Module 5.5 - Photosynthesis Flashcards
Why do living things need energy? (2)
- Animals/plants need energy for photosynthesis, muscle contraction, maintenance of body temperature, active transport, DNA replication, cell division and protein synthesis
- Without energy, these biological processes would stop and the plant or animal would die
What is photosynthesis? (4)
- Storage of energy in glucose
- Energy is stored in glucose until its respired for energy
- The process where the light energy is converted to chemical energy in the form of glucose
- 6H2O + 6CO2 → C6H1206 (glucose) + 6O2
Types of respiration? (2)
- Aerobic respiration: respiration using oxygen
- Anaerobic respiration: respiration without oxygen
Aerobic respiration? (1)
- C6H1206 (glucose) + 6O2 → 6H2O + 6CO2 + energy
Metabolic pathway? (2)
- Series of small enzyme-controlled reactions
- Respiration and photosynthesis
Phosphorylation? (2)
- Adding phosphate to a molecule
- ADP is phosphorylated to ATP
Photophosphorylation? (1)
- Adding phosphate to a molecule using light
Photolysis? (1)
- The splitting (lysis) of a molecule using light (photo) energy
Hydrolysis? (1)
- The splitting (lysis) of a molecule using water (hydro)
Decarboxylation?(1)
- The removal of carbon dioxide from a molecule
Dehydrogenation? (1)
- The removal of hydrogen from a molecule
Redox reactions? (2)
- Reactions that involve oxidation and reduction
- OILRIG
Coenzyme? (2)
- A molecule that aids the function of an enzyme
- Work by transferring a chemical group from one molecule to another
Coenzyme involved in photosynthesis? (3)
- NADP
- Transfers hydrogen from one molecule to another
- NADP can reduce or oxidise a molecule
Coenzymes used in respiration? (3)
- NAD
- Coenzyme A
- FAD
NAD and FAD? (2)
- Transfer hydrogen from one molecule to another this means
- They can reduce or oxidise a molecule
What is also transferred when hydrogen is transferred? (1)
- Electrons are transferred
Coenzyme A? (1)
- Transfers acetate between molecules
Where does photosynthesis take place? (1)
- Chloroplasts
Chloroplasts? (4)
- Small, flattened organelles found in plant cells
- Double membraned (chloroplast envelope)
- Thylakoids are stacked up into structures called grana
- Grana are linked together by bits of thylakoid membrane called lamellae
Photosynthetic pigments? (3)
- Chlorophyll a, chlorophyll b and carotene
- Are coloured substances that absorb the light energy needed for photosynthesis
- Found in the thylakoid membranes & are attached to proteins
Photosystem? (4)
- Protein and pigment
- Used to capture light
- Photosystem I (or PSI) absorbs light at 700 nm
- Photosystem II (PSII) absorbs light at 680 nm
Types of photosynthetic pigments in a photosystem? (2)
- Primary pigments
- Accessory pigments
Primary pigments? (1)
- Reaction centres where electrons get excited during the light-dependent reaction
Accessory pigments? (2)
- Make-up light-harvesting systems which surround reaction centres
- And transfer light energy to them to boost the energy available for electron excitement to take place
Stroma? (3)
- Gel-like substance
- Contained within the inner membrane of the chloroplast and surrounds the thylakoids
- Chloroplasts’ circular DNA found here
What does the inner membrane of the chloroplast contain? (1)
- Enzymes, sugars and organic acids
Starch grains? (1)
- Carbohydrates produced by photosynthesis are stored as starch grains in the stroma
Stages of photosynthesis(2)
- The Light-Dependent Reaction
- The Light-Independent Reaction
The light-dependent reaction? (6)
- Reaction needs light energy
- Takes place in thylakoid membranes of chloroplasts
- Light energy is absorbed by photosynthetic pigments in photosystems
- ATP transfers energy to the light-independent reaction
- Reduced NADP transfers hydrogen to the light-independent reaction
- During the process H2O is oxidised to O2
What happens to light energy after being absorbed by pigments? (3)
- Light energy is converted to chemical energy
