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
How are lipids made using the Calvin cycle?
TP is used to make glycerol and GP is used to make fatty acids. Together, glycerol and fatty acids make lipids.
How are amino acids made using the Calvin cycle?
Some are made from GP.
Is 1 carbon given off to make organic substances with each turn of the Calvin cycle?
No, in reality 5 out of 6 TP molecules regenerate RuBP, while 1 in 6 go to make organic substances. So it is an average of 1 every cycle, but this isn’t really the case.
How many carbons in glucose?
6 - it is a hexose sugar.
How many times does the Calvin Cycle need to turn to make one glucose molecule?
6 times, because:
• 3 turns of the cycle produce 6 molecules of TP.
• 5 out of 6 of these TP molecules are used to regenerate RuBP.
• This means that for every 3 turns, only 1 TP is used to make a hexose sugar.
• This must happen twice to make a hexose sugar, so the cycle must turn 6 times.
How many molecules of ATP are used per Calvin cycle?
3
How many molecules of NADPH are used per Calvin cycle?
2
How many molecules of ATP are used to make one molecule of glucose in the Calvin cycle?
18
3 per turn
How many molecules of NADPH are used to make one molecule of glucose in the Calvin cycle?
12
2 per turn
How is the stroma adapted to carrying out the light-independent reaction?
- Stroma contains all the enzymes needed to carry out the LIR.
- Stroma surrounds the grana so the products of the LDR can readily diffuse there.
- Stroma contains both DNA and ribosomes, so it can quickly and easily manufacture some of the proteins involved in the LIR.
Remember to practise drawing out the Calvin cycle and writing out all of the reactions.
Pg 116 of revision guide
What are the inputs into the LIR?
- CO2 -> Combines with RuBP to give 2 x TP
- NADPH -> Provides H for converting GP to TP
- ATP -> Provides energy to convert GP to TP and TP to RuBP
What are the outputs of the LIR?
- Glucose -> Respiration, synthesis or storage
- NADP -> LDR
- ADP + Pi -> LDR
What are the components involved in the LIR?
• Rubisco -> Combines RuBP with CO2 to make 2 x GP
Describe the entire photosynthesis pathway.
LIGHT-DEPENDENT REACTION
• 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+)
LIGHT-INDEPENDENT REACTION
• 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.
Remember to practise drawing out the entire photosynthesis pathway and writing out all the equations.
Chapter 11 of textbook
Are the optimum conditions for photosynthesis the same in all plants?
No, they vary between plants species.
In general, what are the optimum conditions for photosynthesis?
1) High light intensity of a certain wavelength
2) Temperature around 25*C
3) Carbon dioxide around 0.4%
Why is a low light intensity rate-limiting in photosynthesis?
Light provides energy for the LDR, so the higher the intensity, the more energy it provides.
Which wavelengths of light do chlorophyll a, chlorophyll b and carotene absorb?
Red and blue (green is reflected)
Why do plants appear green?
The chlorophyll reflects green light only (it absorbs the rest).
Why is the wrong wavelength of light rate-limiting in photosynthesis?
The photosynthetic pigments (e.g. chlorophyll) can only absorb certain wavelengths of light.
Why is a too low or high temperature rate-limiting in photosynthesis?
LOW: • Enzymes (e.g. rubisco) become inactive HIGH: • Enzymes denature • Stomata close to prevent water loss, so CO2 cannot enter leaves
Why is a low CO2 concentration rate-limiting in photosynthesis?
CO2 is one of the reactants in photosynthesis, so it can limit the rate if there is an insufficient amount.
What proportion of the atmosphere does CO2 make up?
0.04%
Up to what concentration of CO2 does the rate of photosynthesis increase and why?
0.4% - beyond this the stomata start to close.
Why is a too low or high supply of water rate-limiting in photosynthesis?
LOW:
• Water is a reactant in photosynthesis, so it can limit the rate if there is an insufficient amount
HIGH:
• Soil becoming waterlogged stop the uptake of minerals required to make e.g. chlorophyll a
What are the 3 main limiting factors of photosynthesis?
