Biology A2 Notes

7/27/2019 Biology A2 Notes

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Photosynthesis & Chloroplasts

6CO + 6HO CHO + 6O

Heterotrophsomething which gets its food from other organisms

Autotrophcreates its own food

Photoautotrophuses light & energy to create its own food

ATP - Adenosine Triphosphate (3 phosphate groups)

- Universal energy source.- Powers cellular processes by building and breaking bonds

When we need energy, the third bond is broken by a hydrolysis reaction using

ATPase enzyme.

ATP ADP + Pi + energy

The Electron Transport Chain

ATP is made as a result of what is used in the electron transport chain. As

electrons move along the chain, they lose energy which can be used to drivethe synthesis of ATP to ADP & inorganic phosphate.

Hydrogen molecules removed from compounds are picked up by other

compounds and become reduced. OILRIG (oxidation is loss, reduction is gain)


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Chloroplasts: Structures & Functions

Starch Grain Organelle which contains starch

Lamellae Extension of the Thylakoids (contain

PSI)

Thylakoids Organelle which contains chlorophyll

(and PSI & PSII) found in the Stroma in

stacks called Grana. Increase surface

area for light capture and allowscapture of photons with a wider range

of wavelengths. Light Dependant

Reactions occur in the Thylakoid

Membrane.

Grana (granum) Stack of Thylakoid discs

Stroma The space in a chloroplast surrounding

the Thylakoids. Contains ribosomes

and genetic materials so proteins

required for photosynthesis can be

synthesised. Also contains starch

grains and lipid droplets.

Ribosomes Organelle for synthesis of

Polypeptides

Outer Membrane

(double membrane)

Permeable to most ions and

metabolites.

Inner Membrane

(double membrane)

Highly specialised with transport

proteins


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Chlorophyll Pigments

There are 5 pigments:

- Chlorophyll a- Chlorophyll b- Carotene- Xanthophyll- PhaeophytinAll parts of the plant do not need to carry out photosynthesis and therefore do not have

chloroplasts. The most abundant type of chlorophyll is chlorophyll a which is found in

most places. The benefit of having different types is that it is most efficient as each of

the pigments absorbs and captures light from particular areas, more energy from the

light can be used and photosynthesis is maximised. Plant leaves appear green as all

colours apart from green are absorbed so green is reflected back as chlorophyll a is most

abundant.

Carotenoids

Photosystem ILamellae

Photosystem IIGranum

Light dependent reactionsThylakoid MembraneLight independent reactionsStroma


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LIGHT DEPENDENT REACTIONS

Products of Light Dependent Reactions -

ATP (energy), Oxygen & Reduced NADP

Takes place on the thylakoid membranes of the chloroplasts. It has 2 main

functions:

1. To produce ATP, supplying energy for the synthesis of carbohydrates2. Split water molecules in a photochemical reaction providing hydrogen

ions to reduce CO2 & produce carbohydrates

The smallest unit of light energy is a photon. When a photon of light hits a

chlorophyll molecule, the energy is transferred to the electrons of that

molecule. Photoexcitation occurs & if an electron is raised to a sufficiently

high energy level it will leave the chlorophyll molecule completely. The excited

electron can be picked up by an electron acceptor (carrier molecule). This in

turn results in the synthesis of ATP by one of two processesCyclic & Non-

Cyclic photophosphorylation.


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CYCLIC PHOTOPHOSPHORYLATION

Cyclic photophosphorylation involves only photosystem I & drives the

production of ATP. When light hits a chlorophyll molecule, a light excited

electron leaves the molecule. It is taken up by an electron acceptor and passeddirectly along the electron transport chain to produce ATP. When an electron

returns to the chlorophyll molecule in PSI, it can then be excited in the same

Way.

NON - CYCLIC PHOTOPHOSPHORYLATION

Non cyclic photophosphorylation involves both photosystem I & photosystem

II. It splits water molecules to provide reducing power to make carbohydrates.It also produces more ATP.

Water dissociates into Hydrogen (H+) ions and hydroxide (OH

-) ions, so there

are always plenty of these ions present in the cell. A series ofRedox Reactions

take place.

