Nutrients and Nutrition

7/27/2019 Nutrients and Nutrition

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Nutrients and Nutrition

Nutrients are the chemical substances in food that are required for the

nourishment of an organism. They are required by every living cell in the body for

metabolic reactions that are vital to life as well as for the synthesis of othercompounds needed by the body, reproduction and the growth and repair of damaged

tissues. Examples of nutrients are carbohydrates, proteins, lipids, minerals and

vitamins.

Nutrition, on the other hand, is the entire process by which organisms obtain

nutrients and energy from food. This includes the process of digesting food and

utilising the absorbed nutrients for growth, maintenance and the repair of damaged

tissues. Based on the strategies they deploy to obtain nutrients, living organisms

can be divided into two groups. They are autotrophs and heterotrophs.

AutotrophsAutotrophs are organisms which carry out autotrophic nutrition. Autotrophs get

their name from the words auto which means self and trophos which means feed. This

means that they can synthesise their own food by processing simple inorganic

substances such as carbon dioxide, water and minerals to produce nutrients such as

carbohydrates, lipids and proteins needed by the organism itself. This process is

achieved with the help of light or chemical energy.

Autotrophs can be divided into two groups. They are:

i. Photoautotrophs

ii. Chemoautotrophs

PhotoautotrophsThese are organisms that synthesise organic molecules (food) from carbon dioxide

and water using sunlight as a source of energy and the process known as

photosynthesis. Photo means light. So, photosynthesis means the synthesis using

sunlight as a source of energy. Examples of photosynthetic autotrophs are green

plants and algae.


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ChemoautotrophsChemoautotrophs are organisms that synthesise organic molecules (food) using

energy obtained by the oxidation of inorganic substances such as nitrates and

sulphides. The synthesis is called chemosynthesis which comes from the word chemo

which means chemical. So, chemosynthesis means the synthesis using chemicals as a

source of energy. Most chemoautotrophs are bacteria, such as sulphur bacteria,

which oxidise hydrogen sulphide to sulphur.

HeterotrophsHeterotrophs are organisms which carry out heterotrophic nutrition. Heterotrophs

get their name from the words hetero which means other and trophos which means

feed. These organisms are not able to synthesise their own nutrients but depend on

ready-made food such as plants and animals. Heterotrophic nutrition is then

nutrition in which energy and organic compounds (foods) are obtained by breaking

down other organisms (plant or animal tissues) which are digested and absorbed.

Heterotrophs can be divided into three groups. These are:

i. holozoics

ii. Saprophytes

iii. Parasites

HolozoicsHolozoics are organisms which feed by ingesting solid organic substances and

digesting, absorbing and assimilating them into their bodies; finally, these

substances are egested out of their bodies. The three groups that carry out

holozoic nutrition are:

a. Herbivores (herb = green crop). These organisms only eat plants.

b. Carnivores (carn = flesh). These are organisms which only eat animals.

c. Omnivores (omni = all). These organisms eat both plants and animals.

Nepenthes sp. (pitcher plants) is an example of a carnivorous plant which carries

out holozoic nutrition


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SaprophytesSaprophytism is carried out by any organism that feeds on dead and decaying

organic matter. The organism is called a saprophyte. Saprophytes are also known as

decomposers as they decompose dead organic matter into simpler molecules. Examples

are bacteria and fungi which digest the organic matter externally using digestive

enzymes before absorbing them as nutrients. Examples of saprophytes are rhizopus

(bread mould) and yeast.

ParasitesParasitism is defined as a close association wherein an organism feeds on other

living organisms to obtain nutrients. The organisms which gain from this

association are known as parasites while the losers are called the hosts. The

parasites absorb nutrients from their hosts Examples of parasites are fleas,

various bacteria, fungi and gastrointestinal worms.

Parasites can live inside or outside the bodies of their hosts. Endoparasites are

the parasites that live inside the bodies of their hosts (endo = inside). Examples

are tape worms (Taenia sp.) and round worms (Ascaris sp.).

The tapeworm is an example of a endoparasite

Ectoparasites are the parasites that live outside their hosts (ecto = outside).

Examples are mosquitoes and mites (they suck blood from other organisms).

Lice: an example of ectoparasites


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A Balanced DietA balanced diet is a diet that contains the major nutrients which include

carbohydrates, proteins, vitamins, minerals, water, roughage or dietary fibre and

lipids in the correct proportions. A balanced diet is essential for the healthy

growth and development of the body. The table below shows the nutrients and their

functions.

Nutrients and their functions


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The food pyramidA guide to a balanced diet can be obtained from the food pyramid. See the figure

below. A healthy diet consists of more vegetables, fruits and grain products which

are at the bottom of the pyramid. Items higher on the pyramid must be consumed

less and include fats, oils and sugar.

The food pyramidDaily Energy Requirements

Our body needs energy to carry out vital body functions such as maintaining blood

pressure and body temperature, sustaining regular heartbeats and breathing. Energy

is also required for the body to carry out the biochemical reactions that take

place at the cellular level. These include cell division, cell growth, active

transport, protein synthesis, etc. The sum of all these biochemical reactions is

called metabolism. The energy requirements for the metabolic activities are

derived from the nutrients absorbed by the body.

The energy demand of the body over a specified period of time to carry out

metabolic activities is called the metabolic rate. It is measured in kilojoule

(kJ) units. The higher the metabolic rate, the more will be the energy required

for the metabolic activities. Our metabolic rate is higher when we are running and

lower when we are sleeping.


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The energy required to carry out the biochemical reactions that keep the vital

body functions going is called the basal metabolic rate (BMR). The BMR depends on

various factors such as a persons weight, state of health, sex, age as well as

the climate. For example, the BMR of a man when sleeping is different to the BMR

of a woman when sleeping. Similarly, the BMR of a child when sleeping is differentto that of an adult when sleeping.

Generally, women have a lower BMR than men and children have a higher BMR than

adults. A person living in a cold climate has a higher BMR than a person living in

a hotter climate. There are two main factors influencing the energy requirements

of the body. These are:

i. The basal metabolic rate (BMR)

ii. Physical activities

The variables influencing the bodys energy needsFor example:

A 50kg football player training for 1.5 hours daily would require over 23,027.4 kJ

daily, whereas a 50kg female tennis player training for the same duration would

require approximately 9,838.98 kJ daily. (Source:

http://www.bestsyndication.com/?q=20080318_online_calorie_counter.htm)

The knowledge about the body energy needs can help an individual to stay healthy.

A person who takes a diet containing the calories equal to the energy needed by

the body will remain slim and healthy. If the diet contains excess energy, the

energy turns into fats and the person gains weight. On the other hand, if the diet

contains inadequate energy, the person will lose weight.

Energy Contents of FoodOur body needs energy to carry out vital body functions such as maintaining blood

pressure and body temperature, sustaining regular heartbeats and breathing. Energy

is also required for the body to carry out the biochemical reactions that take

place at the cellular level. These include cell division, cell growth, active

transport, protein synthesis, etc. The sum of all these biochemical reactions is

called metabolism. The energy requirements for the metabolic activities are

derived from the nutrients absorbed by the body.


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A food calorimeter to determine the energy value of food

The amount of energy that is produced from the oxidation of one gramme of food is

known as the energy value of the food. It is measured in joules per gramme (Jg-1).

