CBSE Class 10 Science HOTs Life Processes Set 06

This page has 23 higher order thinking (HOTs) questions with answers for CBSE Class 10 Science Chapter 5, Life Processes, taken from chapter-wise question banks and board-style practice. The questions ask you to predict, justify and apply ideas about photosynthesis and gas exchange in plants, digestion, breathing, blood and lymph, kidneys and dialysis, and each answer is explained step by step.

Short Answer HOTs Questions

Question 1. What would happen if all the green plants disappear from the earth?
Answer:
Green plants are the producers. They make food by photosynthesis, and every food chain begins with them.
If they disappeared, herbivores would starve first, then carnivores and omnivores that depend on them would die too.
Photosynthesis also releases the oxygen we breathe and removes carbon dioxide from the air. Without it, oxygen would run out and carbon dioxide would build up, so almost all life would end.
In simple words: No green plants means no food and no oxygen, so no life.

Teacher's Note:
1. Say that plants are the first link of every food chain.
2. Add the oxygen point for full marks.

Question 2. Explain why a land plant may die if its roots remain waterlogged for a long time.
Answer:
Roots need oxygen for respiration, which gives the energy they use to absorb minerals and water.
In waterlogged soil, the spaces between soil particles are filled with water, so air (oxygen) is not available to the roots.
The roots then respire without oxygen and form alcohol (ethanol) with very little energy. The alcohol is harmful, the roots die, and the whole plant dies.
In simple words: Roots drown for lack of oxygen, so the plant dies.

Teacher's Note:
1. Link waterlogging with lack of air in the soil.
2. Mention anaerobic respiration and the harmful alcohol.

Question 3. Explain how it would benefit deep sea divers if humans also had gills.
Answer:
Gills take in the oxygen dissolved in water, the way fish do.
If humans had gills, divers could remove dissolved oxygen from the water and would not have to carry heavy oxygen cylinders.
They could stay under water for a much longer time and move more freely.
In simple words: Gills would let divers breathe the oxygen dissolved in sea water.

Teacher's Note:
1. Gills work on dissolved oxygen.
2. Connect it with the oxygen cylinder that divers now carry.

Question 4. Explain why, plants have low energy needs as compared to animals.
Answer:
Plants are autotrophs and are mostly stationary. They do not move from place to place in search of food, mates or shelter.
A large part of a plant body (for example wood, bark and xylem) is made of dead cells with no living protoplasm that needs energy.
Animals are heterotrophs, move around and have most of their tissues living, so they need more energy.
In simple words: Plants stay in one place and much of their body is dead tissue, so they need less energy.

Teacher's Note:
1. Compare movement and living tissue in plants and animals.
2. Use the words autotroph and heterotroph.

Question 5. Why do some people need to use a dialysis machine? What does the machine do?
Answer:
Some people have kidneys that have failed. Their kidneys cannot filter urea and extra water and salts from the blood, so these wastes build up in the body.
The dialysis machine (artificial kidney) takes the patient's blood through tubes with a semipermeable lining placed in a dialysing fluid. Urea, excess water and extra salts pass into the fluid by diffusion.
The cleaned blood is pumped back into the patient's body.
In simple words: The dialysis machine does the work of failed kidneys and cleans the blood.

Teacher's Note:
1. Name kidney failure as the reason.
2. Mention the semipermeable tubes and the removal of urea.

Question 6. Why bile juice is necessary for digestion of food however it does not contain enzymes?
Answer:
Bile juice, made by the liver, has bile salts but no enzyme. It still helps digestion in two ways.
(i) It makes the acidic food coming from the stomach alkaline, so that the pancreatic enzymes can work.
(ii) Bile salts emulsify fats, that is, break large fat globules into very small droplets. This gives lipase a larger surface to act on.
In simple words: Bile does not digest food itself, but it prepares fats and the medium for the enzymes.

Teacher's Note:
1. Give both the alkaline medium and emulsification.
2. State clearly that bile has no enzymes.

