Class 10 Science Chapter 6 Important Questions

Animal receive a variety of external information through specialized structures called receptors located in our sense organs.
These are:
(i) Photoreceptors: they detect light.
(ii) Phonoreceptors: they detect sound.
(iii) Olfactoreceptors: they detect smell.
(iv) Gustatory receptors: they detect taste.

Receptors usually present in sense organ aware us about change in the environment. So that our body can represented according to the sensation our receptors convey. Suppose is you touching a hot object is not conveyed immediately and properly due to the malfunctioning of receptors of touch it may become a very dangerous situation for us.

(i) Dendrites conduct a nerve impulse toward cell body(cyton).
(ii) Axon conduct a nerve impulse away from the cell body.

The role of dendrites is to carry nerve impulse towards the cell body of a neuron. It receives information from axon of other neuron through synapsis.

Axon conducts impulses away from the cell body to anther neuron or tissue through synapsis.

Sensory neurons carry 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 conversed voluntary muscles.

Human brain is lodged in a bony case, the cranium which protected 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 balances of the body.

(i) Cerebellum is hurt which affects walking in straight line.
(ii) Smelling part of fore-brain is injured.
(iii) The sensation of feeling full after eating is because of a centre associated with hunger. It is in a separate part of the fore-brain. The sensation of not feeling full is because of injury to this center present in fore brain.

Involuntary actions are controlled by the mid-brain and the hind-brain. Example
(i) Involuntary actions such as blood pressure, salivation and vomiting are controlled by the medulla in the hind brain.
(ii) Mid-brain controls optic reflex such as change in the size of the pupil.

Nervous system: Main parts of nervous system are as follows:
(i) Central nervous system
(ii) Peripheral nervous system, (iii) Autonomous system.
(i) Central Nervous System: It consist of
(a) Brain receives information carrying impulses from all the sensory organs (by sensory nerves) of the body and also from the spinal cord. The brain responds to the information by sending its own instruction (through motor nerves) to the muscle and glands to act accordingly. The brain also stores information and act as organ of thought and intelligence.
Spinal Cord: It is concerned with spinal reflex actions and the conduction of nerve impulses to form the brain.
Peripheral Nervous System: It is composed of Cranial nerves (nerves from the brain) and the spinal nerves. Both of these consist of sensory and motor neurons. So, they carry sensation to and messages from the brain and the spinal cord.
Autonomous Nervous System: It is that part of the peripheral nervous system which controls the activities of the internal organs such as stomach, heart-beat, etc. automatically even without our thinking about them. Its nerves are attached to the smooth muscles and control the activities of internal organs of the body involuntarily, many these nerves are connected with the mid brain and hind brain.

Cerebellum is not functioning properly may affect
(i) Walking in straight line
(ii) riding a cycle
(iii) maintaining the posture and balance of the body
(iv) movement is very coordinate the patient sways in walking and tend to fall towards the affect side.
(v) It is responsible for precision of voluntary actions.

When the decision to move is conveyed by a nerve to a muscle it has to act. In response to nervous electrical impulses. The special proteins of the muscle change both their shape and their arrangement in the cell. This new arrangement of these proteins give the muscle cells a shorter form that causes movement of the muscle.

The cerebral hemispheres are responsible for consciousness, thinking, and intelligent behavior. Animal which do not possess well developed cerebral hemispheres cannot perform intelligent actions. They only show instinctive behavior.

The various overall functions of human brain are:
(i) to receive impulses from all the sensory organs like eye, ear, nose, tongue, skin.
(ii) sending of responses to muscles and glands for proper actions.
(iii) control and coordination of the body activities.
(iv) thinking, storage of past knowledge and experience feeling of conscious and modification of behavior according to situation and experience.

Thinking tissue: The thinking tissue in our body consist of dense networks of intricately arranged neurons.
Location: Thinking tissue sits in the fore-brain.
Function: It receives signal from all over the body. It has regions which receive sensory impulses from various receptors. It has separate areas where information is interpreted considering the information that is already stored in the brain. From this part of the brain, nerves carry signal back to different parts of the body to act upon muscles/ glands according.

The human body is designed so that the brain sits inside a bony box the cranium or skull.
Inside the box the brain is contained in a fluid filled balloon which provide further shock absorption.

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

Cerebellum.

Synapse.
(a) At the end of the axon the electrical impulse sets off the release of some chemicals.
These chemicals cross the gap or synapse and start a similar electrical impulse in a dendrite of the next neuron.
(b) Axon of neuron.

Nervous and muscular tissues.

