Lesson- Control and coordination

                                  Class- 10   

1.      What are plant hormones?

Ans- Plant hormones or phytohormones are chemical substances which are produced naturally in minute concentration in plants for regulating growth and other physiological processes. These chemicals also bring about control and coordination in various activities in plants. Important plant hormones are auxins, gibberellins, cytokinins, etc.

2.      How is the movement of leaves of a ‘Touch –me—not’ plant different from the movement of a shoot towards light?

Ans- The shoot of a plant responds to light by bending towards it. It is a tropic movement. It happens very slowly and this action involves growth. On the other hand, the leaves of sensitive plants respond to touch (Shock) by folding up and drooping. It is a nastic movement. This movement of leaves of sensitive plants does not involve growth. Here, plant cells changes shape by changing the amount of water in the (turgor changes).

Ans- Auxins is responsible for promoting growth in plants.

3.      How do auxins promote the growth of a tendril around a support?

Ans- Auxins are growth promoting hormones. The auxin moves from the side in contact with the support towards the side of the tendril away from the support. As a result, the side having more auxin growth faster than the side in contact with the support. Hence, the tendril coils around the support.

4.      Design an experiment to demonstrate hydrotropism.

Ans- We takes two glass troughs A and B and fills each one of them two- third with soil. In trough A we plant a tiny seedling. In trough B we plant a similar seedling and also place a small ‘clay plot ‘inside the soil. Water the soil in trough A daily and uniformly. Do not water the soil in trough B but put some water in the clay pot buried in the soil. Leave both the troughs for a few days.

Now, dig up the seedling carefully from both the troughs without damaging their roots. We will find that the root of seedling in trough A is straight. On the other hand, the root of seedling in trough B is found to be bent to the right side (towards the clay pot containing water). This can be explained as follows.

In trough A, the root of seedling gets water from both sides (because the soil is watered uniformly).but in trough B, the root gets water oozing out from the clay pot which is kept on the right side. So, the root of seedling in trough B grows and bends towards the source of water to the right side. This experiment show that the root of a plant grows towards water.

5.      What is the difference between a reflex action and walking?

Ans- Reflex action is a spontaneous, automatic response to a stimulus on a specific receptor. It occurs in a fraction of second and is mainly controlled by the spinal cord. Reflex action does not require will of the organisms.

On the other hand, walking is a voluntary action controlled by brain and occurs with the will of the organisms. It takes longer time to react.

6.      What happens at the synapse between two neurons?

Ans- The impulse receives by the dendrites of sensory neurons reaches the axon ending in the form of an electric impulse. At the synape, it causes release of a chemical neurotransmitter, acerylcholine(Ach)from synaptic vesicles in the synaptic cleft. The neurotransmitter passes through the postsynaptic membrane in the adjacent neuron and generates electric impulse. Thus, transmission of impulse is an electrochemical phenomenon.

7.      Which part of the brain helps maintain equilibrium of the body?

Ans- Cerebellum of the hindbrain.

8.      How do we detect the smell of an incense stick?

Ans-The smell of incense stick stimulates olfactory receptor cells present in the olfactory epithelium that lines the nasal chambers. The stimulus generates electric impulse in the sensory cells and from here into the nerve fibers of olfactory nerve. Thus, electric impulses from olfactory receptors are transmitted through olfactory nerve to the olfactory lobes of forebrain. Here these impulses are interpreted in the temporal lobe area of the cerebral hemisphere. 

9.       What is the role of the brain in reflex action?

Ans – In several reflex actions brain acts like a relay centre which transfers impulses from sensory to motor neurons. These are also called cerebral reflexes. For examples, closure of eyes when exposes to bright light and salivation at the sight or smell of tasty food. In spinal reflexes, brain may act as an information collecting center.

10.  How does chemical coordination take place in animals?

Ans- In animals, endocrine glands, when stimulated, release chemical substances called hormones. These are directly poured into the blood which circulates them to all the body tissue cells. Body tissue cells have specific molecules (receptors) to identify specific hormones either on their surfaces or inside their cytoplasm. Once the hormone combines with specific receptor present on target cells, it then transmits the information to bring about the effect.

11.  Why is the use of iodized salt advisable?

Ans- Iodine is essential for the synthesis of thyroxin hormone in the thyroid gland. The thyroxin, in turn, regulates carbohydrate, protein and fat metabolism in the body for growth. Deficiency of iodine results in goiter. Thus, use of iodized salt is advisable to prevent iodine deficiency in the body.

