Aqa gcse Biology unit 3 (b3)

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  • Created on: 05-05-14 21:09

Diffusion, Osmosis and Active transport

What is diffusion? 

It is the movement of molecules from an area of high concentration to an area of low concentration.

What is Osmosis?

It is the diffusion of water through a semi (partially) permeable membrane. The movement of water molecules from an area of high concentration to low.

What is Active transport? 

It is the movement of molecules from an area of low concentration to an area of high concentration. The requires energy to be done.

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Isotonic drinks

What are Isotonic drinks (sports drinks)?

Isotonic drink are drinks that contains a similar level of sugar, ions and water of that of human body. The sugar replaces the amount of sugar released during exercise, and the water and ions replaces the water and ions that are lost via sweating.

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Exchange of materials in humans

What two ways are materials exchanged in humans?

1) Villi in the small intestine

2) Alveoli in the lungs 

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Exchange of materials in humans - villi

What makes the villi so effective at exchanging materials in humans?

It has a large surface area. It also has an extensive network of blood capillaries which help absorb products of digestion. The capillaries help to maintain the concentration gradient.

Capillaries have very thin walls, why is this good for exchange of materials in the human body?

It is good as it provides a short diffusion path.

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Exchange of materials in humans - alveoli

What are Alveoli's?

Are at the end of each bronchiole where thers a tiny air sack known as the alveoliwhere the exchange of carbon dioxide and oxygen takes place by diffusion.

What maximizes the exchange in the alveoli?

  • Large surface area (due to there being millions of alveoli in the lungs) so there is larger surface area for the exchange of materials.
  • They have an excellent supply of blood due to the capillaries being so close to the surface (short diffusion pathway).

What diffuses in and out of the alveoli?

  • Carbon dioxide diffuses out from the blood into the alveoli.
  • Oxygen diffuses in to the blood from the alveoli.


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What happens to the rib-cage and diaphragm during inspiration (breathing in)?

The ribs move up and out due to the intercostals muscle contracting. The diaphragm contracts and flattens.


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What happens to the rib-cage and diaphragm during expiration (breathing out)?

The rib cages move down and in as the intercostals muscle relaxes. The diaphragm also relaxes but moves upwards.

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What is transpiration?

Is the loss of water vapour from the stomata in a plant

What does the stomata allow?

Allows the exchange of carbon dioxide and oxygen by diffusion. It also allows the loss of water.

What is the prime condition for Transpiration?

A warm, dry and windy condition.

How does light affect Transpiration?

Transpiration increases in bright light as the stomata opens wider in increased light.

Why is transpiration faster in high temperatures?

Because evaporation and diffusion are faster in higher temperatures causing more water to be lost via the stomata increasing and speeding up transpiration.

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Transpiration - 2

Why is transpiration faster in windy conditions?

Because water vapour is removed quicker by the wind, speeding up diffusion of more water vapour and keeping the concentration gradient.

Why is transpiration slower in humid conditions?

It is slower as in humid condition there is a high concentration of water vapour present in the air and a high level within the leaves which means that the concentration difference for diffuison to occur is not there.

If the loss of water is faster than the rate at which it is being replaced by the roots in a plant what happens?

The guard cells surrounding the stomata close up the stomata and prevent any more water loss (transpiration) and also stop photosynthesis as Co2 cannot enter the leaves.

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What does the roots absorb form the soil?

Water and ions

What helps to increase the roots surface area?

Root hairs

What is the job of the Xylem?

Movement of water through a plant - from its roots to its leaves via the stem.

Explain the process of how the water reaches the Xylem and leaves?

Water is absorbed from the soil through root hair cells by osmosis. It is transported through the xylem vessels up the stem to the leaves. It then evaporates from the leaves (transpiration).

What is the job of the phloem?

Transport dissolved sugars from the leaves to the rest of the plant.

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The Heart

What does the arteries do?

They carry the blood away from the heart

What does the veins do?

Return blood to the heart

What are capillaries?

They are tiny blood vessels only one cell thick where exchanges of substances occur

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The Heart - 2

What is the name given to the upper right and left chambers in the heart?

The upper chambers are the Right and left atrium

What is the name given to the lower right and left chambers in the heart?