The amount of energy in food can also be expressed as calorie

Different types of food have different energy values. The table below shows the

energy values of different types of foo

VitaminsVitamins are complex organic compounds needed in tiny amounts by humans and

animals to maintain normal good health. Vitamins are not synthesised by the human

or animal body (except vitamin D), so they are obtained from the diet. Vitamins

can be easily destroyed by heat.

General functions of vitamins

The function of vitamins is to act as coenzymes which control various metabolicreactions. Vitamins do not provide energy but are essential for efficient

metabolism, growth, protection and energy regulation in cellular respiration.


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Classification of vitaminsAltogether, 13 different types of vitamins have been identified. They can be

divided into two groups as follows:

i. water-soluble vitamins

ii. fat-soluble vitamins

- Water-soluble vitaminsWater-soluble vitamins dissolve only in water. They are circulated freely around

the body and are absorbed directly into the blood circulatory system. Excess

consumption of these vitamins will be excreted and there is no toxicity when takenin large amounts. Examples of water-soluble vitamins are vitamins B1, B2, B3, B6,

B12, folic acid, vitamin H and vitamin C.

- Fat-soluble vitaminsThese vitamins are only dissolved in oil, fat and organic solvents. They are

absorbed together with fat and bile. They are difficult to excrete and any excess

amount is stored in the body. As such, excess consumption is dangerous. Examples

of fat-soluble vitamins are vitamins A, D, E and K. .

Deficiency in vitaminsIf a person is deficient in one or more vitamins, he/she may develop vitamin

deficiency diseases. Different types of vitamins may cause different deficiency

diseases as shown in the table below.

Sources, functions and effects of deficiency of vitamins B1, B2, B3, B5, B6, B12

What are vitamins?

What are water-soluble vitamins?

What are fat-soluble vitamins?

Minerals


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Minerals are inorganic nutrients found in food or drinks. They cannot be

synthesised by the body and must be obtained from the diet. They do not provide

energy to our body but are essential for various body functions such as

biochemical reactions and developing the molecules. The minerals are classified

into two groups:

i. Macrominerals

These minerals are required by the body in relatively large quantities (major

minerals) of more than 100 mg per day Examples of these minerals are calcium,

magnesium, phosphorus, sodium, potassium and chlorine.

ii. Microminerals

These minerals are required by the body in small amounts of less than 20 mg

per day. These minerals have their own specific functions. Examples are iron,

iodine, zinc and molybdenum.

Dietary FibreDietary fibre or roughage is indigestible plant matter. Basically, it is the

fibrous materials in the diet that consist mainly of the cellulose of the cell

walls of plants.

Food high in fibre contentDietary fibre is not a nutrient and the stomach cannot digest it. However, it is

still important for the digestive process as it helps the food to move through the

digestive system and hold water so that the faeces remains soft, thus easing

defecation.

In addition, the dietary fibre also lowers the cholesterol level in the blood,

reduces the risk of heart diseases and colon cancer. Dieticians recommend that

about 25-50 g of fibre should be incorporated into the diet each day to ensure

good health. Examples of foods high in fibre contents are fruits, grains, cereals,

pasta, legumens, nuts, seeds and vegetables.

Deficiency of dietary fibre can increase the risk of constipation, bowel

irregularities, haemorrhoids, diverticulosis and colorectal cancer. Constipation

occurs when the flow of the digested food in the large intestine is not smooth and

is very slow. In this case, the faeces is dry and hard because much water has been

absorbed into the body. As the result, the defaecation is difficult and painful.


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WaterA human body mass is made of 70% of water. Without water, humans only can survive

for three or four days. Water is important to the human body due to the following

reasons:

i. All metabolic reactions take place in solution, so water plays a role as a

medium for such reactions.

ii. In homeostasis, water plays the main role in thermoregulation.

Thermoregulation is the ability of the body to maintain its body temperature

at a particular level regardless of any internal or external temperature

changes in the environment. For example, on a hot day, sweat glands under the

skin secrete sweat onto the surface of the skin. When the sweat evaporates,

it cools the skin, thus maintaining the internal body temperature.

iii. As blood plasma consists of 92% of water, water plays a role as a medium for

the transportation of digested food, oxygen, excretory substances, minerals

and hormones to the entire body.

iv. Water also helps in the excretory process. Excretory wastes such as urea,

uric acid and excess minerals are removed from the body through perspiration

and urination.

v. Water is also important as a lubricant in our body. It helps to reduce

friction between the bones in the joints.

Choosing Appropriate Diets for Different Target GroupsDifferent groups of people need different diets in order to cater to the proper

nutritional needs of their bodies. Different diets are needed depending on the

age, lifestyle, health condition and specific nutritional needs of people,

especially those with specific diseases. The table below show groups of people and

guidelines for the diet of specific groups.


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MalnutritionMalnutrition is the health condition faced by people eating an improper or

unbalanced diet. It can due to eating less food (under-nutrition), eating too much

food (over-nutrition) or bad eating habits (imbalanced nutrition). There are many

health effects resulting from malnutrition and we shall look at them in detail.

Protein DeficiencyProtein deficiency gives rise to two common health problems. They are:

i. Kwashiorkor

ii. Marasmus

- KwashiorkorKwashiorkor is a health problem related to poverty and is prevalent in developing

countries such as in Africa and South Asia because of protein deficiency in the

diet. It usually affects children aged one to four years. Children suffering from

kwashiorkor have severely bloated abdomens (pot bellies), flaky skins, thin

muscles and are underweight. Their growth is also stunted.

MarasmusMarasmus is widespread in developing countries and occurs among children between

nine to 12 years of age. it is mainly due to poverty and lack of protein and

energy providing nutrients. The symptoms are "an old man's face", being

excessively underweight, thin muscles and stunted growth.


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Effects of Calcium, Phosphorus and Vitamin D DeficienciesCalcium, phosphorus and vitamin D deficiencies in the diet may cause many health

problems such as osteoporosis and osteomalacia.

OsteoporosisOsteoporosis is a disease of the bones and is due to an insufficient dietary

intake of calcium; it is very common among the aged. The lack of calcium causes

the bones to become brittle, porous and fracture easily especially at the hips and

backbone. In severe situations, the backbone shortens and bends forward.

OsteomalaciaOsteomalacia is the softening of the bones due to the deficiencies of calcium,

phosphorus, and vitamin D in the dietary intake. It always occurs in pregnant

women while in children, it is known as rickets.

Bones in the legs of a rickets victim

Effects of an Excessive Intake of Nutrients

Not all health problems are due to the lack of nutrients in the dietary intake.

Health problems are also caused by over-nourishment (excessive intake of food).

The effects of an excessive intake of various nutrients are shown below.


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Excessive intake of carbohydratesThe excessive intake of carbohydrates is one of the bad habits occurring when

consuming food. This excessive intake can lead to various diseases such as obesity

and diabetes mellitus.

Obesity is a condition of a person who is overweight. If a person is obese, the

risks of developing various diseases, such as cardiovascular diseases, strokes,

brain haemorrhages, high blood pressure, atherosclerosis, and diabetes mellitus,

are increased.

Diabetes mellitus is a disease due to the presence of excess glucose in the blood.