Question 7. Explain why constriction of skin blood vessels on a cold winter day is beneficial.
Answer:
Constriction means the blood vessels in the skin become narrower, so less blood flows through the skin.
Less warm blood reaches the skin surface, so less heat is lost from the body to the cold surroundings.
This helps the body to keep its internal temperature steady in cold weather.
In simple words: Narrow skin vessels carry less warm blood to the surface, so the body keeps its heat.

Teacher's Note:
1. Link blood flow with heat loss.
2. Name the result: body temperature is maintained.

Question 8. Predict what would happen if vitamins were broken down during the process of digestion rather than being absorbed intact into the circulation.
Answer:
Vitamins work only when their structure is intact. If they were broken down in digestion, they would lose their function.
The body cannot make most vitamins in enough amounts, so the person would develop vitamin deficiency diseases, for example night blindness, scurvy or rickets.
In simple words: Broken-down vitamins are useless, so deficiency diseases would appear.

Teacher's Note:
1. Say that the vitamin structure must stay intact.
2. Name one deficiency disease as an example.

Question 9. Explain what happen to your throat when you sleep with your mouth open, especially when your nasal passages are plugged as a result of having a cold.
Answer:
Normally the air passes through the nasal passages, where fine hairs and mucus filter it and warm and moisten it.
When we breathe through the open mouth, the air is not filtered, warmed or humidified.
This cold, dry air dries the throat and trachea, which makes the throat sore and dry, and dust and germs can reach it easily.
In simple words: Mouth breathing sends dry, unfiltered air to the throat and dries it.

Teacher's Note:
1. Recall the three jobs of the nasal passage: filter, warm, moisten.
2. Then state the drying effect.

Application and Reasoning HOTs Questions

Question 10. When human urine is allowed to stand for some time, it begins to smell like ammonia. Explain the reason behind this.
Answer:
Urine contains urea, the main nitrogenous waste.
When urine stands, bacteria in the air and container break down the urea and release ammonia (a gas with a pungent smell). That is why it smells of ammonia.
In simple words: Bacteria change the urea of stale urine into ammonia.

Teacher's Note:
1. Name urea as the waste present in fresh urine.
2. Bacterial action produces ammonia.

Question 11. The pancreas of a person suddenly stopped functioning. How will digestion be affected in such a person?
Answer:
Pancreatic juice contains amylase (digests starch), trypsin (digests proteins) and lipase (digests emulsified fats). It also contains bicarbonate that neutralises the acid coming from the stomach.
Without pancreatic juice, the digestion of starch, proteins and fats in the small intestine would be badly affected, and the person would not get enough nutrients from the food.
In simple words: Without the pancreas, starch, protein and fat digestion would be poor.

Teacher's Note:
1. Name the three pancreatic enzymes and their food.
2. Add that the juice also makes the medium alkaline.

Question 12. If a plant is releasing carbon dioxide and taking in oxygen during the day time does it mean that there is no photosynthesis occurring? Justify your answer.
Answer:
No, not necessarily. Respiration goes on all day and night and takes in oxygen and gives out carbon dioxide. Photosynthesis happens only in light and uses carbon dioxide and gives out oxygen.
If the plant shows a net release of carbon dioxide and intake of oxygen in the day, it only means that the rate of photosynthesis is lower than the rate of respiration (for example, in very dim light), or that photosynthesis has stopped.
At the compensation point, the two rates are equal and there is no net gas exchange.
In simple words: Net carbon dioxide release in daytime shows that respiration is faster, not that photosynthesis is absent.

Teacher's Note:
1. Compare the rates of the two processes.
2. Respiration never stops in a living plant.

Question 13. A plant X was enclosed in a glass jar with some lizards. A similar plant Y was enclosed in another glass jar but without lizards. Both the jars are kept under the same light conditions for a few hours. Which plant is likely to photosynthesise more and why?
Answer:
Plant X is likely to photosynthesise more.
The lizards respire and release carbon dioxide into the closed jar. This increases the amount of carbon dioxide, a raw material of photosynthesis, available to plant X.
Plant Y has only the carbon dioxide from its own respiration and the small amount in the jar, so it photosynthesises less.
In simple words: The lizards' breath gives plant X extra carbon dioxide.

