ScienceCBSE Class 10 · Life Processes

Nutrition in Plants and Animals

Updated 14 October 2026 · Fact-checked

Nutrition is how organisms obtain energy and materials from food. Green plants are autotrophs: they make carbohydrates from carbon dioxide and water using sunlight and chlorophyll. Animals and fungi are heterotrophs that depend on food made by others. In humans, food is digested by enzymes along the alimentary canal and absorbed through villi in the small intestine.

Understand Nutrition in Plants and Animals

Why nutrition? Even at rest, the body needs energy to keep its ordered structures in repair, plus raw materials to grow. Food supplies both.

Autotrophic nutrition. Green plants and some bacteria take in simple inorganic substances, carbon dioxide and water, and convert them into carbohydrates in the presence of sunlight and chlorophyll. This is photosynthesis:
$6 C O_{2} + 12 H_{2} O sunlight, chlorophyll C_{6} H_{12} O_{6} + 6 O_{2} + 6 H_{2} O$
Three events take place: (i) chlorophyll absorbs light energy; (ii) light energy is converted to chemical energy and water molecules are split into hydrogen and oxygen; (iii) carbon dioxide is reduced to carbohydrates. These need not happen one immediately after another: desert plants take in carbon dioxide at night and make an intermediate that is acted on in the day. Carbohydrates not used at once are stored as starch, the plant's energy reserve (we store some energy as glycogen).

Chlorophyll is in chloroplasts, the green dots seen in leaf cells. A variegated leaf (money plant, croton), destarched in the dark and then kept in sunlight, gives a blue-black starch test with iodine only in its green parts, showing chlorophyll is needed.
Carbon dioxide enters mainly through stomata, tiny pores on leaves. Guard cells swell when water flows in, opening the pore, and shrink to close it, so the plant can cut water loss when it does not need carbon dioxide. A plant kept with potassium hydroxide (which absorbs carbon dioxide) under a sealed bell jar makes little or no starch, showing carbon dioxide is needed.
Water comes from the soil through roots, as do nitrogen (as nitrates or nitrites, or organic compounds made by bacteria from atmospheric nitrogen), phosphorus, iron and magnesium.

Heterotrophic nutrition. Organisms that use complex food made by others depend directly or indirectly on autotrophs. Fungi such as bread mould, yeast and mushrooms break down food outside the body and absorb it. Parasites such as cuscuta (amar-bel), ticks, lice, leeches and tapeworms feed on a host without killing it. Amoeba takes in food with temporary finger-like extensions that surround it to form a food vacuole, digests it there, and throws out the undigested part. Paramoecium has a fixed shape; cilia sweep food to a particular spot.

Human digestion, step by step.
1. Mouth: teeth crush food; saliva wets it; salivary amylase breaks starch into a simple sugar.
2. Oesophagus: rhythmic muscle contractions, peristalsis, push food along the whole gut.
3. Stomach: gastric glands release hydrochloric acid (acidic medium for pepsin), pepsin (digests proteins) and mucus (protects the stomach lining from the acid). A sphincter releases food slowly into the small intestine.
4. Small intestine (longest part; longer in grass-eating herbivores to digest cellulose, shorter in carnivores): complete digestion of carbohydrates, proteins and fats. Bile from the liver makes the acidic food alkaline for pancreatic enzymes and its salts emulsify fats into small globules. Pancreatic juice has trypsin (proteins) and lipase (emulsified fats). Intestinal juice finally converts proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol. Finger-like villi increase the surface area and, being rich in blood vessels, absorb the digested food.
5. Large intestine: absorbs more water; the rest leaves through the anus, controlled by the anal sphincter.

Nutrition in Plants and Animals: formulas and key facts

Photosynthesis: $6 C O_{2} + 12 H_{2} O sunlight, chlorophyll C_{6} H_{12} O_{6} + 6 O_{2} + 6 H_{2} O$; Raw materials: $C O_{2}$ and water. Conditions: sunlight, chlorophyll. Products: glucose, oxygen, water.
Digestive enzymes and their action: $amylase: starch \to sugar; pepsin, trypsin: proteins; lipase: fats$; Final products: glucose, amino acids, fatty acids and glycerol.
Secretions of the stomach: $H C l + pepsin + mucus$; Acid helps pepsin act; mucus protects the lining.
Role of bile: $acidic food \to alkaline; large fat globules \to small globules$; Emulsification raises the efficiency of lipase.

