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animal cells structure and function

the nucleus - controls all the activities of the cell. it contains the genes on chromosomes. they carry the instructions for making new cells o organisms. 

the cytoplasm - a liquid gel in which most of the chemical reactions needed for llife take place 

the cell membrane - control the passage into and out of the cell

the mitochondria - structures in the cytoplasm where oxygen is used and most of the energy is realsed during resperation 

Ribosomes - where protien synthesis takes place. all the protiens needed in the cell are made here. 

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plant cells

in addition to containing all of the structures in the animal cells all plant and algal cells have : 

a cell wall - made of cellulose that strenghtens the cell and gives it support

many but not all have : 

chloroplasts are found in all green parts of plants. they are green beacause they contain a green substance called chorophyll. Chorophyll abosrbs the light energy to make the food for the plant by the process of photosynthsis.

a permanent vacuole is a spaace in the cytoplasm filled with the cell sap.This is not only the food storage but it also helps to surrport the plant by keeping the cell rigid 

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bacterial cells

each bacterium is a single cell. It is made up of cytoplasm surrounded by a membrane and a cell wall. Inside the bacterial cell iss the genetic material. Unlike an animal or plant cells the genes and genetic information are not contaied in a nucleus, the long strand of DNA is usally circular and found free in the cytoplasm.

many bacterial cells also contain plasmids, which are small circular bits of DNA. These carry extra genetic information. Bacteria may have a slime capsule around around the outside of the cell wall. 

some bacteria also contian at least on flagellum or plural flagella, long protien strands in order to move themselves around. 

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yeast cells

Yeast cells are speciallised to be albe to survive for a long time even when there is very little oxygen avaible. When yeast cells have pleanty of oxygen they use aerobic respiration. They use oxygen to break down sugar to provide energy for the cell. During this process they produce water and carbon dioxide as waste products. 

However, when there is little oxygen the yeast use anaerobic respiration. When yeast cells break down sugar in the absence of oxygen, they produce ethanol and carbon dioxide. 

Yeast cells are an simple cell and contain :


cell wall


cell membrane 

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specialised cells

they can carry out a specific job and hae become specialised in order to do so. 

A specialised cell has become adapted to suit the particular job that it does. As a result, a specialsed cell can often look very different to a tipical plant or animal cell. Sometimes cells become so specialised that they only contian one lone function within the body. examples of this inculde sperm, eggs, red blood cells and nerve cells. 

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fat cells

If you eat more then you need, your body makes fat and stores it in fat cells. These ells help animals inculding us , to survive when food is in a short supply. 

main adaptation inculde 

  • they have a small amount ot cytoplasm and large amounts of fat 
  • they have very few mitochndria as the cell needs very small amounts of energy 
  • they can expand - a fat cell is able to expand to up to 1000 x its original size to make room for the fat. 


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Human cone eye cells

Cone cells are in the light sensitive layer of your eye (the retina). They make it possible for you to see in colour. Cone cells have three main adaptations:

  • the outer segment contains a special chemical (a visual pigment).This changes chemically in coloured light .It needs energy to change it back to its original form. 
  • the middle segment is packed full of mitrochondria.The mitochondria release the energy needed to reform the visual pigment . So you can see continually in colour 
  • The final part is the synapse contecting the cell to the optical nerve. When colouredd light makes your visual pigment chnage, an impulse is triggered. The impluse crosses the synapse and travels along the optical nerve to your brain. 
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Root hair cells

You find the root hair cells close to the tips of growing roots. Plants need to take in lots of water ( and dissovled mineral ions ). The root hai cells help them to extract more of these from the soil and to delliver it to the xylem tissue ,so it is close to the xlyem tissue.It achives this by having adaptions such as : 

  • The root hair increases the suface area increasing the area for the water and ions to move into the cell from 
  • the root hair cells have a large perment vacuole that speeds up the movement of the water by osmosis from the soil to the root hair .  
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Sperm cells

