Sexual Reproduction in Flowering Plants Test - 22

In diplospory, a cell at a position similar to that of the megasporocyte in a sexual ovule forms the embryo sac by mitosis, whereas in apospory the embryo sac is formed from one or more somatic cells located elsewhere in the ovule (aposporous initials).

Pollination by agency of insects is known as entomophily or insect pollination. Bees, butterflies, moths and beetles are main pollinating insects. Insect pollinated flowers are large, conspicuous, bright coloured and have pleasant smell.

1.  They have nectarines on receptacles or on spurs at the base of flower whorls and produce nectar to attract insects. Option A is incorrect. Pollination by agency of birds is known as ornithophily. The common pollinating birds are squirrels, bats, snails etc. the bird pollinated flowers are colourful, mostly red, produce lots of nectar and also exhibit adaptations to protect nectar from insects. Option C is incorrect.

2.  Pollination by bats is known as chiropterophily. The plants produce large, bell shaped and attractive flowers that open at night and produce strong odours and nectar. Option D is incorrect.

3.  Pollination by snails and slug is called as malacophily. These flowers have long blooming period to facilitate access of pollen to snails.

Self-pollination occurs in species with Cleistogamous flowers and in plants in which pollinators are scarce. In Cleistogamous flowers, the sexual structures (androecium and gynoecium) are enclosed by the petals which form a keel. Pollination agents cannot access the stamens and pistils within the keel.

Out of two sperms, when one sperm fertilizes with egg to form a diploid zygote. While the other sperm fuses with the two polar nuclei to develop triploid endosperm, the process is known as double fertilization. Double fertilization is the characteristic feature of angiosperm.

Parthenocarpic is the natural or artificially induced production of fruit without fertilization of ovules. The fruit is therefore seedless. Banana is such an example Banana.

Flowering plants need to get pollen from one flower to another, either within a plant for self-pollination or between plants of the same species for cross-pollination to occur. However, pollen can’t move on its own, so animals or the wind (and water in rare cases) moves the pollen for plants. Many flowers use colours to attract insects, sometimes helped by coloured guiding marks.

1.  Some have ultraviolet marks that can be seen by insects but are invisible to human eyes. Flowers are often shaped to provide a landing platform for visiting insects or to force them to brush against anthers and stigmas. Some flowers have scent to attract insects. Many of these scents are pleasing to humans too, but not all some flowers attract flies with a smell of rotting meat.

2.  Colours can’t be seen in the dark, so scent is important for flowers that are pollinated by night-flying insects such as moths. Most bird-pollinated flowers have lots of nectar, often at the bottom of a tube of petals.

3.  Birds need to brush against anthers and stigmas when reaching for the sugary reward with their long beaks. Some birds, such as t, stitch birds and bellbirds, have special brush-like tips to their tongues to help them soak up the nectar.

Style is traversed by the pollen tube to reach the ovule.lt is of two types - hollow and solid. In hollow styles, the stylar canal is lined by glandular cells, which are usually multinucleate and polyploid whereas solid style has a core of transmitting tissue, composed of thin walled cells, through which, the pollen tube moves.

In majority of dicot seeds, including pea, the endosperm is consumed during seed development and the food is stored in cotyledons and other regions. They are called non-endospermic or exalbuminous seeds.

Seed coat is thick in coconut seed and thin, membranous in groundnut, gram and maize seeds.

1.  Mulberry is pollinated by wind.

2.  Cucumber is pollinated by bees.

3.  Maize is pollinated by wind.

4.  Vallisneria is pollinated by water.

Hence, animal vector is required for the pollination of Cucumber.