Maharashtra Board Class 7 Science Chapter 2 Plants Structure and Function PDF Download

2. Plants: Structure And Function

Let's Recall

1. What helps us to easily identify the plants around us?

2. Which are the various parts of plants?

The root, stem, leaves, flowers, fruits, etc. of different plants are different. We can identify plants with the help of these different charactersitics. Let us now acquaint ourselves with these plant organs in greater detail.

Root

Try This

1. Keep a moistened ball of crumpled paper in a conical flask. Place some soaked moth beans/gram seeds in the flask between the paper and the glass wall. Observe and note the changes in the seeds in two or three days.

The part that grows from inside the seed towards the soil is called the radicle and the part that grows above the soil is called the plumule.

The root that forms from the radicle, grows into the ground. The root is thick near the ground and gradually tapers to a pointed end. This part of the plant growing below the soil for support is called root.

Roots of some plants produce secondary roots; that grow obliquely and spread far and wide in the soil. Roots support the plant. This type of root is called a tap root.

Roots bear hair-like processes near the root tips. These are root hairs. The root tip is delicate. This is the region of the growth of the root. The tip is covered by cap-like structure called the root cap. The root-cap protects the root-tip from injuries.

(2) Take a glass jar and fill three-quarters of it with water. Place an onion on the mouth of the jar in such a way that its roots are towards the water. Observe the growth of the roots for eight days.

Thread-like or fibre-like roots arising from the stem are called fibrous roots.

Thus, there are two main types of roots : tap roots and fibrous roots. Dicotyledonous plants have tap roots while monocotyledonous plants have fibrous roots.

(3) Sow the seeds of plants like mustard, sorghum (jowar), maize (corn), pea, coriander, etc. in an earthern pot. Cultivate the plant for eight days. Once the plants grow 15 to 20 cm high, uproot them carefully while the soil is moist and put them gently in a large conical flask containing water. The soil will get washed off without any harm to the roots. Observe the roots carefully to see which plants have tap roots and which ones have fibrous roots.

Teacher's Note

You can show students real roots from your kitchen or garden. For example, carrot and radish have tap roots, but wheat and rice have fibrous roots that look like threads.

Exam Trick

Remember: Tap root = one thick root that goes deep down, like a tap pushing water down. Fibrous roots = many thin roots spread around, like fibres of cloth.

Points to Remember

Radicle grows down to become the root.
Plumule grows up to become the stem.
Roots help the plant to get water and hold the plant in the ground.
Tap roots are thick and go deep. Fibrous roots are thin and spread wide.
Root cap protects the soft tip of the root.

Plants like maize, sugarcane, sorghum have two types of roots. Some roots are underground whereas some grow from the stem just above the soil. The latter are called adventitious roots. Besides the normal functions like absorption of water and minerals, anchoring and supporting the plant, roots perform some other functions too. Roots show some modifications to perform these additional functions. Some examples of such modified roots are aerial roots, stilt-roots, runners, breathing roots (pneumatophores), etc.

(4) Take some water in a small glass jar. Put a plantlet in it in such a way that its roots are dipped in the water. Mark the water-level on the jar and add 5ml of oil to the water. Record the water-level on the next day.

Discuss your observations in the class.

Use Your Brain Power

1. What would have happened if plants like tamarind, banyan and mango had fibrous roots?

2. What will happen if the root-tip is injured?

3. Which types of roots do the fenugreek, spinach and onion plants have?

Do You Know

Roots emerging from the trunk and branches of a banyan tree grow towards the soil. These roots are called prop roots. What could be the use of these prop roots? In the beginning, the banyan tree has very few prop roots. But later on, their number increases so much that it appears like a small forest.

In Kolkata, a 250 years old banyan tree in the Indian Botanical Garden covers a very large area. It is supported by thousands of prop-roots. Is there any such tree in your neighbourhood?

Find Out

Why are the underground parts of plants like radish, carrot, pea and sweet potato thick, fleshy and swollen? Which part of the plant are they?

Techno-Support

Collect images of different types of roots and send them to your friends via e-mail.

Teacher's Note

Show students a real carrot or radish from the market. Tell them these are storage roots that store food for the plant. This is the same part we eat as vegetables in India.

Exam Trick

Remember: Modified roots = roots that do special jobs. Prop roots of banyan = extra support roots, like extra pillars holding up a building.

Points to Remember

Adventitious roots grow from the stem above the ground.
Modified roots do special jobs like support, breathing, or storing food.
Banyan tree prop roots look like many trees because there are so many of them.
Root hairs absorb water from the soil.

Stem

The stem grows above the soil from the plumule of the sprouting seed. As the sprout grows the length of stem gradually increases, too. There are nodes on the stem. Leaves come out at the nodes. The part of the stem between two nodes is called an internode. The tip or the apical end of the stem is called a bud. Observe a branch of any plant and identify its different parts as per the diagram.

Teacher's Note

Point to a plant in your classroom or school garden. Show students the nodes and internodes on a stem. For example, a sugarcane stem has very clear nodes.

Exam Trick

Remember: Node = knot-like area where leaves come out. Internode = the space between two nodes, like intervals between stations on a railway line.

Points to Remember

Stem is the main part that grows above the ground.
Nodes are places where leaves grow from the stem.
Internodes are the parts between nodes.
Buds are at the tip of the stem and grow into new branches or flowers.

Complete The Chart

(Collect information about other local plants, too.)

Leaf

Leaves grow from the nodes on a stem. Leaves are generally thin, flat and green in colour. The broad, spread-out part of the leaf is called the leaf-blade or lamina and its edge is called the leaf-margin. Leaf margins may be entire, dentate or lobed.

The tip of the leaf is called the leaf apex. It may be tapering, pointed or rounded. Leaves of some plants have a stalk called a petiole. Leaves of some plants do not have a petiole. The portion of the leaf attached to the stem is called the leaf-base. Small leaf-like structures may be present near the leaf-base. These are called stipules. Do you see stipules in all plants?

Leaves of some plants have a single undivided leaf blade and a single mid-rib. Such leaves are called simple leaves. However, the leaf-blade of leaves in some plants is divided into many small parts called leaflets. Such leaves are called compound leaves. Simple leaf and compound leaf are the two main types of leaves.

Teacher's Note

Bring mango and neem leaves to class. Show students how the mango leaf is simple and the neem leaf is compound. Let them feel the difference.

Exam Trick

Remember: Simple leaf = one piece like a single piece of paper. Compound leaf = many small pieces like pages in a book stuck together.

Points to Remember

Leaf blade is the main flat part of the leaf.
Leaf margin is the edge of the leaf.
Petiole is the stalk that joins the leaf to the stem.
Simple leaves have one blade. Compound leaves have many small leaflets.
Stipules are small leaf-like parts at the leaf base.

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