An excited electron from PSI is picked up by an electron acceptor (NADP). The

NADP takes up a hydrogen ion from the dissociated water at the same time to

form reduced NADP. This reduced NADP is used as a source of reducing power

in the light independent reactions of photosynthesis to make glucose.

At the same time, an excited electron from PSII is picked up by another

electron acceptor and passes along an electron transport chain until it reaches

PSI. PSI then receives an electron to replace the one that was lost to the light

independent reactions.

As the chlorophyll molecule in PSII is short of an electron and unstable, an

electron has to be found from somewhere to restore the chlorophyll to its

original state. The electron comes from the splitting of waterPHOTOLYSIS.


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LIGHT INDEPENDENT REACTIONS

Carbon dioxide is converted to carbohydrates. These reactions

occur in the Stroma of the chloroplasts, surrounding the grana.Carbon dioxide readily diffuses into the chloroplast where it is built

up into sugars in a cyclic process called the Calvin cycle.


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The Calvin Cycle

Intermediates of the Calvin Cycle:

- RuBP (Ribulose Biphosphate)- Rubisco (Ribulose Biphophate Carboxylase/Oxygenase enzyme)- GP (Glycerate 3 phosphate)- TP (Triose phosphate) = GALP (Glyceraldehyde 3 phosphate)

- The enzyme Ribisco combines RuBP with CO to form a 6 carbon molecule(unstable) which then splits into 2 GP molecules which are 3 carbons each.

- These molecules are reduced using ATP energy & H+ from NADPH (fromthe light dependent reactions) to form 2 GALP molecules (3 carbons each).

- 1 carbon goes off to make complex molecules; glucose, lipids and aminoacids & the other 5 start the process again converting back into RuBP.

- Products of the Calvin Cycle which pass from independent reaction todependent reactions are: NADP, ADP & Inorganic Phosphate


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ECOSYSTEM

- An ecosystem is a life supporting environment which includes all livingorganisms which interact together, the nutrients that cycle through the

system, and the physical & chemical environment in which the

organisms are living.

Habitatplace where an organism lives

Populationgroup of organisms of the same species

Communityall the populations of different species living in a habitat at any

one time.

Nicherole of an organism, its way of life

Abiotic factorsnon-living elements of the habitat of an organism e.g.sunlight, temperature, soil, ph.

Biotic factorsliving elements of a habitat which affect the ability of a group

of organisms to survive there e.g. the presence of suitable prey will affect the

number of predators in the habitat

BIOMES

- Major ecosystems devised from the biosphere, distinguished by theirsimilar climates and plant communities.

Tropical Rainforest high humidity, warm and plenty of sunlight, rain all year.

Savannah dry tropical grassland

Tropical Woodland wetter than savannah, grassland with thornwoods,

bushes and trees

Desert very little rainfall, often extreme of temp. between day and night

Taiga evergreen forests in cold subarctic & subalpine regions

Tundra very cold, artic & high mountain regions

The major biomes have developed over millions of years due to:

SUCCESSION -Communities of animals and plants colonise an area, and over time are

replaced by other, usually more varied communities


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Primary Succession

- Rock is uninhabited, due to poor conditions for growth such as no soil ormoisture

- Pioneer species such as algae or lichens penetrate the bare rock- The pioneer species break the bare rock, this is mixed with the remains

of dead pioneer species organismsHUMUS, which creates the

foundations of soil

- Once soil is established, plants which require soil such as grasses andferns colonise the area

- Upon the death of primary colonisers, more humus is added to the soil,so the nutrient content develops. Roots hold the soil together and retain

more water

- Secondary colonisers more adapted to the new environment will thencolonise the land

- Larger trees block the growth of smaller plants, due to competition forsunlight & species diversity drops.

- Climax community is self-sustaining & reached where the biodiversityis constant. Not many further changes occur.

Secondary Succession

Occurs as rivers shift their courses after fires & floods and disturbances

cause by humans. Due to primary succession, the soil is already formed

and contains the seeds, tools and soil organisms, which means the

number of plants and animals present right from the beginning of the

succession, are much higher.


