NCERT Class 10 Science Solutions: Control and Coordination

Question:

Neurons are specialized cells that transmit information in the nervous system. They communicate with each other at junctions called synapses.


A synapse is the specialized junction between two neurons, or between a neuron and an effector cell (like a muscle or gland cell), where information is transmitted from one cell to the other. This gap is crucial for the transmission of nerve impulses.
A dendrite is a branched protoplasmic extension of a nerve cell that propagates the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.
An axon is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses known as action potentials away from the nerve cell body.
An impulse, or nerve impulse, is a signal transmitted along a nerve fiber.

Therefore, the gap between two neurons is called a synapse.

The final answer is $\boxed{B}$.

Question:

Plant hormones, also known as plant growth regulators, are chemical compounds produced in plants that control growth and development. Animal hormones are produced by endocrine glands and regulate various physiological processes in animals.


The question asks to identify a plant hormone from the given options.
Option A, Insulin, is a hormone produced by the pancreas in animals, regulating blood sugar levels.
Option B, Thyroxin, is a hormone produced by the thyroid gland in animals, regulating metabolism.
Option C, Oestrogen, is a sex hormone primarily produced in females in animals, responsible for reproductive development.
Option D, Cytokinin, is a class of plant hormones that promote cell division and differentiation, playing a crucial role in plant growth and development.
Therefore, Cytokinin is the only plant hormone among the given options.

Question:

The brain is the central organ of the nervous system responsible for a wide range of functions, including cognitive processes, physiological regulation, and motor control.


The brain is a complex organ with many different parts, each responsible for specific functions.
Thinking, learning, memory, and emotions are all cognitive functions controlled by the brain.
The brain also controls involuntary actions such as breathing and heart rate through the autonomic nervous system.
Maintaining balance and coordinating movements are crucial functions of the cerebellum, a part of the brain.
Therefore, the brain is responsible for all the listed activities: thinking, regulating heartbeat, and balancing the body.

The final answer is $\boxed{D}$.

Question:

Plant hormones, also known as plant growth regulators (PGRs), are chemical substances produced naturally in plants that control or influence developmental processes. Key plant hormones include auxins, gibberellins, cytokinins, abscisic acid, and ethylene. Understanding their roles is crucial for answering questions about plant growth and development.


There are several plant hormones, and the question asks for any two and their functions. Here are two common examples:

1. Auxin:
* Function 1: Promotes cell elongation, which is essential for plant growth, particularly in stems and roots.
* Function 2: Involved in phototropism (bending of plants towards light) and gravitropism (response of plants to gravity).
* Function 3: Plays a role in apical dominance, where the terminal bud inhibits the growth of lateral buds.

2. Gibberellin:
* Function 1: Promotes stem elongation by stimulating cell division and cell elongation.
* Function 2: Aids in seed germination by breaking dormancy and promoting the synthesis of enzymes needed to mobilize stored food.
* Function 3: Involved in flowering and fruit development.

Another valid pair could be:

1. Cytokinin:
* Function 1: Promotes cell division (cytokinesis).
* Function 2: Delays senescence (aging) in leaves.
* Function 3: Promotes lateral bud growth, often working in conjunction with auxins to control the balance of shoot and root development.

2. Abscisic Acid (ABA):
* Function 1: Inhibits growth.
* Function 2: Induces dormancy in seeds and buds.
* Function 3: Plays a crucial role in closing stomata during water stress to prevent excessive water loss.

Students can choose any two of these hormones and state at least one or two of their significant functions.

Question:

Nervous system, Brain, Spinal cord, Voluntary actions, Involuntary actions, Reflex actions, Stimulus, Response.


Involuntary actions and reflex actions are both automatic and do not require conscious thought, but they differ in their complexity and the parts of the nervous system involved.

Involuntary actions are bodily processes that occur without conscious control and are regulated by the autonomic nervous system. These are generally slower and more sustained than reflex actions. Examples include heartbeat, breathing, digestion, and blinking. While they are automatic, they can sometimes be influenced by conscious effort or external stimuli (e.g., holding your breath for a short while, or breathing faster when exercising). The brain, particularly the brainstem and hypothalamus, plays a significant role in regulating these actions.

