Nutrition: Quick Revision

A brief note on Nutrition. Read it before a test. Try each question at the end before you open its answer.

Life processes

• Nutrition, respiration, transport and excretion keep a living thing alive. They need energy all the time, even in sleep.
• Autotrophs make food from carbon dioxide and water. Heterotrophs take food made by others.

Photosynthesis

• Carbon dioxide and water, with sunlight and chlorophyll, give glucose and oxygen. Glucose is stored as starch.
• The balanced equation:

• Three events: light is absorbed; light energy becomes chemical energy and water is split; carbon dioxide is reduced to carbohydrate.
• The oxygen given out comes from water.
• Iodine turns starch blue-black. Only the green parts of a leaf make starch.

Stomata

• Pores on the leaf, most of them on the lower surface. Gases pass in and out; water vapour is lost.
• Guard cells that fill with water swell and open the pore. When they lose water, the pore closes.

Food from others

• Amoeba: pseudopodia trap food in a food vacuole. Paramecium: cilia sweep food into one fixed groove.

Human digestion

• Peristalsis moves food along the canal. Villi absorb the digested food. The large intestine takes back water, and the waste leaves by egestion.

A worked example

What happens to a spoonful of ghee, which is almost all fat, from the moment it is eaten?

1. Mouth and stomach. Saliva has no enzyme for fat, and pepsin acts on proteins, so the fat passes on almost unchanged.
2. Small intestine. Bile breaks the fat into tiny drops. Lipase from the pancreas acts on them.
3. End products. Intestinal juice finishes the work: fatty acids and glycerol.
4. Absorption. The villi take them up and pass them on to the rest of the body.

Practice with new numbers

A program to try

The program lists the juices that act on each food in a meal of rice, dal and ghee.

Mistakes to avoid

• Photosynthesis at night. It needs light. At night a plant only respires.
• Bile as an enzyme. It has none. It makes the food alkaline and breaks fat into drops.
• Fungi eating their food. They digest it outside, then absorb it.
• Egestion and excretion. Egestion removes undigested food; excretion removes wastes made by cells.

Check yourself

1. Write the word equation of photosynthesis.

2. Name one saprophyte and one parasite.

3. Name the three juices that act in the small intestine.

4. What would happen to the stomach wall without mucus?

5. Why are most stomata on the lower surface of a leaf?