Exercise : Solution of Questions on page Number : 92
Plant hormones are chemical substances which bring about the control and coordination in plants.
Abscisic acid is responsible for the wilting and falling of leaves.
Auxin is a plant hormone which makes a stem (or shoot) bend towards light sources.
Auxin hormone is made in the cells of the tip of a plant stem.
The scientific name of sensitive plant is Mimosa pudica.
Auxin is a plant hormone that promotes growth in plants and abscisic is a plant hormone that inhibits growth.
Thigmonasty is the movement of plant, especially prevalent in sensitive plants, which is very quick and can be observed easily. If we touch the leaflets of a sensitive plant, they fold up and droop immediately.
Plant hormones are the chemical substances that control growth in plants. Auxin, gibberelins, cytokinins and abscisic acid are examples of plant hormones.
The stimulus in
(a) Phototropism: Light
(b) Geotropism: Gravity
(c) Chemotropism: Chemicals
(d) Hydrotropism: Water
(e) Thigmotropism: Touch
The folding of leaves in sensitive plants is an example of the movement of a plant parts. It is caused by loss of water (or migration of water).
(a) Roots are positively hydrotropic as well as positively geotropic.
(b) Shoots are positively phototropic but negatively geotropic.
Neither of them are growth movements. They are nastic movements.
(a) This is a thigmonastic movement.
(b) This is a photonastic movement.
(a) Roots bend in the direction of gravity but away from the light.
(b) Shoots bend towards the light but away from the force of gravity.
(a) Roots of a plant respond to gravity.
(b) Shoots of a plant respond to light.
(a) A plant’s response to light is called phototropism.
(b) A plant’s response to gravity is called geotropism.
(c) Plant shoot grows upward in response to light.
(d) Plant roots grow downward in response to gravity.
(e) Tendrils wind around a support in response to touch.
(f) Plant roots grow downwards and in the direction of the force of gravity.
(g) The root of a plant grows downward. This is known as geotropism.
(h) Auxin is the hormone that causes phototropism in plants.
(i) The response of leaves to sunlight is called phototropism.
(a) Phototropism depends on growth. It is the growth of plant stem in response to sunlight.
(b) Thigmonasty does not depend on growth. It is a non directional movement of plant part, such as leaves, in response to touch.
The chemicals that perform the function of control and coordination in plants are called plant hormones.
The four plant hormones and their functions are as follows:
1) Auxin: It promotes cell enlargement and cell differentiation in plants.
2) Gibberelins: It breaks the dormancy in seeds and buds.
3) Cytokinins: It promotes cell division in plants.
4) Abscisic acid: It promotes closing of stomata.
(a) The roots of a plant always grow downwards in response to gravity. This phenomenon is known as geotropism.
(b) The stem of a plant grows upwards in response to light. This phenomenon is known as phototropism.
(a) Stem always grows up and away from the pull of gravity. This phenomenon is known as negative geotropism.
(b) Root always grows downwards and away from light. This phenomenon is known as negative phototropism.
(a) Mimosa pudica folds its leaves and droops almost immediately in response to touch. This phenomenon is known as thigmonasty.
(i) A dandelion flower opens up during the day. (ii) It closes in the night.
This phenomenon is known as photonasty.
(a) A plant root always moves towards water. This phenomenon is known as positive hydrotropism.
(b) (i) Petals of a moonflower close during the day. (ii) They open during the night.
This phenomenon is known as photonasty.
Tendril is a thin thread-like growth on the stems or leaves of a climbing plant.
The two types of tendrils are stem tendrils and leaf tendrils.
Tendrils grow towards a support in response to their touch. This phenomenon is known as thigmotropism.
The five types of tropisms are phototropism, thigmotropism, geotropism, hydrotropism and chemotropism.
Tropic movements are helpful in the growth of plants.
Phototropism is an example of tropic movements. The stems of plants respond to sunlight by growing towards it. The plants also turn their leaves to face the sun. This enables their leaves to get as much sunlight as possible that is required for photosynthesis.
The growth of plant parts in response to chemical stimulus is known as chemotropism.
The growth of a pollen tube towards the ovule induced by a sugary stimulus is an example of chemotropism. This is an example of positive chemotropism as the pollen tube grows towards the stimulus.
|Tropic movements||Nastic movements|
|These are directional movements of plants in response to stimulus.||These are non-directional movements of plants in response to stimulus.|
|Example: The upward growth of a plant stem in response to sunlight.||Example: The folding up of leaves in response to touch.|
|It is the non-directional movement in plants in response to light.||It is the non-directional movement in plants in response to touch.|
Exercise : Solution of Questions on page Number :94
(a) Figure 2 shows the correct position taken by the parts A and B of a plant.
(b) Geotropism is the phenomenon which is exhibited in this figure. Roots of a plant show positive geotropism, whereas stems show negative geotropism.
(a) Abscisic acid
(d) Abscisic acid
The folding up of leaves in a sensitive plant on touching is not a tropism because it is a non-directional movement. Tropism is a directional movement where the direction of the movement of the plant part is towards the stimulus.
The closing of a dandelion flower at dusk is not a tropism because it is a non-directional movement in response to the intensity of light. On the contrary, tropic movement is the movement of plant parts towards the light. It does not depend upon the intensity of light.
