IGCSE Biology 0610: Flower Structure, Pollen and Seed Germination

A botanist compares two plant species growing in the same meadow: a bell-flower, whose brightly coloured flowers are visited by bumblebees, and a meadow grass, whose small green flowers have no petals and hang loosely in the wind.

(a) State the function of each of these structures found inside the bell-flower. (i) anther (ii) stigma (iii) ovule [3]

(b) The meadow grass produces huge numbers of small, light, smooth pollen grains. The bell-flower produces far fewer, larger, sticky pollen grains. Explain how each type of pollen grain is suited to the way it is transferred to a stigma. [2]

(c) The botanist collects seeds from both plants and sets up three sealed trays to test what seeds need in order to germinate. Tray 1 has moist soil at room temperature. Tray 2 has dry soil at room temperature. Tray 3 has moist soil, but all of the air inside the sealed tray has been replaced with nitrogen gas, at room temperature. State the germination requirement being tested by comparing Tray 1 with Tray 2, and the germination requirement being tested by comparing Tray 1 with Tray 3. [2]

Part (a): Functions of flower structures

Each structure inside the bell-flower plays a specific role in sexual reproduction:

(i) Anther: produces pollen grains, which contain the male gametes.
(ii) Stigma: receives pollen grains landing on it during pollination.
(iii) Ovule: contains the female gamete; after fertilisation it develops into a seed.

Part (b): Matching pollen grains to their method of transfer

The meadow grass has no petals to attract insects, so its pollen must travel on the wind. Being small, light and smooth reduces air resistance and lets huge numbers of grains be carried long distances by moving air to reach another flower’s stigma, compensating for the fact that most grains will never land on a stigma.

The bell-flower instead relies on bumblebees. Its pollen is larger and sticky, so grains cling to the bee’s body as it brushes past the anther while feeding on nectar. The bee then carries these grains directly to the stigma of the next bell-flower it visits, making transfer far more targeted, so fewer, larger grains are needed.

Part (c): Identifying germination requirements from the experimental design

Comparing trays isolates one variable at a time by keeping everything else the same:

Tray 1 vs Tray 2: both trays are at room temperature and have the same amount of air, but Tray 1’s soil is moist while Tray 2’s soil is dry. This comparison tests whether water is needed for germination.
Tray 1 vs Tray 3: both trays have moist soil at room temperature, but Tray 3’s air has been replaced with nitrogen gas, removing the oxygen. This comparison tests whether oxygen is needed for germination.

Final answers

(a) (i) Anther – produces pollen (male gametes). (ii) Stigma – receives pollen. (iii) Ovule – contains the female gamete, develops into a seed.
(b) Small, light, smooth pollen suits wind transfer; larger, sticky pollen suits transfer by sticking to a pollinator’s body.
(c) Tray 1 vs Tray 2 tests the need for water; Tray 1 vs Tray 3 tests the need for oxygen.