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Respiration in Plants
Biology · Class 11NCERT pp. 153–1642 sets × 25 questions
Key facts and formulas for Respiration in Plants, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.
Key facts for this chapter
| Idea | Rule or fact |
|---|
| Glycolysis | In cytoplasm, oxygen independent, EMP pathway (Embden, Meyerhof, Parnas). 4 ATP made, 2 used, net 2 ATP and 2 NADH per glucose. Phosphofructokinase is the main regulatory step. |
| Fermentation | Alcoholic: pyruvic acid decarboxylase then alcohol dehydrogenase, CO2 released. Lactic acid: pyruvic acid reduced directly, no CO2. NAD+ is regenerated so glycolysis continues. |
| Link reaction | Pyruvic acid to acetyl CoA + CO2 + NADH in the matrix. Needs NAD+, coenzyme A and Mg2+. |
| Krebs cycle (one turn) | Acetyl CoA + OAA gives citric acid. 3 NADH, 1 FADH2, 1 ATP (GTP) and 2 CO2. Two turns per glucose. |
| Per glucose totals | 10 NADH (2 + 2 + 6), 2 FADH2, 4 ATP by substrate-level phosphorylation, 6 CO2 from the link reaction and Krebs cycle. |
| ETS | Complex I NADH dehydrogenase, II succinate dehydrogenase, III cytochrome bc1, IV cytochrome c oxidase, V ATP synthase. Oxygen is the final acceptor; cyanide blocks complex IV. |
| Chemiosmosis | Protons pumped into the intermembrane space return through F0 to the matrix and F1 makes ATP (Peter Mitchell). DNP is an uncoupler. |
| ATP yield | Classical: 3 ATP per NADH and 2 per FADH2 (38 ATP). Modern: 2.5 and 1.5 (about 32 ATP). |
| RQ | RQ = CO2 released / O2 used. Carbohydrate 1, fat about 0.7, organic acid above 1, anaerobic infinity. |
| Other facts | Fermentation releases under 7% of glucose energy; yeast dies near 13% alcohol. Glycerol enters as PGAL, fatty acids as acetyl CoA. Pathway is amphibolic. |
Three sample questions
Q1. Which of these can serve as a respiratory substrate in some plants, besides carbohydrates?
- Only nucleic acids
- Fats, proteins and organic acids
- Only water
- Chlorophyll
Hint and solution
Hint: Think of the other big food molecules a cell stores or makes besides sugars. Some plants burn these when carbohydrate is short.
- Usual substrate: carbohydrates (glucose) — The question asks for substrates other than carbohydrates. Carbohydrates are the common fuel.
- Others: fats, proteins, organic acids — Under certain conditions some plants respire fats, proteins and even organic acids.
- Nucleic acids, water, chlorophyll are not fuels — Water is a product, nucleic acids store information and chlorophyll traps light, so those options fail.
- Answer: fats, proteins, organic acids — So the correct choice lists fats, proteins and organic acids. Option B.
Answer: B. Carbohydrates are the usual substrates, but under certain conditions some plants use proteins, fats and even organic acids.
Q2. Which of the following is NOT a reason why plants can do without special respiratory organs?
- Each part meets its own gas needs
- Respiration rates are low
- Diffusion distances are short
- Gases are rapidly carried between organs by a transport fluid
Hint and solution
Hint: Recall the three S-words: each part is Self-sufficient, respiration is Slow and distances are Short. One option says something opposite to this.
- Reasons: Self, Slow, Short — Plants manage without respiratory organs because each part meets its own needs, rates are low and distances are short.
- Check A, B, C against the reasons — Options A, B and C match these three reasons, so they are genuine reasons.
- Option D claims fast transport between organs — Gas transport between plant parts is minimal, so D is false as a reason.
- Answer: fast transport fluid statement — The question wants the NOT reason, which is the transport fluid statement. Option D.
Answer: D. Gas transport between plant parts is minimal. The reasons are Self, Slow, Short.
Q3. Why do cells make ATP during respiration rather than using the energy of oxidation directly?
- ATP is a form of heat
- Oxidation gives no energy
- ATP is a building block of proteins
- The cell cannot use the energy of oxidation directly; ATP stores it and releases it where needed
Hint and solution
Hint: Oxidation releases energy in a burst. Ask how the cell keeps it in a usable packet and spends it at the right place.
- Oxidation of food releases energy — Breaking down glucose gives energy, but in a form the cell cannot use straight away.
- ATP = energy currency — The released energy is trapped in the bonds of ATP, which can be spent anywhere in the cell.
- Reject heat, no energy, protein block — ATP is not heat, oxidation does give energy, and ATP is not a protein unit.
- Answer: ATP stores and releases energy — So the cell makes ATP because it cannot use oxidation energy directly. Option D.
Answer: D. ATP is the energy currency of the cell.
How to use this chapter
Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.