(a) The growth movement of plant parts in which the direction of the stimulus determines the direction of the response is known as tropisms.Example: Phototropism, where the stems of plants grow upwards in response to sunlight. (b) The different types of tropisms are: (i) Phototropism: The movement of plant parts in response to light is known as phototropism. The stimulus is light. (ii) Geotropism: The movement of plant parts in response to gravity is known as geotropism. The stimulus is gravity. (iii) Hydrotropism: The movement of plant parts in response to water is known as hydrotropism. The stimulus is water.(iv) Chemotropism: The movement of plant parts in response to chemicals is known as chemotropism. The stimulus is chemicals.(v) Thigmotropism: The movement of plant parts in response to touch is known as thigmotropism. The stimulus is touch.
|Tropisms are the directional movement of plant parts in response to an external stimulus.||Nasties are the non-directional movements of plant parts in response to an external stimulus.|
(a) The growth of plant parts in response to light is known as phototropism. An example of phototropism is the growth of plant stem in the upward direction in response to sunlight.
(b) The stems of plants grow towards sunlight showing positive phototropism.
(c) The movement of p￼lant parts towards the light source is known as positive phototropism, whereas the movement of plant parts away from light is known as negative phototropism.
The stems of plants show positive phototropism as they grow upwards. The roots of plants show negative phototropism as they grow downwards into the soil.
(a) The movement of plant parts in response to gravity is known as geotropism. The growth of plant roots is an example of geotropism.
(b) If the movement of the plant parts is towards the pull of gravity, it is known as positive geotropism; whereas if the movement of the plant parts is in the direction opposite to the pull of gravity, it is known as negative geotropism.
The movement of roots towards the soil is an example of positive geotropism, whereas the movement of plant stem away from the soil in the upward direction is an example of negative geotropism.
(c) Tendrils or climbing organs of a plant exhibit positive thigmotropism.
(a) Control and coordination occur in plants with the help of hormones.
It differs from animals because animals have nervous system which is absent in plants.
(b) The five types of stimuli and the tropisms produced by each of them are:
1. Light produces phototropism
2.Water produces hydrotropism
3. Touch produces thigmotropism
4.Chemicals produce chemotropism
5.Gravity produces geotropism
(c) The movement of plant parts in response to water is known as hydrotropism.
An example of hydrotropism is the movement of plant roots towards water. It is a positive hydrotropism because the roots move towards the stimulus.
(a) If the movement of the response is towards the stimulus, it is known as positive tropism; whereas if the movement of the response is in the direction opposite to the stimulus, it is is known as negative tropism.The movement of roots towards the pull of gravity is an example of positive geotropism, whereas the movement of plant stem in the direction opposite to the pull of gravity is an example of negative geotropism.
(b) The directional movement of plant parts in response to touch is known as thigmotropism. The movement of tendrils of climbing plants towards the things they happen to touch is an example of thigmotropism.
|It is a directional movement of plant parts in response to touch.||It is a non-directional movement of plant parts in response to touch.|
|Example: Bitter gourd||Example: Mimosa pudica|
(b) ascorbic acid
Ascorbic acid is the chemical name of vitamin C and it is not a plant hormone.
Auxin is responsible for the phenomenon of phototropism in plants.
The movement of plant parts in response to the force of gravity is called geotropism.
Exercise : Solution of Questions on page Number : 95
It is a non-directional movement of plant parts in response to light.
Plant stem grows upward opposite to the force of gravity. Hence, it exhibits negative geotropism.
(d) light and gravity
It is because a plant stem grows towards the light in the upward direction against the force of gravity.
(b) closing up of leaves of a sensitive plant on touching with an object
This is a non-directional movement of a plant in response to touch.
(b) (ii) and (iii)
The root of a plant is positively geotropic, negatively phototropic and positively hydrotropic.
(c) inhibit growth
Abscisic acid mainly functions as a growth inhibitor.
(d) rapid cell division and elongation in tendril cells in contact with the support
The growth of tendrils in pea plants is due to the rapid cell division and elongation in tendril cells in contact with the support.
(b) Abscisic acid
Abscisic acid inhibits growth in plants.
(c) abscisic acid
Abscisic acid causes abscission, i.e., falling of leaves and fruits from the plant body.
Hydro means water and tropism means movement. Thus, the movement of plant roots towards the moisture in the soil is called hydrotropism.
The growth of pollen tubes towards the ovule caused by a sugary substance is an example of chemotropism.
Photo means light and tropism means movement. The bending of plant shoots in response to light is called phototropism.
The stimulus in thigmotropism is touch which causes movement.
The bending of the top part of the seedling towards the burning candle is an example of phototropism.
(b) Hydrogen oxide
Water or hydrogen oxide acts as a stimulus in the process of hydrotropism.
The growth movement of a plant part in response to the touch of an object is called thigmotropism.
Exercise : Solution of Questions on page Number :96
This is an example of thigmotropism.
Auxin decreases the growth rate of plant roots.
The leaves of a Mimosa pudica plant show response to touch. This is an example of thigmotropism.