12.  How does our body respond when adrenaline is secreted into the blood?

Ans- Adrenaline is termed as emergency hormone. When a person faces stress or danger, it is secreted in large amount to prepare the body to face emergency situations. It increases the rate of heart beat and breathing, blood pressure, basal metabolic rate and sugar level in blood.

13.  Why are some patients of diabetics treated by giving injections of insulin?

Ans- In patients, suffering from diabetes, the blood sugar level is increased. Therefore, the patient excretes sugar (glucose) in urine, feels excessive thirst and also does excessive urination. Administration of injections of insulin to them lowers the blood sugar level in them.

14.   Which of the following is a plant hormone?

a. Insulin       b. Thyroxine        c. Oestrogen         d. Cytokinin

Ans- Cytokinin

15.  The gap between two neuron is called a

 a. dendrite     b. synapse    c. axon    d. impulse

Ans- Synapse

16.  The brain is responsible for

a.      Thinking                                c. regulating the heart beat

b.      Balancing the body             d. all of the above.

Ans- all of the above

17.  What is the function of receptors in our body? Think of situations where receptors do not work property. What problems are likely to arise?

Ans- The receptor in our body collect information amount changes in the environment around us in the form of stimuli. These then pass the information in the form of nerve impulses to central nervous system (brain or spinal cord)where message is interpreted and appropriate instructions are sent to effectors (muscles or glands) which reveal responses. When receptors do not function normally, the environmental stimuli are not able to create nerve impulses and body does not respond.

18.  Draw the structure of a neuron and explain its function.

Ans- Neurons present in the sense organs detect changes in the environment and transmit this information to central nervous system which interprets the message and send instructions via neurons to effectors for appropriate response.

19.  How does phototropism occur in plants?

Ans-Plant is autotrophs, i.e., they manufacture their own foods in the presence of sunlight. Therefore, they respond to light by growing towards it. Plants also turn their leaves towards the sun to ensure that the latter get maximum sunlight. This phenomenon can easily be depicted by performing simple experiment.

Take two potted plants. Place one plant in the open so that it receives the sunlight. Place the other plant in a room near the window in such a way that it receives sunlight from one side only, i.e., through the window. After some days, observe both the plants. You will notice that the first plant (which was kept in the open) has grown up straight towards light. However, the second plant (which was kept in the room and receiving light from one side) has grown by bending towards the light.

20.  Which signals will get disrupted in case of a spinal cord injury?

Ans- In case of spinal injury, reflex action and involuntary actions will get disrupted.

21.  How does chemical coordination occur in plants?

Ans- In plants, chemical coordination occurs with the help of plant hormones (phytohormones). Specific hormones are secreted in one part of plant and these diffuse to reach specific sites to produce the effect. The response of plants to sunlight occurs by bending of the shoot towards it. It occurs due to slow growth movements and the phenomenon is called positive phototropism.

22.  What is the need for a system of control and coordination in an organism?

Ans- In multicellular animals, body is very complex. Therefore, it is necessary that various organs (parts) of the body of an organism work together in a proper manner to produce proper reaction to a stimulus. For proper control and coordination, higher animals have evolved nervous system and endocrine system.

23.  How are involuntary actions and reflex actions different from each other?

Ans- Reflex action are spontaneous, automatic, mechanical responses to specific stimuli without the will of animal. In reflex actions, spinal cord is generally. Involuntary actions also occur without the will of the animal and anima has no choice in them. However, these are regulated by either midbrain of hind brain.

24.  Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Ans-

s.no	Nervous information	Hormonal information
1. 2. 3. 4. 5.	It is sent as an electrical impulse along axons, and as a chemical across synapse. Information travels rapidly, in milliseconds. Information is directed to specific receptor- one or a few nerve fibers, gland cells or other neurons. i.e, it is addressed by name. It gets response immediately. Its effect is short- lived.	1.      it is sent as a chemical messenger via blood stream. 2.      Information travels slowly. 3.      Information is spread throughout the body by blood, from which the target cells or organs pick it up, i.e., it is addressed to ‘whom it may concern’. 4.      It gets response usually slowly. 5.      Its effects are generally more prolonged.

25.  What is the difference between the manner in which movement in the sensitive plant and movement in our legs takes place?

Ans- Sensitive plant, in response to touch shows quick movement of leaves which fold up and droop. Here, plant cells change shape by changing the amount of water in them (turgor changes) affected by plant hormones. On the other hand, movement in our legs is voluntary action which is controlled by cerebellum part of hind brain. It involves nervous control.