• Light
• Temperature
• CO2
(• Water)
Is water usually considered a limiting factor in photosynthesis?
No, because by the time it becomes so low that photosynthesis is compromised, the plant would long be dying.
What is the common limiting factor for plants?
During the day: CO2
During the night: Light
What is the saturation point?
Where a factor is no longer limiting and something else has become rate-limiting.
Describe the graph for the rate of photosynthesis against a limiting factor.
- Steep at first, usually straight line
- Slowly plateaus
- Eventually is a horizontal straight line
Remember to revise rate-limiting factor graphs.
Pg 118 of revision guide
How do agricultural growers increase plant growth?
They use a glasshouse or polytunnels.
How do glasshouses manage the limiting factor of CO2?
CO2 is added to the air e.g. by burning a small amount of propane in a CO2 generator.
How do glasshouses manage the limiting factor of light?
- Light can get through the glass.
* Lamps provide light at night-time.
How do glasshouses manage the limiting factor of temperature?
- Glasshouses trap heat energy from sunlight, which warms the air.
- Heaters and cooling system, plus air circulation, can be used to maintain optimum temperature
Practice interpreting data on photosynthesis limiting-factors.
Pg 119 of revision guide
Why do plants contain multiple photosynthetic pigments?
Each one absorbs a different wavelength of light, so having many increases the range that can be absorbed.
Do plants only contain photosynthetic pigments?
No, they may also contain pigments for other roles, such as protecting leaves from excess.
Do all plants have the same pigments in their leaves?
No, they all have different types and proportions of pigments.
What technique can be used to investigate the pigments in a plant leaf?
Thin layer chromatography (TLC)
What does TLC stand for?
Thin layer chromatography
What are the parts of a thin layer chromatography set up?
- Mobile phase -> Liquid solvent in TLC
* Stationary phase -> Solid plate with a thin layer of gel on top in TLC
What is the mobile phase?
Where the molecules in TLC can move.
What is the stationary phase?
Where the molecules in TLC can’t move.
In TLC, what is the mobile phase?
A liquid solvent.
In TLC, what is the stationary phase?
Solid plate with a thin layer of gel on top.
e.g. glass with a layer of silica gel
Put simply, how does thin layer chromatography work?
- A sample of pigments is extracted from a plant’s leaves and put on a TLC plate
- The plate is placed vertically in a solvent, which moves up through the gel, carrying the pigments with it.
- Some pigments travel further than others, depending on their solubility, which separates them out.
- The pigments can be identified using their Rf value and comparing it with a database.
What is the Rf value of a pigment?
- The ratio of how far a pigment has travelled in chromatography relative to the solvent
- It is a decimal
- It can be used to identify the pigment
What is the equation for the Rf value of a pigment?
Rf = Distance travelled by spot / Distance travelled by solvent
How can a pigment in thin layer chromatography be identified?
Looking at the Rf value and comparing it to a database of Rf values.
Describe an experiment to compare the pigments in shade-tolerant and shade-intolerant plants.
Use thin layer chromatography (TLC):
1) Grind up several leaves from the shade-tolerant plant with some anhydrous sodium sulphate, then add a few drops of propanone.
2) Transfer the liquid to a test tube, add some petroleum ether and gently shake the tube. 2 layers will form. The top layer is the pigments mixed in with the petroleum ether.
3) Transfer some of the liquid from the top layer into the second test tube with some anhydrous sodium sulphate.
4) Draw a horizontal pencil line near the bottom of a TLC plate. Place a concentrated spot of the liquid from step 3 by adding several drops, allowing each to dry before adding the next. This is the point of origin.
5) When this is dry, put the plate into a small glass container with some prepared solvent (e.g. mix of propanone, cyclohexane and petroleum ether) so that the point of origin is just above the solvent line.
6) Put a lid on the container and leave to develop. As the solvent spreads up the plate, the pigments move with it, but at different rates, so they separate.