The lower chambers are the Right and left ventricle

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The Heart - 3

What is oxygenated blood?

Blood that has a lot of oxygen

What is deoxygenated blood?

Blood with little oxygen and a lot of carbon dioxide

What is the job of the valve?

The job of the valve is to prevent back flow of blood in the heart

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The blood

What 4 components make the blood?

Plasma, red blood cells, white blood cells and platelets

What is the job of the plasma?

To transport carbon dioxide to the lungs and soluble substances (sugars, amino acids etc.) obtained from food (in the small intestine) to other organs.

What is the job of the red blood cells?

To transport oxygen, this is done by the haemoglobin which combines with oxygen in the lungs to make oxyhaemoglobin which can then be split up so the oxygen can diffuse into cells.

What is the job of antibodies?

They are part of the immune system and have the job of fighting against microbes.

What is the job of the platelets?

Their job is to help the blood to clot where there is a cut.

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Why and where is a stent used?

A stent is used in a coronary artery to help unblock the artery.

Advantages and disadvantages of using stents?

Advantages: Common operation with a high success rate

Disadvantages: There are possibilities of complications such as bleeding, allergic reaction and irregular heart beat. Another disadvantage is that the artery may re-close.

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How is the waste product carbon dioxide produced and removed by the body?

Carbon dioxide is produced during respiration and is removed by the lungs.

How is the waste product urea formed and removed by the body?

When the liver breaks down excess amino acids Urea is produced. It is then removed by the kidney and stored in the bladder where it is later released.

How is the temperature maintained?

To increase the body temperature the blood vessels are narrowed and move further away from the skin so less heat is lost. And to decrease the temperature the vessels are widened and closer to the skin so more heat is lost.

How is water maintained by the body?

Water is lost when breathing out (water vapour), and also sweating. And is also lost via the kidneys in the urine. And is gained by drinking and eating.

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Homoeostasis - 2

How is the glucose (blood sugar) level controlled?

Gained by drinking and eating to provide a constant supply of energy for the cells. And is removed from the blood and stored as glycogen.

How does the Kidney filter out the urea from the blood?

The blood contains water, ions, sugar and urea and protein which are filtered into the tubule apart from the protein which remains in the blood as it can not pass through the semi permuable membrane. Then the useful substances are reabsorbed back into the blood leaving all the urea and some excess water and ions in the tubule. These are then passed to the bladder and released.

What is job of the temperature receptors in the skin?

The job of the receptors is to send impulses to the thermoregulatory center in the brain which gives information about the bloods and skins temperature.

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In a dialysis machine why is it important for the dialysis fluid to be moving?

To ensures that there is low concentration of urea in the fluid.

What are the advantages and disadvantages of a dialysis machine?

Advantages: More availability compared to kidney donors. And no drugs required to be taken. And no chance of rejection.

Disadvantages: Have to have long regular sessions on the dialysis machine. Less freedom and have to have a strict diet.

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Kidney transplant

What precautions are taken to reduce the chance of kidney rejection?

They try to find the most similar tissue type. The patient is treated with drugs to weaken (suppress) the immune system so that the body doesn't attack the kidney.

What are the advantages and disadvantages of a kidney transplant?

Advantages: No need to control diet. No sessions required, More freedom.

Disadvantages: Hard to find a donor (tissue type). Possibility of rejection of kidney and are required to take drugs.

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What controls the glucose level (concentration) in the body?

The pancreas by releasing a hormone called insulin.

What is the job of the insulin?

The insulin is responsible for allowing the glucose to enter cells from the blood. It also has the job of converting glucose to glycogen (which is a form of storing energy)

What happens to the glycogen when there is a low glucose level?

Glycogen is converted back into glucose by a hormone known as glucagon which is released by the pancreas. The conversion of glycogen to glucose occurs in the liver.

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Type 1 diabetes

What are the characteristics of type 1 diabetes?

The persons blood's glucose level may go too high as the pancreas is unable to produce enough insulin, which means the glucose cant leave the blood to enter the cells. And glucose is then not able to be converted into glycogen.

How can type 1 diabetes be treated?

By taking Insulin injections, and by carefully controlling your diet and doing exercise.

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What major problems are caused by a rapid increase in human population?

