BiologyICSE Class 9 · Chapter 7

Respiration in Plants ICSE Class 9: Glycolysis, Krebs Cycle, Aerobic and Anaerobic Respiration

Updated 15 October 2026 · Fact-checked

Respiration is the breakdown of food, mainly glucose, in living cells to release energy. In plants it happens in every living cell, day and night. Glycolysis splits glucose into pyruvic acid in the cytoplasm; with oxygen, the Krebs cycle in mitochondria completes it to carbon dioxide and water. Without oxygen, ethanol and carbon dioxide form.

What Respiration in Plants is about

Every living cell needs a steady supply of energy to grow, divide, move materials and repair itself. It gets this by respiration: the oxidation of food (mainly glucose) in cells, releasing energy that is stored as ATP (adenosine triphosphate), the cell's energy currency.

The CISCE 2028 syllabus (Class IX, Plant Physiology (ii)) covers: a brief outline of the process, mentioning glycolysis and the Krebs cycle and their significance; aerobic and anaerobic respiration with chemical equations in each case; gaseous exchange; and experiments on gaseous exchange and on heat production.

Weightage: CISCE publishes no chapter weightage for ICSE Biology. Respiration in Plants is topic 3, Plant Physiology (ii), of the Class IX part of the 2028 syllabus; the Class IX paper (80 marks, 2 hours) is set and marked by the school.Source: CISCE ICSE Biology (Science Paper 3) syllabus, examination year 2028 (Class IX)

Key concepts

What respiration is (and is not)

Respiration: a biochemical process in living cells in which food (glucose) is oxidised step by step, with the help of enzymes, to release energy.

Key facts about respiration in plants:

It takes place in every living cell (root, stem, leaf, flower, seed), all the time, day and night.
Plants have no special breathing organs; gases are exchanged by diffusion through stomata (leaves, young stems), lenticels (woody stems) and the surface of root hairs.
It is a catabolic (breaking-down) process; it releases energy, unlike photosynthesis, which stores it.

Respiration is not breathing: breathing is the physical movement of air in and out of lungs; respiration is the chemical release of energy in cells.

Respiration versus burning: both use oxygen and give CO₂ and water, but respiration is slow, stepwise and enzyme-controlled, at body temperature, and stores energy as ATP; burning is fast, uncontrolled, and releases energy as heat and light.

Worked example

A potted plant is kept in the dark for two days. Does it respire? Does it photosynthesise?

Try it first, then show the solutionSolution

Respiration goes on in all living cells, day and night.
Photosynthesis needs light, so it stops in the dark.

Answer: It respires but does not photosynthesise.

Glycolysis and the Krebs cycle (outline)

Respiration of glucose happens in two main stages:

1. Glycolysis ('splitting of sugar')

Takes place in the cytoplasm.
One glucose (6-carbon) is broken into two molecules of pyruvic acid (3-carbon).
Needs no oxygen: it is common to both aerobic and anaerobic respiration.
Releases a small amount of energy (a net gain of 2 ATP).

2. Krebs cycle (citric acid cycle)

Takes place in the mitochondria.
Needs oxygen: happens only in aerobic respiration.
Pyruvic acid is completely oxidised to carbon dioxide, and hydrogen removed in the cycle finally combines with oxygen to form water.
Releases most of the energy (textbooks give a total of about 38 ATP per glucose for aerobic respiration).

Significance: glycolysis supplies energy even without oxygen and starts every respiration pathway; the Krebs cycle extracts most of the energy from food, which is why mitochondria are called the powerhouse of the cell.

Worked example

Where do glycolysis and the Krebs cycle occur, and which needs oxygen?

Try it first, then show the solutionSolution

Glycolysis: cytoplasm; no oxygen needed.
Krebs cycle: mitochondria; oxygen needed.

Answer: As above.

Aerobic respiration

Aerobic respiration: complete oxidation of glucose in the presence of oxygen, giving carbon dioxide, water and a large amount of energy.

$C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O$ + energy (about 38 ATP)

Pathway: glucose → (glycolysis, cytoplasm) → pyruvic acid → (Krebs cycle, mitochondria, with O₂) → CO₂ + H₂O + energy.

It is the usual form of respiration in plants and animals.

