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NCERT Solutions For Class 10 Biology: Control and Coordination

October 9, 2025

Intext Questions (Page 101)

Question 1: Look at Fig. 6.1. and identify the parts of a neuron.
(i) where information is acquired,
(ii) through which information travels as an electrical impulse
(iii) where this impulse must be converted into a chemical signal for onward transmission.

Alt text
Answer-
(i) Information is acquired at the dendritic tip of the nerve cell.
(ii) Information travels as an electrical impulse along the axon.
(iii) The impulse must be converted into a chemical signal at the end of the axon.


Intext Questions (Page 109)

Question 1: What are plant hormones?

Answer-
Plant hormones (or phytohormones) are chemical compounds used by multicellular organisms (plants) for control and coordination. They help to coordinate growth, development, and responses to the environment. They are synthesised at places away from where they act and simply diffuse to the area of action.

Question 2: How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

Answer-
The two movements differ based on whether or not growth is involved:

  1. Movement of leaves of the sensitive plant: This is an immediate response to a stimulus (touch) and does not involve growth. The plant moves its leaves very quickly by changing the amount of water in certain cells, causing them to swell or shrink.
  2. Movement of a shoot towards light (Phototropism): This is a directional movement caused by growth. It is a slow response mediated by the hormone auxin, which causes cells on the shady side of the shoot to grow longer, resulting in the shoot bending towards light.

Question 3: Give an example of a plant hormone that promotes growth.

Answer-
Examples of plant hormones that help in promoting growth are auxin, gibberellins (which help in the growth of the stem), and cytokinins (which promote cell division).

Question 4: How do auxins promote the growth of a tendril around a support?

Answer-
When a tendril comes in contact with a support, the part of the tendril that is in contact with the object does not grow as rapidly as the part of the tendril away from the object. This difference in growth rate is promoted by the hormone auxin, causing the tendril to circle around the object and thus cling to it.

Question 5: Design an experiment to demonstrate hydrotropism.

Answer-
Hydrotropism refers to the directional growth movement of a plant part in response to the stimulus of water ('hydro').
(The source does not explicitly detail a specific design for hydrotropism, but outlines the method for phototropism in Activity 6.2, which suggests a container and a stimulus). A potential design would involve:

  1. Taking a container and filling it with dry soil or sawdust.
  2. Placing a freshly germinated seedling in the middle.
  3. Placing a porous pot filled with water near the roots on one side, ensuring the rest of the soil remains dry.
  4. After observation over several days, the roots will be seen growing directionally towards the source of water (the porous pot), demonstrating hydrotropism.

Intext Questions (Page 111)

Question 1: How does chemical coordination take place in animals?

Answer-
Chemical coordination in animals takes place via the endocrine system, which uses hormones.

  1. Chemical Signals: Stimulated cells release a chemical compound (hormone) that diffuses all around.
  2. Detection and Transmission: This hormone is secreted directly into the blood and carried to different parts of the body.
  3. Target Action: The hormone acts on target organs or specific tissues, which possess special molecules on their surfaces to detect the compound and recognize the information. This allows for wide-ranging changes and persistent control, reaching all cells regardless of nervous connections.

Question 2: Why is the use of iodised salt advisable?

Answer-
The use of iodised salt is advisable because Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein, and fat metabolism in the body to provide the best balance for growth. If iodine is deficient in the diet, there is a possibility of suffering from the disease goitre, one symptom of which is a swollen neck.

Question 3: How does our body respond when adrenaline is secreted into the blood?

Answer-
Adrenaline is secreted from the adrenal glands when an animal is in a scary situation, preparing the body for fighting or running away. The responses are:

  1. Heart Rate: The heart beats faster, which results in the supply of more oxygen to the muscles.
  2. Blood Diversion: Blood to the digestive system and skin is reduced due to the contraction of muscles around small arteries; this diverts the blood to the skeletal muscles.
  3. Breathing: The breathing rate also increases because of the contractions of the diaphragm and the rib muscles.
    All these responses enable the body to be ready to deal with the situation.

Question 4: Why are some patients of diabetes treated by giving injections of insulin?