The response of dandelion flowers to light that involves the movement of the petals is an example of photonasty.
Roots do not respond to touch.
The rolling up of plant leaves on touching is a thigmonastic movement and it is not related to growth.
The plant hormone auxin is responsible for negative phototropism in roots.
(a) abscisic acid
Abscisic acid inhibit plant growth.
The movement of plant shoots towards the light is an example of phototropism (photo = light; tropism = movement).
Auxin causes phototropism, i.e., bending of plant stems towards the source of light.
Roots bend away from the light source and show negative phototropism.
(d) (ii) and (iv)
The folding up of leaves in sensitive plant as a response to touch and the opening up of leaves of a daisy flower in response to light are nastic movements.
(a) The chemical substance P is auxin.
(b) Auxin remains on the shaded side of the stem.
(c) Auxin increases the growth rate of shoots and decreases the growth rate of roots.
(d) Process Q is positive phototropism, whereas R is negative phototropism.
(e) The general name of chemical substances like auxin (P) is phytohormone. Cytokinins, gibberellins and abscisic acid are other examples of phytohormones.
(a) The part X is the root.
(b) The part Y is the shoot.
(c) The part X (root) will exhibit positive hydrotropism.
(d) The part Y (shoot) could have tendrils on it.
(e) The phytohormone, auxin causes the root to exhibit negative phototropism.
Exercise : Solution of Questions on page Number :97
(a) The phenomenon shown by the flowers of plants A and B is photonasty.
(b) A flower which behaves like the flower of (i) plant A is dandelion and (ii) plant B is moonflower.
(c) The leaves of plant C exhibit thigmonasty.
(d) A plant whose leaves behave like those of plant C is Mimosa pudica.
(e) The plants A and B exhibit the phenomenon based on growth movements.
(a) The stimulus A is water.
(b) The stimulus B is gravity.
(c) The stimulus C is light.
(d) The two stimuli responsible for the straight growth of the branches of a fallen tree are B and C, i.e., gravity and light, respectively.
(a) (i) R is a leaf tendril and (ii) S is a stem tendril.
(b) The growth movement exhibited by R and S is thigmotropism.
(c) The stimulus involved is touch or contact with other objects.
(d) The behaviour of R and S is a tropic movement.
(e) Pea plant is an example of plant type P, whereas bitter gourd plant is an example of the type Q.
(a) (i) X is the carpel and (ii) Y is the stamen.
(b) (i) A is the stigma, (ii) B is the style and (iii) C is the ovary of the flask-shaped organ.
(c) (i) D is the pollen and (ii) E is the anther.
(d) F is the pollen tube.
(e) The phenomenon of growing a long tube in response to a sugary substance in the process of fertilisation in a flower is known as chemotropism.
P is abscisic acid because it is antagonistic to growth and inhibits it.
Q is auxin because it causes bending of shoots towards the light.
R is gibberellins because it increases the cell division in a plant shoot and increases its length.
S is cytokinin because it breaks the dormancy of buds and seeds.
(a) The phenomenon exhibited by the positions of plant parts A and B is geotropism.
(b) The stimulus which causes plant part A to grow and bend upwards and part B to bend downwards is gravity.
Exercise : Solution of Questions on page Number :98
(a) Both the processes are similar as the response is not determined by the direction of the stimulus. They are nastic movement.
(b) The first process of folding up of leaf is thigmonastic and the stimulus is touch. The second process of closing of petals is photonastic and the stimulus is light.
Exercise : Solution of Questions on page Number :115
The two systems of control and coordination in higher animals are the nervous system and the endocrine system.
The two parts of the vertebrate nervous system are the central nervous system and the peripheral nervous system.
After touching a hot object unknowingly, the hand is automatically pulled back at once. This type of action is known as a reflex action.
The three components of a neuron (or a nerve cell) are the cell body, the dendrites and the axon.
(a) The short fibres of a neuron are known as the dendrites.
(b) The long fibre of a neuron is known as the axon.
The cerebrum (forebrain) is the most important part of the human brain.
The cerebellum of the brain maintains posture and balance of the body.
The pons participate in regulating respiration. The cerebellum helps in maintaining balance and posture of the body.
Growth hormone in humans is secreted by the pituitary gland.
The hormones in the human body are made in specialised tissues called the endocrine glands.
The system of glands that produces hormones is called the endocrine system or the hormonal system.
The pituitary gland secretes the growth hormone.
(a) The testes secrete testosterone.
(b) The ovaries secrete oestrogen and progesterone.
(a) Photoreceptor: receptors for light
(b) Thermoreceptor: receptors for heat
(c) Phonoreceptor: receptors for sound
(d) Olfactory receptors: receptors for smell
(e) Gustatory receptors: receptors for taste
Diabetes is caused by the deficiency of a hormone known as insulin.
Goitre is caused by the deficiency of thyroxine in the body.
The thyroid gland requires iodine to make thyroxine hormone.
Diabetes is caused by high sugar level in blood. Diabetic patients are treated by giving injections of insulin as it lowers the blood sugar level by controlling the metabolism of sugar.
Feedback mechanism is the in-built arrangement in our body that controls the timing and amount of hormones released by various endocrine glands.