Worked example

Using the equation, find the mass of carbon dioxide released when 18 g of glucose is fully respired. (C = 12, H = 1, O = 16)

Try it first, then show the solutionSolution

Mr of glucose = 6(12) + 12(1) + 6(16) = 180; Mr of CO₂ = 44.
180 g glucose → 6 × 44 = 264 g CO₂.
18 g glucose → 264 × 18/180 = 26.4 g CO₂.

Answer: 26.4 g

Anaerobic respiration

Anaerobic respiration: incomplete breakdown of glucose without oxygen, releasing little energy. Only glycolysis plus a short final step happens, in the cytoplasm.

In plants and yeast (also called alcoholic fermentation):
$C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2}$ + little energy (2 ATP)
Glucose → ethanol (ethyl alcohol) + carbon dioxide.

It happens in yeast, in germinating seeds under waterlogged soil, in roots of plants in flooded fields and in fleshy fruits stored in airtight conditions. Plants cannot survive long this way: little energy is released, and alcohol is toxic to cells.

In animal muscles (for comparison): during hard exercise, muscle cells short of oxygen form lactic acid:
$C_{6} H_{12} O_{6} \to 2 C_{3} H_{6} O_{3}$ + little energy

	Aerobic	Anaerobic
Oxygen	needed	not needed
Breakdown of glucose	complete	incomplete
Products	CO₂ + H₂O	ethanol + CO₂ (plants, yeast); lactic acid (muscles)
Energy	large (about 38 ATP)	small (2 ATP)
Site	cytoplasm and mitochondria	cytoplasm only

Worked example

Why does bread dough rise when yeast is added and kept warm?

Try it first, then show the solutionSolution

Yeast respires anaerobically on the sugar in the dough.
$C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2}$
The carbon dioxide forms bubbles that make the dough rise; the alcohol evaporates on baking.

Answer: CO₂ from anaerobic respiration of yeast.

Experiment: gaseous exchange (CO₂ given out, O₂ taken in)

A. Carbon dioxide is released

Put germinating seeds in a conical flask and close it with a cork carrying a bent delivery tube that dips into a test tube of clear lime water. Set up a control flask with boiled (dead) seeds.
Result: lime water turns milky with the germinating seeds only: $C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O$ .
Conclusion: living seeds give out CO₂ in respiration.

B. Oxygen is taken in (and CO₂ given out)

Place germinating seeds in a flask with a small tube of KOH solution (which absorbs CO₂). Fit a bent delivery tube that dips into a beaker of water (coloured). Seal well.
Result: after some hours the water rises in the delivery tube.
Explanation: seeds use up oxygen; the CO₂ they release is absorbed by KOH, so the volume of gas in the flask falls and water is pushed up the tube by air pressure.
Control: same set-up with boiled seeds: no rise.

Use green leaves only in the dark for such experiments, or photosynthesis will hide the result.

Worked example

In experiment B, what would happen if the KOH were left out? Why?

Try it first, then show the solutionSolution

Seeds take in oxygen but give out about the same volume of CO₂.
Without KOH, the CO₂ stays in the flask, so the gas volume hardly changes.

Answer: Water would hardly rise.

Experiment: heat is produced in respiration

Take two thermos (vacuum) flasks. In flask A put germinating seeds (e.g. gram or pea). In flask B put an equal amount of seeds killed by boiling and washed with a weak antiseptic (formalin) so that microbes do not grow on them.
Close each with a cork carrying a thermometer with its bulb among the seeds. Note the readings.
Result: after a day or two the temperature in A rises; B stays the same.
Conclusion: living, germinating seeds release heat in respiration.
The vacuum flask prevents heat loss, so the rise can be measured. The antiseptic ensures any heat in B is not from bacteria or fungi respiring.

Worked example

Why are the dead seeds washed with an antiseptic in the heat experiment?

Try it first, then show the solutionSolution

Microbes growing on dead seeds would respire and release heat.
This would raise the temperature of the control and spoil the comparison.

Answer: To prevent heat from microbial respiration.

Respiration in Plants in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Energy from aerobic and anaerobic respiration

Suppose a root cell in a flooded field switches from aerobic to anaerobic respiration and still needs the same amount of ATP as before.

