Samacheer Class 7 Science - Reproductive and Modification In Plants

S. No.
Bisexual flower
Unisexual flower
(a)
It has Androecium and Gynoecium
It has only Androecium or Gynoecium
(b)
It can undergo self pollination and cross pollination e.g : Hibiscus
They can be pollinated only by cross pollination eg : papaya.

Pollen grains are transferred from the anther of one flower to the stigma of another flower of the same kind or different plant.
Plants need to produce pollen grains in larger quantities to increase the chance of pollination.
Cross pollination does introduce variations in characteristics of new plants.
Cross pollination is brought about by agencies like wind, water, animals and Insects of plums, apples.

Transfer of pollen grains from the anther to the stigma is called pollination. There are two types of Pollination.
(a) Self Pollination
(b) Cross Pollination
(a) Self pollination
Pollen grains are transferred from the anther to the stigma of the same flower or to another flower of the same plant.
Plants do not need to produce pollen grains in a large quantity for self pollination.
It does not produce changes in the characteristics of new plants
(b) Cross Pollination
Pollen grains are transferee! for the anther of one flower to the stigma of anoter flower of the same kind or different plant.
Plants need to produce pollen grains in larger quantities to increase the chance of pollination.
Cross pollination does introduce variations in characteristics of new plants, e.g (apples, plums)
Agents like wind, water, insects and animals are helpful for pollination and are known as pollinators.
Wind pollinated plants produce pollen which are light. Insect pollinated flowers are brightly coloured and produce lot of pollen which sticks to the body of insects and are caused to other plants.
Pollination that occurs in nature is called Natural pollination.
Pollination between desired plants can be brought about by artificial methods.

There are some stems that grow under the ground to store food. These underground stems swell and become thick.
There are four types of underground stems:
Rhizome.
Corm
Tuber
Bulb
(i) Rhizome : It is an underground thick stem with nodes and intemodes with scale , leaves at the node. It grows horizontally and has an irregular shape. Rhizome have buds. It gives rise to new stem and leaves. E.g. Ginger and Turmeric.
(ii) Corm: This underground stem is round in shape and flat at the top and bottom. It
is a condensed form of rhizome and bears one or more buds in the axils of scale leaves. Daughter plants arise from their buds. E.g. Colocasia.
(iii) Tuber: It is an enlarged, spherical underground stem that stores food. It has many dormant buds on its surface known as “Eyes”. If we plant a part of tuber with the bud, it grows into a new plant. E.g. Potato.
(iv) Bulb: It is condensed stem which is disc like and stores food in the fleshy leaves. The bulb has two types of leaves.
Fleshy Leaves
Scaly Leaves
The upper part of the stem has a terminal bud and it is covered by many scaly leaves, the inner fleshy leaves store food as seen in Garlic and Onion

Ginger has the following characteristics of a stem.
It has scale leaves
It has nodes and Intemodes
It has axillary buds and a terminal bud.
Therefore Ginger is considered to be a stem but is is a modified underground stem which stores food.

No pollen of rose will get wasted and will not germinate on the stigma of lily flower. This is because pollen of a flower is compatible (match) only with stigma of a flower of the same species.

Name
Modification
1.
Garlic
Underground stem modification
2.
Turnip
Top Root modified for storage (Top shaped)
3.
Rose plant
Stem used for vegetative propagation / Asexual Reproduction by cutting
4.
Maize
Stilt Roots (Adventitious roots produced from the node for mechanical support).