Photosynthesis + Respiration Flashcards
Name the 2 processes within the light dependant stage and describe what each means?
Cyclic photophosphorylation and Non-cyclic photophosphorylation
Photophosphorylation means using energy from sunlight to add Phosphate to ADP.
Cyclic and non-cyclic refers to if the electrons return to where they started.
What is the names for reactions where electrons are lost? Gained? Hydrogen lost? Gained? Oxygen lost? Gained?
E lost= oxidation [OILRIG]
E gain= reduction [OILRIG]
H lost= oxidation [OILRIG]
H gain= reduction [OILRIG]
O2 lost= reduction
O2 gain= oxidation
Describe the process of events in cyclic phosphorylation.
In the thylakoid membrane, photons of light strike photosystem 1 (P700) and the energy is transferred via photosynthetic pigments to chlorophyll a.
The energy is used to excite a pair of electrons in chlorophyll a. The electrons pass to an ‘electron acceptor’ which is reduced (gains electrons) and the chlorophyll is oxidised (loses electrons).
The electrons pass through a series of electron carries through a series of REDOX reactions. As they do this, the electrons lose energy which is used to pump H+ ions into the thylakoid space.
The hydrogen ions then diffuse back into the stroma down their concentration gradient through a molecule called ATP synthase. The diffusion of H+ ions gives ATP synthase the energy to phosphorylate ADP into ATP.
The series of electron carriers is called an electron transport chain and at the end of the ETC the electrons return to chlorophyll a in photosystem 1 so cycle back to the beginning.
Describe the process of events in non-cyclic phosphorylation.
In non-cyclic phosphorylation, there are 2 photosystems involved PS1 (P700) and PS2 (P680)
When photons of light strike PS2 , electrons are excited which then leave and go to an electron acceptor. They pass down the ETC losing energy along the way to pump H+ into the thylakoid space to be used in chemiosmosis to make ATP.
At the end of the ETC, instead of returning to PS2 the electrons pass to PS1. Here they wait until photons of light strike PS1 and the electrons are excited again.
The electrons pass down a different ETC but instead of their energy being used to make ATP they are passed to the end of the chain to NADP.
Associated with PS2 is a group of molecules which break water molecules down when chlorophyll a has been oxidised.
When the water is split, 2 electrons replace those that PS2 lost earlier, 2 H+ join the electrons at the end of the ETC to reduce NADP into reduced NADP and 2 oxygen molecules bind together to form O2 which is released as a waste product.
Where does the light independent stage of photosynthesis take place?
The stroma within chloroplasts
Where does the light dependent reaction take place?
Thylakoid membrane within chloroplasts
What are the inputs and outputs for the light dependant reaction?
Input:
-light
-water
-ADP+P
-NADP
Output:
-Oxygen
-ATP
-reduced NADP
Name the 2 processes within the light dependant stage and describe what each means?
Cyclic photophosphorylation and Non-cyclic photophosphorylation
Photophosphorylation means using energy from sunlight to add Phosphate to ADP.
Cyclic and non-cyclic refers to if the electrons return to where they started
What is the purpose of the light independent reaction?
To produce organic molecules for building new biomass or for use in respiration by fixing carbons.
Define and describe the calvin cycle.
The reactions involved in the light independent stage of photosynthesis are called the Calvin cycle.
Step 1 = carbon fixation
-Each CO2 reacts with RuBP (5C) and this reaction is catalysed by RuBisCO and is called carbon fixation. the resulting 6C molecules are unstable so are broken down into two 3C molecules called GP.
Step 2 = reduction
-Each GP molecule is reduced into TP (3C) and the energy for this is provided by the conversion of ATP to ADP+P and the reducing power is provided by the conversion of reduced NADP to NADP. The ADP+P return to the light dependant stage to resynthesise and NADP returns to be reduced.
Step 3 = regeneration
-1/6 TP (3C) is removed from the calvin cycle and used in the formation of organic molecules such as glucose. 5/6 TP (3C) are used to regenerate RuBP (5C) [5x3C = 3x5C]
What are 5 molecules that TP can be used to make?