Answer-
Patients of diabetes are treated with insulin injections because insulin is the hormone produced by the pancreas that helps in regulating blood sugar levels. If insulin is not secreted in proper amounts, the sugar level in the blood rises, causing diabetes and many harmful effects. Providing insulin through injection helps to regulate the rising blood sugar level.


Exercise Questions (Page 112-113)

Question 1: Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.

Answer-
Cytokinin is a plant hormone that promotes cell division. Insulin, Thyroxin, and Oestrogen are animal hormones.
The correct option is (d) Cytokinin.

Question 2: The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.

Answer-
The electrical impulse travels down the axon, and at the end of the axon, chemicals are released that cross the gap, or synapse, to start a similar impulse in the next neuron.
The correct option is (b) synapse.

Question 3: The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.

Answer-
The brain is the main coordinating centre of the body. Thinking is carried out by the fore-brain. Regulating the heart beat is an involuntary action controlled by the medulla in the hind-brain. Balancing the body and maintaining posture is the responsibility of the cerebellum in the hind-brain.
The correct option is (d) all of the above.

Question 4: What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?

Answer-
Function of Receptors:
Receptors are the specialised tips of some nerve cells. Their function is to detect all information from our environment. They are usually located in our sense organs, such as the inner ear, nose, and tongue. For instance, gustatory receptors detect taste while olfactory receptors detect smell.

Problems Arising from Malfunctioning Receptors:
If receptors do not work properly, the organism will be unable to detect changes in the environment, leading to a failure to respond appropriately.

  1. Protection Failure: If pain or heat receptors fail, the organism cannot detect an urgent and dangerous situation (like touching a hot object). The organism may suffer severe injury, such as getting burnt, because the necessary reflex action or conscious movement would not be triggered quickly enough.
  2. Sensory Loss: Failure of specific receptors, like olfactory receptors, can lead to the inability to smell, which can affect the appreciation of taste during eating.

Question 5: Draw the structure of a neuron and explain its function.

Answer-
Structure of a Neuron:
A neuron (nerve cell) is the fundamental unit of the nervous tissue and consists of three main parts:

  1. Dendrite/Dendritic tip: Branching structure at one end.
  2. Cell body: Contains the nucleus and cellular components.
  3. Axon: The long, single nerve fibre extending from the cell body.

Function of a Neuron:
The nervous tissue is an organised network of neurons specialized for conducting information via electrical impulses from one part of the body to another.

  1. Acquisition: Information is acquired at the dendritic tip.
  2. Impulse Generation: This information sets off a chemical reaction that creates an electrical impulse.
  3. Transmission: The impulse travels from the dendrite to the cell body, and then along the axon to its end.
  4. Synaptic Transfer: At the end of the axon, the electrical impulse releases chemicals that cross the synapse to start a similar impulse in the next neuron or deliver the impulse to other cells, such as muscle cells or glands.

Question 6: How does phototropism occur in plants?

Answer-
Phototropism is a directional, or tropic, movement in response to the stimulus of light.

  1. Detection: When growing plants detect light, a hormone called auxin is synthesised at the shoot tip.
  2. Diffusion and Concentration: If light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot.
  3. Differential Growth: This higher concentration of auxin stimulates the cells on the shady side to grow longer than the cells on the illuminated side.
  4. Bending: Due to this differential growth, the shoot appears to bend towards the light.

Question 7: Which signals will get disrupted in case of a spinal cord injury?

Answer-
The spinal cord is a bundle where nerves from all over the body meet on their way to the brain, and it is also where nerves carry signals back to the body. A spinal cord injury will disrupt two main categories of signals:

  1. Input Information (Sensory Signals): Information received by receptors from the environment and other parts of the body will not be able to travel from the peripheral nerves up to the brain for complex processing and thought.
  2. Output Instructions (Motor Signals): Instructions (messages) from the brain regarding voluntary actions (like moving a chair or writing) will not be able to travel from the brain back down to the muscles.
  3. Reflex Actions: Since reflex arcs are formed in the spinal cord itself, the ability to perform quick, involuntary responses to urgent situations, such as pulling a hand away from heat, will likely be severely impaired.