Teacher's Note:
1. The two jars differ only in the presence of lizards.
2. Carbon dioxide is the raw material that changes.

Question 14. Two green plants are kept separately in oxygen free containers one in the dark and other in the continuous light. Which one will live longer? Give reasons.
Answer:
The plant kept in continuous light will live longer.
In light it carries out photosynthesis and produces oxygen (and food). This oxygen is used by the plant for respiration.
The plant kept in the dark cannot photosynthesise, so it gets no oxygen and dies sooner.
In simple words: Light lets the plant make its own oxygen, so it survives longer.

Teacher's Note:
1. Connect light with photosynthesis and then with oxygen for respiration.
2. The container has no other source of oxygen.

Question 15. Leaves of a healthy potted plant were coated with Vaseline to block the stomata. Will this plant remain healthy for long? Give reasons.
Answer:
No, the plant will not remain healthy for long.
Stomata are the pores for gas exchange. When they are blocked, carbon dioxide cannot enter for photosynthesis and oxygen cannot enter for respiration.
Transpiration also stops, so the upward movement of water and minerals from the roots becomes weak and the leaves get heated up.
In simple words: Blocked stomata stop photosynthesis, respiration and transpiration.

Teacher's Note:
1. List all three functions of stomata.
2. Answer the yes/no part first.

Question 16. The pharynx leads to trachea as well as to the oesophagus. The two openings lie very close to each other. Yet the food we swallow does not normally go to trachea. Why?
Answer:
The opening of the trachea is guarded by a flap-like structure called the epiglottis.
When we swallow food, the epiglottis closes the opening of the trachea, so the food goes into the oesophagus and not into the windpipe.
In simple words: The epiglottis closes the windpipe while we swallow.

Teacher's Note:
1. Name the epiglottis.
2. It acts like a lid on the trachea.

Question 17. All plants give out oxygen during day and carbon dioxide during night. Do you agree with this statement? Give reason.
Answer:
The statement is true only for the net gas exchange, and it is incomplete.
Respiration goes on in plants all the time. In the day, photosynthesis is much faster than respiration. It uses all the carbon dioxide released by respiration and releases extra oxygen, so there is a net release of oxygen.
At night there is no photosynthesis, so only respiration takes place and the plant takes in oxygen and gives out carbon dioxide.
In simple words: Respiration is always on, but in the day photosynthesis hides it.

Teacher's Note:
1. Do not say that respiration stops in the day.
2. Use the words net exchange.

Question 18. Why is it necessary to destarch a plant before photosynthesis process?
Answer:
A leaf may already contain starch made earlier. If we do not remove it, we cannot tell whether starch found in the experiment was made during the experiment.
So the plant is kept in the dark for 24 to 48 hours. It uses up or sends away its stored starch, and then the new starch formed in the experiment can be tested with iodine.
In simple words: Old starch must be removed so that the iodine test shows only new starch.

Teacher's Note:
1. Explain what the plant is kept in the dark for.
2. Remember the 24 to 48 hours.

Question 19. How is lymph an important fluid involved in transportation? If lymphatic vessels get blocked, how would it affect the human body? Elaborate.
Answer:
Lymph carries digested and absorbed fat from the intestine and drains the excess fluid from the spaces between cells back into the blood.
If the lymphatic vessels are blocked, extra fluid collects in the tissues and causes swelling (water retention), and the absorption of fat is poor. The body's defence also becomes weak, because lymph carries white blood cells.
In simple words: Blocked lymph vessels mean swelling and poor fat absorption.

Teacher's Note:
1. Give the two functions of lymph and then the effect of a block.
2. Swelling is the easiest effect to remember.

