Control and CoordinationClass 10 Biology NCERT Solutions
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Q1E X E R C I S E S
Which of the following is a plant hormone?
(a)
Insulin
(b)
Thyroxin
(c)
Oestrogen
(d)
Cytokinin.
Solution
(d) Cytokinin.
Explanation: Insulin, thyroxin, and oestrogen are hormones found in animals. Cytokinin is a plant hormone that promotes cell division.
Q2E X E R C I S E S
The gap between two neurons is called a
(a)
dendrite.
(b)
synapse.
(c)
axon.
(d)
impulse.
Solution
(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.
Q3E X E R C I S E S
The brain is responsible for
(a)
thinking.
(b)
regulating the heart beat.
(c)
balancing the body.
(d)
all of the above.
Solution
(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.
Q4E X E R C I S E S
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Solution
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 signals or nerve impulses. These impulses are then sent to the central nervous system (brain and spinal cord) for processing.
Situations where receptors do not work properly:
Receptors can fail to work due to injury, disease, or genetic defects. For example:
- A blocked nose during a cold can prevent olfactory receptors from detecting smell.
- Damage to the retina can cause photoreceptors in the eye to stop working.
- Nerve damage can affect thermoreceptors (for heat) in the skin.
Problems that may arise:
If receptors do not function properly, the body will not be able to detect environmental changes, which can be dangerous. For instance:
- If pain receptors in the skin are damaged, a person might not realize they have an injury.
- If thermoreceptors fail, a person could get severely burnt without feeling the heat.
- A loss of smell or taste receptors would diminish the ability to detect spoiled food or enjoy meals.
Q5E X E R C I S E S
Draw the structure of a neuron and explain its function.
Solution
Structure of a Neuron:
A neuron consists of three main parts (as seen in Figure 6.1 (a) of the textbook):
- Cell Body (or Cyton): This is the main part of the neuron, which contains the nucleus, cytoplasm, and other organelles.
- Dendrites: These are short, branched, tree-like extensions that arise from the cell body. Their primary role is to receive signals (information) from other neurons.
- Axon: This is a single, long, cylindrical extension that carries nerve impulses away from the cell body to its end terminals. The axon transmits the signal to the next neuron or to an effector cell like a muscle or gland.
(A diagram showing these parts should be drawn).
Function of a Neuron:
The function of a neuron is to transmit information throughout the body in the form of electrical impulses. The process is as follows:
- Information is acquired at the tips of the dendrites.
- This triggers a chemical reaction that creates an electrical impulse.
- The impulse travels from the dendrite to the cell body and then along the axon to its end.
- At the axon terminal, the electrical impulse causes the release of chemical neurotransmitters into the synapse (the gap between two neurons).
- These chemicals cross the synapse and start a similar electrical impulse in the next neuron, thus passing the information along.
Q6E X E R C I S E S
How does phototropism occur in plants?
Solution
Phototropism is the directional growth of a plant in response to a light stimulus. It occurs as follows:
- The plant hormone auxin is synthesized at the tip of the shoot.
- When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot.
- This leads to a higher concentration of auxin on the side of the shoot that is away from the light.
- Auxin stimulates cell elongation. Therefore, the cells on the shady side grow longer and faster than the cells on the side receiving direct light.
- This unequal growth on the two sides of the shoot causes the shoot to bend towards the source of light.
Q7E X E R C I S E S
Which signals will get disrupted in case of a spinal cord injury?
Solution
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:
- Motor Signals (from brain to body): Nerve impulses from the brain that control muscle movement cannot reach the parts of the body below the injury. This can lead to paralysis, the loss of voluntary muscle control.
- Sensory Signals (from body to brain): Nerve impulses from sensory receptors (for touch, pain, temperature, pressure) in the body parts below the injury cannot reach the brain. This results in a loss of sensation in the affected areas.
- Reflex Action Signals: While reflex arcs located within the spinal cord might remain intact, the signals that inform the brain about the reflex action will be disrupted. Therefore, the person would not be aware of the reflex occurring.
Q8E X E R C I S E S
How does chemical coordination occur in plants?
Solution
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:
- Synthesis: Plants produce various hormones in specific parts, such as the shoot tip, root tip, or in fruits and seeds.
- Transport: These hormones diffuse from their site of synthesis to other parts of the plant where they are needed. This transport is much slower than nerve impulse transmission in animals.
- Action: The hormones act on target cells to regulate different processes. They can either promote or inhibit growth and development.
Examples of Hormones and their Functions:
- Auxin: Promotes cell elongation and is responsible for phototropism.
- Gibberellins: Promote stem growth.
- Cytokinins: Promote cell division, especially in fruits and seeds.
- Abscisic acid: Inhibits growth and is associated with the wilting of leaves and dormancy of seeds.
Q9E X E R C I S E S
What is the need for a system of control and coordination in an organism?
