Pollination and fertilization
Q1. Explain the advantages and disadvantages of cross-pollination.
Ans: Advantages of cross-pollination:
a) The offspring are healthier.
b) The seeds are produced in larger numbers and are more viable.
c) The seeds develop and germinate properly and grow into better plants.
d) Results in new varieties because cross-pollination can be carried out between two different varieties of the same species or even two species.
Disadvantages of cross-pollination:
a) It is not always certain as a pollinating agent is always required, and it may or may not be available at a suitable time.
b) Pollen grains have to be produced in abundance to ensure chances of pollination. This results in a lot of wastage of pollen.
c) It is uneconomical for plants as they have to produce flowers that are large, perfumed, and with nectar to attract insects
Q2. Explain how pollination occurs in aquatic plants.
Ans: Pollination in aquatic plants:
(a) By insect or wind in water hyacinth and water lily.
(b) By water in Vallisneria, male flowers are brought close to female flowers on the water surface and pollen grains are carried passively by water currents to reach the stigma.
Q3. Describe the following terms:
Ans: Pollination by birds is called Ornithophily.
Pollination is an important process for flowering plants to survive. Since most flowering plants cannot pollinate on their own, they have to rely on other animals. Many small birds, such as sunbirds and hummingbirds are key pollinators.
The plants that are pollinated by birds are formed in such a way to accommodate birds – like having a sturdy build to support perching and forming flowers with a re-curved, tube-like shape that does not tangle the birds. The flowers are also formed in such a way to allow access to a bird’s beak. Such plants also have brightly coloured flowers with nectars inside them.
Process of Pollination by Birds
The process of pollination by birds is as follows:
i) Birds seek energy-rich nectar by visiting flowers
ii) Most flowers pollinated by birds have nectars hidden deep inside the flower
iii) The pollen sticks to the bird’s head/ neck and back when it tries to reach the nectar
iv) Birds transfer these pollens when visiting other plants
Ans: The process in which the pistil matures before the maturation of another to prevent self-fertility. The examples are ivy and rosebay willowherb.
Ans: Heterostyly is an adaptation to prevent self-pollination and ensure cross-pollination. In this, the flowers are of two or three forms as regards to the length of stamens and styles so that the anthers and stigmas are at different levels. As a consequence pollen from a flower can not reach the stigma of the same flower.
Ans: Flowers that are never open to ensure self-pollination is called cleistogamy. They remain closed so that cross-pollination does not occur.
Cleistogamy has the advantage that the plant produces an assured seed set even in the absence of pollinators and the disadvantage is that self-pollination occurs which reduces the chances of variation and evolution of genetically superior progeny.
Ans: Anemophily or wind pollination is pollination carried out with the help of the wind. This pollination is called anemophilous pollination. The flowers which carry out such type of pollination are wind pollinating flowers. They are small, lightly coloured, and do not produce scent or nectar.
The stamens of these flowers are long and hand out of the flower to help the wind pollinate.
The anthers are loosely attached to the filament and the pollens are very light and dry.
The stigmas are feathery and hang out of the flower. For example, maize.