Using about 38 ATP (aerobic) and 2 ATP (anaerobic) per glucose, how many times more glucose must it use? Why can it not continue for long?

Try it first, then show the solutionSolution

Ratio = 38 ÷ 2 = 19.
It must break down about 19 times as much glucose for the same energy.
Food reserves run out quickly, and the ethanol produced is toxic to the cells.

Answer: About 19 times; food runs out and alcohol poisons the cells.

Memory hook: No oxygen, nineteen times the fuel.

Storing fruit and grain

Suppose a cold-storage owner keeps apples at a low temperature with reduced oxygen to make them last for months.

Explain using respiration.

Try it first, then show the solutionSolution

Apples are living tissue and keep respiring, using up their sugars and getting soft.
Low temperature slows the enzymes of respiration.
Reduced oxygen also slows aerobic respiration, so stored food lasts longer.

Answer: Slower respiration keeps sugars and freshness longer.

Memory hook: Cool and low-oxygen: slow the burn.

Haystack heating

Suppose a farmer stacks damp, freshly cut grass in a big heap and finds it warm inside after a few days.

Explain the heat.

Try it first, then show the solutionSolution

Living plant cells and microbes in the damp heap keep respiring.
Respiration releases some energy as heat.
The heap traps the heat, so the temperature rises.

Answer: Heat from respiration of plant cells and microbes.

Memory hook: Respiring life is a slow stove.

Topics in this chapter

Aerobic and Anaerobic Respiration in Plants and Related Experiments

Respiration in Plants: key facts

Aerobic respiration: $C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O$; + energy (about 38 ATP).
Anaerobic, plants and yeast: $C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2}$; + little energy (2 ATP).
Anaerobic, muscles: $C_{6} H_{12} O_{6} \to 2 C_{3} H_{6} O_{3}$; Lactic acid.
Lime water test: $C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O$; Milky.
Pathway: $glucose glycolysis (cytoplasm) pyruvic acid Krebs cycle (mitochondria) C O_{2} + H_{2} O$; Aerobic route.

Respiration in Plants: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Experiment to show oxygen is used in respiration

Draw the set-up to show that germinating seeds take in oxygen.

Draw

A conical flask containing germinating seeds on moist cotton.
A small test tube of KOH solution hanging inside the flask.
A cork with a bent delivery tube; its other end dips into a beaker of coloured water.
Water shown risen in the tube.

Label

germinating seeds
KOH solution (absorbs CO₂)
airtight cork
delivery tube
water rises
beaker of coloured water

Watch out: Mark the starting level and the risen level.

Experiment to show heat production

Draw the set-up to show that heat is released during respiration.

Draw

Two vacuum flasks side by side.
Flask A with germinating seeds; flask B with boiled seeds washed in antiseptic.
A thermometer in each, its bulb among the seeds, held in a cotton plug.

Label

vacuum flask
germinating seeds
boiled seeds (control)
thermometer
cotton plug

Watch out: Show a higher reading in A.

How the school exam asks Respiration in Plants

The question patterns to expect, and the method that works for each.

Question type	How it is asked	Method
Equations	Write balanced equations for aerobic and anaerobic respiration in plants (and in muscles).	Learn both with energy written outside the equation.
Glycolysis and Krebs cycle	Where, whether oxygen is needed, products, significance.	Two-row table.
Differences	Aerobic versus anaerobic; respiration versus photosynthesis; respiration versus burning.	Table form, both sides.
Experiments	Describe the set-up, control, result and conclusion for CO₂ release, O₂ uptake or heat production; explain a diagram.	Name the chemical and why it is used (KOH, lime water, antiseptic, thermos).
Application	Fermentation, waterlogging, storage of fruits, energy comparisons.	Link to oxygen supply and products.

Tricks to remember Respiration in Plants

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

Glycolysis in the Goo, Krebs in the Kitchen
Glycolysis in cytoplasm (the goo); Krebs in mitochondria (the powerhouse kitchen).
Use it when: Sites.
One-six-six-six
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
Use it when: Aerobic equation.
Yeast makes 'two and two'
Glucose → 2 ethanol + 2 CO₂.
Use it when: Anaerobic equation.
KOH Keeps Out CO₂
KOH absorbs carbon dioxide; lime water detects it.
Use it when: Experiment chemicals.