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EFFECTS OF ABIOTIC FACTORS

ABIOTIC FACTOR EFFECT ON ECOSYSTEM IF IN

MODERATION

EFFECT ON ECOSYSTEM IF TOO

MUCH/LITTLE

Light Plants depend on light forphotosynthesis and must beable to cope in areas with

low levels of light.

Some plants are able to reproduceand thrive in low light levels, having

extra chlorophyll or other

chlorophyll pigments which are

sensitive to lower light levels.

Animals behaviour may be affected

by seasonal light changes, as well as

reproductive patterns.

Temperature There is a range oftemperatures which allow

growth and reproduction forparticular organisms. The

temperature in an area also

affects the rate of enzyme

controlled reactions in plants

Above or below that range,

reproduction does not occur, even if

the organism survives. It is theextreme of temperature which

determines where an organism can

live, not the average.

Wind Wind increases water andheat loss from the body ad

adds to the environmental

stress an organism has to

cope with.

Few species can survive in areas

with strong prevailing winds while

occasional gales and hurricanes can

devastate populations.

WaterWater is vital for living

organisms

So where the supply is limited it will

cause severe problems. Organisms

may die if the stress becomes too

severe if like camels and cacti, the

have adaptations to enable them to

survive.

Oxygen Conc. Oxygen can be in shortsupply in both water and

soil. When water is cold

sufficient oxygen dissolves in

it to support life and vice

versa. Soil is usually well

aerated.

The spaces between soil particles

contain air so there is plenty of

oxygen for the respiration of plant

roots. In waterlogged soil, the air

spaces are filled with water so plant

roots may be deprived of oxygen

and may die.

Edaphic

Factors (soil

structure &

mineral

content)

Plant populations that are

linked by massive root and

rhizome networks, such as

marram grass can survive in

loose, shifting structures

such as sand. They bind the

sand together which makes it

more suited for colonisation

by other species.

Soil that contains high proportion of

sand are light, easily worked and

warmed. However, also easily

drained so water passes through

them rapidly, carry with it minerals

needed for plants. The opposite

occurs for soils made of

predominantly tiny clay particles.


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EFFECT OF BIOTIC FACTORS

TERM & MEANING HOW IT AFFECTS

AN ECOSYSTEM

EXAMPLE

Finding a mate

finding a member of

the opposite sex to

reproduce with

Affects the

biodiversity

allows niches to

carry on. Larger

allele/genetic

diversity

A equine species

becoming extinct

due to

reproduction

isolation

Territoryan area

occupied & defended

by an/a group of

organism (s) from

the same or different

species

Resources are

defended making

sure others can get

them and continue

reproducing

Lions dens

Parasitism & Diseasebiotic factors which

cause weakened

animal relationships.

Where 1 organism

benefits at the

others expense

Diseases can wipeout whole

populations within

a biome

Mixingpopulations &

bringing diseases

Wild pigs


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Competition

- Intraspecific Competitioncompetition for a limitedresource between

members of the same

population or species.

As a result of intraspecific

competition, some

individuals may not

survive, or may not

reproduce and sopopulation growth slows.

- Interspecific Competition occurs when different specieswithin a community compete for the same resources.

Competition will reduce the abundance of the competing

species.


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Energy Transfer In Ecosystem

Gross Primary Productivity (GPP)the rate at which energy is incorporated

into plants. Plants use up to 25% of this accumulated energy for metabolicprocesses. Most importantly, in respiration breaking down glucose to release

energy in the form of ATP.

Net Primary Productivity (NPP)The rest of energy which is stored in body

tissues

NPP = GPP Plant Respiration

The energy in plant material is available to herbivores, but relatively little of itends up as new animal material. Much of the energy is used to drive

respiration then is lost to the atmosphere as heat energy. Some is lost as

chemical energy in metabolic waste products and heat energy in urine.

The energy used to make new animal biomass is known as SECONDARY

PRODUCTION.


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Speciation & Evolution

Mechanisms of SpeciationPopulations that have been isolated for

millions of years can remain effectively the same species. However,populations living next door to each other can begin to form new species.

