Exam practice

The process by which plants make their food is called photosynthesis.

Leaves are green because they contain chlorophyll.

The group of organs that helps to digest food is called the digestive system. (“Digestive gland” is not needed.)

The carbohydrate in food gives us energy.

The jobs that a living body keeps doing inside itself to stay alive are called life processes. Examples: nutrition, respiration and excretion. They go on in both plants and animals.

Four things are needed:

1. chlorophyll, in the green leaves, to catch sunlight;
2. sunlight, which gives the energy;
3. carbon dioxide, taken from the air through the stomata;
4. water, taken from the soil by the roots.

1. Pick a green leaf from a plant that has been in sunlight.
2. Boil it in water for about five minutes, to kill it and make it soft.
3. Turn off the flame. Put the leaf in warm alcohol (90 % ethanol) in a test tube standing in the hot water, to remove its chlorophyll. The leaf turns pale.
4. Wash the leaf in warm water to soften it.
5. Spread it on a white tile and put a few drops of iodine solution on it.
6. The leaf turns blue-black, which shows that it has starch.

No. Photosynthesis needs light: chlorophyll catches the energy of sunlight to make food. At night there is no sunlight, so a plant can’t make food. (A very bright lamp would let it carry on a little.) At night the plant only respires, as it does all the time: it takes in oxygen and gives out carbon dioxide, using up some of the food it made in the day.

The group of organs that breaks down (digests) the food we eat into simple substances that the body can absorb is the digestive system. It has two parts: the alimentary canal (mouth, food pipe, stomach, small intestine, large intestine, anus) and the digestive glands (salivary glands, gastric glands, liver, pancreas, intestinal glands).

Digestive juices contain enzymes, which break food down into simple substances the body can absorb:

• Saliva (salivary glands): its amylase starts to break starch into sugar; it also wets the food so it is easy to swallow.
• Gastric juice (stomach): its hydrochloric acid kills germs and makes the food acidic; its pepsin starts to digest protein.
• Bile (made by the liver, stored in the gall bladder): breaks fat into tiny droplets.
• Pancreatic juice (pancreas): trypsin digests protein, amylase digests starch, and lipase digests fat.
• Intestinal juice (small intestine): finishes the digestion.

In the end, food becomes glucose, amino acids and fatty acids, which are absorbed into the blood.

Draw the outline of a body and, inside it, label: mouth, salivary glands, food pipe (esophagus), liver, gall bladder, stomach, pancreas, small intestine, large intestine and anus. Show the stomach on the left side of the body (your right as you look at it), the liver on the other side, the small intestine coiled in the middle, and the large intestine framing it.

Stomach. A J-shaped bag of muscle. It stores food for a few hours and churns it. Its gastric juice has hydrochloric acid, which kills germs, and pepsin, which starts to digest protein.

Small intestine. A long, coiled tube (about 6 m in an adult). Bile, pancreatic juice and intestinal juice finish digesting food here, and its villi absorb the digested food into the blood.

Leaf. The green part of a plant where photosynthesis happens: its chlorophyll catches sunlight, and it makes glucose and oxygen from carbon dioxide (taken in through its stomata) and water. It also lets water vapor out.