteria. (iii) Rectum. It is last part of large intestine which is broader than colon. The length is 13-15 cm. As the faecal matter collects in colon, the feeling of defaecation occurs. A proper posture helps in pushing the faecal matter into rectum from where it is eliminated or egested through an opening called anus. Normally the opening is guarded by an anal sphincter.

QUESTIONS 1. Define heterotrophic nutrition.

2. What are heterotrophs ?

3. Which types of organisms are called consumers ?

4. What is saprophytic nutrition ?

5. Define saprophyte.

6. What are biogeochemicals ?

7. What is a parasite ?

8. Define a pathogen.

9. What is holozoic nutrition ?

10. Name the various types of organisms on the basis of holozoic

nutrition.

11. Define a herbivore. What is carnivore ?

12. Which type of animal is called omnivore ?

13. Define digestion.

14. What is ingestion ?

15. Define egestion.

16. What is the mode of nutrition in Amoeba ?

17. What type of digestion occurs in Paramoecium ?

18. What is the function of lips in ingestion ?

19. Name the external digestive glands associated with digestive

system of humans.

20. Define digestive system.

21. When do deciduous teeth appear in infants ?

22. Name the types of permanent teeth.

1. Heterotrophic nutrition is that mode of nutrition in which the organisms obtain food from outside sources. 2. Heterotrophs are non-photosynthetic organisms that obtain organic nutrients from outside sources. 3. Heterotrophs are also called consumers because they consume organic food prepared by others. 4. Saprophytic nutrition is a mode of heterotrophic nutrition wherein food is obtained from organic remains. 5. Saprophyte is an organism that obtains its organic nutrients from organic remains. 6. Biogeochemicals are inorganic substances that are absorbed by producers for synthesis of organic food and which circulate repeatedly between the biotic and abiotic components of the environement, e.g., carbon dioxide, water, nitrogen, phosphorus, potassium, chlorine, zinc, calcium, etc. 7. Parasite is an organism that obtains food and shelter from another living organism (called host). 8. Pathogen is a parasite which causes disease in its host. 9. Holozoic nutrition is a type of heterotrophic nutrition which involves ingestion of solid pieces of food. 10. Organisms performing holozoic nutrition are of three types depending upon the source of food — herbivores, carnivores and omnivores. 11. Herbivore is a holozoic organism that feeds on plants or plant parts, e.g., Cow, Buffalo. 12. Carnivore is an animal that feeds qn other animals. 13. Omnivore is an animal that feeds on both plants and animals. 14. Digestion is the enzyme mediated breakdown of complex insoluble components of food into simple soluble and absorbable forms. 15. Ingestion is the intake of solid food by a holozoic organism through a temporary or permanent mouth. 16. Egestion is the process of passing out undigested components of food. 17- Holozoic. 18. Intracellular. 19. Holding of food during biting and crushing. 20. Salivary glands, liver and pancreas. 21. Digestive system is a group of organs and their associated digestive glands that take part in ingestion, digestion, absorption of digested food and egestion of undigested matter. 22. Deciduous or milk teeth begin to appear in infants at the age of 6-11 months and are completed by the age of two years.


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RESPIRATION Respiration (L. respirare— to breathe) is a biochemical process of enzyme mediated stepwise oxidative breakdown of organic compounds inside living cells releasing small packets of energy at various steps. It is, therefore, a catabolic and exergonic process. The organic compounds that undergo oxidative breakdown in respiration are called respiratory substrates. The most common respiratory substrate is glucose. Another related sugar is fructose. Glucose is formed by hydrolysis of storage carbohydrate like starch in plants and glycogen in animals. Energy liberated during oxidative breakdown of respiratory substrate is partly stored in ATP (adenosine triphosphate). The rest is dissipated as heat. enzymes

C6H1206 + 602-> 6C02 + 6H20 + 38ATP out of 686 kcal/2870 kj. Energy stored in ATP is used in carrying out different biological functions required for survival and maintenance of organisms like contraction in muscles, conduction in nerves, maintenance of protoplasmic structures, cyclosis, membrane permeability, biosynthesis, etc. ATP functions as energy currency in various cellular activities. It is built up from ADP and inorganic phosphate, when energy is available. ATP undergoes hydrolysis to liberate inorganic phosphate and energy where the latter is required. The energy available from breakdown of last phosphate bond is 30-5 kj or 7-3 kcal/mol. energy

ADP + (P) -* ATP ATP or ADP - (?)-» ADP + © + Energy Easily available respiratory substrate is essential for liberation ol energy required for body activities. If you have not taken food the whole day, you will feel weak and lazy because of the reduced availability of respiratory substrate and hence insufficient amount of energy. Rate of breathing also indicates the amount of energy being liberated. At rest an adult breathes 12-14/min, adolescent 14-18/min while children breathe at a rate of 18-22/min. During activity, the rate of breathing.increases.

Importance of Respiration 1. Survival. No organism can survive without respiring continuously. It is because respiration liberates energy. Energy is required for every life process. 2. Maintenance of Temperature. Part of energy is liberated as heat. It helps in maintaining body temperature. Excess heat is passed out in exhaled air. 3. Excretion. Some volatile waste products and C02 are passed out during exhalation. 4. Acid-Base Balance. Regular exhalation of C02 maintains the acid-base balance of the body. 5. Intermediates. Respiration produces a number of intermediates that form different biochemicals of the body. 6. Back Flow of Blood and Lymph. Flow of venous blood and lymph is maintained by respiratory movements of abdomen and thorax. 7. Exchange of Gases. It carries oxygen to the cells and take out carbon dioxide from the same.

Respiration 1. Cellular. It is a cellular process which occurs inside living cells. 2. Temperature. Temperature does not rise above 40 °C. 3. Control. It is under biological control. 4. Steps. It is a multistep reaction. 5. Enzymes. A number of enzymes take part in reaction. 6. Energy. It is released in small packets in several steps. 7. Heat and Light. About 50% of energy is liberated as heat. Light is not produced. 8. Storage of Energy. 50% of liberated energy is stored as ATP molecules. 9. Intermediates. Several intermediates are produced. 10. Oxidation. It is terminal where

oxygen combines with hydrogen of

reduced coenzymes.

Combustion It is a non-cellular process. Combustion produces temperature of 600-2000 °C. It is an uncontrolled process. It is single step reaction. No enzyme is involved. It is released in large amount in one step. Whole energy is produced as heat and light. There is no storage of energy. No intermediates are produced. Oxidation is direct where every oxidisable atom is oxidised without relation to presence of hydrogen.

Steps of Respiration In higher animals, respiration consists of four steps—

breathing, external respiration, internal respiration and

cellular respiration. Breathing is the bringing of oxygen

rich fresh air to respiratory surface and taking off carbon

dioxide rich foul air to the outside. External respiration is

the exchange of respiratory gases over the respiratory

surface. Internal respiration is the exchange of gases at the

tissue level and their transport to and Irom the

respiratory surface, Cellular ■ epilation is the actual

breakdown of respiratory substrate that occurs inside the

living cells.

Direct respiration occurs in those cases where there is direct exchange of gases between the cells of the organism and its environment, e.g., plants, Amoeba and some lower animals. Breathing and external respiration are absent in such cases. Indirect respiration occurs in animals where a transport system is involved in carrying gases between the cells and the respiratory surface. Respiratory Gases. They are gases which are either being

consumed or liberated during respiration. Respiratory

gases are also called metabolic gases. They are oxygen and

carbon dioxide. Oxygen is the gas used in oxidative

breakdown of respiratory substrate. It is, therefore, a

reactant. Carbon dioxide is a product of respiration.

Water is also a product of respiration.


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Respiration and Photosynthesis Photosynthesis is a build-up or anabolic process that forms organic substances from inorganic materials with the help of light energy.

Respiration is exactly opposite ol photosynthesis. It is a breakdown or catabolic process in which a respiratory substrate is broken down to

release energy

Young Roots. Air occurs in soil interspaces. Root hairs as well as epiblema cells of the young roots are in contact with them. They are also permeable to metabolic gases. Oxygen of the soil air diffuses through oot hair-epiblema cells and reaches all internal cells of the young root. Carbon dioxide produced by root cells diffuses in the opposite direction. In waterlogged conditions, soil air becomes deficient. In the absence of oxygen, metabolic activity of the root declines and the plant may wither. Older Roots and Stems. In older roots and stems, the surface tissues are impermeable to gases. They have permanently open pores called lenticels. Each lenticel contains a mass of loosely arranged complementary cells that enclose a number of intercellular spaces. Exchange of gases occurs through them. Leaves and Young Stems. Leaves and young stems are ideally suited to quick exchange of gases. The organs have a covering of

nearly impermeable epidermis for reducing loss of water. The epidermis bears a number of aerating pores called stomata (singular

stoma or stomate, Gk. stoma—mouth). Each aerating or stomatal pore is bordered by a pair of guard cells. In most of the plants,

the guard cells are kidney or bean shaped with inner walls being thicker and less elastic than the outer walls. Guard cells contain

chloroplasts which are absent in other epidermal cells. Opening and closing of stomata are regulated.

