photosynthesis

Question 1

photosynthesis definition and purpose

Answer 1

PS: is the process of converting light energy to chemical energy stored in glucose
Purpose: produce usable chemical energy in the form of glucose from light energy

Question 2

photosynthesis equation

Answer 2

light
6CO2 + 6H2O → C6H12O6 + 6O2 + 6H20
chlorophyll

Question 3

chloroplast in relation to PS and where it is found

Answer 3

the location of photosynthesis, cytosol of the cell

Question 4

chloroplasts key components

DRAW DIAGRAM

Answer 4

Grana (stacks of thylakoid discs)

Stroma (fluid between the chloroplast/grana)

Outer/inner membrane

Inter membrane (space between membrane)

Ribosome

Chloroplast DNA

Question 5

which is loaded and unloaded; ATP and ADP + Pi

function?

say in full sentences

Answer 5

loaded: ATP

unloaded: AD + Pi

function: transfers energy

Question 6

which is loaded and unloaded; NADH and NAD+

function?

say in full sentences

Answer 6

loaded: NADH

unloaded: NAD+

function: transfer of electrons and hydrogen ions (protons)

Question 7

which is loaded and unloaded;

NADPH and NADP+

function?

say in full sentences

Answer 7

loaded: NADPH

unloaded: NADP+

function: transfer of electrons and hydrogen ions (protons)

Question 8

which is loaded and unloaded;

FADH2 and FAD

function?

say in full sentences

Answer 8

loaded: FADH2

unloaded: FAD

function: transfer of electrons and hydrogen ions (protons)

Question 9

light dependent reaction; what and where?

Answer 9

what: plants are dependent on light to split water into oxygen and hydrogen.

where: thylakoid membrane of chloroplast

Question 10

light dependent inputs

Answer 10

12 water molecules
12 NADP+
18 ADP + Pi

Question 11

light dependent outputs

Answer 11

6 oxygen molecules
12 NADPH
18 ATP

Question 12

light dependent stage process

DOUBLE CHECK AFTER MS DOIG ANSWERS

Answer 12

1. Light energy hitting the chlorophyll molecules embedded in the grana causes water molecules to split into oxygen, electrons and hydrogen ions. (Water donates electrons to chlorophyll to replace the electrons that leave [as they’re excited because of light hitting] which causes water to split into oxygen and two H+. This process is known as photolysis.)
2. Oxygen leaves the chloroplast (will either diffuse in stomata or be an input in aerobic cellular respiration)
3. The hydrogen ions and electrons (from water molecules) are collected by NADP+ forming NADPH which moves on to the second stage in the stroma of the chloroplast.
4. The movement of H+ (hydrogen ions and electrons) down its concentration gradient (maintained by energy from excited electrons in step 1) generates the high energy coenzyme ATP from ADP + Pi
5. ATP and NADPH coenzymes then move on to the light-independent stage.

Question 13

light independent reaction; what and where?

Answer 13

Glucose is produced from carbon dioxide, NADPH, and ATP through a cycle of reactions

Stroma of chloroplasts

Question 14

light independent inputs

Answer 14

6 carbon dioxide molecules
12 NADPH
18 ATP

Question 15

light independent outputs

Answer 15

Glucose
Water molecules
12 NADP+
18 ADP + Pi

Question 16

light independent process

Answer 16

1. CO2 molecules enter the Calvin cycle and undergo initial reactions. During this, carbon from CO₂ combines with a 5carbon molecule then splits into 2, 3carbon molecules.
2. NADPH molecules (from light-dependent) donate their hydrogen ions and electrons (from split water,)(the NADPH molecules are not NADP+) and ATP molecules break into ADP + Pi to release energy to make further changes faster/easier to the carbon molecules.
3. Carbon molecules continue to change and rearrange as they move around the cycle. Eventually, one specific three-carbon molecule is created and leaves the cycle, going on to to form glucose.
4. Overall, six CO₂ molecules must enter the cycle to produce glucose (carbon dioxide = one carbon; glucose = six carbons).
   Energy for this reaction to occur is supplied by ATP (from the first stage.)
5. Some of the oxygen molecules leftover from the breaking of CO₂ at the beginning of the cycle combine with hydrogen ions from NADPH to create the output water.
6. (A number of other molecules in the cycle (including the key enzyme RuBisCO) assist in the reaction.)

Question 17

chlorophyll

Answer 17

A green pigment located in the grana which absorbs and traps light energy.

Question 18

chlorophyll relating to light?

Answer 18

Chlorophyll absorbs/reflects different wavelengths of light. It is therefore more or less efficient depending on the colour of light.

Absorbs blue/purple, and red most.

Absorbs green least

Most plants reflect green

Question 19

factors affecting rate of photosynthesis

Answer 19

light, light colour, co2 conc, water, enzyme inhibition, temp, pH

Question 20

light in relation to rate of photosynthesis. which type of plants are more/less affected?

AND DRAW DIAGRAM

Answer 20

Light is required for the light-dependent stage of photosynthesis to occur.

Without it, the reaction rate is limited.

