SHORT ANSWER QUESTIONS
Q.1. What is feedback mechanism of hormonic regulation. Take the example of insulin to explain this phenomenon. [Delhi 2019]
Ans. Hormones are secreted in extremely less quantity. Excess or deficiency of such hormones can have harmful effects on our body. A feedback mechanism controls the timing and secretion of hormones released by various glands.
For example: On the rise of blood glucose level, information is sent to pancreas to release insulin. When the appropriate amount of glucose level is obtained in the blood, the release of insulin is stopped.
Q.2. (a) Name the part of human brain which controls: [CBSE 2017-18 C]
(i) voluntary actions (ii) involuntary actions.
(b) State the significance of peripheral nervous system. Name the components of this nervous system and distinguish between their origins.
Ans. (a) (i) Voluntary actions are controlled by Cerebellum (hind brain).
(ii) Involuntary actions are controlled by mid-brain.
(b) Peripheral nervous system facilitates the communication between central nervous system and other body parts.
Components of peripheral nervous system are:
(i) Cranial Nerves: Originating from brain.
(ii) Spinal Nerves: Originating from spinal cord.
Q.3. (a) Name the gland that secrete:
(i) insulin, (ii) thyroxin.
(b) Explain with an example how the timing and amount of hormone secreted are regulated in a human body. [CBSE 2017-18 C]
Ans. (a) Gland that secretes:
(i) Insulin - Pancreas
(ii) Thyroxine - Thyroid gland
(b) The timing and amount of hormone secreted are regulated by the “Feedback mechanisms”. For example:
(i) High glucose level in blood induces the pancreatic cells to produce more insulin which converts glucose to glycogen.
(ii) Low glucose level in the blood does not induce the pancreatic cells to produce insulin so that less conversion of glucose to glycogen occurs.
Q.4. (a) State the role performed b y plant hormones. Name a plant hormone which is essential for cell division.
(b) Name and explain the role of plant hormone involved in phototropism. [CBSE 2017-18 C]
Ans. (a) Role of plant hormones:
Chemical control in the plants is performed through plant hormones. They help to coordinate growth, development and responses to the environment.
Plant hormones auxin and cytokinin help in cell division.
(b) 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.
Q.5. What is geotropism? Draw a labelled diagram of a potted plant showing positive geotropism and negative geotropism. [CBSE 2017-18 C]
Ans. The downward growth of roots due to attraction by earth’s gravity and upward growth of shoots against it, is geotropism.
Q.6. How does feedback mechanism regulate the hormone secretion? Explain with the help of an example. [CBSE 2017-18 C]
Ans. Feedback system is a regulatory mechanism in which presence of certain level of hormone promotes or inhibits its further formation.
Regulation of thyroxine production by its concentration in blood is an example of hormonal feedback system. If the level of thyroxine is more in the blood, this is detected by hypothalamus, which stops producing thyroid stimulating hormone (TSH). Non-availability of TSH results in failure of thyroid to produce thyroxine. This automatically results in reduction of thyroxine in blood.
But if concentration of thyroxine is low in the blood, hypothalamus produces TSH which then passes into circulatoiy system and reaches thyroid gland. Thyroid now begins to secrete more thyroxine.
Q.7. State the source of secretion and function of the following hormones: [CBSE 2016,2017-18 C]
(i) Thyroxin (ii) Insulin (iii) Growth hormone.
|(i) Thyroxin||Thyroid gland||Regulates metabolism of carbohydrates, fats and proteins.|
|(ii) Insulin||Pancreas||Promotes sugar absorption from blood thereby regulating blood-sugar level.|
|(iii) Growth hormone||Pituitary gland||Regulates overall growth of the body.|
Q.8. What are trophic levels? Make a food chain of four trophic levels. [CBSE 2017-18 C]
Ans. Each step/level of the food chain where energy transfer takes place, is called a trophic level.
e.g., (i) Plants → Grasshopper Frog → Snake
(ii) Plants Deer → Hyena Tiger
Q.9. Different parts of brain are associated with specific functions. Name the part of human brain which perform the following functions: [CBSE 2017-18 C]
(a) Sensation of feeling full
(c) Picking up a pencil
(d) Riding a bicycle.
Ans. (a) Cerebrum - Forebrain
(b) Medulla - Hind brain
(c) Cerebellum - Hind brain
(d) Cerebellum - Hind brain
Q.10. (a) What are sensory and motor neurons? Write their function. [CBSE 2018C]
(b) Different parts of brain are associated with specific functions. Name the part of human brain which perform the following functions:
(i) Sensation of feeling full
Ans. (a) Two types of neurons are:
(i) Sensory neurons - They transmit information from the receptors to the central nervous system.
(ii) Motor neurons - They transmit information from the brain to the effector organs.
(b) (i) Forebrain (a centre for hunger)
(ii) Hindbrain (medulla)
Q.11. Name the plant growth hormone which is synthesized at shoot tip. Explain with the help of diagram why does a plant bend towards light during growth. [CBSE 2016]
Ans. (i) Auxin is a phytohormone which is synthesized at shoot tip.