How to solve Nutrition in Plants and Animals questions

For 'describe' and 'explain' questions on nutrition, organise your answer by organ or by step.

1Identify the type of nutrition (autotrophic, heterotrophic: saprophytic-like fungi, parasitic, holozoic like Amoeba and humans).
2For photosynthesis, give raw materials, conditions, products, the three events and where they occur (chloroplasts, stomata for gas exchange).
3For activity questions, state the control and what the result proves (variegated leaf: chlorophyll; KOH: carbon dioxide).
4For human digestion, go organ by organ: secretion, enzyme, substrate, product.
5For 'how is the small intestine adapted', name villi, surface area and blood supply.
6Draw and label the alimentary canal if a diagram is asked: mouth, oesophagus, stomach, liver, gall bladder, pancreas, small intestine, large intestine, anus.

Nutrition in Plants and Animals in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Digestion of fats: bile and lipase

Suppose after a festive meal of fried pakoras your friend asks why washing an oily plate with plain water does not work, while soap does, and whether the body has anything similar for the oil it eats.

Explain how fats are digested in the body, comparing the role of bile salts with the action of soap on oil. Say where this happens and name the end products.

Try it first, then show the solutionSolution

Fats reach the small intestine as large globules, which are hard for enzymes to act on, just as large oil patches on a plate resist plain water.
Bile from the liver contains bile salts that break large fat globules into smaller ones (emulsification), similar to the way soap breaks oily dirt into tiny droplets.
Smaller globules give a larger surface for pancreatic lipase to act on, so digestion is more efficient.
Bile also makes the acidic food from the stomach alkaline so that pancreatic enzymes can work.
Intestinal juice finally converts fats into fatty acids and glycerol, which are absorbed by the villi.

Answer: In the small intestine, bile salts emulsify fats (like soap on oil), lipase from the pancreas digests them, and they end up as fatty acids and glycerol absorbed by the villi.

Memory hook: Bile is the body's soap: it breaks fat into droplets so lipase can finish the job.

Tricks to remember Nutrition in Plants and Animals

Short memory aids. Say each one aloud once, then use it on a question the same day.

Photosynthesis in three steps: ACR
Absorb light, Convert energy and split water, Reduce carbon dioxide.
Use it when: Listing the events of photosynthesis.
Stomach's HPM
HCl, Pepsin, Mucus.
Use it when: Gastric gland secretions and their roles.
Pancreas: TL
Trypsin for proteins, Lipase for fats.
Use it when: Enzymes in pancreatic juice.

Nutrition in Plants and Animals: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Autotrophic vs heterotrophic · 2 marks · Very short answerBoard level

Give two differences between autotrophic and heterotrophic nutrition, with one example of each.

Try it first, then show the solutionSolution

Autotrophs make their own food from simple inorganic substances ( $C O_{2}$ , water) using sunlight; heterotrophs take in complex food made by other organisms (1 mark).
Autotrophs need chlorophyll (or sunlight energy); heterotrophs need enzymes to break down complex food. Examples: green plants; animals and fungi (1 mark).

Answer: Autotrophs (green plants) make food from simple substances using light; heterotrophs (animals, fungi) depend on food made by others and digest it with enzymes.

Example 2: Variegated leaf activity · 3 marks · Short answerHarder board level

A potted croton with variegated leaves is kept in the dark for three days, then in sunlight for six hours. A leaf is boiled in water, then in alcohol in a water bath, and tested with iodine. (a) Why is the plant kept in the dark first? (b) Why is the leaf boiled in alcohol, and why in a water bath? (c) What is observed with iodine and what does it prove?

Try it first, then show the solutionSolution

(a) To use up all the stored starch, so any starch found later was made during the experiment (1 mark).
(b) Alcohol removes chlorophyll so colour changes with iodine are visible; alcohol catches fire easily, so it is heated in a water bath, not directly (1 mark).
(c) Only the parts that were green turn blue-black; the non-green parts do not. Starch was made only where chlorophyll was present, so chlorophyll is necessary for photosynthesis (1 mark).

Answer: (a) Destarching. (b) Decolourise the leaf safely. (c) Blue-black only in green areas: chlorophyll is essential.

Example 3: Role of the stomach · 3 marks · Short answerHarder board level

(a) Name the three secretions of gastric glands and give the function of each. (b) Adults sometimes complain of 'acidity'. Relate this to the stomach's secretions. (c) What would happen if mucus were not secreted?

