Question 1
- Diagrams A and B below are illustrations of the half flower of Crotalaria and its fruit formed after fertilization, respectively. Study them and answer questions 1 (a) to 1 (e).
(i) Named the parts labelled I to X.[5 marks]
(ii) State one function each of the parts labelled I, IV, V, VI and IX.[5 marks]
(b) Name two features of the flower in diagram A that adapt it for insect pollination. 5 marks]
(c) (i) Name the parts of the flower in diagram A that form the structures labelled VIII, IX, and X in the fruit in diagram B.[3 marks]
(ii) Describe the formation of the fruit in diagram B from the flower in diagram A.[5 marks]
(d) (i) Name the type of placentation in the flower in diagram A.[1 mark]
(ii) Give three examples of plants which show the same type of placentation as in 1(d)(i). [3 marks]
(e) State the mode of dispersal of the fruit in diagram B.
Observation
In this question,some candidates that scored high could identify the parts of the Crotalaria flower while those that scored badly, could not. Some could not also identify the parts labelled on the fruit, as well as state the features of the flower that adapt it for insect pollination.
Some of them could not also identify the part of the flower that eventually develops to the parts labelled VII, IX and X on the fruit.
Majority of the candidates had poor knowledge of the detailed process of fertilization and development of fruit in flowering plants.
The expected answers are:
(a) (i) Name of labelled parts
I - standard petal VI - ovule
II - keel petal VII - receptacle/thalamus
III - wing petal VIII - calyx/sepal
IV - stigma IX - fruit wall/pericarp/pod
V - anther X - remains of style
Note: spellings must be correct to score.
(ii) Functions of labelled parts
I / standard petal: attracts/guides pollinators/insects;
IV/ stigma: receives pollen grains;
V/ anther: produces pollen grains;
VI/ovule: develops into seed;
IX/fruit wall/pericarp: protects the seeds.
(b) Features of the flower that adapt it for insect pollination
- colourful/brightly coloured conspicuous/petals;
- hairy stigma;
- long filament;
- presence of nectar.
(c) (i) Part of the flower in diagram A that form the structures labelled
VIII: sepal
IX: ovary
X: style/stigma
(ii) Description of formation of diagram B from Diagram A
- Mature pollen grain from the anther lands on the mature stigma;
- the pollen grain germinates;
- and pollen tube penetrates the style into the ovary
- where double fertilization occurs;
- one of the two male nuclei unites with the egg nucleus to form the zygote;
- the second male nucleus fuses with the central nucleus to form the endosperm;
- the zygote develops into the embryo;
- which forms the seed;
- the ovary forms the fruit;
- the style dries up/shrivels.
(d) (i) Type of placentation
Marginal
(ii) Examples of plants that show the same type of placentation
- Pride of Barbados;
- Delonix/Flamboyant/Flame of the forest;
- Cassia;
- Cowpea/bean
- Moringa/ any correctly named.
(e) Mode of dispersal
Explosive mechanism