7) When the solvent almost reaches the top, take the plate out and mark the solvent front with a pencil. Leave to dry.
8) When the pigment spots appear, measure the distance the solvent front and each spot has travelled.
9) Calculate the Rf values for each pigment and identify each.
10) Repeat for the shade-intolerant plant and compare the pigments present.
(This is RP7)
In TLC, what is the point of origin?
The starting line on which the pigment mixture drop is placed to start with.
In TLC, what is the solvent front?
The further point that the solvent reaches.
Compare and explain the pigments in the leaves of shade-tolerant and shade-intolerant plants.
- Shade-tolerant plants possess a different proportion of photosynthetic pigments -> Allows the plant to make the best use of the light available to it
- Shade-tolerant plants possess a different proportion of non-photosynthetic pigments -> May produce certain pigments to protect the chloroplasts from brief exposure to higher light levels (since they are only adapted to low-light conditions)
What is dehydrogenase?
An enzyme that catalyses NADP being reduced to NADPH in the LDR of photosynthesis.
In the LDR, is NADP an electron acceptor or donor?
Acceptor - it is reduced.
What does dehydrogenase allow to happen?
LDR in photosynthesis
How can the activity of dehydrogenase be investigated?
- Add a redox indicator dye to extracts of chloroplasts
- Like NADP, the dye (e.g. DCPIP) acts as an electron acceptor and gets reduced by the dehydrogenase
- As the dye is reduced, a colour change is seen.
- Use a colorimeter to calculate how quickly this colour change occurs
What dye is usually used to investigate the activity of dehydrogenase?
DCPIP
What is DCPIP?
A redox indicator dye used to investigate the activity of dehydrogenase. It turns from blue to colourless when reduced.
(It essentially acts as NADP, except it changes colour when it accepts electrons)
What colour change is seen with DCPIP?
Turns from blue to colourless when it is reduced.
What is a colorimeter?
A device that measures how much light a solution absorbs when a light source is shone directly through it.
In an experiment, if DCPIP quickly turns colourless, what does this indicate?
A fast rate of photosynthesis.
Describe an experiment to investigate the effect of light intensity on dehydrogenase activity in extracts of chloroplasts.
1) Cut a few leaves into pieces. Remove any rough stalks.
2) Using a pestle and mortar, grind up the leaf pieces with some chilled isolation solution (a solution of sucrose, potassium chloride and phosphate buffer at pH 7). Filter the liquid you make into a beaker through a funnel lined with muslin cloth.
3) Transfer the liquid to centrifuge tunes and centrifuge them at high speeds for 10 minutes. This will cause the chloroplasts to gather at the bottom of each tube in a pellet.
4) Get rid of the liquid from the top of the tubes, leaving the pellet in the bottom.
5) Re-suspend the pellets in fresh, chilled isolation solution. This is your chloroplast extract. Store it on ice for the rest of the experiment.
6) Set up a colorimeter with a red filter and zero it using a cuvette containing the chloroplast extract and distilled water.
7) Set up a rest tube rack at a set distance from a bench lamp. Switch the lamp on.
8) Put a test tube in the rack, add a set volume of DCPIP. Mix the contents of the tube together.
9) Immediately take a sample of the mixture from the tube and add it to the clean cuvette. Then place the cuvette in your colorimeter and record the absorbance. Do this every 2 minutes for the next 10 minutes.
10) Repeat steps 7 to 9 for each distance under investigation.
11) Plot a graph of absorbance against time for each distance from the light source. Compare each graph.
What is contained in the isolation solution in the DCPIP experiment to investigate the activity of dehydrogenase?
- Sucrose
- Potassium chloride
- Phosphate buffet at pH 7
(NOTE: Remember to check the role of sucrose and potassium chloride)
What tubes could be used as a control in the DCPIP experiment to investigate the activity of dehydrogenase?
- Tube containing only DCPIP and chilled isolation solution (no chloroplast extract)
- Tube containing DCPIP and chloroplast extract, but it should be wrapped in tin foil (so no light reaches the contents of the tube)
No change in absorbance should be seen with either.