Reproductive isolation is crucial to speciation and this occurs when fertilisation

is prevented (prezygotic) or when the zygote fails or is unable to breed

(postzygotic)

Allopatric Speciation

Occurs when populations

are geographically far

Sympatric SpeciationOccurs when populations aregeographically near but other barriers prevent

reproduction such as:

Prezygotic

Reproductive Barriers

Postzygotic

Reproductive Barriers

Gametic IsolationSex

cells of opposite sexes are

incompatible - BehaviouralIsolation

Speciation

populations do not

respond to each

others mating calls

- Mechanical IsolationReproductive

organs do not fit

together with all

potential membersof the same species

- Temporal Isolation

Species exist in thesame area but are

reproductively active

at different times of

the year

- Habitat IsolationPopulations occupy

different habitats in

the same area, andtherefore do not

breed

- Hybrid Infertility

Offspring of twodifferent species are

not fertile

- Low Hybrid ZygoteVigourZygote fails

to develop and diesor produces

offspring with severe

disability

- Low Hybrid AdultViabilityOffspring

of two differentspecies are not

healthy enough to

survive


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INVESTIGATING TIME OF DEATH

A number of changes take place in the place of any mammal after

death which can be helpful in estimating the time of death.

- The normal human body temp is 37C, at death the metabolicreactions which have created the body heat slow down and

eventually stop. Although body temp. Starts to fall straight

after death, it plateaus for a while before dropping steadily to

room temp. As a result, the temp. of a body will give some

indication of how long they have been dead.

Rigor Mortisa stiffening effect caused by lack of ATP in themuscles & muscle fibres becoming permanently contracted and

locked solid. On average rigor mortis starts about 2-4 hours after

death, begins in the face & neck and works its way down the body.


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Stages of Succession

- The first colonisers are anaerobic bacteria, which do notneed oxygen and thrive in the lactic acid rick

environment of the muscles after death.- As enzymes break down cells, the bacteria spread & are

joined by several species of flies mostly blowflies.

These insects can arrive on the body within minutes of

death as they are attracted to the moisture and smell of

natural orifices of the body as well as open wounds.

- The main attraction of the body is a site to lay eggs.Maggots begin to hatch and feed on the tissues,

breaking them down.

- The maggots pupate, turn into flies, mate & start thecycle again. As the tissues of the body liquefy, adult flies

can feed on this too.

- Beetles then begin to lay eggs on the carcass & parasiticwasps arrive to lay their eggs in the larvae.

- As the body is digested it also dries out, which doesntsuit the early colonisers. Different species such as the

cheese flies and coffin flies move in.

- As the body becomes too dry for maggots, carcassbeetles, ham beetles and hide beetles feed on the

remains of the muscles and connective tissues

-

At the very end, mites and other larvae will feed on thehair until only dry bones are left.


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Viruses

- Viruses are the smallest ofall microorganisms. Theyare not cells, but

arrangements of genetic

material and protein that

invade other living cells &

take over their

biochemistry to make

more viruses.- Most scientists class viruses as obligate intracellular

parasites meaning they can exist and reproduce as

parasites only in the cells of other living organisms.

The Structure of Viruses

The protein coat or

capsid is made up of

simple repeating

protein units known

as capsomeres,

arranged in different

ways. In some viruses,

the genetic materialand protein coat are

covered by a lipid

envelope, produced

from the host cell. The presence of the envelope makes it

easier for the viruses to pass from cell to cell but it does

make them vulnerable to substances such as ether which will

dissolve the lipid membrane. Viral genetic material can be


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DNA or RNA, and nucleic acid can be single or double

stranded.

Viral RNA directs the synthesis of a special enzyme called

reverse transcriptase which proceeds to make DNAmolecules corresponding to the viral genome.

Viruses attach to their host cells by means ofspecific

proteins (antigens) known as Viral attachment particles

(VAPs) which target proteins in the host cell surface

membrane.