Guard cells have mechanism to increase their osmotic concentration by withdrawing K+ ions from surrounding epidermal cells. Such guard cells also withdraw water from surrounding cells and become turgid. The turgid guard cells swell up. As the outer wall is thin and elastic, guard cells bend ourwardly more than the inner region where wall is thick. However, some bending also occurs here. As the inner walls of the two guard cells bend ourwardly, a pore is created between them. During clcjsure of stomata, the guard cells send out K+ ions. Water also passes out. As the turgidity decreases, the guard cells contract. Their thick inner walls come to touch each other. The pore gets closed. When the stomata are open, gises diffuse into and out of the leaf as per their concentration gradient. A gas which has come from outside first

reaches substomatal chambers. Prom here, it diffuses to all the intercellular air spaces present in between the mcsophyll cells. II the stomata are

open during night, oxygen from outside will diffuse into the leaves and young stems while carbon dioxide will diffuse out. It is due to

respiratory gas exchange. I lere each living cell picks up oxygen and releases carbon dioxide. However, during the day reverse gaseous

exchange occurs despite the occurrence of respiration in each and every cell. It is because of the very high rate of photosynthesis as compared

to respiration. During daytime oxygen diffuses out of the leaves and young stems while carbon dioxide passes from environment into them.

Differences between Photosynthesis 1. Metabolism. Photosynthesis is a synthetic or anabolic process. 2. Energy Relations. It is an endergonic process. 3. Energy Conversion. It converts light energy into chemical energy. 4. Timing. Photosynthesis occurs during the daytime when light is available. 5. Cells. It occurs only in green cells. 6. Carbon Dioxide. It absorbs carbon dioxide. 7. Oxygen. Photosynthesis liberates oxygen. 8. Raw Materials. They are carbon dioxide and water. 9. End Products. They are glucose, other organic substances and oxygen 10. Weight. There is net gain of

weight.

And Respiration Respiration is a breakdown or catabolic process. It is an exergonic process. It liberates chemical energy which is used as such or changed into other forms of energy. Respiration occurs all the time. It occurs in all types of living cells. Respiration liberates carbon dioxide. Respiration consumes oxygen. They are glucose and oxygen. End products are carbon dioxide and water. There is net loss of weight.

Exehange of Gases in Plants Like other living organisms, plants also exchange gases with their environment. However, plants do not possess any transport system for the gases.Different parts of plants exchange gases independently though an internal network of intercellular spaces does exist. The gases move entirely by diffusion. For this, the cell membranes are permeable to them. Intercellular spaces occur throughout the plants for reducing the distance of diffusion between cells and air. Intercellular spaces are also connected with one another so that deep seated cells and tissues are also able to exchange gases with the environment. Being fixed in nature, the energy requirement and hence the rate of respiration of plants is slow as compared to animals, Different parts of the plants respire at different rates. Respiration is rapid in meristematic regions (stem tips, root tips, cambia), buds, growing fruits and germinating seeds. It is slower in mature regions. However, all plants must respire continuously. Plants often die in water-logged soils because the soil is unable to supply sufficient oxygen to roots.


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Breathing Breathing is a physical process of bringing in of fresh air for obtaining oxygen and taking out of foul air for elimination of carbon dioxide. The surface where exchange of gases occurs is called respiratory surface. The organ having respiratory surface is known as respiratory organ, e.g., lungs in human beings, gills in fish, skin in earthworm, trachea in insects. The respiratory organs have three common features ; (i) Large Surface Area. There is a large respiratory surface that is either in contact with environment directly or receives air or water from outside, (ii) Thin Permeable Membrane. The respiratory surface has thin permeable wall for quick diffusion and exchange of gases. (Hi) Abundant Blood Supply. Except in tracheal system, the respiratory surface has abundant blood supply due to presence of a network of blood capillaries. Other features required are (a) Moisture over the respiratory surface and (b) Mechanism for quicker movement of fresh air over the respiratory surface and rapid disposal of foul air. Additional structures are associated with respiratory organs to help them perform their functions, e.g., diaphragm, muscles, rib case, nasal chambers, etc. All the organs connected with bringing in of fresh air to the respiratory surface and expulsion of foul air from the body constitute respiratory system Exchange of Gases in Animals A variety of methods are used for exchange of gases in animals. Specific _ _ respiratory organs are absent in lower animals and protozoan protists. Skin is used EE EE as respiratory surface in some lower animals as well as amphibians. Respiratory EE EE organs include gills, tracheae and lungs 1. Cell Surface Gaseous Exchange. Exchange of gases occurs between cell = EE? surface or plasma membrane and the surrounding medium in protozoan protists, = _= e.g., Amoeba, Paramoecium. They are unicellular organisms. Porifers (= sponges) EE EE and coelenterates (e.g., Hydra) are multicellular animals where every cell is in contact with the surrounding water. Exchange of gases occurs through diffusion across the cell surface. In flatworms and roundworms a regular respiratory surface is absent. Exchange of gases occurs through diffusion across1: the body surface from where it continues inwardly to every cell. However, diffusion is unable to meet the respiratory requirement of individual cells in large sized multicellular animals. For example, diffusion of an oxygen molecule from lung to human toe would take three years. Therefore, a system of internal transport of gases is found in multicellular animals. 2. Gaseous Exchange Through Skin (Cutaneous Respiration). Skin functions as a respiratory surface without being organised into a respiratory organ in Earthworm, Leech, Nereis, Frog and other amphibians. Here skin is thin, vascular, moist, glandular and permeable to gases. Exchange of gases occurs between blood and environment over a thin layer of water kept over the surface of the skin. Besides skin, mucous membrane of buccopharyngeal cavity also takes part in gaseous exchange in Frog. 3. Gaseous Exchange through Tracheal System (Tracheal Respiration). It occurs in insects and some other arthropods. They have a network of tubes called tracheae (singular trachea). Tracheae communicate with outside air through lateral holes of the body called spiracles. Each trachea is branched and rebranched to form very fine tubules called tracheoles. Tracheae and their branches are supported by chitinous rings called taenidia. Tracheoles are without supporting rings. They open into tissue fluid through fine end cells. Inspiration occurs when the abdominal muscles contract. Relxation of abdominal muscles causes exhalation or expiration of foul air. Blood or haemoJymph has no role in exchange of gases.

4. Caseous Exchange through Gills (Branchial Respiration). Gills are respiratory organs in several aquatic animals like Prawn, Crab, Mussel,

Tadpole and fishes. External gills occur in Tadpole, Prawn, Mussel and Crab. Fishes have internal gills. In bony fishes four pairs of gills are

found in two branchial chambers, each covered by an operculum. Operculum has a hole for passage of water. A gill has rakers for filtering

water. There are two rows of gill filaments with each filament made of many leaf like gill lamellae richly supplied with blood capillaries. In

fishes, water enters through mouth, reaches pharynx and then gill chambers. Here it is filtered in rakers and passed through gill lamellae where

exchange of gases occurs. Oxygen from water enters blood while carbon dioxide of blood diffuses out in water. Water carrying carbon dioxide

passes out of gill chamber through the pore in operculum.

5. Gascons Exchange Through l.ungs (Pulmonary Respiration). It occurs in all land vertebrates, even those who have become aquatic

secondarily, i.e., amphibians, reptiles, birds, mammals. The respiratory surface is represented in the form of alveoli. A lung has numerous

alveoli. Each alveolus has an internal surfactant that prevents its collapsing. The wall of the alveolus has a bunch of blood capillaries. Air enters

alveoli during inhalation. Oxygen of inhaled air diffuses into blood while carbon dioxide of the blood passes out into alveoli. Foul air is passed

out of lungs during exhalation.

1.3.1 Respiration in Human Beings Human beings perform pulmonary respiration. Human respiratory system consists of respiratory tract, a pair of lungs and accessory organs that bring about breathing. The accessory organs are thorax, rib cage, diaphragm and their muscles. Thorax is upper air tight chamber of the body which is bounded by rib cage on.the sides, diaphragm on the lower side and neck on the upper side. Diaphragm is a muscular partition between thorax and abdomen. It can straighten as well as become curved upwardly by contraction and relaxation of phrenic muscles. Rib cage consists of vertebral column on the back (thoracic vertebrae), ribs on the sides and sternum in front. The ribs have obliquely placed muscles that can move the rib cage as well as the whole thorax outwardly and upwardly for increasing its girth. Respiratory tract is the passage-way that carries fresh air to respiratory surface and takes out foul air from the same. It has a number of components like external, nostrils, nasal cavities, pharynx, larynx, trachea, bronchi and their branches inside the lungs. External Nostrils. They are two large openings which fprm the proximal part of respiratory tract. The external nostrils or external nares occur above the mouth at the tip of nose. They lead internally into nasal chambers or nasal cavities.


