Fig. 2.1 is a photograph of a spider plant, Chlorophytum comosum. Spider plants can reproduce by producing an identical plantlet, which grows away from the single parent plant.
(a) (i) Identify one feature in Fig. 2.1 that shows that spider plants are monocotyledons.
(ii) Describe the advantages and disadvantages of asexual reproduction in a population of spider plants in the wild.
(b) Fig. 2.2 shows pollen that has been released from the flowers of a hazel tree, Corylus avellana. These flowers are wind‑pollinated.
(i) Explain why a hazel tree has to produce very large amounts of pollen.
(ii) Describe how a stigma from a wind‑pollinated plant is adapted for pollination.
(c) The hazel tree uses cross‑pollination rather than self‑pollination. Describe cross‑pollination.
(d) Outline the events that occur in the flower after pollination.
▶️ Answer/Explanation
(a)(i) Ans: Parallel veins in the leaves or strap-shaped leaves.
Monocotyledons like spider plants have leaves with parallel veins, unlike dicots with branched veins.
(a)(ii) Ans:
- Advantages: Rapid reproduction, no need for pollinators, offspring genetically identical to parent (well-adapted to stable environment).
- Disadvantages: Low genetic variation increases vulnerability to diseases/environmental changes; competition among identical offspring.
(b)(i) Ans: Wind pollination is inefficient, so large pollen quantities increase the chance of pollen reaching a stigma.
(b)(ii) Ans: Feathery/sticky stigmas protrude outside the flower to trap airborne pollen effectively.
(c) Ans: Cross-pollination transfers pollen from anthers of one plant to the stigma of another (same species), promoting genetic diversity.
(d) Ans: Post-pollination events:
- Pollen tube grows down the style.
- Male nucleus travels to the ovule via the pollen tube.
- Fertilization occurs (male + female nuclei fuse).
- Zygote forms, developing into a seed.