Chapter 6 · Control and Coordination

NCERT Class 10 Science Chapter 6 Intext Questions (Page 111)

All 4 questions of NCERT Class 10 Science Chapter 6 Intext Questions (Page 111) — Control and Coordination — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   How ​does ​chemical ​coordination ​take place in animals?
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   Endocrine glands secrete hormones into the blood, which carries them to target organs; feedback regulates the amount secreted.

   Chemical coordination in animals is carried out by hormones, which make up the endocrine system — a second means of control and coordination alongside the nervous system, needed because electrical impulses reach only those cells that are joined by nervous tissue. A stimulus or a change in the body causes an endocrine gland, which is ductless, to secrete its hormone directly into the blood. The blood carries the hormone to all parts of the body, so it can reach every cell whatever the nerve connections. Even so, it acts only on its target organs — the specific tissues whose cells carry the special molecules that recognise it — and it is effective in very small amounts, producing changes that are slow to begin but widespread and long lasting. The timing and the amount of hormone released are regulated by feedback mechanisms, so that hormones are secreted in precise quantities: when the sugar level in the blood rises, the cells of the pancreas detect it and produce more insulin, and as the blood sugar falls, insulin secretion is reduced. For example, in a frightening situation adrenaline is secreted by the adrenal glands into the blood; acting on its target organs, it makes the heart beat faster, diverts blood from the digestive system and the skin to the skeletal muscles, and increases the breathing rate, so that the body is ready to fight or to run away.

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2. Q2
   Why ​is the use of ​iodised ​salt ​advisable?
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   Iodine is needed for thyroxin; its lack causes goitre, and iodised salt supplies it cheaply to everyone.

   Iodine is necessary for the thyroid gland to make the hormone thyroxin, and thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. If iodine is deficient in the diet, the gland cannot make enough thyroxin: metabolism and growth are poorly regulated, and there is a possibility of suffering from goitre, one symptom of which is a swollen neck, since the thyroid gland itself lies in the neck and enlarges. In children a continued shortage also holds back physical and mental development. Ordinary food and plain salt supply very little iodine, and in many places the soil and water contain almost none, whereas salt is eaten daily by everybody in small and fairly steady amounts. Adding a small measured quantity of an iodine compound to common salt is therefore a cheap and reliable way of supplying the daily requirement of iodine to the whole population, and this is why the use of iodised salt is advisable.

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3. Q3
   How ​does our ​body ​respond ​when ​adrenaline is secreted into ​the blood?
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   Adrenaline makes the heart beat faster, diverts blood to the skeletal muscles and increases breathing, preparing the body to fight or run away.

   Adrenaline is secreted by the adrenal glands directly into the blood, which carries it to different parts of the body, and it acts on its target organs. The heart beats faster, so that more oxygen is supplied to the muscles. The blood going to the digestive system and to the skin is reduced, because the muscles around the small arteries in these organs contract, and this diverts the blood to the skeletal muscles. The breathing rate also increases, because of stronger contractions of the diaphragm and the rib muscles, so that more oxygen is taken in. In addition the pupils of the eyes widen and stored glycogen is broken down to glucose, giving the muscles fuel as well as oxygen. All these responses together enable the body to be ready to deal with the situation, that is, to fight or to run away.

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4. Q4
   Why are some ​patients ​of ​diabetes treated ​by ​giving injections of ​insulin?
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   Their pancreas makes too little insulin, so injections replace it; insulin is a protein, so it is not given by mouth.

   Insulin is a hormone produced by the pancreas which helps in regulating the blood sugar level; normally, when the sugar level in the blood rises, the cells of the pancreas detect it and secrete more insulin, and secretion falls again as the level drops. In these patients the pancreas does not secrete insulin in proper amounts, so the sugar level in the blood rises and stays high, which causes many harmful effects; this condition is diabetes. Insulin is therefore given from outside to make up for what the pancreas fails to produce, and it brings the raised blood sugar down and keeps it within the normal range. It has to be given as an injection and not by mouth because insulin is a protein: swallowed, it would be broken down into amino acids by the digestive enzymes of the alimentary canal before it could act, whereas injected it reaches the blood unchanged. Since the injections only replace the missing hormone and do not repair the pancreas, they have to be continued.

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