What are the two types of respiration?
- Aerobic
* Anaerobic
Compare aerobic and anaerobic respiration in terms of the amount of ATP produced.
Aerobic produces more ATP.
Compare briefly the stages of aerobic and anaerobic respiration.
Both start with the process of glycolysis, but the stages after differ.
What are the 4 stages of aerobic respiration?
1) Glycolysis
2) Link reaction
3) Krebs cycle
4) Oxidative phosphorylation
What are the 2 stages of anaerobic respiration?
1) Glycolysis
2) Fermentation
Where does glycolysis happen in respiration?
In the cytoplasm.
Describe the process of glycolysis in respiration.
1) Glucose is phosphorylated by the hydrolysis of two ATP molecules into ADP and Pi. The Pi’s join on to make phosphorylated glucose (glucose biphosphate).
2) The phosphorylated glucose is split into two triose phosphate molecules (TP).
3) Each TP molecule is oxidised using NAD, which becomes NADH. So in total, 2 NAD is used.
4) Each TP is converted into pyruvate, which regenerates two ATP molecules per TP. So in total, 4 ATP are produced.
Describe how ATP and NAD are used/produced in each stage of glycolysis.
How many are used/produced in net in total?
- Glucose -> Phosphorylated glucose (Uses 2 ATP)
- 2 x TP -> 2 x Pyruvate (Uses 2 NAD and produces 4 ATP)
- 2 ATP produced in net
- 2 NAD used in net
Describe in one sentence what happens in glycolysis in respiration.
Glucose is converted to two pyruvate molecules.
What happens to the pyruvate molecules produced in glycolysis?
They are actively transported out of the cytoplasm into the matrix of the mitochondria.
Where does the link reaction happen?
In the matrix of the mitochondria.
Describe in one sentence what happens in the link reaction.
A pyruvate molecule is converted to acetyl CoA.
Describe the link reaction in words.
- Pyruvate is oxidised to acetate by losing a carbon dioxide and two NAD molecules being reduced.
- Acetate combines with coenzyme A (CoA) to produce acetyl coenzyme A (acetyl CoA).
Describe how ATP and NAD are used/produced in each stage of the link reaction.
How many are used/produced in net in total?
• Pyruvate -> Acetate (1 NAD used)
- 1 NAD used in net
- No ATP is made or used in net
What is the name for CO₂ being lost from pyruvate in the link reaction?
Decarboxylation
What is the overall equation for the link reaction?
Pyruvate + NAD + CoA -> Acetyl CoA + NADH + CO₂
What must you remember about the link reaction relative to glycolysis?
It happens twice for every glucose molecule, since glycolysis produces two pyruvate molecules.
Where does the Krebs cycle take place?
In the matrix of the mitochondria.
Describe the Krebs cycle in words.
- Acetyl CoA (2C) joins onto a 4-carbon molecule (oxaloacetate), producing a 6-carbon molecule (citrate) while releasing CoA
- The 6-carbon citrate loses 1 CO₂ and 1 NAD is reduced to NADH, so it is converted into a 5-carbon compound
- The 5C compound loses 1 CO₂, 1 NAD is reduced to NADH, 1 ATP is produced, 1 FAD is reduced to FADH₂ and another NAD is reduced to NADH -> This produces a 4C compound (oxaloacetate)
- The cycle repeats
Describe how ATP, FAD and NAD are used/produced in each stage of the link reaction.
How many are used/produced in net in total?
- 6C -> 5C (1 NAD used)
- 5C -> 4C (2 NAD used, 1 FAD used, 1 ATP produced)
- 3 NAD used in net
- 1 FAD used in net
- 1 ATP produced in net
Describe in one sentence what happens in the Krebs cycle.
A series of oxidation-reduction reactions that take place in the matrix of mitochondria.
What must you remember about the Krebs cycle relative to glycolysis?
It happens twice for every glucose molecule, since glycolysis produces two pyruvate molecules, each of which enter the Krebs cycle as acetyl CoA.