Try it first, then show the solutionSolution

(a) Hydrochloric acid: creates an acidic medium for pepsin; pepsin: digests proteins; mucus: protects the inner lining from the acid (1½ marks).
(b) Too much acid released in the stomach causes pain and irritation, felt as 'acidity' (½ mark).
(c) The acid would act on the stomach's own lining and damage it (1 mark).

Answer: (a) HCl, pepsin, mucus with roles above. (b) Excess acid. (c) The lining would be damaged by acid.

Example 4: Small intestine · 5 marks · Long answerHarder board level

(a) Name the juices that act on food in the small intestine and their sources. (b) State the final products of digestion of carbohydrates, proteins and fats. (c) How is the small intestine designed for absorption? (d) Why do herbivores have a longer small intestine than carnivores?

Try it first, then show the solutionSolution

(a) Bile from the liver, pancreatic juice from the pancreas, intestinal juice from glands in the intestinal wall (1½ marks).
(b) Carbohydrates to glucose; proteins to amino acids; fats to fatty acids and glycerol (1½ marks).
(c) Numerous villi increase the surface area; they are richly supplied with blood vessels that carry absorbed food to all cells (1 mark).
(d) Grass contains cellulose, which needs a long time to digest; meat is easier to digest (1 mark).

Answer: (a) Bile, pancreatic and intestinal juices. (b) Glucose; amino acids; fatty acids and glycerol. (c) Villi with large area and blood supply. (d) Cellulose digestion needs a longer intestine.

Example 5: Designing a control · 3 marks · Short answerHOTS / competency

In the bell-jar experiment, plant A has a watch-glass of potassium hydroxide beside it and plant B does not; both are destarched, sealed with vaseline and kept in sunlight for two hours. (a) What result is expected with the iodine test? (b) What is the role of plant B? (c) A student forgets the vaseline seal. Predict how this would affect the result and why.

Try it first, then show the solutionSolution

(a) A's leaf shows little or no blue-black colour; B's leaf turns blue-black (1 mark).
(b) B is the control: everything is the same except carbon dioxide is available, so the difference shows that carbon dioxide is needed (1 mark).
(c) Air from outside could enter A's jar and supply carbon dioxide, so A might also make starch and the experiment would not show the effect clearly (1 mark).

Answer: (a) Starch in B only. (b) Control. (c) Leaks let in $C O_{2}$ , spoiling the comparison.

Where students lose marks in Nutrition in Plants and Animals

The slips examiners see most often, and what to write instead.

Mistake: Missing conditions in photosynthesis
Students write only the reactants and products.
Wrong working
$6 C O_{2} + 12 H_{2} O \to C_{6} H_{12} O_{6} + 6 O_{2} + 6 H_{2} O$ with nothing over the arrow.
Right working
Sunlight and chlorophyll written over the arrow.
Do this: Always include both conditions.
Usually costs: ½ mark.
Mistake: Confusing the roles of bile
Bile is called an enzyme.
Wrong working
Bile contains enzymes that digest fat.
Right working
Bile salts emulsify fats; lipase digests them. Bile also makes the food alkaline.
Do this: Bile has no digestive enzyme; it emulsifies and neutralises.
Usually costs: 1 mark.
Mistake: Wrong reason for HCl in the stomach
Students say the acid digests food.
Wrong working
HCl digests proteins.
Right working
HCl creates the acidic medium in which pepsin digests proteins.
Do this: Link HCl to pepsin.
Usually costs: ½ to 1 mark.
Mistake: Incomplete activity answers
Steps are listed without purposes.
Wrong working
Keep the plant in the dark, boil in alcohol, add iodine.
Right working
Dark: destarch; alcohol: remove chlorophyll; iodine: test starch; result shows chlorophyll is needed.
Do this: Give each step with its reason and the conclusion.
Usually costs: 1-2 marks in 3-mark activity questions.

Exam tips

Organise digestion answers organ by organ in a short table if allowed: organ, secretion, enzyme, action.
Use NCERT terms: peristalsis, emulsification, villi, sphincter, gastric glands.
In the photosynthesis equation, write 6 $H_{2} O$ on the product side as NCERT does.
For diagrams of the alimentary canal, label the liver, gall bladder and pancreas as well as the tube.
Box items (such as dental caries) are not assessed; focus on the main text.

