• All parts of a plant that are above the ground form the shoot system. It includes stems, leaves, flowers, fruits, etc.
• The stem is a very important part of a plant. A stem shows nodes and internodes.
Functions of a Stem:
• Stems hold leaves in position and help them to spread out, as the stem and its branches grow. This ensures that they get enough sunlight for photosynthesis.
• Stems bear flowers, buds, leaves, and fruits.
• Stems act as pipelines and conduct water and mineral salts from the roots to the leaves.
• Similarly, they carry the food manufactured by the leaves to other parts of the plant.
• Green stems have chlorophyll and can carry out photosynthesis.
• Stems have nodes from which leaves arise. The space between two nodes is called an internode.
• Stems of certain plants are modified to perform special functions.
For storage of water:
• Stems of plants such as cactus and jade swell up to store water in them.
For storage of food:
• Potato, onion, and ginger are modified stems that store food.
• There are three kinds of underground stems: tubers (e.g., potato), rhizomes (e.g., ginger), and bulbs (e.g., onion and garlic).
Onion Potato Ginger
For multiplication of the plant:
• Rhizomes, bulbs, and tubers also help in multiplication of the plant.
• Stem cuttings of some plants such as rose, jasmine, and hibiscus grow into new plants.
To manufacture food:
• Stems of some plants become leaf-like and flattened (e.g., cactus) and perform photosynthesis.
• Stems may be modified as thorns, like in bougainvillea or hard and sharp prickles, as in rose, to protect the plant from being eaten by animals.
Prickles of rose stem
• Stems of some plants are modified to form special structures called tendrils.
• Tendrils help plants such as climbers, which have weak stems, they attach themselves to other supports tree trunk, wall etc.
• For example, Passion flower and grapes have tendrils.
• Leaves are known as food factories of the plant.
• They are located at the nodes of stems and have a characteristic shape and size.
• The flat, green portion of the leaf is called leaf blade or lamina.
• Petiole is a narrow, stalk-like structure that connects the leaf to the stem.
Structure of a leaf
• A network of branching veins forms a supporting framework and also serves to transport raw material and manufactured food into and out of the lamina.
• Midrib, a continuation of the petiole, is the central vein of the leaf. Smaller veins grow from the midrib.
• The arrangement of veins in a leaf is termed as venation.
• Venation may differ from one type of plant to another.
Different venation observed in different leaves
• If the veins run parallel to one another from the base to the tip of the leaf, the leaf is said to have parallel venation, e.g., banana and onion.
Parallel venation in banana leaf
• Leaves of some plants have veins arranged in a net-like pattern on both sides of the midrib. This kind of venation is called reticulate venation, e.g., Peepal (Bodhi) and Mango.
Reticulation venation in a leaf
Functions of a Leaf:
• Leaf performs following functions:
• Leaves manufacture food in the presence of sunlight.
ii. Exchange of gases:
• Stomata help in exchange of gases which are important for respiration and photosynthesis.
• Evaporation of excess of water in vapour form and exchange of carbon dioxide takes place through stomata.
iv. Modifications for special functions:
• In certain plants; leaves perform functions like:
• Providing support and protection
• Vegetative propagation
• Trapping insects
• Leaves of some plants are also modified to form special structures called tendrils.
• Tendrils help plants to attach themselves to a support.
• Plants having tendrils are generally weak climbers.
• Leaves of certain plants modify to form spines.
• Spines also reduce the amount of water lost from the plant.