Health and disease, Year 8: more practice

Oranges

提示Look for the food rich in vitamin C.

为什么Citrus fruits are rich in vitamin C. Without it the body cannot make and repair the tissue that holds the gums and skin together.

The skin makes vitamin D when it is exposed to sunlight

提示Your body can manufacture this nutrient itself, not just eat it.

为什么Vitamin D helps the body absorb calcium for bones. Without it the bones can stay soft and bend.

Iron is needed for haemoglobin, so the blood carries less oxygen

提示Think about what red cells carry around the body.

为什么Haemoglobin in red blood cells carries oxygen. Without enough iron the body cannot make it, so less oxygen reaches the cells.

A disease caused by a lack of a nutrient in the diet

提示It is about something missing.

为什么Scurvy, rickets and anaemia are examples. They are cured by eating enough of the missing nutrient.

Carbon monoxide

提示It also comes out of car exhausts.

为什么Carbon monoxide joins on to haemoglobin instead of oxygen. The heart must work harder to supply the body.

It slows down the nervous system and brain activity

提示Think of the opposite of speeding up.

为什么Messages travel more slowly, so judgement, balance and reactions are affected.

The single cell carries out all the life processes itself

提示Think about how many cells it has.

为什么A bacterium or amoeba feeds, respires, excretes, grows and reproduces inside one cell.

By splitting in two (binary fission)

提示The cell makes a copy of itself.

为什么A bacterium copies its genetic material and divides in two. In good conditions this can happen every 20 minutes or so.

Carbon dioxide

提示It forms bubbles in the dough.

为什么Yeast respires the sugars in dough and releases carbon dioxide. The gas bubbles stretch the dough and it rises.

The athlete uses more energy

提示Think about how much each person burns.

为什么Energy needs depend on how active you are. Taking in more than you use is stored as fat, and less than you use makes you lose mass.