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)