(a) (i) List three points of difference between nervous and hormonal mechanisms for control and coordination in animals.

(ii) How are auxins related with the bending of plant shoot towards unidirectional light? Explain.

OR

(b) (i) Name the disorder which a person is likely to suffer from due to the following:

(I) Over-secretion of growth hormone

(II) Deficiency of oestrogen in females

(III) Less secretion of thyroxine

Also name the gland that secretes each of the hormones mentioned above.

(ii) How is the timing and amount of hormone released regulated? Explain with the help of an example.

(a) (i) Three points of difference between nervous and hormonal mechanisms for control and coordination in animals are:

1. Nervous system controls and coordinates the functions of the body by electrical and chemical means whereas the endocrine system uses only chemical means.
2. Nervous system has a rapid action whereas endocrine system has a slow action.
3. Nervous system is a quick and short-term method whereas endocrine system is a slow and long-term method.

(ii) Auxins are plant hormones that promote cell growth and cell division. When a plant shoot is exposed to unidirectional light, auxins accumulate on the side of the shoot that is away from the light source. This causes the cells on that side to grow more, resulting in the bending of the shoot towards the light source.

OR

(b) (i) (I) Over-secretion of growth hormone can lead to gigantism or acromegaly. The pituitary gland secretes growth hormone.

(II) Deficiency of oestrogen in females can lead to menstrual irregularities and infertility. The ovaries secrete oestrogen.

(III) Less secretion of thyroxine can lead to hypothyroidism. The thyroid gland secretes thyroxine.

(ii) The timing and amount of hormone released is regulated by feedback mechanisms. For example, when the blood sugar level rises after a meal, the pancreas releases insulin. Insulin stimulates the cells to take up glucose from the blood, which reduces the blood sugar level. When the blood sugar level falls, the pancreas reduces the release of insulin. This is an example of negative feedback mechanism.