Name the part of gynoecium that determines the compatible nature of pollen grain.
The pistil has the ability to recognise, the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible). If it is of the right type, the pistil accepts the pollen and promotes post-pollination events that lead to fertilisation. If the pollen is of wrong type, the pistil rejects the pollen.
The ability of the pistil to recognise the pollen is followed by its acceptance or rejection. It is the result of a continuous dialogue between pollen grain and the pistil mediated by chemical components of the pollen interacting with those of the pistils.
Name the common function that cotyledons and nucellus perform.
The common functions that cotyledons and nucellus perform are as follows
(i) Storage of reserve food material.
(ii) Nourishment Cotyledons nourishes embryo and nucellus nourishes embryo sac.
$$ \begin{aligned} &\text { Complete the following flow chart }\\ &\text { Pollen mother cell } \rightarrow \text { Pollen tetrad } \rightarrow \text { Pollen grain }\left\langle\begin{array}{l} \text { Vegetative cell } \\ \ldots . . . . . . . . . . . . . . . . . . \end{array}\right. \end{aligned} $$
$$ \begin{aligned} &\text { }\\ &\text { Pollen mother cell } \text { Pollen tetrad } \text { Pollen grain }\left\langle\begin{array}{l} \text {(i) Vegetative cell } \\ \text { (ii) Generative cell }\end{array}\right. \end{aligned} $$
The process of formation of microspores from a Pollen Mother Cell (PMC) through meiosis is called microsporogenesis. The microspores, as they are formed, are arranged in a cluster of four cells i.e., the microspore tetrad.
As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains (male gametophyte). When the pollens mature, it contains two cells the vegetative cell (bigger) and generative cell (smaller).
Microsporogenesis : (a) A microspore tetrad
(b) A microspore maturing into a pollen grain
Indicate the stages where meiosis and mitosis occur ( 1,2 or 3 ) in the flow chart.
$$ \text { Megaspore mother cell } \xrightarrow{1} \text { Megaspores } \xrightarrow{2} \text { Embryo sac } \xrightarrow{3} \text { Egg } $$
$$ \text { Megaspore mother cell }(2 n) \xrightarrow{\text { Meiosis }} \text { Megaspores } \xrightarrow{\text { Mitosis }} \text { Embryo sac (n) } \xrightarrow{\text { Meiosis }} \text { Egg. } $$
The diploid Megaspore Mother Cell (MMC) undergo meiosis and forms a linear tetrad of four haploid megaspores. Three mitotic divisions, inside the functional (one) megaspore form the embryo sac (eight haploid nuclei), while the other three megaspores degenerate.
The embryo sac is a seven-celled and eight nucleated structure. Three micropylar, Three chalazal and one central. The three micropylar cells are collectively known as egg-apparatus, which, consists of two synergids and one egg cell.
While three chalazal cell form antipodal cell. The central cell is in the form of two nucleated cell till the fertilisation occurs and called as polar nuclei.
$$ \text { A diagrammatic representation of the mature embryo sac } $$
In the diagram given below, show the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of egg apparatus.
Following compatible pollination, the pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores. The contents of the pollen grain ( 2 mole nuclei) move into the pollen tube. Pollen tube grows through the tissues of the stigma and reaches the ovary.
After reaching the ovary, pollen tube, enters the ovule through the micropyle and then enters the embryo sac by passing into one of the synergids through the filiform apparatus. It leads to the degeneration of that synergid.
The pollen tube breaks to release its contents (2 male nuclei). Out of the two male gametes one fuses with egg and the other fuses with central cell and fertilise.
$$ \text { Longitudinal section of a flower showing path of pollen tube growth } $$
The component cells of the egg-apparatus in an embryo sac include, two synergids, one egg cell and the filiform apparatus.
$$ \text { A diagrammatic representation of the mature embryo sac } $$