This happens when too much sugar is in the dietary intake (including

carbohydrates) and the pancreas is not producing enough hormone insulin to convert

the glucose to glycogen. Diabetes can lead to various diseases such as kidney

diseases, cataracts, blindness and heart problems. In addition, wounds become very

difficult to heal.

Excessive intake of lipids

Coronary artery in human filled by plague

Excessive lipids (saturated fats) in the dietary intake may cause many diseases

such as hypertension, high blood pressure and atherosclerosis.

Atherosclerosis is a situation when there is deposit of plaque in the internal

lining of the blood vessels. This deposit blocks the blood flow and in severe

cases, it even stops the blood flow altogether, leading to heart attacks

(myocardial infarction).


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Excessive intake of minerals

Kidney stones most made of calcium and oxalate

Excessive intake of minerals, such as salty food, in the dietary intake can lead

to various diseases such as high blood pressure, heart problems, strokes and theformation of kidney stones.

Kidney stones are formed because of an excessive intake of salt and the lack of

water in the diet. Kidney stones develop from the crystallisation of urine which

accumulates in the kidneys. The stones are made of calcium and oxalate. Their

presence complicates the kidney function and make urination painful. The stones

can be expelled together with the urine.

Human Digestive SystemThe human digestive system also called the gastrointestinal system. This system

starts at the mouth and ends at the anus. The parts along the mouth and the anus

are called the alimentary canal. The parts of the human digestive system are shown

in figure below.

Duodenum is located at the first part of small intestine while the rest of small

intestine is known as ileum. The large intestine consists of caecum, colon, and

rectum. Small intestine and large intestine are the longest parts in this system.

From the ducts to the gut, there are some accessory organs connected to this part;

the liver, the gall bladder and the pancreas.


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Physical digestion and chemical digestionThe digestion involves two processes which is physical and chemical digestion. The

breaking down of food particles is the physical digestion. Chewing food particles

is an example of the process in which the food particles will be broke into

smaller particles. This process is important to increase the surface in the

chemical process. Peristalsis is the other physical digestion involves in the

digestion of food. This process helps to move the food particles down the

elementary canal.

The physical digestion is too different from the chemical digestion. If the

physical digestion is the process involve of the body part such as teeth, ileum,

colon and others. Chemical digestions are the processes that involve the chemicals

contained in our body. This type of digestion involves the process of breaking

down the food particles into the small and simple molecules and also into soluble.These processes involving hydrolysis; the enzyme reactions in the presence of

water and each enzyme are specific for a type of food.

Some of the chemical contained in our body and known as digestive juices. The

digestive juices are; saliva, gastric juice, pancreatic juice and intestinal

juice. All these juice contain enzymes that involve in the hydrolysis process.

Each enzyme has their own factors to maximize their performance. For example, an

enzyme needs an acidic medium to perform well. In the stomach, hydrochloric acids

will prepare an acidic medium for the bile secreted to facilitate digestion of

fats. Digestive juices are secreted by the digestive glands.

Food DigestionFood digestion is a process where large and complex organic compounds of food

components, consisting of carbohydrates, proteins, and lipids, are broken down

into simpler molecules by the digestive enzymes through the process of hydrolysis.

The final products of the digestive processes are glucose molecules, amino acids,

glycerol and fatty acids which can be absorbed by the cells so that they can carry

out the metabolic processes.

The Human Digestive SystemThe human digestive system starts at the mouth and ends at the anus. It is

sometimes called the gastrointestinal system and has a length of about 7-9 m long.

The human digestive system is shown in the figure below.

The human digestive system


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The duodenum is located at the first part of the small intestine while the rest

ofthe small intestine is known as the ileum. The large intestine consists of the

caecum, colon and rectum. The small and large intestines are the longest parts of

the digestive system. There are some accessory organs connected to the system such

as the liver, the gall bladder and the pancreas. They also have roles to play inthe digestive process.

The food enters the mouth into the oesophagus, then to the stomach, small

intestine and large intestine before it is excreted at the anus. Various digestive

processes consisting of physical digestion and chemical digestion occur as at

various stages of the digestive system as the food moves from the mouth to the

anus.

Physical Digestion and Chemical DigestionThe digestion involves two processes. They are:

i. physical digestion

ii. chemical digestion

- Physical DigestionPhysical digestion is the breaking down of large pieces of food into smaller onesby mechanical means. The physical digestion occurs at various parts of the

digestive system.

- Chemical digestionA chemical reaction breaks down complex food into simpler molecules using specific

digestive enzymes. The process is called hydrolysis. The digestive juices, such as

saliva, gastric juice, pancreatic juice and intestinal juice, contain enzymes

which help in the hydrolysis process. In the stomach, hydrochloric acid provides

an acidic environment for the enzymes to function while bile secreted by the liver

emulsifies the fats and helps in the digestion of fats.

Digestion of Carbohydrates, Protiens and Lipids in the Human Body

We shall look at the digestion of carbohydrates, proteins and lipids through the

digestive system.


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The mouthThe first digestion process of the food occurs in the mouth. It involves the

physical digestion of chewing food by the teeth. This process breaks the food into

smaller sizes, thus increasing the surface area of the food for the action by the

enzymes. Here, the first chemical digestion also takes place where food is mixed

with saliva secreted by salivary glands. The saliva juice contains water, an

enzyme called salivary amylase and mucus. The salivary amylase breaks down the

starch into maltose (simple sugar) according to the following equation:

The mucus moistens the food particles, rolling and shaping them into a food lump

called the bolus.

The oesaphagusThe moist food bolus is swallowed and moved through the muscular tube line called

the oesophagus. The movement of the bolus along the oesophagus is achieved by a

process called peristalsis. Peristalsis is a series of rhythmic wave-like

movements caused by the musclar contraction and relaxation of the longitudinal and

circular muscles along the oesophageal wall. The peristalsis continues until the

food reaches the stomach. The figure below shows the peristalsis along the

oesophagus.

The stomachThe stomach is the main organ of digestion and is located below the diaphragm. The

lining of the stomach contains the gastric gland that secretes gastric juice. The

food is chewed through the muscular relaxation and contraction of the stomach

muscles. In the process, it is mixed with the gastric juice to become a semi-fluid

and partly digested food called chyme. The figure below shows the secretion of

gastric juice in the stomach.

- Secretion of gastric juiceThe environment in the stomach is highly acidic due to the hydrochloric acid

contained in the gastric juice. This environment (pH 1.5-2.0) is necessary for the

optimal action of the enzymes. Besides this, it stops the activity of the salivary

amylase and at the same time kills bacteria and parasites in the food.

- Protein DigestionBesides the gastric juice containing the hydrochloric acid, there are also

digestive enzymes in the stomach called the pepsin and rennin. These enzymes are

responsible for the digestion of the proteins. Pepsin hydrolyses protein into

polypeptide.


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On the other hand, the enzyme rennin curdles milk. The enzyme catalyses the

soluble milk protein (caseinogens) to become insoluble milk protein (casein).

The contraction and relaxation of the stomach moves the chyme, the semi-solid and

partly digested food, from the stomach into the duodenum of the small intestine.