 There will be: More non-renewable energy resources used up - More co2 emission. More industrial waste will also be produced - More pollution. More land will be used up for farming and space for people to live in. And land will also be needed for waste dumping.

How is the increase population increase Land pollution?

More toxic chemicals from farming will be needed such as pesticides (kill insects that eat the crops) and herbicides (kill unwanted plants). If they get to unwanted places they can disturb food chains. These can also be washed from land into water.

How is the increase population increase water pollution?

The increase population will result in more toxic chemicals polluting the water from industrial processes. And will also result in more Sewage waste and fertilizer which can also cause water pollution.

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Pollution - 2

How is the increase population increase Air pollution?

More smoke is produced by incomplete combustion of fossil fuels will cause soot to be formed on buildings & trees. And smoke in the air will make it harder to breath. More sulfur dioxide will cause acid rain. More carbon dioxide & methane will increase the greenhouse effect & contribute to global warming.

What is the Greenhouse effect?

Its how methane and carbon dioxide act as an insulating layer by preventing alot of heat escaping the earths atmosphere. The greenhouse effect is needed because without it the earth would be far to cold and with too much it would be far to warm.

What is deforestation?

The process of cutting down trees, clearing and removal of natural forests by humans.

What is biodiversity?

Is the variety of plant and animal life in the world or in a particular habitat

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Pollution - 3

How does deforestation effect Co2 levels?

It increases the Co2 level as it reduces the rate at which Co2 is removed from the air and locked up (in the wood). And the wood obtained from deforestation is burnt which releases the locked up Co2.

How does deforestation effect biodiversity?

It reduces it as the area where the deforestation it done so the habitats of animals are destroyed (resulting in the loss of organisms that could be of future use).

What are the reasons for deforestation?

To have more land for growing crops from which bio fuels can be made. Some lands are also used to grow more crops & cattle for food such as rice crops. These crops & cattle release methane into the air (greenhouse gas).

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What are peat bogs and what are they used for?

They are areas of wetland where over thousands of years decaying plants have formed into peat. They are used as compost to help grow plants. And are also burnt to use as fuels (which releases a large amount of Co2).

Why is it important for peat free compost to be used rather than peat based compost?

Because peat bogs have a large amount of Co2 locked up inside them. When processed to make peat based compost it releases the Co2 which is locked within it & using peat free compost prevents this from happening which preserves & prevents the destruction of the habitat (peat bog).

What may happen if the earths temperature went up by few degrees?

It may cause:

Big changes in the earths climate, or rise in sea levels, or reduce biodiversity, or result in change in migration patterns and distribution of species.

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What are biofuels?

They are fuels made from natural products (biomass) by anaerobic fermentation.

Why is there less energy in the biomass of an organism as the number of stages in the food chain increase?

It is because the energy is used & lost via movement, waste and by heat loss.

How can you minimize energy loss in the biomass of an organism?

By reducing the number of stages in the food chain, or by limiting the movement of the animal and by controlling the temperature of the surroundings.

What are mycoproteins?

It is a meat-free, high quality protein suitable for vegetarians. It is produced by the fungus fusarium, which is grown on glucose syrup in aerobic conditions. The biomass is then harvested and purified.

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Batch biogas generator

How does a batch biogas generator work?

It works by putting waste material into a tank with an anaerobic bacteria where it is left to ferment until the biogas is produced. The gas is then collected. The tank is then cleaned and refilled and the slurry (waste material) can be sterilized and used a s a fertiliser.

What are the advantages and disadvantages of batch biogas generators?

Advantages: Useful for small-scale production. Can be cleaned easily if contaminated.  Disadvantages: Takes alot of time & energy to set up. Takes up to 4 weeks before methane is produced. Only small batches of biogas is made.

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Continuous biogas generator

How does a Continuous biogas generator work?

Waste is continuously added to the tank. The gas is collected. This then continues for a long period of time. The slurry is then collected, sterilised and used as a fertiliser.

What are the advantages and disadvantages of Continuous biogas generators?

Advantages: Efficient - Methane is produced continuously. The waste material is used continuouslyDisadvantages: More complex & expensive to set up. Cant control temperatures so works slow in the winter. Large amount of gas need storing.

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