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Virus Life Cycles

Bacteriophages inject their genome into the host bacterial

cell but the bulk of the viral material remains outside the

bacterium. The viral DNA forms a plasmid within the

bacterium. The viruses that infect animals get into the cells in

several ways. Some types are taken into the cell by

endocytosis & the host cell then digests the capsid, releasing

the viral genetic material. The viral envelope fuses with the

host cell surface, releasing the rest of the virus inside the cell

membrane. Plant viruses usually get into the plant cell using

a vector (often an insect) to pierce the cellulose cell wall.

2 routes of infection

- Lysogenic PathwayMany viruses are non-virulentwhen they first get into the host cell. They insert their

DNA into the host DNA so it is replicated every time the

host cell divides. This inserted DNA is called a provirus.

During this period oflysogeny, when the virus is part of


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the reproducing host cells, the virus is said to be

dormant.

- Lytic PathwaySometimes the viral genetic material isreplicated independently of the host DNA straight after

entering the host. Mature viruses are made & eventually

the host cell bursts, releasing large numbers of new

virus particles to invade other cells. The virus is said to

be virulent (disease causing) & the process of

replicating & killing cells is known as the lytic pathway.

1.Bacteriophage attracts bacterium2.Phage DNA is injected into host cell. It brings about

the synthesis of viral enzymes

3.A. Viral DNA is incorporated into host cell DNA &replicated each time the bacterium divides, without

causing any damage.

B. OR Phage DNA inactivates the host DNA and takes

over the cell biochemistry

4.Phage DNA is replicated. New phage particles areassembled as new protein coats are made around

phage DNA. The enzyme lysozyme is synthesised or

released

5.Lysis the bacterial cell bursts due to the action oflysozyme, releasing up to 1000 phages to infect other

bacteria & the cycle begins again.


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RETROVIRUSES

Retroviruses have a more complex life cycle. Their

genetic material is viral RNA. This cannot be used asmRNA but is translated into DNA using reverse

transcriptase.

1.The retrovirus attacks an animal cell2.Viral RNA enters the host cell. This RNA cannot be

used as mRNA.

3.Viral RNA is translated into viral DNA by reversetranscriptase in the cytoplasm

4.Viral DNA is incorporated into the host DNA in thenucleus. It directs the production of new viral genome

RNA, mRNA and coat proteins.

5.New viral particles are assembled and leave the hostcell by exocytosis. Viral DNA remains in the nucleus

so the process is repeated.

6.The host cell continues to function as a virus makingfactory, while the new viruses move on to infect

other cells.


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Bacteria

Cell Wall

Protects against rupture due to

osmosis and keep shape. Rigid wall

containing giant molecules

consisting of amino sugars and

peptidogylcan

Cytoplasm - About 75% water

in which are dissolved

proteins (mainly enzymes)

Lipoproteins, sugars, amino

acids and fatty acids, inorganic

salts, and the waste productsof metabolism.

Capsule

A slime layer or

capsule is made up ofadditional materials

that are laid down on

the outer surface of

the wall. Capsules are

firmly attached,

whereas slime layers

may diffuse into the

surrounding medium.

Flagella & Pilli

Flagella are rigid protein strands that arise from basal bodies in the

plasma membrane in some bacteria. They bring about movement by

rotating from their base, driven by the basal body.

Pilli are tiny tubular structures that arise from the cell membrane of

some bacteria. They enable bacteria to attach to surfaces and to other

bacteria.

Mesosomes

Infoldings of the plasma

membrane found in some

bacterial cells. In the

photosynthetic bacteria, theyare where the photosynthetic

pigments are housed.

Plasmids

Additional hereditary material

small rings of DNA, present in the

cytoplasm ofsome but not all

bacteria.

Plasma Membrane - Consists

of phospholipids and proteins

arranged in the fluid mosaic

model. Carbohydrates attach

to some lipids forming

glycolipids and some proteinsforming glycoproteins on the

outer surface membrane.

Ribosomes - Sites of

protein synthesis.

Bacterial ribosomes are

known as 70S ribosomes

because they are smaller

than those in the

cytoplasm of plant and

animal cells and fungi

(called 80S ribosomes)


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There are two different types of

bacterial cell walls which can be

distinguished by Gram Staining.

