CBSE Class 10 Science Control and coordination Sure Shot Questions Set 04

This is Set 04 of sure shot questions for CBSE Class 10 Science Chapter 6, Control and Coordination, with step-by-step answers and a Teacher's Note for each question. It collects the board-style questions asked most often, from reflex arc, synapse and parts of the brain to phototropism, plant hormones, adrenaline, insulin and iodised salt.

Very Short Answer Questions (1 Mark)

Question 1. Which is the largest and most prominent part of the brain?
Answer:
The cerebrum (part of the forebrain) is the largest and most prominent part of the human brain. It is the main thinking part, the seat of memory, intelligence and will power.
In simple words: The cerebrum is the biggest part of the brain.

Teacher's Note:
1. Cerebrum is in the forebrain and cerebellum is in the hind brain.
2. Do not mix the two names.

Question 2. How is the spinal cord protected in the human body?
Answer:
The spinal cord is enclosed in a bony cage called the vertebral column (backbone). It is also covered by membranes (meninges) and cerebrospinal fluid, which absorb shocks.
In simple words: The backbone forms a bony cage around the spinal cord.

Teacher's Note:
1. The brain is protected by the cranium and the spinal cord by the vertebral column.
2. Mention the bony part by name.

Question 3. Name two tissues that provide control and coordination in multicellular animals.
Answer:
Nervous tissue and muscular tissue provide control and coordination in multicellular animals. The nervous tissue carries the messages and the muscular tissue carries out the response.
In simple words: Nerves send the message and muscles act on it.

Teacher's Note:
1. Hormones from endocrine glands are the chemical means of coordination.
2. Name the tissue, not the organ.

Question 4. Which endocrine gland secretes the growth hormone?
Answer:
The pituitary gland, situated at the base of the brain, secretes the growth hormone. Under-secretion in childhood causes dwarfism and over-secretion causes gigantism.
In simple words: The pituitary is the gland that gives growth hormone.

Teacher's Note:
1. The pituitary is also called the master gland.
2. Link the hormone with its disorders.

Short Answer Questions (2 and 3 Marks)

Question 5. What is reflex action? Describe the steps involved in a reflex action.
Answer:
Step 1: A reflex action is a sudden, automatic response to a stimulus, without the will (thinking) of the animal. It is controlled by the spinal cord.
Step 2: The receptor (for example the skin) detects the stimulus and a sensory neuron carries the impulse to the spinal cord.
Step 3: In the spinal cord the impulse passes to a motor neuron, which carries it to the effector (muscle or gland), which gives the response.
The path taken by the nerve impulses is called the reflex arc.

In simple words: A reflex is a very quick, automatic reaction that skips the thinking brain.

Teacher's Note:
1. Write the steps as a flow chart for full marks.
2. Give an example such as withdrawing the hand from a hot object.

Question 6. Why does the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron take place but not in the reverse direction? Explain.
Answer:
Step 1: At the axonal end of a neuron, the electrical impulse releases chemicals (neurotransmitters) into the synapse, the small gap between two neurons.
Step 2: These chemicals cross the gap and start a similar electrical impulse in the dendrite of the next neuron.
Step 3: The neurotransmitter is stored only at the axonal end, not at the dendritic end.
Final answer: Since the chemical is released only from the axonal side, the synapse works like a one-way valve.
In simple words: A synapse is a one-way valve because only the axon end releases the chemical.

Teacher's Note:
1. Name the chemical messenger as neurotransmitter.
2. The impulse always goes dendrite to cell body to axon to the next neuron.

Question 7. "Reflex arcs continue to be more efficient for quick responses". Justify this statement giving reason.
Answer:
Step 1: The thinking process of the brain is not fast enough to respond to a sudden danger.
Step 2: A reflex arc is formed in the spinal cord, so the impulse takes a short route without waiting for the brain.
Final answer: Reflex arcs give quick responses to harmful stimuli, so damage to the body is reduced. They also save the brain from overloading, so reflex arcs are more efficient for quick responses even after complex neuron networks have evolved.
In simple words: Reflexes are the body's emergency shortcut.

Teacher's Note:
1. Compare the length of the reflex path with the path through the brain.
2. Reflex actions have nothing to do with the will.