What is the role of NAD in respiration?
It works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.
What is the significance of the Krebs cycle? (4)
- It breaks down macromolecules into smaller ones -> Pyruvate is broken down into CO₂
- It produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation
- It regenerates the 4C (oxaloacetate) molecule to combine with acetyl CoA, which would otherwise accumulate
- It is a source of intermediate compounds used by cells in the manufacture of other important substances, such as fatty acids, amino acids and chlorophyll.
Name all the products of the Krebs cycle and where they go.
- 1 CoA -> Reused in the next link reaction
- Oxaloacetate (4C) -> Regenerated for use in the next Krebs cycle
- 2 CO₂ -> Released as waste product
- 1 ATP -> Used for energy
- 3 NADH -> To oxidative phosphorylation
- 1 FADH₂ -> To oxidative phosphorylation
Where does oxidative phosphorylation take place?
Across the inner mitochondrial membrane.
Describe oxidative phosphorylation in words.
1) Hydrogen atoms are released from NADH and FADH₂ (as they’re oxidised to NAD and FAD).
2) The H atoms split into H⁺ and e⁻.
3) The electrons move down the electron transport chain made of electron carriers, losing energy at each carrier.
4) This energy is used to pump H⁺ from the mitochondrial matrix into the intermembrane space.
5) This forms an electrochemical gradient, which moves H⁺ back across the inner mitochondrial membrane and into the mitochondrial matrix (via ATP synthase. This movement drives the synthesis of ATP from ADP and Pi. This process is called chemiosmosis.
6) The electrons are released into the matrix of the mitochondrion at the end of the transport chain.
7) In the matrix, the H⁺, e⁻ and O₂ combine to form water. Oxygen is the final electron acceptor.
Describe oxidative phosphorylation in one sentence.
Energy carried by electrons from reduced coenzymes (NADH and FADH₂) is used to make ATP.
What happens to NAD and FADH₂ in oxidative phosphorylation?
They are oxidised to NAD and FAD.
What happens to the regenerated coenzymes after oxidative phosphorylation?
They return to the Krebs cycle.
What is the electron transport chain in respiration?
A series of electron carriers that move H⁺ ions across the inner mitochondrial membrane.
By what protein do H⁺ ions move from the intermembrane space to the matrix in oxidative phosphorylation? What does this do?
ATP synthase channel -> Uses the movement of H⁺ to drive the synthesis of ATP from ADP and Pi.
Describe the movement of H⁺ ions in oxidative phosphorylation.
They move using proton pumps into the intermembrane space and then return to the matrix through ATP synthase channels.
What two processes does oxidative phosphorylation involve?
- Electron transport chain
* Chemiosmosis
What is chemiosmosis?
The movement of ions down an electrochemical gradient through ATP synthase channels, which is used to produce ATP from ADP and Pi.
What is oxygen referred to in oxidative phosphorylation?
The final electron acceptor.
Remember to practise drawing out the diagram for oxidative phosphorylation.
Pg 124 of revision guide
What is the importance of oxygen in aerobic respiration?
- It is the final electron acceptor in oxidative phosphorylation, so it accepts the electrons and H⁺ ions
- Without its role, H⁺ and e⁻ would “back up” along the chain and the process would come to a halt
- In other words, there would not be any NAD or FAD left for glycolysis and the Krebs cycle to continue
Remember to practise drawing out the electron transport chain energy diagram.
Pg 291 of textbook
What is the advantage of the electron transport chain in respiration?
It allows energy to be released from the electrons in small amounts, so there is less wasted as heat.
How many ATP can be made from one glucose molecule in aerobic respiration?
32
How many ATP are produced per NADH and FADH₂ molecule in oxidative phosphorylation?
- NADH = 2.5 ATP
* FADH₂ = 1.5 ATP
Do the calculation to show how many ATP can be produced from 1 glucose molecule in aerobic respiration.