- Glucose so by extension fructose and sucrose
-Glycerol and fatty acids so by extension triglycerides
-Nucleotides so by extension ATP, DNA, RNA
-Amino acids so by extension proteins
List 5 factors that affect photosynthesis.
Temperature
-Light intensity
-CO2 availability
-Water availability
-Wavelength of light
Define what is meant by a limiting factor.
A condition that prevents the rate of a process from going higher
Explain why temperature can be a limiting factor for photosynthesis.
At temperatures below the optimum, the molecules lack kinetic energy so collisions are less frequent and the rate of reaction is slower.
At temperatures above the optimum, the enzymes can begin to denature as the active site changes shape and reactants are no longer complementary so can’t react.
Explain why light intensity can be a limiting factor for photosynthesis.
An increase in light intensity (of appropriate wavelengths) will increase the rate of photosynthesis as there will be more protons striking the photosystems.
Explain why CO2 can be a limiting factor for photosynthesis.
As CO2 is a reactant in photosynthesis, the more CO2 there is, the faster carbon fixation occurs.
Explain what you would use to measure the rate of photosynthesis in an experiment.
You would use a photosynthometer which is a piece of equipment that can measure volume of O2 or CO2 produced. It is a syringe attached to some tubing that connects to the plant.
Explain 4 additional things you would do when designing an experiment to measure rate of photosynthesis.
Add sodium hydrogen carbonate to the water in the test tube to provide CO2.
Keep a thermometer in the water to control temperature.
Wavelength of light can be controlled by filters.
Prior to experiment plants should be kept in the dark to ensure previous products have been used up
Define the terms: obligate anaerobe, obligate aerobe and facultative anaerobe.
Obligate anaerobe: an organism that cannot survive in the presence of oxygen
Obligate aerobe: an organism that can only survive in the presence of oxygen
Facultative anaerobe: an organisms that can synthesise ATP by aerobic respiration, but can switch to anaerobic respiration in the absence of oxygen. It can complete its full life cycle in either anaerobic or aerobic conditions.
Name the two types of anaerobic respiration and state the distinction between the two.
Alcoholic fermentation and lactate fermentation.
They are distinguished by the final product they form
Explain why you can’t respire aerobically without oxygen.
The ETC in oxidative phosphorylation can’t continue as oxygen is the final electron acceptor so without it the electrons have no where to go. Without an operational ETC, the hydrogen ion concentration gradient that ATP synthase relies on cannot be maintained so no ATP can be produced. Therefore no oxidative phosphorylation.
Additionally, it means that NAD and FAD are left in their reduced forms as there is nothing for them to donate electrons to. This means there is nothing to take away the H+ so therefore substrate phosphorylation can’t occur either.
What is the principle of anaerobic respiration?
To have a mechanism for regenerating NAD from reduced NAD without oxygen. This will allow some substrate phosphorylation to continue.
Describe what happens in lactate fermentation
Each pyruvate molecule accepts electrons and hydrogens from reduced NAD (NADH) to become lactate and this is catalysed by lactate dehydrogenase.
The NAD that is regenerated is used in glycolysis to allow it to continue so a net gain of 2 ATP can be produced through substrate level phosphorylation.
What is the overall reaction for lactate fermentation.
Glucose + 2ADP + 2P(i) -> 2 lactate + 2 ATP
Describe what happens in alcoholic fermentation
Each pyruvate molecule is converted into CO2 and ethanal and this is catalysed by pyruvate decarboxylase.
Each ethanal molecule accepts electrons and hydrogen from NADH to become ethanol and this is catalysed by alcohol dehydrogenase.
The NAD that is regenerated is used in glycolysis to allow it to continue so a net gain of 2 ATP can be produced through substrate level phosphorylation.
What is the overall reaction for ethanol fermentation
glucose + 2ADP + 2P(i) -> 2 Ethanol + 2CO2 + 2ATP
What is an advantage of anaerobic respiration over aerobic respiration?
Can occur without the presence of sufficient oxygen.
What is an advantage of aerobic respiration over anaerobic respiration?
Higher net yield of ATP (32 vs 2)
What is an advantage and disadvantage of lactate fermentation?
