CBSE Class 10 Science Sample Paper 2026–27: Biology MCQs Q1–9 Explained
Try Biology questions 1–9 in the official Science sample paper, then use this 12:33 TutorMax walkthrough to check the reasoning behind your choice. Jump directly to a question below.
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What this episode covers
Seven multiple-choice questions and two assertion–reason questions in the Biology section of one combined Science paper. Chemistry, Physics and longer answers are outside this episode.
TutorMax’s explanations are not an official CBSE video or marking scheme. The narration uses text-to-speech; on-screen captions are part of the video. The notes below summarise the reasoning and are not a verbatim transcript. YouTube selectable closed captions were unavailable when checked.
Keep the reasoning, not just the answer letter
Attempt the official question before watching its explanation. Afterwards, close the answer and explain the key idea in your own words. If you can only remember the letter, revisit the relevant note.
Q1 · Photosynthesis: reduction and oxidation
Track the two reactants separately. Carbon dioxide is reduced as carbohydrate forms; water is oxidised. The oxygen released comes from water. An option must describe both changes correctly.
Revisit this explanation on YouTube ↗Q2 · Limewater and the black-coated tank
Respiration releases carbon dioxide in light and darkness. Photosynthesis needs light and uses carbon dioxide. A black covering blocks light, so a plant can keep respiring without photosynthesis removing the carbon dioxide. Compare the stated experimental conditions.
Revisit this explanation on YouTube ↗Q3 · Kidney reabsorption
Reabsorption means useful substances return from the kidney tubule to the blood. Glucose is recovered; salts and water are reabsorbed according to the body's needs. Do not confuse this return journey with secretion into the tubule.
Revisit this explanation on YouTube ↗Q4 · Anther removal and bagging
Removing immature anthers removes the flower's own pollen source. Bagging keeps out pollen from other flowers. Together, these steps prevent normal pollination and subsequent seed and fruit formation in the stated experiment. This is not a method of asexual reproduction.
Revisit this explanation on YouTube ↗Q5 · Contraception: blocked transport
These procedures interrupt transport so sperm and egg cannot meet and fuse. They do not directly stop the testes or ovaries producing gametes. Distinguish fertilisation from implantation, which happens later.
Revisit this explanation on YouTube ↗Q6 · Chromosome numbers
Male and female gametes of the same species normally carry one chromosome set each. Fertilisation combines the two sets. Keep the requested order clear: female gamete first, ordinary adult body cell second.
Revisit this explanation on YouTube ↗Q7 · Food chain and consumer levels
Start with producers, then count feeding steps. A primary consumer eats a producer; a secondary consumer eats a primary consumer. The secondary consumer is at the third trophic level because producers already occupy level one. Arrows point from food to eater.
Revisit this explanation on YouTube ↗Assertion–reason method
Decide whether each statement is true before asking whether the reason explains the assertion. Use the option key printed on your paper; do not assume the letters are identical in every test.
Revisit this explanation on YouTube ↗Q8 · Breathing in water and air
For this textbook comparison, lower oxygen availability in water means aquatic animals need to move water across their breathing surfaces more rapidly. The comparison does not claim an identical breathing rate for every species or environmental condition.
Revisit this explanation on YouTube ↗Q9 · Energy transfer: 1% versus 10%
Ask what the percentage is measured against. The textbook's 1% figure refers to sunlight captured by green plants in a terrestrial ecosystem. The approximate 10% rule concerns transfer between successive trophic levels. These are different comparisons.
Revisit this explanation on YouTube ↗Can you use the idea in a changed example?
These questions are original TutorMax practice, not official CBSE questions. Try them without the video or notes. They check a few ideas from this episode, not whole-subject readiness.
Fresh practice 1
A plant's gamete has 12 chromosomes. How many are in the other gamete and an ordinary body cell? Explain the change.
Check the reasoning
12 and 24. Each gamete carries one set; fusion combines two sets. Ordinary body-cell division then preserves that number. Getting the numbers right without explaining fusion is a reason to revisit Q6.
Fresh practice 2
Grass → grasshopper → frog. Name the frog's consumer role and trophic level.
Check the reasoning
Secondary consumer, third trophic level. Grass is the producer at level one; the grasshopper is the primary consumer at level two. Count consumer steps separately from trophic levels. Revisit Q7 if you called the frog a tertiary consumer.
Fresh practice 3
Producers store 8,000 J. Using the approximate 10% model, how much reaches primary and then secondary consumers?
Check the reasoning
About 800 J, then 80 J: multiply by 0.1 at each transfer. This simplified model is not an exact measurement for every ecosystem. Revisit Q9 if you used 1% or skipped a feeding step.
Choose your next step
If an idea was unclear, revisit the concept guide. If the idea makes sense but you misread the options, return to that video chapter and explain why the tempting choice fails. Then use the paper-review guide to plan your next attempt.
Video and authored source package checked 6 October 2026.