Solution
A system of control and coordination is essential for the survival and proper functioning of a multicellular organism for the following reasons:
- Response to Environment: It enables the organism to respond to various stimuli in its environment (like light, heat, sound). This is crucial for protection from harm and for finding food or mates.
- Integration of Body Functions: Multicellular organisms have complex bodies with specialized tissues and organs performing different functions. Control and coordination ensure that all these parts work together in an integrated and systematic manner.
- Homeostasis: It helps in maintaining a constant internal environment within the body, regardless of external changes. This includes regulating body temperature, blood sugar levels, and water balance.
- Voluntary and Involuntary Actions: It controls all actions of the body, from voluntary movements like walking to involuntary processes like heartbeat and breathing, ensuring that life processes continue smoothly.
Q10E X E R C I S E S
How are involuntary actions and reflex actions different from each other?
Solution
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 occurs without the conscious control of an individual, typically regulating internal body functions. |
| Control Center | Primarily controlled by the spinal cord (via a reflex arc). | Controlled by the mid-brain and hind-brain (medulla). |
| Purpose | Mainly for protection and immediate response to danger. | To regulate ongoing life processes like breathing, digestion, and heartbeat. |
| Speed | Extremely fast, as it bypasses the thinking process of the brain. | Generally slower or rhythmic and continuous. |
| Example | Pulling the hand away from a flame. | The beating of the heart, digestion of food, salivation. |
Q11E X E R C I S E S
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Solution
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 signals (neurotransmitters in the nervous system and hormones in the endocrine system).
Contrast (Differences):
| Feature | Nervous Mechanism | Hormonal Mechanism |
|---|---|---|
| Mode of Transmission | Information is transmitted as electrical impulses along nerve fibres. | Information is transmitted as chemical hormones through the bloodstream. |
| Speed of Transmission | Very rapid, almost instantaneous. | Slow, as hormones travel through blood. |
| Area of Effect | The effect is localized and specific, affecting only the target muscle or gland. | The effect is widespread and can affect multiple organs simultaneously. |
| Duration of Effect | The effect is short-lived. | The effect is generally long-lasting. |
| Connectivity | Reaches only those cells connected by nervous tissue. | Can reach all cells of the body via the bloodstream. |
Q12E X E R C I S E S
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Solution
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 swell or shrink to cause movement. | Based on the contraction and relaxation of specialized proteins within muscle cells. |
| Control System | No specialized nervous or muscular tissue. Information is transmitted via electrical-chemical signals between cells. | Controlled by a complex nervous system. Nerve impulses from the brain command the muscles to act. |
| Type of Control | Involuntary response to a stimulus (touch). | Primarily a voluntary action controlled by conscious thought. |
| Specialized Tissues | Does not involve specialized muscle tissue. | Involves specialized tissues: nervous tissue for control and muscular tissue for action. |
| Relation to Growth | The movement is independent of growth. | The movement is a change in position and is not related to growth. |
Q1QUESTIONS (In-chapter)
What is the difference between a reflex action and walking?
Solution
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 controlled by the spinal cord. The brain is only informed. | It is controlled by the brain. The cerebellum maintains posture and balance. |
| Thinking Involved | No thinking or conscious decision-making is involved. | It is a result of conscious thought and decision-making. |
| Purpose | It is mainly a protective mechanism to avoid harm. | It is performed to move from one place to another for a specific purpose. |
| Example | Pulling your hand away immediately after touching a hot object. | Deciding to get up and walk to another room. |
Q2QUESTIONS (In-chapter)
What happens at the synapse between two neurons?
Solution
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 the gap and bind to receptors on the dendrite of the second neuron. This binding initiates a new electrical impulse in the next neuron, thus allowing the nerve signal to be transmitted from one neuron to another.
Q3QUESTIONS (In-chapter)
Which part of the brain maintains posture and equilibrium of the body?
Solution
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.
Q4QUESTIONS (In-chapter)
How do we detect the smell of an agarbatti (incense stick)?
Solution
We detect the smell of an agarbatti through our sense of smell, which involves the following steps:
- The burning agarbatti releases chemical particles into the air.
- When we inhale, these chemicals enter our nasal cavity and come in contact with the olfactory receptors located in the nose.
- These specialized receptors detect the chemical stimulus (smell) and convert it into an electrical impulse.
- This impulse is then transmitted by sensory nerves to the fore-brain.
- The fore-brain has a specific region that interprets this signal, allowing us to perceive the characteristic smell of the agarbatti.
Q5QUESTIONS (In-chapter)
What is the role of the brain in reflex action?
Solution
In a reflex action, the primary pathway for the response (the reflex arc) is formed in the spinal cord. This allows for an extremely fast response without involving the brain's thinking process. However, the information about the stimulus and the response is also sent to the brain. The brain's role is secondary; it becomes aware of the event after the reflex action has already occurred. This allows the brain to process the situation, understand the danger, and potentially modify future behavior, but it does not control the immediate reflex itself.
