Section 5- Photosynthesis Flashcards
What is photosynthesis?
The biochemical process where plants absorb light energy using chlorophylls.
What are the 2 main reactions that occur in photosynthesis?
The light dependent reaction
The light independent reaction
Where does the light dependent reaction occur?
Occurs across the thylakoid membrane.
What is the grana in a chloroplast?
Stacks of disk like structures called thylakoids
Thylakoids contain chlorophyll
What is the stroma in a chloroplast?
Fluid-like matrix, also contains starch grains.
Where does the light-dependent reaction occur in the chloroplast?
Grana/ Thykaloid
Where does the light-independent reaction occur in the chloroplast?
Stroma
What are the products of the light-dependent reaction?
Reduced NADP
ATP
Oxygen
What are the key steps of non-cyclic photophosphorylation?
Photolysis of water Photoionising PS2 The electron transport chain ATP synthesis Reduction of NADP
What is the photolysis of water in non-cyclic photophosphorylation?
A photon strikes water inside thylakoid
Water splits into 2 electrons, 2 hydrogen ions and oxygen
Oxygen releases as waste products
What is the photoionising of PS2 in non-cyclic photophosphorylation?
Energy from photon of light is transferred to electrons in PS2
Electrons become energised, leave the photosystem and join electron transport chain.
Pigment becomes oxidised.
Electrons replaced by those from photolysis of water.
What is the electron transport chain in non-cyclic photophosphorylation?
Energy from electron pumps hydrogen ion across the membrane into lumen of thylakoid
Once all of energy is used the electron joins PS1.
What is ATP synthesis in non-cyclic photophosphorylation?
Electrochemical gradient of hydrogen ion means that they will move back into the stroma by facilitated diffusion
Movement of hydrogen ion = chemiosmosis
Provides energy for phosphorylation of ADP into ATP by ATP synthase
What is the reduction of NADP in non-cyclic photophosphorylation?
Electrons in PS1 will become excited by light energy and leave the photosystem into the stroma
Electrons & excess hydrogen ions from photolysis of water are collected by oxidised NADP
Makes reduced NADP
What is the Calvin cycle?
CO2 + RuBP catalysed by rubisco- makes 3x Glycerate-3-phosphate.
G3P is reduced to triose phosphate by 1x reduced NADP and 1x ATP.
3 carbon TP is used to recycle RuBP, 5/6 TP converted to RuBP using energy from ATP.
Remaining 1/6 molecules of TP are made into glucose
What other organic compounds are made in the Calvin cycle?
Plants will add nitrate from the soil to glucose to make amino acids
Lipids are made from glycerol (produced from triosephosphate) and fatty acids (produced from glycerate-3-phosphate)
What is the light dependent reaction also known as?
Non-cyclic photophosphorylation
What is the light independent reaction also known as?
The Calvin Cycle
What is cyclic photophosphorylation?
Only involves PS1
When light energy excites electrons in PS1 they leave and join electron transport chain
Energy is used to pump hydrogen ions into thylakoid driving process of chemiosmosis
Energy is used to phosphorylate ADP into ATP
Electrons return to PS1
What is the substance that combines with carbon dioxide in a chloroplast?
Ribulose bisphosphate
How is NADP reduced in the light-dependent reaction of photosynthesis?
Electrons in PS1 become excited by light energy and leave photosystem into stroma.
They’re collected along with excess hydrogen ions from photolysis of water by NADP.
This made reduced NADP
Precisely where within a plant cell are the electron carriers involved in the light-dependent reaction found?
On the thylakoid membranes
of the grana in the chloroplast
What is the role of ribulose bisphosphate in the Calvin cycle?
It combined with carbon dioxide to produce 2 molecules of glycerate-3-phosphate
How is reduced NADP, from the light-dependent reaction, used in the light-independent reaction?
Used to reduce glycerate-3-phosphate to triose phosphate
Apart from reduced NADP, which other product of the light-dependent reaction is used in the light-independent reaction?