Brain is located in bony cranium which is fluid filled to absorb the shocks. Spinal cord is further protected by vertebral column or backbone. Spinal cord is further protected by a fluid present in the vertebral column cavity.

Nervous system is one of the most important system of the body. It regulates, coordinates and links the activities of different organs.
The central nervous system includes the brain and spinal cord.
Brain: The human brain is highly developed and shows great advancement over that of any other animal in the size of the cerebral hemisphere as well as the mid brain, cerebellum, medulla oblongata, etc.
The adult brain is dividing into the following parts:
1. Fore-brain: It consists of the following parts:
(a) Cerebrum: It forms about two third of the human brain. A deep longitudinal tissue divides the cerebrum into two hemispheres which are held together by a horizontal sheet of fibrous tissue. Cerebrum contains an outer grey matter and an inner white matter. Grey matter shows many convolutions which are directly linked with intelligence of the organism. Cerebrum controls the function of perception of smell, sight hearing, ability of speech and movements of various parts of the body.
2. The mid brain: It is thick walled area which serves as center for certain visual and auditory reflexes. The mid-brain contains a group of nerve cells which regulates involuntary actions of muscles on which our thinking has not control.
3. The hind-brain: It consist of three centers namely, cerebellum, pons and medulla oblongata.
Cerebellum: It controls coordination and adjustment of movement and posture.
Pons: It forms the floor of the brain stem. It serves as a neuronal link between the cerebral cortex and the cerebellum.
Medulla oblongata: It is the regulating center for swallowing, coughing, sneezing and vomiting. It takes part in regulation of respiration.
The spinal cord: The spinal cord is cylindrical and has the same diameter as the little finger. Medulla of the extends downwards to form spinal cord that lies protected in the backbone. It is hollow and possesses a central canal. It is not uniform in thickness.
The spinal cord is the great highway for most nerve impulses. It conducts impulses to and fro from the brain. It also acts as reflex center. Spinal cord is formed of two types of nervous tissues the grey matter and white matter. The grey matter surrounds the central entirely of nerve cells. Two upward and two downward dorsal and ventral horns can be seen in the T.S of spinal cord.
Functional of spinal cord: (i) All the stimuli and responses are passed from and to the brain through the spinal cord.
(ii) It is a center of reflex actions.

In certain animals the nerve nets (nerve net is formed by nerve cells) condense into a nerve mass. This nerve mass is called ganglion.

The specific set of nerves that mainly controls and integrates the function of internal organs is called automatic nervous system. It controls the body organs, such as heart, blood vessels, glands, smooth muscles and uterus in the body; these are not directly under control of our will. Autonomic nervous system consists of: (i) Sympathetic and (ii) Para-sympathetic systems. They have opposite effect on the organ that’s why if one stimulates the organ the other inhibits its action.

Control and coordination in human beings: This system of controlling and coordination can be divided into two parts:
(i) Nervous system.
(ii) Hormonal system.
Both the system control, coordinate the various functions in human body. Nervous system controls the various functions by the units called neurons. Neurons receive the information by sensory nerves and transfer them through motor actions.
The hormones are the chemicals secreted by endocrine glands. The endocrine glands do not have ducts so they are called ductless glands. Hormones also control the functions of various organs of the body. In this way it is true that the nervous system and hormonal system in human body together perform the functions of control and coordination.

Brain collects information around the body through nerves. Make decisions based on the information and conveys decisions to muscles for action.
When a nerve impulse reaches the muscle the muscle fiber must move. Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to nervous electrical impulses. Now arrangement of these proteins give the muscles cells a shorter form and this lead to movement of the muscles. After the actions is over, reserve process take place and the muscles take their original size and shape.

Tropic movements in plants are growth related. Plants shown by the plants towards or away of stimulus or away from. This growth causing tropic movement regulated by the plant hormone called auxin.

The phenomenon of regulation of flowering and germination of seeds by photoperiodic stimulus is called photoperiodism.

The control and coordination system in higher organism perform two functions:
(i) It make the various body organs and organ systems to work in organized pattern and in a coordinated way. For example, when we eat, our hand bring food to the mouth, teeth and jaw muscles chew salivary glands secrete saliva, etc.
(ii) Control and coordination also aids in maintaining a steady storage between the internal environment of an organism and the external environment. For example, during summer we sweat more, evaporation of sweat cool us. Due to loss of water in precipitation we feel thirsty to make the water loss good. Both sweating and thirst are responsible for keeping the temperature and water content of the body at an optimum state.

Plant Hormone: these are special chemical compound which are synthesised at places away from where they act and simply diffuse to the area of action. Different plant hormone help to coordinate growth, development and responses to the environment.
(a) Auxin hormone promotes growth.
(b) Cytokinin promotes cell division.
(c) Abscisic Acid inhibits growth.
(d) Auxin promotes the growth of a tendril around a support.