Sperm cells are usually released along way from the egg they are going to ferrtilise.They contian the genetic information from the male parent . Depending on the animal they need to travel throught ethier waterr or the reprooductive system to reach and egg. Then they have to break into the egg. Sperm cells have several adaptations to make all this possible : 

  • long tail whips from side to side and helps move the sprem towards the egg 
  • the middle section is full of mitochondria, which provide the energy for the tail to work
  • the acrosome stores digestive enzymes to break down the outer layers of the egg 
  • a large nucleus contains the gentic information to be passed on 
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diffusion is the spreading out of partiles of a gas, or any substance in solution. This results in the net movement of particles. The net movement is from an area of a high concentration to an area of lower concentration. This takes place due to the random movement of particles. All the particcles are moving and bumping into on another and this makes them move about. 

Rates of diffusion are effected ny the difference in concentration between the two areas as the steper the concentration gradient the faster the rate of difffusion . as if there is only a small diffferece the movement will be slow . But if there is a higher difference then there is a faster net movement of partilces. 


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A tissue is a group of cells with a similar structure anf function working together. Muscular tissue can contract to brin about movement. Glandular tissue contains secretory cells that can produce substances such as enzymes and hormones. Epithelial tissue covers the outside of your body as well as you internal organs 

Plant aslo have tissues. Epidermal tissues cover the surfaces and protect them. Mesophyll tissues contian lots of chloroplasts and can carty out photosynthesis. Xlyem and pholem are the transport tissues in plants.They carry water and dissolved mieral ions from the roots up to the leaves and dissoled food from the leaves around the plant. 

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Organs are made up of tissues. One orga can contain serveral tissues all working together. For example, the stomach is an organ inolved in the digestion of food. It contians ;

  • muscular tissue to churn up the food and digestive jucies of the stomach together
  • glandular tissues, to produce the digestive jucies and enzymes to break down the food. 
  • epithelial tissue, which covers the inside and outside of the organ. 

an organ is a collection of tissues working together to carry out important functions within yourr body. 

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Organ system - digestive system

The digestive system of humans and other mammals exchanges substances with the enviroment.The food you take in and eat is made up of large insoluble molecules. Yoour body cannot abosb and use these molecules so they need to be broken down or digested to form smaller, soluble molecules. These can then be abosrbed and used by your cells. 

the digestive sytem is a musculat tube that squeezes your food through it. It starts at one end with your mouth, and finishes at the other end with your anus. The digestive system contains many different organs. There are also glands involed such as the panceareas and salivary glands. These glands make and realease the digestive juscies and enzymes for the breakdown of your food. 

After the food is broken down within the small instestine the soluble food molecules are absorbed into your blood.This is helped by the large surfac area and blood supply of the small instine meaning an quicker diffusion. and then the waste is past through until all usalble nutrients are gone and the waste is removed as faeces.

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Plant organs

Animals aren't the only organisms to have organs and organ systems - plants also have them. 

Plants have differentiatied cells that form specialised tissues. These inculde mesophyll,xylem and phloem.Within the body of a plant, tissues such as these are arranged to form organs. Each organ carries out its own specific function. 

Plant organs inculde the leaves, stems and roots, each or which has a very specific job to do. :

  • Pholem transports dissolved food around 
  • Xlyem transports water and minerals 
  • Mesophyll tissue carries out photosynthiese 
  • Epidermal tissue covers the plant.
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Photosynthesis can be summed up by the equation :Carbon dioxide + water ---> Glucose + oxygen

The cells in algae and the leavesof a plant are full of small green parts called chloroplasts. They contain a green substance called chlorophyll.

During Photosynthesis, light energy is absorbed by the chlorophyll in the chloroplasts. This energy is then used to convert carbon dioxide from the ai plus water from the soil into a simple sugar Glusoce and the waste prodcut Oxygen. 

