5A - Photosynthesis and Respiration Flashcards
What do plants need energy for?
Processes like: • Photosynthesis • Active transport • DNA replication • Cell division • Protein synthesis etc.
What do animals need energy for?
Processes like: • Muscle contraction • Maintenance of body temperature • Active transport • DNA replication • Cell division • Protein synthesis etc.
What is photosynthesis?
The process by which energy from light is used to make glucose from water and carbon dioxide.
What energy transfer occurs in photosynthesis?
Light energy -> Chemical energy
What is the overall symbol equation for photosynthesis?
6CO2 + 6H2O (+ Energy) -> C6H12O6 + 6O2
What is respiration?
The process by which energy is released from glucose.
What are the two types of respiration?
- Aerobic
* Anaerobic
What does aerobic respiration produce?
- Carbon dioxide
* Water
What is the overall symbol equation for aerobic respiration?
C6H12O6 + 6O2 -> 6CO2 + 6H2O (+ Energy)
Does anaerobic respiration have the same products in all organisms?
No, it is different in:
• Plants and yeast
• Humans
What does anaerobic respiration produce in plants and yeast?
- Ethanol
* Carbon dioxide
What does anaerobic respiration produce in humans?
• Lactate
Can a cell get energy from glucose?
Not directly.
How does a cell get energy from glucose?
- Energy released from glucose in respiration is used to make ATP.
- This carries energy around the cell to where it’s needed.
How is ATP produced?
- Condensation reaction between ADP and Pi
- Uses energy from an energy-releasing reaction (e.g. respiration)
- Catalysed by ATP synthase
Where in an ATP molecule is energy stored?
In the phosphate bonds.
See diagram pg 112 of revision guide
How does ATP move to the correct part of the cell?
It diffuses to where it is needed.
How is ATP used?
- Hydrolysis reaction forms ADP and Pi
- Releases energy
- Catalysed by ATP hydrolase
What are the enzymes involved with ATP?
- ATP synthase
* ATP hydrolase
What are some properties of ATP that make it a good energy source?
- Stores and releases only a small, manageable amount of energy -> Little is wasted as heat
- Small and soluble -> Easily transported
- Easily broken down -> Instant energy release
- Can be quickly re-made
- It can make other molecules more reactive by phosphorylation
- ATP can’t pass out of the cell -> Cell always has an immediate supply of energy
Define metabolic pathway.
A series of small reactions controlled by enzymes.
Give an example of a metabolic pathway.
- Respiration
* Photosynthesis
Define phosphorylation.
Adding phosphate to a molecule.
Define photophosphorylation.
Adding phosphate to a molecule using light.
Define photolysis.
The splitting of a molecule using light energy.
Define photoionisation.
When light energy excites electrons in an atom or molecule, giving them more energy and causing them to be released.
Define hydrolysis.
The splitting of a molecule using water.
Define decarboxylation.
The removal of carbon dioxide from a molecule.
Define dehydrogenation.
The removal of hydrogen from a molecule.
Define redox reactions.
Reactions that involve both oxidation and reduction.
Define oxidation in terms of electrons and hydrogen.
- Loss of electrons
* Loss of hydrogen
Define reduction in terms of electrons and hydrogen.
- Gain of electrons
* Gain of hydrogen
What is a coenzyme?
A molecule that aids the function of an enzyme.
How do coenzymes work?
By transferring a chemical group from one molecule to another.
Name the coenzymes involved in photosynthesis.
• NADP
Name the coenzymes involved in respiration.
- NAD
- Coenzyme A
- FAD
What is the difference between NADP and NAD?
NADP is used in photosynthesis, while NAD is used in respiration.
What is NADP involved in and what does it do?
- Photosynthesis
* Transfers hydrogen from one molecule to another.
What is NAD involved in and what does it do?
- Respiration
* Transfers hydrogen from one molecule to another.
What is FAD involved in and what does it do?
- Respiration
* Transfers hydrogen from one molecule to another.
What is coenzyme A involved in and what does it do?
- Respiration
* Transfers acetate between molecules
Do NADH/NAD/FAD reduce or oxidise?
They can do both.
In which part of the cell does photosynthesis happen?
Chloroplasts
What are chloroplasts?
- Flattened organelles surrounded by a double membrane.
* Photosynthesis occurs here.
What are thylakoids?
Fluid-filled sacs in chloroplasts that are stacked up to form grana.
What are grana?
Stacks of thylakoids.
What are lamellae?
Bits of thylakoid membrane that join together grana.
What is the stroma?
A fluid within the inner membrane of chloroplasts that contains enzymes, sugars and organic acids.
What do thylakoid membranes contain?
Photosynthetic pigments (e.g chlorophyll) attached to proteins.
Where is chlorophyll found?
In thylakoid membranes.
What is chlorophyll?
A photosynthetic pigment found in thylakoid membranes of chloroplasts.
What are 3 photosynthetic pigments found in thylakoid membranes?
- Chlorophyll a
- Chlorophyll b
- Carotene
How are photosynthetic pigments found?
Attached to proteins.
What is a photosystem?
A photosynthetic pigment attached to a protein.
What does the stroma contain?
Enzymes, sugars and organic acids.
How are carbohydrates produced by photosynthesis stored if they are not used immediately?
They are stored as starch grains in the stroma of chloroplasts.
Describe the structure of chloroplasts.
- Double membrane surrounds the stroma (substance that contains enzymes, sugars and organic acids)
- Stacks of thylakoid membranes (containing photosynthetic pigments attached to proteins) are in the stroma
- Stacks of thylakoid membranes form grana
- Grana are joined by lamella
- Starch grains also may be found in the stroma
What are the stages of photosynthesis?