(a) An endocrine gland is a ductless gland. For example, thyroid is an endocrine gland.
(b) An exocrine gland is a gland that has a duct. Example: salivary gland.
(c) Pancreas acts both as an endocrine gland and an exocrine gland.
Iodine is necessary in our diet for the proper functioning of the thyroid gland. Lack of iodine in our diet can cause a deficiency of thyroxine hormone.
Diabetes is characterised by large quantities of sugar in the urine of a person. Deficiency of insulin hormone causes diabetes.
The nose and the tongue contain receptors of chemical stimuli.
The retina of an eye contains light-sensitive cells.
The nervous system and the endocrine system are the two main communication systems in an animal body.
(a) Thyroid, pituitary, thymus and ovary are types of ductless glands.
(b) Adrenalin, insulin, thyroxine and estrogen are types of hormones.
The central nervous system consists of the brain and the spinal cord.
Coughing, yawning and blinking of eyes are examples of reflex actions.
Iodine is needed in our diet because it helps the thyroid gland in making thyroxine hormone.
Reflex actions are those actions which we do without thinking to protect ourselves. Coughing is a reflex action as it clears our windpipe.
(a) The two examples of effectors are muscles and glands.
(b) Our nervous system allows us to react to our surroundings. Information from receptors passes along the sensory neurons to our brain. Our brain sends impulses along the motor neurons to our muscles.
(c) A neuron which carries an impulse to the brain is called a sensory neuron.
(d) A neuron that carries a message for action to a muscle or a gland is known as a motor neuron.
Exercise : Solution of Questions on page Number :116
(a) There are five sense organs in our body. They are the eyes, the ears, the nose, the tongue and the skin.
(b) A receptor is a cell present in the sense organs that is sensitive to specific stimuli.
Example: The eyes have light receptors which can detect light and the ears have sound receptors which can detect sound.
An effector is a part of body which can respond to a stimulus according to the instructions given from the nervous system.
Example: Muscles and glands of the human body.
(a) The spinal cord is a part of the central nervous system. It is a cylindrical structure enclosed by a bony cage called the vertebral column. It is responsible for spinal reflex actions and the conduction of nerve impulses to and from the brain.
(b) The medulla controls various involuntary actions such as the heart beat, breathing, blood pressure and peristaltic movements of the alimentary canal.
(a) The three types of nerves which make up the peripheral nervous system are the spinal nerves, the cranial nerves and the visceral nerves.
|A reflex action is an involuntary action that is a rapid and automatic response to stimuli.||Walking is a voluntary action that requires our thinking and is in our control.|
(c) When the smell of the incense stick reaches our nose, the olfactory receptors present in our nose detect it and send this information to our brain in the form of electrical signals. The brain interprets this information as the smell of incense stick where it has been already stored.
(a) The endocrine glands secrete chemical substances called hormones.
(b) Receptors receive stimuli from the surrounding environment and send the messages conveyed by them to the spinal cord and the brain as electrical impulses through the sensory nerves. On the other hand, effectors respond to stimuli according to the instructions sent from the nervous system.
(b) The functions of testosterone hormone is to control the development of male sex organs and male characters such as deepening of voice, moustache, beard and other body hair.
The functions of oestrogen hormone is to control the development of female sex organs and female characters such as feminine voice and soft skin.
a) The hindbrain has three regions: the pons, the cerebellum and the medulla.
The pons take part in regulating the respiration.
The cerebellum helps in maintaining posture and balance of the body.
The medulla controls various involuntary actions such as the heart beat, breathing, blood pressure and peristaltic movements of the alimentary canal.
(b) The cerebrum is the logical part of the brain. It is the site of our faculties such as learning, reasoning, intelligence, personality and memory. All of our thoughts, sensations, actions and movements are controlled by the cerebrum.
(a) The human brain can be broadly divided into three regions: the forebrain, the midbrain and the hindbrain.
(b) The cranium is a bony box in the skull which protects the brain.
(a) Chemical coordination takes place through hormones in human beings. Hormones instruct the brain when to pace up or slow down a particular function.
(b) Iodised salt contains iodine which is essential for making thyroxine by the thyroid gland.
The function of insulin hormone is to lower the blood sugar level. Insulin controls the metabolism of sugar. Deficiency of insulin causes diabetes. Diabetic patients are treated by giving injections of insulin.
|Nervous system||Endocrine system|
|Made of neurons.||Made of secretory cells called glands.|
|Messages are transmitted in the form of electric impulses.||Messages are transmitted in the form of chemicals called hormones.|
|Messages are transmitted along nerve fibres.||Messages are transmitted through the bloodstream.|
(a) The function of thyroxine hormone is to control the rate of metabolism of carbohydrates, fats and proteins in the body.
(b) The function of adrenaline hormone is to regulate heart beat, breathing rate, blood pressure and carbohydrate metabolism.
(c) The function of growth hormone is to control the development of bones and muscles.
The major endocrine glands present in the human body are the pineal gland, hypothalamus gland, pituitary gland, thyroid gland, parathyroid glands, thymus, pancreas, adrenal glands, testes in males and ovaries in females.
The pancreas, testes and ovary also function as exocrine glands.