The small intestineThe small intestine is divided into three structural parts:

i. The deodenum

ii. The jejunum

iii. The ileum

- The deodenumThe duodenum is the first part of the small intestine and it receives the chyme

directly from the stomach. Here, the chyme is broken down using the enzymes. The

duodenum does not have any glands that secrete digestion juices but it only

receives secretions from the gall balder of the liver and the pancreas.

The LiverThe liver secretes bile and stores it in the gall bladder. Bile is not an enzyme

but it aids in the emulsifying of lipids by breaking them down into tiny droplets,

increasing the surface area for the action of the enzymes. Bile also functions to

create the alkaline environment (pH 7.6-8.6) in the duodenum necessary for the

optimum action of the digestive enzymes (produced by the pancreas) and at the same

time, it helps to reduce and neutralises the acidity of the chyme. Bile flows into

the duodenum via the bile duct.

The PancreasPancreas secrete pancreatic juice containing three digestive enzymes, namel, the

pancreatic amylase, trypsin and lipase which flow into the duodenum via the

pancreatic duct. These enzymes help in the digestion of starch, proteins and

lipids in the chyme and function optimally in an environment with the pH 7.1-8.2.

- The digestion of starch, proteins and lipidsThe digestion of starch, proteins and lipids occurs in the duodenum using enzymes

obtained from the pancreas.


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i. Starch

Strach is converted to maltose using pancreatic amylase,

ii. Proteins

The polypeptides are broken down by the enzyme trypsin into peptides,

iii. Lipids

Lipids are broken down by the enzyme lipase into fatty acids and glycerol.

They are small enough to be absorbed directly by the epithelial lining of the

small intestine,

- The ileumThe ileum is located at the bottom part of the small intestine. The functions of

the ileum are to absorb bile and the secretion of enzymes for the digestion of

peptides and disaccharides. The products of the digestion of the peptides are

amino acids while the products of the digestion of disaccharides are the

monosaccharides which are absorbed directly along with fatty acids and glycerol.

The vitamins and minerals are very small molecules which can be absorbed directly

by the body without undergoing digestive processes.

The digestion of proteinsProtein digestion involves the breaking down of peptides into amino acids using

the enzyme erepsin,

The end products of the protein digestion are fatty acids and glycerol which are

small enough to be absorbed directly by the epithelial lining of the ileum.

The digestion of carbohydratesThe digestive process breaks carbohydrates into disaccharides and finally into

monosaccharides. Monosaccharides are the end products and exist either in the form

of glucose, fructose or galactose; they are absorbed by the epithelial lining of

the ileum.


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The Digestive System of RuminantsRuminants (cows, goats and sheep) feed on plant materials which contain a large

amount of cellulose. Cellulose is a polysaccharide and is extremely insoluble. It

can be broken down into glucose with the help of the enzyme called cellulase. So,

the ruminants are adapted in order to digest cellulose with the help of this

enzyme.

In ruminants, the digestive system consists of a stomach with the following four

chambers :

i. The rumen

ii. The reticulum

iii. The omasum

iv. The abomasum

Inside the first two chambers are large populations of bacteria and protozoa. The

microorganisms secrete enzymes called cellulase which help in the digestion of

cellulose. This also allows the ruminants to carry out rumination, the process of

rechewing partially digested food.

The relationship between the microorganisms and the ruminants is symbiotic where

both parties benefit from the relationship. The ruminants obtain food from the

digestion of the cellulose while the microorganisms obtain food, shelter and

space.

The digestive process of the ruminants consists of four stages, one at each of the

stomach chambers:.

Step

1.

The rumen

When a ruminant first chews and swallows grass, it enters the rumen. The

rumen is a large fermentation chamber with a very high population of

bacteria and protozoa. The bacteria secrete the enzyme called cellulase

necessary for the break-down of the cellulose. Parts of the digestive

products (glucose and fatty acids) are absorbed by the ruminant while the

others are absorbed by the bacteria and protozoa.

Step

2.

The reticulum

The reticulum is the second chamber in a ruminant's digestive system. In


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this chamber, a further hydrolysis of cellulose is undertaken. At some

point, the partially digested food in the form of balls called "cud" is

returned to the mouth (regurgitated) to be chewed again. This helps to

further break down the cellulose. This movement of the partly digested food

to the mouth is helped by the antiperistalsis of the eosophagus.

Step

3.

The omasum

After the second chewing, the food flows directly to the omasum. This is the

third chamber of the ruminants stomach. Here, the product of cellulose

digestion, glucose, is absorbed by the body. Water is drained from the cud

and absorbed into the body.

Step

4.

The obamasum

The obamasum is known as the true stomach. Here, the gastric juice

(containing the hydrochloric acid) is secreted to complete the digestion of

proteins and other food substances. The food (chyme) is passed to the small

intestine where it is further digested in the normal way and absorbed by the

body.

The Digestive System of RodentsRodents (mice, squirrels) have a different digestive system from ruminants. They

have a long caecum located between the small and large intestines. In the caecum,

there is a high concentration of symbiotic bacteria and protozoa which secrete the

cellulase to digest cellulose.

In order to obtain the maximum nutrients, rodents eat some of their faeces and

allow the food to pass through the digestive tract twice. The first faecal pallets

produced at night are normally soft and watery containing partially digested food.

These faecal pallets are eaten again and pass through the digestive tract for a

second round of digestion. In this way, more nutrients are absorbed. The second

dry and hard faecal pallets are produced during the day.

Problems Associated with Food Digestion

There are a few problems associated with the digestion of food, namely:

i. The incomplete digestion of food

ii. Gallstones in the gall bladder

The incomplete digestion of food


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Incomplete digestion is caused by the types of food that we consume and the way

they are consumed. Excessive intake of food at any one time, oily food, hot food

(such as strong curries), and not chewing properly are some of the most common

factors causing the incomplete digestion of food. They may lead to nausea,

vomiting and abdominal pains.

To ensure the complete digestion of food, the food must be chewed slowly and oily

and hot food should be avoided. In this way, the digestive enzymes can function

optimally and food will be completely digested.

Gallstones in the gall bladder

When bile contains an excessive amount of cholesterol, there is a tendency for the

cholesterol to crystallise and form gall stones in the bile duct. The gallstones

vary in size, from the size of sand to the size of a ping pong ball depending on

the severity of the gallstone formation.

A problem occurs when the gallstones become big enough to obstruct the movement of

bile from the gall bladder to the stomach. When this happens, the digestion of

lipids cannot take place. This leads to the following symptoms:

i. prolonged and continuous pains

ii. nausea and vomiting

iii. fever or chills

iv. yellowish colour of the skin or whites of the eyes

v. clay-coloured stools

The gallstones may also be formed in the pancreatic duct. In this case, the

gallstones may block the flow of the pancreatic juice leading to severe pains and

incomplete digestion of food.

Adaptations of the Digestive SystemThe digestive system is suitably adapted to increase the rate of absorption and

this is achieved via the following:

i. Increasing the surface area of the lining of the small intestine by having a

long intestine (about 5-6 metres long) and a folded surface which is is

covered by a finger-like projection called the villi.

ii. The thin epithelial wall of about one cell thick. This allows the easy flow


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of the movement of the digestive system across the wall.

iii. A moist surface.

iv. Plenty of blood vessels for efficient transportation of digestive products.

