Transport and respiration

Transport in humans

The heart pumps blood around the body through blood vessels.

• Arteries carry blood away from the heart at high pressure; they have thick muscular walls.
• Veins carry blood back to the heart; they have valves to stop backflow.
• Capillaries are one cell thick, so substances pass easily between blood and cells.

Blood contains red cells (carry oxygen), white cells (fight infection), platelets (help clotting) and plasma (carries dissolved food, carbon dioxide and hormones).

Transport in plants

• Xylem carries water and mineral salts up from the roots.
• Phloem carries sugars made in the leaves to other parts of the plant.
• Transpiration is the loss of water vapour from leaves through stomata. It is faster when it is hot, dry, windy and bright.

Respiration

Respiration releases energy from food in every living cell. It is not the same as breathing.

• Aerobic respiration: glucose + oxygen → carbon dioxide + water + energy
• Anaerobic respiration in muscles: glucose → lactic acid + a little energy
• Anaerobic respiration in yeast: glucose → ethanol + carbon dioxide + energy (used in brewing and baking)

Breathing

Air enters through the trachea, bronchi and bronchioles to the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out. Lime water turns milky with carbon dioxide, showing that exhaled air contains more of it.

Check yourself

1. Give one difference between arteries and veins.
2. Write the word equation for aerobic respiration.
3. State two conditions that increase the rate of transpiration.