Reflex actions, on the other hand, are rapid, automatic, and predictable responses to a specific stimulus. They are designed for immediate protection or to maintain bodily balance. Reflex actions typically involve a reflex arc, which is a neural pathway that bypasses the higher centers of the brain (like the cerebrum) and is primarily controlled by the spinal cord. This allows for a much faster response. Examples include withdrawing your hand from a hot object, the knee-jerk reflex, or coughing. While the spinal cord initiates the reflex, the signal also travels to the brain, so you become aware of the action after it has occurred.

In summary:
Involuntary actions are continuous, regulated processes controlled by the autonomic nervous system, involving higher brain centers to some extent.
Reflex actions are rapid, protective responses mediated by a reflex arc, primarily involving the spinal cord, with minimal or delayed involvement of higher brain centers.

Question:

Reflex action is a rapid, involuntary response to a stimulus. The brain’s role is not direct in the execution of a simple reflex arc, but it plays a crucial role in processing the information and initiating voluntary responses or learning from the reflex.


In a simple reflex action, the signal travels from the receptor to the spinal cord (or brainstem in some cases) via a sensory neuron. The spinal cord then processes the signal and sends a command through a motor neuron to the effector (muscle or gland), resulting in an immediate response. The brain is generally NOT involved in the rapid, automatic execution of this basic reflex arc. However, sensory information from the reflex action is relayed to the brain, allowing it to become aware of the event. The brain can then:

1. Process the information: It analyzes the sensory input and understands what happened.
2. Initiate voluntary response: Based on the reflex, the brain can decide to take further voluntary action. For example, if you touch something hot, the reflex pulls your hand away, but your brain then makes you decide to be more careful next time or to seek medical attention.
3. Learn and adapt: The brain stores the information about the stimulus and response, which can influence future behavior and learning. For instance, after a painful reflex, you learn to avoid that stimulus.
4. Higher-level control: In some more complex reflexes, the brainstem (a part of the brain) might be involved in processing, but for most simple reflexes, the spinal cord is the primary center.

Therefore, while the brain is not the direct controller of the rapid, involuntary action in a simple reflex, it plays a vital role in interpreting the event, enabling conscious awareness, and facilitating learned responses.

Question:

Chemical coordination in animals primarily relies on the endocrine system, which involves hormones produced by glands. These hormones travel through the bloodstream to target cells and organs, regulating various bodily functions.


Chemical coordination in animals is achieved through the action of chemical messengers called hormones. These hormones are produced and secreted by specialized glands, collectively known as endocrine glands. Examples of endocrine glands include the pituitary gland, thyroid gland, adrenal glands, pancreas, and gonads.

Once secreted, hormones are released directly into the bloodstream. The bloodstream acts as a transport system, carrying these hormones to specific target cells or organs throughout the body. Target cells have specific receptors on their surface or inside them that can bind to particular hormones. This binding is highly specific, much like a lock and key mechanism, ensuring that each hormone acts only on its intended targets.

Upon binding with their receptors, hormones trigger a specific response within the target cells. This response can be diverse, influencing a wide range of physiological processes. For instance, hormones regulate growth and development, metabolism, reproduction, mood, and the body’s response to stress or emergencies.

This system of chemical signaling through hormones allows for slow but widespread and long-lasting effects, coordinating complex bodily functions that are essential for maintaining homeostasis and adapting to changing environments. Unlike nervous coordination, which is rapid and localized, chemical coordination is a more gradual but pervasive process that ensures the synchronized functioning of different organ systems.

Question:

Reflex actions are involuntary, rapid, and automatic responses to stimuli, controlled by the spinal cord. Walking is a voluntary, coordinated action involving conscious thought and control from the brain.


The fundamental difference between a reflex action and walking lies in their control mechanisms, speed, and purpose.

