Plant physiology for NEET: the chapters students skip and later regret

Summary: Plant physiology feels like chemistry dressed up as Botany, so students postpone it. Learn each pathway as a flow chart with its location and its ATP and NADPH accounts, keep one table for plant growth regulators, and revise these three chapters every month so they do not fade before Class 12 ends.

Why these chapters get skipped

By the time plant physiology is taught in Class 11, students have already felt comfortable in Zoology and are busy with Physics numericals. The Botany physiology chapters arrive full of cycles, enzymes and molecule names, and they feel like chemistry. So they get a quick reading, a promise to "do it properly in revision", and then Class 12 starts.

Most students who skip these chapters in Class 11 end up trying to learn the Calvin cycle and Krebs cycle for the first time in the last two months, alongside everything else. That is the regret in the title. The chapters are shorter than they look, and they are logical once you see each pathway as a story with a start, a location and a balance sheet.

What is in the syllabus now

After the NMC revision, the plant physiology unit in NEET covers three NCERT chapters: Photosynthesis in Higher Plants, Respiration in Plants, and Plant Growth and Development. Transport in Plants and Mineral Nutrition were removed from the syllabus. That makes the remaining three chapters more concentrated, since every question in the unit now comes from a smaller area.

Photosynthesis in Higher Plants

Split the chapter into the light reaction and the biosynthetic phase, and learn where each happens in the chloroplast.

• Pigments and light: chlorophyll a and b, carotenoids, the action and absorption spectra.
• Light reaction: the two photosystems and their reaction centres (P680 in PS II, P700 in PS I), splitting of water and release of oxygen, the Z scheme, and cyclic and non-cyclic photophosphorylation.
• Chemiosmosis: how the proton gradient across the thylakoid membrane drives ATP synthase.
• Calvin cycle: carboxylation by RuBisCO, reduction and regeneration.
• C4 pathway and photorespiration: Kranz anatomy, PEP carboxylase, and why C4 plants avoid photorespiration.
• Factors affecting photosynthesis: Blackman's law of limiting factors, light, carbon dioxide, temperature and water.

Worked example: the Calvin cycle account

Each turn of the Calvin cycle fixes one molecule of carbon dioxide, using 3 ATP and 2 NADPH. A glucose molecule has six carbons, so the cycle must turn six times to make one glucose. That needs 6 × 3 = 18 ATP and 6 × 2 = 12 NADPH. NEET often asks one of these three numbers, and the student who has worked it out once never has to memorise it.

Respiration in Plants

Build the chapter as one long flow chart on a single page:

1. Glycolysis in the cytoplasm, glucose to two pyruvate
2. Fermentation, when oxygen is absent, to ethanol or lactic acid
3. Pyruvate to acetyl CoA in the mitochondrial matrix
4. The TCA (Krebs) cycle in the matrix
5. The electron transport system and oxidative phosphorylation on the inner mitochondrial membrane

Beside each step write where it happens, what goes in, what comes out, and how many NADH, FADH₂ and ATP are made. Then read the NCERT section on the respiratory balance sheet carefully. It explains the theoretical net gain of 38 ATP per glucose and the assumptions behind it, and questions are asked on those assumptions as well as the number.

Two more ideas to learn well: why respiration is called an amphibolic pathway, and the respiratory quotient. RQ is 1 for carbohydrates, and NCERT gives the example of tripalmitin, a fat, with an RQ of about 0.7. Proteins fall in between.

Plant Growth and Development

The first half is about growth: its phases, growth rates (arithmetic and geometric), and the terms differentiation, dedifferentiation and redifferentiation. The second half is plant growth regulators, and it is where the marks are.

Fill in the discovery of each regulator from the NCERT text too, since the names of the scientists and the organisms they worked on are asked. Match-the-column questions on this table are common, so revise it from both sides: effect to regulator and regulator to effect.

Read your current NCERT edition for this chapter rather than an old guide. Some sections were trimmed in the rationalised book, and the NMC syllabus follows the current text.

A three-week plan

After the three weeks, put a 30-minute revision of these chapters into your timetable every month. Pathways are forgotten faster than facts because they have many linked parts. Our notes on Photosynthesis, Respiration in Plants and Plant Growth and Development are useful for the revision passes.

Common questions