Gram positive bacteria have a thick

layer of peptidoglycan containing

chemicals such as teichoic acid. The

crystal violet in the stain binds to

the acid & resists decolouring,

leaving the positive PURPLE/BLUEin

colour.

Gram negative bacteria have a

thinner layer of peptidogylcan with no teichoic acid. Any crystal

violet which does bind is readily decolourised & replaced with red

safranine in the stain, so the cells appear RED in colour.

Classifying Bacteria- by shape

Cocci (spherical)

Bacilli (rod shaped)

Spirilla (twisted/spiral)

Vibrios (comma shaped)


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Reproduction of Bacteria

Bacteria can reproduce in two main ways. The most common

is Asexual Reproduction (binary fission) splitting into two.One the bacterium reaches a certain size, the DNA is

replicated and the old cell wall begins to break down around

the middle of the cell. Enzymes break open the circular piece

of DNA allowing the strands to unwind and be replicated.

Another form of reproduction is Sexual reproduction. In very

rare conditions, bacteria can reproduce using what appear to

be different forms of sexual reproduction. There are 3 waysin which genetic material from one bacterium cab be taken in

and used as part of the DNA of another bacterium.


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Transformation

A short piece of DNA is released by a donor and actively

taken up by a recipient where it replaces a similar piece of

DNA. Only occurs in certain types of bacteria.

Transduction

Takes place when a small amount of DNA is transferred from

one bacterium to another by a bacteriophage. Bacteriophage

attaches to the bacterial cell wall. Enzymes are released to

break down the cell wall. New bacteriophage forms and

some bacteria DNA is included by mistake

Conjugationgenetic information is transferred from one

bacterium to another by direct contact. The donor cell is

similar to a male cell and this produces a sex pillus, a

cytoplasmic bridge between the two cells through which DNA

is transferred to the recipient cell, similar to the female cell


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Endotoxins

- Lipopolysaccharides (part ofthe outer layer of gram

negative bacteria)

- Rarely fatal- Tend to cause symptoms

such as fever, vomiting &

diarrhoea

- E.g. Salmonella & E.coli- However symptoms may

indirectly lead to death

Exotoxins

- Soluble proteins produced & released into the body by bacteria as theymetabolise and reproduce.

- There are many different types; some damage cell membranes causinginternal bleeding, some act as competitive inhibitors to

neurotransmitters, whilst others directly poison cells.

- Rarely cause fevers but so include some of the most dangerous bacterialdiseases.

- E.g. Clostridium botulinum produces one of the most toxic substancesknown, botulinum toxin


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BENEFICIAL BACTERIA

- Many bacteria in the body is beneficial,helping to break down food and keeping

pathogens at bay by outcompeting them. Thenormal growth of bacteria on your skin or in

your gut is referred to as the skin flora or

gut flora

-Probiotic drinks and foods contain cultures of these

good bacteria to help support the normal healthy

bacterial flora of the gut.

- Bacteria also play a vital role in the ecosystems of the natural world. Themajority of bacteria are decomposers. They break down organic

material to produce simple inorganic molecules such as CO2 and water.

- They release inorganic nitrogen which returns to the soil in the nitrogencycle, and also sulphur compound which returns to the soil or water.

- Another important aspect of bacteria is in the carbon cycle is the factthat some microorganisms produce the enzyme cellulase. This enzymebreaks down the cellulose produced in plant cell walls to give sugars

which can then be used as food by a wide range of other

microorganisms.


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INVADING THE BODY

Pathogens are transmitted in a variety of ways:

- Vectors - a living organism that transmits infection from one host toanother E.g. Insects Malaria

- Fomites inanimate objects that carry pathogens from one host toanother E.g. Hospital towels & bedding

- Direct Contact many sexual diseases are spread by direct contact ofgenital organs E.g. Gonorrhoea or Syphilis

- Inhalation coughing, sneezing, &talking release droplets which contain

pathogens E.g Tuberculosis & Influenza

- Ingestion Contaminated food therisk is greatest in raw or undercooked

food E.g. Salmonella

- Inoculation directly through a break in the skin either throughcontaminated medical instruments or shared needles in drug abuse. An

infected animal may also bite or lick you. E.g. H.I.V or Rabies


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BARRIERS TO ENTRY

SKIN- An impenetrable layer toughened by keratin, a fibrous structural

protein

- Forms a physical barrier between the pathogen laden environment &the blood rich tissues beneath the skin

- Sebum, an oily substance produced by the skin contains chemicals whichinhibit the growth of microorganisms

- Natural skin flora prevent disease by competing successfully for aposition on the skin & produce substances that inhibit the growth of

other microorganisms

MUCUS & TEARS- Surfaces of internal tubes & ducts are more vulnerable than skin

however these epithelial layers also produce defensive secretions. Many

produce MUCUS.