Practice questions on Nutrition in Plants and Animals

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which of the following is NOT needed for autotrophic nutrition?
(a) carbon dioxide (b) chlorophyll (c) sunlight (d) pepsin
Hint
One option is a human digestive enzyme.
Answer
(d) pepsin.
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Stomata close when the plant does not need carbon dioxide for photosynthesis.
Reason (R): Large amounts of water can be lost through stomata.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Why would a plant shut a pore?
Answer
(a). Closing stomata cuts water loss when carbon dioxide is not needed.
Q3 · 3 marks · Short answerBoard level
Describe how the opening and closing of a stomatal pore is controlled. Name two raw materials besides carbon dioxide that a plant takes from the soil, and say what nitrogen is used for.
Hint
Guard cells change shape with water.
Answer
Guard cells swell when water flows into them, opening the pore; when they lose water and shrink, the pore closes. From the soil: water and minerals such as nitrogen, phosphorus, iron, magnesium (any two). Nitrogen is used to make proteins and other compounds; it is taken as nitrates or nitrites or as organic compounds made by bacteria.
Q4 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Suppose in a lab, Test tube A has 1 mL of 1% starch solution with 1 mL of saliva, and test tube B has 1 mL of starch solution with 1 mL of water. Both are left for 30 minutes and iodine is added.
(a) In which tube does the blue-black colour appear? (1 mark)
(b) Name the enzyme responsible for the difference and its product. (1 mark)
(c) Predict what would happen if tube A were kept at a very low temperature, given that enzymes are biological catalysts, and suggest why tube B is needed. (2 marks)
Hint
Iodine turns blue-black only if starch remains.
Answer
(a) Tube B (starch remains). (b) Salivary amylase; it breaks starch into a simple sugar. (c) Enzyme action would slow down, so more starch would remain and A might also turn blue-black or show a weaker change. B is the control showing that starch does not break down without saliva.
Q5 · 3 marks · Short answerHarder board level
Compare how Amoeba and human beings obtain and digest food, giving two similarities and two differences.
Hint
Think of where digestion happens and what does it.
Answer
Similarities: both take in complex food (heterotrophs); both break complex substances into simpler ones that are absorbed and remove undigested matter. Differences: Amoeba uses temporary finger-like extensions to form a food vacuole and digests inside the single cell; humans have a specialised alimentary canal with organs, glands and enzymes in different regions.
Q6 · 3 marks · Short answerHOTS / competency
A patient has had his gall bladder (which stores bile) removed and is advised to eat less fatty food. Using your knowledge of digestion, explain the advice, and say which other enzyme-related step would be less efficient.
Hint
What does bile do to fats and to the acidic food from the stomach?
Answer
Bile salts emulsify fats into small globules, increasing the surface for lipase. With less bile available at a meal, large fat globules are digested less efficiently, so a low-fat diet is advised. Bile also makes the acidic food alkaline for pancreatic enzymes; without enough bile, pancreatic enzymes such as lipase and trypsin would act less efficiently.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Three events in photosynthesis?Show answer
Absorption of light by chlorophyll; conversion of light to chemical energy and splitting of water; reduction of $C O_{2}$ to carbohydrates.
2.In what form do plants store extra carbohydrate?Show answer
Starch.
3.Enzyme in saliva?Show answer
Salivary amylase.
4.What does trypsin digest?Show answer
Proteins.
5.What increases the surface area for absorption in the small intestine?Show answer
Villi.
6.Name two parasites from NCERT.Show answer
Cuscuta (amar-bel), ticks, lice, leeches, tapeworms (any two).

Nutrition in Plants and Animals: frequently asked questions

What is the difference between autotrophic and heterotrophic nutrition?

Autotrophs make their own food from carbon dioxide and water using sunlight and chlorophyll. Heterotrophs depend on complex food made by other organisms.

What are the raw materials and conditions for photosynthesis?

Raw materials: carbon dioxide and water. Conditions: sunlight and chlorophyll. Products: glucose (carbohydrate), oxygen and water.

How are fats digested in our body?

In the small intestine, bile salts emulsify fats into small globules, pancreatic lipase breaks them down, and intestinal juice converts them into fatty acids and glycerol.

What is the role of saliva in digestion?

Saliva wets food for smooth passage and contains salivary amylase, which breaks starch into a simple sugar.

Why does the stomach not digest itself?

Mucus secreted by gastric glands protects the inner lining from the hydrochloric acid under normal conditions.