These DAV Class 6 Science Notes and DAV Class 6 Science Chapter 8 Notes – Structure and Function of the Living Organisms: Plants act as excellent revision resources, particularly in preparation for board exams.
Structure and Function of the Living Organisms: Plants Class 6 DAV Notes
→ There are two main parts in the flowering plant, viz. the root system and the shoot system.
A. The Root System: The part of the plant which grows below the ground and is composed of roots is called the root system.
Functions of roots:
- Root absorbs water and minerals from soil.
- Root holds the plant into the soil.
- In some plants, root also stores food.
- Roots bind the soil together and thus prevent the soil from getting washed away by rains or blown away by winds.
→ Classification of root system: The root system is classified into two main types:
→ Tap Root System: On germination of seed, a single root grows downwards. It branches into smaller lateral roots. This type of root system is called tap root system. Examples: pea. mustard, bean, gram, etc.
→ Fibrous Root System: On germination of seed, several roots grow at the same time. This type of root system is called fibrous root system. Examples: maize, wheat, rice, grasses, etc.
→ Modifications of the root: In many plants, roots often perform special functions. Such roots are called modified roots. The following are some of the modifications of roots:
→ Modification of roots for food storage: In some plants, roots are modified for food storage. Roots in such plants are swollen because of the stored food. Examples: carrot, sweet potato, turnip, beetroot, etc.
→ Modification of roots for support: In some plants, extra roots develop from aerial parts of the stem or branches. These roots go into the soil and thus give extra support to the plant. Examples: prop roots of banyan, stilt roots of maize.
→ Parasitic Roots: Roots of parasitic plants do not grow on soil rather they grow on their host. Such roots penetrate into the stem of the host plant so that they can get water and minerals from the host plant. Such roots are called sucking roots.
B. The Shoot System: The part of the plant which grows above the ground and is composed of stem, leaves, flowers, fruits and seeds; is called the shoot system.
→ The Stem: Stem is the main part of the shoot system and it usually grows above the ground. The stem bears leaves at regular intervals. The point from which a leaf comes out is called the node of the stem. The part between two nodes is called internode.
→ Functions of Stem:
- Stem keeps the plant straight and upright.
- Stem transports water and minerals (absorbed by roots) to all plant parts.
- Stem transports food (prepared by leaves) to other plant parts.
- Stem holds the leaves in such a way that they get the optimum sunlight so that they can perform photosynthesis.
- In some plants, stem also stores food.
- Green stems; of young plants; also perform photosynthesis.
→ Modifications of Stem: Following are some of the modifications of stem:
→ Modification of stem for food storage: In some plants, stem is modified to store food. Such stems remain underground. It looks like a root but nodes, internodes and scale leaves are present. Examples: ginger, potato, colocasia, etc.
→ Modification of stem for support: In some plants, stems are modified to support the weak stem of the plant. Example: tendrils of a pea plant; which are coiled structures. The tendril coils around a support such as a pole, a branch of a tree, etc.
→ Modification of stem for manufacturing food: In some plants, stem is leaf¬shaped, fleshy and green. Such stems manufacture food. Example: cactus.
2. The Leaf: A leaf is a broad, flat and green structure in plant. A leaf grows from the node of the stem. The flat and broad part of the leaf is called leaf blade or lamina. Leaf is attached to the stem by a short structure called petiole. The petiole continues through the lamina to a mid-rib. The mid-rib branches out into a fine network of veins. Veins transport water, minerals and food in plants. They also provide support to the leaf.
→ Functions of leaf:
(а) Leaf is the main site of photosynthesis. Thus, leaf is the place where food is manufactured in plants.
(б) Leaf helps in exchange of gases; through small pores called stomata.
→ Modifications of leaf: Following are some of the modifications of leaf:
→ Leaf Spine: In some plants, leaves are modified into hard and pointed structures called spines. They protect the plant from grazing animals. They also prevent loss of water due to excessive hot climate.
→ Leaf Pitcher: Leaves in some plants are modified into pitcher-like structures. Such structures trap insects in insectivorous plants. Examples: pitcher plant, dew plant, etc.
→ Leaf Tendril: In some plants, leaves are modified into highly coiled structures; called tendril. They help the plant in climbing to a support. Examples: pea, gloriosa, etc.
→ Leaf Modified as a reproductive organ: In some plants, leaves have buds which produce new plants, e.g. Bryophyllum.
3. The Flower: A flower is the reproductive structure of a plant. A flower consists of several rings or whorls of structure.
→ Sepals: These are green leaf-like structures which form the outermost whorl of the flower. The outermost whorl of the flower is called calyx. It provides protection to the bud before it blooms.
→ Petals: These are colourful structures and form the second whorl of the flower. The second whorl of the flower is called corolla. The petals attract insects and birds which help in pollination.
→ Stamens: These are slender tube-like structures which form the third whorl of the flower. The third whorl is called androecium. A stamen bears anther at the top. The anther produces pollen grains. Pollen grain takes part in reproduction.
→ Pistils: The central whorl of the flower is composed of pistils. The pistil is composed of a swollen part at the base which is called ovary. There is a tub-like structure in the middle: called style. There is a flat structure at the top; called stigma.
→ The ovary produces ovules which take part in reproduction. Pollen grains are deposited at stigma; after pollination. Pollen grain germinates at the stigma and grows a tube; called pollen tube. The pollen tube penetrates through the style and reaches the ovary. Pollen grains fuse with ovules and form seeds.
→ Functions of flower:
- Flower is the reproductive organ of a plant. It grows into a fi’uit and produces seeds.
- Flowers have great economic importance. Many ornamental flowers are grown in gardens and parks.
- Flowers are important source of perfumes and scents.
- Some flowers are dried and used as spices, e.g. cloves and saffron.
4. The Seed: A seed is a small hard structure containing a baby plant and stores food for its growth. When a seed gets proper moisture and temperature, it germinates and gives rise to a young plant; called seedling.
5. The fruit: After fertilization, the ovary grows into a fruit. A fruit is defined as a mature or ripened ovary.
Functions of a fruit:
(a) Fruit protects the seed against injury and other unfavourable climatic conditions.
(b) Fruit helps in dispersal of seeds.
(c) Fruit stores food, e.g. in tomato, apple, mango, etc.
→ Bark: The thick brown covering on the trunk that provides protection to the stem.
→ Fibrous root system: Several roots that grow out at the same time from the base of the stem.
→ Node: The point, in a stem, where the leaf is attached.
→ Parasitic roots: The roots that absorb water and minerals from other plants.
→ Pistil: The female part of a flower.
→ Prop roots: Additional roots which grow, and hang down from the branches, to give additional support to trees.
→ Root system: The part of the plant, which grows below the ground.
→ Seedling: A young plant.
→ Shoot system: The part of the plant, which is found above the soil.
→ Stamen: The male of a flower.
→ Stomata: Tiny pores, on the surface of leaves, which help in exchange of gases.
→ Tap root system: A single root grows downwards into the soil.
→ Tendrils: Spring-like outgrowths, from the stem, or leaves, to support the plant.
→ Whorls: The rings of structures in a flower- flower consists of several rings like sepal, petal, stamen and pistil.