photosynthesis

Question 1

What is photosynthesis?

Answer 1

Photosynthesis is the process of photoautotrophs converting light energy into chemical energy/glucose.

Question 2

What is the equation for photosynthesis/inputs and outputs?

Answer 2

Inputs: Carbon dioxide+water
Outputs: Glucose+oxygen+water
Equation: 6CO2+12H2O–(sunlight)–> C6H12O6+6O2+6H2O

Question 3

What two key parts of the C3 plant play a role in photosynthesis?

Answer 3

Leaf→ Leaves have cells called mesophyll cells which contain chloroplast which contain chlorophyll which is essential for initiating photosynthesis.
Stomata→ The stomata opens during the day to allow CO2 ( an input of photosynthesis ) into the leaf. However at night they close to preserve water.

Question 4

What are the inputs and outputs of the light dependent stage of photosynthesis?

Answer 4

Inputs: 12H2O + 12 NADP+ + 18 ADP+Pi
Outputs: 6O2 + 12 NADPH and 18ATP

Question 5

Explain the process of the light dependent stage

Answer 5

1. Sunlight excites electrons
2. Water splits into O2 and H+, donating an electron to chlorophyll
3. The excited electron and H+ ion produce NADPH and ATP
4. Oxygen releases the NADPH and ATP, ready for the next stage.

Question 6

Where does the light dependent stage occur?

Answer 6

In the thylakoid.

Question 7

What are the inputs and outputs of the light independent stage?

Answer 7

Inputs: 6CO2+12 NADPH+18 ATP
Outputs: C6H12O6+12 NADP+ + 18 ADP + Pi + 6H2O

Question 8

Where does the light independent stage occur?

Answer 8

stroma

Question 9

What is the process of the light independent stage

Answer 9

1. CO2 from stroma enters the cycle
2. Carbon reacts producing carbon based molecules
3. Glucose and water form which can then be used for cellular respiration.

Question 10

What is rubisco and why can it be an issue?

Answer 10

An enzyme in the light independent stage that the majority of the time bonds to CO2. However sometimes it binds to O2, which is a PROBLEM because that initiates photorespiration, which is very energy expensive.
So a higher oxygen concentration and a lower CO2 concentration= more photorespiration
And a lower oxygen concentration and a higher CO2 concentration= less photorespiration
Occurs more often in hot/dry conditions due to the decreased amount of CO2 being dissolved as the stomata closes to preserve water, meaning no gas exchange occurs.
All of this occurs in the light independent stage in the stroma as C3 plants try to produce glucose.

Question 11

What are the two key factors that influence rubisco

Answer 11

Substrate concentration
When stomata is open, CO2 can enter the plant, increasing its concentration, and increasing the likelihood that Rubisco will bind to CO2.
When stomata is closed, there is no gas exchange, increasing the concentration of O2 as opposed to CO2, meaning that the chances of Rubisco bonding to the active site of oxygen increases.

Temperature
At a regular temperature, Rubisco’s affinity for CO2 is higher. However in warmer temperatures, affinity for O2 increases, meaning Rubisco is more likely to bond to O2.

Question 12

C3 plants and adaptations

Answer 12

C3 ( three carbon 3-PGA ) 90% of plants lose advantage in hot dry because of photorespiration.
Trees
Fruits
Vegetables
C3 plants have no features for fighting photorespiration.

Question 13

C4 plant adaptations

Answer 13

Corn
Sugarcane
Weeds

C4 plants have the same light dependent stage as C3 plants, however their light independent stage is different, with initial carbon fixation occurring in mesophyll cells, and the remaining specialised cells occurring in bundle sheath cells.

Mesophyll cells are constantly pumping CO2 into bundle sheath cells, meaning there is a higher concentration of CO2 for Rubisco than O2. PEP enzyme is in C4 and cam plants fix carbon to malic acid ( temporarily ) so they shift it to bundle sheath cells.

Whilst C4 plants use more energy than C3 plants to prevent photorespiration from happening, it’s still better than actually allowing photorespiration to occur as that is MORE energy expensive. C4 plants are better than C3 plants in hot/dry conditions.

Question 14

CAM plants and their adaptations

Answer 14

Cacti
Pineapple
Orchids
Light dependent stage is the same as C3 and C4 however their light independent stage is different.
At night the stomata opens allowing CO2 to enter, which is stored as four carbon molecules in the vacuoles ( malate ) of mesophyll cells.
During the day the stomata is closed to prevent water loss ( as CAM plants are generally found in hot/dry conditions ), however photosynthesis can still occur and the malate stored can enter the calvin cycle leading to the production of glucose. This allows the concentration of CO2 to be higher than O2.
CAM plants store malic acid to use at night ( PEP enzyme )

Question 15

Factors that affect the rate of photosynthesis

Answer 15

Temperature and pH
Light
CO2
Water

Question 16

How does light affect photosynthesis rate

Answer 16

An increase in light can cause an increase in photosynthesis to a certain point, until it reaches the saturation point, and the rate of photosynthesis plateaus.

Question 17

Temperature and pH, how does it affect the rate of photosynthesis

Answer 17

Enzymes essential for photosynthesis work best at an optimal temperature adapted to the plant’s environment.

C4 and CAM plants prefer hot and dry temperatures, whereas C3 plants prefer cooler temperatures.

Question 18

Carbon dioxide and how does it affect the rate of photosynthesis

Answer 18

A saturation point occurs as CO2 increases, assuming that light and water are unlimited and the temperature is optimal, meaning that the enzyme is fully saturated. An increase in CO2 concentration increases the rate of photosynthesis to a certain point.

Question 19

How does water affect photosynthesis

Answer 19

Influences if the stomata of a plant is open or closed. Prevents water loss but also prevents gas exchange.

Decreased water = closed stomata = lower CO2 = higher O2 = decreased rate of photosynthesis.