Playbook
Plant Biology
29 q · 3% HARD. Plant Tissues + Meristems (11 q · xylem-water-up / phloem-food-bidirectional / apical-vs-lateral meristem), Photosynthesis (10 · light/dark reactions, chloroplast site, 6CO₂+6H₂O→C₆H₁₂O₆+6O₂), Seed/Fruit/Embryo (4), Transpiration + Tropisms (3 · 33% HARD — chapter's HARD pool, vaseline-on-leaf experiment design). Apply strand because each subtopic demands mechanism-tracing, not just recall.
- questions in the bank
- 29
- tagged HARD
- 3%
- subtopic(s)
- 5
- worked examples
- 2
When you’ll see it
A plant-tissue function question (xylem vs phloem direction, meristem location), a photosynthesis-equation or site question, a seed/fruit/embryo development question, or a transpiration / tropism / plant-process experimental question.
How this chapter is tested
29 q in 10 years, 1 HARD. Plant Biology is the Apply strand workhorse — every subtopic requires tracing a plant process, not just naming a structure. Plant Tissues + Meristems (11 q) is the biggest subtopic: xylem carries water + minerals UP (root → leaves, one-direction, via transpiration pull + root pressure); phloem carries food (sugars from photosynthesis) BIDIRECTIONALLY (source → sink, via pressure-flow). Meristems are growth tissues: apical meristem (tips → length, primary growth), lateral meristem (sides → width, secondary growth, only in dicots).
Photosynthesis (10 q) — site = chloroplast (specifically thylakoid for light reactions, stroma for dark reactions). Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Light-dependent reactions split water (H₂O → 2H⁺ + ½O₂ + 2e⁻), produce ATP + NADPH. Light-independent (Calvin cycle) uses ATP + NADPH to fix CO₂ into glucose. The pigment is chlorophyll (absorbs red + blue light, reflects green — that's why leaves look green).
Transpiration, Tropisms and Plant Processes (3 q, 33% HARD) is the chapter's Apply pocket. The HARD 2021 PYQ is the classic vaseline-on-leaf experiment: vaseline on upper surface vs vaseline on lower surface vs control. Stomata are MOSTLY on the LOWER surface in most dicots → vaseline-lower blocks most transpiration → that leaf loses LEAST mass. Tropisms: phototropism (toward light), geotropism (toward gravity for roots), hydrotropism (toward water), thigmotropism (toward touch — vine tendrils). All are auxin-mediated growth responses.
The sub-skills
The rules and habits that decide whether you get a question right.
Xylem vs phloem direction + function
Xylem: dead cells (tracheids + vessels), carries WATER + dissolved minerals from roots UPWARD only (one-direction, via transpiration pull + root pressure). Phloem: living cells (sieve tubes + companion cells), carries FOOD (sugars from photosynthesis) BIDIRECTIONALLY from source (leaves) to sink (fruits, roots, growing parts).
Meristem location + growth type
Apical meristem: at root tips + shoot tips → PRIMARY GROWTH (increases length). Lateral meristem (vascular cambium + cork cambium): along stem + root sides → SECONDARY GROWTH (increases width / girth) — only in dicots + gymnosperms; monocots lack lateral meristem (no secondary growth, that's why grass stems don't thicken).
Photosynthesis equation + site
6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Site: chloroplast. Light reactions in THYLAKOID membranes (produce ATP + NADPH, split H₂O → O₂). Dark reactions / Calvin cycle in STROMA (fix CO₂ into glucose using ATP + NADPH). Pigment: chlorophyll a (primary), chlorophyll b, carotenoids — absorb red + blue, reflect green.
Transpiration physics
Water loss from plant aerial parts (mostly leaves, mostly via STOMATA). Stomata mostly on LOWER leaf surface in dicots. Cohesion-tension theory: water column held together by cohesion (H-bonds) + adhesion to xylem walls → transpiration pull lifts water from root to leaf. Factors: temperature, humidity (low → more), wind, light (stomata open in light).
2 worked examples from the bank
Real past-year questions illustrating the playbook. Click to reveal options + solution.
Example 1 · Plant Biology · Transpiration, Tropisms and Plant Processes
Example 2 · Plant Biology · Seed, Fruit and Embryo Development
Traps to expect
Distractor shapes specific to this chapter. The page-wide Traps section covers the bank-level patterns.
Phloem one-direction (like xylem)
Phloem is BIDIRECTIONAL — moves food from source (any photosynthesising leaf) to sink (any consuming tissue). Direction depends on time of year + plant part. Distractor says 'phloem moves food upward only' or 'phloem moves food downward only'. Only xylem is strictly one-direction (root→leaf, never reverse).
Photosynthesis happens at night
Light-DEPENDENT reactions need light → only daytime. Light-INDEPENDENT (Calvin cycle / dark reactions) can technically run without direct light BUT depend on ATP + NADPH from the light reactions — so in practice photosynthesis stops without light. Plants RESPIRE 24/7 (release CO₂); photosynthesis is daytime only.
Vaseline-on-upper-surface = no effect
In most dicots stomata are mostly on the LOWER surface, so vaseline on UPPER surface blocks fewer stomata + less transpiration. But it's NOT zero effect — some stomata + cuticular transpiration still occur upper. Distractor says 'upper-vaseline leaf transpires same as control'. Reality: upper-vaseline transpires slightly less than control; lower-vaseline transpires MUCH less than both.
Drill every plant biology question
29 questions from the bank, scoped to 5 bundled subtopics.
Related playbooks
Often paired with this one — drill these next if you found the worked examples above tractable.