Photohormones are plant hormones which are also called growth regulators. They help to coordinate growth development and responses to environment.
Phytohormone and its Function
(i) Auxin: Help the plant shoots/roots to respond to stimuli like light, gravity, touch, etc.
(ii) Gibberellins: They help in the growth of stem.

(a) Function of Auxins
(i) Growth: It plays a vital role in cell elongation during growth. It promotes the growth of shoot.
(ii) Root formation: It helps in root formation. When auxin is applied to the cutting of the stem artificially the formation of roots can be initiated.
In germinating roots, higher concentration of auxins inhibits the growth.
(iii) Parthenocarpy (seedless food): It is observed that after pollination there is sharp rise in auxin content of the ovary which helps in the formation of fruit. An application of auxin causes formation of seedless fruits without pollination and fertilization.
(b) Function of gibberellins
(i) Effect on stem elongation: Gibberellins are found to cause stem elongation in genetically dwarf variety. It has no effect on tall verities.
(ii) Germination of seeds: It is now known to control the germination of seeds of some high plants such as lettuce, cereals etc.
(iii) Flowering: Gibberellins induces flowering in the long day plants in short day conditions.
(iv) Parthenocarpy: Gibberellins are found to induce parthenocarpy.
(v) Increase in size: Gibberellins application on plants also cause increase in size of leaves and flowers in some plants.
(c) Function of cytokinins
(i) Cell divisions: One of the main functions of the cytokinins is in cell divisions, cell expansion and differentiate that’s why cell growth.
(ii) Initiation of roots and shoots: Experimental evidences show that kinins affect the initiation of roots and shoots and their growth.
(iii) Remove apical dominance: Kinins are also found effective in removing the apical dominance and help in growth of lateral buds.
(iv) Abscisic Acid: This group compounds is now isolated from dormant seeds, buds and other parts of the plant. Activities of abscisic acid are in contrast to gibberellins and cytokinins. Abscisic acid retards growth promotes leaf and fruit fall and causes dormancy of seeds, tubes and bulbs. It also aging of leaves.

The function of nervous system:
(i) It regulates involuntary action.
(ii) It control and coordinates voluntary muscular activities.
(iii) It keep us informed about the outside world through the sense organs.
(iv) It enables us to think reason and remember.
(v) It controls all the reflex actions in our body, thus protection it from harm.

Reflex arc is the pathway taken by the nerve impulses and responses in a reflex action that’s why from the receptors organs like skin to the spinal cord and from the spinal cord to the effector organs like muscles.
The advantages of Reflex action are:
(i) It enable the body to give quick responses to give quick responses to harmful stimuli and thus protects our body.
(ii) It minimizes the overloading of brain.

The function of human brain are:
(i) The brain receives information carrying impulses from all the sensory organs of the body.
(ii) The brain responds to the impulses brought in by sensory organs by sending its own instruction to the muscles and glands causing them to function accordingly.
(iii) The brain correlates the various stimuli from different sense organs and produces the most appropriate and intelligent response.
(iv) The brain coordinates the bodily activities so that the mechanisms and chemical reactions of the body work together efficiently.
(v) The brain stores information so that behavior can be modified according to the past experience. This function makes brain the organ of thought and intelligence.

(i) Plant use electrochemical means to convey information from cell to cell.
(ii) Sensitive plants move very quickly in response to touch that are independent of the direction of the stimuli.
(iii) The folding up and dropping of leaves of the sensitive plant touch-me-not when lightly touch is an example.
(iv) Plants cells change shape by changing the amount of water in them resulting in swelling or shrinking thereby changing shape.

It is the directional growth or movement of a plant organ in response to an external stimulus.
Growth towards the stimulus is positive tropism and growth away from the stimulus is negative tropism.
Tropic movements are classified as follows depending on the type of stimulus causing it:
(i) Phototropism is the movement of part of the plant in response to light.
(ii) Geotropism is the upward and downward growth of shoots and roots in response to the pull of earth or gravity.
(iii) Hydrotropism is the movement of a part of the plant in response to water.
(iv) Chemotropism is the movement of a part of the plant in response to a chemical stimulus.
If the plant part shows movement growth towards the chemical it is called positive chemotropism and if the plant part shows movement or growth away from the chemical it is called negative chemotropism.
For example, the growth of pollen tube towards a chemical which is produced by an ovule during the process of fertilisation in a flower.

