Q. The shape of guard cells changes due to change in the:

  • (a) protein composition of cells.
  • (b) temperature of cells.
  • (c) amount of water in cells.
  • (d) position of nucleus in cells.
  • Ans. (c) amount of water in cells.
 Explanation :

The amount of water in guard cells causes change in their shape. When water enters into the guard cell, it causes the stomatal pore to open. Similarly, if the guard cells shrink as a result of water loss, the pore closes.

Q. Which of the following is a plant hormone?

(a) Insulin

(b) Thyroxine

(c) Oestrogen

(d) Cytokinin

Ans. (d) Cytokinin

 Explanation :

Cytokinin is a plant hormone that plays an important role in plant growth and development. In plants, it aids embryogenesis, cell division, chloroplast differentiation, and a variety of other processes.

Q. The brain is responsible for :

(a) thinking

(b) regulating the heart beat

(c) balancing the body

(d) all of the above

Ans. (d) all of the above

 Explanation :

The cerebellum of the brain is involved in muscle coordination, muscle tone, and balance. The medulla oblongata regulates heartbeat and controls consciousness and arousal. The cerebrum is the centre of brain for higher-order thinking functions such as learning, memory, language, and speech.

Q. Involuntary actions in the body are controlled by:

(a) Medulla in fore brain

(b) Medulla in mid brain

(c) Medulla in hind brain

(d) Medulla in spinal cord

Ans. (c) Medulla in hind brain

 Explanation :

The involuntary activities are controlled by the medulla oblongata in the hind brain. Involuntary movements have a slower speed than voluntary movements. The beating of the human heart is the best example of this.

Q. Choose the incorrect statement about insulin.

(a) It is produced from pancreas.

(b) It regulates growth and dev elopment of the body.

(c) It regulates blood sugar level.

(d) Insufficient secretion of insulin will cause diabetes.

Ans. (b) It regulates growth and development of the body.

 Explanation :

Growth hormone is a peptide hormone that promotes growth, cell reproduction, and regeneration. Insulin is made in the pancreas by beta cells found in the Islets of Langerhans. It is essential for the absorption of blood sugar by the cells. Along with glucagon, it regulates blood sugar levels.

Q. Select the mismatched pair.

  • (a) Adrenaline : Pituitary gland
  • (b) Testosterone : Testes
  • (c) Estrogen : Ovary
  • (d) Thyroxine : Thyroid gland

Ans. (a) Adrenaline : Pituitary gland

 Explanation :

The adrenal glands produce adrenaline, which activates the body’s fight-or-flight response. The testes, which are responsible for the development of male sexual traits, produce testosterone. The ovaries, which are responsible for the development of female sexual traits, produce oestrogen. Thyroxine is a hormone generated by the thyroid gland to accelerate the production of oxidative metabolism in cells.

Q.Why are some patients of diabetes treated by giving injections of insulin?

Ans. Insulin is secreted by beta cells of Islets of Langerhans of pancreas. They convert excess glucose to glycogen stored in liver thus lowering glucose level in the blood. In diabetes patients, the sufficient amount of insulin is not secreted by pancreas so they have high sugar level in their blood. To control the sugar level they are treated by giving insulin injections.

Q. Give an example of plant hormone that promotes growth?

Ans. Auxin is a plant hormone that promotes growth.

Q. Which part of the brain maintains posture and equilibrium of the body?

  • Ans. Cerebellum of the hind brain maintains posture and equilibrium of the body.

Q. Which signals will get disrupted in case of a spinal cord injury?

Ans. Spinal cord controls mainly the reflex actions. So, reflex actions and involuntary actions will get disrupted.

Q. How does phototropism occur in plants?

Ans. The directional movement or orientation of plant parts in response to stimulus light is called phototropism. Shoot of the plant shows positive phototropism whereas roots show negative phototropism. Bending of shoot towards light is brought about by the action of auxin hormones. Auxin hormone is synthesised by the meristematic tissue which is present at the tip of the stem. When a plant receives sunlight from above auxin gets distributed uniformly on both the sides of plant and plants grow straight. But if we keep a plant near a window it receives light from one side. Auxin which is secreted at the tip of shoot diffuses to the parts which do not receive sunlight. Hence the parts in shady regions grow faster due to more auxin concentration than the parts which receive sunlight. So, stem bends towards light.

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Q. What are plant hormones?

  • Ans. Plant hormones or phytohormones are the chemical substances present in plants which coordinate and control various activities of plants like growth, development, response to stimuli etc. There are different types of hormones like auxins, gibberellins, cytokinins, abscisic acid, ethylene etc.

Q. How do auxins promote the growth of a tendril around a support?

  • Ans.The movement of tendril around a support is caused by the action of auxin hormone. Auxin which is synthesised at the tip diffuses from the tip to the region that is away from the support. The region containing more auxin will grow faster than the part which is in contact with the support causing the tendril to curl around the support.