Question 20. Reflect on the statement, “Kidneys filter 180 L of fluid from the blood to make 1.8 L of urine”.
Answer:
About 180 L of fluid (glomerular filtrate) is filtered out of the blood in a day, but only about 1.8 L leaves the body as urine. That is only 1.8 ÷ 180 = 1%.
The other 99% is selectively reabsorbed into the blood. Glucose, amino acids, salts and most of the water are taken back, and only wastes such as urea and the excess water are passed out.
So the kidneys do not waste useful substances.
In simple words: The kidneys filter a lot and give back nearly everything useful, so only 1% goes out as urine.

Teacher's Note:
1. Calculate the percentage: 1.8 out of 180 is 1%.
2. Use the term selective reabsorption.

Question 21. Plants can sustain slower transport needs. Justify.
Answer:
Plants are stationary autotrophs and have low energy needs, so their cells do not need a fast supply of materials.
Many plant tissues are dead (for example xylem), and the living cells are close to the surface where gases move in by diffusion.
Water moves up the xylem by transpiration pull, and food moves slowly through the phloem. This slow transport is enough for the plant's needs.
In simple words: Plants need little energy, so slow transport is enough.

Teacher's Note:
1. Link slow transport to low energy needs.
2. Mention the xylem and phloem.

Question 22. (i) Why there is difference in the volume of filtrate formed and the concentration of urine excreted?
(ii) In some people glucose is detected in urine. Explain.
Answer:
(i) About 180 L of filtrate is formed per day but only about 1.8 L of concentrated urine is passed out. This is because useful substances and most of the water are selectively reabsorbed from the filtrate in the renal tubule, and some wastes are added by tubular secretion.
(ii) The tubule can reabsorb glucose only up to a limit. If the blood glucose is very high (for example in diabetes), more glucose is filtered than can be reabsorbed, and the extra glucose passes into the urine.
In simple words: The tubule takes back most of the filtrate; very high blood sugar overloads this and glucose escapes in urine.

Teacher's Note:
1. Part (i): filtration is much greater than excretion.
2. Part (ii): mention a limit to reabsorption.

Case Based HOTs Question

Question 23. Not all plants carry out photosynthesis by the same mechanism. In most plants, photosynthesis depends directly on the gaseous carbon dioxide that diffuses into the leaf through the stomata. However, some plants such as pineapple have the ability to store carbon dioxide in the vacuoles of the leaf cells as part of a complex carbon compound. This complex compound is transported to the chloroplasts and releases carbon dioxide when required, for photosynthesis to occur.
(A) This special photosynthesis mechanism is believed to have evolved as an adaptation to conserve water for survival in dry conditions.
(i) Which process in the plants does this photosynthesis mechanism minimise to help the plant survive in dry conditions?
(ii) How is the ability to store carbon dioxide as a complex compound likely to help minimise the process referred to in (i)?
(iii) When are such plants likely to take in carbon dioxide from the environment?
(B) The complete process of photosynthesis occurs inside the chloroplasts and the raw materials needed for the process are carbon dioxide and water.
(i) Write the mechanism of photosynthesis.
(ii) What is the source of oxygen produced during the process of photosynthesis?
Answer:
(A)(i) The process minimised is transpiration (loss of water vapour through stomata).
(ii) Since carbon dioxide is stored, the stomata need not stay open in the hot day to let carbon dioxide in. Keeping the stomata closed in the day reduces water loss.
(iii) Such plants take in carbon dioxide from the environment at night, when the stomata open and the loss of water is small.
(B)(i) Photosynthesis takes place in these steps: absorption of light energy by chlorophyll; conversion of light energy into chemical energy with splitting of water into hydrogen and oxygen; and reduction of carbon dioxide to carbohydrates. Overall: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of sunlight and chlorophyll).
(ii) The oxygen released comes from water molecules.
In simple words: Pineapple-type plants store carbon dioxide at night so that the stomata can stay shut in the heat of the day.

Teacher's Note:
1. Part (A)(iii) is night, not day, because the stomata must stay closed in the day.
2. Remember that the oxygen released comes from water.