Grade 12 — Term 2
3 study notes · 30 practice questions · Aligned with NIE syllabus
Counted in the Idasara Academy app, which you open with a free account. The free notes, revision, practice and library pages for each lesson are linked below.
This term in the Idasara Academy app has 3 lessons (NIE Unit 4). For each lesson, this page gives you the points you must know and one exam-style question with its answer. None of it needs an account.
Lessons in This Term
Resource acquisition and transport in plants
What you must know
- Water potential gradient: Water always moves spontaneously from a region of higher (less negative) water potential to lower (more negative) water potential.
- Root pressure and guttation: Under low transpiration and high soil moisture, root pressure pushes water droplets out through hydathodes at leaf margins (guttation), distinct from dew.
- Stomatal opening mechanism: Influx of K+ and Cl- ions into guard cells driven by proton-ATPase pumps lowers their water potential, causing water intake by osmosis, turgor increase, and pore opening due to radially oriented cellulose microfibrils.
Try one question
According to the pressure-flow hypothesis of phloem translocation, what directly drives the bulk flow of sap from source to sink?
- A. Active pumping of sucrose along the sieve plate pores
- B. Turgor pressure gradient generated by osmotic water movement
- C. Capillary action in sieve tube elements
- D. Transpirational pull from the stomata
Show the answer
Answer: B. Turgor pressure gradient generated by osmotic water movement. Active loading of sucrose at source cells lowers water potential, causing water to enter by osmosis and generating high turgor pressure. At the sink, sucrose unloading increases water potential, water leaves, and low turgor pressure results. The resulting hydrostatic turgor pressure gradient drives bulk flow.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Plant reproduction
What you must know
- Pollen tube guidance: Chemical attraction guides pollen tube growth down style through micropyle; synergids secrete chemical attractants.
- Ploidy levels: Zygote/embryo is 2n; Endosperm is 3n; Seed coat (testa) is 2n (maternal tissue). In the embryo sac, the egg, synergids and antipodal cells are n; the central cell holds two haploid (n) polar nuclei.
- Self-pollination vs Cross-pollination mechanisms: Dichogamy (protandry/protogyny), dioecy, self-incompatibility, and heterostyly prevent self-pollination and promote genetic diversity.
Try one question
In the angiosperm embryo sac during double fertilization, what products are formed by the fusion of the two male gametes with their respective targets?
- A. Diploid zygote (2n) and triploid primary endosperm nucleus (3n)
- B. Haploid embryo (n) and diploid endosperm (2n)
- C. Triploid zygote (3n) and diploid seed coat (2n)
- D. Diploid embryo (2n) and haploid antipodal tissue (n)
Show the answer
Answer: A. Diploid zygote (2n) and triploid primary endosperm nucleus (3n). One sperm nucleus (n) fuses with the egg cell nucleus (n) to form the diploid zygote (2n), while the second sperm nucleus (n) fuses with the diploid central cell / two polar nuclei (2n) to form the triploid primary endosperm nucleus (3n).
A model question written by Idasara on the exam pattern. It is not from a past paper.
Plant responses to signals
What you must know
- Photoperiodism & Phytochrome: Plants detect day/night length using phytochrome pigment converting reversibly between Pr (inactive, absorbs red 660nm) and Pfr (active, absorbs far-red 730nm); critical dark period regulates flowering.
- Phototropism mechanism: Blue light activates phototropins on illuminated side, causing asymmetric lateral transport of auxin to shaded side where higher auxin induces faster cell elongation, bending shoot toward light.
- Hormone antagonism: Apical dominance reflects balance between auxin (from apex, inhibitory) and cytokinins (from roots, stimulatory) on axillary buds.
Try one question
Which plant hormone is primarily responsible for inducing stomatal closure during severe drought stress to prevent water loss?
- A. Abscisic acid (ABA)
- B. Gibberellin (GA₃)
- C. Cytokinin
- D. Auxin (IAA)
Show the answer
Answer: A. Abscisic acid (ABA). Abscisic acid (ABA) is the major stress hormone synthesized in roots and leaves in response to water deficit; it triggers potassium and anion efflux from guard cells, decreasing turgor and closing stomata.
A model question written by Idasara on the exam pattern. It is not from a past paper.
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