- Light energy is used to add a phosphate group to ADP to form ATP
- Light energy is used to reduce NADP to form reduced NADP
Reduced NADP?(2)
- An energy-rich molecule
- It can transfer hydrogen/electrons to other molecules
The Light-Independent Reaction? (4)
- Calvin cycle
- Doesn’t use light energy directly but relies on the products of the light-dependent reaction
- Takes place in the stroma of the chloroplasts
- ATP and reduced NADP supply the energy and hydrogen to make glucose from CO2
Photophosphorylation? (2)
- In the light-dependent reaction ATP is Made
- Light energy absorbed by the photosystems is used for three things
What is the light energy absorbed by the photosystems used for? (3)
- Photophosphorylation
- Making NADPH from NADP
- Photolysis
How are photosystems linked together? (3)
- By electron carriers
- Electron carriers are proteins that transfer electrons
- The photosystems and electron carriers form
Electron transport chain? (1)
- A chain of proteins through which excited electrons flow
Types of photophosphorylation? (2)
- Non-cyclic
- Cyclic
Non-cyclic photophosphorylation (1)
- Produces ATP, NADPH and O2
How do high-energy electrons move from PSII to PSI? (5)
- Light energy is absorbed by PSII
- Light energy excites electrons in chlorophyll
- Electrons move to higher energy level
- Electrons have more energy
- High-energy electrons move along the electron transport chain to PSI
What happens to PSII when excited electrons leave? (3)
- Excited electrons are replaced
- Light energy splits water into protons (H+), electrons and oxygen
- H2O → 2H+ + ½O2
Proton concentration gradient? (5)
- Excited electrons lose energy as they move along electron transport chain
- The energy lost is used to transport protons into the thylakoid via proton pumps
- Thylakoid has a higher concentration of protons than the stroma
- This forms a proton gradient across membrane
- Protons move down concentration gradient into stroma
Proton pumps? (1)
- Membrane proteins
How do protons move down the proton concentration gradient? (2)
- Via an enzyme called ATP synthase
- Energy from movement combines ADP and inorganic phosphate (Pi) to form ATP
How is NADPH generated? (4)
- Light energy is absorbed by PSI
- Excites electrons again to an even higher energy level
- Electrons & H+ (from stroma) are transferred to NADP
- NADP is reduced to NADPH
Chemiosmosis/ chemiosmotic theory? (2)
- Process of electrons flowing down the electron transport chain
- Creating a proton gradient across the membrane to drive ATP synthesis
Cyclic photophosphorylation? (2)
- Only produces ATP
- Only uses PSI
Why is cyclic photophosphorylation called cyclic? (5)
- Electrons from the chlorophyll molecule aren’t passed onto NADP
- Electrons are passed back to PSI via electron carriers
- Electrons are recycled and can repeatedly flow through PSI
- Cyclic photophosphorylation doesn’t produce NADPH or O2
- Cyclic photophosphorylation produces small amounts of ATP
Calvin cycle? (5)
- Takes place in the stroma of the chloroplast
- Also known as carbon dioxide fixation
- Turns CO2 + RuBP into TP
- Needs ATP and H+
- RuBP is regenerated
Carbon fixation? (1)
- Carbon from CO2, is fixed into an organic molecule
RuBP? (2)
- Ribulose bisphosphate
- A 5-carbon compound
TP? (2)
- Triose phosphate
- Can make glucose and other useful organic substances
How is GP generated? (4)
- CO2 enters leaf through the stomata
- CO2 diffuses into stroma
- CO2 dioxide + RuBP form unstable 6-carbon compound
- 6-carbon compound bread down into two molecules of glycerate 3-phosphate (GP)
RuBisCO? (1)
- Ribulose bisphosphate carboxylase catalyses the reaction between CO2 + RuBP
How is TP generated? (4)
- ATP energy to turn GP into TP
- Requires H+ NADPH
- NADPH is recycled to NADP
- TP is converted into many organic compounds
Why is NADPH recycled to NADP? (1)
- To be re-used in the light-dependent stage
How is RuBP regenerated? (2)
- Five out of every six molecules of TP produced is used to regenerate RuBP
