Topic 15 (Hormones)

Question 1

What are hormones?

Answer 1

A chemical substance produced by a gland, transported in the blood (plasma), and alters the activity of one or more
specific target organs.

Question 2

Where are hormones produced?

Answer 2

Hormones are produced by ductless glands or endocrine glands, and are secreted directly into the bloodstream.

Question 3

What are some main endocrine glands and hormones in the body?

Answer 3

*Pituitary gland
*Ovaries (in women)
*Testes (in men)
*Hypothalamus
*Adrenal gland (medulla)
*Kidney
*Pancreas

Question 4

What are the effects of adrenaline?

Answer 4

*It increases the rate of breathing.
*It increases the rate of heartbeat.
*It causes the pupil of the eye to dilate.
*It increases the rate of blood clotting.
*It causes the arterioles to the skin and intestines to constrict.
*It increases the metabolic rate (i.e. the rate
of aerobic respiration) in the muscles.
*It stimulates the liver and muscles to
convert glycogen to glucose.

Question 5

What is the importance of adrenaline?

Answer 5

*More oxygen can be taken into the body for aerobic
respiration.
*Oxygen and glucose can be transported more quickly to
the muscles.
*Vision is enhanced to help the person see the danger
more clearly.
*If the skin is cut, the blood will clot faster to prevent
excessive loss of blood.
*The person looks pale and digestive activity
decreases, but more blood is sent to the muscles.
*More energy will be released in the muscles.
*More glucose will be available for muscle contraction.

Question 6

What are the effects of insulin and glucagon?

Answer 6

*Insulin decreases blood glucose concentration.
*Glucagon increases blood glucose concentration.

Question 7

What are the differences between the endocrine and nervous controls?

Answer 7

ENDOCRINE CONTROL:-
Involves hormones (chemical
substances).
Hormones are transported by the blood.
Usually slow.
May be short-lived (e.g. adrenaline) or
long-lived (e.g. growth hormone).
Always involuntary.
May affect more than one target organ.

NERVOUS CONTROL:-
Involves nerve impulses
Impulses are transmitted by neurons.
Usually quick.
May be short-lived (e.g. adrenaline) or long-lived (e.g. growth hormone).
Short-lived.
Always involuntary.
Usually localized.

Question 8

What is homeostasis?

Answer 8

*Homeostasis is the maintenance of a constant internal environment.
*The internal environment refers to conditions within the body of the organism. The external environment is
the environment in which an organism lives.

Question 9

Why does the body temperature have to be kept constant?

Answer 9

Enzymes in the body can only work within a certain range of temperatures.

Question 10

Why must tissue fluid be kept at a constant pH and water potential?

Answer 10

*A drastic change in the pH of tissue fluid will affect enzyme reactions in cells.
*Drastic changes in the water potential will also affect the cells.

Question 11

Why does the blood glucose concentration have to be kept constant?

Answer 11

Glucose is needed for cellular respiration, thus a drastic change in glucose concentration can affect cellular activity.

Question 12

How is the blood glucose concentration regulated when it is above normal levels?

Answer 12

1) Stimulus - blood concentration rises above normal.
2) Receptors (also the control center) - Receptors in the pancreas are stimulated.
3) The Islets of Langerhans secrete insulin into the bloodstream.
4) Blood transports insulin to the liver and muscles.
5) Glucose is absorbed more quickly by the cells.
6) Insulin causes the liver and muscles to convert excess glucose to glycogen. Glycogen is stored in the liver and muscles.
7) Blood glucose concentration decreases. This gives a feedback to the receptor to reduce insulin production. And, then blood glucose concentration goes back to normal.

Question 13

How is the blood glucose concentration regulated when it is below normal levels?

Answer 13

1) Stimulus - blood concentration falls below normal.
2) Receptors (also the control center) - Receptors in the pancreas are stimulated.
3) The Islets of Langerhans secrete glucagon into the bloodstream.
4) Blood transports the glucagon to the liver and muscles.
5) Glucagon causes the conversion of stored glycogen back to glucose.
6) From the liver, glucose enters the bloodstream.
7) Blood glucose concentration increases. This gives a feedback to the receptor to reduce glucagon production. And, then blood glucose concentration goes back to normal.

Question 14

What happens when the blood lacks insulin?

Answer 14

If there is no insulin in the bloodstream, glucose cannot be stored as glycogen. This gives rise to a condition
known as diabetes mellitus.
*Diabetes mellitus is also called type 1 diabetes

Question 15

How can type 1 diabetes be treated?

Answer 15

Insulin injections. It is also important to maintain a good diet and to do regular exercise.

Question 16

What are the structures involved in regulating body temperature?

