CBSE Class X Science Chapter 6 Control and Coordination Questions and Answers

In-Text Questions (Page 105)

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

The differences between a reflex action and walking are:

• Reflex Action: It is an automatic, involuntary, and rapid response to a stimulus (such as pulling back a hand from a hot object) that occurs without thinking. It is controlled primarily by the spinal cord.
• Walking: It is a voluntary action based on deciding what to do next. It requires conscious thought and is controlled by the brain (specifically the cerebellum for maintaining posture and balance).

Q2: What happens at the synapse between two neurons?

At the synapse (the gap between two neurons):

1. When an electrical impulse reaches the end of the axon of one neuron, it sets off the release of chemical compounds.
2. These chemicals cross the synapse gap.
3. They start a similar electrical impulse in the dendritic tip of the next neuron.

Figure 6.1: (a) Structure of neuron, (b) Neuromuscular junction

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

The cerebellum, which is a part of the hind-brain, is responsible for maintaining the posture and equilibrium (balance) of the body.

Q4: How do we detect the smell of an agarbatti (incense stick)?

The smell of an agarbatti is detected as follows:

• Olfactory receptors present in our nose detect the smell particles from the environment and set off an electrical impulse.
• This signal is transmitted through sensory nerve cells to the fore-brain, which contains separate specialized areas for detecting smell.
• The fore-brain interprets this sensory information by combining it with stored experience to recognize the scent of the agarbatti.

Figure 6.3: Human brain

Q5: What is the role of the brain in reflex action?

In a reflex action, the direct response is produced immediately by a reflex arc formed in the spinal cord so that quick protective action takes place without waiting for the brain's conscious thought process. However, the role of the brain is to receive the information input regarding the event, as the sensory signals also travel up to the brain where it is recorded and stored in memory.

Figure 6.2: Reflex arc

In-Text Questions (Page 108)

Q1: What are plant hormones?

Plant hormones (or phytohormones) are chemical compounds synthesized in tiny quantities in one part of a plant body (away from where they act) that diffuse to their site of action to control and coordinate growth, development, and responses to the environment.

Q2: How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

Movement of Leaves of Sensitive Plant	Movement of Shoot Towards Light
It is independent of growth.	It is dependent on growth (directional growth movement).
It is a non-directional response to touch.	It is a directional (phototropic) response towards light.
It is very quick and occurs due to changes in water amount (turgor changes) in cells.	It is a slow movement caused by unequal growth driven by the hormone auxin.

Figure 6.4: The sensitive plant

Q3: Give an example of a plant hormone that promotes growth.

Auxin (or Gibberellins / Cytokinins) is an example of a plant hormone that promotes growth.

Q4: How do auxins promote the growth of a tendril around a support?

When a tendril comes in contact with a support, auxin diffuses away from the side in contact toward the side away from the support. The higher concentration of auxin stimulates the cells on the side away from the object to grow longer and faster compared to the side in contact. This differential rate of growth causes the tendril to circle and cling around the support.

Q5: Design an experiment to demonstrate hydrotropism.

Experimental Setup to Demonstrate Hydrotropism:

1. Take a porous tray filled with moist soil/sawdust and plant a few germinating seeds in it.
2. Place an unglazed porous clay pot filled with water at one side inside the tray.
3. Keep the setup undisturbed for a few days.
4. Observation: As seeds germinate, the roots initialy grow downwards due to gravity, but as they grow further, they bend towards the clay pot containing water instead of growing straight down.
5. Conclusion: Roots show positive hydrotropism by growing directionally toward a water source.

Figure 6.5: Response of the plant to the direction of light

In-Text Questions (Page 111)

Q1: How does chemical coordination take place in animals?

In animals, chemical coordination takes place through hormones secreted by specialized endocrine glands directly into the bloodstream. Blood carries these chemical compounds throughout the body to specific target organs or target tissues where they bind to cells via specialized surface molecules to regulate physiological processes, growth, and metabolism.

Figure 6.7: Endocrine glands in human beings (a) male, (b) female

Q2: Why is the use of iodised salt advisable?

Iodine is necessary for the thyroid gland to synthesize the hormone thyroxin. Thyroxin regulates carbohydrate, protein, and fat metabolism in the body to provide the best balance for growth. If iodine is deficient in our diet, thyroxin synthesis is impaired, which can lead to a condition called goitre characterized by a swollen neck. Therefore, iodised salt is advisable to prevent goitre.

Q3: How does our body respond when adrenaline is secreted into the blood?