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Nasal Cavities (Nasal Chambers). They are two chambers or cavities which lie above the buccal or oral cavity and are separated from the same by a bony plate. Anterior part of nasal cavities contain hair for filtering out large dust particles. Inner parts have olfactory epithelium over the roof for perceiving odour. The sides and floor appears pinkish due to presence of a large number of blood capillaries. The pseudostratified epithelium of this region has mucus j secreting glands, ciliated and nonciliated cells. This region functions as air I conditioner. It changes temperature and moisture of the incoming air at par j with that of the body. Mucus contains lysozyme and other antimicrobial agents for killing the microbes. Dust particles are also trapped in the mucus. Beating '\ of cilia push the contaminated mucus towards the external nostrils. Nasal cavities open into pharynx with the help of internal nostrils or internal nares (singular naris). The latter can be closed with the help of uvula. Pharynx. It is the common passage for respiratory and digestive systems. Larynx (Voice Box). Pharynx opens into anterior wider part of trachea called larynx. The opening is called glottis. A small leaf-like cartilaginous flap called epiglottis covers the glottis during swallowing to prevent entry of food and water in respiratory tract. Incomplete covering by epiglottis during swallowing causes coughing. Internally larynx contains two vocal cords which vibrate when air passes in between them. The vibrations are converted into speech with the help of palate, buccal cavity, tongue and lips. Position of larynx is indicated externally in males in the throat region by a protuberance called Adam's apple. Trachea (Wind Pipe). It is a tube that arises from the base of larynx, passes through neck and reaches upto the middle ol thorax. Trachea is

10-12 cm long and 2-3 cm broad. It is supported by incomplete C-shaped cartilaginous rings. Internally trachea is lined by ciliated and mucus

secreting epithelium for trapping liner dust particles and microbes and pushing them towards the anterior end through beating ol cilia.

1.3.1 Respiration in Human Beings Human beings perform pulmonary respiration. Human respiratory system consists of respiratory tract, a pair of lungs and accessory organs that bring about breathing. The accessory organs are thorax, rib cage, diaphragm and their muscles. Thorax is upper air tight chamber of the body which is bounded by rib cage on.the sides, diaphragm on the lower side and neck on the upper side. Diaphragm is a muscular partition between thorax and abdomen. It can straighten as well as become curved upwardly by contraction and relaxation of phrenic muscles. Rib cage consists of vertebral column on the back (thoracic vertebrae), ribs on the sides and sternum in front. The ribs have obliquely placed muscles that can move the rib cage as well as the whole thorax outwardly and upwardly for increasing its girth. Respiratory tract is the passage-way that carries fresh air to respiratory surface and takes out foul air from the same. It has a number of components like external, nostrils, nasal cavities, pharynx, larynx, trachea, bronchi and their branches inside the lungs. External Nostrils. They are two large openings which fprm the proximal part of respiratory tract. The external nostrils or external nares occur above the mouth at the tip of nose. They lead internally into nasal chambers or nasal cavities. Nasal Cavities (Nasal Chambers). They are two chambers or cavities which lie above the buccal or oral cavity and are separated from the same by a bony plate. Anterior part of nasal cavities contain hair for filtering out large dust particles. Inner parts have olfactory epithelium over the roof for perceiving odour. The sides and floor appears pinkish due to presence of a large number of blood capillaries. The pseudostratified epithelium of this region has mucus j secreting glands, ciliated and nonciliated cells. This region functions as air I conditioner. It changes temperature and moisture of the incoming air at par j with that of the body. Mucus contains lysozyme and other antimicrobial agents for killing the microbes. Dust particles are also trapped in the mucus. Beating '\ of cilia push the contaminated mucus towards the external nostrils. Nasal cavities open into pharynx with the help of internal nostrils or internal nares (singular naris). The latter can be closed with the help of uvula. Pharynx. It is the common passage for respiratory and digestive systems. Larynx (Voice Box). Pharynx opens into anterior wider part of trachea called larynx. The opening is called glottis. A small leaf-like cartilaginous flap called epiglottis covers the glottis during swallowing to prevent entry of food and water in respiratory tract. Incomplete covering by epiglottis during swallowing causes coughing. Internally larynx contains two vocal cords which vibrate when air passes in between them. The vibrations are converted into speech with the help of palate, buccal cavity, tongue and lips. Position of larynx is indicated externally in males in the throat region by a protuberance called Adam's apple. Trachea (Wind Pipe). It is a tube that arises from the base of larynx, passes through neck and reaches upto the middle ol thorax. Trachea is

10-12 cm long and 2-3 cm broad. It is supported by incomplete C-shaped cartilaginous rings. Internally trachea is lined by ciliated and mucus

secreting epithelium for trapping liner dust particles and microbes and pushing them towards the anterior end through beating ol cilia

They form a fluid-filled thin sac called pleural sac. The pleural sac (i) Protects the lungs from mechanical shock and injury, (ii) Keeps the lung surface moist. (Hi) Provides frictionless movements to lungs. Thoracic cavity is air tight and the pleural sacs of the lungs are in contact with its inner lining. Left lung is 2-lobed and larger. Right lung is three lobed but shorter. Each lobe is further divided internally into segments and segments into lobules. A lobule receives a bronchiole. Lobule is further divided into a large number of alveoli. The two lungs are estimated to have about 300 million alveoli each. Alveoli provide a large surface area for gaseous exchange. It is 80 m2. lungs . They are a pair ol pinkish to greyish, conical, spongy and elastic sacs that occur in the thoracic cavity, one on each side. Their lower broad surfaces rest over the diaphragm. The latter also function as the floor of thoracic cavity. Each lung is covered by two membranes or pleura, internal visceral and outer partietal.


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How Breathing Takes Place (Mechanism of Breathing) Breathing or the process of taking in fresh air and releasing foul air can be easily observed because thorax shows alternate expansion and contraction. It is involuntary though it can be prevented for a brief period. Rate of breathing is controlled by respiratory centre of brain. Expansion of thorax causes fresh air to be drawn in. Contraction of thorax causes foul air to be expelled. Therefore, breathing consists of two steps, inspiration and expiration. Inspiration or Inhalation. It is bringing of fresh air into lungs for exchange of gases. During inhalation, thoracic cavity enlarges due to two types of inspiratory muscles, phrenic and external intercostals. Phrenic muscles straighten the diaphragm by moving its curved part downwards. It increases length of thorax. Contraction of external intercostal muscles pushes the rib cage in outward and upward direction. It increases girth of thorax. Being air tight, increase in size of thoracic cavity causes expansion of lungs. It decreases air pressure in the lungs. As a result outside air rushes into lungs through external nostrils, nasal cavities, internal nostrils, pharynx, larynx, trachea, bronchi, bronchioles to alveoli. While passing through respiratory tract, the incoming air is : (i) Filtered by hair present in anterior part of nasal cavities. (ii) Cleansed of dust and microbes throughout respiratory tract.by lysozyme, mucus and cilia. (Hi) Air conditioned (bringing temperature of inhaled air to that of body) with the help of blood capillaries present below nasal epithelium. (if) Moistened by water vapours from wet epithelium. Exchange of Cases. It occurs in the alveoli. Fresh air has high concentration of oxygen and a very low concentration of carbon dioxide. As a result, oxygen diffuses from alveolar air to blood present in capillaries around the alveoli. Carbon dioxide diffuses from blood into alveolar air. Expiration or Exhalation. It is throwing out or expulsion of foul air from the lungs after exchange of gases. Expiration or,exhalation is a passive process caused by relaxation of inspiratory muscles. Relaxation of phrenic muscles causes the diaphragm to bulge into thorax resulting in shortening of thoracic cavity. Relaxation of external intercostal muscles pulls the rib cage inwardly and downwardly. It reduces the girth of thorax. Reduction in size of thoracic cavity causes compression of lungs. This leads to expulsion of air from lungs to the outside through respiratory tract consisting of alveoli -> bronchioles -» bronchi -> trachea-> larynx--> pharynx-> internal nostrils-> nasal cavities-> external nostrils.

