3.2 Flashcards
What is an absorption spectra
A graph which shows how much light a particular pigment absorbs (doesn’t say whether that wavelength is actually used in photosynthesis)
What are the 3 families of pigments
- Chlorophyll (a and b)
- carotenoids
- xanthophylls
Which regions to chlorophyll a and b mainly absorb light
red and blue-violent regions, so they reflect green
How does the absorption spectra work
The different pigments can be shown to absorb different wavelengths of light by making separate solutions of each and shining light through them
What is the action spectra
A graph which shows the rate of photosynthesis at different wavelengths of light
How does the action spectra work
The amount of carbohydrate synthesised or oxygen produces by the plant is exposed to different wavelengths of light
There is a close correlation between action and absorption spectra (action above absorption line). What does this suggest?
That the wavelengths of light absorbed by the pigments are used in photosynthesis.
what is the Calvin cycle
The third biochemical step and occurs in the stroma of chloroplasts.
What happens in the calvin cycle
The ATP and reduced NADP from the light dependent stage are used here. ATP used as the energy store and redNADP provides the reducing power to reduce CO2, and fix carbon into carbohydrate.
What happens to RuBP in the calvin cycle
RuBP combines with CO2 to form an unstable 6C compound. Catalysed by enzyme rubisco
What happens to GP in the calvin cycle
The 6C compound splits into GP, which is phosphorylated by ATP and reduced by redNADP to form TP
What happens to TP in the calvin cycle
Some of the TP formed can be built into glucose phosphate then starch by condensation reaction. Most TP formed enters a series of reactions driven by ATP which regenerates RuBP.
What is the point of the calvin cycle
The starting point for making all organic substances needed by the plant - TP and GP are converted into useful organic substances like carbs, lipids and proteins.
How does TP form carbs like hexose sugars/glucose
Formed by joining 2 TP molecules together
How does TP and GP form triglycerides
Triglycerides are composed of glycerol and fatty acids. Glycerol synthesised from TP, and fatty acids from GP
What was the experiment to investigate the sequence of events in the calvin cycle
- Alga Chlorella was exposed to 14CO2.
- After time intervals of 5 and 30 seconds, a sample of algae was added to hot ethanol to stop enzyme reactions in the cells.
- The radioactive compounds were separated by paper chromatography.
Why was GP the most present in the autoradiograph analysis
because formed first in calvin cycle
How is optimal photosynthesis achieved
Light intensity, temperature and CO2 concentration must all be optimal
How does light intensity affect photosynthesis
As light intensity increases, the rate of photosynthesis increases until the saturation point is reached.
What happens after the saturation point is reached
Beyond the saturation point, light intensity won’t increase the rate of photosynthesis so another factor like CO2 concentration has become limiting.
What does the law of limiting factors state
When a chemical process is affected by more than one factor, its rate is limited by that factor which is nearest its minimum value. If the value of this factor is increased, then the rate will increase until some other factor becomes limiting.
Investigation for the effect of light on rate of photosynthesis
-Immobilised algae, bathed in hydrogen carbonate indicator, can be used to determine the rate of photosynthesis.
-The rate of photosynthesis is difficult to measure directly, but there’s a direct correlation between the rate of photosynthesis and rate at which carbon is fixed into carbohydrate.
-As CO2 is removed, pH of indicator will increase, causing a colour change
What colour does the hydrogen carbonate indicator change if the rate of photosynthesis is LOWER than rate of respiration
Yellow (high CO2)
What colour does the hydrogen carbonate indicator change if rate of photosynthesis and respiration is equal (compensation point)
Red (atmospheric CO2 level)
What colour does the hydrogen carbonate indicator change if rate of photosynthesis is higher than the rate if respiration (Co2 concentration decreases and pH increases)
Purple (low CO2)