- Regenerating RuBP uses the rest of the ATP produced by the light-dependent reaction
What are TP and GP used to make? (3)
- Carbohydrates
- Lipids
- Amino acids
How are carbohydrates made? (2)
- Hexose sugars from two TP molecules
- Larger carbohydrates from combining hexose sugars
How are lipids made? (2)
- Glycerol - which is synthesised from TP
- Fatty acids - which is synthesised from GP
What are some amino acids made? (1)
- GP
How does the Calvin cycle make one hexose sugar? (7)
- For every 1 of CO2 used 2 of TP is formed
- 3 turns of cycle produces 6 of TP
- 5 out of 6 of TP are used to regenerate RuBP
- To make a hexose sugar, 3 turns of the cycle produces only one of TP
- Two of TP are needed to form 1 of hexose
- Cycle must turn six times
- Six turns need 18 ATP +12 reduced NADP
Optimum conditions for photosynthesis in temperate climates? (3)
- High light intensity of a certain wavelength
- Temperature around 25 °C
- Carbon dioxide at 0.4%
High light intensity of a certain wavelength? (5)
- Light is needed to provide energy for light-dependent reactions
- Higher the intensity of light, the more energy it provides
- Certain wavelengths of light are used for photosynthesis
- Photosynthetic pigments absorb red and blue light
- Green light is reflected, which is why plants look green
Temperature’s effect on enzymes? (3)
- Photosynthesis involves enzymes
- If the temperature falls below 10 °C the enzymes become inactive
- If the temperature is more than 45 °C they may start to denature
High temperature’s effect on stomata? (2)
- Stomata close to avoid losing too much water
- Causes photosynthesis to slow down because less CO2 entering the leaf
Stomatal aperture? (1)
- The width of the opening of stomata
High temperature’s effect on thylakoid membranes? (3)
- Membranes may be damaged
- Number of sites available for electron transfer reduces
- Reduce the rate of light-dependent stage reactions
High temperature’s effect on membranes around chloroplasts? (3)
- Membranes around the chloroplasts could be damaged
- Enzymes important in the Calvin cycle will be released into the cell and not to the stroma
- Reduce the rate of the light-independent stage reactions
High temperature’s effect on chlorophyll? (3)
- Chlorophyll could be damaged
- Reduce the amount of pigment that can absorb light energy
- Reduce the rate of the light-dependent stage reactions
Carbon dioxide at 0.4%? (3)
- Carbon dioxide makes up 0.04% of the gases in the atmosphere.
- Increasing this to 0.4% gives a higher rate of photosynthesis
- But any higher and the stomata start to close
Light, Temperature and CO2 as limiting factors of photosynthesis? (3)
- All three have to be at the right level for photosynthesis to happen quickly as possible
- If any of these factors is too low or too high, it will limit photosynthesis
- These factors could become the limiting factor based on the environmental conditions
Saturation point? (2)
- When a factor is no longer limiting the reaction
- Something else has become the limiting factor
How can water stress affect photosynthesis? (4)
- Plants don’t have enough water
- Stomata will close to preserve water they do have
- Less CO2 enters the leaf for the Calvin cycle
- Photosynthesis slows down
Light intensity’s effect on the levels of GP, RuBP and TP in the Calvin cycle? (2)
- At low light intensity the products of the light-dependent stage will be in short supply
- Conversion of GP to TP and RuBP is slow
Temperature’s effect on the levels of GP, RuBP and TP in the Calvin cycle? (4)
- All reactions in Calvin cycle are catalysed by enzymes
- At low temperatures all reactions will be slower as enzymes work more slowly
- Levels of RuBP, GP and TP will fall
- GP, TP and RuBP are affected the same way at high temperatures as enzymes will denature
Carbon Dioxide concentration’s effect on the levels of GP, RuBP and TP in the Calvin cycle? (2)
- At low CO2 concentrations conversion of RuBP to GP is slow
- As less CO2 entering the leaf to combine with RuBP