What happens to Oxygen and Carbon Dioxide ? External Respiration. It is exchange of gases that occurs at the respiratory surface. Oxygen has a higher partial pressure in the alveolar air than inside the blood circulating over the alveolar surface. Carbon dioxide has higher partial pressure in blood as compared to alveolar air. Therefore, oxygen diffuses into blood while carbon dioxide passes out of the blood. 97% of oxygen combines with haemoglobin of red blood corpuscles to form oxyhaemoglobin. Only 3% of oxygen dissolves in blood plasma. Internal Respiration. It is exchange of gases that occurs between blood and tissues. Blood containing oxygen or oxyhaemoglobin is called oxygenated blood. From lungs the oxygenated blood passes into heart through pulmonary veins. It reaches the left part of the heart which pumps the same to the whole body. In body tissues, oxygen separates from haemoglobin and diffuses into individual cells through the tissue fluid. Inside the cells oxygen is used up in oxidative breakdown of respiratory substrate. It releases energy. Carbon dioxide is produced in the process. It diffuses into blood through tissue fluid. It is more soluble in water. In blood 23% of carbon dioxide combines with haemoglobin to form carbaminohaemoglobin. The remaining travels as sodium bicarbonate (70%) and carbonic acid in the plasma to reach lungs. Carbon monoxide has very high affinity for haemoglobin. The product is carboxyhaemoglobin. It cannot carry oxygen. It is cause of death in

closed rooms heated by burning coal or wood.

Differences between External Respiration and Internal Respiration External Respiration Internal Respiration 1. Place. It occurs at the respiratory surface. It occurs around the tissues. 2. Cisco us Exchange. It takes place between blood It occurs between blood and cells, and air. 3. Cell Respiration. It is not connected directly It is connected directly with cell respiration, with cell respiration.

Inhalation/Inspiration 1. Action. Inhalation is bringing in of fresh air from outside. 2. Rib Cage. It is pushed outwardly and upwardly. 3. Diaphragm. It contracts and becomes nearly flat. 4. Thoracic Cavity. It increases in size. 5. Air Pressure. Air pressure decreases in lungs. 6. Respiratory Muscles. They contract to bring about inhalation. 7. Type of Process. Inhalation is an active process. 8. Result. Air rushes from outside and causes inflation of lungs. 9. Oxygen. Inhaled air has an oxygen concentration of 20-84%. 10. Carbon Dioxide. Its concentration in inhaled air is 0 04%.

Exhalation/Expiration It is passing out of foul air to the outside. It is pulled inwardly and downwardly. It relaxes and becomes dome-shaped. It decreases in size. There is increase in air pressure in the lungs. They relax to cause exhalation. Exhalation is a passive process. Air is expelled from lungs causing their deflation. Exhaled air has an oxygen concentration of 15-7%. Its concentration in exhaled air is 4-0%.


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Aerobic and Anaerobic Respiration Sachs (1890) discovered that respiration can occur with or without oxygen. Therefore, there are two types of respiration, aerobic and anaerobic.

Aerobic Respiration It is a multistep complete oxidative breakdown of respiratory substrate into carbon dioxide and water with the help of oxygen acting as a terminal oxidant. Aerobic respiration is the usual mode of respiration in all higher organisms and most of the lower organisms. The reason is that it yields maximum amount of energy. enzymes

C6H1206 + 602-> 6C02 + 6H20 + 686 kcal or 2870 kj The energy is stored in some 38 molecules of ATP. Aerobic respiration occurs in two steps, glycolysis and Krebs cycle. Glycolysis Glycolysis or EMP (Embden, Meyerhof and Parnas) pathway is the first step of respiration which is common to both aerobic and

anaerobic modes of respiration. It occurs in cytoplasm. Respiratory substrate is double phosphorylated before it undergoes lysis to produce 3-

carbon compound, glyceraldehyde phosphate. NADH2 and ATP are produced when glyceraldehyde is changed to pyruvate.

Anaerobic Respiration It is a multistep breakdown of respiratory substrate in which atleast one end product is organic and which does not employ oxygen as an

oxidant. Anaerobic respiration occurs in many lower organisms, e.g., certain bacteria, yeast. In human body it occurs regularly in red blood cells

and during heavy exercise in muscles (striated muscles). Anaerobic respiration occurs entirely1 in the cytoplasm. It has two steps. The first step

is glycolysis. Here, respiratory substrate glucose breaks down into two molecules each of pyruvate, ATP and NADH2. Pyruvate is converted

into ethyl alcohol (C2H50H) in Yeast and certain bacteria. It is changed to lactic acid (CH3CHOH.COOH) in muscle cells when oxygen

utilisation is faster than its availability as during vigorous exercise. It creates an oxygen debt in the body. No such debt occurs in blood

corpuscles.

Fermentation (L. fermentum—froth). It is anaerobic breakdown of carbohydrates by microorganisms producing alcohol, organic acids and a

variety of other products alongwith heat and waste gases. Fermentation is used in brewing industry (for producing wine, whisky, beer), baking

industry (for

Differences Between Aerobic and Anaerobic Respiration Aerobic Respiration 1. Method. It is the common method of respiration. 2. Steps. It is completed in 3 steps—glycolysis, Krebs cycle and terminal oxidation. 3. Oxygen. It requires oxygen. 4. Breakdown. Respiratory substrate is completely broken down. 5. End Products. They are inorganic. 6. Toxicity. End products show little toxicity. 7. Occurrence. It occurs partly in cytoplasm and partly in mitochondria, 8. E.T.C. An electron transport chain is required. 9. Energy. In releases 686 kcal or 2870 kj of energy per mole of glucose. 10. ATP. The liberated energy is used in forming 36-38 ATP molecules per mole of glucose. Anaerobic Respiration It occurs permanently only in a few organisms. In others it may occur as a temporary measure to overcome shortage of oxygen. There are two steps— glycolysis and anaerobic breakdown of pyruvic acid. Oxygen is not required. Respiratory substrate is incompletely broken down. Atleast one end product is organic. Inorganic products may or may not be present. The organic end product is generally toxic. Anaerobic respiration is carried out entirely in cytoplasm. Mitochondria are not required. ETC is not required. Energy liberated is 36-50 kcal or 150-210 kj per mole of glucose.

The liberated energy is used in synthesis of 2 ATP molecules.

Modes of Transport Lower organisms are mostly aquatic or semiaquatic. Most of their transportation occurs through diffusion. Diffusion also occurs in higher organisms for cell to cell movement of materials. Entry of materials into cells involves both passive (without energy) and active (with energy) transport. Intracellular transport takes place through cyclosis and diffusion. A long distance transport system occurs in higher organisms. It is different in plants and animals. Animals have a circulatory system while plants have vascular strands for this function.

1.4.1. Transportation in Human Beings It is carried out by the circulatory system. Circulatory system is a system of organs, tubes and a blood-like fluid that circulates various materials inside the body. In human body circulatory system is made of tubes, a pumping heart, blood and-lymph. Circulatory system consisting of tubes (capillaries, arteries and veins), heart and blood is called blood vascular system. The system having tubes, nodes and lymph is called lymphatic system.


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Blood It is a mobile fluid connective tissue of reddish colour that circulates in the human body, supplying nutrients and oxygen to all the living cells and taking away waste products as well as carbon dioxide from them. An adult human has 5-6 litres of blood. Blood is made up of two components, plasma and blood corpuscles. 1. Plasma. It is pale yellow slightly alkaline (p¥i 7-4) transparent fluid matrix of blood. It constitutes 55% of the blood. Plasma consists of 92% water and 8% solutes. The solutes are of five types, (i) Proteins. They form the major fraction of solutes (6-5% of total plasma). The important proteins are immunoglobins (antibodies), lysozymes (antimicrobial), fibrinogen, prothrombin (both for blood clotting) and transport proteins, (ii) Nutrients. They are glucose, amino acids, vitamins, fatty acids and fat drops. (Hi) Excretory Products. Urea, creatine, creatinine and uric acid, (iv) Inorganic salts. The major inorganic ingredients are sodium and chloride. They constitute 0-9% of the plasma. All other essential inorganic elements are also present in the blood. (v) Other Substances. Metabolic gases (oxygen, carbon dioxide), hormones, cholesterol and heparin are carried by plasma. Heparin does not allow blood to coagulate inside blood vessels.