Some of the Glucose produced during photosynthesis is used immediately by the cells of the plant. However, alot of the Glucose made is converted into insoluble starch ans stored

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Leaf adaptations for a photosynthesis

The leaves of plants are perfectly adapted for photosynthesis beacause 

  • most leaves are broad, giving them a big surface area for light to fall on 
  • they contain chlorophyll in the chloroplasts to absorb the light energy. 
  • they have air spaces that allow carbon dioxide to get to the cells, and oxygen to leave them via diffusion 
  • they have veins, which bring plenty of water to the cells of the leaves. 


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limiting factors

LIght ; Is the most obiovus limiting factor affect the rate of photosynthesis and when there is pleanty of light plants can quickly  do lot of photosynthesis but if there isn't then less will ultimatly take place. this trend is contiuned until a differnet factor stops the risse in the photsynthesis. 

Temperture ; temperture effects all chemical reactions, inculding photsynthesis as when the temputre rises the rate of photosynthesis rises. However , photosynthesis is controlled by enzymes and these same enzymes become denatured at 50oc -60oc so when the temputre gets to high the increase stops as the photosynthesis stops as the enzymes become denatured 

Carbon dioxide : futher is factor of photosynthesis as it is a key part of photosynthesis as it is needed for the plant to be able to do photosynthesis as the larger the conentration the more that can be used in the photosynthesis 


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How plants use glucose

Plant cells and algal cells , like any other living cell respires contiunally so it uses the glucose that was made in the photosynthesis. This glucose and oxygen is broken down for the reperation of the cells. The energy realeased by this process allows smaller molecules to build up into bigger ones. Some of the glucose is changed into starch to be storage.Plants also use a more complex carbohydrate (cellulose) to strenghten the cell walls. 

Plants also use the glucose from the photosynthesis to make amino acids .They do this by combing the sugars with both nitrate ions and other mineral ions from the soil . These amino acids are then bulit up into proteins to be used in the cells. This uses energy created via resperation. 

Plants and algae also use glucose form photosynthesis and energy from resperaiton to bulid up fats and oils. These may be used in cells as an energy store. They are sometimes used in the cells as an energy store. They are sometimes used in the cell walls to make them stronger. In addition, plants often use fats or oils as an energy store. 

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Starch + plants

Plants store the spare glucose as starch so it will not effect the water balance, this means that the plants can store large amounts of starch in thier cells 

So,the main energy store in plants is starch and it is found all over a plant. It is stored in the cells leaves. The starch provides a supply of energy for when it is dark or low light levels.

Insoulble starch is kept in special storage areas of a plant. Many plants produce tubers and blubs. These help them to survive through winter.They are full of stored starch.We often take advantage of these by eating them oursleves like potatoes which are full of starch 

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Factor effecting living organisms

Temperature - In cold climates tempture is always a limiting factor . For example, artic plants are small. This in turn affects the number of herbivores that can survive in this one area.

Nutrients - The level of mineral ions availble has a big impact on the distribution of plants.Carnivorous plants such as Venus fly traps thrive where nitrate levels are very low becasue they can trap and digest animall prey.The nitrates theey need are provided when they break down the animal protien. Most other plants struggle to grow in these areas with low levels of mineral ions. 

Amount of light - Light limits photosynthesis,so it also affects the distribution of plants and animals.Some plants are adapted to living in low light levels.They may have more chlorophyll or bigger leaves .However, most plants need plenty of light to grow well. Additionally the breeding cycles of animals depend on how long the day lenght so they can only survie in regions where this is right for them

Availbilty of water - The availbilty of water is important in both the distirbuution of plants and animals accross the world as the higher the availblity of water the more that can surive there as there is less competion.   

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The simplest way to sample an area is to use a quadrat. Quadrats are used to investigate the size of a population of plants or animals that move very very slowly. 

