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.
(a) Fig. 5.1 shows part of a monkey flower plant.
(i) State two pieces of evidence, visible in Fig. 5.1, that show that monkey flower plants are pollinated by insects.
(ii) The monkey flower plant in Fig. 5.1 reproduces sexually. Describe the advantages and disadvantages of sexual reproduction for monkey flower plants.
(b) Monkey flower plants were introduced to Europe from North America about 200 years ago. Scientists measured the leaf area of five monkey flower plants growing in Europe and five monkey flower plants growing in North America. Their results are shown in Table 5.1 and Table 5.2.
(i) Using the data in Table 5.2, calculate the mean leaf area for plants growing in North America. Give your answer as a whole number and include the unit.
(ii) State a conclusion for the results shown in Table 5.1 and Table 5.2.
(iii) Ancestors of monkey flower plants had a much smaller leaf area. Explain how the monkey flower plants have developed a larger leaf area over time.
▶️ Answer/Explanation
(a)(i) Evidence of insect pollination:
1. Large, colorful petals (attract insects).
2. Spotted patterns/nectar guides (direct insects to reproductive parts).
Alternative: Anthers/stigma enclosed within petals (require insect contact).
(a)(ii) Sexual reproduction in monkey flowers:
Advantages:
– Genetic variation → better adaptation to environmental changes.
– Disease resistance (diverse offspring).
Disadvantages:
– Requires pollinators (energy-intensive).
– Slower than asexual reproduction.
(b)(i) Mean leaf area (North America):
\[ \text{Mean} = \frac{290 + 310 + 300 + 305 + 300}{5} = \frac{1505}{5} = 301 \, \text{cm}^2 \]
(b)(ii) Conclusion:
European monkey flowers have larger leaves (mean = 320 cm²) than North American plants (mean = 301 cm²).
(b)(iii) Evolution of larger leaves:
1. Mutations caused variation in leaf size.
2. Natural selection favored plants with larger leaves (more photosynthesis).
3. Over generations, alleles for larger leaves became common.