Health and disease, Year 8: microbes and lifestyle

A unicellular organism

HintIt starts with the Latin for 'one'.

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

Yeast

HintBakers buy it fresh or dried.

The whyIt respires using the sugar in the dough and gives off carbon dioxide gas, and the bubbles make the dough swell.

Bacteria

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

The whyMost 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

HintIts membrane can flow and change shape.

The whyThe 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

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

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

Vitamin D

HintSkin makes it in sunlight.

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

Iron

HintIt is needed to make the red pigment in blood.

The whyThis 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

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

The whyIt 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)

HintThink about why drinking and driving is so dangerous.

The whyA 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

HintThe body makes up the shortfall out of its stores.

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