- Glycolysis -> 2 ATP (net)
- Glycolysis -> 2 NADH -> 2 x 2.5 = 5 ATP
- Link reaction (x 2) -> 2 NADH -> 2 x 2.5 = 5 ATP
- Krebs cycle (x 2) -> 2 ATP
- Krebs cycle (x 2) -> 6 NADH -> 6 x 2.5 = 15 ATP
- Krebs cycle (x 2) -> 2 FADH₂ -> 2 x 1.5 = 3 ATP
Total ATP = 32
What is it important to remember when calculating the number of ATP molecules produced per glucose molecule in aerobic respiration?
The link reaction and Krebs cycle happen twice per glucose molecule.
What is the effect of mitochondrial disease?
- Mitochondrial diseases affect the functioning of proteins in oxidative phosphorylation or the Krebs cycle, reducing ATP production
- This may cause the rate of anaerobic respiration to increase to try and make up for the shortage
- This results in lots of lactate being produced, which leads to muscle fatigue and weakness. Some also diffuses into the blood, leading to high lactate concentrations.
Describe the entire process of aerobic respiration in detail.
GLYCOLYSIS:
1) Glucose is phosphorylated by the hydrolysis of two ATP molecules into ADP and Pi. The Pi’s join on to make phosphorylated glucose (glucose biphosphate).
2) The phosphorylated glucose is split into two triose phosphate molecules (TP).
3) Each TP molecule is oxidised using NAD, which becomes NADH. So in total, 2 NAD is used.
4) Each TP is converted into pyruvate, which regenerates two ATP molecules per TP. So in total, 4 ATP are produced.
LINK REACTION:
• Pyruvate is oxidised to acetate by losing a carbon dioxide and two NAD molecules being reduced.
• Acetate combines with coenzyme A (CoA) to produce acetyl coenzyme A (acetyl CoA).
KREBS CYCLE:
1) Acetyl CoA (2C) joins onto a 4-carbon molecule (oxaloacetate), producing a 6-carbon molecule (citrate) while releasing CoA
2) The 6-carbon citrate loses 1 CO₂ and 1 NAD is reduced to NADH, so it is converted into a 5-carbon compound
3) The 5C compound loses 1 CO₂, 1 NAD is reduced to NADH, 1 ATP is produced, 1 FAD is reduced to FADH₂ and another NAD is reduced to NADH -> This produces a 4C compound (oxaloacetate)
4) The cycle repeats
OXIDATIVE PHOSPHORYLATION:
1) Hydrogen atoms are released from NADH and FADH₂ (as they’re oxidised to NAD and FAD).
2) The H atoms split into H⁺ and e⁻.
3) The electrons move down the electron transport chain made of electron carriers, losing energy at each carrier.
4) This energy is used to pump H⁺ from the mitochondrial matrix into the intermembrane space.
5) This forms an electrochemical gradient, which moves H⁺ back across the inner mitochondrial membrane and into the mitochondrial matrix (via ATP synthase. This movement drives the synthesis of ATP from ADP and Pi. This process is called chemiosmosis.
6) The electrons are released into the matrix of the mitochondrion at the end of the transport chain.
7) In the matrix, the H⁺, e⁻ and O₂ combine to form water. Oxygen is the final electron acceptor.
Which part of aerobic respiration do other respiratory substrates enter?
Krebs cycle
Describe how lipids can be used in respiration.
- Lipids hydrolysed to glycerol and fatty acids
- Glycerol -> Phosphorylated and converted into TP -> This enters the Krebs cycle
- Fatty acids -> Broken down into 2-carbon fragments -> Converted to acetyl CoA -> This enters the Krebs cycle
- The breakdown of fatty acids also releases many H atoms, which are used in oxidative phosphorylation
Why do fatty acids release more energy than the same mass of carbohydrates?
They release very many H atoms when broken down, which are used in oxidative phosphorylation to make ATP.
Describe how proteins can be used in respiration.