As light increases, the photosynthesis rate increases – until a saturation point is reached

The increase in the rate of photosynthesis towards point X is because the plant is exposed to greater light energy, which can energise the chlorophyll within many more plant cells, thus increasing overall photosynthesis.
After X, the rate on the graph plateaus

photosynthesis is still occurring at a high rate after point x, just no longer increasing

affect all type plants the same

Question 21

causes for plateau in rate of ps in light

Answer 21

1. Reached the maximum possible rate of photosynthesis, assuming the other factors of photosynthesis are unlimited.

Maximum possible rate cannot increase as the enzymes within chloroplasts are operating at their full capacity. In this case, it is known as a light-saturation curve, as the plant is saturated with light, and point X is known as the saturation point

2. One of the other inputs or requirements for photosynthesis is limiting the rate

Question 22

light colour in relation to rate of photosynthesis

Answer 22

The wavelength (and therefore colour,) also impacts this process

the greatest rate of photosynthesis occurs when a plant is exposed to violet or red light

the rate of photosynthesis is relatively low under green light

Question 23

CO2 conc. in relation to rate of photosynthesis. which type of plants are more/less affected?

DRAW DIAGRAM

Answer 23

Carbon dioxide is an input in PS

The initial increase is due to chloroplasts having a higher concentration of CO₂ molecules for the light-independent stage.

The rate of photosynthesis increases as CO₂ concentration increases, but only up until point X where it starts to plateau.

As carbon dioxide concentration increases, the rate of photosynthesis increases, up until a certain point.

Plants need CO₂ to photosynthesis.

If CO2 levels decreases, stomata opens, plants take in CO₂ from the atmosphere via open stomata on their leaves.
If stomata are closed or there are low CO₂ levels in the atmosphere, however, CO₂ may limit the rate of photosynthesis.

C4 and CAM are less affected by CO2 conc than C3

Question 24

causes for plateau in rate of ps in CO2 conc.

Answer 24

1. The theoretical maximum rate of photosynthesis can be reached with increasing CO₂, (assuming light and water are unlimited and temperature is optimal.) This is because the enzyme-catalysed systems within the chloroplast are fully saturated and operating as fast as possible.
2. Limiting Factor
   Low CO₂ levels make it more likely that O₂ is bound and photorespiration occurs, thus removing an opportunity for photosynthesis and decreasing the overall photosynthetic rate. As such, low CO₂ concentrations can be debilitating to plants

Question 25

water in relation to rate of ps. which type of plants are more/less affected?

Answer 25

Water 💧
Water can also influence the rate of photosynthesis as it is an input in the light dependent stage of photosynthesis and influences the opening and closing of stomata

Less Water
1. Plants close their stomata to conserve water → this also limits the gaseous exchange of CO₂ and O₂with the environment
2. CO2 can no longer (enter the leaves through open stomata and) be an input of the light-independent stage
3. O2 produced in the light-dependent stage can no longer be released.
4. When stomata closed, O₂ is most likely more abundant than CO₂,
5. Rubisco is more likely to bindO₂and initiate the wasteful photorespiration pathway, rather than photosynthesis.
6. Plant wastes energy and loses an opportunity to photosynthesise, which decreases the overall rate of photosynthesis

C4 AND CAM NOT AFFECTED UNLESS EXTREME WATER CONDITIONS

Question 26

temperature in relation to rate of ps

DRAW DIAGRAM

Answer 26

Photosynthesis is an enzyme controlled reaction (such as rubisco). Therefore factors which affect enzyme rate will also affect photosynthesis.

• rate of PS greatest at optimal temp
• higher than optimal temp = enzymes denature, lowering rate of PS
• lower than optimal temp = less frequent enzyme-substrate collisions within chloroplast, lower rate of PS

Question 27

pH in relation to rate of PS

DRAW DIAGRAM

Answer 27

Similarly, enzymes function best at their optimal pH → greatest rate of photosynthesis

Above and below the optimal pH, enzymes denature.

Question 28

enzyme inhibition in relation to rate of PS

DRAW DIAGARAM

Answer 28

Competitive inhibitors,
Bind to the active sites of enzymes to prevent the catalysis of substrates.
Reversible

Non-competitive inhibitors
Bind to an allosteric site of an enzyme
Causes a conformational change to the active site meaning the substrate can no longer bind
Irreversible

The effect of competitive reversible inhibitors can be gradually overcome if the substrate concentration is continually increased.

increasing substrate concentration does not reduce the effect of irreversible inhibitors or reversible noncompetitive inhibitors.

This means that the maximum possible rate of reaction is reduced in the presence of irreversible inhibitors or reversible non-competitive inhibitors.

Question 29

CRISPR-Cas9 in PS

Answer 29

improve photosynthetic efficiencies and crop yields

Question 30

why do we need to improve photosynthetic efficiencies and crop yields?

Answer 30

Most crops, such as wheat, rice, fruit and vegetables are C3 plants, leaving them susceptible to photorespiration (especially in drier/hotter conditions).

World population growing – increased food demands.

Question 31

How can CRISPR-Cas9 help in improving photosynthesis efficiency and crop yields?

Answer 31

*CRISPR may be used to improve the efficiency of rubisco and reduce photorespiration by making C3 plants more like C4/CAM plants

*CRISPR-Cas9 to engineer crops that bypass photorespiration, somewhat mimicking the function of C4 and CAM plants.

*Editing crop genomes could enable farmers to maximise crop productivity without clearing any additional land.
*Increase plant resistance to infection
*Improve shelf life of fruits/vegetables