The adaption of the digestive system (1) small intestine (2) A section of a small

intestine to show the villi (3) Enlarged illustration of a villus (4) Epithelium

with microvilli and goblet cell

Absorption of Digested FoodDepending on the type of digestive products, various mechanisms are utilised that

allow these products to be absorbed from the lumen of the intestine.

Monosaccharides (glucose, galactose, fructose)

Their absorption across the epithelial cells into the blood capillaries is

achieved through secondary active transport and facilitated diffusion mechanisms.

They are absorbed directly into the blood capillary network contained in each of

the villi.

Fatty acids and glycerolFatty acids and glycerol utilis the simple diffusion mechanism to move across the

epithelial cells. The movement is achieved by first transforming the fatty acids

and glycerol into tiny droplets of lipids which then move into the lacteals

located at the centre of each the villus. The lacteals combined to form a larger

vessel of the lymphatic system and a network throughout the body.

Fat-soluble vitaminsFat-soluble vitamins diffuse directly across the epithelial cells and directly

into the lacteal located at the centre of each villus.

Water-soluble vitaminsWater-soluble vitamins diffuse directly into the blood capillary network contained

in the villi.


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WaterWater is absorbed via osmosis.

- Transportation of Nutrients to Body CellsAt the villus, the water-soluble nutrients (monosaccharides, amino acids and

minerals) enter the blood capillaries whereas the lipid-soluble nutrients enter

the lacteal and then into the lymphatic vessels. The blood capillaries bring the

nutrients into the liver via the hepatic portal vein first for assimilation

(regulating, processing and filtering) before sending them to the heart to be

circulated throughout the body. On the other hand, the lymphatic vessel connected

to the heart is where lipid-soluble nutrients are circulated throughout the body.

The functions of the liver are:

i. Regulation of the glucose level in the blood

ii. Deamination

iii. Storage

iv. Detoxification

v. Production of bile

vi. Synthesis of plasma proteins

Regulation of the glucose level in the bloodThe liver functions to regulate the amount of glucose released into the body

system. In a situation where the sugar level in the blood is high, the liver

stores the glucose as glycogen.

DeaminationDeamination is the process where amino acids are broken down into glucose and

urea. In this way, the liver can regulate the amount of amino acids in the blood

so that it remains constant in the blood. When an excess amount of amino acids is

present in the blood, deamination occurs and the glucose and urea are released

from the body via urination.

- StorageThe liver can act as a storage for nutrients. Examples of nutrients stored in the

liver are the fat-soluble vitamins A and D and water soluble B12. At the same


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time, it can also store minerals ions such as iron, potassium, cobalt, zinc and

copper.

- DetoxificationThe liver also functions as a detoxifier of poisonous substances. There are manytoxic substances entering the body such as alcohol, drugs, and other harmful

chemicals. The liver metabolises these toxic substances and the products are

excreted from the body through urination.

- Secretion of bileThe liver secretes bile which is stored in the gall bladder. Bile contains

greenish bile pigments and bile salts which are transported to the duodenum for

the digestion and absorption of fats and fat-soluble vitamins. The process of

digestion involves the emulsification of fats into tiny droplets which increase

the surface area for optimal action by the lipase.

- Synthesis of blood plasma proteinsThe liver is a site for the synthesis of blood plasma protein proteins such as

prothrombin and fibrinogen. These plasma proteins are necessary for blood clotting

processes.

- Assimilation of Digested Food by the Liver and CellsAssimilation is a process where absorbed food in the liver or cell is utilised for

the purposes of growth, reproduction and repair.


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What is Defecation?

After the digestion process in the small intestine, the left-over products,

consisting mostly of undigested food substances and dietary fibre, enter the colon

(large intestine). The undigested food moves along the colon aided by the rhythmic

contraction and relaxation of the colon muscle walls (peristalsis) where further

absorption of water (90% of it) and other minerals (with the help of symbiotic

bacteria) takes place. The final compressed food residue is called faeces.

The faeces consists of mainly undigested food residue, dead epithelial cells, bile

pigments and bacteria which are stored temporarily in the rectum. When the rectum

is full, the faeces is expelled out of the anus via the contraction and relaxation

of the sphincter muscles. The process of the expulsion of the faecal materials out

of the body through the anus is called defecation.

Structure of the large intestine

The large intestine is about 1.5 metre long and consists of three main components:

i. the caecum and appendix

ii. the colon

iii. the rectum

The main functions of the large intestine are the following:

i. Absorption of 90% of the water, compressing the undigested food into faecal

materials.

ii. Absorption of minerals with the help of symbiotic bacteria.

iii. Storage of the faecal materials before defecation.

The Formation of Faecal Materials

There are various processes occurring in the large intestine before the faecal

materials are formed. These are:

i. Absorption of water and compression of faecal materials

About 90% of the water content of the undigested food materials are absorbed

here. This makes the food residue hard and it becomes more of a semi-solid.


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It is also compressed and compacted to become faeces.

ii. Absorption of minerals with the help of symbiotic bacteria

The symbiotic bacteria, Escherichia E. coli, which are present in the colon,

undergo metabolic processes and produce vitamins B and K which are absorbed

through the colon wall.

iii. Lubrication of the faecal materials

The faecal materials are lubricated by the mucus secreted by the wall of the

colon and move along the colon via the action of peristalsis.

iv. Storage

The faecal materials are stored for about 12-24 hours before defecation. Thedefecation is achieved via the relaxation and contraction of the anal

sphincter muscles which expell the faeces out through the anus.

Problems related to Defecation

There are a number of problems related to defecation. They are:

i. Constipation

ii. Haemorrhoids (piles)

ii. Colon cancer

- ConstipationConstipation is the condition in which the faecal materials are dry, hard and

difficult to expel out of the anus. Constipation is caused because a large amount

of water has been removed, making the faeces dry and hard; its movement along the

colon is also slow.

Constipation can be overcome by following diet that is rich in fibre. Food that is

rich in fibre can facilitate the movement of undigested food materials along the

colon. Consuming more liquids also helps in overcoming the problem of

constipation.


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- Haemorrhoids (piles)Haemorrhoids is the condition of abnormally swollen and inflamed veins in the

rectum and anus. It is caused by prolonged constipation where too much pressure is

being applied to the rectum, causing the blood veins to swell and bulge. In

extreme cases, the veins can rupture causing bleeding during defaecation.

Colon cancerColon cancer is a growth developing in the tissues of the colon. There are many

reasons for the cancer to develop; the main one would be a diet deficient of fibre

as well as infrequent elimination of faeces. The prolonged contact between the

colon and undigested food, containing toxic substances such as carcinogens, can

lead to the formation of cancer.

Good Eating HabitsGood eating habits means consuming food in the right proportions and of the right

quality at the right time intervals. These include:

i. Eating at the right time and not taking too many snacks

ii. Practising a balanced diet

iii. Consuming the right amount of water

iv. Consuming food rich in fibre

v. Use the food pyramid as a guide to food intake

vi. Eating food in the right amounts without over- or under-eating

vii. Avoiding food rich in sugar, fats and salt

Health Problems Related to Bad Eating HabitsThere are many health problems related to bad eating habits. They are:

i. Obesity

ii. Anorexia nervosa

iii. Bulimia

iv. Gastritis


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- ObesityObesity can be defined as a body weight and size of about 20% above normal. It is

caused by the excessive storage of energy in the form of fats resulting from the

excessive intake of energy-rich food such as carbohydrates and fats. Lack of

exercise also contributes to obesity. People with obesity are susceptible to

various diseases such as cardiovascular diseases, hypertension and diabetes

mellitus. Obesity can be reduced by the practice of having a balanced diet and

regular exercise.