Lactate can be converted back to pyruvate when there is sufficient O2 so the molecule’s energy isn’t lost.
Lactate fermentation releases lots of H+ ions which makes the surroundings acidic and causes muscle fatigue.
What is an advantage and disadvantage of alcoholic fermentation?
The production of ethanol doesn’t become toxic as quickly so can be maintained for longer than lactate production.
Because alcoholic fermentation produces CO2 which is exhaled, it cannot be converted back to pyruvate.
How do you measure the rate of respiration in yeast?
Measure the volume increase or decrease in a closed system as gas is used or produced. This can be by bubbling into water.
Where does glycolysis take place and what is significant about this?
Glycolysis takes place in the cytoplasm of cells so can occur if mitochondria aren’t present
+ Summarise glycolysis in 3 steps then state how many ATP are produced in this stage.
1) 2 phosphates, from ATP converting to ADP, are added to glucose in order to convert it into an unstable 6C compound called hexose bisphosphate.
2) The hexose bisphosphate breaks down into 2 triose phosphate (TP) molecules that each have 3C.
3) The 2 TP molecules are oxidised into 2 pyruvate molecules. Hydrogens are removed from the TP and collected by 2 NAD molecules to become NADH. As hydrogens are removed this is called dehydrogenation.
Overall, what are the products of glycolysis and what happens to them?
2 pyruvate molecules which travel to the matrix of the mitochondria to take part in the link reaction.
2 NADH which delivers H+ and e- to the cristae of the inner membrane of the mitochondria to take part in oxidative phosphorylation.
2 ATP (4ATP -2ATP) which are used to power processes in the cell.
Summarise what happens to one pyruvate* in the link reaction (2 steps) and state where this occurs?
*this would happen twice per glucose molecule as 1 glucose produces 2 pyruvate.
The link reaction occurs in the matrix of the mitochondria
1) Carbon and O2 are removed from pyruvate to form one CO2 molecule (this is decarboxylation), Simultaneously, hydrogen is removed from pyruvate and collected by NAD to form NADH (this is dehydrogenation)
What is left after the decarboxylation and dehydrogenation only contains 2C and is called an acetyl group
2) This acetyl group is collected by a molecule called coenzyme A to form acetyl-coenzyme A and it carries the acetyl group until it takes part in the Kreb’s cycle.
OVERALL, what are the products of the link reaction and what happens to them?
2 acetyl groups which remains in the matrix until taking part in the Kreb’s cycle.
2 NADH which delivers H+ and e- to the cristae of the inner membrane of the mitochondria to take part in oxidative phosphorylation.
2 CO2 which is a waste product and leaves the mitochondrion and cell by simple diffusion.
Summarise what happens to one acetyl group* in the Kreb’s cycle and state where this occurs?
*this would happen twice per glucose molecule as 1 glucose produces 2 pyruvate
The Kreb’s cycle occurs in the matrix of the mitochondria.
1) The acetyl group (2C) from acetyl-coenzyme A reacts with oxaloacetate (4C) to form citrate (6C). The coenzyme A is free to collect another acetyl group from the link reaction.
2) the citrate undergoes oxidative decarboxylation, losing CO2 and Hydrogen which is taken up by NAD. This forms a 5C intermediate molecule.
3) this intermediate molecule is decarboxylated to produce CO2 and dehydrogenated in order to regenerate the oxaloacetate. This produces enough hydrogen to reduce 2 NAD and 1 FAD. This also releases enough energy to produce 1 ATP
OVERALL, what are the products of the Kreb’s reaction and what happens to them?
2 coenzyme A which are free to return to the link reaction
6 NADH which delivers H+ and e- to the cristae of the inner membrane of the mitochondria to take part in oxidative phosphorylation.
2 FADH2 which also delivers H+ and e- to the cristae of the inner membrane of the mitochondria to take part in oxidative phosphorylation.
4 CO2 which is a waste product and leaves the mitochondrion and cell by simple diffusion.
2 ATP which are used to power processes in the cell.
Define the term coenzyme and give 3 full examples from aerobic respiration.