2. Blood Corpuscles. They are also called formed elements. Blood corpuscles constitute 45% of the blood. They are of three types — red blood corpuscles, white blood corpuscles and blood platelets. All of them are synthesized inside red bone marrow. (/J Red Blood Corpuscles (RBCs, Erythrocytes). They are circular, biconcave discs of 7".m diameter and 2 U.m thickness. Nucleus, mitochondria, endoplasmic reticulum and ribosomcs arc absent. Each red blood corpuscle contains about 100 million haemoglobin molecules. Haemoglobin is iron containing protein pigment which is specialised to transport oxygen and to a small extent carbon dioxide. It provides reddish colour to blood. A healthy adult male has about 15 mg of haemoglobin per 100 ml of blood. It is 12-13 mg/100 ml of blood in healthy female. Number of red blood corpuscles is 5 million/ml in healthy males and 4-5 million/ml in healthy female. Life span of RBCs is 120 days. 5 to 6 million RBCs are being destroyed and replaced every second in our body. New RBCs are formed in red bone marrow. Older RBCs are destroyed in spleen and liver. The process of destruction of RBCs is called haemolysis. Spleen also stores a large number of fresh RBCs for meeting any emergency. It is, therefore, also called blood bank of the body. (ii) White Blood Corpuscles (WBCs, Leucocytes). They are colourless, nucleated, blood corpuscles of different shapes and sizes (8-15 (Am). The normal value is 5000 - 8000 per ml of blood. Life span is 12 hours to several days. White blood corpuscles are of two types, granulocytes and agranulocytes. Granulocytes possess large sized granules in their cytoplasm. Their nucleus is lobulated. Depending upon their reaction, granulocytes are of three subtypes— basophils, eosinophils (acidophils) and neutrophils. Agranulocytes are devoid of granules. Their nucleus is without lobes. They are of two subtypes, monocytes and lymphocytes. White blood corpuscles are soldiers of the body both in defence and offence. They are either phagocytes or immunocytes. Phagocytes ingest germs. Immunocytes secrete antibodies against foreign bodies. It is the basis for immunity against various pathogens. (Hi) Blood Platelets (Thrombocytes). They are colourless non-nucleated cell fragments of various shapes with a size of 2-3 |J.m. The number is 0-15 -0-45 million/ml of blood. Life span is 7—10 days. Blood platelets help in blood clotting. Functions of Blood

1. Transport of Nutrients. Sugars, amino acids, minerals and vitamins are picked up by blood from intestine and transported to different parts of the body for storage and assimilation. 2. Transport of Oxygen. It transports oxygen from the respiratory surface to the tissues for utilisation in respiration. 3. Transport of Carbon Dioxide. Carbon dioxide formed during respiration is taken by blood to the respiratory surface for elimination. 4. Transport of Waste Products. It carries nitrogenous wastes from various parts of the body to the kidneys for separation and elimination. 5. Transport of Hormones. Endocrine glands pour their hormones into blood for transport to target tissues. 6. Maintenance of Water Balance. Circulating blood provides water and inorganic salts in the region of deficiency and removes the same in the area of excess. 7. Regulation of Body Temperature. Blood distributes heat to all parts of the body. It also conducts heat to the surface for dissipation. 8. Maintenance of pH. Blood maintains the pH of tissue fluids with the help of various buffers. 9. Body Defence. Blood contains phagocytic leucocytes, and immunocytes for defence against germs. ^ 10. Plugging Areas of Injury. In the region of injury the blood coagulates and seals the region to prevent loss of body fluids and check the

entry of germs.

Blood Clotting (Maintenance by Platelets) In the region of injury or leakage from a blood vessel, blood oozes out. The platelets rupture and release a substance called thromboplastin. In the presence of calcium, thromboplastin acts on protein prothrombin and forms a proteolytic enzyme called thrombin. Vitamin K is essential for formation of prothrombin in liver. Thrombin acts on a soluble protein fibrinogen and changes it into fibrin. Fibrin undergoes rapid polymerisation to form long fibres. The fibres form a network over the damaged wall of blood vessel and exposed part of the skin. It entraps blood corpuscles and forms a jelly like mass called blood clot. The clot contracts and solidifies. A liquid called serum is expelled. Clotting time is 2-5 minutes for superficial cuts and 4-10 minutes for deeper cuts. Serum

It is watery fluid expelled from a contracting blood clot. It is whitish as compared to yellowish nature of blood plasma. Fibrinogen is absent. So are formed elements, prothrombin and many other proteins.


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The Tubes— Blood Vessels

Human blood flows inside tubes called blood vessels. Blood vessels are of three types— arteries, veins and capillaries. Arteries. They are blood vessels which carry blood coming from heart to various organs of the body. Blood flows inside the arteries with jerks

due to pumping activity of the heart. As the blood is pumped into an artery, it expands. With the flow of blood from it, the artery contracts

partially. Arteries, generally, carry oxygenated blood. Only pulmonary arteries transport deoxygenated blood from heart to lungs. The wall of

the arteries is thick and clastic. Lumen is narrow. Most arteries arc deep seated except a few ones where the pulse can be lelt.

Veins. They are blood vessels which carry blood from various parts of the body towards the heart. Blood flows smoothly and slowly inside

veins. Internal valves prevent back flow. Wall is less thickened and less elastic as compared to that of arteries. Lumen is wide. Veins carry

deoxygenated blood except pulmonary veins that bring oxygenated blood from lungs to the heart. Veins are generally superficial.

Capillaries. They are very narrow blood vessels (4—10 U.m) having a single layered wall (endothelium), which form network inside body organs. Movement of blood is very slow (1 mm/sec) so as to provide time for exchange of materials. The wall has very fine pores for exchange of substances between blood and tissue fluid. Some plasma also filters out of blood capillaries to become component of tissue fluid. Extra tissue fluid passes into lymph capillaries. White blood corpuscles can come out of capillaries for the fighting infections. The phenomenon is called diapedesis. An artery divides and redivides to form finer branches called arterioles. Each arteriole gives rise to a bunch of capillaries that reach every part of the organ. The capillaries reunite to produce very fine blood vessels of second type called venules. Venules join to form a vein.

Heart It is a conical muscular structure that brings about circulation of blood by its pumping activity. The broader base is upwards while the narrow pointed apex is downwards and tilted towards left. Heart is reddish in colour with a size of our fist (12 cm length, 9 cm breadth) and a weight about 300 gm (250 gm in women). Heart lies in the thoracic cavity in between the two lungs. It rests over the diaphragm obliquely. Feeling of the presence of heart on the left side is due to forceful beating of its apical or ventricular region. Heart is covered by a narrow fluid filled membranous sac called pericardium. It helps in frictionless movement as well as provides protection from shock. Heart has four chambers. Two upper or superior chambers are smaller and thin walled. They are called auricles or atria (sing, atrium). The other two lower or inferior chambers are larger and thick walled. They are called ventricles. An irregular transverse groove called coronary sulcus occurs between the auricles and ventricles. An oblique groove called interventricular sulcus occurs between the two ventricles. The left ventricle in larger and more thick walled. An interauricular septum separates the two auricles while an interventricular septum forms a partition between the two ventricles. The two types of septa separate the right side of the heart from the left side. Right auricle opens into right ventricle through an aperture guarded by a tricuspid valve supported by fine fibres called chordae tendineae. The left auricle or atrium opens into left ventricle through an aperture guarded by a bicuspid valve. It is also supported by chordae tendineae. Right ventricle opens into a pulmonary arch. The opening is guarded by a semilunar pulmonary valve. Left ventricle opens into aorta with a semi-lunar aortic valve between the two. Heart receives blood from veins and pumps the same into arteries. Deoxygenated blood from the whole body enters right auricle through a superior vena cava (from upper parts of the body), inferior vena cava (from middle and lower parts of the body) and coronary sinus (from walls of the heart). Right atrium expands during the flow of deoxygenated blood into it. It contracts to pour the same into right ventricle which expands to accommodate the same. On contraction, right ventricle pumps the deoxygenated blood into pulmonary arch. This blood is then taken to lungs by two pulmonary arteries for oxygenation. The oxygenated blood is brought back into left atrium or auricle which dilates to accommodate the same. The blood is poured into left ventricle which on contraction sends the oxygenated blood to different body parts through aorta. Both the auricles get filled up simultaneously. It is called diastole. They contract together or undergo systole to pour their blood into their respective ventricles. This causes diastole of the two ventricles. The distended ventricles undergo systole or contraction to pass their bloods to pulmonary arch and aorta. A i.iidi.u cycle consisting of one filling and emptying ol the chambers ol the heart is of 08 sec duration. It consists of auricular systole, ventricular systole and joint diastole. Backward flow of blood is prevented by valves. The partitions between the right and left sides of the heart are useful in separating oxygenated and deoxygenated bloods. The mechanism provides efficient supply of oxygen to all body parts. This occurs in animals having high energy needs like birds and mammals. They spend a

Artery

1. Direction of Flow. It carries blood from heart to an organ. 2. Speed. Blood flow is rapid in artery. 3. Jerks. Blood flows with jerks. 4. Pressure. Blood flows under pressure 5. Internal Valves. They are absent. 6. Wall. It is thick and elastic. 7. Lumen. Narrow. 8. Type of Blood. Artery carries oxygenated blood except pulmonary arteries. 9. Occurrence. It is deep seated. 10. Collapsibility. Artery is not collapsible.. 11. Blood After Death. It does not contain blood after death.

Vein

It brings blood from an organ towards the heart. Blood flow is slow in vein. Blood flows smoothly. There is little pressure. Internal valves are present to prevent back flow. It is comparatively thinner and little elastic. Wide. Vein carries deoxygenated blood except pulmonary veins. It is superficial. Vein is collapsible. Vein is full of blood even after death.