(i) Thyroxine (d) Controls the metabolic rate
(ii) Adrenaline (c) Prepares the body for an emergency
(iii) Insulin (e) Regulates the amount of sugar in blood
(iv) Estrogen (a) Causes breasts to develop in females
(v) Testosterone (b) Causes the males to start producing sperms
It is an example of a reflex action. The stimulus in this example is pain which is felt by the foot on touching the drawing pin. This pain is sensed by a receptor in the foot. The receptor triggers an impulse to a sensory neuron which transmits the message to the spinal cord. Here, the impulse is passed on to a relay neuron which, in turn, passes it to a motor neuron. The motor neuron passes the impulse to a muscle in the foot. The muscle, then, contracts and pulls the foot away from the drawing pin.
Puberty and adolescence are results of the activities of testosterone in males and oestrogen in females. In males during puberty, testosterone secretion is increased resulting in the development of male sex organs and male characters such as deeper voice, moustache, beard and more body hair.
Similarly, in females, oestrogen secretion is increased at the time of puberty resulting in the development of female sex organs and female characters such as feminine voice, soft skin and mammary glands.
Neurons are similar to other cells in the following manners:
(a) Both consist of cytoplasm
(b) Both contain nuclei
(c) Both are bounded by cell membranes
|A receptor is a cell (or a group of cells) present in a sense organ which is sensitive to a particular types of stimuli such as light, sound, smell, taste, heat and pressure.||An effector is a part of the body which can respond to a stimulus according to the instructions sent from the nervous system.|
|Eyes have light receptors; ears have sound receptors, etc.||Muscles and glands are examples of effectors.|
|The cerebrum is a part of the forebrain.||The cerebellum is a part of the hindbrain.|
|It is the site of our faculties such as learning, reasoning, intelligence, personality and memory.||It helps in maintaining posture and balance of the body. It also enables us to make precise and accurate movements.|
|Voluntary action||Involuntary action|
|A voluntary action is under the control of one’s will.||An involuntary action is not under the control of one’s will.|
Digestion is an involuntary action as it occurs inside our body without our conscious choice.
CNS stands for Central Nervous System.
(a) The cerebrum consists of two cerebral hemispheres.
(b) The spinal cord has spinal nerves attached to it.
(a) Adrenaline prepares the body for action.
(b) Insulin controls the amount of glucose in blood.
(c) Testosterone gives boys a deep voice.
(d) Oestrogen gives girls soft skin.
Exercise : Solution of Questions on page Number :117
(a) The smell of food is a stimulus.
(b) Olfactory receptors present in our nasal passage perceive the smell.
(c) Salivary gland (effector) is stimulated to secrete saliva.
(a) A neuron is the structural and functional unit of the nervous system.
(b) Classification of the nervous system into various parts:
(c) Autonomic nervous system is the part of nervous system that controls and regulates the functions of internal organs of the body by its own.
Its main function is to control and regulate involuntary body functions like heartbeat, blood flow, breathing and digestion.
(d) Voluntary nervous system is the part of the nervous system that is responsible for carrying motor and sensory information both to and from the central nervous system (CNS). It is associated with voluntary control of body movements through the actions of skeletal muscles. It is also responsible for sensing external stimuli, which helps the body to remain in touch with its surroundings.
For example, when the skin is penetrated by a sharp object like a pin, the pain is detected by the pain receptor. The nerve impulses are generated in the sensory nerves and conducted to the brain. The brain sends instructions to the skeletal muscles (effector muscle) through the motor nerves to remove the pin. Then the muscle acts accordingly and removes the pin.
(a) Reflex action is a rapid and automatic response to a stimulus. It is not under the voluntary control of the brain. For example, if we unknowingly touch a hot plate, we immediately move our hand away from it.
(b) The path travelled by an impulse during a reflex action is called a reflex arc.
Spinal reflex arc:
|Involuntary actions||Reflex actions|
|These are normal involuntary actions of internal or external organs of the body.||These are sudden involuntary responses to external stimuli.|
(a) The function of the nervous system is to coordinate the activities of our body. The nervous system helps all the other systems of our body to work together.
(b) The main organs of the human nervous system are the brain, the spinal cord and the nerves.
Human nervous system:
(c) When the sense organs such as eyes, ears, nose, tongue or skin are affected in our body, they send message to the brain in the form of electrical impulses through the sensory neurons. The brain analyses this message and decides the action to be taken. The brain, then, sends out instructions to the muscles of the concerned body part through the motor neurons. The concerned body part, then, acts according to the instructions sent by the brain.
(a) A neuron is a structural and functional unit of the nervous system. A neuron or nerve cell has three components: the cell body, the dendrites and the axon.
Diagram of a neuron:
(b) Synapses are microscopic gaps present in between pairs of adjacent neurons over which nerve impulses pass from one neuron to the next.
A nerve impulse, on reaching the terminal end of an axon, releases chemicals called neurotransmitters at its tip. These chemicals cross the synapse and start the impulse in the next neuron or to an effector organ.