You would use the same size quadrat every time and sample as many areas as possible whislt using a random selecter to place it down in completely random locations.To truely reflect the distribution of the organisms in the selcted area.You need to take a number of random readings and then find the mean number of organisms per meter squared. This technique is then called quantitive sampling.You can use quantitive sampling to compare the distribution of the same organism in different habbitats. You can use quantitative sampling to compare the variety of organisms in a number of different habitats.

Sampling is also used to measure changes in the distribution of organisms over time. You do this by repeating your measurements at a reguar tie intervals.Finding the range and the median and the mode data can aslo give you useful information.  

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Sampling along a transect is another way of measuring the distrubution of organisims.There are different types of transect althought a line transect is most commonly used.

Transects are not random. You streach a tape between two points.You sample the organisms along that line at regular intervals using a quadrat.This shows you how the distribution of organisms changes along that line. You can also measure some of the phycial factors, such as ,light levels and soil pH that might affect the growth of the plants along the transect.


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Enzymes - how they work

The substrate of the reaction fits into the active site of the enzyme.Once it is in place the enzyme and the substrate bind together.The reation then takes place rapidly and the products are realeased from the surface of the enzyme.Remeber that an enzyme can also join to smaller molecules together as well as breaking large ones down. 


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Enzymes - biological catalysts

In your body, chemical reaction rates are controlled by enzymes. These are special biological catalysts that speed up reactions. 

Enzymes are large protien molecules.The long chains of amino acids are folded to produce a molecule with a specific shape. allows other molecules (substrates) to fit into the enzyme protien. We call this the active site of an enzyme and it is vital to the way it works.

Enzymes are involved in:

  • building large molecules from lots of smaller ones
  • ( one molecule into another
  • breaking down large molecules into smaller ones.

Enzymes do not change in any way they just make the reation happen faster. and the different enzymes do different reactions.  

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Factor effecting enzymes

Temperature - Like other reactions the higher the temperature the faster the reaction happens with enzymes this is only ture up to tempture of about 40oc.After this the protien structure of the enzyme is affected by the high tempture.The long amino acid chains begin to unravel.As a result, the shape of the active site changes. We say the enzyme has been denatured. It can no longer act as a catalyst. so the rate of reactioon begins to drop. The opimum temperature for most human enzymes is about 37oc

pH - The shape of the active site of an enzyme comes from forces between the different parts of the protien molecule. These forces holds the folded chains in place. A change in the pH affects these forces. That's why it changes the shape of the molecule. As a result, the active site is lost, so th enzyme no longer acts as a catalyst. Different enzymes have different pH levels at which they work best. A change in the pH can stop them working completely.


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Enzymes in digestion

Carbohydrates - Enzymes that break down carboyhdrates are called carbohydrases.Starch is the most common carbohydrate and is broken down into sugars by silva and the small intestine with the enzyme amylase. Amylase is made in the salivary glands. So the digestion can start. Additionaly in the panreas so starch can be digested in the small intestine as well. 

Proteins - The breakdown of protien food like meat , fish and cheese into ammino acids is catalysed by protease enzymes. Proteases are produced by your stomach, your pancreas and your small instestine.The breakdown of protiens into amino acids takes place in your stomach and small intestine.

Fats - The lipids that you eat are roken down into fatty acids and glycerol in your small intestine.The reaction is catalysed by lipase enzymes.These are made in the pancreas and you small intestine. Again , the enzymes made in the pancreas are passed into the small intestine.Once your food molecules have been completely digested into soluble glucose, amino acids , fatty acidds amd glycerol they leave your small intestine and are then passed on through the blood stream to cell that need them   

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Enzymes in industry and at home

enzymes in industry 

Proteases are used to make baby foods. They predigest some of the protien in the food.When babies first begin to eat soild foods they are not very good at digesting it so they then predigest it to make iit easier for them to cope with it. 

Carbohydrases are used to convert starch into sugar (glucose) syrup. We use huge quantities of sugar syrup in food production. Providing a cheap source of sweetness for food manifacutures to use.