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lot of extra energy for keeping the body temperature constant. In reptiles and amphibians, the energy needs are lesser as the body temperature varies with the temperature of the environment. Their heart is 3-chambered. Mixing of oxygenated and deoxygenated bloods occurs in them. The heart is 2-chambered in fishes. Fish heart pumps only venous blood. It is oxygenated in gills from where the blood flows to the rest of the body. Heart Beat

Rhythmic expansion and contraction of heart is called heart beat. The expansion is called diastole while the contraction is known as systole. Actually, the auricles and the ventricles undergo diastole and systole separately but being forceful only ventricular contraction and expansion constitute the heart beat. The rate of heart beat is 70-72/min in adult human male and 80/min in adult females. Heart beat is listened with the help of stethoscope. There is a low pitched sound of longer duration called lubb and a high pitched sound of shorter duration known as dup. Lubb is produced on the simultaneous closure of atrioventricular valves (bicuspid and tricuspid valves) while dup is produced on the simultaneous closure of semilunar valves (aortic and pulmonary valves). Heart beat is controlled by a special mass of muscles that is capable of generating electric current for contraction of different parts of heart. It consists of sinoatrial node (SAN in right auricle), atrioventricular node (AVN in right auricle), bundle of His and its branches (wall of ventricles). Sinoatrial node is also called pacemaker as impulse for heart beat originates from it. Pulse

It is repeated throbs felt in a superficial artery like radial artery over the-wrist below the base of the thumb. The throb is due to forceful pumping of blood into arteries during ventricular systole. Pulse can be felt by placing the thumb over the radial artery. Number of throbs per minute is counted. It is pulse rate. Pulse rate is equal to rate of heart beat. Blood Pressure

It is the pressure exerted by forceful flow of blood on the elastic wall of the arteries. It is measured in mm of Hg by an instrument called

sphygmomanometer. The instrument has an inflatable cuff, a compressible rubber bulb, a screw and a connected mercury manometer.

Stethoscope is required. Rubber cuff is wrapped just above the elbow. Air is pumped into it by repeated pressing of the bulb till the

manometer shows high pressure. Diaphragm ol stethoscope is now pressed against the area ol brachial artery in the region of fold of the

elbow. Air is released slowly. First sound of blood flowing into brachial artery gives systolic pressure. With further release of air, a stage comes

when the sound disappears. It is diastolic pressure. The normal systolic pressure is 120 nun Hg while diastolic pressure 80 nun Hg. A higher

value (say 150/90 nun Hg) is called hypertension (high blood pressure) while a lower value (say 110/70 nun I Ig) is known as hypotension

(low blood pressure). Both are harmful.

Single circulation In fishes, the blood flows through the heart only once while completing the full circuit of the body. It is called single circulation. The heart receives and pumps only venous blood. It reaches gills where oxygenation of blood occurs. The oxygenated blood passes to all parts of the body. It returns to heart on deoxygenation.

Double Circulation

It is passage of the same blood twice through the heart first on the right side, then on the left side in order to complete one cycle. Double circulation has

two components, pulmonary circulation and systemic circulation.

(i) Pulmonary (lirculaiion. It is movement of blood from heart to the lungs and back. Deoxygenated blood of the body enters the right auricle, passes

into right ventricle which pumps it into pulmonary arch. With the help of two separate pulmonary arteries the blood passes into the lungs. Here the

arteries break up into arterioles and then capillaries for oxygenation. Capillaries join to form venules and then veins. Oxygenated blood comes back to

left auricle ol heart through four pulmonary veins, two from each lung. (ii) Systemic Circulation. It is the circulation of blood between heart and different parts of the body except lungs. Oxygenated blood received by left auricle passes into left ventricle. The left ventricle pumps it into aorta for supply to different body parts including walls of the heart with the help of arteries. Inside the organs the arteries break up into arterioles and then capillaries. Capillaries provide oxygen and nutrients to tissues. They receive carbon dioxide and wastes from the tissues. Capillaries unite to form venules which join to produce veins. Veins take the deoxygenated blood to the heart but now into the right auricle. Importance. Double circulation ensures quick and efficient supply of oxygenated blood to all body parts for meeting the higher energy needs and for thermoregulation of body in mammals and birds. It supplies the whole of deoxygenated blood directly to lungs for quicker oxygenation. Double circulation is an improvement over single circulation as the heart pumps both the types of bloods (oxygenated and deoxygenated) forcefully through the body. In amphibians and reptiles, the double circulation is incomplete due to mixing of the blood. It is complete in birds and mammals


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Lymphatic System It is a system of capillaries, vessels and lymph nodes which is specialised to collect lymph from tissue fluid and carry the same to blood in the region of subclavian veins.

Lymph It is a light yellow viscous fluid that is formed from tissue fluid by special lymph capillaries for passage into venous blood. Tissue fluid itself is blood plasma filtered out of the blood capillaries. Lymph does not contain RBCs and blood platelets. Leucocyte count is low but the lymphocyte content is quite high due to passage of lymph through lymph nodes. Lymph is specialised to collect tissue secretions which cannot pass directly into blood, e.g., hormones from endocrine glands, plasma proteins from liver, fats from intestine. Lymph also carries more waste products.

Lymph Vessels Lymph is formed inside fine blind tubes called lymph capillaries. The lymph capillaries are permeable to even macromolecules so that tissue secretions directly pass into lymph. Lymph capillaries join to form lymph vessels. Lymph vessels are similar to veins but have thinner walls and more numerous valves. At places lymph vessels bear swellings called lymph nodes. Lymph nodes or lymph glands are seats of lymphocyte maturation. Lymph rich tissues occur at several places, e.g., adenoids, tonsils, spleen, thymus. Lymph nodes filter out germs and foreign particles. Lymph vessels ultimately form two ducts which open into right and left subclavian veins.

Lymph Functions 1. Lymph (unctions as a middleman that exchanges materials between blood and tissue fluid. 2. Blood volume continues to decrease due to filtration of blood plasma from blood capillaries. Lymph collects the same and puts it back

into blood 3. They mature inside the lymph nodes and released into lymph passing through the same. 4. Hormones, macromolecules, plasma proteins and other secretions of the tissues are first poured into lymph for passage into blood. 5. . It picks up digested fat from alimentary canal for pouring into blood. 6. Wastes from tissues are first passed into lymph before they are poured into blood for separation in kidneys.

Transportation in Plants Unlike animals, some materials pass in and out of plants through diffusion. For gaseous diffusion to occur, the plants possess stomata and lenticels. During the daytime the photosynthetic organs obtain carbon dioxide from outside by diffusion. The same is used for synthesis of food. Oxygen is released as a by-product. It passes out of the plant by diffusion. Simultaneously, a lot of water vapours pass out. Other materials required for building plant body are obtained from soil, e.g., nitrogen, phosphorus, other minerals, water .They have to be transported to long distances depending upon the size of the plant. The food manufactured by leaves has to be similarly passed to all parts for utilisation. Therefore, a proper system of transportation is required by plants. However, plants have a large proportion of dead cells. They do not move. Therefore, they have low energy needs. The transport systems are slow. Further, there are two independent pathways having conducting tubes. One is xylem that moves water and minerals from soil to aerial parts. The other is phloem which carries food from the region of availability (e.g., leaves, storage organs) to the areas of utilisation (all living cells, growing points, storage organs, developing fruits). Xylem (Wood) It is a complex tissue which transports sap (water and minerals). Xylem has four types of cells—xylem fibres, xylem parenchyma, tracheids and vessels. Only xylem parenchyma arc living cells. Others arc dead, empty and lignified. Vessels and tracheids arc called tracheal)' elements because they take part in transport of sap (water + minerals). Vessels are long multicellular tubes which arc formed by end to end union of several cells without cross walls. Tracheids are elongated cells with pointed ends. Both the tracheary elements have pits or other thin unlignified areas for element to element movement of water. Xylem parenchyma takes part in lateral flow of water. Tracheids are conducting elements of non-flowering plants. Vessels occur mostly in angiosperms where they form the main conducting elements. The number of tracheids is small in angiosperms. Phloem It is complex tissue which takes part in transport of food. Phloem has four types of cells — sieve tubes, companion cells, phloem parenchyma and phloem fibres. Only phloem fibres are dead cells. Others are living cells. Sieve tubes are conducting channels of phloem. They are elongated multicellular tubular channels formed by end to end union of numerous sieve tube elements. The end walls or septa between adjacent sieve tube elements are bulged out and have pores. They are called sieve /plates. Sieve tube elements do not have a nucleus. Their functioning is controlled by adjacent nucleated companion cells.

Differences between Blood Capillaries and Lymph Capillaries. Blood Capillaries Lymph Capillaries

1. Ends. Blind ends are absent Blind end is present on one side.

2. Colour. They are red in colour. They are nearly colourless.

3. Diameter. Blood capillaries are narrower. They are comparatively wider. i. Pores. Pores arc narrow. Pores are larger so that even macromolecules can pass through them.