Question 8. (a) Define reflex arc.
(b) Trace the sequence of events which occur in our body when a bright light is focussed on your eyes.
Answer:
(a) The pathway taken by the nerve impulses in a reflex action, from the receptor organ to the spinal cord and back to the effector organ, is called the reflex arc.
(b) Bright light on the eye is the stimulus. The sequence is:
Photoreceptors (receptors) in the eye → sensory neuron → brain → motor neuron → muscles of the iris (effector) → the pupil gets smaller.
In simple words: A reflex arc is the nerve route of a reflex, and bright light makes the pupil shrink.

Teacher's Note:
1. Name the receptor and the effector in every reflex example.
2. The shrinking pupil protects the retina.

Question 9. Mention three major regions of brain. Write one function of each.
Answer:
The brain has three major regions:
1. Forebrain: It is the main thinking part of the brain. It controls memory, intelligence and the voluntary actions, and also has the centres of hunger and smell.
2. Midbrain: It controls reflex movements of the head and neck in response to visual and auditory stimuli.
3. Hindbrain: It has the cerebellum (balance of the body), the pons (breathing) and the medulla (involuntary actions such as heartbeat and vomiting).
In simple words: The forebrain thinks, the midbrain relays reflexes, and the hindbrain keeps the body balanced and running.

Teacher's Note:
1. Learn the brain regions along with one function each.
2. Medulla controls involuntary actions, cerebellum controls balance.

Question 10. What are plant hormones? Name the plant hormones responsible for the following:
(i) Growth of stem
(ii) Promotion of cell division
(iii) Inhibition of growth
(iv) Elongation of cells
Answer:
Plant hormones (phytohormones) are chemical substances produced naturally in plants in very small amounts. They control and coordinate growth, development and the responses to the environment.
(i) Growth of stem: gibberellin (auxin also helps).
(ii) Promotion of cell division: cytokinin.
(iii) Inhibition of growth: abscisic acid.
(iv) Elongation of cells: auxin.
In simple words: Gibberellin makes stems grow, cytokinin divides cells, abscisic acid stops growth and auxin lengthens cells.

Teacher's Note:
1. Make a table of five hormones with one function each.
2. Ethylene is the gaseous hormone that ripens fruits.

Question 11. Define phototropism. Name the plant hormone which is responsible for phototropism.
Answer:
Phototropism is the movement of a part of a plant in response to light. Shoots grow towards light (positive phototropism) and roots grow away from light (negative phototropism).
The hormone responsible is auxin. It is made at the shoot tip and causes the cells on the shaded side to grow longer, so the shoot bends towards light.
In simple words: Phototropism is growth bending in response to light, controlled by auxin.

Teacher's Note:
1. Name the stimulus whenever you name a tropism.
2. Auxin moves to the shady side.

Question 12. Name the hormones secreted by the following endocrine glands and specify one function of each: (a) Thyroid (b) Pituitary (c) Pancreas.
Answer:
(a) The thyroid secretes thyroxine, which regulates the metabolism of carbohydrates, fats and proteins.
(b) The pituitary secretes growth hormone, which controls the growth and development of the body.
(c) The pancreas secretes insulin, which lowers the blood sugar level.
In simple words: Thyroxine controls metabolism, growth hormone controls growth and insulin controls blood sugar.

Teacher's Note:
1. Write one hormone and one function for each gland.
2. Do not forget that the thyroid needs iodine.

Question 13. (a) How does chemical coordination take place in animals?
(b) It is advised to use iodised salt. Give reason.
Answer:
(a) Chemical coordination in animals takes place through hormones. Endocrine glands secrete hormones directly into the blood. The blood carries them to the target organs, which then respond.
(b) Iodine is necessary for the thyroid gland to make the hormone thyroxine. Iodine deficiency in the diet causes goitre, so we should use iodised salt.
In simple words: Hormones travel in the blood, and iodine in salt keeps the thyroid healthy.

Teacher's Note:
1. Use the words hormone, blood and target organ in (a).
2. Name the disease goitre in (b).

Question 14. Why is chemical communication better than electrical impulses as a means of communication between cells in a multicellular organism?
Answer:
Step 1: Electrical impulses are very quick, but they can reach only those cells that are connected by nervous tissue.
Step 2: After generating and transmitting an impulse, the cells need some time to reset, so they cannot continuously transmit impulses.
Final answer: Chemical messengers (hormones) spread through the blood to all the cells of the body, whether or not they are connected by nerves, and their effect lasts longer. So chemical communication is better for the whole body.
In simple words: Hormones in the blood reach every cell, while nerves reach only connected cells.

