(a) Do all pollen grains remain viable for the same length of time? Support your answer with two suitable examples. [2½]
(b) How are pollen grains stored in pollen banks? [½]
(a) Do all pollen grains remain viable for the same length of time? Support your answer with two suitable examples. [2½]
(b) How are pollen grains stored in pollen banks? [½]
No — pollen viability is not the same for all species; it varies widely with the species and the surrounding conditions.
(a) Pollen viability varies (with two examples):
- No, pollen grains do not all remain viable for the same length of time. Viability depends on the species and on temperature and humidity.
- Example 1 — short viability: In cereals like rice and wheat, pollen grains lose viability within about 30 minutes of release.
- Example 2 — long viability: In members of Rosaceae, Leguminosae and Solanaceae, pollen remains viable for months.
(b) Storage in pollen banks:
- Pollen grains are stored by cryopreservation — freezing in liquid nitrogen at −196 °C.
- Such stored pollen can be used later in crop-breeding programmes.
Marking Scheme
- 1½ mark: clear answer — No, pollen grains do not all remain viable for the same time (varies with species and conditions).
- 21 mark: first example — rice/wheat (cereals), viable for about 30 minutes.
- 31 mark: second example — Rosaceae/Leguminosae/Solanaceae, viable for months.
- 4½ mark: pollen banks store pollen by cryopreservation in liquid nitrogen at −196 °C.
Hint
No — cereals (rice/wheat) ~30 minutes vs Rosaceae/Solanaceae months; banks freeze pollen in liquid nitrogen at −196 °C.
Quick Oral Answer
No, pollen viability varies with species and conditions — it is barely 30 minutes in cereals like rice and wheat but months in Rosaceae, Leguminosae and Solanaceae; in pollen banks it is preserved by freezing in liquid nitrogen at minus 196 degrees Celsius for use in breeding.
Analysis & Explanation
Concept — pollen viability:
Pollen viability is the period during which a shed pollen grain can still germinate on a stigma and effect fertilisation. It is genetically fixed for a species but is also strongly influenced by temperature and humidity.
The contrast to state (needs two clear examples):
- Very short-lived: in the grass family (rice, wheat), pollen stays viable for only about 30 minutes.
- Long-lived: in Rosaceae, Leguminosae and Solanaceae, pollen can remain viable for months.
This contrast is exactly what earns the 2½ marks — a bald 'No' without examples scores poorly.
Exam trap:
- Do not confuse viability of pollen with longevity of seeds; the question is about pollen, so the 30-minute (cereals) vs months (Rosaceae/Solanaceae) contrast is required.
- For storage, the precise term is cryopreservation in liquid nitrogen at −196 °C — not merely 'kept cold'.
Real-world application:
Pollen banks, like seed banks, conserve germplasm; stored pollen is used in plant breeding to cross parents that flower at different times or grow in different places, aiding crop improvement.
Common Mistakes
- 1Answering only 'No' without giving the two contrasting examples — the examples carry most of the marks.
- 2Confusing pollen viability with seed longevity/dormancy, which is a different concept.
- 3Writing a vague storage method ('kept in fridge') instead of cryopreservation in liquid nitrogen at −196 °C.
Interesting Facts
In rice and wheat, pollen loses its ability to fertilise within just 30 minutes of being shed — one reason cereal breeders must time crosses very precisely.
In a few species of Rosaceae, Leguminosae and Solanaceae, pollen has been stored for years in liquid nitrogen and still successfully fertilised flowers.
Pollen banks, like the more familiar seed banks, are a form of ex-situ germplasm conservation used to safeguard the genetic diversity of crop plants.
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Frequently Asked Questions
Do all pollen grains stay viable for the same time?
No. Pollen viability varies with species and with temperature and humidity. In cereals like rice and wheat it is only about 30 minutes, whereas in Rosaceae, Leguminosae and Solanaceae pollen can stay viable for months.
How is pollen stored in a pollen bank?
Pollen is stored by cryopreservation — freezing it in liquid nitrogen at −196 °C. Stored this way, it can be used later in crop-breeding programmes.
Why is pollen viability important in plant breeding?
Knowing how long pollen stays viable lets breeders time crosses correctly, and preserving viable pollen in banks allows crossing of plants that flower at different times or grow in distant places, aiding crop improvement and germplasm conservation.