Sometime the glucose is then reacted with the enzyme isomerase and this is used to change it into the glucose syrup into a much sweeter fructose. 

enzymes at home

biological detergents can use proteases and lipases to help remove the stains at much lower temture to help save electricity. 

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Advantages and disadvantages of using enzymes


Enzymes can solve industrial problems like they can make the reactions be able to occur at lower temputures . So they run at a cheaper rate. 

use the substrate more efficently 


are expensive to make the enzymes 

they get easily denatured at to high a temputres so the tempture must be kept at certain conditions. 

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aerobic respiration

During anerobic reperiation, glucose reacts with oxygen.This reaction releases eneergy that your cells can use.This energy is vital for all cell actives in your body. 

equation : glucose + oxygen --> carbon dioxide + water (+ energy ) 

reasons for respiration 

  • living cells need energy to carry out the basic functions of life. They bulid u large molecules from smaller ones to make new cell material. Much of the energy released is used up in these synthesis reactions
  • in animals , energy from resperiation is used to make musclues contract.Muscles are working all the time. All muscular activites require and use energy 
  • Animals required the energy to keep there bodies at a constant temperture

Mitochondria - most recations of resperiation are conducted within the mitrochondria of your cells. and they are found in almost all cells. They have a large surface area of the inner membrane for the enzymes involed in the reactions

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Anaerobic respiration

Sometimes you can't supply enought oxygen to your musscles fast enough. When this happens the muscle cells still get the energy from glucose by using anerobic resperation , which is resperation without the presence of oxygen.In anaerobic respiration the glucose is not broken down completely. It produces lactic acid instead of carbon dioxide and water.

If you are fit , then you heart and lungs will be able to keep a good supply of oxygen going to your muscles while you exercise. If you are unfit, your muscles will run short of oxygen much sooner. 

Muscle fatigue - Using your muscles fibres vigoroulsy for a long time can make them become fatigued. This means that they stop contracting effeicently. One cause of muscle fatigue is the bulid up of lactic acid.It is made by anaerobic respiration in muscle cells.Bloo following through the muscles removes this lactic acid.

Anerobic respiration is not as effeicent as aerobic respiration.This is because the glucose molecules are not fully broken down. So far less energy is released in this process. The end product of anaerobic respiration is lactic acid so only a small amount of energy is realsed.

Glucose --> lactic acid (+ energy) 

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Oxygen debt

If you have been exerrciseing hard , you often end up out of breath for some time this is lenght of time depends on how fit you are. 

The waste lacti acid during anaerobic repiration is a problem.You cannot simply get rid of lacti acid by breathing it out like you can do with carbon dioxide. As a result the lacti acid has to broken down to produce the carbon dioxide and water.This needs oxygen to be able to take place.The amount of oxygen that you need to break down the lactic acid is known as you oxygen debt. 

The larger the amount of lactic acid you have the larger the pxygen debt there will be to pay off. 

oxygen debt repayment :

Lactic acid + oxygen --> carbon dioxide + water. 

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The cell division in normal body cells produces two identical cells and is called mitosis.As a result of mitosis all your body cells have the same chromosomes .This means they have the same gentic information. In asexual reproduction, the cells of the offspring are produced by mitosis from the cells of the parent. This is why they contain exactly thee same alleles as thier parent with no genetic variation. 

How it works - Before a cell divides ti produces new copies of the chromosomes in the nucleus. Then the cell divides once to form two genticaly identical cells. 

Why - to rapidly replace dead cells like on your skin. 


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In the early development of an animal and plant embryos the cells are unspecialised.Each one of them can become any type of cell.In many animals, the cells become specialised very early in life. By the time a human baby is born most of it's cells have become speciallised. They have differentitated. Some of the genes have been switched on and other have been switched off. 

This means that when, for example a muscle cell divides by mitosis it can only form more muscle cells. and this cell division is only used for the repair of dammaged tissue and to replace worn out cells. This is beacause in most adult cells differentiation has already occured. Specialised cells can divide by mitosis but then they can only form the same sort of cell. 