Respiration in Plants: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Example 1: Site of glycolysis · 1 mark · MCQExam level

Glycolysis takes place in the:
(a) mitochondria
(b) cytoplasm
(c) chloroplast
(d) nucleus

Try it first, then show the solutionSolution

Glycolysis occurs in the cytoplasm.

Answer: (b)

Example 2: Plants respire at night · 1 mark · Assertion-reasonHarder exam level

Assertion (A): Plants give out carbon dioxide at night.
Reason (R): Plants respire only at night.
(a) Both (A) and (R) are true, and (R) is the correct explanation for (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
(c) (A) is true and (R) is false.
(d) (A) is false and (R) is true.

Try it first, then show the solutionSolution

At night there is no photosynthesis, so CO₂ from respiration is released: A true.
Plants respire day and night: R false.

Answer: (c)

Example 3: Equations · 3 marks · Short answerExam level

Write balanced equations for (a) aerobic respiration, (b) anaerobic respiration in yeast. State where each mainly occurs.

Try it first, then show the solutionSolution

(a) $C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O$ + energy: cytoplasm and mitochondria.
(b) $C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2}$ + energy: cytoplasm only.

Answer: As above.

Example 4: Differences · 3 marks · Short answerExam level

Give three differences between aerobic and anaerobic respiration.

Try it first, then show the solutionSolution

Oxygen needed versus not needed.
Complete versus incomplete breakdown of glucose (CO₂ + H₂O versus ethanol + CO₂).
Much energy (about 38 ATP) versus little (2 ATP).

Answer: As above.

Example 5: Respiration versus photosynthesis · 4 marks · Short answerHarder exam level

Give four differences between respiration and photosynthesis.

Try it first, then show the solutionSolution

Respiration breaks down food; photosynthesis makes it.
Respiration releases energy; photosynthesis stores it.
Respiration uses O₂ and gives CO₂; photosynthesis uses CO₂ and gives O₂.
Respiration occurs in all living cells day and night; photosynthesis only in green cells in light.

Answer: As above.

Example 6: Heat experiment · 4 marks · Long answerHarder exam level

Describe an experiment to show that heat is produced during respiration. Why is a vacuum flask used?

Try it first, then show the solutionSolution

Flask A: germinating seeds; flask B: boiled seeds washed with antiseptic (control).
A thermometer in each; note readings.
After a day or two, A shows a rise; B does not: respiration releases heat.
A vacuum flask prevents heat loss, so the rise can be detected.

Answer: As above.

Example 7: Interpret the result · 3 marks · Short answerHOTS / competency

In a sealed flask with germinating seeds and a tube of KOH, coloured water rises 4 cm up the delivery tube in 6 hours. (a) What gas is being used up? (b) What happened to the gas given out? (c) What result do you expect if the seeds are boiled first?

Try it first, then show the solutionSolution

(a) Oxygen, used in aerobic respiration.
(b) CO₂ was absorbed by KOH.
(c) No rise: dead seeds do not respire.

Answer: As above.

Example 8: Mass calculation · 3 marks · Short answerHOTS / competency

A germinating seed respires 0.9 g of glucose aerobically. Calculate the mass of oxygen used and of water formed. (C = 12, H = 1, O = 16)

Try it first, then show the solutionSolution

180 g glucose uses 6 × 32 = 192 g O₂ and forms 6 × 18 = 108 g H₂O.
O₂ = 192 × 0.9/180 = 0.96 g.
H₂O = 108 × 0.9/180 = 0.54 g.

Answer: 0.96 g oxygen; 0.54 g water.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 2 + 1 + 2 marks.

Seeds and lime water

Suppose a student sets up two flasks, P with soaked, germinating gram seeds and Q with the same number of boiled seeds, each joined by a delivery tube to a test tube of clear lime water, and leaves them for a day.

