Biology- Photosynthesis

Question 1

What is the word equation for photosynthesis?

Answer 1

Carbon dioxide + water —–> Glucose + Oxygen

Question 2

Define Photosynthetic pigments

Answer 2

Pigments in a chloroplast or membrane of bacteria which absorb light energy for photosynthesis.

Question 3

Define Photolysis

Answer 3

Using light energy to split something.

Eg. Photolysis of water

Question 4

Define Photophosphorylation

Answer 4

Using light energy to make ATP form ADP and Pi

Question 5

Define Photoionisation

Answer 5

Chloroplasts absorb light energy via the photosynthetic pigments (eg chlorophyll) where 2 electrons get excited by photons and leave the chlorophyll molecule (photoionisation) and the chlorophyll molecule is oxidised

Question 6

Where does the light dependent reaction take place?

Answer 6

Takes place in the Thylakoid membrane

Within Photosystems PSI and PSII

Question 7

What are the steps in the light dependent reaction?

Answer 7

1) Photons from light energy are absorbed by the photosynthetic pigments in the photo-systems of chlorophyll molecules. Here photoionisation takes place and excited electrons leave the chlorophyll molecule to bind to an electron acceptor. The photolysis of water replaces the excited electrons.
2) The electron acceptor gets reduced by the excited electrons and the electrons are passed down the electron transport chains (cytochromes) through a series of redox reactions. The redox reactions make ATP (photophosphorylation)
3) PSI photoionisation occurs and the excited electrons reduce another electron acceptor.
4) The redox reactions through electron transport chain proteins such as ferradoxin produce Reduced NADP (NADP + H+ from photolysis) and ATP and oxygen (a wast product).

Question 8

What are the types of the light dependent reaction and their products?

Answer 8

• Non cyclic photophosporylation:
  Makes Reduced NAPD, ATP and Oxygen(waste product and inhibitor)
• Cyclic photophosphorylation:
  Makes ATP Only
  only involved photosystem 1

Question 9

What are the stages in the light independent reaction / Calvin Cycle?

Answer 9

Carbon Fixation:

• Rubisco fixes Ribulose (RuBP) to CO2 to make a 6 carbon molecule (very unstable)
• 6 Carbon molecule breaks apart into 2 molecules of 3-phosphoglycerate ( 3-PGA A 3 carbon molecule)

Reduction:

• ATP is hydrolised releasing energy
• NADPH is oxidised to provide H+ ions to reduce 3-PGA into G3P (glyceraldehyde 3 phosphate)

Regeneration:
- Using energy from the hydrolysis of ATP, G3P + ATP are used to make RuBP and the cycle restarts.

Question 10

How are carbohydrates formed from the light independent reaction?

Answer 10

Once G3P is produced some may be used and made into carbohydrates (eg glucose)
which is used by the plant for various needs.

Question 11

What is the structure of chlorophyll?

Answer 11

• Contains a porphorin ring (carbon, nitrogen and oxygen) in a 20 sided ring.
• Mg (magnesium atom) centre
• Hydrocarbon tail is anchored into the thylakoid membrane
• The ring structure contains delocalised electrons that absorb light energy to begin the light dependent reaction for photosynthesis.

Question 12

Where does the light dependent reaction take place?

Answer 12

In the thylakoid membrane of the chloroplast. Takes place between photosystems I and II.

Question 13

Where does the light independent reaction take place?

Answer 13

Within the stroma

Question 14

What was Calvins “lollipop” experiment?

Answer 14

Experiment was done to figure out the photosythesis metabolic pathway.

Question 15

In Calvins lollipop experiment why was C^14 (radioactive carbon) used?

Answer 15

Used for identification on an x-ray film jto work out the products made and in what order during the metabolic pathway.

Question 16

In Calvins lollipop experiment why was hot methanol used?

Answer 16

Denatures enzymes of algae preventing chemical reactions from taking place further.

Question 17

In Calvins lollipop experiment why was two way chromatography used?

Answer 17

To separate the pigments after the first chromatograph for more detail. (the compounds get separated)

Question 18

In Calvins lollipop experiment why was algae used?

Answer 18

Algae is used because…

• Photosynthetic
• short germination period
• Large supply

Question 19

What are the main limiting factors of photosynthesis?

Answer 19

• CO2 concentration
• Temperature
• Light intensity
• pH
• Rubisco (enzyme/substrate conc)

Oxygen is an inhibitor of photosynthesis.

Question 20

How does light intensity affect the rate of photosynthesis?

Answer 20

As light intensity increases so does the rate of photosynthesis as more photons are being absorbed by photosynthetic pigments. Once the maximum number of photons are being absorbed at a time, the light intensity begins to plateau as this is now not the limiting factor.

Question 21

How does CO2 concentration affect the rate of photosynthesis?

Answer 21

As the CO2 concentration increases so does the rate of photosynthesis as their is more CO2 available to be used in photosynthesis. However eventually the CO2 concentration will reach a point where any additional CO2 will have no effect in the rate and therefore the graph begins to plateau as the CO2 concentration is no longer the limiting factor.

Question 22

How does temperature affect the rate of photosynthesis?

Answer 22

As the temperature increases so does the rate of photosynthesis as enzymes have increased kinetic energy and therefore there are more successful collisions forming enzyme substrate complexes (ESC’s). As the temperature is higher the rate of CO2 diffusion increases so this is less likely to be the limiting factor.
Once past optimum temperature enzymes begin to denature so the active sites are not complimentary to the substrates as bonds between R-groups (hydrogen bonds) break so the tertiary structure is changed.

Question 23

How does pH affect the rate of photosynthesis?

Answer 23

Below and above optimum pH enzymes are denatured so the active site is not complimentary to the substrates since Ionic bonds between the R-groups are broken and the tertiary structure is changed.
At optimum pH the enzymes work efficiently and bind with substrates forming enzyme substrate complexes which increase the rate of photosynthesis.

Question 24

How does enzyme/substrate concentration affect the rate of photosynthesis?

Answer 24

As E/S concentration increase the rate of photosynthesis increase as more E/S can bind together forming ESC’s. As E?S reach a point where they are not equal in amounts the rate of photosynthesis begins to plateau as the enzymes or substrates stop being the limiting factor, and the other either E/S concentration becomes the limiting factor.

Question 25

What affect does oxygen have on the rate of photosynthesis?

Answer 25

Oxygen inhibits the rate of photosynthesis as oxygen increase the rate of photosynthesis decreases due to O2 being a competitive inhibitor. This means that and increased Oxygen concentration could bind to more enzymes in place of substrates preventing ESC’s from forming so photosynthesis cannot happen hence the rate decreases.

Question 26

Define limiting factor.

Answer 26

The rate of a physiological process will be limited by the factor which is in shortest supply. Any change to the level of a limiting factor will affect the rate of reaction.

Question 27

What is the chemiosmotic theory?

Answer 27

The mechanism by which ATP is produced during the light dependent stage of photosynthesis.

Question 28

What are the steps in producing ATP during photosynthesis? (chemiosmotic theory)

Answer 28

• H+ ions are pumped into the thylakoid chambers from stroma using protein carriers (protein pumps)
• Energy comes from electron release in photolysis and this increases the H+ concentration in the thylakoid membrane.
• This creates a concentration gradient of H+ (Protons) across the thylakoid membrane. There is a lower concentration in the stroma than within the thylakoid space.
• Protons only pass through ATPsynthase channel proteins.
• Protons cause enzyme to catalyse APD + Pi to for ATP.