(ii) When a plant is exposed to light coming from one side of the plant then auxin located at the shoot tip diffuses towards the shaded side of the shoot. High concentration of auxin in the shaded region stimulates the cells to grow longer in comparison to the region exposed to light. So the shoot tends to bend towards the light.
Q.12. Name the hormone which regulates carbohydrate, protein and fat metabolism in our body. Which gland secretes this hormone? Why is it important for us to have iodised salt in our diet? [CBSE 2016]
Ans. Thyroxine regulates carbohydrates, protein and fat metaboslism in our body.
Thyroxine is secreted from thyroid gland. Deficiency of iodine in our food causes (goitre) where the thyroid gland to enlarges as it needs to absorbs more amount of iodine. Iodine is required to make thyroxine. Therefore, iodine is added to salt to supplement iodine requirement.
(b) (i) Dendrite (ii) Axon
Q.13. Name the two components of central nervous systems in humans. [CBSE 2012, 2016]
Ans. The two components of Central Nervous System in human are brain and spinal cord.
Q.14. In the absence of muscle cells, how do plant cells show movements? [CBSE 2016]
Ans. Plants do not have nervous system and muscles. Even then they exhibit well coordinated and controlled movements. Plants possess chemical coordination. They respond to stimuli by secreting chemical substances called as plant growth regulators. They either stimulate or retard growth. Five major types of plant growth hormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene.
Certain changes in the orientation of plant parts in relation to other parts caused by intrinsic or external stimuli are non-directional, growth independent movements. They are referred as nastic movements. Thus, plants show movements due to growth or change in turgor pressure.
Q.15. (a) Write two points of differences between enzymes and hormones. [CBSE 2016]
(b) Name one endocrinal gland in our body which performs dual function. Write the functions.
Ans. (a) Differences between enzymes and hormones:
|(i) Are produced by exocrine glands.||(i) Are produced by endocrine glands.|
|(ii) Site of secretion and action is same.||(ii) Site of secretion and action is different.|
(b) Pancreas performs dual function. It produces enzymes like Trypsin, Lipase etc., which aid in digestion. It also produces insulin hormone which regulates blood-sugar level.
Q.16. Name the largest part of the hind-brain. [CBSE 2016]
Q.17. Name the system which facilitates the communication between the central nervous system and the other body parts of the body. [CBSE 2016]
Ans. Peripheral nervous system.
Q.18. What is synapse? In a neuron cell how is an electrical impulse created and what is the role of synapse in this context? [CBSE 2015]
Ans. Synapse is the junction between two adjustment neuron or nerve cells, i.e. between axon ending of one and the dendrite of the next.
Transmission of Nerve Impulse. The information acquired at the end of the dendritic tip of a neuron sets off a chemical reaction which creates an electrical impulse. This impulse travels from the dendrite to the cyton along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals, which cross the synapse and start a similar electrical impulse in a dendrite of the next neuron. In this way nerve impulses travel in the body.
Synapse helps in transmitting impulses from one neuron to another.
Q.19. “As the blood sugar level in our body falls insulin secretion is reduced.” Justify this statement in the reference of feedback mechanism that regulates the timing and amount of hormone released. [CBSE 2015]
Ans. Insulin is a hormone that regulates our blood sugar level by converting it into glycogen which can be stored.
Hence, if there is more levels of sugar in blood then more insulin is produced and if the sugar level is less then insulin production is also reduced.
This is because of feedback mechanism where the blood sugar itself acts as a feedback for more or reduced insulin synthesis.
Q.20. State the role played by ovaries in a human female. [CBSE 2015]
Ans. Roles of ovary:
(i) Ovaries produce female gametes, ova.
(ii) It also produces a female sex hormone called estrogen. Estrogen is essential for development of secondary sex organs in female as well as secondary sexual characters like high pitch voice, development of mammary glands.
LONG ANSWER QUESTIONS
Q.1. Draw a diagram of cross-sectional view of human brain as given below on your answer sheet and label: [CBSE 2017-18 C]
(а) The part that helps in perform ing voluntary actions.
(b) The part that controls salivation and vomiting.
(c) The largest part of forebrain.
(d) A fluid that protects the brain.
Ans. (a) Cerebrum
(d) Cerebrospinal fluid
(e) Meninges or three membrane covering the brain.
Q.2. Name the two components of central nervous system. How are they protected? Name the component which is considered as highest coordinating centre of the body. Describe its three regions. [CBSE 2016]
Ans. Brain and spinal cord are the two components of central nervous system.
Human brain is protected by a bony skull, also called as cranium. Internal to the skull it is covered from outside by three membranes called meninges. In between the meninges there is a fluid called as cerebrospinal fluid. Beneath the membranes brain is subdivided into three major parts namely fore-brain, midbrain and hind brain.
Brain is considered as highest coordinating centre of the body.
Its three regions are given below:
(a) Fore-brain is the main thinking part of the brain. It has different regions or areas such as:
(i) Sensory area — It receives sensory impulses from various receptors.
(ii) Auditory area — It is concerned with hearing.
(iii) Olfactory area — It is concerned with smell.
