The Regulators of Life
Q1. Fill in the blanks:
1. The loss of water from the plants is known as _____________. (Transpiration)
2. Nervous system is absent in _______ and ____________. (plants, unicellular organism)
3. Response to the stimulus of touch is called __________ whereas response to the stimulus of chemicals is called as _____________. (eismonastic movement, chemotropism)
4. Brain is the main ____________ centre of the body. (coordinating)
Q2. Name the following:-
1. Growth of plant in response to external factors.
2. Maintenance of steady state by different system in an organism.
3. Cells that assist the neurons in their function.
4. The small gap between the consecutive neurons.
5. Part of the brain that co – ordinates the voluntary movements.
6. Name the sense organs.
Ans. Eyes, ears, nose, tongue and skin are the five sense organs.
Q3. Give scientific reasons.
1. Roots of plants grow away from light.
i. The root system of plants always grows downwards in response to the stimulus of gravity and water.
ii. This makes sure that the roots will find soil and water.
iii. Hence, the roots of plants grow away from light.
2. Hormones secreted by the endocrine glands are present everywhere in the body.
i. Endocrine glands do not have ducts to store or transport their secretions called hormones.
ii. The hormones are directly released into the blood stream and reach concerned body parts through blood.
iii. Hence, hormones secreted by the endocrine glands are present everywhere in the body.
3. Insulin plays an important role in controlling the sugar level of blood.
i. When the sugar level of the blood rises, it is detected by the cells of the pancreas which respond to the situation by producing more insulin.
ii. As the sugar level of the blood falls, the secretion of insulin is reduced.
iii. Thus, insulin plays an important role in controlling the sugar level of blood.
Q4. Answer the following questions:
1. Explain the following terms:
a. Hydrotropic movement: - The movement or growth of the root system of a plant in response to the stimulus of water is called hydrotropic movement.
b. Chemical control in animals: chemical control in animals is brought about by chemical substances called hormones. These hormones are secreted by the endocrine glands.
2. Differentiate between:
Voluntary and Involuntary movements
i. Voluntary movements are controlled by cerebrum and cerebellum.
ii. We have thinking control over these movements.
i. Involuntary movements are controlled by medulla oblongata.
ii. We do not have thinking control over these movements.
3. Write a short note on
a. Reflex action
i. The sudden action in response to some happenings in the environment is called as reflex action.
ii. It is an involuntary action which we perform automatically.
iii. The path way taken by nerve impulses in a reflex action is called reflex arcs. Reflex arcs allow rapid response.
iv. A nerve from all over the body meet in a bundle in such a connection is commonly called as the spinal cord, before impulses are sent to the brain.
v. Hence, reflex arcs are formed in the spinal cord, although the messages reach the brain.
vi. Pulling away our hand on toughing a hot object, narrowing of the eyes in sunlight, watering of the mouth on smelling something delicious etc. are examples of reflex action.
b. Co – ordination in plants.
i. Plants do not have a nervous system or muscular system and sense organs like eyes, ears, nose, etc.
ii. The plants can still sense the presence of stimuli like touch, light, gravity, water, etc., and respond to them by the action of hormones in them.
iii. So, plants co – ordinate their behaviors against environmental changes by using hormones.
iv. Hormones bring about various movement in response to stimulus.
v. It is the result of such co – ordination that the lotus opens in the morning and the tube rose at night; stem grow towards light and the root towards gravity; the leaflets of the mimosa plant close on being touched and the explosive fruit of balsam burst open to scatter the seeds.
Answers in one sentence
1. Name two plants in which tendrils are present.
Ans. Grapevine and pea plant.
2. Give one example of chemotropism.
Ans. The growth of pollen tube towards the ovule is an example of chemotropism.
3. Which plant hormone is responsible for wilting of leaves?
Ans. Abscissic acid is the hormone responsible for wilting of leaves.
4. Which animals do not have nervous system?
Ans. Unicellular animals like Amoeba do not have a nervous system.
5. What kind of nervous system is present in Hydra?
Ans. In Hydra, the nervous system is of primitive type of consisting of a nerve net.
6. What is a neuron?
Ans. Neuron or nerve cell is a specialized cell capable of creating and transmitting electro – chemical impulses.
7. What is the function of hormones in arthropods?
Ans. Hormones induce colour changes and also regulate development in arthropods.
8. Why is thyroid secretion important in frogs?
Ans. In frogs the metamorphosis, i.e. development of a frog from tadpole is stimulated by thyroid secretion.
9. What is Venus fly trap?
Ans. Venus fly trap is an insectivorous plant which looks and smells like a flower to insects.
10. What is the function of dendrites?Ans. Dendrites pick up all the information from the environment and transmit them to the cell body.