Photosynthesis

Question 1

Adaptations of plants for photosynthesis?

Answer 1

Leaves have large SA.
Leaves are thin, short diffusion distance.
Transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath.
Palisade cells.
Stomata open and close in response to sunlight.
More:
Xylem, air spaces.

Question 2

Structure of chloroplast?

Answer 2

Site of photosynthesis
Double membrane (outer and inner)
Contains discs called thylakoids (chlorophyll)
Stack of thylakoids = granum
Thylakoids are surrounded by a fluid material called stroma.

Question 3

Why do plants need different pigments?

Answer 3

To increase the range of wavelengths of light energy they absorb, increasing rate of photosynthesis.

Question 4

Describe the Light Dependant Reaction

Answer 4

Photon of light hits chlorophyll, channeled to chlorophyll A.

Photoionisation, electrons become excited and emitted from chlorophyll A.

Electrons enter an electron carrier system, moving down an electron transport chain, through a series of redox reactions, releasing energy along the way, used to pump protons from the stroma into thylakoid space.

Protons accumulate in thylakoid space, then diffuse back into stroma down a chemiosmotic gradient, passing through ATP synthase, photo phosphorylating ADP to make ATP.

Question 5

Whats the difference between non/cyclic photophosphorylation?

Answer 5

In cyclic photophosphorylation:
ATP is produced.
No reduced NADP is produced.
Electrons are continuously recycled.
Photolysis does not take place.

In non-cyclic photophosphorylation:
ATP and reduced NADP are produced.
Electrons in PSII are replaced by photolysis.

Question 6

Calvin cycle

Answer 6

CARBON FIXATION - The Rubisco enzyme (Ribulose bisphosphate carboxylase) catalyses the reaction of RuBP (Ribulose Bisphosphate) with CO2 to produce 2x Glycerate-3-Phosphate (G-3-P).

REDUCTION - NADPH reduces G-3-P into 2x Triose Phosphate (TP) with energy being provided by ATP. NADP is reformed and goes back to the light dependent stages to be reduced again.

REGENERATION - 2 X TP are converted into organic compounds e.g. glucose, cellulose, starch, lipids, amino acids and nucleotides. Most TP is used to regenerate RuBP using ATP for more turns of the Calvin cycle. Regeneration occurs because RuBP is quickly converted into GP, it is present in the Stroma in small concentrations, it therefore needs to be regenerated from TP.