photosynthesis Flashcards
Explain why we need energy.
- Plants need energy for photosynthesis, active transport and protein synthesis
- Animals need energy for muscle contraction, cell division and DNA replication
Explain why photosynthesis is vital on Earth
- Its the way that energy can get into ecosystems
- Turns a colourless gas (CO2) into glucose then starch
- Produces O2 as a by-product for aerobic respiration
What is the balanced chemical equation for photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2
Describe where photosynthesis takes place
Photosynthesis takes place in the palisade mesophyll in the chloroplast that contains chlorophyll
Describe the structure of the chloroplast
- Disc-shaped, surrounded by a double membrane
- Grana are made of stakced thylakoids
- Lamella attach thylakoids in adjacent grana
- The stroma contains enzymes, sugars and organic acids
How does the structure of the chloroplast maximise the rate of the light dependant reaction?
- ATP synthase channels with granal membrane
- Large surface area of thylakoid membrane for ETC
- Photosystems position chlorophyll to enable maximum absorption of light
How does the structure of the chloroplast maximise the rate of the light-independent reaction?
- Has its own DNA and ribosomes for the synthesis of enzymes like rubisco
- Concentration of enzymes and substrates in stroma is high
List the organelles inside a chloroplast
- Outer and inner membrane
- Thylakoids and thylakoid membrane
- Grana
- Stroma
- Starch grain
Describe the thylakoid membrane
- A phospholipid bilayer
- Has chlorophyll pigment, ATP synthase and an electron transport chain embedded inside of it
Where does the light-dependent reaction take place?
In the thylakoid membrane
List the steps of the light-dependent reaction
- Photoionisation
- Photolysis
- Chemiosmosis
What does the light dependant reaction produce?
ATP and reduced NADP
Explain photoionisation
- Chlorophyll molecules absorb light energy exiciting the electrons
- Which raises the electron to a higher energy level
- They are emitted into the electron transport chain
Explain photolysis
To replace the excited electrons, light energy splits H2O into protons (H+), electrons (e-) and oxygen (O2)
Write the balanced chemical equation for photolysis
2H2O → 4H+ + 4e- + O2
What happens to the products of the photolysis of water?
- H+ ions: move out of thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
- e-: replace electrons lost from chlorophyll
- O2: used for respiration or diffuses out of leaf as waste gas
Explain chemiosmosis
- Energy in the excited electrons is used to pump H+ ions from the stroma to the thylakoids across a diffusion gradient
- The H+ ions diffuse back into the stroma via ATP synthase
- The energy from this movement combines ADP and inorganic phosphate to form ATP
- Light energy is absorbed by chlorophyll, exciting electrons again to a higher energy level
- The electrons are transferred to NADP, along with an H+ ion from the stroma to form reduced NADP
Write the balanced chemical equation for chemiosmosis
NADP + 2H+ + 2e- → reduced NADP
How is a proton concentration gradient established during chemiosmosis
Some energy released from the ETC is coupled to the active transport of H+ ions (protons) from the stroma into the thylakoid space
Where is reduced NADP produced in the light dependent reaction?
The stroma
Where do the H+ ions and electrons used to reduce NADP come from?
- H+ ions come from the photolysis of water
- Electrons: NADP acts as the final electron acceptor of the electron transfer chain
Where does the calvin cycle take place
The stroma of chloroplasts
What does the calvin cycle produce?
Triose phosphate from CO2 and ribulose bisphosphate
Name the 3 main stages in the Calvin cycle
- Carbon fixation
- Reduction
- Regeneration
Explain carbon fixation in the Calvin cycle
- CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplasts
- CO2 is combined with ribulose biphosphate (C5) and the reaction is catalysed by rubisco
- Creating an unstable 6-carbon intermediate which is broken down into 2 molecules of glycerate 3-phosphate
Explain reduction in the Calvin cycle
- Hydrolysis of ATP from LDR provides energy to reduce glycerate 3-phosphate into triose phosphate
- Requires reduced NADP and ATP
- Forms NADP and ADP
Explain regeneration in the Calvin cycle
Some triose biphosphate is converted into glucose or used to synthesise RuBP (ribulose bisphosphate)
How does the light-independant reaction result in the production of useful organic substances?
1C leaves the cycle so some of the TP is converted into useful organic molecules
Explain the uses of triose phosphate and glycerate 3-phosphate
- Makes carbohydrates - hexose sugars by joining 2 triose phosphate molecules
- Lipids - made by using glycerol synthesised from triose phosphate and fatty acids which are synthesised by glycerate 3-phosphate
- Amino acids - made from glycerate 3-phosphate
Explain why the Calvin cycle needs to turn 6 times to make 1 hexose sugar
- 3 turns of the cycle produce 6 molecules of triose phosphate
- 5 triose phosphate molecules are used to regenerate ribulose diphosphate (RuBP)
- So 3 turns of the Calvin cycle produce 1 triose phosphate to make sugar
- A hexose sugar has 6 carbons so two triose phosphate molecules are needed
State the roles of ATP and reduced NADP in the light-independent reaction
- ATP - reduction of glycerate 3-phosphate to triose phosphate and provides phosphate group to convert ribulose phosphate into ribulose diphosphate
- Reduced NADP - coenzyme transports electrons needed for reduction of glycerate 3-phosphate to triose phosphate
State the number of carbon atoms in RuBP (ribulose diphosphate), GP (glycerate 3-phosphate) and TP (triose phosphate)
- RuBP - 5
- GP - 3
- TP - 3
Define limiting factor
The factor that determines maximum rate of reaction, even if other factors change to become more favourable
List the limiting factors of photosynthesis
- Temperature
- CO2 concentration
- Light intensity
- Mineral levels
Explain why temperature is a limiting factor in photosynthesis
The light-independent reaction is temperature sensitive, it is enzyme-controlled (rubisco)
Explain why CO2 is a limiting factor of photosynthesis
Needed as a source of carbon to make triose phosphate and glycerate 3-phosphate in the light independant reaction
Explain why light intensity is a limiting factor of photosynthesis
Needed to excite electrons in the chlorophyll (photoionisation) and photolysis of H2O into e-, O2 and H+
Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis
- Artificial light at night
- Artifical heating
- Addiction of CO2 to greenhouse atmosphere
Why do farmers try to overcome the effect of limiting factors on photosynthesis?
- To increase yield
- Additional cost must be balanced with yield to ensure maximum profit
