Question

a. Describe the function of different parts of leaves as seen in a cross section. b. What are different modifications of roots and stems? Give examples of each

Answer 1

describe the function of different parts of leaves as seen in cross section-

cuticle: A waxy layer that prevent water loss by evaporation. The cuticle is transparent and very thin to allow maximum light penetration.

Upper Epidermis: A protective layer of cells that produces the cuticle. The epidermis is is also transparent and very thin to allow maximum light penetration.

Palisade Mesophyll: Rod shaped cells that contain large numbers of chloroplasts for photosynthesis. These cells are located close to the leaf surface to maximise light absorption. They are upright, elongated and tightly packed together in order to increase the surface area for light absorption. Chloroplasts are found near the palisade cell surface to maximise light absorption and to reduce the distance that carbon dioxide and oxygen have to diffuse (to / from the chloroplast stoma)

Spongy Mesophyll: These cells are smaller than those of the palisade mesophyll and are found in the lower part of the leaf. They also contain chloroplasts, but not quite as many. These cells have large air spaces between them that allow carbon dioxide and oxygen to diffuse between them. The air spaces also gives these cells a large surface area to maximise the diffusion of carbon dioxide into the cell and oxygen out of the cell.

Vein: Plant veins consists of xylem (vessels that carry water) and phloem (vessels that carry dissolved nutrients such as sugar). These vessels play an essential role in transporting water to the chloroplasts in the mesophyll tissues for photosynthesis. They also transport the sugar produced by photosynthesis away from these cells to the rest of the plant tissues to be used as an energy source or stored.

Lower Epidermis: A protective layer of cells. The lower epidermis produces a waxy cuticle too in some plant species. The lower epidermis contains pores called stomata that allow carbon dioxide and oxygen to move in and out of the plant respectively.

stomata: Tiny pores (small holes) surrounded by a pair of sausage shaped guard cells. These cells can change shape in order to close the pore. In very hot conditions water inside the leaf evaporates and the water vapour can escape through the stomata. Closing them prevent reduces water loss, but also limits the diffusion of carbon dioxide and oxygen in and out of the leaf.

Different modifications of roots and stem-

modification in root system

The root is an underground part of the plant that absorbs water and minerals from the soil and anchors the plant firmly. In some plants, the roots change their shape and get modified to absorb and transport water and minerals from the soil to different parts of the plant. They are also modified for support, food storage, and respiration.The root modifications to perform two major functions- Physiological and Mechanical

for food storage - for eg., the taproots of carrot and turnip get swollen to store food.

For better Respiration - In some halophytes such as Rhizophora that grow in swampy areas, the roots emerge out of the ground and grow upwards to get oxygen for respiration.

Nodulated Roots - Roots of the leguminous plants are modified into root nodules which contain nitrogen-fixing bacteria such as Rhizobium. They help in fixing the atmospheric nitrogen into nitrates and make it available to the plants.

modification in stem syatem -

Stem modifications, either aboveground, underground, or aerial, enable plants to survive in particular habitats and environments.

for eg. Modified stems that grow horizontally underground are either rhizomes, from which vertical shoots grow, or fleshier, food-storing corms.

New plants can arise from the nodes of stolons and runners (an aboveground stolon): stems that run parallel to the ground, or just below the surface.

Potatoes are examples of tubers: the swollen ends of stolons that may store starch.

the stem modification that has enlarged fleshy leaves emerging from the stem or surrounding the base of the stem is called a bulb; it is also used to store food.

Aerial modifications of stems include tendrils, thorns, bulbils, and cladodes