It is diffuiclut to make animal clones as animal cells differentiate perment;y in early embryo development . The cells can't change back. Animal clones can only be made by cloning embryo's in one way or another , althtought adult cells can be used to make this. 

Plants keep growing all thier lives. The plant cells produced don't differentaite until they are in thier final postion in the plant. Even then the differentitation isn't permanent. You can move a plant cell from part of plant to another as there it can redifferentitate and become a completely different cell you can't do this with animal cells once and mucsle cell all way an animal cell

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The female gametes or ova are made in the ovaries. The male gametes or sperm are made in the testes. The gametes are formed by meiosis - cell division where the chromosomes number is reduced by half. When a cell divides to  form gametes, the chromosomes are copied do there are four sets of chromosomess.The cell then divides twice in quik succesion to form four gametes , each with a single set of chromosomes. Each gammete that is produced is slightly different from all the others. They contain random mixtures of the orignal chromosomes pairs. This introduces variety. 


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The differences between asexual and sexual reproduction are reflected in the different types of cell division involed.

In asexual reproduction the offspring are produced as a result of mitosis from thee parent cells . So they contain exactly the same chromosomes and the same genes as their parents. There is no variation in the genetic material. 

In sexual reproduction the gametes are produced by meiosis in the sex organs of the parents.This introduces variety as each gamete is different. Then when the gametes fuse, one of each pair of chromosomes, and so one of each pair of genes, comes from each parent.The combination of genes in the new pair of chromosomes will contain alleles from each paraent. This also helps to produce variation in the characteristics of the offspring. 

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Gregor Mendel

He carried out breeding expriments using peas. He used ssmooth , wrinkled , green and yellow peas for his work he cross bread the peas and counted the different offspring carefully. He found chacteristics were inherited in clear predictable patterens

Mendel explained his results by suggesting there were separate units of inhherited material. He realised that some were dominant over others and that they had never mixed togheter. Mendels analysed his records and found thatthey where unheared of at his time and in 18666 Mendel finally publish his results. He had never seen or heared of chromosomes of genes . Yet Mendel explianed some of the basic ideas and laws of genetics with mathemtical models. `


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The genetic code - the long strands of your DNA are made of combinations of four different chemical bases.These are gouped together into threes and each group of three codes for an amino acid. Each gene is made up of hundrends or thousands of these bases. The order of the bases controls the orde in which the amino acids aare put tigether so that they make a particular protein for use in your body cells. Each gene codes for a particular protien for use in your body cells . Each gene codes for a particular commbination of amino acids, wwwhich make a sppecifc protien. A change orr mutation in a single group of bases can be enough to change or diisrupt the whole protien structure and the way it works. 

DNA fingerprinting - except for idetical twins, your DNA is unqiue to you. Other members of your family will have strong similarites in thier DNA . However , each indival has there own unique patteren . These unique patterns can be used to identify you via your DNA. 

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Genetic terms

Homozygous - an idividual with two identical alleles for the same charateristic

Heterozygous - an idividual with two different alleles for the same charateristic 

Genotype - this describes the genetic makeup of an idividual regarding a particular charcteristic 

Phenotype - this describes the physical apperance of an individual regarding a particular characteristic. 

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Genetic lottery

When the genes from parents are combined, it is called a genetic cross.We can show this using a genetic diagram. This can show us 

  • The alleles for a charcteristic carried by the parents
  • the possible gametes which can be formed from these 
  • how these could combine to form the charateristic in their offspring. The genotype of the offspring allows you to work out the possible phenotypes too. 

When looking at the possibillity of inheriting genetic disorders.

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really useful for my mock. thanks! shame I couldn't print it out in pdf cuz tsr was having a '503 fault' butb really useful anyway thanks!



Still faulty, could this be fixed please? Thanks




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