Question 1

Q1: Which of the following is a plant hormone? (a) Insulin (b) Thyroxin (c) Oestrogen (d) Cytokinin.

Accepted Answer

(d) Cytokinin. Explanation: Insulin, thyroxin, and oestrogen are hormones found in animals. Cytokinin is a plant hormone that promotes cell division.

Question 2

Q10: How are involuntary actions and reflex actions different from each other?

Accepted Answer

Although all reflex actions are involuntary, there are key differences between general involuntary actions and reflex actions: | Feature | Reflex Action | Involuntary Action | |---|---|---| | Definition | A rapid, automatic response to a specific, often harmful, external stimulus. | An action that o...

Question 3

Q11: Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Accepted Answer

Both nervous and hormonal systems are responsible for control and coordination in animals, but they function differently. Comparison (Similarities): - Both systems help in integrating various body activities. - Both enable the organism to respond to stimuli. - Both involve the use of chemical signal...

Question 4

Q12: What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?

Accepted Answer

The movement in a sensitive plant and the movement in our legs differ fundamentally in their mechanism and control. | Feature | Movement in a Sensitive Plant | Movement in Our Legs | |---|---|---| | Underlying Mechanism | Based on changes in the amount of water (turgor pressure) in the cells. Cells...

Question 5

Q2: The gap between two neurons is called a (a) dendrite. (b) synapse. (c) axon. (d) impulse.

Accepted Answer

(b) synapse. Explanation: A synapse is the junction or gap between the axon terminal of one neuron and the dendrite of another, across which nerve impulses are transmitted.

Question 6

Q3: The brain is responsible for (a) thinking. (b) regulating the heart beat. (c) balancing the body. (d) all of the above.

Accepted Answer

(d) all of the above. Explanation: The brain performs all these functions. The fore-brain is the main thinking part, the hind-brain (medulla) regulates involuntary actions like heart beat, and the cerebellum (part of hind-brain) is responsible for balancing the body.

Question 7

Q4: What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?

Accepted Answer

Function of Receptors: Receptors are specialized cells or nerve endings located in our sense organs (like skin, eyes, ears, nose, and tongue). Their function is to detect stimuli from the environment, such as light, sound, heat, pressure, or chemicals, and convert this information into electrical si...

Question 8

Q5: Draw the structure of a neuron and explain its function.

Accepted Answer

Structure of a Neuron: A neuron consists of three main parts (as seen in Figure 6.1 (a) of the textbook): 1.  Cell Body (or Cyton): This is the main part of the neuron, which contains the nucleus, cytoplasm, and other organelles. 2.  Dendrites: These are short, branched, tree-like extensions that ar...

Question 9

Q6: How does phototropism occur in plants?

Accepted Answer

Phototropism is the directional growth of a plant in response to a light stimulus. It occurs as follows: 1. The plant hormone auxin is synthesized at the tip of the shoot. 2. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. 3. This leads to a highe...

Question 10

Q7: Which signals will get disrupted in case of a spinal cord injury?

Accepted Answer

A spinal cord injury can disrupt the communication between the brain and the parts of the body below the site of the injury. The signals that will be disrupted are: 1.  Motor Signals (from brain to body): Nerve impulses from the brain that control muscle movement cannot reach the parts of the body b...

Question 11

Q8: How does chemical coordination occur in plants?

Accepted Answer

Chemical coordination in plants is achieved through plant hormones, also called phytohormones. Unlike animals, plants do not have a nervous system. The process of chemical coordination is as follows: 1.  Synthesis: Plants produce various hormones in specific parts, such as the shoot tip, root tip, o...

Question 12

Q9: What is the need for a system of control and coordination in an organism?

Accepted Answer

A system of control and coordination is essential for the survival and proper functioning of a multicellular organism for the following reasons: 1.  Response to Environment: It enables the organism to respond to various stimuli in its environment (like light, heat, sound). This is crucial for protec...

Question 13

Q1: What is the difference between a reflex action and walking?

Accepted Answer

The difference between a reflex action and walking is as follows: | Feature | Reflex Action | Walking | |---|---|---| | Nature of Action | It is an involuntary, rapid, and automatic response to a stimulus. | It is a voluntary action, consciously controlled. | | Control Center | It is primarily contr...

Question 14

Q10: Design an experiment to demonstrate hydrotropism.

Accepted Answer

Aim: To demonstrate that plant roots grow towards water (positive hydrotropism). Materials: A wire mesh or sieve, freshly germinated bean seeds, moist sawdust. Procedure: 1. Take a sieve and line it with moist sawdust. 2. Place a few germinated bean seeds on the sawdust. 3. Suspend the sieve in the...

Question 15

Q11: How does chemical coordination take place in animals?

Accepted Answer

Chemical coordination in animals is carried out by the endocrine system. This system consists of various endocrine glands that produce and secrete chemical messengers called hormones directly into the bloodstream. The blood then transports these hormones throughout the body to specific target organs...

Question 16

Q12: Why is the use of iodised salt advisable?

Accepted Answer

The use of iodised salt is advisable because iodine is an essential mineral required by the thyroid gland to produce the hormone thyroxin. Thyroxin regulates the metabolism of carbohydrates, fats, and proteins in the body, which is crucial for balanced growth and development. A deficiency of iodine...

Question 17

Q13: How does our body respond when adrenaline is secreted into the blood?

Accepted Answer

When adrenaline is secreted into the blood by the adrenal glands, usually in response to a stressful or dangerous situation, it prepares the body for a 'fight or flight' response. The key responses are: 1. Increased Heart Rate: The heart beats faster, pumping more blood to supply oxygen and nutrient...

Question 18

Q14: Why are some patients of diabetes treated by giving injections of insulin?

Accepted Answer

Diabetes is a disorder in which blood sugar levels become too high. This is often caused because the pancreas does not produce sufficient amounts of the hormone insulin. Insulin's function is to help regulate blood sugar levels by enabling body cells to absorb glucose from the blood for energy. When...

Question 19

Q2: What happens at the synapse between two neurons?

Accepted Answer

A synapse is the small gap between the axon terminal of one neuron and the dendrite of the next neuron. When an electrical impulse reaches the end of the axon of the first neuron, it triggers the release of chemical substances called neurotransmitters into the synapse. These chemicals diffuse across...

Question 20

Q3: Which part of the brain maintains posture and equilibrium of the body?

Accepted Answer

The cerebellum, which is a part of the hind-brain, is responsible for maintaining the posture and equilibrium (balance) of the body. It also coordinates the precision of voluntary actions like walking, riding a bicycle, or picking up a pencil.

NCERT Solutions