When adrenaline is secreted into the blood during emergency situations, the body responds in the following ways:

• The heart beats faster, supplying more oxygen to the muscles.
• Blood flow to the digestive system and skin is reduced due to contraction of muscles around small arteries, diverting blood to skeletal muscles.
• The breathing rate increases due to contractions of the diaphragm and rib muscles.
• Together, these responses prepare the body to deal with scary situations (fight or flight).

Q4: Why are some patients of diabetes treated by giving injections of insulin?

Insulin is a hormone produced by the pancreas that helps regulate and lower blood sugar levels. In diabetic patients, insulin is either not secreted in sufficient amounts or not utilized properly, causing blood sugar levels to rise dangerously. Injections of insulin help reduce and control blood sugar levels to prevent harmful effects.

Chapter End Exercises (Page 112)

Q1: Which of the following is a plant hormone?

(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin

Answer: (d) Cytokinin

Q2: The gap between two neurons is called a

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

Answer: (b) synapse

Q3: The brain is responsible for

(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above

Answer: (d) all of the above

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?

Function of receptors: Receptors are specialized nerve cell tips located in sense organs (like eyes, ears, nose, tongue, skin) that detect changes and signals from the surrounding environment.

Problems when receptors do not work properly:

• Environmental stimuli will not be detected in time.
• For example, if heat/pain receptors in skin fail to work, touching a hot surface will not trigger a reflex pull-back, resulting in severe burns.
• If gustatory or olfactory receptors fail, taste or smell perception is lost, preventing detection of spoiled food or gas leaks.

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

Figure 6.1 (a): Structure of neuron

Functions of parts of a neuron:

• Dendrite: Acquires information from the environment or preceding nerve cells and initiates an electrical impulse.
• Cell Body: Processes the chemical impulse and conducts it toward the axon.
• Axon: Carries the electrical impulse over a long distance from the cell body to the nerve ending.
• Nerve Ending: Releases chemical signals across the synapse gap to pass information to the next neuron or effector organ.

Q6: How does phototropism occur in plants?

Phototropism is the growth movement of a plant part in response to light. When a growing shoot detects light from one direction, the growth hormone auxin, synthesized at the shoot tip, diffuses toward the shady side of the shoot. The higher concentration of auxin stimulates the cells on the shady side to grow longer than those on the illuminated side. This unequal cell elongation causes the plant stem to bend toward the light source (positive phototropism).

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

In case of a spinal cord injury, the following signals will be disrupted:

• Reflex action signals, as reflex arcs formed in the spinal cord will be broken.
• Sensory signals coming from various body organs traveling to the brain for processing.
• Motor signals sent from the brain to voluntary muscles for bodily movement.

Q8: How does chemical coordination occur in plants?

Chemical coordination in plants occurs through plant hormones (phytohormones). Stimulated plant cells synthesize specific hormones (such as auxins, gibberellins, cytokinins, and abscisic acid) that diffuse through cells to their target regions. These compounds coordinate cell division, stem elongation, direction of growth, and response to environmental stimuli.

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

A system of control and coordination is essential in an organism because:

• Multi-cellular organisms have specialized organs that must work in harmony to respond effectively to environmental changes.
• It protects the organism from harm through rapid protective actions (like reflex movements).
• It ensures proper timing and localization of body growth and development.
• It regulates internal organ functions like heartbeat, respiration, blood pressure, and metabolism.

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

Involuntary Actions	Reflex Actions
Regulated continuously by the mid-brain and hind-brain (medulla).	Controlled primarily via reflex arcs located in the spinal cord.
Occur internally without conscious choice to maintain body functions (e.g., heartbeat, digestion, salivation).	Occur quickly in response to sudden external environmental stimuli (e.g., withdrawing hand from heat).
Slow to moderate continuous processes.	Extremely rapid and sudden movements.

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

Nervous Mechanism	Hormonal Mechanism
Information travels in the form of electrical impulses along nerve cells.	Information travels via chemical compounds carried in the blood.
Transmission is very rapid.	Transmission is relatively slow.
Reaches only specific cells connected directly by nervous tissue.	Reaches almost all cells of the body via circulation.
Response is short-lived and immediate.	Response is persistent and long-lasting.

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

Movement in Sensitive Plant	Movement in Our Legs
No specialized nervous or muscle tissue is present.	Controlled by specialized nervous tissue and voluntary muscle tissue.
Plant cells change shape by altering water content (swelling or shrinking).	Muscle cells change shape using specialized proteins that rearrange in response to electrical signals.
Involuntary directional response to touch stimulus.	Voluntary action controlled and decided consciously by the brain.