NCERT Solutions for Class 10 Science Chapter 7

Endocrine glands or ductless glands produce hormones and directly pour their secretion in the blood. These glands do not go on producing hormones. Their secretion is controlled by feedback information system. Thus their over production of hormones is controlled.
For example, a hormone called TSH is secreted by pituitary gland. TSH stimulates the production of thyroxine from the thyroid gland. But if there is over production of thyroxine hormone, this hormone acts on pituitary gland and controls the production of TSH. As a result, the production of thyroxine by the thyroid gland is controlled. Thus, TSH and thyroxine control the level of each other. This mechanism of opposing effect is called feedback mechanism.

Sensory neurons carry sensory impulse from receptors to the nerve cell body or to the region which receives sensory impulses. Whereas motor neurons carry information of action to be carried by the conserved voluntary muscles.

Human brain is lodged in a bony case, the cranium which protects it from injuries. It is wrapped in three sheets of connective tissue, known as meninges. The space between the meninges is filled with cerebrospinal fluid which helps in absorption of shocks.

Fore-brain is responsible for precision of voluntary action.
Cerebellum is responsible for maintaining the posture and keeping balance of the body.

Reflex actions are controlled by spinal cord, although the information input also goes on to reach the brain. However, conditioned reflexes (based on previous experiences), such as salivation after seeing good food are controlled by cerebral cortex of brain.

Adrenaline causes the heart beat faster, resulting in supply of more oxygen. It causes reduction in supply of blood to the digestive system and skin. This diverts the blood to our skeletal muscle. The breathing rate also increases. All these responses together help an athlete to prepare for running.

The directional (tropic) response of plants shown by the plants towards or away of the stimulus such as light, water, gravity, etc. is known as tropism.
Tropic movements in plants are growth related. Plants respond to stimuli slowly by growing in a particular direction, either towards stimulus or away from. This growth causing tropic movement is regulated by the plant hormone called auxin.

Receptors are sensory structures (organs/tissues or cells) present all over the body. The receptors are either grouped in case of eye or ear, or scattered in case of skin. Functions of receptors: They sense the external stimuli such as heat or pain. They also trigger an impulse in the sensory neuron which sends message to the spinal cord. When the receptors are damaged, the external stimuli transferring signals to the brain are not felt. For example, in the case of damaged receptors, if we accidentally touch any hot object, then our hands might get burnt as damaged receptors cannot perceive the external stimuli of heat and pain.

The movement of plant in response to light is called phototropism. Stem shows positive phototropism as follows: When growing plants detect light, a hormone called auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

The reflex arc connections between the input and output nerves meet in a bundle in the spinal cord. In fact, nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. In case of any injury to the spinal cord, the signals coming from the nerves as well as the signals coming to the receptors will be disrupted.

Plants respond to stimuli by showing movements. The growth, development, and responses to the environment in plants is controlled and coordinated by a special class of chemical substances known as hormones. These hormones are produced in one part of the plant body and are translocated to other needy parts. For example, a hormone produced in roots is translocated to other parts when required. The five major types of phytohormone are auxins, gibberellins, cytokinins, abscisic acid, and ethylene. These phytohormones are either growth promoters (such as auxins, gibberellins, cytokinins, and ethylene) or growth inhibitors such as abscisic acid.

The maintenance of the body functions in response to changes in the body by working together of various integrated body systems is known as coordination. All the movements that occur in response to stimuli are carefully coordinated and controlled. In animals, the control and coordination movements are provided by nervous and muscular systems. The nervous system sends messages to and away from the brain. The spinal cord plays an important role in the relay of messages. In the absence of this system of control and coordination, our body will not be able to function properly. For example, when we accidentally touch a hot utensil, we immediately withdraw our hand. In the absence of nerve transmission, we will not withdraw our hand and may get burnt.

Involuntary actions cannot be consciously controlled. For example, we cannot consciously control the movement of food in the alimentary canal or pumping of blood through heart. These actions are however directly under the control of the brain. On the other hand, the reflex actions such as closing of eyes immediately when bright light is focused show sudden response and do not involve any thinking. This means that unlike involuntary actions, the reflex actions are not under the control of brain.

A reflex action is a rapid, automatic response to a stimulus. It does not involve any thinking. For example, we close our eyes immediately when the bright light is focused. Walking, on the other hand, is a voluntary action. It is under our conscious control.

Cerebellum, a part of hindbrain is responsible for maintaining posture and equilibrium of the body.

Reflex actions are sudden responses, which do not involve any thinking. For example, when we touch a hot object, we withdraw our hand immediately without thinking as thinking may take time which would be enough to get us burnt. The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves (input) and responding to it quickly (output) is called a reflex arc. The reflex arcs –connections present between the input and output nerves − meet in a bundle in the spinal cord. 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. However, the brain has no role to play in the creation of the response.

Plant hormones or phytohormones arenaturally-occurring organic substances. These are synthesized in one part of the plant body (in minute quantities) and are translocated to other parts when required. The five major types of phytohormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene. Gibberellins help in the growth of the stem. Auxins help in the growth of the stem. Cytokinins promote cell division. Abscisic acid is one example of a hormone which inhibits growth.

These tendrils are sensitive to touch. When they come in contact with any support, auxin (a growth hormone) diffuses from the part of the tendril in contact with the object to other side, which is not in the contact. Therefore the part of the tendril in the contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.

Chemical coordination takes place in animals with the help of hormones. Hormone is the chemical messenger that regulates the physiological processes in living organisms. It is secreted by glands. The regulation of physiological processes and control and coordination by hormones comes under the endocrine system. The nervous system along with the endocrine system in our body controls and coordinates the physiological processes.

Adrenalin is a hormone secreted by the adrenal glands in case of any danger or emergency or any kinds of stress. It is secreted directly into the blood and is transported to different parts of the body. When secreted in large amounts, it speeds up the heartbeat and hence supplies more oxygen to the muscles. The breathing rate also increases due to contractions of diaphragm and rib muscles. It also increases the blood pressure. All these responses enable the body to deal with any stress or emergency.

Diabetes is a disease in which the level of sugar in the blood is too high. Insulin, a hormone secreted by the pancreas, helps in regulating the blood sugar levels. This is the reason why diabetic patients are treated by giving injections of insulin.