(iv) Gustatory area — It is concerned with taste.
(v) Optic area — It is concerned with sight.
(vi) Association area — This area interprets various sensory informations and makes decision how to respond.
(vii) Motor area — Decisions made by association area are passed on to this area which control the movement of voluntary muscles.
(b) Midbrain comprises of four lobes. So it is also known as copra quadrigemina. Actions of involuntary muscles are controlled by the mid-brain and hind-brain.
(c) Hind-brain comprises of cerebellum, pons varolii and medulla oblongata. Cerebellum is the second largest part of brain that coordinates muscular activity of the body as well as maintains body equilibrium or posture. Pons connects cerebellum and medulla oblongata and functions as a relay centre among different parts of brain. It possesses pneumotaxic area of respiratory centre. Medulla oblongata lies below cerebellum and continues behind spinal cord. Involuntary actions like blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain.
Q.3. With the help of suitable examples explain the terms phototropism, geotropism and chemotropism. [CBSE 2016]
Ans. The stimulus oriented movement of plant or plant part is called tropism. The direction of movement is related to the direction of stimulus. These movements are always growth oriented movements. They are of different types namely phototropism (growth movement in response to light), hydrotropism (water), geotropism (force of gravity), thigmotropism (contact) and chemotropism (chemicals).
(i) Phototropism is a directional growth movement which occurs in response to unidirectional exposure to light. The region of photoreception is shoot apex where auxin is produced. Auxin moves from illuminated region to the shaded region. This causes more growth on the dark side of stem causing it to bend towards the source of light. Movement of shoot towards light is called phototropism.
(ii) Roots are positively geotropic and negatively phototropic. Shoots are positively phototropic and negatively geotropic.
(iii) Growth of pollen tube inside the style, ovary and ovule in response to the chemicals produced by them is an example of chemotropism.
Q.4. (a) Define hormone. Write four characteristics of hormones in humans.
(b) Name the disorder caused by the following situations:
(i) Under secretion of growth hormone.
(ii) Over secretion of growth hormone.
(iii) Under secretion of insulin.
(iv) Deficiency of iodine. [CBSE 2016]
Ans. (a) Hormones are chemical informational molecules that are required in minute quantities and are directly poured in the blood stream by the glands. They act on a specific organ called target organ. So their site of production varies from site of action.
Their characteristics are:
(i) They are poured into blood stream.
(ii) Are generally proteinaceous or steroid.
(iii) Their secretion is regulated by feedback mechanism.
(iv) Their site of action and secretion is different.
(b) (i) Dwarfism
Q.5. Name the hormone which is released into the blood when its sugar level rises. Name the organ which produces this hormone and its effect on blood sugar level. Also mention the digestive enzymes secreted by this organ with one function of each. [CBSE 2016]
Ans. When blood sugar level rises in blood, a hormone named ‘insulin" is produced by β-cells of islet of Langerhans in the organ Pancreas. Pancreas also produces pancreatic juice which contains pancreatic enzymes such as trypsin, pancreatic amylase and pancreatic lipase.
Insulin promotes glucose absorption by individual cells and absorption and formation of glycogen in liver and muscles. This reduces glucose level in blood. As soon as the blood sugar comes to normal the pancreatic cells stops secretion of insulin.
Pancreas secretes slightly alkaline pancreatic juice which contains three major following enzymes:
(i) Trypsin which digests proteins.
(ii) Lipase which digests fats.
(iii) Amylase which digests carbohydrates.
Q.6. What are phytohormones? List four types of phytohormones. Where are these synthesised? [CBSE 2016]
Ans. Plants possess chemical coordination. They respond to stimuli by secreting chemical substances called as plant growth regulators. They either stimulate or retard growth. Five major types of plant growth hormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene.
These plant growth regulators are also known as phytohormones.
These are synthesised at shoot apices, leaves, developing embryos, root tips etc.
Q.7. What is meant by reflex-action? With the help of a labelled diagram trace the sequence of events which occur when we touch a hot object. [CBSE 2015]
Ans. Reflex action is defined as an unconscious, automatic and involuntary response of effector, i.e. muscle and gland to a stimulus which is monitored through the spinal cord.
Sequence of events when we touch a hot object are:
(a) Receptor organ skin receives the stimulus and activates a sensory nerve impulse.
(b) Sensory neuron carries the message in the form of sensory impulse to the spinal cord.
(c) The spinal cord acts as a modulator. The neurons of spinal cord transmit the sensory nurve impulses to motor neuron.
(d) Motor nerve conducts these impulses to the effector organ hand which responds by pulling back the hand away from the hot object.
Q.8. Write the names of the hormones secreted by pituitary gland and adrenal gland. State their functions in the body. [CBSE 2015]
|Hormones secreted by||Functions|
|(1) Pituitary gland:|
|Regulates growth and development of the body.|
|(2) Adrenal gland:|
|(i) Prepares the body for facing an emergency situation.|
(ii) Increases heart rate, resulting in more oxygen supply to muscles.
(iii) Reduces blood supply to skin and digestive; system.
(iv) Increases breathing rate.