AQA Biology Module 2

Revision notes for b2 exam

  • Created by: Emma
  • Created on: 09-01-11 15:12

Animal Cells

Nucleus – controls the cells activities

Cytoplasm – where many chemical reactions take place

Cell membrane – controls the movement of materials in and out of the cell

Mitochondria – where energy is released during aerobic respiration

Ribosome’s – where proteins are made (synthesised)

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Plant Cells

Nucleus – controls the cells activities

Cytoplasm – where many chemical reactions take place

Cell membrane – controls the movement of materials in and out of the cell

Mitochondria – where energy is released during aerobic respiration

Ribosome’s – where proteins are made (synthesised)

Cell wall – rigid for support

Chloroplasts – contain chlorophyll for photosynthesis

Permanent vacuole – contains cell sap

Not all plant cells have chloroplasts with chlorophyll 

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Specialised cells

When an egg is fertilised it begins to grow and develop.

At first there is a growing ball of cells.

Then as the organism gets bigger some of the cells change and become specialised.

There are many different specialised cells

Some cells in plants may become xylem or root hair cells

Some cells in animals will develop into nerve of sperm cells.

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Molecules move randomly because for the energy they have.

Diffusion is the random movement of molecules from an area of high concentration to an area of lower concentration

The large the difference in concentration the faster the rate of diffusion the faster the rate of diffusion.

Diffusion of oxygen into cells of the body from the blood stream as the cells are respiring (and using up oxygen)

The diffusion of carbon dioxide into actively photosynthesising plant cells

The diffusion of simple sugars and amino acids from the gut through the cell membranes.

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Osmosis is the movement of water.

Just like diffusion the movement of molecules is random and require no energy from the cell.

Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated solution.

No solute molecules can move across the membrane.

The cell membrane is partially permeable.

Water is needed to support cells because chemical reactions take place in solution.

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Carbon dioxide + water (+ light energy) ----à glucose + oxygen

The carbon dioxide is taken in by the leaves and water through the roots.

The chlorophyll in the leaves traps the energy needed for photosynthesis.

In photosynthesis the sugar glucose (a carbohydrate) is made.

Oxygen is given off as a waste gas.

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Structure of the leaf

Upper epidermis – waxy cuticle waterproof layer to stop water loss

Palisade layer – palisade cells at top of leaf so they are closer to light, tightly packed together and full of chloroplasts

Spongy layer – cells not tightly packed together have a larger surface area available for gas exchange and some chloroplasts.

Lower epidermis – guard cells open and close the stomata to control water loss

Stomata allows gases to move in and out of the leaf

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Limiting factors

Light, temperature and amount of carbon dioxide can limit the rate of photosynthesis.

Light provides energy for the process

If it’s cold enzymes do not work affectively

Carbon dioxide may be limited in an enclosed space such as a greenhouse.

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How plants use glucose

The product of photosynthesis is glucose; glucose is used as energy in the respiration process.

Glucose is also combined with other nutrients (mineral ions) by the plant to produce new materials.

Glucose is stored by some plants as insoluble starch. It is stored as an insoluble substance so that it no effect on osmosis.

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Why do plants need minerals?

Plant roots take up mineral salts for healthy growth.

Nitrates are taken from the soil for producing amino acids. There are used to make proteins for growth. A plant that is deficient in nitrate has stunted growth.

Plants also take up magnesium ions through the roots which are essential for making chlorophyll. If the plant is deficient in chlorophyll it will have yellow leaves.

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Pyramids of biomass

Biomass is the mass of living material in plants and animals.

A pyramid of biomass represents the mass of the organisms at each stage in a food chain.

It is more accurate than a pyramid of numbers as it represents the mass of the product rather than the amount.

You can draw pyramids of biomass to scale to give a more accurate picture.

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Energy losses

Not all of the food eaten can be digester, so energy is lost in faeces (waste materials)

Some of the energy is used for respiration, which releases energy for living processes.

This includes movement so the more something moves the more energy it uses and less is available for growth.

In animals that need to keep constant body heat energy from the previous stage of the food chain is used simply to sustain temperature.

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Energy in food production

The shorter the food chain the less energy loss. It is therefore more efficient for us to eat plants than it is to eat animals.

We can artificially produce meat more efficiently by –

Preventing the animal from moving so it doesn’t waste energy on movement

Keeping the animal at a warmer temperature so it doesn’t use as much energy to keep a constant body temperature.

This is seen as cruelty by many people and is controversial.

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Detritus feeders (such as some types of worm) may start the process of decay by eating dead animals or plants and producing waste materials.

Decay organisms then break down the waste and dead plants and animals.

Decay organisms are microorganisms (bacteria and fungi),

Decay is faster warm and wet (oxygen) WOW

All of the materials from the waste and dead organisms are recycled.

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The carbon cycle

Photosynthesis removes co2 from the atmosphere.

Green plants as well as animals respire. This returns co2 to the atmosphere.

Animals eat green plants and build the carbon into their bodies.

When plants or animals die (or produce waste) microorganisms release co2 back into the atmosphere through respiration.

A stable community recycles all of the nutrients it takes up.

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Enzyme structure

Enzymes are biological catalysts – they speed up reactions.

Enzymes are large proteins and each has a particular shape.

The shape has an area where another molecule can fit in which is called the active site.

Too high a temperature will change the enzymes shape, and it will no longer work – it has then become denatured.

Enzymes can catalyse the build up of small molecules into large molecules or vice versa.

Enzymes lower the amount of energy necessary for a reaction to take place – the ‘activation energy’.

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Factors affecting enzyme action

Reactions take place faster when it’s warmer.

Higher temperatures mean the molecules move around more quickly so collide with each other more often and with more energy.