Teacher's Note:
1. Give one limitation of electrical impulses and one advantage of chemical messages.
2. Chemical communication is slower but more widespread.

Teacher's Note:
1. Present the points in a two-column table.
2. Write at least three pairs of points.

Question 16. Name the hormone required for the following. Also mention the name of the endocrine gland from which that hormone is secreted:
(a) Lowering of blood glucose.
(b) Development of moustache and beard in human males.
(c) Metabolism of carbohydrates, fats and proteins.
Answer:
(a) Insulin, secreted by the pancreas.
(b) Testosterone, secreted by the testes.
(c) Thyroxine, secreted by the thyroid gland.
In simple words: Insulin, testosterone and thyroxine come from the pancreas, testes and thyroid.

Teacher's Note:
1. Pair every hormone with its gland.
2. Testosterone is the male sex hormone.

Question 17. A squirrel is in a scary situation. Its body has to prepare for either fighting or running away. State the immediate changes that take place in its body so that the squirrel is able to either fight or run.
Answer:
Step 1: The nervous system stimulates the adrenal glands to secrete more adrenaline into the blood.
Step 2: Adrenaline increases the heartbeat and the breathing rate, and sends more blood to the skeletal muscles. It also makes the liver release stored glucose into the blood.
Final answer: All these changes provide a lot of energy and oxygen to the muscles, so the squirrel can fight or run away.
In simple words: Adrenaline puts the whole body on high alert for fight or flight.

Teacher's Note:
1. Adrenaline is the emergency hormone.
2. Mention at least three effects.

Question 18. (A) Sagar saw a beautiful rose and smelled it. As he was smelling it, he happened to touch a thorn and pull his hand away. State TWO differences and similarities each in the way the nervous system performs the two actions.
(B) Are all involuntary actions reflex actions? Justify.
Answer:
(A) Differences: (1) Smelling the rose is a voluntary action controlled by the brain (forebrain), whereas pulling the hand away is a reflex action, controlled by the spinal cord. (2) Smelling is a slower action, while the reflex action is very quick.
Similarities: (1) In both, a receptor (olfactory receptor or the pain receptor in the skin) detects the stimulus and sensory neurons carry the information. (2) In both, the nerve impulse is electrical along a neuron and chemical across the synapse, and the information also reaches the brain.
(B) No. Involuntary actions such as the heartbeat, breathing and the movements of the food pipe go on without our will and without any sudden stimulus, and are controlled by the medulla and the autonomic nerves. A reflex action is an involuntary response to a stimulus, controlled by the spinal cord. So all reflex actions are involuntary, but not all involuntary actions are reflexes.
In simple words: Smelling is a thinking action while pulling away is a reflex, and not every involuntary action is a reflex.

Teacher's Note:
1. Present differences and similarities in separate lines.
2. Heartbeat is a good example of an involuntary but non-reflex action.

Question 19. In animals, hormones can be secreted by one organ and can act on multiple organs. Justify this statement by explaining the effect of a single animal hormone on three organs.
Answer:
Step 1: Take the hormone adrenaline, which is secreted by the adrenal glands.
Step 2: Heart: the heartbeat increases, so that more oxygen is supplied to the muscles.
Step 3: Diaphragm and rib muscles: the breathing rate increases.
Step 4: Small arteries of the digestive system and skin: they contract, so the blood supply to them falls and more blood is directed to the skeletal muscles.
Final answer: One hormone, adrenaline, acts on the heart, the breathing muscles and the blood vessels, which shows that a hormone can act on many organs.
In simple words: Adrenaline from the adrenal glands changes the working of many organs together.

Teacher's Note:
1. Choose a hormone you know well and name three organs.
2. Adrenaline travels in the blood, so it reaches all the organs.

Long Answer Questions (5 Marks)

Question 20. What is 'phototropism'? How does it occur in plants? Describe an activity to demonstrate phototropism.
Answer:
Step 1: Phototropism is the directional movement of a plant part in response to light. The shoot bends towards light (positive phototropism) and the root bends away from light (negative phototropism).
Step 2: It is caused by the hormone auxin. When light falls on the shoot from one side, auxin made at the tip diffuses towards the shady side. The cells on the shady side grow longer, so the shoot bends towards the light.
Step 3: Activity: Take two potted plants. Keep plant A in the open, so that light comes from above. Keep plant B near a window, so that light comes from one side only. Observe both for a few days.
Step 4: Observation: Plant A grows straight up, whereas plant B bends towards the window.
Conclusion: The shoot responds to light by growing towards it, which is positive phototropism.
In simple words: A plant bends towards light because auxin makes the shaded side grow longer.

