STPM Biology - chapter 2:Revision essay question 9

9. Explain how the following plant tissues are adapted for their functions.

Answer:

    i. Epidermis
       It is a protective tissue to protect inner tissue. Epidermis secrete cutine which forms a layer or waxy cuticle on the outer surface. This will reduces water loss by evaporation from the plant and entry of pathogens. It is transparent and allows light to reach the mesophyll layears of leaves for photosynthesis. Stomatal pores in epidermis allow gaseous exchange.

     ii. Parenchyma tissue
         It is the ground tissue of stems, roots and leaves of plants. When the cells are turgid and tightly packed they provide support for herbaceous plants. In leaves they form the mesophyll cells contain chloroplast and help carry out photosynthesis. They store starch, proteins and lipids. In a transverse section, the cell is usually round in shape. They are loosely packed together with many large intercellular air spaces to allow gaseous exchange. They are potentially meristematic and can form secondary meristematic tissue such as vascular cambium and cork cambium. The parenchyma cells in flowers and pericarp contain chromoplasts to attract pollinating agents and help in the dispersal of fruits and seeds.

   iii. Collenchyma tissue
        Cells are polygonal-shaped and elongated. The cells are closely packed together and no intercellular air spaces. It acts as a supporting tissue to provide the herbaceous plant with mechanical strength and flexibility. Some of the collenchyma cells contain chloroplasts which can carry out photosynthesis.

   iv. Sclerenchyma fibres
        It is elongated, polygonal-shaped with tapering ends. Mature sclerenchyma tissue consist consists of dead cells tightly packed with no intracellular air spaces. It have thick, lignified secondary cell walls impermeable to water, solutes and gases. The cells have no protoplasm with narrow empty lumen in center. Sclerenchyma acts as supporting tissue which provide the plants with mechanical strength and rigidity. The tapered ends of the sclerenchyma fibres overlap and interlock with another, further increasing their combined strength.

   v. Sclereids

       They have different shapes but are usually shorter than sclerenchyma fibres. They can be grouped into bundles, can form complete tubes located at the periphery or can occur as single cells or small groups of cells within parenchyma tissues. They consist of dead cells with thicker lignifid walls. Simple branching pits are present in the walls and called ramiform pits. It acts as protective tissue which gives strength and support to the plant structures or organs.

Assignment submitted by group 1  2011/2012 (IBM)