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.
