Health and disease, Year 8: microbes and lifestyle

A unicellular organism

提示It starts with the Latin for 'one'.

为什么Bacteria, yeast and amoebas are examples. That single cell has to feed, respire, get rid of waste and reproduce by itself.

Yeast

提示Bakers buy it fresh or dried.

为什么It respires using the sugar in the dough and gives off carbon dioxide gas, and the bubbles make the dough swell.

Bacteria

提示They are far smaller than an animal cell and have no nucleus.

为什么Most bacteria are harmless and many are useful, but a few kinds make people ill when they multiply in food or in the body.

It surrounds the food and engulfs it

提示Its membrane can flow and change shape.

为什么The amoeba pushes out parts of itself around a food particle until the particle is enclosed inside, where it is digested.

By diffusion across its cell membrane

提示Every part of it is very close to the water around it, so no transport system is needed.

为什么Because the organism is so tiny, oxygen dissolved in the water spreads into it quickly enough to reach every part.

Vitamin D

提示Skin makes it in sunlight.

为什么The body needs this vitamin to absorb calcium from food. Without it, growing bones do not harden properly.

Iron

提示It is needed to make the red pigment in blood.

为什么This mineral is part of haemoglobin, which carries oxygen in red blood cells. With too little, less oxygen reaches the muscles, so the person tires easily.

Tar

提示It is sticky and dark brown, and stains a smoker's fingers and teeth.

为什么It collects in the air passages and the tiny air sacs. It damages cells and makes it harder for oxygen to pass into the blood.

It gets longer (they react more slowly)

提示Think about why drinking and driving is so dangerous.

为什么A slower nervous system means a longer delay between seeing a hazard and responding to it, which is why even a small amount affects driving.

It falls

提示The body makes up the shortfall out of its stores.

为什么When food supplies too little energy, the body uses its stored fat to make up the difference, so mass goes down.