Plant tissues

• What is a leaf?

  A plant organ, like any organ, the leaf contains different tissues.
• What are the top and bottom of the leaf covered in and what is the function of the upper epidermis?

  A layer of very thin cells called epidermal cells which form epidermal tissue. The epidermis protects the surface of the leaf. The upper epidermis is transparent which allows light to pass through to the photosynthetic cells below. The upper epidermis is covered in a thin layer of oily material called the waxy cuticle, this reduces the evaporation of water from the surface of the leaf, preventing the leaf from drying out.
• What is the function of the lower epidermis?

  It has tiny pores called stomata which allow carbon dioxide to enter the leaf and oxygen to leave. Stomata help to control the amount of water vapour that can pass out of the leaf. On either side of the stomata we find guard cells.
• What do we find near the top of the leaf?

  Palisade mesophyll, this consists of palisade cells which are packed full of chloroplasts. Chloroplasts contain chlorophyll which absorb light energy needed for photosynthesis.
• What is found under the palisade mesophyll?

  The spongy mesophyll which is full of air spaces, this allows for carbon dioxide to diffuse from the stomata through the spongy mesophyll to the palisade cells. Oxygen also diffuses from the palisade cells through the spongy mesophyll to the stomata.
• What is the function of the xylem tissue?

  To transport water from the roots to the stem and leaves. Some of the water is then used in photosynthesis. They xylem also transports dissolved mineral ions such as magnesium which is used to make chlorophyll.
• What is the function of the phloem tissue?

  To transport dissolved sugars produced by photosynthesis from the leaves to the rest of the plant. The sugars can be used immediately e.g. glucose used in respiration. The sugars can also be stored for example, as starch.
• What is translocation?

  The movement of sugars and other molecules through phloem tissue.
• Where do we find meristem tissue?

  At growing tips e.g. shoots and roots. Meristem tissue contain stem cells which can differentiate into different types of plant tissue.
• what are the parts of the cross-section of a leaf?

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