Q6QUESTIONS (In-chapter)
What are plant hormones?
Solution
Plant hormones, also known as phytohormones, are chemical compounds produced by plants that regulate their growth, development, and responses to environmental stimuli. They are synthesized in one part of the plant and transported to other parts where they act. They control processes such as cell division, cell elongation, flowering, fruit ripening, and tropic movements (like response to light and gravity). Examples of plant hormones include auxins, gibberellins, cytokinins, and abscisic acid.
Q7QUESTIONS (In-chapter)
How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Solution
The movement of leaves of the sensitive plant (Mimosa pudica) is different from the movement of a shoot towards light in the following ways:
| Feature | Movement of Sensitive Plant Leaves | Movement of a Shoot Towards Light |
|---|---|---|
| Type of Movement | Nastic movement (non-directional). | Tropic movement (directional). |
| Cause of Movement | Caused by changes in turgor pressure (amount of water) in the cells at the base of the leaves. | Caused by differential growth stimulated by the hormone auxin. |
| Growth-Dependent | It is independent of growth. | It is a growth-dependent movement. |
| Speed of Response | Very rapid and immediate. | Very slow, occurring over hours or days. |
| Stimulus | The stimulus is touch (thigmonasty). | The stimulus is light (phototropism). |
Q8QUESTIONS (In-chapter)
Give an example of a plant hormone that promotes growth.
Solution
An example of a plant hormone that promotes growth is Auxin. Auxin is synthesized at the shoot tip and helps cells to grow longer. Other examples include Gibberellins, which help in the growth of the stem, and Cytokinins, which promote cell division.
Q9QUESTIONS (In-chapter)
How do auxins promote the growth of a tendril around a support?
Solution
Tendrils are sensitive to touch. When a tendril comes into contact with a support, the following process occurs:
- The side of the tendril in contact with the support experiences a stimulus.
- The plant hormone auxin diffuses from the side in contact to the side away from the support.
- This results in a higher concentration of auxin on the side of the tendril that is not touching the support.
- The higher concentration of auxin stimulates faster cell growth and elongation on this outer side.
- The side in contact with the support grows more slowly. This differential growth causes the tendril to curve and coil around the support, allowing the plant to cling to it.
Q10QUESTIONS (In-chapter)
Design an experiment to demonstrate hydrotropism.
Solution
Aim: To demonstrate that plant roots grow towards water (positive hydrotropism).
Materials: A wire mesh or sieve, freshly germinated bean seeds, moist sawdust.
Procedure:
- Take a sieve and line it with moist sawdust.
- Place a few germinated bean seeds on the sawdust.
- Suspend the sieve in the air. Keep the sawdust moist by sprinkling water on it periodically.
- Leave the setup undisturbed for a few days and observe the growth of the radicles (young roots).
Observation:
Initially, the roots will grow downwards through the holes of the sieve due to gravity (geotropism). After some time, the roots will be observed to bend back and grow towards the moist sawdust in the sieve.
Conclusion:
The roots bend away from gravity and towards the source of moisture. This demonstrates that roots are positively hydrotropic, meaning they grow towards water.
Q11QUESTIONS (In-chapter)
How does chemical coordination take place in animals?
Solution
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 or tissues. Hormones act as signals, regulating various physiological processes such as growth, development, metabolism, and response to stress. The timing and amount of hormone secretion are controlled by feedback mechanisms, ensuring that they are released in precise quantities when needed.
Q12QUESTIONS (In-chapter)
Why is the use of iodised salt advisable?
Solution
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 in the diet can lead to a condition called goitre, which is characterized by a swollen neck due to the enlargement of the thyroid gland. Consuming iodised salt ensures a sufficient intake of iodine, thereby preventing goitre and ensuring the proper functioning of the thyroid gland.
Q13QUESTIONS (In-chapter)
How does our body respond when adrenaline is secreted into the blood?
Solution
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:
- Increased Heart Rate: The heart beats faster, pumping more blood to supply oxygen and nutrients to the muscles.
- Increased Breathing Rate: The rate of breathing increases, providing more oxygen to the blood.
- Blood Diversion: Blood flow is reduced to the digestive system and skin and is diverted to the skeletal muscles, which need more energy for rapid action.
- Energy Release: It stimulates the liver to convert glycogen into glucose, releasing more energy for the muscles. All these responses work together to enable the body to deal with the emergency situation with increased strength and speed.
Q14QUESTIONS (In-chapter)
Why are some patients of diabetes treated by giving injections of insulin?
Solution
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 insulin is deficient, glucose remains in the blood, leading to high blood sugar and various harmful effects. To manage this condition, diabetic patients are given injections of insulin. This external supply of the hormone helps to lower their blood sugar levels to a normal range.