Additional science AQA biology

A few thing which you need to know for an AQA addtional science Gcse


Parts of an animal cell and there meanings.

Plant and animal cells have similarities and differences.Animal cells have the following parts:

Nucleus- contains genetic material that controls the activities of the cell.

cytoplasm- a gel like substance where most chemical reactions happen. it contains enzymes that control chemical reactions.

cell membrane- holds the cell together and controls what goes in and out

mitochondria- these are where most of the reactions for respiration happen.Respiration releases energy  that the cell needs to work.

Ribosomes- these are where protiens are made in the cells

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Parts of the plant cells

Plants cells have all the bits that animal cells have plus a few extra:

Rigid cell walls- made of cellouse.It supports the cell and strengthens it.

Permanent vacole- contains sap, a weak solution of sugar and salt.

Chloroplasts- these are where photosynthesis occurs. this makes food for the plants. they contain green substance called chlorophyll.

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Photosynthesis equation




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pyramids of biomass

100 dandilions... feed...10 rabbits...feeds....1 fox  Each bar on a pyramid of biomass shows the mass of living materialat that stage of the food chain - basically how much all the organisms at each level would weigh if you put them all together.So the one fox above would have a big biomass and the hundred fleas would have a very small biomass. Biomass pyramids are usually always in the shape of a pyramid. The big bar along the botom of the pyramid always presents the producer (ie a plant), the next bar is the primary consumer (the animal that eats the plant),then the secondary consumer (the animal who eats the primary consumer) and so on.   

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Enzymes and respiration

Enzymes help build amino acids and protiens. They catalyse protein synthesis by joining together amino acids. these protiens could be emzymes.

Respiration involves many reactions all of which are catalysed by enzymes.Respiration is the process of releasing energy from the breakdown of glucose and goes on in every cell in your body. It happens in plants too. all living things respire. 

Aerobic respiration needs plenty of oxygen. Aerobic respiration is respiration using oxygen. its the most efficient way to release energy from glucose. most of the reactions in aerobic respiration happen inside mitochondia.

glucose + oxygen -> carbon dioxide+water+energy   

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Enzymes and Digestion

Digestive enzymes break down big molecules into smaller ones.

starch protiens and fat are big molecules. they are too big to pass through the walls of the digestive system. sugars, amino acids, glycerol and fatty acids are much smaller molecules.they can easily pass through the walls of the digestive system. The digestive enzymes break down the big molecules into smaller ones.

Amylase coverts strach into simple sugars. Amylase is made in three places 1) the salivary gland 2) The pancreas 3) the small intestines

Protease converts protiens into amino acids. protease is made in three places 1) The stomach 2) The pancreas 3) the small intestines

 Lipase converts fats into glycerol and fatty acids.Lipase is made in two places 1) the pancreas 2) the small intestine 

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Bile and stomach acids

Bile neutralises the stomach acid and emulsifies fats. bile is produced in the liver. it's stored in the gall bladder before it is released into the small intestines. the hydrochloric acid in the stomach makes the PH to acidic for emzymes in the small intestines to work properly. Bile neutralises the acids and makes the conditions alkaline. The enzymes in the small intestines work better in alkaline conditions.

It emulsifies fats. in other words it breaks the fat into tiny droplets. this gives it a much bigger surface area of fat for the enzyme lipase to work on which makes its digestion faster.

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The digestive system

The Breakdown of food is catalysed by Enzymes. different enzymes breakdown different food molecules.

salivary gland- these produce amylase enzymes in the saliva.

The liver- where bile is produced bile neutralises stomach acids and emulsifies fats.

gall bladder- where bile is stored before it is released

large intestine- where excess water is absorbed from the food

rectum- where the faeces are stored

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More about the digestive system

The small intestine- produces protease, amylase and lipase enzymes to complete digestion

The pancreas- produces protease and lipase enzymes. it releases these into the small intestine.

the stomach - it pummels the food with it muscular walls. it produces the protease enzyme pepsin. it produces hydrochloric acids for two reasons 1)to kill bacteria and 2) to give the right PH for protease enzymes to work.(PH2 acidic)

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uses of enzymes

Enzymes are used in biological detergents. Enzymes are the biological ingredients in biological detergents and washing powders. they're mainly protien digesting enzymes (protease) and fat digesting enzymes (lipase) because enzymes attack animal and plant matter they're ideal for stains like food or blood.

