3.3.2 Photosynthesis Flashcards
Describe how ATP is synthesised
ATP is synthesised via condensation reaction between ADP and P¡ (inorganic phosphate) using energy from an energy-releasing reaction
What enzyme catalyses ATP synthesis?
Enzyme ATP synthase
Where is the energy stored in ATP?
Energy is stored as chemical energy in the phosphate bond
What happens when ATP arrives (via diffusion) to a part of cell that needs energy?
- ATP is hydrolysed back into ADP and P¡
- Chemical energy is released from phosphate bond and used by cell
What enzyme catalyses ATP hydrolysis?
ATP hydrolase
ADP and P¡ are _____
recycled
Draw an ATP molecule
Name and explain 6 properties that ATP has that makes it a good energy source
- Stores or releases only a small, manageable amount of energy at a time
- ∴ no energy is wasted as heat
- It’s a small, soluble molecule ∴ it can be easily transported
- (Easily) broken down in 1 step = energy can easily released instantaneously
- It can be quickly re-made
- Can make other molecules more reactive by transferring one of its phosphate groups to them (phosphorylation)
- ATP can’t pass out of cell = cell always have immediate supply of energy
Define a metabolic pathway
Series of small reactions controlled by enzymes
e.g. respiration and photosynthesis
Define Phosphorylation
Adding phosphate to a molecule
e.g. ADP → ATP
Define Photolysis
Splitting (lysis) of a molecule using light (photo) energy
Define Photophosphorylation
Adding phosphate to a molecule using light
Define Photoionisation
- When light energy excites electrons in an atom
- Giving them more energy and causing them to be released
- Release causes atom to become positively-charged ion
Define Hydrolysis
Splitting (lysis) of a molecule using water (hydro)
Define Decarboxylation
Removal of CO2 from molecule
Define Dehydrogenation
Removal of hydrogen from molecule
Chloroplasts contain _________ _____
Photosynthetic pigments
What are photosynthetic pigments (e.g. chlorophyll a, chlorophyll b and carotene)?
Coloured substances that absorb light energy
Where are pigments found?
Thylakoid membranes = attached to proteins
What is a photosystem?
Protein + pigment
Name the 2 photosystems used by plants to capture light energy
- Photosystem I (PSI)
- Photosystem II (PSII)
What are carbohydrates that are produced by photosynthesis and not used straight away stored as and where?
As starch grains in the stroma
Where does the the light-dependent reaction occur?
Takes place in thylakoid membranes
Photosystems are linked by _____ ____
electron carriers
What are electron carriers?
Proteins that transfer electrons
Photosystems and electron carriers form an ____ ______ ____
electron transport chain
What is an electron transport chain?
Chain of proteins through which excited electrons flow
Light-dependent reaction includes 2 types of photophosphorylation. Name them.
- Non-cyclic Photophosphorylation
- Cyclic Photophosphorylation
Name the 4 main stages in the light-dependent reaction (non-cyclic photophosphorylation).
- Light energy excites electrons in chlorophyll
- Photolysis
- Energy from excited electrons make ATP…
- … and generates reduced NADP
The Light-dependent Reaction
Describe Stage 1
- Chlorophyll (PSII) absorbs light
- Light energy excites electrons in chlorophyll
- Electrons move to higher energy level
- High-energy electrons are released from chlorophyll and move down electrons transport chain to PSI
The Light-dependent Reaction
Describe Stage 2
- Light energy splits water into protons (H+ ions), electrons & oxygen = photolysis
- Electrons used to replace electrons that passed out of chlorophyll along electron carriers
The Light-dependent Reaction
Describe Stage 3
- Excited electrons lose energy as they move down electron transport chain
- Energy lost = used to pump H+ ions into thylakoid space, creating proton gradient
- Protons can now diffuse back into stroma via enzyme ATP synthase
- Catalysed by ATP synthase
- Energy from movement combines ADP and P¡ to form ATP
The Light-dependent Reaction
Describe Stage 4
- (Light energy is absorbed by PSI which excites electrons to even higher energy level)
- Electrons + protons (from stroma) are transferred to NADP = combine to reduce NADP to reduced NADP
The Light-dependent Reaction
Describes what happen in cyclic photophosphorylation
- ‘Cyclic’ ∵ electrons from chlorophyll molecule aren’t passed onto NADP
- But passed back to PSI via electrons carriers
- ∴ electrons are recycled
What is chemiosmosis/the chemiosmotic theory?
The process of electrons flowing down electrons transport chain & creating a proton gradient across the membrane to drive ATP synthesis
Cyclic photophosphorylation uses only ____
PSI
Cyclic photophosphorylation produces only ____ _______ of _____
small amounts of ATP
Where does the light-independent reaction (aka Calvin cycle) take place?
Takes place in the stroma
___ and ___ required to keep Calvin cycle going
ATP and H+ ions
Name the 3 stages in the light-independent reaction
- CO2 + RuBP = 2x of GP
- ATP + reduced NADP = Reduction of GP → TP
- RuBP is regenerated
The Light-independent Reaction
Describe stage 1
- CO2 enters through stomata & diffuses into stroma
- CO2 combines with RuBP
- Catalysed by enzyme rubisco
- Gives an unstable 6C which breaks down quickly into 2x GP (3C)
The Light-independent Reaction
Describe stage 2
- (Hydrolysis of) ATP provides energy to change GP → TP (3C)
- Reduced NADP provides H+ ions so it can reduce GP → TP
- Reduced NADP is recycled to NADP
- TP is then converted into useful organic compounds (e.g. glucose) & some continues in Calvin cycle to regenerate RuBP
The Light-independent Reaction
Describe stage 3
- 5/6 of TP produced used to regenerate RuBP NOT make hexose sugars
- Regenerating RuBP uses rest of ATP produced by light-dependent reaction
What are TP and GP molecules used to make?
