Human body systems, Year 8: more practice

The oesophagus

提示It runs through the chest.

为什么Muscles in the wall of the oesophagus squeeze the food down in waves.

To absorb water from the undigested food

提示Think about what is left at the end.

为什么Undigested food moves into the large intestine, where water is absorbed. What is left forms faeces.

A hinge joint

提示It only bends in one direction.

为什么A hinge joint allows movement backwards and forwards in one plane, like a door hinge.

A ball-and-socket joint

提示The end of the bone is round.

为什么The ball-shaped end of the upper arm bone fits into a cup in the shoulder, giving movement in many directions.

Protease

提示Its name suggests what it acts on.

为什么Protease works in the stomach and small intestine. The amino acids can then be absorbed.

They give a large surface area for absorbing food

提示Think about how a bigger lining lets more nutrients cross at once.

为什么Villi are tiny finger-like projections. A larger surface area means more digested food can be absorbed at once.

Diffusion

提示Molecules spread from high to low.

为什么Food molecules diffuse through the thin wall of a villus. The blood carries them away, which keeps the concentration low.

Carbon dioxide

提示It is a waste gas from respiration.

为什么The blood in the lung capillaries is high in carbon dioxide, so it diffuses into the alveoli.

So gases only have a short distance to diffuse

提示Think about how far oxygen has to travel to reach the blood.

为什么A thin wall means a quick diffusion of oxygen into the blood and carbon dioxide out of it.

They make it by photosynthesis

提示Plants do not eat.

为什么Plants make glucose from carbon dioxide and water using light, then respire it to release energy.

Your muscles need more oxygen for respiration, and more carbon dioxide must be removed

提示Think about what working tissues use up and what they give off.

为什么More respiration in the muscles uses oxygen faster and makes more carbon dioxide.

Arteries

提示They have thick, muscular walls.

为什么Arteries carry blood at high pressure away from the heart. Veins return it.

The ribs move down and in, and the diaphragm relaxes and moves up

提示The opposite of breathing in.

为什么The chest volume goes down and the pressure rises, so air is pushed out.

Respiration

提示One happens in the lungs and one in the cells.

为什么Breathing moves air into and out of the lungs. Respiration happens in cells and releases energy from glucose.