Answer 16

*Hairs
*Sweat glands
*Sensory receptors (thermoreceptors)
*Subcutaneous fat
*Blood vessels

Question 17

How does the body lose heat? (more heat loss)

Answer 17

1) The skin arteriole dilates, increasing blood flow to skin.
2) The shunt vessel constricts.
3) More blood flows to the skin surface. This leads to greater heat loss.

Question 18

How does the body lose heat? (less heat loss)

Answer 18

1) The skin arteriole constricts, decreasing blood flow to skin.
2) The shunt vessel dilates.
3) Less blood flows to the skin surface. This leads to less heat loss.

Question 19

What is the function of the hypothalamus?

Answer 19

The hypothalamus in the brain monitors and regulates the body temperature.

Question 20

What happens when the body temperature begins to rise?

Answer 20

1) Body temperature rises above normal.
2) Thermoreceptors in the skin and the hypothalamus are stimulated.
3) The arterioles of the skin dilate and the shunt vessels constrict. This dilation of the arterioles is called vasodilation. It allows more blood to flow through blood capillaries in the skin. More heat will be lost through the skin by radiation, convection and conduction.
4) Sweat glands become more active. More sweat is produced. As more water in the sweat evaporates from the skin surface, more latent heat of vaporization is lost from the body. This is an efficient mean of losing heat.
5) The metabolic rate is decreased. This reduces the amount of heat released within the body.
6) Body temperature decreases.

Question 21

What happens when the body temperature begins to fall?

Answer 21

1) Body temperature falls below normal.
2) Thermoreceptors in the skin and the hypothalamus are stimulated.
3) The arterioles of the skin constrict and the shunt vessels dilate. This constriction of the arterioles is called vasoconstriction. It allows less blood to flow through blood capillaries in the skin. This reduces the heat lost by radiation, convection and conduction.
4) Sweat glands become less active. Less sweat is produced. As less water in the sweat evaporates from the skin surface, less latent heat of vaporization is lost from the body.
5) The metabolic rate is increased. This increases the amount of heat released within the body.
6) When the above responses are not sufficient to prevent a drop in body temperature, shivering occurs. This is a spasmodic contraction of the skeletal muscles. It increases the amount of heat released.
7) Body temperature increases.

Question 22

What is tropism?

Answer 22

The growth and movement of plants are affected by external stimuli such as light, gravity, water and chemical
substances, as well as foreign body.
This growth movement is called a tropic movement or tropism.

Question 23

What is phototropism?

Answer 23

Phototropism is a response which a plant part grows towards or away from a unidirectional light source.

Question 24

What is gravitropism?

Answer 24

Gravitropism is a response in which a plant part grows towards or away from gravity.

Question 25

What is a clinostat?

Answer 25

We can use an instrument called a clinostat to study tropisms in plants. A clinostat can be used to negate the effect of a stimulus.

Question 26

How do tropisms work?

Answer 26

*Tropisms in plants involve
receptors and effectors.
*A growth promoting substance
called auxin plays an important
role in tropisms.

Question 27

What is the role of auxin in plant tropisms? (phototropism)

Answer 27

When light shines on the shoot on all sides:
1) The tip of the shoot (receptor) is sensitive to the stimulus of light.
2) The tip produces auxin.
3) Auxin diffuses down from the tip to the region of cell elongation.
4) Auxin is evenly distributed to all sides of the shoot.
5) The shoot grows vertically upwards.

Question 28

What is the role of auxin in plant tropisms? (phototropism)

Answer 28

When the light shines on the shoot on one side:
1) The tip of the shoot is stimulated by unidirectional light and produces auxin.
2) Auxin diffuses down from the tip and accumulates in the shaded side of the shoot.
3) Cells on the shaded side elongate faster than cells on the side with light, hence the shoot bends towards the light.

Question 29

What is the role of auxin in plant tropisms? (gravitropism)

Answer 29

When the shoot is placed horizontally:
1) The tip of the shoot is stimulated by stimulus of gravity and produces auxin.
2) Auxin accumulates on the lower side of the shoot.
3) Cells on the lower side elongate faster than cells on the upper side, hence the shoot bends upwards.

Question 30

What is the role of auxin in plant tropisms? (gravitropism)

Answer 30

When the root is placed horizontally:
1) The tip of the shoot is stimulated and produces auxin.
2) Auxin accumulates on the lower side of the root, inhibiting cell elongation here.
3) Cells on the upper side elongate faster than cells on the lower side, hence the root bends downwards.

Question 31

What is the importance of tropisms?

Answer 31

1) Positive phototropism in shoots causes shoots to grow towards sunlight. This enables leaves to absorb the maximum amount of sunlight for photosynthesis.
2) Negative gravitropism in shoots causes the shoots to grow away from the earth into the atmosphere. This enables them to obtain sunlight for photosynthesis.
3) Positive gravitropism in roots causes the roots to grow downwards into the earth. This enables them to anchor the plant firmly in the soil. It is from the soil that roots obtain water and mineral ions.