Plant Structure, Growth, and Reproduction: Topic 9.3 and 9.4

Question 1

Explain apical growth in plant shoots, including phototropism and the role of auxin.

Answer 1

Apical meristems are found at the apex of roots and stems and allow plants to grow taller and produce new leaves and fruits, and allow roots to extend through the soil. Apical growth is controlled by plant hormones called phytohormones that are released from the shoot apex and control stem growth and the formation of new nodes, one of the main phytohormones, auxin, promotes growth by promoting cell division and cell elongation by changing patterns of gene expression. Auxin also prohibits growth in the shoot apex by inhibiting growth in the lateral buds called a phototropism, this is a positive tropism for the stems of the plants as they grow towards the light but a negative tropism for the roots as they grow away from the light.

Question 2

what are the functions of each part of an animal pollinated flower

Answer 2

Stigma - pollen landing pad
Style - supports the stigma
Ovary - Produces female sex cells by meiosis
Anther - produces male sex cells by meiosis
Filament - supports the anther
Petals - Attract pollinators
Sepals - protect developing flower

Question 3

Outline the relationship between flowers and pollinators (mutualistic).

Answer 3

Flowers and pollinators have a mutualistic relationship that’s beneficial in both ways because the animal gets nectar/pollen from the flower and the plant gets pollinated/fertilized, most flowering plants have coevolved with pollinator species

Question 4

Distinguish between pollination and fertilization in flowering plants.

Answer 4

Pollination is when pollen from the anther is transported to the stigma of a flower by some vector is either self-pollination (pollen from the anther of the same plants falls onto its own stigma (less genetic variation)) or cross-pollination (pollen from the anther of one plant to the stigma of another - more genetic variation). Fertilization is the fusion of haploid nuclei (male pollen grain fuses with the female ovule to produce a diploid zygote)

Question 5

Describe how flowering is controlled in short-day plants.

Answer 5

Flowering in short-day plants happens when days are short and nights are long and it’s controlled by phytochromes that absorb wavelengths of light. The inactive form of phytochrome Pr is the inactive form that absorbs red light to rapidly convert it into the active phytochrome, Pfr, which absorbs FAR red light that rapidly converts it back into Pr. Since sunlight contains more red light Pfr is more prominent during the day and Pr is more prominent at night. In short-day plants more Pfr inhibits plant growth so when the night is less than the critical length Pfr levels are lower due to less sunlight exposure which promotes flowering. Flowering is also due to changes in gene expression in the shoot apex.