NCERT Solutions for Class 10 Science Chapter 6th Control and Coordination

Reflex Action:- It is an automatic, quick response to a stimulus. Example: Pulling your hand away from a hot object.

• It happens without thinking.
• It is controlled by the spinal cord.
• It protects the body from harm.

Walking:- It is a voluntary action that you do with conscious control. Example: Walking to school or the market.

• It requires thinking and coordination.
• It is controlled by the brain.
• It helps in movement and daily activities.

At the synapse (the small gap between two neurons), the following steps take place:

• An electrical impulse reaches the end of the first neuron.
• This causes the neuron to release chemicals called neurotransmitters into the synaptic gap.
• These chemicals cross the gap and reach the second neuron.
• They trigger a new electrical impulse in the second neuron.

The cerebellum is the part of the brain that maintains posture and equilibrium of the body.

When an agarbatti burns, it releases smell particles into the air. These particles enter our nose when we breathe. Inside the nose, there are special smell-detecting cells called olfactory receptors. These receptors send signals to the brain through the olfactory nerve. The brain then understands the signal and we recognize the smell.

The brain does not control reflex actions, but it receives information after the action is done. Reflex actions are controlled by the spinal cord for a quick response.

Plant hormones are natural chemical substances made by plants that help in controlling and coordinating their growth, development, and responses to the environment. They are also called phytohormones.

Main types of plant hormones:

1. Auxins – Help in growth of stem and bending of plant toward light.
2. Gibberellins – Help in growth of stems, seed germination, and flowering.
3. Cytokinins – Help in cell division and growth of new leaves.
4. Abscisic acid – Stops growth and helps plant survive during stress (like lack of water).
5. Ethylene – Helps in ripening of fruits.

Sensitive plant movement is quick, temporary, due to touch, and does not involve growth.

Shoot movement is slow, permanent, due to light, and involves growth.

Auxins are plant hormones that help in the growth of stems, root development, and bending of plants towards light (phototropism). They play a key role in cell elongation and overall plant growth.

When a tendril (a thin, curling part of a climbing plant) touches a support, the cells on the side away from the support receive more auxin.
Auxins promote cell elongation, so the cells on the outer side grow faster than those on the side touching the support. This unequal growth causes the tendril to bend and curl around the support.

In animals, chemical coordination is carried out by hormones, which are chemical messengers. These hormones are produced by special glands called endocrine glands.
Hormones travel through the bloodstream to different parts of the body and control various functions like growth, metabolism, reproduction, mood, etc.

The use of iodised salt is advisable because iodine is essential for the proper functioning of the thyroid gland, which produces the hormone thyroxine. This hormone regulates the body’s metabolism.
A lack of iodine in the diet can cause a disease called goitre, where the thyroid gland in the neck becomes swollen.

When adrenaline is released into the blood (during fear, stress, or danger), it prepares our body to face the situation. This is called the "fight or flight" response.
The body shows the following changes:

1. The heart beats faster to send more oxygen to muscles.
2. Breathing becomes faster to take in more oxygen.
3. More energy is released by breaking down stored sugar.
4. Blood is sent more to muscles and less to skin and digestive system.

Some patients of diabetes are treated with insulin injections because their pancreas does not produce enough insulin or does not produce it at all.
Insulin is a hormone that helps control the level of sugar (glucose) in the blood. Without enough insulin, sugar builds up in the blood, which can be harmful.

Correct answer: (d) Cytokinin
Cytokinin is a plant hormone that helps in cell division and growth.

Correct answer: (b) Synapse
The synapse is the gap between two neurons where signals are passed using chemical messengers.

Correct answer: (d) All of the above
The brain controls thinking, heartbeat regulation, and body balance, so all the given functions are correct.

Function of receptors:
Receptors are specialized cells present in sense organs (like eyes, ears, skin, nose, and tongue). They detect different types of stimuli from the environment such as light, sound, smell, touch, and taste. These receptors send messages as electrical signals to the brain or spinal cord for processing and response.

If receptors do not work properly:

1. The body will not be able to sense changes in the environment.
2. It may not respond correctly to danger or other stimuli.
3. For example, if touch receptors in the skin are damaged, the person may not feel pain from a hot object and may get injured.

Phototropism is the growth of a plant in response to light. It happens because of a plant hormone called auxin. When light comes from one side, auxin moves to the shaded side of the plant. This causes the cells on that side to grow faster, making the plant bend towards the light.

In case of a spinal cord injury, the signals between the brain and the rest of the body will get disrupted. This includes:

1. Sensory signals(from body to brain) – such as touch, pain, and temperature.
2. Motor signals(from brain to body) – that control muscle movement and reflexes.

Chemical coordination in plants takes place with the help of plant hormones (also called phytohormones). These hormones are chemical messengers that control and coordinate various activities like growth, development, and responses to the environment.

Different hormones have different functions, such as:

1. Auxins – help in growth of stem and bending towards light
2. Gibberellins – help in seed germination and growth
3. Cytokinins – help in cell division
4. Abscisic acid – controls falling of leaves and closing of stomata
5. Ethylene – helps in ripening of fruits

All organisms need a system of control and coordination to:

1. Respond to changes in their surroundings (like light, sound, touch, temperature).
2. Carry out body functions in an organized way (like movement, digestion, breathing).
3. Maintain balance between different parts of the body.
4. Protect the body from harm through quick responses (like reflex actions).

Difference between Involuntary Actions and Reflex Actions:

Involuntary Actions:

1. These are actions that happen automatically without our control.
2. Controlled by the brain.
3. Example: Beating of the heart, breathing, digestion.
4. They are slow and continuous.

Reflex Actions:

1. These are quick and automatic responses to a stimulus.
2. Controlled by the spinal cord.
3. Example: Pulling hand away from a hot object.
4. They are sudden and protective.

The nervous system uses electrical impulses to send messages through nerves. It works very fast and controls actions like movement or reflexes. The response is usually short-term and controlled by the brain and spinal cord. For example, pulling your hand away from a hot object is controlled by the nervous system.

The hormonal system (also called the endocrine system) uses chemical messengers called hormones. These hormones are released by endocrine glands into the bloodstream and work slowly. The effects are usually long-lasting and can affect multiple organs. For example, insulin controls the sugar level in the blood.

Difference between movement in a sensitive plant and movement in our legs:

Movement in a sensitive plant (like Mimosa pudica):

1. This movement happens in response to touch (a stimulus).
2. It is a nastic movement (non-directional).
3. It does not involve muscles.
4. It is caused by changes in water pressure in plant cells.
5. It does not involve the brain or nerves.

Movement in our legs:

1. This is a voluntary movement, controlled by our brain.
2. It happens due to muscle contraction and relaxation.
3. It involves the nervous system and muscular system.
4. The movement is purposeful and directional.