• Proteins hydrolysed to amino acids
• Amino groups are removed (deamination)
Where they enter the pathways depends on the number of carbons:
• 3 carbons -> Converted to pyruvate
• 4 or 5 carbons -> Enter elsewhere in the Krebs cycle
Why must anaerobic respiration happen in the absence of oxygen?
- Neither the Krebs cycle nor the electron transfer chain can continue because soon all the FAD and NAD will be reduced.
- So no FAD or NAD are available to take up the H⁺ produced during the Krebs cycle and so the enzymes stop working.
- This leaves only glycolysis as a potential source of energy.
(NOTE: Remember to check why anaerobic respiration cannot involve the link reaction or Krebs cycle)
What is the purpose of the second step of anaerobic respiration (fermentation)?
- It removes the pyruvate produced in glycolysis
- It regenerates NAD from NADH produced in glycolysis
This allows glycolysis to continue, so some ATP can be produced.
What is the name for the second stage of anaerobic respiration in plants and yeast?
Alcoholic fermentation
What is the name for the second stage of anaerobic respiration in animals?
Lactate fermentation
What is produced by anaerobic respiration in:
• Animals
• Plants and Yeast
- Animals -> Lactate
* Plants and Yeast -> Ethanol and CO₂
Describe the process of anaerobic respiration in animals.
- NADH is oxidised to NAD
* This converts pyruvate into lactate
What happens to the lactate produced in anaerobic respiration in animals?
It is oxidised back to pyruvate.
Describe the process of anaerobic respiration in plants and yeast.
- Pyruvate loses a CO₂ and NADH is oxidised to NAD
* This produces ethanol
Describe two ways of measuring the rate of respiration in organisms.
- Rate of CO₂ production
* Rate of O₂ consumption
How do yeast respire?
- When plenty of oxygen is available -> Aerobically
* When no oxygen is available -> Anaerobically
In respiration experiments involving yeast, how can you switch between aerobic and anaerobic respiration?
Placing a paraffin layer on the yeast solution stops oxygen reaching it.
Remember to revise yeast respiration experiments.
Pg 126 of revision guide
What equipment can be used to indicate the rate of aerobic respiration in a small living organism?
Respirometer
What small animal can be used in respiration experiments?
Pg 127 of revision guide
Describe the structure of a respirometer.
- 2 closed test tubes connected by a manometer (U-shaped capillary tube filled with coloured liquid)
- KOH solution at the bottom of each test tube
- Syringe at top of one of the test tubes
- Woodlice on gauze in this test tube
- Tap on top of other test tube
- Glass beads on gauze in this test tube
Describe an experiment to investigate the rate of respiration in woodlice.
1) Set up a respirometer in a water bath at 15°C (optimum for yeast):
• 2 closed test tubes connected by a manometer (U-shaped capillary tube filled with coloured liquid)
• KOH solution at the bottom of each test tube
• Syringe connected to one of the test tubes
• Woodlice on gauze in this test tube
• Tap on top of other test tube
• Glass beads on gauze in this test tube
2) Tap is opened and the syringe is removed for 10 minutes to allow the apparatus to equilibrate and the respiration rate to stabilise
3) After this, the tap is closed and the syringe is attached
4) The syringe is used to reset the manometer, so the ends of the fluid are at the same height at either side of the U
6) The volume on the syringe is recorded
7) As the experiment is run, the liquid will move up the U-tube on the side of the woodlice
8) At the end of a set time period, the syringe is used to reset the manometer and the volume on the syringe is recorded.
9) The difference in the two syringe readings is the volume of O₂ used in that time (since any CO₂ is absorbed by the KOH).
10) Repeat the experiment and calculate a mean rate of oxygen consumption.
What is the purpose of the second tube in a respirometer?
It acts as a control.
Why are glass beads placed in the control tube of a respirometer when investigating woodlice respiration?
It acts as a substitute for the woodlice (as a control).
What is the liquid used in a respirometer to absorb CO₂?
Potassium hydroxide solution (KOH)
What indicates the rate of aerobic and anaerobic respiration in yeast?
The rate of CO₂ production.