- Anorexia nervosaAnorexia (an "without", orexis "appetite") is a psychological eating disorder

mostly affecting adolescent girls and women and is characterised by a constant

fear of weight gain and a change in the body shape. As a result, the person has no

appetite for food, suffers excessive weight loss and has a distorted image of a

healthy body. Sufferers continue to think that they look overweight although in

actual fact, they are bone-thin.

This condition can lead to various diseases such as disruption in the functions of

the heart, endocrine and reproductive systems. It can be overcome by proper

counselling to correct the fear of gaining weight and other emotional stresses.

- BulimiaBulimia (boulima "ravenous hunger") is a psychological eating disorder where

there are occasions when the person has the urge to consume a large amount of food

(binge eating) in a short period of time and is unable to stop eating during the

binge. This is quickly followed by a sense of guilt of having taken too much food

and purging the food out of the body via self-induced vomiting. In some cases,

laxatives are used to get rid of the food.

The person with bulimia may have the normal body mass, but the repeated purging of

the food out of the body may result in injury to the digestive tract at the same

time causing an imbalance of salts and minerals in the body. This increases therisks of other diseases such as failure of the kidneys, liver or heart. This

disease can be overcome by counselling to eliminate the psychological urge of

consuming too much food in a short period of time and feeling guilty about it.

- GastritisGastritis is the condition in which the epithelial lining of the stomach is

inflamed and eroded. In a normal body, the epithelial lining of the stomach wall

is covered with mucus which protects the lining from hydrochloric acid. The

prolonged and continuous absence of food in the stomach causes the acid to act on

the lining and damage it. In severe cases, the damage can develop into a hole


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causing a gastric ulcer. There is a possibility that stomach cancer may also

develop

Gastritis is due to bad eating habits such as the over-consumption of alcohols,

drugs, ( e.g., aspirin), irregular food intake and stress. The symptoms of

gastritis include pains in the upper abdomen, loss of appetite, heartburns, nausea

and loss of weight.

Evaluating Eating HabitsGood eating habits are important for the maintainance of good health. Apart from

good eating habits, emphasis must also be given to the amount of nutrients in the

food, its freshness and the amount of food additives such as colouring agents and

preservatives being added to the food.

Good eating habits are also reflected in the body weight and size. The body weight

and size can be measured using the body mass index (BMI). The following table

shows the BMI as an indicator of the body size and weight which reflect the eating

habits.

Effects of a Defective Digestive SystemA defective system is a system that does not function normally. There are many

parts in the digestive system and the defect of any part of this system will have

an overall effect on the process of digestion. We shall look at each of the parts,

the defects that might occur and the effects that follow.

- The MouthAny defect in the mouth may be related to the process of chewing. This can lead to

solid food not being properly broken down; the food is then not properly digested.

- The Salivary GlandsA defect in the salivary glands normally means the defective secretion of saliva.

This leads to the improper digestion of food in the mouth. The food might alsotaste different from its normal taste.

- The OesophagusDefects in the oesophagus include its weak relaxation and contraction. The food

bolus moving down the oesophagus is impaired.

- The StomachProblems in the stomach include a lack of the secretion of mucus, acids and

enzymes. This will cause poor food digestion and the formation of stomach ulcers.


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- The DuodenumDefects in the duodenum include a damaged epithelial lining. This reduces the

efficiency of nutrient absorption.

- The Large IntestineDefects in the large intestine include poor contraction and relaxation of the

stomach muscles. They will result in the slow movement of food down the colon,

leading to constipation.

Taking Care of the Digestive SystemWe need to care of our digestive system. This is to ensure that the system is

functioning properly and the nutrients are absorbed efficiently and assimilated by

the cells. There are several practices one can follow to ensure that the digestivesystem is healthy. These include:

i. Having a balanced dietary intake

ii. Drinking a lot of water

iii. Taking food at regular time intervals

iv. Avoiding junk food and food with high sugar and fat contents


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Elements Required by PlantsElements are required by plants to synthesise organic molecules (carbohydrates,

nutrients, minerals) necessary for their optimal growth and development. An

element such as carbon dioxide is obtained directly from the atmosphere whereas

elements such as hydrogen and oxygen are obtained from water from the soils. Other

elements in the form of minerals are obtained from the soils.

The elements required by plants can be classified as follows:

i. Macronutrients

ii. Micronutrients

- MacronutrientsMacronutrients are elements that are required by plants in large quantities. These

elements include carbon, hydrogen, oxygen, nitrogen, potassium, calcium and

magnesium.

- MicronutrientsMicronutrients are elements that are required by plants in small quantities. These

elements include boron, molybdenum, iron, copper and zinc.

- Knops SolutionKnops solution is a complete cultured solution containing all the necessary

elements needed for optimal growth and development.

Plants can be grown using a cultured solution such as Knops solution. The

function of a particular element to the growth and development of the plant can

also be determined by eliminating a particular element from Knops solution. The

physical characteristics of the plants, such as the colour of the leaves, height

of the plant and thickness and hardness of the stems, are then observed and

compared with the control culture containing all the elements as in Knops

solution.


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Functions and Effects of Nutrients Deficiencies in PlantsThe functions of macronutrients and micronutrients and the effects of their

deficiencies in plants are shown the table below.

The Discovery of PhotosynthesisMany experiments were conducted by scientists leading to the discovery of

photosynthesis. We shall look at the prominent scientists who contributed

immensely to the discovery of photosynthesis. They are:

i. Jean Baptista van Helmont

ii. Joseph Priestley

iii. Jan Ingenhousz

- Jean Baptista van HelmontJean Baptista van Helmont conducted the experiment in 1640 and he was able to show

that the growth of plants is due to the water absorbed by the plants and not

because of the soil. The figure below shows the experiment conducted by Van

Helmont. Experiment showing that the growth of plants is due to the absorption of

water.

Van Helmont used a young willow tree weighing 2.3 kg and soil weighing 91 kg. He

watered the plant regularly and covered the pot it was planted in with a metal

plate drilled with tiny holes to allow the flow of gas and water. The metal plate

prevented dust from mixing with the soil.

After five years, the plant grew achieving the weight of 76.6 kg, an increase of

76.6 kg - 2.3 kg = 74.3 kg. However, the soil weight was 90.65 kg, a decrease of

91kg - 90.65 kg = 0.35 kg, indicating almost no change. He concluded that the

increase in the weight of the plant was due to water and not the soil.

- Joseph PriestleyJoseph Priestley conducted his experiment in 1772. In the experiment, he was able

to show that plants emit gases that can support combustion and respiration. The

figure below shows the experiment conducted by Priestley.

Experiment showing that plants emit gas that supports combustion and respiration


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In the first experiment, lighted candles and a mouse were placed in an airtight

container. Very soon, the flame was extinguished and the mouse died. This was due

to the lack of oxygen to support the combustion and respiration.