The plant hormones regulate many function in plants which are as follows:
(i) Germination of seeds or breaking the dormancy of seeds.
(ii) Growth of root, stem and leaves.
(iii) Flowerings of plants,
(iv) Ripening of fruits,
(v) Movement of stomata in leaves and
(vi) Phototropism, geotropism, chemotropism and nastic movement.
Characteristic and Function of Hormones
(i) Hormones are the secretions of endocrine glands or tissues.
(ii) They are poured directly into the blood and carried throughout the body by blood circulatory system.
(iii) Hormones have their effects at the sites different from the sites where they are made. So they are also called chemical messengers.
(iv) They act on specific tissue or organs are called target organs.
(v) They coordinate the activities of the body and also its growth.
(vi) They are secreted in extremely minutes’ quantities.
(vii) Chemically hormones may be polypeptides and proteins, amino acids, and their derivatives or steroids.
(viii) Hormones help the body to cope with emergency demands such as infection, trauma, dehydration, starvation and extreme temperature.

(i) Endocrine glands: They are structure or group of cells or tissue which manufactures hormones and secretes them directly into the bloodstream to act at distant sites in the body known as targets organs or cells.
(a) They are ductless glands and are located at different parts of the body.
(b) The endocrine glands present in human includes hypothalamus, pituitary, pineal, thyroid, parathyroid, pancreas, adrenal, testes (in male) and ovaries (in female).
(c) Some endocrine glands like pancreas, testis and ovary perform dual functions that’s why both exocrine and endocrine functions.
(ii) Hypothalamus gland is present in brain.
(a) It produce releasing hormones.
(b) It regulates the secretion of hormones from pituitary gland.
(iii) Pituitary glands is present at the base of the brain. It is also known as the matter gland as it controls to the other endocrine glands.
The pituitary gland secretes five hormones:
(a) Growth hormone regulates the growth and development of bones and muscles.
(b) Trophic hormone regulates the secretion of hormones from other endocrine glands like adrenal glands like adrenal glands, thyroid gland, testes and ovaries.
(c) Prolactin hormone regulates the function of mammary glands in females.
(d) Vasopressin hormone regulates water and electrolyte balance in the body.
(e) Oxytocin hormone regulates the ejection of milk during lactation.
(f) Pineal gland is present in the brain near to the pituitary gland. It secretes melatonin hormone which delays sexual development and promotes sleep.
(iv) Thyroid gland is presented just below the neck.
(a) Iodine is necessary for the thyroid gland to make thyroxine hormone.
(b) It secretes a hormone called thyroxine which regulates the metabolism of carbohydrates, fats and proteins in the body so as to provide the best balance for growth.
(v) Parathyroid glands are four in number which are embedded in the thyroid gland.
(a) They secrete a hormone called calcitonin, which regulates calcium and phosphate levels in the blood.
(vi) Adrenal glands are two in number which are located one on top of each kidney.
(a) Adrenal glands secretes two hormone adrenalin and corticoids.
(b) The function of adrenalin and corticoid hormones are to regulate blood pressure, heart beat, breathing rate, carbohydrates metabolism and mineral balance.

(i) Pancreas is present just below the stomach in the body.
(a) It secretes two hormones insulin and glucagon.
(b) The function of insulin hormone is to lower the blood glucose.
(c) The function of glucagon hormone is to increase the blood glucose.
(d) Pancreas is exocrine as well as endocrine gland. The endocrine part is called the islets of Langerhans.
(ii) Testes in male are present outside the lower abdomen in scroyum.
(a) They secrete male sex hormone called testosterone.
(b) The function of testosterone hormone is to regulate male accessory sex organs and secondary sexual character like moustache, beard and voice.
(iii) Ovaries in female sex hormone called estrogen and progesterone.
(a) They secrete two female sex hormones called estrogen and progesterone.
(b) The function of estrogen hormone is to regulate the development of female accessory sex organs and secondary sex characters such as mammary gland, soft skin, hair pattern and feminine voice.
(c) The function of progesterone hormone is to control the uterus changes in menstrual cycle. It also helps in the maintenance of pregnancy.

Six reflex actions of the body are:
(i) When we see a speeding car moving towards us we move aside.
(ii) We withdraw our hands on being pricked by a pin.
(iii) We withdraws our hands on touching very hot substance.
(iv) We close our eyes on seeing direct sun or extremely bright source of light.
(v) We close our eyes on hearing a loud noise.
(vi) We shiver on feeling cold.
Reflex arc in all the above cases is same because in all the cases, the stimulus is received by sense organs. Then this information is carried to spinal cord through sensory nerves. Thus, information from spinal cord is sent to the effectors such as muscles motor neurons.