CBSE Class 10 Science HOTs Control And Coordination Set 05

This is Set 05 of higher-order thinking (HOTS) questions for CBSE Class 10 Science Chapter 6, Control and Coordination, with step-by-step answers and a Teacher's Note for every question. The questions ask you to reason about reflex actions, the receptor and effector roles of organs, tropic and nastic movements, hormone sprays used by farmers, and hormonal disorders in real situations.

Short Answer Type HOTS Questions

Question 1. Why is oxytocin called as 'birth hormone'?
Answer:
Step 1: Oxytocin is a hormone released from the posterior part of the pituitary gland.
Step 2: At the end of pregnancy it stimulates strong contractions of the smooth muscles of the uterus, which push the baby out.
Final answer: Oxytocin brings about the uterine contractions needed for child birth, so it is called the birth hormone. It also helps in the release of milk after birth.
In simple words: Oxytocin makes the uterus contract at the time of delivery.

Teacher's Note:
1. The name of a hormone often tells its job, so link 'birth hormone' with the uterus.
2. Do not confuse it with prolactin, which helps in making milk.

Question 2. How do you support the statement that 'pancreas' is the overall controller of the blood glucose level?
Answer:
Step 1: The pancreas has cells that sense the level of sugar in the blood.
Step 2: When the blood sugar rises, these cells secrete more insulin. Insulin helps the cells to take up glucose and the liver to store it as glycogen, so the sugar level falls.
Step 3: When the blood sugar falls, insulin secretion is reduced automatically. This is a feedback mechanism.
Final answer: By secreting insulin in the right amount, according to the blood sugar level, the pancreas keeps the blood glucose within a narrow range. If it fails, diabetes results.
In simple words: The pancreas adds or cuts down insulin, like a thermostat, to keep sugar steady.

Teacher's Note:
1. Use the words 'feedback mechanism' and 'insulin' in the answer.
2. Remember that the same pancreas also makes digestive juice.

Question 3. An alcoholic person when drunk, generally walks clumsily. Why?
Answer:
Step 1: The cerebellum, a part of the hind brain, controls the posture and balance of the body and the precision of voluntary movements.
Step 2: Alcohol affects the working of the cerebellum, so the muscles are no longer coordinated properly.
Final answer: Alcohol affects the cerebellum, so the person cannot maintain balance and walks clumsily.
In simple words: Alcohol disturbs the brain part that keeps the body steady.

Teacher's Note:
1. Link each symptom with the brain part that controls it.
2. Medulla controls involuntary actions, cerebellum controls balance.

Question 4. A farmer is having a big guava farm, he wants big and healthy fruits to improve his economy. What hormones should be used and why?
Answer:
Step 1: Auxins promote cell enlargement and fruit growth, and gibberellins help in the growth of the stem and fruits.
Step 2: Cytokinins promote cell division, so more cells are formed in the young fruit.
Step 3: Ethylene should be used only at the end, to ripen the fully grown fruits.
Final answer: Auxins, gibberellins and cytokinins for growth of big fruits; ethylene for ripening.
In simple words: Growth hormones make the fruit big, and ethylene makes it ripe.

Teacher's Note:
1. Match every hormone with its function before writing the answer.
2. Ethylene is the only gaseous plant hormone.

Question 5. A person walks across a room in barefeet and puts his foot on a drawing pin lying in the floor. He lets out a cry. Explain what happens in his nervous system in bringing about this response.
Answer:
Step 1: The pain receptor in the skin of the foot detects the pin and sends an impulse along a sensory neuron to the spinal cord.
Step 2: In the spinal cord the impulse passes through a relay neuron to a motor neuron, which carries it to the muscles of the leg. The muscles contract and the foot is pulled away. This is a reflex action.
Step 3: Information also travels to the brain, which is how the person feels the pain and cries out.
Final answer: Pain receptor → sensory neuron → spinal cord → motor neuron → leg muscle (reflex), and the message then reaches the brain, so the person cries.
In simple words: The foot moves away first through the spinal cord, and the brain gets to know a moment later.

