AQA Additional Biology B2

All the major points of the additional science biology - Pre 2011 Spec

Very detailed. Whoever rated this 1 star must be very stupid.

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  • Created by: PhilMoze
  • Created on: 21-01-12 19:40

Animal Cells - Non-specialised

A typical Animal cells has many features -

  • Nucleus - contains the genetic information and controls the cell. Has a membrane on which the Ribsomes are attached, Nucleus controls the differation of the cell.
  • Cytoplasm - where the chemicals reactions occurs, contains the mitocondria that release energy from glucose
  • Mitocondria - where the release of energy from glucose occurs, more mitocondria are present in muscle cells.
  • Cell Membrane - Controls the substances which move inside and outside of the cell. In osmosis it is the selectivly permenable membrane which allow omosis to occur
  • Ribosomes - Where protien synthesis occurs, the animo acids are combines into protiens for growth, new ezynmes etc..
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Plant cells - Non specialised

These have the same features as an animal cells however they also have:

  • Vacuole - This is where the cell sap is contained. It makes the cell more sturgid and supports the cell.
  • The cell wall - Also provides support and give ridgidness to the plant. Made of cellulose
  • Chloroplasts - these are filled with chlorophyll, a green pigment which is needed for photosynthsis to occur. Remember that respiration occurs in the ribosomes, and plants both photosynthsis' and respire.
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Specialised Cells

A cell which has been adapted to a specific purpose is called a specialised cell.

  • red blood cells - have no nucleus, have a large surface area through the shape, and contain haeoglobin to help carry more oxygen
  • Nerve cells - these have a long axon, which have carry neuropluses over long distances around the body
  • sperm cells - only have half genetic information (gamete), and have tails to ensure they swim fast. Large numbers of mitocondria are present next to the tail to provide energy. Have enzymes at the head to break into the egg.
  • White blood cells - Can change shape to engulf microbes

Plant cells -

  • xylem cells - dead cells and are hollow to allow the movement of water
  • palisade cells - these contain lots of cloroplasts to ensure they get lots of glucose from the light levels
  • Root hair cells - large surface area, allow more water to be absorbed
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Diffusion and Osmosis

Diffusion - the movement of particles from an area of high concentrention, to an area of low concentration. Diffusion is used to move oxygen from the blood into the cell, and also to move carbon dioxide out of the cell.

Osmosis - The movement of water from an area of high water concentration to an area of low water concentration. OR the movement of water from a high solution concentrate, to an area of low solution concentration. It only occurs through a partially permeable membrane. The effect is that both solutions become equally dilute over a period of time. It follows the concintration gradient

The rate of both diffusion and osmosis is based on the differences of concentrations. For example, in omosis if there was a great difference between concentration, the rate would be much faster than if the concentration differcence wasn't as large.

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This is the process of using light energy to provide food (glucose). It occurs in green plants, which contain chlorophyll.

                                        light energy
Carbon dioxide + Water ---------------> Glucose + Oxygen

Some of the glucose made is used in respiration instantly, however much is converted into starch which is insoluble and is stored.

The oxygen is used in respiration or else leaves through the stomata through diffusion.

The water is provided through the xylem transport.

Carbon dioxide enters through the stomata.

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Factors that effect photosynthesis

As shown in the previous slide, a number of things are needed for photosynthesis, if we control these conditions we can improve plant growth, eg in a greenhouse

  • Carbon dioxide air concentration - a higher lever of carbon dioxide would improve the growth This is because it is needed in photosynthesis.
  • Light Intensity - a low level of light can result in lower rates as there isn't enough energy to convert the carbon dioxide and water. When the level of light doesn't improve the rate, the other factors must be the limiting factor
  • Temperature - as the tempertature increases the enzymes which control photosynthsis become more effective. However past the peak, they become denatured and their active site becomes unable to cope.

There will always be a factor which limits the rate, and the one which is lacking is the limiting factor.

We can control conditions to improve plant growth by increasing carbondioxide levels, provding more light, and controling the temperture at around 40. Depending on the plant.

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Plant minerals

There are two main minerals which we must know about:

Nitrates - these are needed to make amino acids which are then used for protien. Which nitrates it could led to stunted growth. Nitrates enter the plant through the roots.