Question 8: How does chemical coordination occur in plants?

Answer-
Chemical coordination in plants is achieved through plant hormones (or phytohormones).

  1. Synthesis and Diffusion: These hormones are synthesised at specific places in the plant (like the shoot tip) and simply diffuse to the area where they act. Unlike the fast electrical impulses of animals, chemical communication in plants is slower, steady, and persistent.
  2. Coordination of Growth: Plant hormones like auxins, gibberellins, and cytokinins coordinate growth, development, and directional responses to the environment. For example, auxin causes differential growth leading to phototropism (bending towards light), while abscisic acid acts as a hormone that inhibits growth.

Question 9: What is the need for a system of control and coordination in an organism?

Answer-
A system of control and coordination is necessary in organisms for several reasons:

  1. Appropriate Response to Environment: Organisms need to detect changes in the environment and evoke an appropriate movement in response. For example, a cat running when it sees a mouse.
  2. Controlled Movement: All movement, in response to the environment, must be carefully controlled. The system ensures that the movement made depends on the event that is triggering it.
  3. Maintenance of Body Design: In multicellular organisms, control systems ensure that the growth and development of the body are coordinated and that the design of the body is carefully maintained (e.g., fingers growing only on arms, not faces).
  4. Efficiency: Systems like reflex arcs provide efficient ways of functioning for quick responses in urgent situations.

Question 10: How are involuntary actions and reflex actions different from each other?

Answer-
Both are muscle movements over which we do not have any conscious thinking control, but they differ in complexity and control centres:

FeatureReflex ActionsInvoluntary Actions
Control CentrePrimarily controlled by reflex arcs formed in the spinal cord itself.Primarily controlled by the mid-brain and hind-brain (specifically the medulla and cerebellum).
Response TypeSudden actions in response to dangerous or urgent external stimuli (input). They are typically simple muscle movements (e.g., pulling a hand away from a flame).Necessary actions for life maintenance happening continuously inside the body without thought.
ExamplesChange in the size of the pupil; pulling the hand back from a hot object.Beating of the heart, blood pressure, salivation, vomiting, and digestion of food.

Question 11: Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Answer-
The nervous system and the hormonal (endocrine) system both provide control and coordination, but they differ in their mode of transmission, speed, and reach:

Comparison (Similarities in Function):
Both systems provide control and coordination activities. Both use specialized tissues to transmit information. Both systems are crucial for responding to the environment and maintaining the body.

Contrast (Differences):

FeatureNervous Mechanism (Electrical Impulses)Hormonal Mechanism (Chemical Signals)
Medium of TransmissionElectrical impulses travel along networks of neurons.Chemical compounds (Hormones) are secreted directly into the blood and diffuse to target cells.
Speed of ActionVery fast (excellent for fast responses).Slower than nervous impulses, but steady and persistent.
Reach and RangeReaches only those cells connected by nervous tissue (limited range).Can potentially reach all cells of the body regardless of nervous connections (wide-ranging changes).
Duration of ResponseResponses are often short-lived.Responses are often long-lasting (e.g., controlling growth and metabolism).
LimitationsCells need time to reset their mechanisms before generating a new impulse, limiting continual transmission.Slower onset of action.

Question 12: What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?

Answer-
Movement in Sensitive Plant (Mimosa):

  1. Mechanism: The movement is independent of growth. It occurs due to changes in the amount of water in certain plant cells, causing them to swell or shrink.
  2. Control: Information is communicated using electrical-chemical means, but without specialised nervous or muscular tissue.
  3. Nature: It is a quick, immediate response to an external stimulus (touch).

Movement in Our Legs (Voluntary Action):

  1. Mechanism: Movement is caused by the contraction and shortening of specialised muscle cells. This occurs because special proteins in muscle cells change their shape and arrangement in response to nervous electrical impulses.
  2. Control: It is a voluntary action controlled by the fore-brain. The brain processes information, makes a decision about how to respond, and passes this information to motor areas that control the movement of voluntary muscles.
  3. Nature: It is a complex, thought out action (e.g., walking or moving a chair).

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