(i) · 2 marks
In which tube does the lime water turn milky? Write the equation.
Answer
Answer: The tube from P: $C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O$
(ii) · 1 mark
What is the purpose of flask Q?
Answer
Answer: Control: shows that the CO₂ comes from living (respiring) seeds.
(iii) · 2 marks
If P were kept in a bright light with green seedlings instead of seeds, why might the lime water stay clear?
Answer
Answer: Green seedlings photosynthesise in light and use up the CO₂ released by respiration, so little reaches the lime water.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

State two differences between glycolysis and the Krebs cycle. (2 marks) (2 marks)

Step	Marks
Glycolysis in cytoplasm; Krebs cycle in mitochondria	1
Glycolysis needs no oxygen (little energy); Krebs cycle needs oxygen (most energy)	1

Describe an experiment to show that carbon dioxide is given out in respiration. (3 marks) (3 marks)

Step	Marks
Germinating seeds in a flask connected to a test tube of lime water	1
Control with boiled seeds	1
Lime water turns milky only with germinating seeds: CO₂ released	1

Where students lose marks in Respiration in Plants

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

Mistake: Respiration confused with breathing
Everyday use of 'breathing' for 'respiration'.
Wrong working
Plants respire through their leaves by breathing in oxygen.
Right working
Respiration is the oxidation of food in every living cell; gases diffuse through stomata, lenticels and root surfaces.
Do this: Respiration is chemical and cellular.
Usually costs: 1 mark.
Mistake: Plants respire only at night
Students see CO₂ released only at night.
Wrong working
Plants photosynthesise by day and respire by night.
Right working
Plants respire day and night; by day photosynthesis uses up the CO₂.
Do this: Respiration never stops in a living cell.
Usually costs: 1 mark.
Mistake: Wrong products of anaerobic respiration in plants
The muscle equation is written for plants.
Wrong working
In plants, glucose → lactic acid.
Right working
In plants and yeast: glucose → ethanol + CO₂.
Do this: Plants make alcohol; muscles make lactic acid.
Usually costs: 1 mark.
Mistake: Unbalanced respiration equations
Coefficients are dropped.
Wrong working
C₆H₁₂O₆ + O₂ → CO₂ + H₂O
Right working
$C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O$
Do this: Six of each beside glucose.
Usually costs: 1 mark.
Mistake: Missing the role of chemicals in experiments
Set-ups are described without saying what KOH or the antiseptic does.
Wrong working
KOH is placed in the flask.
Right working
KOH absorbs the CO₂ released, so a drop in gas volume shows oxygen uptake.
Do this: Always state why each chemical is there.
Usually costs: 1 mark.

