Photosynthesis In Plants Flashcards
What is the equation for photosynthesis? (Word + symbol)
Carbon dioxide + water = glucose + oxygen
6CO2 + 6H2O = C6H12O6 - 6O2
== light energy + chlorophyll
What does the chloroplast contain?
-Outer and inner membrane (chloroplast envelope)
-Granum (a system of membranes arranged in stacks)
-Thylakoid (the membrane that stacks to make granum, where the green pigment is found)
-Lamellae (join the grana together, act as a skeleton within the chloroplast)
-Stroma (a matrix surrounding the membrane stacks, contains all enzymes needed to complete the process of photosynthesis)
What pigments make up chlorophyll and what colour are they?
Chlorophyll A - blue green
Chlorophyll B - yellow green
Carotenoids - Orange carotene and yellow xanthophyll
Phaophytin - grey
What is the absorption spectrum?
Describes the range of the amount of light of different wavelengths that a photosynthetic pigment absorbs, usually represented as a graph.
You can compare rate of photosynthesis with wavelength of light, first done by T.W Engelmann in the late 1800s. This resulted in the action spectrum.
What is the action spectrum?
A way of demonstrating the rate of photosynthesis against the wavelength of light
What is the Rf value and how do you calculate it?
The ratio of the distance travelled by the pigment to the distance travelled by the solvent alone
Rf value = distance travelled by solute (photosynthetic pigment) / distance travelled by solvent
What is the difference between photosystem I and photosystem II?
They contain different pigments so absorb different wavelengths of light.
Where does the light dependent reaction take place?
In the thylakoid membranes
What are the two main functions of the light dependent reaction?
To split water molecules (photolysis) to provide hydrogen ions to reduce carbon dioxide and produce carbohydrates in the light independent stage
To produce ATP which is needed to supply the energy to produce those carbohydrates
What is a photon?
A small unit of light
What processes occur in the light dependent reaction and where does it occur?
Cyclic and non cyclic phosphorylation
Occurs in the thylakoid membrane
What process occurs in the light independent reaction and where does it occur?
The Calvin cycle
Occurs in the stroma
Cyclic phosphorylation
Photon hits a chlorophyll (PS1) and energy is transferred to elections making them excited. Leaves PS1 and is accepted by an electron acceptor and passed along the electron transport chain to produce ATP. It then returns to PS1 and starts again.
Non cyclic phosphorylation
Photons hit the chlorophyll (PSII) and the electron gets excited meaning it leaves the chlorophyll and is picked up by an electron acceptor. It is then passed along the electron transport chain and goes to PS1 to replace the lost electrons from reduction of NADP for the light independent reaction. This leaves PSII unstable. PSII then gains an electron from photolysis.
What is the light independent reaction
The Calvin cycle
What is the Calvin cycle?
CO2 combines with ribulose biphosphate (RuBP) (5C), it then goes through the rate limiting enzyme RUBISCO resulting in a highly unstable 6C compound which immediately splits into 2 molecules of GP (3C compounds). This is then reduced (a hydrogen is added) forming 2 molecules of GALP (3C). The hydrogen comes from reduced NADP and the energy required comes from ATP. 1/6 reactions are synthesised into glucose and 5/6 replace RuBP and the cycle restarts.
What is the product GALP used for
-Production of glucose (gluconeogenesis)
-Provides energy for cell functions
-Converted to acetyl coenzyme A to synthesise fatty acids
What is a limiting factor?
A factor that affects the plants ability to photosynthesise
What are the 3 main limiting factors of photosynthesis
-Light
-Carbon dioxide
-Temperature
Light as a limiting factor
Amount of light available affects the amount of chlorophyll excited and therefore the amount of NADP and ATP produced. More NADP and ATP means reactions of the light independent stage can progress at their maximum rate.
Carbon dioxide as a limiting factor
If there is not enough CO2 available for the Calvin cycle, the reactions can’t progress at their maximum rate.
Temperature as a limiting factor
Many of the reactions are controlled by enzymes and therefore are sensitive to temperature.
