(a) (i) How does a farmer use dormancy of seed to his advantage? [1]
(ii) Differentiate between pea seed and castor seed. [1]
OR
(b) Identify the stage of follicle where primary oocyte undergoes first meiotic division. Also mention the products of this division. [2]
(a) (i) How does a farmer use dormancy of seed to his advantage? [1]
(ii) Differentiate between pea seed and castor seed. [1]
OR
(b) Identify the stage of follicle where primary oocyte undergoes first meiotic division. Also mention the products of this division. [2]
(a)(i) Use of seed dormancy by a farmer:
Because dormant seeds do not germinate immediately, the farmer can store them safely for long periods and sow them at the right (favourable) season, avoiding germination during storage or off-season. This helps in stocking seeds for the next crop.
(a)(ii) Pea seed vs Castor seed:
- Pea seed → non-endospermic (ex-albuminous): the endosperm is consumed during development, so food is stored in the fleshy cotyledons.
- Castor seed → endospermic (albuminous): food is stored in the endosperm, which persists in the mature seed.
OR
(b) Stage and products of the first meiotic division:
- Stage: the primary oocyte completes its first meiotic division inside the (tertiary / mature) Graafian follicle, just before ovulation.
- Products: one large haploid secondary oocyte (retains most cytoplasm) and one small haploid first polar body.
Marking Scheme
- 1(a)(i) 1 mark: dormancy lets the farmer store seeds and sow them at the appropriate/favourable season (prevents untimely germination).
- 2(a)(ii) 1 mark: pea = non-endospermic (food in cotyledons); castor = endospermic (food in endosperm).
- 3OR (b) 2 marks: 1 mark — Graafian (tertiary/mature) follicle stage before ovulation; 1 mark — products are a secondary oocyte and a first polar body (haploid, unequal division).
Hint
For (a) think storage and correct sowing time, and food stored in cotyledons (pea) vs endosperm (castor). For OR (b) it is the Graafian follicle, giving an unequal division.
Quick Oral Answer
A farmer uses seed dormancy to store seeds and sow them in the right season; a pea seed is non-endospermic with food in its cotyledons while a castor seed is endospermic with food in the endosperm. In the OR part, the primary oocyte completes meiosis I in the Graafian follicle just before ovulation, producing a secondary oocyte and a first polar body.
Analysis & Explanation
Concept (a) — Seed dormancy and seed types:
- Dormancy is a state where a viable seed does not germinate even in favourable conditions, due to hard/impermeable seed coats, immature embryos, or inhibitors. For a farmer this is useful: seeds can be stored and sown at the correct season, giving control over the cropping cycle.
- Endospermic vs non-endospermic seeds is a classic 'differentiate' point:
- Pea (non-endospermic): stores food in cotyledons; endosperm used up during embryo development.
- Castor (endospermic): retains a food-rich endosperm at maturity.
Concept (b) — Oogenesis timing:
- Oogenesis begins in the foetus but the primary oocyte is arrested in prophase I for years.
- Around the time of ovulation, inside the Graafian follicle, the primary oocyte completes meiosis I to give an unequal division: a secondary oocyte + a first polar body.
- Meiosis II of the secondary oocyte is then completed only if fertilisation occurs.
Exam trap:
- For (a)(ii), the required distinction is endospermic vs non-endospermic (food storage), not just 'shape/colour'.
- For (b), name the Graafian follicle specifically and state that the division is unequal (secondary oocyte + first polar body), not two equal cells.
Common Mistakes
- 1For (a)(ii) writing only superficial differences (size, colour) instead of the key point: pea is non-endospermic (food in cotyledons) while castor is endospermic (food in endosperm).
- 2For OR (b) naming the primary/secondary follicle instead of the Graafian follicle where meiosis I is completed just before ovulation.
- 3Stating that meiosis I gives two equal cells; it is an unequal division yielding one secondary oocyte and one small first polar body.
Interesting Facts
Seed dormancy allows some seeds to remain viable for years; date palm seeds and lotus seeds have famously germinated after centuries of dormancy.
Castor and maize are endospermic (albuminous) seeds, whereas pea, gram and bean are non-endospermic — a favourite comparison in CBSE exams.
A woman's primary oocytes are arrested in prophase I from before birth, so an egg ovulated at age 30 has been paused mid-meiosis for about three decades.
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Frequently Asked Questions
Why is a pea seed called non-endospermic and a castor seed endospermic?
In a pea seed the endosperm is completely used up during embryo development, so reserve food is stored in the fleshy cotyledons, making it non-endospermic. In a castor seed the endosperm persists in the mature seed and stores food, making it endospermic (albuminous).
At which stage does the primary oocyte complete its first meiotic division?
It completes the first meiotic division inside the Graafian (tertiary/mature) follicle, just before ovulation, producing an unequal pair: one large secondary oocyte and one small first polar body, both haploid.