Task One
- State the function of photosystem II, photosystem I and the calvin cycle in the production of glucose and sucrose.
- Photosynthesis is a two step process with light dependent and independent reactions. Light dependent reactions convert light energy to chemical energy and light independent reactions use the chemical energy to make organic molecules.
- Light dependent reactions occur on thylakoid membrane and may occur via cyclic or non-cyclic processes; both processes include light exciting chlorophyll leading to release of electrons that pass through an electron transport chain, creating ATP (photophosphorylation)
- Non-Cyclic: Chlorophyll in photosystems 1 and 2 absorbs light, leading to photoactivation: a release of high energy electrons. Electrons from photosystem 2 go through ETC, producing ATP via chemiosmosis. Electrons from photosystem 1 reduce NADP+ to NADPH + H+. Electrons from photosystem 2 replace those lost in photosystem 1, electrons lost in photosystem 2 replaced by electrons generated from photolysis of water. Oxygen is by-product.
- Cyclic (only photosystem 1 involved): High energy electrons released by photoactivation pass through ETC (producing ATP) and then return to photosystem 1. Electrons in cyclic photophosphorylation do not produce NADPH + H+, which is required for light independent reactions. Thus, though cyclic phosphorylation constantly creates ATP, the chemical energy cannot be used to create organic molecules.
- Light independent reactions occur in the stroma and uses the ATP and NADPH + H+ from non-cyclic photophosphorylation. It is also known as the Calvin cycle and has three main steps:
- Carbon Fixation:
Enzyme rubisco (RuBP carboxylase) catalyzes attachment of carbon dioxide to 5-carbon compound ribulose bisphosphate (RuBP). The new 6-carbon compound breaks down to two 3-carbon molecules: glycerinate-3-phosphate (G3P)
- Reduction:
Each G3P molecule is phosphorylated by ATP and reduced by NADPH + H+, converting them to glyceraldehyde phosphate, a trios phosphate (TP)
- Regeneration of RuBP:
For every 6 TP, only one can be used to create half a sugar molecule. The other 5 TP molecules are reorganized to regenerate RuBP (using ATP). The cycle repeats multiple times to construct chains of sugars (sucrose)
- Draw the molecular structures of glucose, fructose and sucrose.
- Distinguish between the structure and function of the three polysaccharides of glucose.
- glycogen- multiple branches, animal storage of glucose
- cellulose- branched and unbranched varieties, main structural component of plants
- starch- branched, plant storage glucose
- Compare the leaf and root structure and vascular tissue organization in stem and roots of monocotyledonous and dicotyledonous plants. [State which sugar cane is.]
- Leaves: Monocots have parallel veins from stem to tip; dicots have branching veins
- Root structure: Monocots do not have main roots but have smaller roots that branch out; dicots have main roots that grow downwards
- Vascular tissue organization: Monocots have vascular bundles spread across the stem, with bundles closer to the sides of the stem rather than the center; dicots have vascular bundles circular
Task Two
- State the meaning of 'allocation of photo-assimilates'.
- The allocation/grouping of a certain amount of compounds formed through assimilation in light dependent reactions (monosaccharides) from a plants leaves to its sinks
- Explain what the author means by the phrase 'heterotrophic sinks'.
- The areas of a plant in which sucrose is stored: fruits, roots, etc.
- Describe the structure and function of a plasmodesmata between the mesophyll and parenchyma cells.
- Plasmodesmata are microscopic communication bridges between the cell walls of two plant cells; they facilitate the movement of sucrose from mesophyll cells to parenchyma cells
- Hypothesize the effect of a pH or temperature change on plasmodesmata structure and function. [Hypotheses must include a why!]
- A change in pH or temperature would denature proteins that make up the plasmodesmata, which would probably prevent it from functioning efficiently
- Distinguish the structure and function of xylem and phloem.
- Xylem vs. Phloem:
- Structure: Non-living vs living; thin walled sieve tubes w/ pores at ends vs tubes with no cross walls
- Function: Transports nutrients from leaves to sinks/growing parts vs water/minerals from roots to aerial parts (leaves)
Task Three
- Distinguish between, in your own words, the apoplastic route and symplastic route of ion movement in plants.
- Apoplastic route: through the cell wall
- Symplastic route: through the cytoplasm (via plasmodesmata)
- Draw the pathway of sucrose from mesophyll cell [site of production], to the SE/CC.
- Draw and annotate a diagram to describe the pressure flow model of water and sugar transport in xylem and phloem. [direction and substance are a must!] [you may add onto the previous drawing if you like].
- Annotate your drawing to distinguish between the different transport mechanisms [diffusion, osmosis, facilitative diffusion, primary active transport, secondary active transport ex. SUT1 ] that occurs in the xylem/phloem pressure flow model of sucrose and water transport.