A receptor in a sense organ is in touch with the dendrites of the sensory neuron. When a stimulus acts on the receptor, a chemical reaction is initiated that produces an electrical impulse in the receptor. This impulse travels from the dendrites of the sensory neuron (say A) to its cell body and, then, along its axon. At the end of the axon of the sensory neuron A, the electrical impulse releases chemical substances called neurotransmitters into the synapse which cross the synapse and start a similar electrical impulse in the dendrites of the next neuron (say B). From the dendrites, this electrical impulse is carried to the cell body and, then, to the axon of the second neuron.
(a) The nervous system and the endocrine system together perform the functions of control and coordination in human beings.
(b) The central nervous system consists of the brain and the spinal cord. It is responsible for the coordination and control of the activities of the nervous system. It directs incoming messages to the motor neurons which are connected to the part of the body that will respond to a stimulus.
(c) The various functions of the brain are as follows:
(i) It receives information-carrying nerve impulses from all the sensory organs of the body.
(ii) It responds to the impulses brought in by the sensory organs by sending instructions to the muscles and glands making them function accordingly.
(iii) It correlates the various stimuli from different sense organs and produces the most appropriate and intelligent responses.
(a) The five endocrine glands found in the human body are:
Pituitary gland which secretes growth hormone.
Thyroid gland which secretes thyroxine hormone.
Parathyroid gland which secretes parathormone.
Pancreas which secretes insulin.
Adrenal glands which secrete adrenaline.
(b) Hormones reach the target organ through the blood and act on it.
(c) Hypothalamus regulates the secretion of hormones from the pituitary gland.
(d) An increase in the amount of adrenaline in our body increases our heart beat, breathing rate, blood flow into the muscles and causes the liver to put more stored glucose in our blood. All these actions of adrenaline produces a lot of energy in our body very quickly and enable us to take quick action.
(e) Iodine deficiency in our diet causes goitre. The main symptom of goitre is swelling of the thyroid gland which is present in the neck.
A receptor is a cell (or a group of cells) which present in a sense organ and is sensitive to a particular type of stimulus such as light, sound, smell, taste, heat or pressure.
Sense organs contain receptors. The ear, nose and eye are sense organs, a muscle is not.
The pancreas acts as an exocrine as well as an endocrine gland. The salivary, pituitary and parathyroid glands are endocrine glands.
The cerebellum is a part of the hindbrain which helps in maintaining posture and balance of the body.
As many as 31 pairs of nerves arise from the spinal cord.
The hindbrain consists of three centres called the pons, the cerebellum and the medulla.
The forebrain consists mainly of the cerebrum.
The midbrain does not have any further divisions.
The spinal cord is a cylindrical structure.
(d) (ii) and (iv)
Cerebral reflexes are those reflex actions which involve the brain. They occur in the organs present in the head as these organs are directly connected to the brain.
Exercise : Solution of Questions on page Number :118
Iodine is required for the synthesis of thyroxine hormone by the thyroid gland.
(a) adrenaline : pituitary gland
Adrenaline is secreted by the adrenal glands which are located on top of the kidneys.
(b) it regulates growth and development of the body
Insulin is produced in the pancreas. It regulates blood sugar level and its deficiency causes diabetes. The growth and development of the body is regulated by the growth hormone.
The spinal cord is a tubular structure connected to the medulla oblongata of the brain.
(b) medulla in the hindbrain
The medulla controls various involuntary actions such as heart beat, breathing, blood pressure and peristaltic movement in the body.
Chewing is a voluntary action, while actions like vomiting, heart beat and salivation are involuntary.
Adrenaline released from the adrenal gland prepares our body for action in emergency situation. Hence, it is called emergency hormone, i.e., hormone of fight or flight.
The medulla controls the involuntary actions like the peristaltic movements of the alimentary canal.
Testosterone is the male sex hormone which is associated with male puberty.
The pituitary gland does not occur in pairs, while the adrenal gland, testis (in male) and ovary (in female) do.
A synapse is a functional junction between the axon of a neuron and the dendrites of the next neuron. It is separated by a small gap known as the synaptic cleft.
(d) nervous and endocrine systemsThe life processes in humans are controlled and regulated by the endocrine and the digestive system. They work together to communicate, integrate and coordinate the functions of various organs and other systems of the body.
(c) his blood sugar was high.
Insulin controls the blood sugar level. Hence, the doctor advised him to take an injection of insulin to bring his sugar level to normal.
(a) the cerebrum
All the voluntary actions of our body are controlled by the cerebrum. The cerebrum is the largest and the most prominent part of the brain.
(a) thyroid gland requires iron to synthesise thyroxine.
Statement (a) is incorrect. Iodine is required for the synthesis of thyroxine hormone by the thyroid gland.
The pituitary gland is an endocrine gland, while the ovary, testis and pancreas are heterocrine glands. Those glands which are partly exocrine (with duct) and partly endocrine (without duct) are known as heterocrine glands. Here, the exocrine part releases secretion into the duct, while the endocrine part releases hormones into blood.
The medulla controls various involuntary actions such as the heart beat, breathing, blood pressure and the peristaltic movement in the body.
Exercise : Solution of Questions on page Number : 119
(d) less secretion of growth hormone
Dwarfism is characterised by retarded physical growth and a normal brain. It is caused due to the hypo-secretion of growth hormone.