Magnesium - this is used to build chlorophyll. Without magnesium the plant would have white/yellow leaves and so it would reduce the rate of photosynthesis.

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Food Chains and Pyramids of Biomass

Food chains is a representation of energy transfers between organisms. We can link food chains together to form food webs. Food chains have these features:

  • Not often more than 4 organism long - poor energy transfers
  • Start with the sun as a source of energy, then have a producer then consumer

Pyramids of Biomass are a representation of the mass of living material at each stage in a food chain. They are always in a shape of pyramid (unlike pyramids of numbers) as energy is lost at every stage of the chain.

At the bottom of the pyramid is the producer, which is a plant. Then the 1st Consumer (herivore), following this are the 2nd consumers which are carnivores.

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Energy Transfers and Improving efficiency

Energy is lost at every level of the food chain because of :

  • movement - energy is used for respiration
  • heat - warm blooded animals need to remain warm and this uses energy, this doesn't apply to cold blooded creatures as much
  • waste products - energy is lost through undigested waste
  • not everything of the previous organism was eaten - this would mean that some of the biomass decomposes before it can be past on

These factors mean that often only 10% of energy is passed onto the next stage.

To improve effiency it is possible to reduce the number of stages in a food chain. It is also possible to limit the amount of energy lost, through limiting movement, and reducing the need to keep warm. This is used often in farming, through indoor reered animals, eg battery cage chickens.

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Recycling and the Carbon Cycle

Recycling of materials is very important in nature, as it ensures that they are returned into the enviroment. This occurs through decay, and is often done by microorganisms which release materials back into the atmosphere and soil. Human use microbes in compost and in sewage works.

The carbon cycle is more specific and involes the recycling of carbon in nature. CO2 is put back into the atmopshere through respiration, from plants, animals and microorganisms which help decay. It is taken out of the air mainly through photosynthsis, through then which is is transfered through the food chain.

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Enzymes Inside Cells

Enzymes are biologic catalysts. They increase the rate of reations within the body (in this slide - the cell). Enzymes are made of protien made of animo acids. They have an active site on which the reaction occurs, and work at an optimum pH and temperture. These are specific to the enzyme.

In cells they:

  • help respire
  • build protiens
  • photosythesis

Aerobic respiration is the release of energy from glucose, and it uses enzymes to catalyse process. Aerobic respiration requires oxygen and occurs within the mitocondria.

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Enzymes outside cells

These are used in the digestive process to break down different molecues the body needs to be small enough to absorb into the blood.

  • Protease is produced in the stomach, pancreas and small intestine, however it prefers acidic conditions and so works best in the stomach. It digests protiens into animo acids.
  • Amylase is produced in the salivary glands, the pancreas and small intensine. It prefers alkaine conditions and it digests starch and break in down into glucose which is smaller molecule.
  • Lipase is produced in the pancreas and small intensine. It prefers alakine conditions. It breaks down fats into fatty acids and glycerol.

Bile is produced in the gall bladder (liver) and is added into the system after the stomach. It neutralsies the acidic conditions of the stomach into an alkaine, and also emulfies the fat so it has a larger surface area. Bile isn't an enzyme however plays an important role in digestion.

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Enzymes in Industry

Some microoganisms produce enzymes which can be used in industry for our benefit. In the home:

  • Biological detergents - these contain protien digesters, and fat digesters. They can be good as they don't require as high tempertures, and they come from organisms which can be grown easily. However some people may be allergic and they are water soluble which means they can be hard to remove from a water source.

In industry:

  • Baby food protien predigestion - allows it to be easily digested by the baby
  • Carbohydrases - allows starch into sugar syrup
  • Isomerase - used to produce a sugar which is used in slimming foods.
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Homeostasis Overview

To ensure we stay alive and that enzymes work effectivly we must ensure that our bodys conditions are controlled. Some of the things which we must control are:

  • Water and ion content - a too high ion content can interfer with osomosis and can dause damage. We control these through our water and food intake
  • Blood Glucose Levels - This is controled by the pancreas, and produced by the hormone insulin.  The condition where the blood glucose levels aren't controlled is called Diabetes. And can be fatal.
  • Temperature - this is controlled by the thermoregulatory system in the brain. The ideal temperture for the HUMAN body is 37 degrees. This is because of our specific enzymes.
  • The control of waste products - we must remove products which could be dangerous to the body by removing it through urine (made of urea) and also through breathing out carbon dioxide.
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Blood Glucose Control

The blood glucose is monitored by the pancreas and then it produces insulin to reduce the level of glucose.