Practice questions on Respiration in Plants

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 · MCQExam level
The end products of aerobic respiration are:
(a) ethanol and CO₂
(b) lactic acid
(c) CO₂ and water
(d) glucose and oxygen
Hint
Complete oxidation.
Answer
(c)
Q2 · 1 mark · MCQExam level
Lime water turns milky because of:
(a) oxygen
(b) carbon dioxide
(c) water vapour
(d) ethanol
Hint
CaCO₃.
Answer
(b)
Q3 · 3 marks · Very short answerExam level
Name: (a) the stage of respiration common to aerobic and anaerobic pathways, (b) the organelle called the powerhouse, (c) the gas given out in alcoholic fermentation.
Hint
Glycolysis...
Answer
(a) Glycolysis (b) Mitochondrion (c) Carbon dioxide
Q4 · 2 marks · Short answerExam level
Give two differences between respiration and burning.
Hint
Speed; enzymes.
Answer
Respiration is slow, stepwise and enzyme-controlled at body temperature; burning is fast and uncontrolled at high temperature. Respiration stores energy as ATP; burning releases it as heat and light.
Q5 · 2 marks · Short answerHarder exam level
Why are germinating seeds better than green leaves for showing CO₂ release, unless the leaves are kept in the dark?
Hint
Photosynthesis.
Answer
Green leaves photosynthesise in light and use up the CO₂ they release, hiding the result. Seeds have no chlorophyll and respire rapidly.
Q6 · 2 marks · Short answerHarder exam level
What is the significance of (a) glycolysis, (b) the Krebs cycle?
Hint
Without oxygen; most energy.
Answer
(a) It begins the breakdown of glucose and supplies some energy even without oxygen. (b) It completes the oxidation of pyruvic acid to CO₂ and releases most of the energy of aerobic respiration.
Q7 · 2 marks · Short answerHarder exam level
Explain why it is harmful to water potted plants so much that the soil stays waterlogged.
Hint
Root oxygen.
Answer
Waterlogging drives air out of the soil, so roots lack oxygen. They respire anaerobically, getting too little energy, and the alcohol formed damages them; the roots may rot.
Q8 · 2 marks · Short answerHarder exam level
Write the equation for anaerobic respiration in muscles and give one reason why muscles feel tired after a sprint.
Hint
Lactic acid.
Answer
$C_{6} H_{12} O_{6} \to 2 C_{3} H_{6} O_{3}$ + energy. Lactic acid builds up in the muscles, causing fatigue and cramps.
Q9 · 2 marks · Short answerHarder exam level
In the heat-production experiment, the thermometer in the control flask also rose slightly. Suggest two errors that could cause this.
Hint
Not all dead; microbes.
Answer
Some seeds were not killed by boiling and kept respiring; the antiseptic wash was not done properly, so microbes grew and respired (also the flask may not have been at the same starting temperature).
Q10 · 3 marks · Short answerHOTS / competency
A sugar solution with yeast is kept in a sealed bottle fitted with a balloon. Predict what happens to (a) the balloon, (b) the sugar, (c) the smell of the solution after a few days. Write the equation.
Hint
Fermentation.
Answer
(a) The balloon inflates with CO₂. (b) The sugar is used up. (c) It smells of alcohol. $C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} O H + 2 C O_{2}$
Q11 · 3 marks · Short answerHOTS / competency
Glucose (180 g) respired aerobically gives 6 × 44 = 264 g of CO₂. What mass of CO₂ is given by the same 180 g respired anaerobically by yeast? Which process wastes more of the energy stored in glucose, and where does it go?
Hint
2CO₂.
Answer
Anaerobic: 2 × 44 = 88 g CO₂. Anaerobic respiration releases far less energy (2 versus about 38 ATP); most of the energy stays locked in the ethanol.

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.Energy currency of the cell?Show answer
ATP.
2.Product of glycolysis?Show answer
Pyruvic acid (two molecules).
3.Where does the Krebs cycle occur?Show answer
In the mitochondria.
4.Products of anaerobic respiration in yeast?Show answer
Ethanol and carbon dioxide.
5.Chemical that absorbs CO₂ in experiments?Show answer
Potassium hydroxide (KOH).
6.Energy from aerobic respiration of one glucose (textbook)?Show answer
About 38 ATP.
7.Openings for gas exchange in woody stems?Show answer
Lenticels.
8.Why are dead seeds washed with formalin in the heat experiment?Show answer
To stop microbes respiring and producing heat.

Best order to study it

Learn the definition of respiration and how it differs from breathing and burning.
Learn glycolysis and the Krebs cycle as a two-row table.
Learn the aerobic and anaerobic equations and the comparison table.
Learn the three experiments: set-up, control, result, chemical roles.
Practise application questions (fermentation, storage, waterlogging).

Quick revision checklist

The night before the exam: can you do each of these without looking?

Can you write both respiration equations, balanced?
Can you say where glycolysis and the Krebs cycle happen and which needs oxygen?
Can you give three differences between aerobic and anaerobic respiration?
Can you describe the lime water, KOH and thermos flask experiments?
Can you explain why plants release CO₂ only at night, though they respire all day?

Respiration in Plants: frequently asked questions

Do I need the steps of glycolysis and the Krebs cycle?

No. The syllabus asks only for a brief outline mentioning the terms glycolysis and Krebs cycle and their significance: where they happen, whether oxygen is needed, what they produce and how much energy.

Is the 38 ATP figure exact?

It is the classic textbook value used in ICSE answers. Modern measurements give a somewhat lower figure, but 38 ATP is the accepted answer at this level.

Why use germinating seeds in respiration experiments?

They respire very fast (growing embryos need much energy), and they have no chlorophyll, so photosynthesis does not interfere.

Why do roots die in waterlogged soil?

Water fills the air spaces, so roots get little oxygen; they respire anaerobically, get little energy and produce alcohol, which is toxic.

Based on: CISCE ICSE 2028 Science (52) Biology (Science Paper 3) syllabus, Classes IX and X