Question

Answer the following questions:

1. Explain the following terms:

(a) Hydrotropic movement

(b) Chemical control in animals

2. Differentiate between:

Voluntary and Involuntary movements

3. Write a short note on:

(a) Reflex action

(b) Co-ordination in plants

Answer 1

1.

(a) Hydrotropic movement: Hydro means water and tropic means movement so the response of plants towards water is termed as hydrotropic movement. For example, roots of a plant are positively hydrotropic i.e., they always tend to grow towards the moist soils for the absorption of water.

(b) Chemical control in animals: The control and coordination that is brought about by hormones constitute the chemical control in animals. Hormones are the chemical substances which are directly secreted into the blood stream by the ductless glands called as the endocrine glands. Hormonal actions are quite slower but long lasting. Together with the nervous system they control various activities of the animal's body.

2.

Voluntary movements	Involuntary movements
Voluntary movements are controlled by fore brain or cerebrum.	Involuntary movements are controlled by medulla oblongata and spinal cord.
Voluntary actions are under the individual's controls, initiated by himself and by his own consciousness.	Involuntary actions are not under the individual's control.
Voluntary movements require thinking.	Involuntary movements do not require thinking.
Voluntary movements are slow.	Involuntary movements are fast.
Example: walking, speaking, clapping	Example: heartbeat, movement of food in the alimentary canal, blinking of eyes

3.

(a) Reflex action:

The automatic action or response provoked by a stimulus is known as a reflex action. The reflex actions, however, show sudden responses and do not involve any thinking.

When we accidentally touch a hot object, we withdraw our hands immediately without thinking. If we do not do this, our hands will burn. The sensory nerves detect the heat. They are connected to the nerves, which move the muscles of the hand. Such a connection of detecting the signal from the nerves (input), and responding to it immediately (output) is called a reflex arc.

A reflex arc makes instant and automatic responses possible. It connects the input nerve and output nerve, and meets in a bundle in the spinal chord. In fact, nerves from all over the body meet in a bundle within the spinal cord, on their way to the brain. Therefore, the information input reaches the brain.

(b) Co-ordination in plants: The co-ordination in plants, unlike animals, is not controlled by the nervous system. Plants show response to external stimuli by movements. The movement shown by the plants can either be growth−dependent movements or growth−independent movements. The growth and certain other biological activities of plants are controlled by plant hormones such as auxins, gibberellins, cytokinins and ethylene.