Photosynthesis

Question 1

What is the photosynthesis equation

Answer 1

6CO2 + 6H2O —-> C6H12O6 + 6O2

Light + plant

Question 2

Where is the site of photosynthesis

Answer 2

Chloroplast

Question 3

Outline the structure of the chloroplasts

Answer 3

Has 3 membranes - outer, inner, thylakoid
Has 3 compartments - intermembrane space, stroma, thylakoid space

Question 4

Where do the light reactions and carbon fixation occur

Answer 4

Light reactions take place on the thylakoid membrane
Carbon fixation occurs in the stroma

Question 5

What is the light reaction phase

Answer 5

It captures light energy and converts it to chemical energy using pigment and protein complexes embedded in the thylakoid membrane

Question 6

Elaborate on how photosystems capture light energy

Answer 6

Photosystems are protein complexes that contain the chlorophyll molecule
Chlorophyll absorbs light energy
Light energy absorbed by chlorophyll produces high energy electrons (from water)
High energy electrons then travel through the photosynthetic electron transport chain

Question 7

Outline the process of the electron transport chain

Answer 7

Photosystems 2 hydrolyses water, spitting it into 1/2 O2 and 2H+. 2 free high energy electrons are produced
2 high energy electrons power cytochrome complex in electron transport chain, active transport of H+ into the thylakoid space
Photosystems 1 uses light energy to reenergise electrons
High energy electrons are then used in the reduction reaction where NADP+ is reduced to NADPH (NADP+ reductase)
Flow of H+ from high to low conc (thylakoid space to stroma) through ATP synthase powers phosphorylation of APD + Pi into ATP

Question 8

What occurs in the light reaction

Answer 8

Water is split. O2 is produced. ATP and NADPH are produced

Question 9

What is the relation between the light reactions and the Calvin cycle

Answer 9

The ATP and NADPH produced in the light reactions are used to fix low energy CO2 and produce high energy sugar molecules

Question 10

What are the 3 steps to the Calvin cycle

Answer 10

Fixation, Reduction, and Regeneration

Question 11

Where does the Calvin cycle occur

Answer 11

In the stroma

Question 12

What is fixation

Answer 12

5 carbon molecule + CO2 —> 2 x 3 carbon low energy molecules
Occurs 3 times. Totalling 6 x 3 carbon low energy molecules

Question 13

What is reduction

Answer 13

The low energy 3 carbon molecules are converted into high energy 3 carbon molecules using 6 ATP and 6NADPH
Yields 6 x 3 carbon high energy molecules
One high energy carbon molecule is taken out, and further used to produce glucose (high energy 6 carbon sugar)

Question 14

What is regeneration

Answer 14

Converting the remaining 3 carbon molecules back into original 5 carbon molecule
Uses 3ATP

Question 15

What is the output of the Calvin cycle, and how many CO2 must it fix to produce glucose

Answer 15

Output is a high energy 3 carbon sugar which goes on to make high energy 6 carbon glucose
Must fix 6 CO2 molecules to produce one glucose molecule

Question 16

Outline the similarities and differences between the glucose energy supply in plants and animals

Answer 16

Both plants and animals breakdown glucose in cellular respiration to generate ATP
Animals must have an external source of glucoses, whereas plants produce glucose during photosynthesis

Question 17

Outline the similarities and differences between the ATP energy supply of plants and animals

Answer 17

ATP is generated in both respiration and photosynthesis
ATP synthase is responsible for ATP phosphorylation in both processes
ATP synthase requires proton gradient across membrane in both chloroplast and mitochondrion

Question 18

Outline the H+ concentration gradients in both chloroplasts and mitochondrion

Answer 18

In mitochondrion, H+ pumped from matrix into inter membrane space. H+ then diffuses through ATP Synthase, powering the phosphorylation of ATP.
In chloroplast, H+ pumped from stroma into into thylakoid space. H+ then diffuses through ATP Synthase, powering phosphorylation of ATP.

Question 19

Outline the symbiotic theory

Answer 19

Explains how eukaryotic cells evolved from prokaryotic cells.
Mitochondria and chloroplasts are descendants of specialised bacteria that somehow survived endocytosis by another species of prokaryote or some other cell type, and became incorporated into the cytoplasm (instead of digested by the cell).
Ancestral prokaryote ingested aerobic bacterium, then photosynthetic bacterium.
Most likely mitochondria engulfed first as almost all eukaryote cells have mitochondria, and chloroplasts would be largely useless without mitochondria (chloroplasts produce glucose for cellular respiration in mitochondria)