Reflex Action:
– Involuntary: Not under conscious control. You don’t decide to pull your hand away from a hot object; it happens automatically.
– Rapid: Very quick to protect the body from harm.
– Simple Neural Pathway (Reflex Arc): Involves a sensory neuron, an interneuron (often in the spinal cord), and a motor neuron. The signal bypasses the brain for speed.
– Protective: Primarily serves to prevent injury or maintain homeostasis.
– Examples: Blinking, withdrawing your hand from a hot stove, knee-jerk reflex.

Walking:
– Voluntary: Requires conscious thought and decision-making. You decide when and where to walk.
– Coordinated: Involves complex sequences of muscle movements controlled by the brain (cerebellum for coordination, motor cortex for initiation).
– Complex Neural Pathway: Involves higher brain centers, basal ganglia, cerebellum, and spinal cord pathways.
– Locomotion and Exploration: Used for moving from one place to another, exploring the environment, and performing various tasks.
– Examples: Walking to school, walking across a room, walking for exercise.

Question:

Receptors are specialized cells or organs that detect stimuli from the environment or within the body. These stimuli can be physical (like light, sound, touch) or chemical (like taste, smell, hormones). When a stimulus is detected, receptors generate a signal that is transmitted to the nervous system for processing and response.


Receptors are the sensory units of our body. Their primary function is to detect specific types of stimuli. Think of them as the “eyes” and “ears” for different sensations. For example:
– Light receptors in our eyes detect light, allowing us to see.
– Sound receptors in our ears detect sound waves, enabling us to hear.
– Touch receptors in our skin detect pressure, temperature, and pain, helping us feel our surroundings.
– Chemical receptors in our nose and tongue detect molecules, giving us our sense of smell and taste.
– Internal receptors monitor things like blood pressure and glucose levels.
Once a stimulus is detected, the receptor converts this stimulus into an electrical or chemical signal. This signal is then passed along nerve pathways to the brain or spinal cord, where it is interpreted, leading to a specific response, which could be a conscious action or an unconscious bodily adjustment. In essence, receptors are crucial for us to perceive our environment, maintain homeostasis, and react to changes.

Question:

Auxins are plant hormones that promote cell elongation. Tendrils are modified plant structures that help in climbing. Phototropism and thigmotropism are plant responses to light and touch respectively.


When a tendril comes into contact with a support, auxins play a crucial role in its growth around it. Here’s how:

1. Differential Distribution of Auxins: The side of the tendril that is in contact with the support receives less light (if the plant is exposed to unidirectional light) or experiences a differential stimulus due to touch. This unevenness leads to a higher concentration of auxins accumulating on the side away from the support (the shaded or less-touched side).

2. Cell Elongation: Auxins promote cell elongation by increasing the elasticity of the cell wall and stimulating the uptake of water into the cells.

3. Growth Response: Since the side of the tendril with more auxin elongates more rapidly than the side with less auxin, the tendril bends towards the support. This differential growth causes the tendril to curl and twine around the support, securing the plant.

4. Thigmotropism: This coiling response is a form of thigmotropism, which is a plant’s growth movement in response to touch. The auxin-mediated differential growth is the mechanism behind this thigmotropic movement.

Question:

Iodine is an essential nutrient for the proper functioning of the thyroid gland. The thyroid gland produces hormones that regulate metabolism. Iodine deficiency can lead to various health problems, particularly affecting thyroid hormone production. Iodised salt is salt that has had a small amount of iodine added to it.


The use of iodised salt is advisable because iodine is crucial for the synthesis of thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3). These hormones play a vital role in regulating metabolism, growth, and development, especially brain development in children. A deficiency in iodine can lead to several health issues, collectively known as Iodine Deficiency Disorders (IDDs). The most common and visible manifestation of severe iodine deficiency is goitre, which is the enlargement of the thyroid gland. More significantly, iodine deficiency during pregnancy and early childhood can cause irreversible mental retardation and developmental delays. Iodised salt is a simple, cost-effective, and widely accessible way to ensure that the population receives an adequate intake of iodine, thereby preventing these preventable diseases and promoting overall public health.

Question:

Our sense of smell relies on olfactory receptors in our nose detecting airborne chemical molecules. When a substance is heated, it releases these molecules (vapors) which travel through the air and bind to these receptors, triggering a signal to the brain that we perceive as smell.


