Getting to know plants (Part-3)

 Getting to know plants 


Q.8. Explain the structure of the leaves.
Ans. The leaf is a thin, broad, flat and green part of a plant which is attached to the stem (or branch). Leaves of different plants have different shapes and sizes, but all of them have the same basic structure.
The flat green portion of a leaf is called leaf lamina or leaf blade. Leaves grow at the nodes of the stem. They are attached to the stem by a stalk called petiole. The lines of the leaves are called veins. A thick vein runs in the middle of the lamina, called midrib. The arrangement of veins in the lamina on a leaf is called venation. Veins transport water and minerals to the leaves. They also provide support to the leaves.
There are minute pores on the surface of a leaf, called stomata. The stomata helps in the exchange of gases and helps in the process of transpiration. The leaves of plants contain a green coloured pigment called 'chlorophyll'. Chlorophyll can absorb (or trap) energy from sunlight.
                                  
                                                 
Q.9. What is venation and what are its types?
Ans. The arrangement of veins in the lamina (or leaf blade) is called venation of the leaf. There are two man types of venation in the leaves:
  • Reticulate venation: The veins in a leaf occur in an irregular way forming a net-like design on both sides of midrib. For example, Neem, Mango, Peepal, China rose, Rose, Orange, Guava etc have reticulate venation in their leaves.
  • Parallel venation: The veins in a leaf run parallel to one another on both sides of the mid rib. For example, Wheat, Paddy (rice), Maize, Millet, Sugarcane, Bamboo, Barley, Lily, Banana etc have parallel venation in their leaves.
                                               
Q.10. What are the functions of the leaves of a plant?
Ans. The leaves of a plant have three main functions:
  • Plants release a lot of water into the air through the process of transpiration. This process helps in cooling the leaves, just as sweating helps us in keeping cool.
  • Leaves prepare their food in the presence of sunlight and a green colored substance (chlorophyll) present in them. For this, they use water and carbon dioxide from air. This process is called photosynthesis. Oxygen is given out in this process. This can be written as:
                                            
           The simplest food prepared by photosynthesis is glucose. Some of the glucose is converted into starch . This starch is stored as food in various parts of the plant (including leaves).
  • Leaves exchange gases through the small pores present under their surface. These minute spores are called stomata.

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