Paper 2 - Photosynthesis Flashcards
Properties of ATP
Releases small, manageable amounts of energy — Energy is not wasted as heat
Small and soluble molecule — Can easily diffuse around cell to where it’s needed
Easily hydrolysed — Energy released instantaneously
Quickly re synthesised— Constant supply of energy to the cell
Can phosphorylate other molecules when hydrolysed — Makes other molecules more reactive
Cannot pass out of the cell through membrane — Cell always has immediate supply of energy
Light dependent reaction - photoionisation
- When a chlorophyll in PSII absorbs light energy and electrons become excited
- The electrons leave the chlorophyll molecule = oxidation
- These electrons are taken up by an electron carrier = reduction
Light dependent reaction - Making ATP
- A chain of protein electron carriers in a membrane through which excited electrons flow = electron transport chain
- Electrons lose energy at each stage
- This energy is used to transport protons (H+) into the thylakoid
- Protons diffuse back into the stromatolites via the channel by ATP synthase
- ADP + Pi — ATP
- Light is used for this process = photophosphorylation
- This is known as chemiosmosis
LDR - Making NADPH
- Light energy is absorbed by PSI = excitation of electrons
- Electrons are transferred to NADP (coenzyme) along with H+ from storma = NADPH
- Used in light independent reaction
LDR - Photolysis of water
- Loss of electrons when light strikes a chlorophyll molecule = shortage of electrons
- If chlorophyll continues to absorbs knight energy, electrons must be replaced
- Replacement electrons are provided from H2O molecules that are split using light energy
- Photolysis of H2O = H+ and O2
- Oxygen is either used in respiration or diffused out as a waste product
Non cyclic phosphorylation
Form of LDR which produces both ATP and NADPH and uses both PSI and PSII
Cyclic Phosphorylation
Form of LDR which produces small amounts of ATP, doesn’t produce NADPH and only uses PSI
Light Independent Reaction - The Calvin Cycle
- Occurs in the storma
- CO2 combines with ribulose biphosphate (5C) - catalysed by rubisco enzyme
- CO2 and RuBP produces 2 molecules of glycerate phosphate (3C)
- ATP produced in LDR provides energy to reduce GP to triode phosphate
- Reduced NADP from the LDR is used to reduce GP to TP (provides hydrogen)
- Some TP molecules (1/6) are converted to organic substances e.g. glucose, sucrose and amino acids
- Most TP molecules (5/6) are used to regenerate RuBP, using ATP from the LDR, which supplies the phosphate.
Products of The Calvin Cycle
Explain why the apparatus needs to be airtight
So that they’re not artefacts such as air bubbles, which would increase the volume of gas measured and so, provide an unreliable result
Explain why the temperature of the water bath needs to be kept constant
Soo that it is only the light intensity that is affecting the rate of photosynthesis, not temperature
Suggest an advantage of providing an additional source of CO2
To ensure that there’s sufficient CO2 and O2 and they don’t limit the rate of photosynthesis
Suggest a reason for carrying toy the experiment in a dark room
To prevent other light falling on the plant as thus may fluctuate and will affect the light intensity and so the rate of photosynthesis
Suggest why the plant is kept in the dark before the experiment begins
In order to prevent starch from interfering, we remove the starch by keeping the plant in the dark. When in the dark, the photosynthesis doesn’t occur and the stored starch is sued up
Suggest why measuring the volume of gas produced by the plant in this experiment and may not be an accurate measure of photosynthesis
Gases are often fluid and nice subtle and can come out quickly as bubbles so may be difficult to count