ATP
Where in the plant cell is the enzyme that is involved in the Calvin Cycle found?
Stroma of the chloroplasts
What proportion of TP is converted to RuBP?
5/6
How many carbons does RuBP, G3P, TP and glucose have?
RuBP- 5c
G3P- 6c
TP- 3c
Glucose- 6c
What is most of the energy from the sun, fixed into?
Chemical energy by photosynthesis
Why is there no build-up of phosphate ions when they enter chloroplasts?
Used in phosphorylation of ATP in the light-dependent reaction
Catalysed by ATP synthase
Why can only triose phosphate be transported via a specific carrier protein?
Carrier proteins are complementary
Have tertiary structure specific to substrate
What is the role of coenzymes in a leaf cell?
NAD can accept hydrogen to be reduced
Reduced NAD carries electrons to electron transport chain
Coenzyme A carries acetate to Krebs cycle
How would the rate of photosynthesis affect the rate of translocation?
If photosynthesis decreases, the rate of translocation will decrease
Less sucrose will be actively transported into the phloem so less decrease in the water potential
Less water diffuses in by osmosis
Leads to less pressure gradient
What is the purpose of chromatogrpahy?
To separate different components in a sample
What are the factors affecting the rate of migration of different pigments?
Solubility
Mass
Affinity to paper
What is the formula for Rf value?
Distance moved by pigment
/
Distance moved by solvent
What is the procedure to using chromatography to separate photosynthetic pigments?
- Grind leaf sample onto filter paper on pencilled line
- Suspend paper in solvent but just so the bottom is touching
- Once solvent has run up paper, mark pencil line of distance travelled
- Find Rf value for each pigment spot
In chromatography, why is it important to use a pencil line and not pen?
A pen may dissolve in the solvent
Why do chlorophyll contain several different photosynthetic pigments?
So they can absorb energy from a wide range of wavelengths
What is the function of dehydrogenase in chloroplasts?
It catalyses the acceptance of electrons by NADP in the light-dependent reaction
What is the purpose of DCPIP?
Redox indicator that acts as an alternate electron acceptor instead of NADP
Turns blue to colourless when reduced
Why is the chloroplast chilled in an ice-bath?
To lower activity of enzymes to prevent them breaking down the chloroplasts
What is the control in the photosynthesis practical?
Fill capillary tube with chloroplast and distilled water
Why are the stalks of the leaves removed in the photosynthesis practical?
They do not contain any chloroplasts
What is the loose procedure to investigating the effect of different wavelengths of light using DCPIP?
Observe capillary tubes filled with chloroplast extract and DCPIP solution under different colour wavelengths
Time how long it takes solution to match control tube (green)
How is the rate of reaction calculated in the DCPIP practical?
Rate= 1000/time
In the photosynthesis practical, using DCPIP, an additional tube containing oxidised DCPIP without leaf extract was included.
Why?
To prove presence of chlorophyll is causing reduction reaction
In the photosynthesis practical with DCPIP, what causes the DCPIP to change colour?
Reduction of DCPIP by electrons
From light-dependent reaction
In the photosynthesis practical, with DCPIP, why is a tube set up with DCPIP, no leaf extract, in light?
To show light doesn’t affect DCPIP, causing colour change
Shows chloroplasts are needed
In the photosynthesis practical into the effect of different wavelengths of light, what is the reason for the change when the tube is exposed to green light?
Chlorophyll doesn’t absorb light of wavelength
Green light can be used
Little photosynthesis
Other than the temperature and pH, give two factors which should be kept constant during an investigation into photosynthesis?
Light intensity
Photosynthesising cells number
Carbon dioxide
Time
If no buffer was used, what would happen to the pH of a solution in a photosynthesis practical?
pH increase
More CO2 removed
Why would reducing light intensity affect the amount of oxygen released by seaweeds?
Light is limiting factor
Fewer electrons released from chlorophyll
Less photolysis of water