Teacher's Note:
1. Write the path of the impulse in order as a flow chart.
2. The quick withdrawal is a reflex, the cry is felt and decided by the brain.

Question 6. The tongue may be considered to be a receptor and an effector organ. Why?
Answer:
Step 1: The tongue has taste buds with gustatory receptors that detect taste, so it works as a receptor.
Step 2: The tongue is also a muscular organ. It can respond to a stimulus by moving, for example while speaking or pushing food, so it works as an effector.
Final answer: The tongue detects taste (receptor) and responds by muscular movement (effector).
In simple words: The tongue both senses taste and moves when told to.

Teacher's Note:
1. A receptor detects a stimulus and an effector responds to it.
2. Name the receptor type: gustatory for taste.

Question 7. Why is the closing of a Dandelion flower at dusk (when it gets darker) not a tropism?
Answer:
Step 1: Tropism is a directional movement, in which the plant part bends towards or away from the stimulus, by growth.
Step 2: The closing of a dandelion flower at dusk is a non-directional movement that depends on the intensity of light, and it does not involve growth.
Final answer: It is a nastic (photonastic) movement, not a tropism, because it is non-directional and independent of growth.
In simple words: A tropism has a direction; the flower simply closes when it gets dark.

Teacher's Note:
1. Ask two questions: is the movement directional and does it involve growth?
2. If both answers are no, it is nastic.

Question 8. Why is the folding up of the leaves of a sensitive plant on touching with a finger not a tropism?
Answer:
Step 1: Tropism is a directional growth movement towards or away from a stimulus.
Step 2: When the leaves of the sensitive plant are touched, they fold up whatever the direction of the touch. The movement is caused by a change in the amount of water in the cells (loss of turgor), not by growth.
Final answer: It is a nastic movement because it is non-directional and does not depend on growth.
In simple words: The leaf folds by losing water, not by growing, so it is not a tropism.

Teacher's Note:
1. Compare with the bending of a shoot towards light, which needs growth.
2. The sensitive plant is Mimosa pudica (touch-me-not).

Question 9. Amrit takes three jars A, B and C. Jar A has ice cold water, jar B has lukewarm water and jar C has water at normal temperature. Amrit placed his finger in jar A and B and felt the water to be cold and hot respectively. Now, again he placed his finger in jar B, C and A in the same sequence. Soon, he was not able to distinguish hot and cold water in the jars. Formulate the possible reason for the above observations of Amrit.
Answer:
Step 1: The temperature receptors in the skin of the finger send impulses to the brain through sensory neurons.
Step 2: When the same kind of stimulus acts again and again, the receptors become less responsive and the chemicals (neurotransmitters) released at the nerve endings run low. The brain then receives only weak signals.
Final answer: Continuous stimulation tires the receptors and the synapses, so Amrit could no longer tell hot water from cold water.
In simple words: When the same stimulus keeps acting, the body stops noticing the difference.

Teacher's Note:
1. Think of how a bad smell is hardly noticed after some time.
2. Receptors respond mainly to a change in the stimulus.

Question 10. Samir brought 200 unripe mangoes. His mother suggested he should keep them in a closed room and cover it with papers. What would be the reason behind this?
Answer:
Step 1: Ripening fruits release ethylene, a gaseous plant hormone that hastens fruit ripening.
Step 2: In a closed room covered with papers, the gas is not lost. Its concentration builds up around the mangoes.
Final answer: The trapped ethylene gas speeds up the ripening of the mangoes.
In simple words: The fruits make a ripening gas and the closed room keeps it in.

Teacher's Note:
1. Ethylene is the only plant hormone that is a gas.
2. One ripe fruit kept with raw fruits ripens them for the same reason.

Question 11. Imagine what would happen if your neurons were disc shaped?
Answer:
Step 1: A neuron is long and branched. Its dendrites collect information and its long axon carries the impulse over a long distance.
Step 2: A disc-shaped neuron would have no long axon and no branched dendrites, so impulses could not travel efficiently from one part of the body to another.
Final answer: The transfer of messages over long distances would be affected, and coordination would become slow or impossible.
In simple words: The shape of a neuron suits its work of carrying messages far and fast.