Insulin simulates the liver to convert the glucose into insouble glycogen, so therefore lowers the blood glucose levels.

The pancreas is continually adjusting the amount of insulin released to keep the blood glucose levels stable.

If the pancreas doesn't produce enough insulin it can cause diabetes, which can be treated through insulin injections or through control of the diet.

Insulin was discovered by Banting and Best, who expermented on dogs. They successfully treated diabetes on a human in 1922 through an injection of insultin from a dog. However they had to ensure it was pure enough for a human injection.

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Uses receptors which are sentitive to temperture throughout the body.

When the body is too hot:

  • Open superfical capillaries - closer to the skin, more heat loss
  • Sweating - through process of evaporation, takes heat away from the skin
  • Vessel dilation - increase surface area exposed, increasing heat loss.

When the body is too cold:

  • Shunt vessels open - closer into the blood, less heat loss
  • no sweat glands
  • Shivering - increases muscle activity so heat released through respiration
  • Blood vessels constrict - less surface area to loss heat from
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Genetic Disorders

Two examples which are required are:

  • Huntington's disease - this is a disorder of the nervous system and is called by one dominante allele. It can be passed on by ONE parent who has the disorder.
  • Cystic Fibrosis - this is a disorder of the cell membrane (so it effects the respiriritory system), and is caused by a homozygous recessive allele. So it must be inheritied from BOTH parents, who are CARRIERS, who may not have the diease themselves.

A carrier is someone who carries a faulty allele, however the diease doesn't present itself as it is often a homozygous recessive that causes the diease, and they have a dominate allele.

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Inheritance of Sex

Every female egg contains ** chromosome. However a male sperm cell contains XY choromone. This leads to a 50:50 chance of a male or female reproduction.

Egg and sperm cells are gametes, which means they only contain half the genetic information.

Females are: **

Males are: XY

It is a matter of chance on whether a male or female is produced.

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This is the process by which cells replicate themselves, into genetic ideniticals. It creates 2 new cells by first replicating it's choromsomes before spliting and then forming 2 seperate new cells.

Mitosis occurs in any body cell to create new tissues. It is an example of asexual reproduction.

It also occurs following fertilisation, when the first new body cell has been made. It then continues replicating until the cells begin to form an embyro.

Cells produced through mitosis are zygotes as they contain the full genetic information.

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This is where 4 new cells are made, however they only contain half the genetic information. These are called gametes, and are produced in the ovaries and testes. They are used in sexual reproduction.

The choromsome replicate themselves, and then split, the cells then divide, and divide again, which leaves 4 cells, and half genetic information.

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Genetics In General

Alleles can be dominant or recessive. A dominate allele will control the characteristics of the gene if it is present, however if only recessive alleles are present, that shall then control the characteristic.

The form in which the gene presents itself is called the PHENOTYPE

Homozygous dominants are represented by double captial letters eg. BB (for brown eyes).

Hetrozygous alleles are shown through a mix of alleles eg. Bb (still brown eyes, as dominante is still present)

Homonzygous recessive are shown through non-caps eg. bb (this is a phenotype of blue eyes).

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Genetic Diagrams

Genetic diagrams are used to show the chance of a certain charateristic showing itself when reproduction occurs.

you must idenitify the alleles of the parents, then place each of them a seperate gamete, and then cross the gametes from each parent. Remember to write the phenotype of each combination and then state the likeihood of each occuring.

eg a homozygous dominant of brown eyes, with a homozygous recessive with blue eyes, has a 50:50 chance of brown eyes or blue eyes.

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Stem Cells and Differentiation of Cells

Stem cells are cells which are found in bone marrow, and also in embryo's.

They are being researched into being used to treat diesases through growing organs and tissues from them, as they would have the same genetic information already.


Differenatiation of cells occurs when a cell adapts to perform a specific job within the organism. Plant cells can continually adapt throughtout life, however an animal cells remains fixed to a job until it dies. Some examples are nerve cells, blood cells and muscle cells.

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Joyce Jay


Brilliant, very detailed and helpful! :D Good job

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