Enzymes are used to change foods. the protiens in some baby foods are pre-digested using protien digesting enzymes  (protease) so they're easier for the baby to digest. glucose syrup can be turned into fractose syrup isomerase enzymes. fructose is sweeter, so you can use less of it.

using enzymes in industry takes a lot of control. enzymes are usually helpful in industry. they speed up reactions without the need for high temperatures and pressures.     

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Advantages to using enzymes.


they're specific, so they only catalyse the reaction you want them to.

Using lower temperatures and pressure means a lower cost and it saves energy.

Enzymes work for a long time, so after the intital cost of buying them you can continually use them.

they are biodegradable and therefore cause less enviromental pollution

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Disadvantages to using enzymes


some people develop allergies to the enzymes

enzymes can be denatured by even a small increase in temperature. they're also susceptible to poisons and changes in PH.

contamination of the enzymes with other substances can affect the reaction. 

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Homeostasis is the maintenance of a constant internal enviroment. there are 6 main things that need to be controlled.

1) the body temperature cant be to hot ot to cold.

2) water content mustnt get too high or low or too much water could move in and out of the cellsand damage them.

3) if the ion content of the body is wrong the same thing could happen

4) the blood sugar level needs to stay between the limits.

5) carbon dioxide is a waste product of respiration. its toxic in high quantities so its got to be removed.

6) urea is a waste product made from excess amino acids.

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Body temperature

Body temperature must be carefully controlled. All enzymes work best at a certain temperature. The enzymes within the human body work best at about 37.c. if the body gets too hot or too cold the enzymes won't work properly and some really important reactions could be disrupted. there is a thermoregulatory centre in the brain which acts as your own personal thermostat. it contains receptors that are sensitive to the temperature of the blood flowing through the brain. the thermoregulatory centre also recieves impulses from the skin, giving info about skin temperature. if you're getting to hot or too cold, your body can respond to try and cool you down or warm you up

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Reponses from the body when you are too hot or too

When you're to hot:

1)you're hair lies flat 2) sweat is produced by sweat glands and evaporates from the skin, which removes heat.3) The blood vessels supplying the skin dilate so more blood floes close to the surface of the skin. this makes it easier for heat to be transfered from the blood to the enviroment.

when you're too cold:

1) hair stands up to trap an insulating layer of air

 2) blood vessels supplying skin capillaries constrict to close off the skins blood supply   

3)when you're cold you shiver too. this releases some energy as heat

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The Kidneys and homeostasis

kidneys act like a filter to clean the blood. The kidney perform three main roles: 1) removel of urea from the blood 2)adjustments of ions in the blood 3) adjustments of water content in the blood.

removal of urea

protiens can't be stored by the body, so any excess amino acids are converted into fats and carbohydrates which can be stored.this process occurs in the liver.urea is produced as a waste product from this reaction. urea is poisonous. it is released into the blood stream by the liver and the kidney's filter it out of the blood and it's excrete from the body in urine.  

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Adjustment of ion content

Ions such as sodium are taken into the body in food and then absorbed into the blood.If the ion content of the body is wrong this could mean to much or too little water is drawn into cells by osmoisis. having the wrong amount of water can damage cells.excess ions are removed by the kidneys. some ions are also lost in sweat. but the important thing to remember is the the balance is always maintained by the kidneys

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Adjustment of water content

water is taken into the body as food and drink and is lost from the body in three main ways : 1) in urine 2) in sweat 3) in the air as we breathe out. The body has to constantly balance the water coming in against the water going out. our bodies can't control how much we lose in our breath but we do control the other factors. this means the water is balanced between 1) liquids consumed 2) Amount sweated out 3) Amount coming out as urine .

on a cold day, if you don't sweat, you will produce more urine which will be pale and dilute. on a hot day, you sweat a lot, and you'll produce less urine which will be dark coloured and concentrated. The water lost when it is hot is replaced by the water in food and what you drink so the balance is restored 

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