5. Contents. They contain blood. They contain lymph.


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Transpiration Transpiration is loss of water in vapour form from the exposed parts of a plant. Aerial parts of the plants are always losing water through

transpiration. Nearly 99% of water absorbed by a plant is lost through transpiration. There are three types of transpiration- lenticular, cuticular

and stomatal. lentical.inspiration is the loss of water in vapour form from lenticels present in the bark of stems. It is only 0.1% of the total. Cuticular transpiration is loss of water in vapour form through the cuticular covering of the leaves and other aerial parts. Amount of cuticular transpiration depends upon the thickness of the cuticle and presence of cracks. Major part of transpiration is stomatal transpiration, 50-97% of total. Stomatal transpiration is loss of water vapours through stomata present over leaves and other soft aerial parts. It will always occur whenever stomata are open for gaseous exchange. Intercellular spaces of the leaves are in contact with mesophyll cells as well as outside air through stomata. Outside air is seldom saturated with water vapours while the intercellular spaces are nearly always saturated with water due to evaporation from the wet walls of mesophyll cells. Therefore, water vapours diffuse from intercellular spaces to outside. More water vapours come from mesophyll cells to replace them. The process continues. Transport of Water and Minerals

There is a continuous system of water conducting channels (vessels and tracheids) from near the root tips to near the shoot tips. In the roots the surface cells are in contact with soil particles and soil water. Ions and water are absorbed from the soil. They are pulled and pushed up by various forces to reach every cell requiring the same. The various steps involved in transport of water and minerals are as follows : I. Mineral Absorption. It occurs in the growing parts of the root. Both the surface or epiblema cells as well as root hairs take part in mineral absorption. Mineral absorption is an active process which involves expenditure of energy. Being an active process, mineral absorption occurs against concentration gradient. It creates a difference in the concentration of ions between the roots and the soil, with more salts being present inside the root than in the soil solution. 2. Absorption of Water. Root hair zone is the region of water absorption. The inside of the root has higher osmotic concentration than the soil solution. Root hairs are in contact with soil interspaces having capillary water. The root hairs pick up water which is transferred inwardly due to still higher osmotic concentration. It reaches the cells surrounding the xylem channel. Salts accumulated in the basal part of xylem channel cause osmotic entry of water into xylem and form column of water. It also creates a positive pressure known as root pressure. This is, however, unable to push water to any great hight. Root pressure is often absent, atleast during the day time. column present in the xylem comes under tension or negative pressure. A negative pressure or tension of 10-20 atmospheres occurs in the water column of the plant. Water column does not break due to two forces: (a) Cohesion force among the water molecules, (b) Adhesion force between water molecules and wall of the xylem channels. Rise of Water. Tension or negative pressure of the water column results in its upward pull. Since it develops due to transpiration, it is called transpiration pull. Transport of Food and Other Substances

Food materials are translocated from the region of their manufacture or storage to the region of their utilisation. The region of supply of food is called source while the area of utilisation is called sink. The direction of translocation can be downward, upward or both. The food manufactured by leaves passes into the storage region and other sinks in the downward direction as well as towards growing points and developing fruits in the upward direction. The translocating nutrients consist of soluble carbohydrates (mostly sucrose), amino acids, organic acids, hormones and other organic solutes. Translocation occurs thorough phloem. The channels of transport are sieve tubes (sieve cells in nonflowering plants). Sieve tubes are specialised for this purpose. They are devoid of nuclei and internal membranes. The cytoplasm of one tube cell is continuous with that of adjacent sieve tube cells through sieve plates. The force required for translocation is produced by companion cells which lie adjacent to sieve tube cells.

Xylem 1Tissue. Xylem is water or sap conducing plant tissue. 2. Living Cells. Xylem has only one type of living cells. 3. Dead Cells. Xylem has three types of dead cells— fibres, tracheids and vessel elements. 4. Conducting Elements. There are two types of conducting elements, tracheids and vessels. 5.Septa. Vessels do not possess septa. 6.Metabolic Inhibitors. Conduction is not influenced by metabolic inhibitors like heat, cold or poison. 7.Pressure. Transport occurs due to presence of negative pressure.

Phloem It is food conducting plant tissue. It has three types of living cells. Phloem has only one type of dead cells, i.e., phloem fibres. There are only one type of conducting elements, i.e. sieve tubes. Sieve tubes have porous septa called sieve plates. Conduction is inhibited by heat, cold and poison. Transport takes place due to presence of positive pressure.


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Mechanism of Pholem Transport

The transport of organic solutes or nutrients occurs through a physical process but entry and exit of nutrients from the phloem can occur only through an active process which utilises energy from ATP. With the help of energy, food materials pass into the phloem from the region of manufacture or storage (source end). After entering the sieve tubes the nutrients being in high concentration, exert an osmotic pressure which causes entry of water into this region. A high turgor pressure develops. It forces the nutrients to pass towards the region which has low turgor pressure. The movement is like a mass flow (Munch 1930). Low turgor pressure is maintained in the area where soluble food is being withdrawn for consumption or storage by an active process.

1.5. EXCRETION Excretion (L. ex— out, crenere— to sift) is the elimination of metabolic waste products from the body. Waste products are unwanted and often toxic by-products of metabolism. Removal of waste products maintains a favourable internal environment in the body. A process related to excretion is osmoregulation. Osmoregulation is regulating osmotic pressure of body fluids by controlling the amount of water and salts in the body, retaining the latter in case of deficiency and eliminating the same if in excess. Excretory system is a system of organs and tissues that take part in separation, collection and voiding of waste products. Differences Between Excretion and Osmoregulation

Waste Products

1. Nitrogenous Waste Products. They are the major waste products which are formed during breakdown of extra amino acids, nucleic acids and alkaloids. The important nitrogenous waste products are urea, uric acid, creatine, creatinine, hippuric acid and ammonia. 2. Non nitrogenous Waste Products. Oxalic acid, lactic acid. 3.exsseschemicals Excess minerals, drugs, pigments, vitamins, hormones, cholesterol, etc.

1.5.1. Excretion in Human Beings In human beings excretion mainly occurs through a urinary system. Urinary or excretory system consists of organs that take part in separation, conduction, temporary storage and elimination of urine (an excretory product) made up of nitrogenous waste products, some salts and water. It has a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Kidneys. They are a pair of reddish brown, solid, slightly flattened, bean-shaped structures which lie in the abdominal cavity attached to dorsal body wall one on either side of vertebral column. Left kidney lies at slightly higher level and nearer the midline than the right one. The size is

10 cm in length, 5-6 cm in breadth and 4 cm in thickness. Each kidney has a convexity on the outer side and a concavity on the inner side. Concave side has a fissure or hilus for entry of a renal artery, exit of a renal vein and ureter. Renal artery brings oxygenated blood laden with waste products. Renal vein carries deoxygenated blood from which waste products have been removed. Structural and functional units of kidneys are nephrons (uriniferous tubules). About 1 million nephrons occur in each kidney. A nephron has two parts, Malpighian body and renal tubule. Malpighian body (= renal corpuscle) consists of a blind cup-shaped broader end of nephron called Bowman's capsule and a bunch of fine blood vessels or capillaries called glomerulus. Glomerulus develops from an afferent arteriole. It gives rise to an efferent arteriole. The diameter of efferent arteriole is less than that of afferent arteriole. As a result blood comes under pressure in the glomerulus. It functions as filtration unit. Bowman's capsule which accomodates one glomerulus, is lined by flat cells some of which have fine pores to allow passage of materials filtered out of a glomerulus. Renal tubule has three parts— proximal convoluted tubule (PCT), loop of Henle and distal convoluted tubule (DCT). Distal tubule opens into

a collecting tubule. Collecting tubules join to form collecting ducts that give rise to pyramids. Pyramids form calyces which open into pelvis.

Pelvis leads into ureter. All parts of the renal tubule arc covered by a network of pertitubutar capillary formed from efferent arteriole. The

peritubular capillaries join to form renal venule.

Mechanism of urine formation, it has four components — glomerular filtration, selective rcabsorption, tubular secretion and concentration. (i) Glomerular Filtration. Blood flows inside glomerulus under pressure due to narrowness of efferent arteriole. As a result it undergoes pressure filtration or ultrafiltration. All small volume solutes (e.g., urea, uric acid, amino acids, hormones, glucose, ions, vitamins) and water are filtered out and enter the Bowman's capsule. The product is called nephric or glomerular filtrate. Its volume is 125 ml/min (180 litres/day). (ii) Reabsorption. Nephric filtrate is also called primary urine. It passes into proximal convoluted tubule. The same is surrounded by peritubular capillaries. The latter reabsorb all the useful components of nephric filtrate, e.g, glucose, amino acids, vitamins C, calcium, potassium, sodium, chloride, bicarbonate and water (75%). Selective absorption also occurs in the region of distal convoluted tubule.

Excretion Function. It removes by-products of metabolism called waste products. Protection. It protects the body from toxicity of waste products. Elimination. It always involves elimination of waste products.