Teacher's Note:
1. Structure and function go together in biology.
2. Name the parts: dendrites, cell body and axon.

Question 12. Pancreas is both endocrine and exocrine in nature. Suppose the exocrine part becomes damaged then how will it affect your body?
Answer:
Step 1: The exocrine part of the pancreas secretes pancreatic juice with digestive enzymes into the small intestine through a duct.
Step 2: If this part is damaged, the enzymes will not be available for the digestion of carbohydrates, proteins and fats.
Final answer: Digestion of food will be hampered. Blood sugar control by insulin (endocrine part) would continue.
In simple words: A damaged exocrine pancreas means poor digestion, not a sugar problem.

Teacher's Note:
1. Exocrine glands have ducts, endocrine glands do not.
2. The islets that make insulin are the endocrine part.

Question 13. On touching a hot plate we suddenly withdraw our hand. Which category of neurons became active first and which one next?
Answer:
Step 1: Sensory neurons become active first. They carry the impulse from the receptors in the skin to the spinal cord.
Step 2: The spinal cord passes the message to the motor neurons, which become active next and carry the impulse to the muscles of the hand.
Final answer: Sensory neurons first, then motor neurons.
In simple words: First the message goes in (sensory), then the order comes out (motor).

Teacher's Note:
1. Sensory neurons go towards the spinal cord, motor neurons go away from it.
2. Write the full pathway to earn all the marks.

Question 14. Using the following words below, construct a reflex arc. Sensory nerves, receptor, effector, stimulus, brain or spinal cord, response, motor neurons.
Answer:
Step 1: A reflex arc starts with a stimulus and ends with a response.
Step 2: The impulse is picked up by the receptor and carried by the sensory nerve to the spinal cord (or brain). From there the motor neuron carries it to the effector.
Final answer: Stimulus → Receptor → Sensory nerves → Brain or spinal cord → Motor neurons → Effector → Response.

In simple words: A reflex arc is the shortest path from the stimulus to the response.

Teacher's Note:
1. Learn the sequence as a flow chart.
2. The spinal cord is the centre for most reflexes.

Question 15. Why are the electrochemical signals not an efficient means of communication in plants?
Answer:
Step 1: Plants do not have a nervous system, that is, no specialised tissue like neurons to carry electrochemical signals.
Step 2: The signal has to pass slowly from cell to cell, and it can reach only the cells that are connected to the cell where it started.
Final answer: Because plants have no specialised conducting tissue, electrical-chemical signals are slow and limited, so plants depend on hormones.
In simple words: Without nerves, a plant's electrical signal moves slowly, so it uses hormones instead.

Teacher's Note:
1. Compare with animals, which have neurons for fast signals.
2. Link the answer to the use of plant hormones.

Case Based and Application HOTS Questions

Question 16. A gardener observes weed growth in grass lawns. What is the best way to prevent it?
Answer:
Step 1: Weeds in a lawn are mostly dicotyledonous plants, while the lawn grass is monocotyledonous.
Step 2: The gardener can spray a synthetic auxin such as 2,4-dichlorophenoxyacetic acid (2,4-D). It acts like a weedicide.
Final answer: Spraying 2,4-D kills dicot weeds without harming the monocot grass.
In simple words: A synthetic auxin sprayed on the lawn kills the weeds but spares the grass.

Teacher's Note:
1. Auxins in a large amount act as weedicides.
2. Name the type of plants affected: dicot weeds.

Question 17. A farmer wants to grow seedless cucumbers to increase the yield and decrease the cost of cultivation. What is the best possible or efficient way of doing it without using organic pesticides?
Answer:
Step 1: The process of developing fruits without forming seeds is called parthenocarpy.
Step 2: It can be induced by spraying the flowers with plant hormones, auxins and gibberellins.
Final answer: Spray auxin and gibberellin to induce parthenocarpy. This raises the yield in a short time and lowers the cost of cultivation.
In simple words: Hormone sprays can make the fruit grow without seeds.

