Chapter 10 Photosynthesis Flashcards
State the function of the upper epidermis of a leaf
- Transparent cells (no chloroplasts) which covers the upper surface of the leaf
- Allows light to pass through
- Protect the inner cells
- Produce the cuticle
State the function of the cuticle on a leaf
- Waxy, waterproof layer covering the upper epidermis of the leaf
- Reduces water from evaporating from the leaf
State the function of the lower epidermis of the leaf
- Transparent, covers the lower surface of the cell
- Allows light to pass through, protects inner cells and sometimes also produces a cuticle
Name the different layers of which a leaf consists
- Upper epidermis
- Lower epidermis
- Cuticle
- Mesophyll layer
- Vascular bundles
- Stomata
Describe the mesophyll layer?
- it is the middle layer of the leaf situated between the two epidermises.
- the mesophyll layer just below the upper epidermis is called the palisade mesophyll cells.
- the palisade mesophyll is where most photosynthesis takes place.
- The mesophyll layer in the lower part of the leaf just above the lower epidermis layer is called the spongy mesophyll cells.
- spongy mesophyll cells are loosely arranged and rounder with large air spaces between them
- this allows for gaseous exchange by diffusion between the cells.
What are vascular bundles or veins?
- The vascular bundles are made upof xylem and phloem.
- Xylem is made up of tiny tubes called xylem vessels which transports inorganic substances.
- Phloem is made up of phloem sieve tubes and companion cells.
Describe the stomata and its fuctions.
- Stomata are found in the lower epidermis between the cells.
- These are small pores with two guard cells on either side of the opening.
- they control the opening and closing of a stoma.
- the stomata allow gaseous exchange where carbon dioxide and oxygen can diffuse in or out of the leaf.
- allows transpiration to take place.
- guard cells contain few chloroplasts so some photosynthesis can take place her.
Study diagram on page 177
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Discuss the ways in which the structure of a leaf has adapted to carry out photosynthesis.
- Very large suface area for maximum amount of light.
- thin to allow light to penetrate.
- thin to reduce distance of diffusion.
- supported by a stem and petiole to expose as much of it as possible.
Describe how the upper and lower epidermis layers are adapted to support photosynthesis
- Tranparent to allow light to pass to the mesophyll layer
Describe how the palisade mesophyll layer in a leaf is adapted to carry out photosynthesis
- Closely packed cells to absorb more light
- Cells are near the surface of the leaf to maximise light interception
- Cells are arranged at right angles to the leaf surface to reduce the number of cell walls light needs to travel through
- Cells have large numbers of choloroplasts to maximise light absorbtion
Describe how the spongy mesophyll layer is adapted to carry out photosynthesis
- Cells are round and loosely arranged to have air spaces, which act as reservoirs for gases and assist in gaseous exchange
- Mesophyll cells in general have large vacuoles to push chloroplasts to the edge of the cell
- Mesophyll cells in general have thin cell walls for a short diffusion pathway
Describe how chloroplasts are adapted to carry out photosynthesis
- Can move within the mesophyll to the light
- Can move away from intense light to avoid damage
Describe how stomata are adapted to assist in photosynthesis
- Holes in the lower epidermis for gases to enter and leave during gaseous exchange
Describe how xylem and phloem assist in the process of photosynthesis
- Xylem is present for the transport of water to chloroplasts in the mesophyll cells
- Phloem for translocation of the products of photosynthesis away from the leaf
Name the steps in carrying out starch tests on leaves
Take a green leaf which was exposed to sunlight for a few hours (where glucose was produced and changed into starch for storage)
- Boil the leaf until flabby (to destroy cell walls, membranes, cytoplasm and enzymes for iodine penetration
- Place the leaf in a test tube with ethanol and then in a beaker with boiling water until the leaf is decolourised (for chlorophyll to be dissolved and extracted)
- Rinse the leaf in hot water (to soften it which is hardened by alcohol)
- Spread the leaf in a shallow petri dish or on a white tile and cover it with yellow-brown iodine solution for a few minutes
If the leaf turns blue-black, starch is present
Describe how starch would be removed from a plant
- Place potted plant in dark cupboard for 48 hours
- This will ensure that no starch will be formed in the leaves during that period
- Any starch already present will be converted to glucose to be transported out of the leaves
- When the leaf is now tested no starch will be present
- The plant is now said to be destarched
Describe how one would show that light is essential for photosynthesis
- Destarch a potted geranium plant
- Select one leaf at the top of a leafy shoot, but do not remove it
- Wrap a strip of aluminium foil around this leaf and make sure it can not receive any light
- Expose the plant to sunlight for 4-6 hours
- Remove the leaf and the foil and test the leaf for starch
- The exposed parts will turn blue-black
- The covered portion will stain brown
- Starch did therefore not form when light was not received, and light is necessary for starch formation and thus for photosynthesis