Life Processes in Animals: questions with answers

A ruminant partially chews the grass and swallows it into the stomach, where partial digestion takes place. The partially digested food is then brought back to the mouth for gradual, thorough chewing, and the thoroughly chewed food passes down the canal again. A cow spends about 8 hours a day on that chewing.

Birds have no teeth. Food is ground in the gizzard, a muscular chamber. Its walls contract and relax against the food. Small stones inside the gizzard help with this grinding.

During rumination, a buffalo chews partly digested food again. It is not chewing fresh grass saved in its mouth or finishing a mouthful before swallowing it for the first time.

The walls of the alimentary canal gently contract and relax in a wave-like motion. This wave pushes the food forward, and it happens all along the canal, not in the food pipe alone.

Saliva breaks down starch into sugar, a simpler substance. It does not merely release sugar already present in the food. Digestion includes breaking down complex food substances into simpler substances; making smaller pieces alone does not complete digestion.

Iodine gives a blue-black colour when it reacts with starch. So a tube that turns blue-black still holds starch. A tube that stays orange-brown, or turns only faintly blue-black, holds starch that saliva has already broken down into sugar.

The finger-like projections increase the surface area for absorption in the small intestine. Digested nutrients pass through this lining into the blood. Damage to these projections reduces nutrient absorption. Digestive juices break down food into simpler substances.

The alimentary canal is the passage the food itself travels: mouth, food pipe, stomach, small intestine, large intestine, anus. The liver and the pancreas are not on it. No food passes through either of them. Each one instead pours its juice into the small intestine, where the juice acts on the food. The liver makes bile. The pancreas makes pancreatic juice.

In the model the two balloons stand for the lungs, the rubber sheet stands for the diaphragm, and the bottle stands for the chest. That is why the model works by moving the sheet: in the body it is the diaphragm that moves and the lungs that follow.

The exchange of gases does not happen in the windpipe. The windpipe carries the air down and forms the two branches that enter the lungs. Those branches divide into smaller and finer branches. The finest branches end in the small balloon-like sacs called alveoli. The walls of these sacs are thin, and fine blood vessels lie all around them. Oxygen and carbon dioxide are exchanged there.

Air enters the nostrils and passes into the nasal passages. From there it goes down the windpipe. The windpipe divides into two branches, one for each lung. Inside the lungs these divide into finer and finer branches. The finest branches end in the alveoli, the small balloon-like sacs. Nothing along this path is skipped, and the air does not stop at the windpipe.

Many animals breathe through their lungs: birds, elephants, lions, cows, goats, lizards and snakes. But the structure of those lungs is quite different from one another. 'Has lungs' is one fact; 'has the same lungs' is another, and it is not true.

Both animals really do breathe through lungs, and the chapter names them together. But it adds at once that the structure of the lungs of these animals is quite different. Two animals can both breathe through lungs and still have lungs that are built in quite different ways.

The complete word equation is: Glucose + Oxygen gives Carbon dioxide + Water + Energy. Oxygen helps break down glucose, releasing energy. The missing terms are oxygen and energy, in that order.

The air around us is a mixture of gases. That air is rich in oxygen, so oxygen makes up a large part of it, but it is not the whole of it. The same air has only a very small amount of carbon dioxide in it. So we breathe in air rich in oxygen, not oxygen by itself. It is the air we breathe out that has more carbon dioxide and less oxygen.