Teacher's Note:
1. Seedless fruits are formed without fertilisation.
2. Banana and grapes are common examples.

Question 18. What happens if gibberellins are sprayed on a sugarcane crop? Sugarcane stores carbohydrates as sugar in its stems.
Answer:
Step 1: Gibberellins help in the growth of the stem by increasing the length of the internodes.
Step 2: Longer stems can store more sugar.
Final answer: The stems become longer, which increases the crop yield.
In simple words: A longer sugarcane stem holds more sugar.

Teacher's Note:
1. Gibberellins and auxins both help the stem to grow.
2. Cytokinins act on cell division.

Question 19. A boy presents with delayed development of secondary sexual characteristics at the age of 16 years. The deficiency of which hormone is responsible for this condition?
Answer:
Step 1: At puberty the testes of a boy release the male sex hormone testosterone.
Step 2: Testosterone is responsible for the changes such as growth of moustaches and beard, deepening of voice and muscle growth.
Final answer: Deficiency of testosterone.
In simple words: Boys need testosterone for the changes of puberty.

Teacher's Note:
1. In girls the corresponding hormone is oestrogen.
2. Say from which gland the hormone is secreted: the testes.

Question 20. A patient presents with double vision, hunger, anxiety and sudden weight gain. The blood tests revealed low circulating levels of sugar. What can be the reason for these symptoms?
Answer:
Step 1: Insulin, secreted by the pancreas, lowers the blood sugar level.
Step 2: Low blood sugar means that too much insulin is being secreted.
Final answer: Excess secretion of insulin by the pancreas lowers the blood sugar level.
In simple words: Too much insulin pulls the blood sugar down too far.

Teacher's Note:
1. Too little insulin gives diabetes, too much gives low sugar.
2. Insulin is made by the beta cells of the islets of Langerhans.

Question 21. Why does deficiency of thyroid hormone lead to weight gain in women?
Answer:
Step 1: Thyroxine regulates the metabolism of carbohydrates, proteins and fats.
Step 2: With less thyroxine, the metabolic rate falls, so fewer calories are used and the extra food is stored as fat.
Final answer: Low thyroxine slows the metabolism, so the body gains weight.
In simple words: Less thyroxine means a slower body engine and more stored fat.

Teacher's Note:
1. Thyroxine needs iodine for its synthesis.
2. Remember: under-secretion of thyroxine causes goitre or cretinism.

Question 22. The meristematic tissue, located at the tip of the stem of a plant, is responsible for the secretion of a chemical substance K. A particular process L, in which the plant stem bends toward a light source, is facilitated by the chemical substance K. However, this very same chemical K has an opposite effect on the plant root. It induces bending in the root of the plant away from the light source in a process named M.
(A) Identify the chemical substance K.
(B) What could be the preference of K, to remain at the site of incident sunlight or in the shade?
(C) What will be the effect of chemical K on the growth rate of (i) a root, and (ii) a stem?
(D) What are the names of process L and M?
(E) Write the general name of chemical substances such as K. List another substance that belongs to the same class of chemical substances.
Answer:
(A) K is the plant hormone auxin, made at the shoot tip.
(B) Auxin prefers to stay in the shade, on the side away from light.
(C) (i) It slows down the growth of the root cells on the shaded side. (ii) It speeds up the growth (cell elongation) of the stem cells on the shaded side.
(D) L is positive phototropism (of the stem) and M is negative phototropism (of the root).
(E) Such substances are called plant hormones or plant growth regulators (phytohormones). Another example is gibberellin (also cytokinin, abscisic acid, ethylene).
In simple words: Auxin collects on the shady side, so the shoot bends to the light while the root bends away.

Teacher's Note:
1. Auxin collects on the side away from light.
2. The same hormone can make the stem grow faster on that side and the root grow slower.

Teacher's Note:
1. Check the table against what you have learnt, since the uses of cytokinin and auxin are often interchanged by mistake.
2. Ethylene mainly ripens fruits.