Carbohydrates, lipids and amino acids
Describe how hexose sugars made (carbohydrates)
Made by joining 2 TP molecules together
Draw the Calvin cycle (include the no. of carbons)
Describe how larger carbohydrates (e.g. sucrose, starch, cellulose) are made
Made by joining hexose sugars together in different ways
Describe how lipids are made
Made using glycerol, which is synthesised from TP, and fatty acids, which are synthesised from GP
Describe how some amino acids are made
Some amino acids are made from GP
Explain why the Calvin cycle needs to turn 6 times to make 1 hexose sugar
- 3 turns of cycle = 6x TP ∵ 2x TP are made for every 1 CO2 molecule used
- 5/6 TP used to regenerates RuBP
- Means for 3 turns = only 1 TP is produced that’s used to make hexose sugar
- But hexose sugar has 6 C ∴ 2x TP needed to form 1 hexose sugar
- Means cycled must turn 6 times to produce 2x TP that can be used to make 1 hexose sugar
6 turns of cycle need ___ ATP and ___ reduced NADP from
light-dependent reaction
6 turns of cycle need 18 ATP and 12 reduced NADP from light-dependent reaction
What are coenzymes?
Molecules that aids function of an enzyme
How do coenzymes work?
Work by transferring a chemical group from 1 molecule to another
Name a coenzyme in photosynthesis
NADP
Explain how NADP is a coenzyme
- Transfers hydrogen from 1 molecule to another
- Means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule
Name 3 limiting factors of photosynthesis
- Light intensity
- Temperature
- Carbon dioxide concentration
Describe how light intensity affects the rate of photosynthesis
- Higher intensity of light = more energy for light-dependent reaction
- Rate of photosynthesis ↑
Describe and explain what happen to the rate of photosynthesis at too high temperatures
- High temps = enzymes denature
- Photosyntheis stops
- High temps = stomata close to avoid losing too much water
- Causes photosynthesis to slow down ∵ less CO2 enters leaf when stomata are closed
Describe how could you test the effect of light intensity on the rate of photosynthesis
- Source of white light placed at a specific distance from pondweed
- Pondweed placed (stem side up - cut stem at slant) in sodium hydrogen carbonate solution to photosynthesis for 5 mins
- Number of bubbles produced are counted
- Variables (e.g. temperature, time) should be controlled
- Experiment repeated thrice with light source at same distance = mean no. bubbles calculated
- Whole experiment is repeated with light source at different distances from pondweed
- Convert distances from lamp to light intensity
- Process your data and use suitable statistical test to investigate correlation between light intensity and rate of photosynthesis
Give the formula for converting distances from lamp to light intensity
1/d²
d = distance from plant to lamp
Name a use suitable statistical test to investigate correlation between light intensity and rate of photosynthesis
Spearmen’s rank (correlation coefficient)
What does Spearmen’s rank allow you to do?
Allows you to work out the degree to which 2 sets of data are correlated
What is Spearmen’s rank given as (name the range of the values)?
Given as value between 1 and -1
Spearmen’s Rank
1 = _____ ______ _____
1 = strong positive correlation
Spearmen’s Rank
-1 = _____ ______ _____
-1 = strong negative correlation
Spearmen’s Rank
0 = ___ _________
0 = no correlation
What do you do to the value you get form Spearmen’s rank?
Compare your result to critical value to find if correlation is significant
(Above critical value = accept hypothesis)
Describe and explain how an increase in temperature and a reduction in light intensity will affect the growth of plants. (3)
- Growth will decrease (at higher temperature)
- Rate of respiration will increase at higher temperature
- Photosynthesis decreases as there’s less light
ADP levels can be a ____ ______
limiting factor
When measuing the rate of photosynthesis of plants in terms of oxygen produced, suggest what units you could use
e.g. cm3 min-1 g-1
Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis. (5)
- In dark, no ATP production in photosynthesis
- Some tissues unable to photosynthesis/produce ATP
- ATP can’t be stored
- Plant uses more ATP than produced in photosynthesis
- ATP for active transport
Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period. (3)
- Used in respiration
- CO2 produced
- Some parts of plant are eaten/decompose
Herbicides affect the light-dependent reaction (namly the production of oxygen and the electron transport chain).
Suggest how herbicides cause a reduction in the production of oxygen by plants (3)
- Binds to chlorophyll molecules
- Stops release of electrons from chlorophyll
- Stops movement of electrons down electron transport chain
- ∴ break down of water reduces
Herbicides affect the light-dependent reaction (namly the production of oxygen and the electron transport chain).
Suggest how herbicides cause the death of plants (3)
- Less ATP
- For light-independent reaction
- ∴ less sugars produced for respiration
- Rate of respiration is greater than rate of photosynthesis
Explain why high levels of oxygen reduce the rate of photosynthesis (effect is greater at higher temperatures). (2)
- More RuBP combines with O2 than CO2
- Competitive inhibition (for rubisco)
- Less RuBP regenerated
A buffer is used to maintain a constant pH. Explain why the pH of the suspension would increase during photosynthesis in the absence of a buffer. (1)
Decrease in carbon dioxide/hydrogencarbonate ions
When measuing the rate of photosynthesis of plants, how can you keep the temperature constant? (1)
Place bottle/test tube in beaker of water