(c) testosterone from the testes and estrogen from the ovary
The dramatic changes in the body features associated with puberty are mainly due to the secretion of testosterone from the testes (in male) and estrogen from the ovary (in female).
(a) gustatory receptors detect taste, while olfactory receptors detect smell
Gustatory receptors detect taste; olfactory receptors detect smell; while auditory receptors detect sound.
(b) the pons
The pons take part in the regulation of respiration in the human body.
(c) dendrite → cell body → axon → axon end
In a neuron, the electrical impulse travels from the dendrites to the cell body and from the cell body to the axon and, then, to the axon end.
(d) axon end of one neuron to the dendrite end of the adjacent neuron.
In a synapse, a chemical signal is transmitted from the axon end of one neuron to the dendrite end of the adjacent neuron.
(c) axon end
The conversion of an electrical signal to a chemical signal occurs at the axon terminal.
(d) Receptors → Sensory neuron → Spinal cord → Motor neuron → Muscle
The pathway taken by a nerve impulse in a reflex action is called reflex arc.
The correct sequence of the components in a reflex arc is given below:
Receptors → Sensory neuron → Spinal cord → Motor neuron → Muscle
(c) (i) and (iv)
Statements (i) and (iv) are correct, while statements (ii) and (iii) are not. Sensory neurons carry signals from the receptors to the brain or the spinal cord, while motor neurons carry signals from the brain or the spinal cord to the effector organs like muscles and glands.
The gustatory receptors which detect taste are present in the tongue.
The olfactory receptors which detect smell are located in the nose.
(c) cerebral reflex
The contraction of the pupil of the eye in the presence of a bright light is an example of cerebral reflex. A reflex action that involves the brain is called cerebral reflex. It is found in the organs present in the head that are directly connected to the brain.
The pituitary gland secretes a hormone known as growth hormone which controls the growth of the human body. Deficiency of growth hormone can make the person very short, while excess of this hormone can make a person very tall.
Exercise : Solution of Questions on page Number : 120
Under-secretion of thyroxine hormone from the thyroid gland can lead to goitre.
The pancreas secretes a hormone called insulin. Insulin lowers the blood sugar level. Deficiency of insulin can lead to a disease called diabetes.
It is advised to use iodised salt to prevent goitre. It is because the thyroid gland requires iodine to synthesise thyroxine hormone. Deficiency of iodine in the body can lead to the under-secretion of thyroxine hormone which, in turn, can lead to goitre.
The adrenal glands are often called glands of emergency. It secretes adrenaline hormone which prepares the body for action.
(a) P is a receptor. The five organs which contain receptors are: eyes, ears, nose, tongue and skin.
(b) Q represents sensory nerves. Sensory nerves bring impulses from sensory organs to the CNS.
(c) R is an effector organ. Effectors are part of the human body which can respond to a stimulus according to the instructions sent from the CNS though the motor nerves. Two examples of effector organs are the muscles and glands.
(d) S represents motor nerves. Motor nerves carry impulse from the CNS to the effector organs like the muscles or glands.
(e) Messages travel in the form of electrical impulses or nerve impulses through sensory nerves (Q) and motor nerves (S).
A represents neurons. Neurons are the largest cells in the human body, which look like electric wires.
(i) B represents the axon.
(ii) C represents the dendrites.
The microscopic gap D is known as a synapse. A synapse is a functional junction between a pair of adjacent neurons over which nerve impulses can pass.
A neuron transmits messages to and from the central nervous system. It is the structural and functional unit of the nervous system.
The three types of neurons are sensory neurons, motor neurons and relay neurons.
(a) (i) P is a thermoreceptor.
(ii) Q is a sensory neuron.
(iii) R is the spinal cord.
(b) (i) S is a relay neuron. The impulse from the spinal cord is passed on to a relay neuron.
(ii) T is a motor neuron. From the relay neuron, the impulse is passed on to a motor neuron.
(c) U is a muscle.
(d) Reflex action is the phenomenon in which the hand is pulled away quickly from a hot plate. It is performed automatically by an individual.
(e) The effector organ is the muscle of the arm.
X is the pituitary gland. It is located just below the brain.
The chemical substance (Y) released from the pituitary gland is human growth hormone.
Under-secretion of growth hormone leads to a condition known as dwarfism. In dwarfism, the person remains very short.
Over-secretion of growth hormone causes a condition known as gigantism. In gigantism, the person grows very tall.
The pituitary gland (X) is a part of the endocrine system.
A. represents the endocrine system. The endocrine system is composed of glands.
C. represents hormones. Hormones are the chemical messengers of the body and they travel slowly through the bloodstream.
D. represents endocrine glands that are made up of tissues. Hypothalamus, thyroid, thymus, pancreas and adrenal glands are some of the endocrine glands present in the human body.
B. represents the nervous system. It comprises the brain, spinal cord and nerves.
E. represents nerve fibres. They transmit messages very quickly in the form of electrical impulses.
The nervous system (B) controls the working of the endocrine system (A).
Exercise : Solution of Questions on page Number : 121
The structure P is the spinal cord. It is a cylindrical structure that begins in continuation with the medulla and extends downwards.
(i) The bony cage Q is the vertebral column. The spinal cord is enclosed by the vertebral column.
