CBSE Notes Class 6 Science Chapter 4 Getting to Know Plants

Plants are alive, just like people and animals. Living things all do certain things: They grow and die, need energy, nutrients, air and water, and produce young ones. They are made up of cells. They react to what's around them. Life is not possible without plants. We find plants everywhere around us. Some are small while others are big. Some are found in water and others are present on land in roadside, house, school and farmhouse. 

1.0Plants on the Basis of Size

• Plants on the basis of size and the nature of their stem can be classified into three categories :- 
• Small plants/herbs 
• Medium plants/shrubs
• Big plants/trees 
• There is another type of plant that can differ from herbs, shrubs and trees. 
• These are plants with weak stems and cannot stand upright. Some of these spread out on the ground and are called creepers. 
• For example strawberry, pumpkins, watermelon. Others climb up with the help of the support, for example grapevine, money plant, beanstalk and gourd. 
• They are called climbers.

2.0Design of Plant Body

Root System 

• Roots act like straws absorbing water and minerals from the soil. 
• Tiny root hairs emerge out of the root helping in the absorption. 
• Roots help to anchor the plant in the soil so it does not fall over. 
• Roots also store extra food for future use like in carrot, sweet potatoes. 

Structure 

(i) Tap root system 

• In this system, a single root (primary root) comes out from the seed after germination. 
• Many branches and sub-branches come out from this main root called “Lateral roots” and spread out into the soil. 
• It is found in most of the dicot plants. e.g. Mango, neem, pine, sheesham, pea, carrot, radish, turnip and beetroot. 
• Primary Root + Lateral Roots = Tap root system (main root) 

(ii) Fibrous Root System 

• Many plants do not have a main root. 
• Instead they have a cluster of fine roots, which come out from the base of the stem. 
• These roots do not go down as deep into the soil as tap roots. 
• It is found in most of the monocot plants. e.g. Grasses, cereals (like maize, rice and wheat) bamboo, sugarcane and onion.

Functions of root 

• Anchoring the plant: Roots help to anchor (fix) the plant firmly into the ground. 
• Absorption of water and nutrients from the soil. Plants absorb water and minerals from the soil. Plants use these to manufacture food. 
• Preventing soil erosion: Roots help to bind the soil particles together, thereby preventing them from being carried away by water and wind

Shoot System 

The part of a plant above the ground consisting of stem, branches, leaves, flowers and fruits is called shoot system. 

1. Functions of stem 

• Stems keep the plant upright or they support the plant. 
• They act like the plant's plumbing system, conducting water and nutrients from the roots and food from the leaves to other plant parts. A set of thin tubes from the root are connected to thin tubes in the stem, water and minerals pass through these tubes to leaves, flowers, buds and fruits.

2. Leaves 

• The leaf is a flat green outgrowth of the stem. 
• The wide flat green portion of the leaf is called lamina or leaf blade. 
• The thin portion of leaf by which it is joined to the stem is called stalk or petiole. 
• The petiole extends into the leaf as the midribs and joins the stems at the leaf base. 
• The thin lines arising from the petiole and midribs and spreading across the leaf are called veins. 
• The veins branch into veinlets. 
• The veins provide support to the leaf and carry water, minerals and food. 
• The arrangement of veins on a leaf is called venation. 

Functions of the leaf 

• The leaves on their surfaces have tiny pores called stomata. Through these pores, plants take in gasses for respiration and photosynthesis. The gasses produced during these processes are also given out through stomata. 
• The process by which plants throw out excess water in the form of vapor is called transpiration. 
• Leaves manufacture food for the plant body. The process of manufacturing food by the leaves is called photosynthesis. Leaves require water, carbon dioxide, sunlight and chlorophyll for making food.

Carbon dioxide + Water Light Chlorophyll Glucose + Oxygen

• In some plants, leaves bear buds in the marginal notches from which new plants grow and develop. e.g., Bryophyllum. 

3. Flowers, Fruits and Seeds 

• A flower is the reproductive organ of a plant. 
• A typical flower has a stalk called a pedicel, which joins it to stem. 
• The upper most part of the pedicel is wider and is known as thalamus. 
• On the base of thalamus, the different parts of the flower are arranged in concentric rings and whorls
• Sepals : The outermost whorl of the flower consists of sepals. These are the green, leaf-like structures at the base of the flower. Sepals protect the flower during its development and support the flower when it blooms. (ii) 
• Petals : The second whorl consists of petals. These are colorful structures that surround the inner parts of flowers. Its function is to attract the pollinators. 
• Stamen : The third whorl of flower consists of stamen. These are male reproductive parts of flowers. Each stamen has two parts, a thin stalk called filament and a knob-like structure called another. Anther produces a powdery substance called pollen. 
• Carpel : It is a single elongated structure in the center of the flower. It is broader below and tapers at the top, and is also known as pistil. It is the female reproductive part of a flower. It has three parts, a sticky top portion called stigma, an enlarged base called ovary, and a stalk called style that connects these two. The ovary contains tiny bulb-like structures called ovules (can be one or more), which later become seeds.