When an agarbatti is lit, its combustible material and the fragrant compounds within it undergo a chemical reaction called combustion. This heating process causes the volatile aromatic chemicals present in the agarbatti to vaporize. These vapors are released into the surrounding air. As we inhale, these airborne molecules enter our nasal cavity. Inside the nose, specialized cells called olfactory receptor neurons are present. These receptors have specific molecular structures that can bind to the agarbatti’s aromatic molecules. When the molecules bind to their corresponding receptors, it initiates a nerve impulse. This impulse is then transmitted through the olfactory nerve to the brain, specifically to the olfactory bulb, which processes the signal and allows us to perceive the characteristic smell of the agarbatti.

Question:

Hormones and their role in regulating blood sugar. Insulin’s function as a blood sugar lowering hormone. Diabetes mellitus as a condition of high blood sugar. Types of diabetes and their causes.


Diabetes mellitus is a chronic condition characterized by high blood glucose levels. This occurs when the body either doesn’t produce enough insulin or cannot effectively use the insulin it produces. Insulin is a hormone produced by the pancreas that helps glucose (sugar) from food move from the bloodstream into cells for energy. In some patients with diabetes, their pancreas doesn’t produce enough insulin (Type 1 diabetes) or their cells become resistant to the insulin that is produced (Type 2 diabetes, in some cases). When the body’s own insulin production is insufficient or ineffective, external insulin injections are given to supplement or replace the body’s natural insulin. This helps to lower blood glucose levels by enabling glucose to enter cells, thereby preventing the long-term complications associated with hyperglycemia (high blood sugar).

Question:

The neuron is the basic functional unit of the nervous system. Its primary role is to transmit information in the form of electrical and chemical signals. Key components include the cell body (soma), dendrites (receive signals), and axon (transmits signals).


The function of a neuron is to transmit information throughout the body. This is achieved through a process called nerve impulse transmission. When a neuron receives a stimulus, it generates an electrical signal called an action potential. This action potential travels down the axon to the axon terminal. At the axon terminal, the electrical signal is converted into a chemical signal, in the form of neurotransmitters. These neurotransmitters are released into the synapse, the gap between two neurons, and bind to receptors on the dendrites of the next neuron, thus passing the signal along. This allows for rapid communication between different parts of the body, enabling functions like thought, movement, and sensation.

Question:

The spinal cord acts as a crucial communication highway between the brain and the rest of the body. It transmits sensory information from the body to the brain and motor commands from the brain to the body.


A spinal cord injury disrupts the transmission of nerve signals. Sensory signals, which carry information about touch, pain, temperature, and body position from various parts of the body to the brain, will be unable to reach the brain if the injury is above the point of sensory input. Similarly, motor signals, which carry instructions from the brain to muscles to initiate movement, will be unable to reach the muscles below the level of the injury. This results in a loss of sensation and/or voluntary movement in the affected body parts. Depending on the location and severity of the injury, different types of signals and bodily functions can be disrupted.

Question:

Plant hormones, also known as plant growth regulators (PGRs), are chemical compounds produced in plants that regulate growth and development. There are five main classes of plant hormones: auxins, gibberellins, cytokinins, abscisic acid, and ethylene. Some of these hormones promote growth, while others inhibit it.


An example of a plant hormone that promotes growth is Auxin. Auxins are a group of hormones that play a crucial role in cell elongation and division, leading to increased plant growth. They are involved in processes such as root formation, bud development, and fruit development. Another example of a growth-promoting hormone is Gibberellin, which stimulates stem elongation, seed germination, and flowering. Cytokinins also promote cell division and differentiation, contributing to growth.

Question:

The central nervous system (CNS) is divided into the brain and spinal cord. The brain is further divided into three main parts: the cerebrum, cerebellum, and brainstem. Each part has specialized functions. Maintaining posture and equilibrium involves coordinating muscle movements and balance.


The cerebellum is the part of the brain that plays a crucial role in coordinating voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity. It receives information from sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements. Therefore, the cerebellum is responsible for maintaining posture and equilibrium of the body.