- MUCUS contains lysozymes, enzymes capable ofdestroying microbialcell walls, particularly against gram positive bacteria, breaking cross

linkage in the the peptidoglycans in the bacterial cell wall.

- Lysozymes are also present in tears, the secretions produced to keep theeyes moist & to protect them from the entry of pathogens.

- Part of the non-specific defence of the bodyGUT

- Saliva in the mouth has bacterial properties. Some polypeptidesproduced in the salivary glands destroy bacteria while others slow down

bacterial growth.

- Acid in the stomach destroys the majority of ingested microorganisms.-

The natural flora in the gut usually competes successfully for bothnutrients and space with any microorganisms which manage to get

through the stomach & produces anti-microbial compounds

- VOMITING is effectively removing many of the microorganismsphysically from the system when the body is infected.


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NON SPECIFIC RESPONSES TO INFECTION

Inflammation is a common way in which our bodies respond to infection.

- Special cells called mast cells are found in the connective tissue belowthe skin & around blood vessels. When this tissue is damaged, mast cellsalong with damaged white blood cells release chemicals known as

HISTAMINES.

- These cause the blood vessels in the area to dilate, causing local heat &redness. The raised temp. reduces the effectiveness of pathogen

reproduction in the area.

- Histamines also make the walls of the capillaries lady as the cells formingthe walls separate slightly. As a result, fluid including plasma, WBCs &

antibodies is forced out of the capillaries causing swelling.

- The WBCs & antibodies destroy the pathogens.Fever occurs when a pathogen infects the body which cause the hypothalamus

to reset to a higher temp. This helps in 2 ways:

- A raised temp. will reduce the ability of many pathogens to reproduceeffectively & so they cause less damage.

- Specific response works better at a higher temp. & therefore will bemore successful at combating the infection.

Phagocytosis involves white blood cells. There are 2 main types of white blood

cells; the granulocytes which have granules that can be stained in their

cytoplasm & agranulocytes which have no granules.

- Phagocyte is a general term for white blood cellswhich engulf & digest pathogens and any other

foreign material in the blood & tissues.

- There are two types of phagocytes; neutrophilswhich are granulocytes & make up 70% of the

white cells & macrophages which areagranulocytes and make up about 4%. They

accumulate at the site of infection to attack

invading pathogens. Phagocytes can sometimes

be seen as pus which may ooze out of the wound

or it may be reabsorbed into the body.

NEUTROPHIL

MACROPHAGE

INTERFERONSGroup of chemicals producedwhen cells are invaded by viruses.

Interferons are proteins that inhibit viral replication within the cells. They bind toreceptors in the surface membranes on uninfected cells, stimulating a pathway which

makes the cells resistant to infection by viruses by preventing viruses reproducing.


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THE SPECIFIC RESPONSE TO INFECTION

The immune system enables the body to recognise anything that is non-self

and to remove it from the body as efficiently as possible. Each organism carries

its own unique antigens or the cell surface membrane. There are 2 main types

of White blood cells involved in the immune systems;

- Lymphocytes are agranulocytes, made in the white bone marrow- Macrophages are also agranulocytes which move freely through the

tissue after leaving the bloodstream

KINDS OF LYMPHOCYTES

B cells

-

are made in the bone marrow- found in lymph glands & freein the body

- have membrane boundglobular receptor proteins on

their cell surface membrane

which are identical to the

antibodies they will later

produce

- all antibodies are known asimmunoglobulins (IgM)T cells

- made in the bone marrow but mature and become active in the thymusgland

- Surface of each T cell displays thousands of identical T-cell receptors.There are 2 main types of T-cells; T killer cellsproduce chemicals that

destroy pathogens & T helper cellsinvolved in the process which

produces antibodies against the antigens on particular pathogen.