(ii) R represents the meninges. The spinal cord is surrounded by membranes called the meninges.
x represent the number of pairs of spinal nerves. They are 31 in number.
S is the brain. The central nervous system consists of the brain and the spinal cord.
The reflex actions involving the spinal cord (P) are known as spinal reflexes.
(a) The part A functions as an endocrine gland. The glands that secrete their secretions directly into the blood are called endocrine glands. Part A of the pancreas secretes insulin (a hormone) directly into the bloodstream.
(b) Insulin is a hormone which is secreted by the pancreas. It controls the blood sugar level.
(c) Deficiency of insulin in the body can lead to diabetes. Diabetes can be treated by giving injections of insulin.
(d) Pancreatic juice contains digestive enzymes like pancreatic amylase, trypsin and lipase. The pancreatic juice goes into the small intestine where complete digestion of food takes place.
(e) Digestion is the process where the enzymes present in the pancreatic juice are used to break down the food.
(i) A represents the thyroid gland. It is attached to the wind pipe in the human body.
(ii) B represents thyroxine. It regulates the metabolism of carbohydrates, fats and proteins in the body.
The non-metal element C is iodine. It is essential for the synthesis of thyroxine hormone by the thyroid gland.
Sea foods like fish provide sufficient amount of iodine in the diet of a person.
(i) D represents the disease called goitre. It is characterised by abnormal enlargement of the thyroid gland in the neck.
(ii) E represents iodised salt. It is advised to use iodine in cooking food in order to prevent goitre.
When a piece of thread is tightly tied around an animal’s pancreatic duct, the pancreatic juice containing digestive enzymes will not be able to reach the small intestine. The pancreatic juice contains enzymes which help in the digestion of food. In its absence (due to the blockage of the pancreatic duct), the animal would have difficulty in digesting certain food substances.
However, the pancreas being an endocrine gland releases insulin directly into the blood. Since, the main function of insulin is to maintain the blood sugar level in the body, the animal will not suffer from diabetes.
The liver is the target organ for both adrenaline and insulin. Target organs and target cells are specific organs and cells upon which hormones act and produce their effects.
(a) (i) W represents the pancreas. It is located just below the stomach in the human body.
(ii) X represents insulin, which is secreted by the pancreas.
The function of insulin (X) is to maintain the sugar level in blood.
(i) Y represents diabetes, which is a disease caused by increased blood sugar level.
(ii) The person Z is known to be diabetic.
A person suffering from diabetes (Y) should control his/her diet, reduce his/her weight and do regular physical exercises. He/she should regularly take proper medication to control the sugar level in blood.
P is adrenal glands.
Q is kidneys.
R is adrenaline hormone.
S is glucose.
Humans have two adrenal glands, which are located on top of the kidneys. They are often called emergency glands. They secrete adrenaline into the bloodstream. It is secreted in large amounts when a person is frightened.
Adrenal gland brings about temporary changes in the body which allow glucose from the liver to go into the bloodstream. This provides a lot of energy in a very short time.
The glands A are the ovaries.
The hormones C and D, secreted by the ovaries, are oestrogen and progesterone, respectively.
The glands B are the testes. The hormone E, released by the testes, is testosterone.
(i) The gametes F are ova or eggs. They are produced by the ovaries.
(ii) The gametes G are sperms. Sperms are produced by the testes.
The secretion of hormones C (oestrogen) and D (progesterone) in females andAnswer: 44 hormone E (testosterone) in males are associated with puberty.
Exercise : Solution of Questions on page Number : 122
The organ A is the brain. The brain is located inside the skull of our body at the top of the spinal cord.
(i) B is the cranium. The brain is protected by a bony box in the skull called the cranium.
(ii) C are meninges. The brain is surrounded by three layers of membranes called the meninges.
(iii) D is the cerebrospinal fluid. It is present in between the meninges and protects the brain from mechanical shocks.
The organ E is the spinal cord. The brain (organ A) and the spinal cord (organ E) together make central nervous system.
A person walking barefoot lifts his foot at once on stepping on to a sharp piece of stone. The spinal cord (E) is involved in this action. Those reflexes that involve only the spinal cord are called spinal reflexes.
A person closes his eyes at once when he steps out from a darkened room to bright light. The brain (A) is involved in this action. Those reflexes that involve only the brain are known as cerebral reflexes.
The pathway taken by nerve impulses in a reflex action is called a reflex arc. It is an automatic response to a stimulus. When a stimulus is given to a receptor, the receptors produce an impulse in the sensory fibre. The sensory fibre carries this message in the form of an electrical stimulus across the synapse. From the synapse, the impulse travels in the motor fibre and stimulates the effector organ to produce the desired response.
The correct order for a simple reflex arc is:
(b) →(d) → (a) → (c).
Receptors are sensory structures (organs/ tissues/ cells) that detect changes in the environment, which are called stimuli, and turn them into electrical impulses to be transferred to the brain. The tongue has taste buds which can detect chemicals in food and identify taste. Hence, it is considered as receptor.
Effector is an organ that responds to stimulus. The tongue is a muscular organ that can respond to a stimulus. Hence, it is also considered as an effector organ.