Q. How does chemical coordination occur in plants?

  • Ans. Chemical coordination occurs in plants with the help of phytohormones also called plant hormones. They bring about control and coordination in various activities which occur in plants. They are synthesised in minute quantities in one part and diffuse to other part of plants where they show their effect. There are various types of phytohormones like auxins, gibberellins, cytokinins, ethylene, abscisic acid etc. These phytohormones bring about various activities in plants like cell elongation, differentiation, fruits ripening, opening and closing of stomata, promotes growth, overcomes dormancy in seeds, senescence of leaves etc.

Q. What is the need for a system of control and coordination in an organism?

  • Ans. Multicellular organisms are highly complex. Every activity needs to be regulated so that the activities can occur in proper time and correct sequence. Various organs and parts of the body should work together in a coordinate manner to perform a particular function. For proper control and coordination in higher organisms both nervous and endocrine system play the major role. For example: While riding a bicycle there should be proper coordination between our hands and handle of our cycle.

Q. What happens at the synapse between two neurons?

  • Ans.Synapse is a point of contact between the axon terminals of one neuron with the dendrite of another neuron. The terminals of axon are swollen which contains a chemical called acetylcholine which is a neurotransmitter, which induces impulses in the dendrites of next neuron. Synapse acts as one way valve which prevents the back flow of impulses from axon terminals. So impulse moves from dendrites through cyton to axon. It allows the nerve impulses in one direction.

Q. What is the role of brain in reflex action?

  • Ans. Reflex actions are mainly controlled by spinal cord. For quick response to the stimulus spinal cord is generally involved but the information also reaches the brain where the thinking process occurs. Brain does not play any role for quick response to reflex action. But some reflex actions are only controlled by brain called cerebral reflexes like salivation at the sight of tempted food.

Q. How do we detect the smell of an agarbatti (incense stick)?

  • Ans. Olfactory receptors present in the nose detect the smell of incense stick. Impulse is generated in response to this stimuli and it is carried by sensory neuron to the olfactory lobes of forebrain. There the impulses are interpreted and we can easily detect the smell of incense stick.

Q. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to rise?

  • Ans.Receptors are specialised cells in our body which respond to the changes that occur in our body i.e., stimulus. They pass the information in the form of sensory impulses to central nervous system through sensory nerves. If receptors do not work properly impulses will not be generated in response to the stimuli and our body cannot provide an appropriate response to the changing environment. For example, if olfactory receptors do not work properly we cannot detect any smell whether it is good or bad.

Q. Why is the use of iodised salt advisable?

  • Ans. Iodine is an essential component for synthesis of thyroxin hormone. Thyroxin hormone is secreted by thyroid gland which regulates the basal metabolism of our body by oxidation of carbohydrates, proteins and fats. It regulates the general growth of our body and deficiency of this hormone leads to disorders like simple goitre, cretinism, myxedema etc. So it is advised to use iodised salt in the food.

Q. How does our body respond when adrenaline is secreted into the blood?

Ans. Adrenaline is an emergency hormone secreted by adrenal glands to deal with emergency situations. When adrenaline is secreted in large amounts under situations like stress, anger, fear etc. it increases our heart beat, increases breathing rate, raises blood pressure, more glucose is released to blood stream to provide energy to face the emergency situation.

Q. How does chemical coordination take place in animals?

Ans. Chemical coordination in animals is brought about by hormones. Hormones are secretions of endocrine glands which are poured directly into the blood stream. They are carried by blood to the target organs. Target organs have specific receptor which identifies the specific hormones and coordinates or regulates their specific functions. They transmit the information and brings about the effect.

Q. Draw the structure of a neuron and explain its functions?

Ans. Neuron or nerve cell is the structural and functional unit of nervous system. The three parts of the neuron are cyto or cell body, dendrites and axon.

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1. Dendrites are fine, branched cytoplasmic projections of cyton which are the site of receiving information and they conduct these impulses to cyton.

2. Cyton receives impulses from dendrites and passes through axon. Cyton contains nucleus, nissl’s granules and other cell organelles.

3. Axon is a long process from cyton which is surrounded by an insulating sheath called myelin sheath. Axon conducts nerve impulses away from cyton. The terminals of axon are swollen which contains chemicals called neurotransmitters. This chemical sends a new impulse in the dendrites of adjacent neurons.

Q. How is the movement of leaves of the sensitive plant different from the movement of shoot towards light?

Ans.
Movement of leaves of sensitive plant Movement of shoot towards light
It is an example of nastic movement. It is an example of tropic movement.
It does not involve growth and movement is fast. It involves growth and movement is slow.
It occurs due to changes in turgour pressure in the cells of the leaves. Auxin hormone plays an important role in phototropism movement. It occurs due to differential growth because of unequal distribution of auxins.
It occurs due to stimulus of touch. It occurs due to stimulus of light.

Q.What is the difference between a reflex action and walking?

Ans.
Reflex Action Walking
It is an involuntary action which is not under the control of our will. It is a voluntary action which is under the control of our will.
Spinal cord controls the reflex action. Cerebellum of hind brain controls walking.
It is a spontaneous, automatic, quick response to a stimulus performed unconsciously. It is under conscious control and it takes longer time.
It occurs suddenly and we do not have to learn it. We have to learn it as we grow up.