In the second experiment, a lighted candle and mouse were placed in an airtight

container together with a plant. Priestley found that the flame did not go off and

the mouse remained alive. This indicated that the plant was able to replenish the

oxygen consumed by combustion and respiration. At that time, Priestley did not

know that the gas emitted by the plant was oxygen.

- Jan IngenhouszIngenhousz carried out his experiment in 1779 and found that leaves emit oxygen in

the presence of sunlight. In addition, he showed that the green portion of the

plant (chlorophyll) is responsible for the emission of oxygen. His findings

revealed that sunlight and chlorophyll are the important components for

photosynthesis.

The Structure of LeavesThe main organ for photosynthesis is the leaf. It is highly adapted to receive the

maximum amount of sunlight and for the diffusion of carbon dioxide into the leaf

and oxygen out of the leaf. It is also very well adapted for the absorption of

minerals and water from the roots.

The figure below shows the cross-section of a leaf. The cross -sectional structure

shows the following parts of the leaf:

i. The cuticle

ii. The upper epidermis

iii. The palisade mesophyll

iv. The spongy mesophyll

v. The lower epidermis

Adaptation of Plants of Different Habitats to Carry Out PhotosynthesisPlants from various habitats (plants in tropical areas, floating plants, plants in

the deserts and submerged plants) have unique characteristics to ensure that

photosynthesis can be carried optimally.


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The Structure of ChloroplastThere are three main components in chloroplast:

i. The stroma

ii. The grana (singular: granum)

iii. The starch grains

- The StromaThe stroma is a gel like (semi-fluid) matrix which fills the chloroplast. In the

stroma, there are the grana and starch grains. The stroma also contains enzymes

responsible for the dark reaction (reaction without light) of photosynthesis.

- The GranaGrana are made of stacks of thylakoids. A thylakoid is the membrane-like structure

of the plant where the chlorophyll (the green pigment) is embedded. The light

reaction of photosynthesis (reaction with light) takes place in the thylakoids.

- Starch grainsStarch grains are embedded in the stroma. They act as temporary places for thestorage of photosynthetic reactions.

The Mechanism of PhotosynthesisThere are two types of photosynthesis. These are:

i. Light photosynthesis

ii. Dark photosynthesis

Each of these types of photosynthesis involves a different mechanism. We shall at

each of them in detail.

- Light PhotosynthesisLight reactions take place in the presence of light and occur in the thylakoids of

the grana. Light energy captured by the chlorophyll releases electrons and energy

from the chlorophyll molecules. At the same time, the light energy splits the


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water molecules into hydrogen ions (H+) and hydroxyls ions (OH-). This process is

called photolysis.

The electrons released by the chlorophyll combine with hydrogen ions (H+)to form hydrogen atoms.

The hydroxyl ions lose their electrons and form hydroxyl groups which arebroken down to form water and oxygen.

The energy released from the chlorophyll molecules is used in theproduction of the adenosine triphosphate (ATP) which results in energy rich

molecules. The final products of light reactions are hydrogen, water,

oxygen and ATP. The ATP and hydrogen are used in dark reactions.

Dark PhotosynthesisDark photosynthesis occurs in the absence of light and takes place in the stroma

of the chloroplast. This reaction is assisted by photosynthetic enzymes and in the

presence of ATP produced in light reactions. In these reactions, the atmospheric

carbon dioxide which diffuses into the leaves is combined with hydrogen (produced

in the light reactions) and is reduced to glucose (simple sugar).

The glucose produced by the dark reactions is converted to starch and is stored as

starch grains in the chloroplast. It is then transformed into sucrose and

circulated around the plant. Starch is also used to produce the cellulose of the

cell walls. Glucose may also be converted to proteins and fats required by the

plant.

Similarities and Differences between Light and Dark ReactionsThe similarities between light and dark reactions are as follows:

i. Both reactions occur in the chloroplast

ii. Both are photosynthetic reactions

The differences between light and dark reactions are as follows:


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Factors Affecting the Rate of PhotosynthesisPhotosynthesis only takes place in the presence of light, as well as when there

are carbon dioxide, water and chlorophyll available. The rate of photosynthesis

therefore depends on the following factors:

i. Light intensity

ii. Carbon dioxide concentration

iii. The temperature

iii. The amount of water available

- Light intensityIf the amount of carbon dioxide and the temperature are kept constant, the rate of

photosynthesis is directly proportional to the light intensity. This means that as

the light intensity increases, the rate of photosynthesis increases. This

relationship is true to a certain point where the light intensity is concerned.

Beyond this point, the rate of photosynthesis remains constant. Any further

increase in the light intensity has no effect on the rate of photosynthesis. This

point is called the saturated point and beyond this point, we say that the rate of

photosynthesis has saturated.

The figure below shows the effect of light intensity on the rate of

photosynthesis.

Beyond the saturation point, the rate of photosynthesis remains constant even if

the light intensity is being increased further. This is because the temperature

and the concentration of the carbon dioxide become the limiting factors governing

the rate of photosynthesis.

If the light intensity is increased further, there will come a point where the

chlorophyll will be damaged and the rate of photosynthesis will slow down.

- Carbon dioxide concentrationThe relationship between the concentration of carbon dioxide with the rate of

photosynthesis is similar to the relationship of light intensity with the rate of

photosynthesis discussed above. This is to say that, if the light intensity and

the temperature are kept constant, the concentration of carbon dioxide is directly

proportional to the rate of photosynthesis. The higher the concentration of carbon

dioxide, the higher is the rate of photosynthesis.


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This relationship holds true until a saturation point. Beyond this point, any

increase in the concentration has no effect on the rate of photosynthesis. The

rate remains constant. The figure below shows the relationship between the

concentration of carbon dioxide with the rate of photosynthesis.

- The temperatureWhen the light intensity and concentration of the carbon dioxide are kept

constant, an increase in the temperature increases the rate of enzyme activities

and hence, increases the rate of photosynthesis. The rate increases until the

maximum rate at the temperature of about 25-30 degrees Centigrade is reached. If

the temperature is increased further, the enzymes are denatured and the rate of

photosynthesis drops drastically. At a sufficiently high temperature, all the

enzymes are denatured and no photosynthesis can take place.

- The amount of water availableThe amount of water available is not a limiting factor for photosynthesis. This is

because the amount of water needed for photosynthesis is very small. However, the

amount of water available affects the rate of photosynthesis indirectly. When the

amount of water available is insufficient, the plant wilts and the stomata in the

leaves close. In this situation, the diffusion of carbon dioxide is unable to take

place and photosynthesis cannot be carried out.

-

Differences in the rate of photosynthesis throughout the day

The rate of photosynthesis is not constant throughout the day but fluctuates

depending on the intensity of light and the temperature. In the early morning, the

rate of photosynthesis is low because the light intensity and the temperature are

low; it slowly increases and reaches its maximum at noon when the light intensity

and the temperature are at the maximum.

The rate of photosynthesis saturates at midday because the concentration of carbon

dioxide becomes the limiting factor. In the evening, the rate of photosynthesis

decreases and reaches its minimum point at sunset. When there is no sunlight, thedark reaction of photosynthesis takes place. The figure below shows the variations

in the rate of photosynthesis throughout the day.


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The green housePlants grow very well in the tropics where the temperature, sunlight and rainfall

are at an optimum. However, this is not the case in countries located in the

northern and southern hemispheres where four seasons winter, spring, autumn and

summer exist. In such places, the rate of photosynthesis and hence, the

productivity of crops, vary throughout the year.

