AQA GCSE Biology Unit B3 Chapters 1-2

Osmosis and diffusion involve the movement of substances from a higher concentration to a lower concentration.

A cell may need to take up a substance against the concentration gradient. This involves energy and is called active transport

For example, plants taking mineral ions from the soil will need to use active transport because there is a very high concentration of mineral ions in the plant compared to in the soil.

• The lungs exchange oxygen and carbon dioxide with the atmosphere.
• They have a very large surface area provided by millions of alveoli (air sacs).
• The surfaces of the lungs are moist and thin so that diffusion takes place quickly
• The lungs also have a very rich blood supply which maintains a high concentration gradient because the gases are taken away quickly

The food that we eat is digested in the gut into small, soluble molecules. In the small intestine these are absorbed by the blood.

Finger-like projections in the small intestine called villi greatly increase the surgace area for absorption to take place.

Fish gills also show all the same characteristics that other exchange surfaces show in that they are thin, have a large surface area and have a rich blood supply.

• Gases diffuse in and out of leaves through stomata
• Oxygen is taken in for respiration and is also a waste product of photosynthesis.
• Carbon dioxide is needed for photosynthesis and is a waste product of respiration

Leaves are flat and very thin so that the gases don't need to diffuse very far. There are also internal air spaces.

Water and mineral ions are taken up from teh soil by the roots. The roots have thousands of root hairs to increase their surface area.

Plants take up water through the roots. The water passes to the leaves. It evaporates from the leaves through the stomata in a process known as transpiration.

Guard cells control the size of stomata to make them close to prevent water loss and to dilate to increase water loss.

On hot days, transpiration happens quicker because there is more energy causing the water to evaporate. On dry days, transpiration happens more rapidly because the air can hold more water. On windy days any build up of humidity around the plant is blown away.

The heart pumps blood around the body. The blood is pumped to the lungs where it picks up oxygen and loses carbon dioxide and then back to the heart. THen it is pumped to the rest of the body.

Arteries take blood away from the heart. The blood returns in veins.

Capillaries are very small vessels that are between the arteries and veins. They carry the blood through the organs and allow the exchange od substances with all the living cells in the body.

• The lungs exchange oxygen and carbon dioxide with the atmosphere.
• They have a very large surface area provided by millions of alveoli (air sacs).
• The surfaces of the lungs are moist and thin so that diffusion takes place quickly
• The lungs also have a very rich blood supply which maintains a high concentration gradient because the gases are taken away quickly

The food that we eat is digested in the gut into small, soluble molecules. In the small intestine these are absorbed by the blood.

Finger-like projections in the small intestine called villi greatly increase the surgace area for absorption to take place.

Fish gills also show all the same characteristics that other exchange surfaces show in that they are thin, have a large surface area and have a rich blood supply.

• Gases diffuse in and out of leaves through stomata
• Oxygen is taken in for respiration and is also a waste product of photosynthesis.
• Carbon dioxide is needed for photosynthesis and is a waste product of respiration

Leaves are flat and very thin so that the gases don't need to diffuse very far. There are also internal air spaces.

Water and mineral ions are taken up from teh soil by the roots. The roots have thousands of root hairs to increase their surface area.

Plants take up water through the roots. The water passes to the leaves. It evaporates from the leaves through the stomata in a process known as transpiration.

Guard cells control the size of stomata to make them close to prevent water loss and to dilate to increase water loss.

On hot days, transpiration happens quicker because there is more energy causing the water to evaporate. On dry days, transpiration happens more rapidly because the air can hold more water. On windy days any build up of humidity around the plant is blown away.

The heart pumps blood around the body. The blood is pumped to the lungs where it picks up oxygen and loses carbon dioxide and then back to the heart. THen it is pumped to the rest of the body.

Arteries take blood away from the heart. The blood returns in veins.

Capillaries are very small vessels that are between the arteries and veins. They carry the blood through the organs and allow the exchange od substances with all the living cells in the body.

• When you exercise your muscles need more energy so that they can contract.
• You need to increase the rate at which oxygen and glucose reach the muscle cells and remove carbon dioxide more quickly.
• The heart rate increases and the blood vessels supplying the muscles dilate to allow more blood containing oxygen and glucose to reach the muscles.
• The breathing rate and the depth of each breath increases too to allow a greater take-up oxygen and release of carbon dioxide at the lungs.
• The body may also use up glycogen - a storage compound of glucose present in the muscles

glucose --> lactic acid + (a little energy)

If you use your muscles for a long time they get tired or fatigued. When your muscles can't get enough oxygen for aerobic respiration, they start to respire anaerobbically.

This is inefficient and produces toxic lactic acid as a waste product

Lactic acid is what causes the fatigue. When the exercise is finished, the lactic acid has to be completely broken down. So you sill need to take in a lot of oxygen to do this. This is called the oxygen debt.

lactic acid + oxygen --> carbon dioxide + water

The body has two kidneys. Their job is to filter the blood, excreting substances you don't want and kepping those that the body needs.

After filtering the blood, all of the sugar (except in diabetics) and many of the dissolved ions and water needed by the body are reabsorbed.

All of the urea and some ions dissolve in the remaining water and are excreted in the urine.

Sugar and dissolved ions may be reabsorbed against the concentration gradient (ie active transport).

If a person has a diseased kidney, a dialysis machine can filter the blood for them. The blood flows between partially permeable membranes.

The dialysis fluid contains the "right" concentration of useful substances that the patient's blood needs e.g. glucose and mineral ions. This means that through diffusion, the patient's blood gets the same concentration of substances as they should have.

Dialysis needs to be carried out at regular intervals.

• For most patients a kidney transplant is a better option than dialysis.
• However, a donor kidney must be found with the same tissue type.
  • To prevent rejection:
• The recipient's bone marrow is treated with radiation to stop white blood cell production
• The recipient has to take immunosuppresant drugs
• After the operation, the recipient must be kept in sterile condistions to prevent infection.