Plants: tissue, systems and organs

Cards (26)

    • The leaf is a plant organ adapted specifically for photosynthesis
    • You should be able to observe and draw of a transverse section of a leaf
  • Wax Cuticle:
    • Protective layer on top of the leaf prevents water from evaporating
  • Upper Epidermis:
    • it is thin and transparent to allow light to enter the palisade mesophyll
  • Palisade mesophyll:
    • column shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis
  • Spongy Mesophyll:
    • contains internal air space that increases surface area to volume ratio for the diffusion of gases ( mainly carbon dioxide)
  • Lower Epidermis:
    • Contains Guard cells and Stomata
  • Guard Cells:
    • absorbs and loses water to open and close the stomata, to allow carbon dioxide diffuse in and oxygen to diffuse out
  • Stomata:
    • where gas exchange takes place; opening during the day and closing during the night. Evaporation of water also takes place here. In most plants, its found a great concentration under the leaf to reduce water loss
  • Vascular Bundle:
    • contains xylem and phloem to transport substances to and from the leaf
  • Xylem:
    • Transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from the stomata
  • Phloem:
    • transports sucrose and amino acids around the leaf
  • Root hair cells
    • Adapted for the efficient uptake of water by osmosis
    • Adapted for the efficient uptake of mineral ions by active transport
  • Root hairs
    Single-celled extensions of epidermis cells in the root which increase the surface area of the cells significantly
  • Increased surface area of root hairs
    Increases the rate of the absorption of water by osmosis and mineral ions by active transport
  • Structure of a root
    • Specifically allows it to maximise absorption of water by osmosis
    • Specifically allows it to maximise absorption of mineral ions by active transport
  • Pathway of water into and across a root
    1. Root hair cell
    2. Root cortex cells
    3. Xylem
    4. Leaf mesophyll cells
  • Transpiration
    The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
  • Xylem
    • Substance called lignin is deposited in the cell walls
    • Xylem cells die and become hollow
    • Xylem cells join end-to-end to form a continuous tube
    • Lignin strengthens the plant to help it withstand the pressure of the water movement
    • Movement in xylem only takes place in one direction - from roots to leaves
  • Movement in xylem only takes place in one direction - from roots to leaves (unlike phloem where movement takes place in different directions)
    • Air movement, humidity, temperature and light intensity all have an effect on the rate at which transpiration occurs
    • The table below explains how these four factors affect the rate of transpiration when they are all high; the opposite effect would be observed if they were low
  • Stomata and guard cells
    • Control gas exchange and water loss
    • Found predominantly on the underside of the leaf
  • Guard cells
    Have cell walls with unevenly distributed cellulose - the inner wall is thicker and the outer wall is thinner to aid opening and closing of the stomata
  • Guard cells are flaccid
    They pull together, closing the stomata and reducing water loss via transpiration
  • Stomata distribution
    • Predominantly on the underside of the leaf where it is cooler and shaded (lower light intensity) - this leads to less transpiration and therefore less water loss
  • Translocation
    The transport of soluble products of photosynthesis (sugars and amino acids) around the plant in the phloem tubes
  • Phloem tubes
    • Made of living, elongated cells
    • Allow easy flow of substances from one cell to the next through pores in the end cell walls (sieve plates)