Photosynthesis

Question 1

Oxidation is…

_____ of oxygen
_____ of hydrogen
_____ of electrons

Answer 1

gain
loss
loss

Question 2

Reduction is…

_____ of oxygen
_____ of hydrogen
_____ of electrons

Answer 2

loss
gain
gain

Question 3

Explain the light dependent reaction and where it takes place

Answer 3

inside of the thylakoid disks

• Light energy excites electrons in the chlorophyll causing them to move to the electron transport chain
• These electrons are passed along the chain, losing energy as they travel
• The electrons need to be replaced in the chlorophyll molecule. To do this light energy is used to split a water molecule
• Water is split into H and O. H is then further split into H+ and electrons (photolysis of water)
• The electrons from the water replace the electrons in the chlorophyll. The energy given off by travelling electrons are used to move H+ across the membrane
• This sets up a conc gradient with the H+ which then move down through facilitated diffusion via ATP synthase
• This activates ATP synthase which converts ADP + Pi –> ATP
• The H+ which was transported by ATP synthase and the electrons which reach the end of the ETC are collected by NADP which becomes NADPH

Question 4

Explain the light independent reaction (Calvin cycle) and where it takes place

Answer 4

Takes place in the stroma

• CO2 reacts with RuBP(5C) with the help of enzyme rubisco
• An unstable 6C compound is formed
• This quickly breaks down into 2 molecules of glycerate-3-phosphate (GP)
• Energy from ATP allows reduced NADP to react with GP
• The GP is reduced to form TP and the NADP is reformed to be used again
• Most TP molecules are used to regenerate RuBP with the help of ATP allowing the cycle to continue
• The remaining TP is converted into organic substances such as starch, amino acids, glucose etc

Question 5

Explain the limiting factor of photosynthesis - carbon dioxide

Answer 5

The graph begins to increase until it reaches a certain point where it plateaus. It is directly proportional up until this point. This is because another factor has become a limiting factor. This means that the rate of reaction will no longer increase. CO2 is needed to react with RuBP in the Calvin cycle so without it, photosynthesis can no longer continue

Question 6

Explain the limiting factor of photosynthesis - light intensity

Answer 6

This graph begins to increase until it reaches a certain point where it plateaus. It is directly proportional until this point. This is because another factor has become limiting. This means that the rate if reaction will no longer increase. Light is needed for photolysis and photoionisation so photosynthesis cannot take place without it

Question 7

Explain the limiting factor of photosynthesis - temperature

Answer 7

The graph slowly increases as it gains more kinetic energy. This allows the rate of reaction to increase. It will then reach the optimum temperature where after this it will begin to denature the enzyme. This is where the active site changes shape as the tertiary structure if the protein also changes. This will then decrease the rate of reaction until it eventually stops

Question 8

Define the light compensation point

Answer 8

The point where photosynthesis exceeds the rate of respiration

which means oxygen is being used as quickly as it is produced

Question 9

Define the chemiosmotic theory

Answer 9

The process of electrons flowing down the ETC and creating a proton gradient across the membrane to drive ATP synthesis is called chemiosmosis

Question 10

How do farmers increase plant growth?

Answer 10

Create optimum conditions in glasshouses

LF - CO2 = CO2 is added to the air

LF - light = light can get in through glass, lamps provide light at night time

LF - temperature = glasshouses trap heat from sunlight, heaters and cooling systems can also be used to keep a constant optimum temperature

Question 11

Revise practicals from RG or exercise book