The working of these cells depend on special proteins known as major

histocompatibility complex (MHC) proteins, which display antigens in the

cell surface membranes

Helper

Cells

B

Cells

T

Cells

Killer

Cells

Lymphocytes


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ANTIBIOTICS- Bacteriostaticthe antibiotic used completely inhibits the growth or the

microorganism

-- Bactericidalthe antibiotic used will destroy almost all of the pathogens

present


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DIFFERENT TYPES OF IMMUNITY

- Natural Active Immunitywhen the body comes into contact with aforeign antigen and the immune system is activated & antibodies are

formed & the pathogen is destroyed. The body actively makes the

antibodies.

- Natural Passive Immunityduring pregnancy, preformed antibodies arepassed from the mother to the foetus through the placenta. The baby

gets extra protection from antibodies taken in through breast milk. This

provides the baby with temporary immunity until its own system

becomes active.

INDUCING IMMUNITY

- Immunisation is the process of protecting people from infection bygiving them passive or active artificial immunity.

- Vaccination is the procedure by which you immunise people to produceimmunity

Artificial Passive Immunity occurs when antibodies are formed

in one individual, extracted & injected into another individual.

Artificial Active Immunity is when small amounts of antigen

(vaccine) are used to produce immunity in a person


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CORE PRACTICALS

1.Studying The Ecology On An Area- Techniques such as taking a transect can be used to

study the topography of an area the shape, height &

depth of the land surface.

- Quadrats can be used to give valid & reliable measuresof the numbers and types of plants.

- The animal communities can be investigated by manymethods, including quadrats, nets, pitfall traps & taking

soil samples.

- The abiotic factors which affect a habitat such as rainfall& temperature & edaphic factors such as soil type & pH

are also measured & recorded to give as much

information as possible about the ecology of the area.


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2.Effect of temperature on a living organism- It is possible to model the effect of increasing

temperature on the development of living organism in

the laboratory.

- There are many different experimental procedureswhich can be used such as germination of seeds, the

growth rate of young seedlings, or the hatching rate of

brine shrimps.- The temperature differences for the investigation need

to be controlled very carefully


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3. Gel Electrophoresis- Gene probes are short DNA sequences that are

complementary to specific sequences which are beingsought. Each probe is labelled, either with a radioactive

element or with a fluorescent molecule

- Large amounts of the gene probes are added to thefilter and bind with complementary DNA strands in a

process known as hybridisation

- Excess probes are washed away & either X-ray picturesare taken of the filter, or the filter is placed under UV

light to show up the DNA regions


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4.Polymerase Chain Reaction (PCR)- Amplifying the DNA- Adapts the natural process in which DNA is replicated in

the cell, making it possible to produce enough DNA for a

profile from tiny traces of biological material

- Primers (small sequences of DNA which must join to thebeginning of the separated DNA strands before copying

can begin) & a good supply of the four nucleotide bases

are mixed together in a PCR vial and placed in a PCR

machine.

- The mixture is heated to 90-95C which causes hydrogenbonds to break so DNA strands separate

- The mixture is then cooled to 55-60C so the primersbind to the single DNA strands

- The mixture is then heated again to 75C which is theoptimum temperature for DNA polymerase enzyme to

build the complementary strands of DNA.

- The process is repeated about 30 times to give approx. 1billion copies of the DNA.


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5.Effect Of Different Antibiotics On Bacteria- The effect of different antibiotics on bacteria can be

investigated using standard microbiological techniques.- An agar plate is seeded with a known bacterial culture- Filter paper discs containing different antibiotics, or

different concentrations of the same antibiotics, are

placed in the agar & the plate is sealed.

- A control culture of microorganisms with knownsensitivity to the antibiotic is grown at the same time

under the same conditions- The level of inhibition of bacterial growth gives a

measure of the effectiveness of the drugs.

Documents

Biology A2 Notes