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

Page No. 105

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

• Reflex action is the involuntary action that occurs in response to stimuli. 
• They occur without the involvement of conscious areas of the brain. 
• All the reflex actions are unconscious. 
• Reflex action occurs brain and spinal cord of the central nervous systems. 
• This kind of response occurs within a fraction of a second.
  
• On the other hand, voluntary actions are those which occur under the control of the cerebellum of the brain. 
• Walking is learnt as we grow. Walking is controlled by the brain. This kind of response takes a longer time.

Q2: What happens at the synapse between two neurons?
Ans: A synapse is a tiny gap between the end of one neuron's axon and the dendrite of another neuron. It functions as a one-way valve for transmitting signals. Here’s how it works:

• The axon of the first neuron releases chemicals into the synapse.
• These chemicals cross the synapse and trigger an electrical impulse in the dendrite of the next neuron.
• This process ensures that signals travel in only one direction.

This mechanism is essential for the rapid transmission of nervous impulses throughout the body.

DendriteQ3: Which part of the brain maintains the posture and equilibrium of the body?
Ans: The cerebellum, located in the hindbrain, plays a crucial role in:

• Maintaining posture of the body.
• Ensuring equilibrium during movement.
• Coordinating voluntary actions for precision.

Without the cerebellum, activities like walking or riding a bicycle would be challenging.

Q4: How do we detect the smell of an agarbatti (incense stick)?
Ans: The thinking part of our brain is the forebrain. It has separate areas that are specialized for hearing, smelling, sight, taste, touch, etc. The fore-brain also has regions that collect information or impulses from various receptors. 

When the smell of an incense stick reaches us, our forebrain detects it. Then, the forebrain interprets it by putting it together with the information received from other receptors and also with the information already stored in the brain.

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

• The brain plays minimal role in reflex actions.
• Reflex actions are quick, involuntary responses to stimuli, occurring without conscious thought.
• They are primarily controlled by the spinal cord through a mechanism called the reflex arc.
• When a stimulus (e.g., touching something hot) is detected, it is sent through sensory nerves to the spinal cord.
• The spinal cord processes the information and sends an immediate response through motor nerves to the muscles, causing an automatic reaction (e.g., pulling the hand away).
• The brain is aware of the response, but does not directly control it.
• The brain processes the sensory information after the reflex action has occurred, which is why reflex actions are so quick — the brain's conscious involvement would take longer.
• In summary, the spinal cord is responsible for the quick response (reflex), while the brain only becomes aware of it after the response has already occurred.
• Reflex arcs are formed in the spinal cord, and the information (input) reaches the brain.
• The brain is only aware of the signal and the response that has taken place.
• The brain has no role to play in the creation of the response.

Page No. 108

Q1: What are plant hormones?
Ans: Plant hormones are the fluid that are secreted within the plant also known as phytohormones. Plant hormones regulate the growth and development of the plant. 
Examples of plant hormones include:

• Auxin - promotes cell elongation and growth.
• Gibberellins - stimulate stem growth.
• Cytokinins - encourage cell division.

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

Q3: Give an example of a plant hormone that promotes growth.
Ans: Auxin is an example of a growth-promoting plant hormone. Auxins are responsible for cell elongation in the shoot and accelerates growth.

Q4: How do auxins promote the growth of a tendril around a support?
Ans: Auxins are hormones produced at the shoot tip of plants. They play a crucial role in growth, particularly in tendrils. Here's how they work:

• When a tendril touches a support, auxins promote faster growth on the side away from the support.
• This uneven growth causes the tendril to coil around the support.
• The result is a structure that resembles a watch spring, allowing the plant to cling effectively.

Q5: Design an experiment to demonstrate hydrotropism.
Ans: To demonstrate hydrotropism in plants.
Procedure:

• Plant a seedling in a vessel containing soil.
• Adjacent to the seedling put a porous pot containing water.
• Leave thset-upup for few days.

Observation:
On examining the roots it is observed that the roots bend towards the source of water and do not grow straight.

Result:
It confirms that the plant shows hydrotropism as the roots bend towards the porous pot of water. As hydrotropism is a plant growth response in which the direction of growth is determined by a stimulus of a gradient in water concentration.

Experiment of Hydrotropism

Page No. 111

Q1: How does chemical coordination take place in animals?
Ans: Chemical coordination in animals occurs through hormones, which act as chemical messengers. These hormones are:

• Secreted by glands in the body.
• Responsible for regulating various physiological processes.

This process is part of the endocrine system, which works alongside the nervous system to control and coordinate bodily functions. Key points include:

• Hormones travel from one part of the body to another to exert their effects.
• A feedback mechanism helps regulate hormone action.

Q2: Why is the use of iodized salt advisable?
Ans: The use of iodized salt is important for several reasons:

• Iodine is essential for the thyroid gland to produce the hormone thyroxin.
• Thyroxin helps regulate the metabolism of carbohydrates, fats, and proteins in the body.
• A deficiency in iodine can lead to an enlarged thyroid gland, known as goitre.
• Goitre is often characterised by a swollen neck.

Therefore, incorporating iodized salt into our diet supports the normal functioning of the thyroid gland.

Q3: How does our body respond when adrenaline is secreted into the blood?
Ans: Adrenalineis a hormone released by the adrenal glands during times of danger or stress. When it enters the bloodstream, it triggers several responses in the body:

• Increased heart rate: This helps supply more oxygen to the muscles.
• Faster breathing: The diaphragm and rib muscles contract more, allowing for increased oxygen intake.
• Higher blood pressure: This ensures that blood reaches vital organs and muscles more efficiently.
• Blood diversion: Blood flow to the digestive system and skin decreases, redirecting it to the skeletal muscles.

These changes prepare the body to effectively respond to stress or emergencies.

Q4: Why are some patient of diabetes treated by giving injections of insulin?
Ans: Diabetes occurs when the pancreas does not produce enough insulin, a hormone that regulates blood sugar levels. This leads to high blood sugar levels, which can cause various health issues. Insulin injections are given to:

• Help convert excess sugar in the blood into glycogen.
• Control and lower blood sugar levels effectively.
• Prevent complications associated with diabetes.

Page No. 112

Exercises 

Q2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Ans: (b) Synapse
The gap between two neurons is called a synapse. At the synapse, chemicals are released that help transmit signals to the next neuron.

Q3. The brain is responsible for
(a) thinking.
(b) regulating the heartbeat.
(c) balancing the body.
(d) all of the above.
Ans: (d) all of the above
The brain is responsible for thinking, regulating the heartbeat and balancing the body.

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?
Ans: Receptors are sensory structures (organs/tissues or cells) present all over the body. The receptors are either grouped in the case of the eye or ear or scattered in the case of the skin.
Functions of receptors:

• They sense external stimuli such as heat or pain.
• They also trigger an impulse in the sensory neuron which sends a message to the spinal cord.

When receptors do not function properly, various problems can arise, including:

• Inability to feel pain, leading to injuries.
• Difficulty in sensing temperature changes, risking burns or frostbite.
• Impaired senses, such as taste and smell, affecting nutrition and safety.

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

Structure of Neuron

Functions of the three parts of a neuron:

• Axon: It conducts messages away from the cell body.
  
• Dendrite: It receives information from the axon of another cell and conducts the messages towards the cell body.
  
• Cell body: It contains a nucleus, mitochondria, and other organelles. It is mainly concerned with maintenance and growth.

Q6. How does phototropism occur in plants?
Ans: The growth movement in plants in response to light stimulus is known as phototropism. The shoots show positive phototropism and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source.