The productivity of crops is highest in summer when there is sufficient light

intensity and a suitable temperature. In winter, there is no crop productivity

since there is minimal sunlight and the temperature is the lowest. In order to

ensure a continuous supply of crops, such as fruits and vegetables, some plants

are grown in green houses.

In the green houses, farmers can control and regulate the amount of light

intensity, temperature, carbon dioxide as well the amount of water so as to create

the optimum conditions for photosynthesis and hence, maximise the crop yields.

These conditions allow crop productions throughout the year regardless of changes

in the weather outside the green houses.

Why Are Plants Important?

Green plants are sources of energy for many living organisms including humans and

other heterotrophs. Life on earth cannot be sustained without the presence ofgreen plants. Other examples of the importance of plants are:

i. The ecosystem

Green plants emit oxygen and release carbon dioxide. The plants help in the

balance of nature in the ecosystem by replenishing the oxygen in the

atmosphere which is used by other living organisms.

ii. Climate control

Plant helps to control the climate. The destruction of forests on a massive

scale leads to global warming. Excessive clearing of these forests at slopes

leads to soil erosion. Plants also help in water catchment areas to ensure

continuous water supplies for human consumption. Plants in the city, such as

in parks, help to cool the city and make it more conducive for living.

iii. Medicine

Plants are the sources of many types of medicine which can cure diseases.

Most of the plants in the forests have not been fully explored for theirpotential in the development of new drugs and vaccines. The indiscriminate


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clearing of the forests means that these potential sources are lost forever.

A Caring Attitude Towards PlantsA caring attitude towards plants would result in the following:

i. No indiscriminate clearing of forests. Selected logging should be encouraged.

ii. Replanting of plants soon after logging or forest clearing.

iii. Systematic and sustainable forest management.

iv. The clearing of forests is mainly for wood. Alternative products to replace

wood for the construction industry should be encouraged.

- Need to Improve the Quality and Increase the Quantity of Food

The need to improve the quality of food and increase food production is due to the

increasing human population and hence, an increase in the demand for food. The

population of Malaysia is expected to reach 70 million in 10 years' time and

appropriate action based on the national food production policy must be taken so

that adequate food is available for everyone.

Diversification in food production in one of the alternatives to ensure that

sufficient amounts of food are made available to everyone. The most efficient way

of improving the quality of food and increase food production is by the use of

technology.

Methods of Improving the Quality of Food and Increasing Food ProductionThere are various ways in which technology can be used to improve the quality of

food and increase production. Examples where technology can be used are:

i. Direct seeding

ii. Hydroponics

iii. Breeding

iv. Tissue culture

v. Genetic engineering


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vi. Soil management

vii. Biological control

- Seeding machineTechnology can be used in seeding such as in the planting of paddy. A special

drilling machine is used to sow the seeds directly into the soil. In this way, the

seeding can be done faster and efficiently and production costs are lowered. In

addition, higher production is achieved.

- HydroponicsHydroponics is the planting and growing of plants in a cultured solution insteadof in the soil. The cultured solution contains all the necessary macronutrients

and micronutrients. Normally, the hydroponics is carried out in green houses where

the light intensity, concentration of carbon dioxide and the temperature can be

controlled to provide optimum conditions for the growth of the plants.

- Selective BreedingSeveral cows of the same types

Selective breeding is a process whereby parents of plants or animals of desirable

characteristics and traits are chosen to produce offspring. In the case of plants,

better yields of high nutritional values, greater resistance to diseases and a

short maturity time are chosen. This means that only high quality and quantity

products are being produced.

- Tissue CultureTissue culture is the growing of tissues of a living organism in a cultured

solution of suitable nutrients and hormones. This is carried out outside the body

of the plants. Many plants, such as oil palm, papayas, bananas, etc., have beenproduced or cloned in large quantities via tissue cultures. The clones have the

same traits and characteristics as the parents, including better yields of high

nutritional values, great resistance to diseases, a short maturity time, etc. In

this way, high quality products are produced.

- Genetic EngineeringGenetic engineering is the manipulation of the DNA involving the deletion or

insertion of the gene (segment of DNA) to produce a new organism with desirable

traits. The organism produced via genetic engineering is called a geneticallymodified organism (GMO). The GMO has been used extensively in agriculture to


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improve crop productions in terms of the yields, nutritional contents as well as

resistance to pathogens and pests.

- Soil ManagementTractor working the soil

The soil is the medium for the growth of plants. The management of the soil in

terms of its chemical, physical and biological properties is important to ensure

that the soil texture, the contents of the organic matter, water contents and

microorganisms are always available for every cycle of the crop production. This

ensures that the soil quality is sustainable for each crop cycle.

Some practices of good soil management are crop rotations, use of a controlled

amount of fertilisers, contour planting to prevent erosion and the use of plant

legumes as a ground cover to increase soil fertility and prevent soil erosion.

- Biological ControlLady birds

Biological control is the natural control of pests using natural predators. Such a

method is environmentally friendly as no poisonous or toxic chemical pesticides

are involved. Examples of natural biological control methods are the use of

ladybirds which prey on mealybugs which suck the juices from leaves, flowers and

fruits. The rats which destroy paddy plants can be controlled by introducingsnakes and owls which are natural predators of rats.

The Need for Food ProcessingFood processing is a method of transforming raw food materials into food suitable

for human consumption. The main purpose of food processing is to eliminate food

spoilage. Food spoilage is caused by:

i. The action of microorganisms

ii. The oxidation of food

- The action of microorganismsThe action of microorganisms, such saprophytic bacteria and fungi, on

carbohydrates and protein in the food produces products with unpleasant smells;

they are toxic when consumed.


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- The oxidation of foodThe oxidation of food is the reaction between oxygen and food; this results in

changes in the taste, colour and nature of the food. The oxidation of bananas and

apples causes their change of colour when they are cut.

There are various reasons for food processing. These are:

i. Extending the life span of the food

ii. Avoiding wastage of food

iii. Diversify the use of food

iv. For sufficient food supplies

Methods of Food ProcessingFood processing and preservation have been practised from early days. The

techniques involved are adding of sugar, salt or vinegar to the food, drying in

the sun, smoking, fermentation and cooking. The modern methods of food processing

are:

i. Pasteurisation

ii. Sterilisation

iii. Refrigeration

iv. Canning

v. Irradiation

The basic principle of food processing is to kill the microorganisms, thus

preventing (inhibiting) their activities or growth. When the microorganisms are

killed or when they are inactive, the food lasts longer. The methods of food

processing and their effects on the microorganisms are shown in the table below.

Effects of Processed Food on HealthProcessed food is normally devoid of nutritional contents. This is because the

vitamins and nutrients have been destroyed during the heating process. In

addition, processed food contains many chemicals in the form of food


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preservatives, flavouring, colouring, stabilisers, etc. Some of these chemicals

are harmful to health.

It is advisable to consume more fresh organic fruits and vegetables than processed

food. When choosing processed food, it is a good practice to read the food labels

to determine the type of chemicals present in the food. In this way, we are aware

of the type and the quality of the processed food before consuming it.

Documents

Nutrients and Nutrition