However if the temperature is too high the enzymes denature as the active site changes shape so they cannot join with molecules.

Enzymes work best in certain acidic or alkaline conditions.

If the pH is too acidic or alkaline for the enzyme then the active site could change shape so it would become denatured.

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Aerobic respiration

Glucose + oxygen --à carbon dioxide + water (+energy)

Aerobic respiration is the release of energy from food when oxygen is available.

The process takes part mostly in the mitochondria.

The energy released is used to –

Build larger molecules from smaller ones

Enable muscle contraction in animals

Maintain a constant body temperature in mammals and birds.

Build sugars nitrates and other nutrients in plants into amino acids and then proteins.

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Enzymes in digestion

Digestion involves the breakdown of large, insoluble molecules into smaller soluble molecules.

Amylase (carbohydrase) is produced by the salivary glands, the pancreas and the small intestine. It catalyses the digestion of starch into sugars in the moth and small intestine.

Protease is produced by the stomach, the pancreas and small intestine. It catalyses the digestion of proteins into amino acids in the stomach and small intestine.

Lipase is produced by the pancreas and small intestine. It catalyses the breakdown of lipids (fats and oils) to fatty acids and glycerol.

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Speeding up digestion

Protease enzymes in the stomach work best in acid conditions, Glands in the stomach will produce hydrochloric acid.

Amylase and lipase work in the small intestine. They work best when the conditions are slightly alkaline.

The liver produces bile that is stored in the gall bladder. Bile is squirted into the small intestine and neutralises the stomach acid. It makes the conditions slightly alkaline.

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Making use of enzymes

Biological washing powders contain enzymes that digest food stains. They work at a lower temperature that ordinary washing powders so can save us money.

Protease enzymes to pre digest proteins in some baby foods.

Isomerases to convert glucose into fructose to reduce amount of fat in sweet foods as less is needed.

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Controlling internal conditions (Homeostatis)

The processes in your body that help to maintain constant internal environment are known as homeostatis.

We must remove waste products produced through chemical reactions from the body.

Carbon dioxide is a waste product of respiration it is excreted through the lungs

Some of the amino acids we take in are not used. They are converted into urea by the liver and excreted by the kidneys in the urine which can be stored in the bladder.

The water and ion content of cells must be carefully controlled. If they aren’t then too much or too little water may move in and out of cells by osmosis.

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Controlling body temperature

The thermeoregulatory centre of the brain and receptors in the skin detect changes in temperature.

The thermeoregulatory centre controls the body’s response to a change in internal temperature.

If the core temperature rises-

Blood vessels near the surface of the skin dilate allowing more blood to flow through the skin capillaries. Heat is lost by radiation.

Sweat glands produce more sweat. This evaporates from the skins surface. The energy required for it to evaporate come from the skins surface so we cool down

Hair lies flat to reduced trapped air

If the core temperature falls-

Blood vessels near the surface of the skin constrict and less blood flows through the skin capillaries. Less heat is then radiated.

We ‘shiver’ – muscles contract quickly which require respiration and come of the energy produced is released as heat.

Hair pulled up erect to trap insulating layer of air.

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Controlling blood sugar

The pancreas monitors and controls the level of sugar in our blood.

I f there is too much sugar in our blood the pancreas produces the hormone insulin that results in the excess sugar being stored in the liver as glycogen.

If insulin is not produced the blood sugar level may become fatally high.

If the pancreas is not producing enough insulin, this is known as diabetes.

It can sometimes be controlled by diet of the person may need insulin injections.

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Cell division and growth

Cell division is necessary for the growth of an organism or for the repair if tissues are damaged.

Mitosis results in two identical cells being produced from the original cell.

A copy of each chromosome is made before the cell divides and of each chromosome goes to each new cell.

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Stem cells

Stem cells are unspecialised.

They can develop (differentiate) into many different types of specialised cell.

 Stem cells are found in the embryo and in adult bone marrow.

Many embryonic stem cells that we carry research out on are from aborted embryos or are ‘spare’ embryos from fertility treatment.

This results in ethical issues and much debate as it can be argued that you are destroying the life to obtain these stem cells for research.

The use of stem cells from adult bone marrow is still limited by the number of different types of specialised cell we can develop them into.

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Cell division in sexual reproduction

Cells in reproductive organs eg testes and ovaries divide to form sex cells (gametes)

Before division a copy of each chromosome is made.

The cell now divides twice to form four gametes (sex cells)

This type of cell division is called meiosis.

Each gamete has only one chromosome from the original pair.

All of the other cells are different from each other and the parent cell.

Sexual reproductions results in variation as the sex cells (gametes) from each parent fuse, So half the genetic information comes from the father and half from the mother.

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From Mendel to DNA

Gregor Mendel was a monk who worked out how characteristics were inherited.

His ideas were not accepted for many years.

Genes are short lengths of DNA (deoxydribonucleic acid) which make up chromosomes and control our characteristics.

Genes code for combinations of specific amino acids which make up proteins.

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Inheritance in action

Human beings have 23 pairs of chromosomes

One pair are the sex chromosomes

Females are ** and males are XY

Genes controlling the same characteristic are called alleles

If an allele ‘masks’ the effect of another it is said to be dominant.

The allele where the effect is ‘masked’ is said to be recessive

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Inherited conditions in humans

Huntingtons disease is a disorder of the nervous system; it is cause by a dominant allele, so even if one parent has it the disease can be inherited by a child.

Cystic fibrosis is a disorder of cell membranes; it is cause by recessive allele so parents may be carriers (Cc). Only if both parents are either carriers or have the disorder does a child inherit it.

Embryos can be screened to see if they carry alleles for one of these or other genetic disorders.

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hiuu billy


Nice, detailed without droning on:].




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