1) Light-dependent reaction
2) Light-independent reaction
Where does the light-dependent reaction take place?
In thylakoid membranes.
Where does the light-independent reaction take place?
In the stroma.
What is another name for the light-dependent reaction?
Non-cyclic phosphorylation
What is another name for the light-independent reaction?
Calvin cycle
Describe the light-dependent reaction of photosynthesis.
• Light energy is absorbed by the chlorophyll, which excites the electrons until they are released. This is called photoionisation.
• Light energy is also used in the photolysis of water in the thylakoid space, which produces H+ ions, oxygen and electrons. The electrons stabilise the excited chlorophyll.
• The excited electrons from the chlorophyll move down the electron transport chain, through a proton pump and then electron carrier (into the stroma). They lose energy, which is used to actively transport H+ ions from the stroma into the thylakoid space.
• The thylakoid now has a higher concentration of H+ ions than the stroma, so they move down the concentration gradient into the stroma through the enzyme ATP synthase (a.k.a. ATP synthase channel)
• The energy from this movement is used to combine ADP and Pi to form ATP.
• The electrons that have moved through the electron carrier into the stroma now join with the H+ ions that have been pumped into the stroma and NADP to give NAPH.
(NADP+ + 2e- + 2H+ -> NADPH + H+)
Give the equation for the photolysis of water.
H2O -> 1/2O2 + 2e- + 2H+
How is the reduction of a coenzyme shown?
A H is added on the end (e.g. NADPH)
What is the equation for the production of NADPH in the LDR?
NADP+ + 2e- + 2H+ -> NADPH + H+
What is the name of the enzyme that transports H+ ions in and out the stroma during the LDR?
- Out of the stroma: Proton pump
* Into the stroma: ATP synthase channel
Describe the path of electrons from the chlorophyll in the LDR.
Chlorophyll -> Proton pump -> Electron carrier -> Stroma -> NADP+
How do ATP synthase channels produce ATP?
As protons pass through, they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP.
What is chemiosmosis?
The process by which electrons flow down the electron transport chain and create a proton gradient across the membrane to drive ATP synthesis.
What happens to the oxygen produced in the LDR?
• Used in respiration
OR
• Diffuses out of the plant
What is the most important product of the LDR and why?
NADPH, because it is used in the LIR.
Remember to practise drawing out the LDR stage of photosynthesis and writing it out in full.
Pg 272 of textbook.
What is an alternative for of the LDR?
- Cyclic photophosphorylation
- The electrons from the chlorophyll molecule aren’t passed onto NADP but are passed back to chlorophyll.
- This means the electrons can be reused, but no NADPH or O2 is produced.
(DON’T THINK YOU NEED TO KNOW THIS THOUGH)
What are the inputs into the LDR?
- Light -> Photolysis + Photoionisation
- H2O -> Provides H+ ions and e-
- ADP + Pi -> To produce ATP
- NADP -> To work as a co-enzyme and form NADPH
What are the outputs of the LDR?
- ATP -> LIR
- NADPH -> LIR
- O2 -> Aerobic respiration
What are the components involved in LDR?
- Chlorophyll -> Provides e-
- Electron carrier -> Passes e- along
- Proton pump -> Pumps H+ into thylakoid
- ATP synthase channel -> Move H+ ions into stroma, making ATP
Remember to revise the diagram showing how the LDR and LIR are linked.
Pg 114 of revision guide
Where does the Calvin cycle take place?
Stroma of the chloroplasts
What are the outputs from the LDR that are inputs into the LIR?
- ATP
* NADPH
Describe the light-independent reaction of photosynthesis.
- Carbon dioxide (1C) diffuses into the stroma, where it combines with ribulose biphosphate, RuBP, (5C) to form 2 molecules of glycerate 3-phosphate, GP, (3C). This is catalysed by rubisco.
- The hydrolysis of 2 ATP provides energy and 2 NADPH provides H+ ions to convert 2 GP into 2 molecules of triose phosphate, TP, (3C). The ATP forms ADP + Pi, while NADPH becomes NADP.
- 1 carbon from the 2 x TP molecules is used to start forming organic substances, like glucose, while the remaining 5C regenerate RuBP using energy from 1 ATP.
- The cycle repeats, each time providing 1 carbon to make organic substances.
Is all of the ATP from the LDR used in the LIR?
Yes
Describe the light-independent reaction in terms of reactions.
- CO2 + RuBP -> 2 x GP (Catalysed by rubisco)
- 2 x GP -> 2 x TP (2 ATP and 2 NADPH used)
- 2 x TP -> RuBP (1 ATP used) + 1C to organic compounds
What is GP and how many carbons does it have?
- Glycerate 3-phosphate
* 3 carbons
What is TP and how many carbons does it have?
- Triose phosphate
* 3 carbons
What is RuBP and how many carbons does it have?
- Ribulose bisphosphate
* 5 carbons
How many carbons are given to useful organic substances with each cycle of the Calvin cycle?
1
Which enzyme is involved in the light-independent reaction and what does it do?
- Rubisco
* Catalyses the reaction of CO2 with RuBP to give 2 molecules of GP
What is ATP used for in the light-independent reaction?
Providing energy for:
• Conversion of 2 x GP into 2 x TP
• Conversion of 2 x TP into RuBP
(2ATP is needed for both of these)
What is NADPH used for in the light-independent reaction?
Providing hydrogens to convert 2 x GP into 2 x TP.
2NADPH is needed for this
What is the Calvin cycle the starting point for?
The production of all organic substances a plant needs.
How are carbohydrates made using the Calvin cycle?
- Hexose sugars -> Made by joining two TP molecules together
* Larger carbohydrates -> Joining hexose sugars in different ways