Photosynthesis

Question 1

Adaptations of leaf

Answer 1

Large SA
Minimised overlapping
Thin
Transparent cuticle and epidermis
Narrow long upper mesophyll cells
Numerous stomata, short diffusion distance
Stomata open and close depending on light intensity
Many air spaces
Network of xylem and phloem

Question 2

Structure of grana

Answer 2

Stacks of thylakoids that contain chlorophyll.
Some connected by lamallae.
Light dependant
Large SA

Question 3

Structure of stroma

Answer 3

Fluid filled matrix, light ind reaction, contains starch granules

Question 4

Light dependent reaction purpose

Answer 4

To add Pi to ADP to make ATP.

Split water to H+ ions and OH- ions, photolysis

Question 5

Light dependent reaction, chemiosmosis

Answer 5

At photosystem 2, photoionisation of chlorophyll. Electron moves down transfer chain and replaced by electron from water.
Electron powers proton pump, stroma to thylakoid membrane.
Photosystem 1, photoionsation again, electron replaced by electron from transfer chain. From here can return to pump more protons (cyclic phosphorylation) or aid in addition of proton to NADP.
Protons in lumen can also diffuse to stroma and power ATP synthase.

Question 6

How chloroplasts are adapted to capturing sunlight

Answer 6

Thylakoid membrane provide large SA for attachment of chlorophyll. e- carriers and enzymes.
Proteins in grana hold chlorophyll precisely to max absorb.
Granal membranes have ATP synthase channels, selectively permeable to H+.
Chloroplasts have DNA and ribosomes to manufacture proteins involved.

Question 7

Calvin cycle

Answer 7

CO2 combines with RuBP (5C), catalysed by rubisco.
Produces 6C compound that is unstable and breaks down into 2 glycerate 3-phosphate.
Reduced NADP reduces GP to triose phosphate using energy from ATP.
NADP goes back to light dependant.
TP converted to organic substances such as starch, cellulose, proteins.
5/6 TP used to regen RuBP.

Question 8

How chloroplast adapted to light independant

Answer 8

Fluid of stroma contains enzymes needed (membrane bound chloroplast).
Stroma fluid surrounds grana and so products of light dependant can diffuse quickly into stroma from grana.
Contains DNA and ribosomes to make proteins needed.
Starch grains for sugar storage after photosynthesis.

Question 9

Compensation point

Answer 9

Point where there is no net exchange of gases in or out of plant at a specific light intensity (CO2 and O2 absorbed and used same)

Question 10

Photosynthetic pigments

Answer 10

Chlorophyll a, b

Beta carotene, xanthophyll

Question 11

Rf values of pigments

Answer 11

Chlorophyll b: lowest
Carotenoids: close to 1
Chlorophyll a: middle

Question 12

What does Rf value tell you about molecules

Answer 12

Molecules with higher affinity to stationary phase like large molecules have lower Rf value. Therefore larger and less soluble.

Question 13

Main factors for rate of photosynthesis

Answer 13

Light intensity, CO2 conc, temp

Question 14

How does light intensity affect rate of photosynthesis

Answer 14

Greater light intensity = more light energy supplied to plant and faster light dependent stage. More ATP and NADPH for Calvin Cycle produced.

Question 15

How does CO2 conc increase rate of photosynthesis

Answer 15

Required for Calvin Cycle when CO2 is combined with RuBP. More CO2 present = can occur more often.

Question 16

How does temp affect rate of photosynthesis

Answer 16

Photosynthesis is enzyme controlled so it will increase rate until denaturing.
Temp has no effect on light dependent reactions because driven by energy from light rather than kinetic.
Calvin cycle has enzymes such as rubisco therefore is affected by temperature.
However increasing temp causes stomata to close to reduce water loss and affects permeability of thylakoid membrane, proton gradient affected.