Coenzymes are molecules that carry atoms from one reaction to another.
Coenzyme A carries an acetyl group
NAD carries hydrogen
FAD carries hydrogen
Define the term oxidative phosphorylation
The addition of a phosphate to ADP to make ATP when the energy to make this happen comes from the oxidation of NADH and FADH2.
What is the electron transport chain and describe how it works to facilitate chemiosmosis.
A series of proteins in the inner membrane of mitochondria.
The proteins (electron carriers) receive electrons from NADH and FADH2 and pass them down the chain to the next electron carrier via a series of REDOX reactions.
Describe how chemiosmosis works to facilitate ATP synthase.
As electrons are passed from one carrier to the next, energy is released which is used to pump H ions from the matrix into the intermembrane space.
The pumping of H+ ions into the intermembrane space generates a hydrogen ion concentration gradient. This causes hydrogen ions to pass back into the matrix through proteins called ATP synthase by facilitated diffusion.
Describe how ATP synthase resynthesises ATP.
When hydrogen ions pass back into the matrix through proteins called ATP synthase by facilitated diffusion, this causes the ATP synthase to spin. This pushes one part into another over and over again, each time pushing ADP + P together to form ATP.
What happens to the electrons at the end of the ETC? Why is this useful?
They join with oxygen and the H+ ions that have passed through ATP synthase to produce water. Therefore oxygen is the final electron acceptor.
This is useful as the reaction uses up the H+ ions in the matrix so helps to maintain the hydrogen gradient.
How much ATP does 1 NADH and 1 FADH2 produce?
NADH = 2.5
FADH2 = 1.5
Explain how many ATP are produced in oxidative phosphorylation from 1 glucose molecule.
28 ATP overall
This is because 1 glucose will produce 10 NADH and 2 FADH2.
As we know, 1 NADH produces 2.5 ATP and 1 FADH2 produces 1.5 ATP. So 10 x 2.5 = 25 and 2 x 1.5 = 3 and 25+ 3 = 28
Make 6 distinctions between chemiosmosis in chloroplasts and mitochondria.
-Location
-Source of electrons
-Source of H+
-Final electron acceptor
-Hydrogen ion concentration
-ATP production
-located in the thylakoid membrane vs located in cristae of the inner membrane
-Electrons sourced from photons exciting those in PS1 or from non-cyclic phosphorylation in PS2 vs from NADH and FADH2
-Hydrogen ions sourced from photolysis of water vs dehydrogenation during glycolysis, the link reaction and Kreb’s cycle
-Final electron acceptor of PS1 vs oxygen
-H+ gradient in thylakoid space into stroma vs intermembrane space into matrix
-ATP produced in photophosphorylation vs oxidative phosphorylation
What is meant by a respiratory substitute?
organic molecules that can be used in respiration to release energy used to make ATP.
List 3 respiratory substitutes and their RQ.
Carbohydrates = 1.0
Protein = 0.9
Lipids = 0.7
How do you calculate RQ?
CO2 produced/O2 consumed
How can scientists measure RQ and what is an issue with interpreting results?
They use a respirometer in order to measure RQ during a particular activity.
A common issue is that an RQ can be a mix of different molecule types e.g 0.9 could be a blend of lipids and carbohydrates as opposed to proteins.
Explain why anaerobic respiration does/ doesn’t affect RQ. State and explain an exception.
Anaerobic respiration doesn’t affect RQ as there is no O2 consumed.
However in yeast, the anaerobic respiration increases RQ as alcoholic fermentation produces CO2 but uses no O2.
Explain how a respirometer works and how this can be used to measure RQ.
A respirometer consists of a sealed chamber which can have soda lime present or not to absorb CO2. Over time the volume of gas in the chamber changes which can be measured by how far a droplet of coloured liquid moves up a glass tube.
This can be used to calculate RQ by comparing how far the droplet moves with soda lime present (just O2 consumed) and with soda lime absent (O2 consumed + CO2 produced). These measurements can be put into the equation:
Distance moved w soda lime (P) - distance moved w/o soda lime (A) / distance moved with soda lime (P)
or P-A / P =RQ