Teacher's Note:
1. Write definition, mechanism, activity and conclusion in this order.
2. Remember that auxin collects on the side away from light.

Question 21. (a) Draw the structure of a neuron and label the following on it: nucleus, dendrite, cell body and axon.
(b) Name the part of neuron:
(i) Where information is acquired
(ii) Through which information travels as an electrical impulse.
Answer:
(a) Diagram of a neuron:

(b) (i) Information is acquired at the tips of the dendrites. It sets off a chemical reaction that creates an electrical impulse. (ii) The information travels as an electrical impulse from the dendrite to the cell body and then along the axon. At the end of the axon the impulse releases chemicals, which cross the synapse to the next neuron.
In simple words: Dendrites receive the message and the axon carries it onwards.

Teacher's Note:
1. Draw the neuron with dendrites on the left and the axon on the right.
2. Add an arrow to show the direction of the impulse.

Teacher's Note:
1. Learn one site of synthesis for every hormone.
2. Use a small table for the answer to part (a).

Question 23. (a) Define reflex arc. Draw a flow chart showing the sequence of events which occur during sneezing.
(b) List four plant hormones. Write one function of each.
Answer:
(a) The pathway or route taken by nerve impulses in a reflex action is called a reflex arc.
Flow chart for sneezing:
Irritating particle in the nose (stimulus) → receptors in the nasal cavity → sensory nerve → medulla of the hind brain (which has the reflex centre for sneezing) → motor nerve → muscles of the diaphragm and ribs (effectors) → sneeze (forceful breathing out).
(b) Auxin: promotes cell elongation and the growth of the stem. Gibberellin: helps in the growth of the stem. Cytokinin: promotes cell division. Abscisic acid: inhibits growth and causes wilting of leaves (ethylene ripens fruits).
In simple words: A reflex arc is the nerve route of a reflex, and sneezing follows the same chain of steps.

Teacher's Note:
1. Draw the flow chart with arrows between the boxes.
2. Give one function with every hormone name.

Question 24. (A) How is the blood sugar level regulated in the human body?
(B) (i) Which hormone is secreted into the blood when you are under stress? Name the gland that secretes this hormone.
(ii) How does it help the body to cope up in an emergency situation?
Answer:
(A) The timing and amount of insulin released are regulated by a feedback mechanism. When the blood sugar level rises, the cells of the pancreas detect it and secrete more insulin, which lowers the sugar level. As the blood sugar falls, insulin secretion is reduced.
(B)(i) Adrenaline is secreted by the adrenal glands, which lie on top of the kidneys.
(ii) It makes the heart beat faster and the breathing rate rise, so more oxygen reaches the muscles. Blood supply to the digestive system and the skin is reduced and more blood is sent to the skeletal muscles. These changes prepare the body to fight or run.
In simple words: The pancreas uses feedback to keep sugar steady, and adrenaline prepares the body for emergencies.

Teacher's Note:
1. Use the example of insulin to explain a feedback mechanism.
2. Adrenaline is the stress hormone.

Question 25. (a) An old man is advised by his doctor to take less sugar in his diet. Name the disease from which the man is suffering. Mention the hormone due to imbalance of which he is suffering from this disease. Which endocrine gland secretes this hormone?
(b) Name the endocrine gland which secretes growth hormone. What will be the effect of the following on a person: (i) deficiency of growth hormone (ii) excess secretion of growth hormone?
Answer:
(a) The man is suffering from diabetes mellitus. It is caused by the imbalance (deficiency) of insulin, which is secreted by the pancreas.
(b) Growth hormone is secreted by the pituitary gland.
(i) Deficiency of growth hormone in childhood causes dwarfism.
(ii) Excess secretion of growth hormone causes gigantism (very tall person).
In simple words: Diabetes comes from too little insulin; growth hormone problems change a person's height.

Teacher's Note:
1. Write disease, hormone and gland as a short chain.
2. Dwarfism means short and gigantism means very tall.