Osmoregulation It maintains osmotic pressure of body fluids. It protects the body from adverse conditions present in external environment. Elimination of water and salts depends upon the internal conditions.

There is elimination in case of excess water and salts. The same are

retained in case of deficiency.


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(iii) Tubular Secretion (Augmentation). It occurs mostly in the distal convoluted tubule which is also surrounded by peritubular capillaries. Smaller amount of tubular secretion also takes place in the area of proximal convoluted tubule. Tubular secretion is active secretion of waste products by the blood capillaries into the urinary tubule. It ensures removal of all the waste products from blood, viz., urea, uric acid, creatinine. Extra salts, K+ and H+ are also secreted into urinary tubule to maintain a proper concentration and pH of the urine. (iv) Concentration of the Urine. 75% of water content of nephric filtrate is reabsorbed in the region of proximal convoluted tubule. Some 10%

of water passes out of the filtrate through osmosis in the area of loop of Henle. It is because loops of Henle are immersed in hyper-osmotic interstitial fluid. Further concentration takes place in the area of collecting tubule in the presence of hormone called antidiuretic hormone (ADH) or vasopressin. The hormone is secreted only when concentrated urine is to be passed out. It is not secreted when a lot of water is taken. Absence of antidiuretic hormone produces a dilute urine. Hormone action, therefore, maintains osmotic concentration of body fluids. Deficiency of ADH causes excessive, repeated, dilute urination (diabetes insipidus). 2. Ureters. They are a pair of whitish narrow distensible muscular tubes of about 30 cm length. Each ureter arises from hilus part of the kidney. It moves downwardly and opens obliquely into urinary bladder. Ureters carry urine from kidneys to the urinary bladder. The passage of urine in the ureter occurs through peristalsis. 3. Urinary Bladder. It is a median pear shaped distensible sac that occurs in the pelvic part of abdomen. It stores urine brought by the two ureters. The storage capacity is 300-800 ml. 4. Urethra. It is a tube that takes urine from urinary bladder to outside. The opening of urinary bladder into urethra is guarded by a ring of muscles or sphincter. Urethra is 4 cm long in females and about 20 cm long in males. Its opening is separate in females but is common with reproductive tract in males. Micturition (Urination)

Urge for micturition occurs when urinary bladder comes to have 300-400 ml of urine. However, urine can be retained in the urinary bladder till it gets filled upto maximum capacity, 700-800 ml. At this time the urge becomes painful. Voluntary micturition can be carried any time. Total amount of urine excreted per day is about 1-6 - 1-8 litres. The quantity increases with larger intake of fluids and decreases with lesser intake of them. Urine

It is a transparent fluid produced by urinary system. Urine has an amber colour due to presence of urochrome. Urine contains 96% water, 2.5% organic substances and 1-5% inorganic solutes. Reaction is acidic in the beginning but becomes alkaline on standing due to decomposition of urea to form ammonia. Water— 96% Organic Substances— 2S%, e.g., urea, uric acid, creatine, creatinine, water soluble vitamins, hormones, oxalate. Inorganic Solutes— 1 -5%, e.g., sodium, chloride, phosphate, sulphate, magnesium, calcium, iodine.

Functions of Kidneys/Urinary or Excretory System (i) Waste Products. Excretion of nitrogenous and other waste products. (ii) Toxic Chemicals. The system takes part in expelling toxic chemicals that happen to enter the body. (Hi) Water Balance. Maintenance of water balance in the body by producing dilute urine in excess when water intake is high and concentrated urine in case of lesser water intake or excessive sweating. (iv) Excess Materials. Elimination of excess water soluble vitamins, drugs and other substances. (v) Regulation of Salt Content. Regulation of salt content in the body by excreting salts when in excess and retaining them when deficient. (vi) Maintenance of pH. pW of body fluids is maintained by excretion or non-excretion of H+ ions. (vii) Regulation of Blood Pressure. By controlling the fluid content, kidneys regulate blood pressure.

Accessory Excretory Organs 1. Skin. It contains sweat and sebaceous glands. Sweat glands excrete a fluid called sweat. Sweat consists of water (99-5%), traces of lactic acid, amino acids, urea and salt. Sebaceous glands secrete oil or sebum for lubricating hair. It has wax, sterols and other lipids. 2. Liver, (i) Extra amino acids are deaminated and toxic ammonia is converted into less harmful urea in liver, (ii) Liver degrades haemoglobin of worm out erythrocytes into bilirubin and biliverdin (bile pigments) for elimination. (Hi) It passes cholesterol, lecithin, excess vitamins, drugs and toxic substances into bile for elimination. 3. Lungs. They eliminate carbon dioxide and some aromatic substances. 4. Large Intestine. It excretes heavy metals and toxins into faecal matter. 5. Salivary Glands. Small quantities of toxins, excess drugs and salts are excreted by salivary glands. They are passed into alimentary canal through saliva.

Artificial Kidney or Haemodialysis Kidney is a very important organ which is essential for maintaining internal homeostasis as it is engaged in elimination of the nitrogenous and other metabolic by-products. Even if one kidney is damaged, the second kidney can carry on the function of excretion completely. However, if both the kidneys are damaged, a new compatible kidney has to be grafted. Till that period, waste products are removed with the help of haemodialysis (blood dialysis) or artificial kidney. Artificial kidney is a physico-chemical device to remove excretory products from blood in case of temporary disfunction (due to toxins) or near failure of kidneys. It is based on the principle of dialysis or separation of smaller solutes or ions from larger particles with the help of an ultrafilter. The artificial kidney or dialysis machine consists of a number of cellophane tubes embedded in a dialysatc or dialysing fluid. The dialysing fluid has the same osmotic concentration as that of blood. Flowcvcr, it contains more of glucose. Nitrogenous waste products, phosphates and sulphates arc excluded. Blood from an artery, or a vein fitted to a pumping mechanism, is mixed with heparin, cooled at 0° C and passed into cellophane tubes of artificial kidney. Nitrogenous waste products, sulphate and phosphate of blood pass into dialysing fluid. Purified blood is warmed and mixed with antiheparin. It is passed back into vein. The whole process takes 3-4 hours.

Uses


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1. Toxins. Haemodialysis helps in removing toxins from the body before they are able to damage the body permanently.

2. Uraemia. Patients suffering from kidney infections and uraemia (excess of urea in blood) are provided relief for some time. 3- Renal Failure. In case of near permanent damage to kidneys, haemodialysis provides time to the patient to find a kidney donor.

4. Normal Life. In between two dialyses, a patient can lead a near normal life.

5. Clean Procedure. Haemodialysis is a clean procedure where chances of infection are minimum.

1.5.2. Excretion in Plants Plants do not produce nitrogenous wastes like urea and uric acid because extra amino acids and nucleotides are not formed. They produce other types of waste products, called secondary /metabolites, e.g., alkaloids, tannins, aromatic oils. Excess of water is got rid off through transpiration. Excess of oxygen formed during day in photosynthetic organs can be considered as waste. It passes out through diffusion. The other wastes of plant metabolism are as follows. (i) Nitrogenous Waste Products. They are byproducts of general metabolism. The common ones are alkaloids, e.g., quinine, morphine, atropine. (ii) Organic Acids. They are metabolic intermediates. Some of them are without any other use. Rather on accumulation they may prove toxic, e.g., oxalic acid. (Hi) Tannins. They are complex aromatic compounds which are formed as secondary metabolites. (iv) Latex. It is an emulsion of varied composition which is exereted by special tubular cells called laticifers. if) Resins. They are oxidation products of aromatic oils. (r/) Gums. They are degradation products of cell wall. It saline habitats, the plants have to absorb excess salts that are required to be eliminated.

Mechanism

Plants do not have any mechanism to collect, transport and throw out their waste products. They have adopted varied strategies to protect their living cells from waste products. 1. Waste products arc stored in older leaves which soon fall often. 2. Resins, gums, tannins and other waste products arc deposited in the old xylem which soon becomes non-functional, e.g., heart wood. (iii) Bark. Bark consists of dead cells which is peeled off periodically. Tannins and other wastes are deposited in the bark. Incidentally, tannins are raw material for dyes and inks. (iv) Central Vacuole. Most plant waste products are stored in central vacuole of their cells. They are unable to influence the working of cytoplasm due to presence of a selectively permeable membrane called tonoplast. (v) Root Excretion. Some waste substances are actually excreted by the plants in the region of their roots. (vi) Detoxification. The toxic oxalic acid is detoxified by formation of calcium oxalate which gets crystallised into needles (raphides), prisms (prismatic crystals), stars (sphaeraphides) and crystal sand. Excess of calcium is also precipitated as calcium carbonate crystals, e.g., cystolith. (vii) Salt Glands. They excrete excess salts obtained from the habitat. Hydathodes also have an excretory function.

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LIFE PROCESSES - Weebly · movements are a major criterion which distinguishes living beings from the non-living ones. Movements are taking place all the time. Movements. Changes