BIOLOGY [3 marks Question Answer]

Depending on the size, plants are classified into three groups:

1. Herbs:They are very small plants with soft and green stems. Eg. Mint, spinach.
2. Shrubs: They are medium-sized plants with woody stems. The branches are almost the same size arising from the stem immediately above the soil. e.g. Rose, jasmine.
3. Trees: Tall plants with thick, hard, and woody stem are called trees. They bear woody branches and leaves at some distance above the ground. e.g. Coconut, mango

Gymnosperms are plants having naked seeds, i.e., seeds are not enclosed in fruits. The seeds are borne on woody structures called cones, and hence called conifers or coniferous trees. They produce male and female cones for reproduction instead of flowers. Gymnosperms are mostly tall trees growing on mountains. They have well-developed roots, thick and woody stems, and long needle-shaped leaves. They are evergreen plants.
Examples:Pine, cycas, cedar, Ginkgo, spruce, etc.

On the basis of time taken to complete their life cycle, plants are divided into three groups :

1. Annuals:These plants complete their life cycle in one season in a year.
   e.g. Wheat, rice.
2. Biennials:These plants complete their life cycle in two years i.e. in the first year, they bear root, stem and leaves and in the second year, they produce flowers, fruits and seeds.
   e.g. Carrot, radish, turnip.
3. Annuals:These plants life for more than two years and bear flowers, fruits and seeds every year. e.g. Mango, Banyan.

On the basis of a place where a plant grows (its habitat), plants are classified into three groups :

1. Mesophytes:Plants which grow on land and need moderate amount of water, e.g. Potato, tomato.
2. Hydrophytes:Plants that need maximum water to grow and hence live in water. They may be floating or partially/completely submerged.
   e. g.Lotus, Hy dr ilia.
3. Xerophytes:Plants that grow on dry land like deserts and need minimum amount of water to live. They have thin and spiny leaves to reduce water loss.
   e.g. Cactus, babul.

Rhizobium bacteria are found living in the root nodules (small swollen structures on roots) of leguminous plants like the pea, bean, etc. These bacteria trap the nitrogen from the atmosphere and convert it into nitrates (mineral salts) which can be easily absorbed by the plants from the soil along with the water. It is observed here that the bacteria provide food to the host plant and the host plant, in turn, provides shelter for the bacteria. This kind of relationship wherein two organisms live in harmony each benefiting from such a relationship is called symbiosis. The organisms are called symbionts.