Additional questions on Homeostasis
Monacia Williams, Contributor

Last week's lesson ended with some short-answer questions on homeostasis. Did you attempt to answer them? I hope you did! If you did, now you can compare your answers with my answers. Give yourself a pat on the back for each correct answer! Congratulations are in order for you!

Answers

1. a. How does metabolism change during exercise? The answer is, " it increases."

How does this influence energy release? Energy release also increases due to the increase in the rate of respiration. Respiration is a metabolic activity which provides the body with energy.

b. The body attempts to lose more energy during exercise. Exercise requires energy and this energy is produced by respiration. One kind of energy which is produced during respiration is heat energy and this heat energy can cause the body temperature to increase. The body cannot retain this heat energy and hence must lose it.

c. How do we approach this question? What does an increase in body temperature bring about? It brings about sweating which in turn brings about a change (lowering) in the body temperature which then causes the sweating to stop. Sounds confusing, doesn't it? But this is how negative feedback mechanism works. In negative feedback mechanisms a regulatory method is switched off by the change which it brings about.

d. During rest, excess sugar is converted to glycogen and stored in the liver and/or the muscles.

e. This question requires you to use the information given by the graph. The graph shows three peaks in the blood glucose level accompanied by corresponding peaks in the level of the hormone. This suggests that the hormone does not remain in the gut after the sugar is converted but is secreted after each meal. This means that a single dose of the hormone would not be able to adequately control the blood sugar level since one dose would only be sufficient for one meal and the level of glucose will rise after each meal.

(ii)

We saw in a. and b. that exercise increases respiration. We also know that respiration uses glucose as a raw material. This means that during exercise the glucose level is going to decrease due to respiration so there would be no storage of glucose, hence the body would not need to secrete insulin - the hormone which is involved in storage of glucose. The answer is "the hormone level will decrease".

How well did you do? If you did not do so well, I suggest that you spend some time reading over until you thoroughly understand the topic.

Let us try one more question on the topic. This time we will try an essay type question.

(a) Explain how, in a healthy person, the body temperature and (ii) the blood sugar, are returned to normal after they have risen above normal levels. 9 marks

(b) Account for the effect of exercise on

(i) the breathing rate, and

(ii) the pulse rate 6 marks

One thing that I have noticed over the years is that many students have difficulty interpreting questions and because of this they lose valuable marks. So, spend a few minutes reading and rereading the question until you are sure what the focus of the question is.

What is this question about? What are the indicator word/words? "Return to normal after they have risen above normal". This means that the focus is on homeostasis, since this is how the body returns processes that have shifted from their set points back to normal.

Answer

(i) The body controls and maintains its temperature and its blood sugar levels by homeostasis. The control of these involves negative feedback mechanisms.

The blood is responsible for transporting heat throughout the body; this means that any increase in heat production will be first detected in the blood. As the blood passes through the hypothalamus of the brain the increase in temperature is detected. The hypothalamus feeds back this information to sensory receptors in the body to bring about the following changes:

• sweat glands in the skin increase the production of sweat. The sweat evaporates and cools down the skin.
• Blood vessels near to the surface of the skin dilate causing more blood with heat to be brought to the surface. Heat is then lost from the blood by radiation.

These two features combine to reduce the body temperature and bring it back to 37oC which is the set point.

(ii) The control of the blood sugar involves the secretion of the hormone insulin. After digestion and assimilation take place the amount of glucose in the blood rises. This triggers the cells of the Islet of Langerhans to produce insulin. Insulin promotes the conversion of glucose to glycogen by the liver. This causes the glucose level to be returned to normal.

Answers similar to the ones above will enable you to achieve full marks. Next week we will look at the answers for the second part of the question after which we will begin looking at Nervous coordination. See you then, have a good week!

Monacia Williams teaches at Glenmuir High School. Send questions and comments to kerry-ann.hepburn@gleanerjm.com