3B - Photosynthesis Flashcards
What happens to light energy that hits the leaf but is not absorbed?
Light that is not absorbed by pigments is either transmitted right through the plant or reflected (green light)
Compare the absorption spectra of chlorophyll a and b and carotenoids compared to the action spectrum for photosynthesis.
When comparing the absorption spectra of the different pigments to the action spectrum for photosynthesis it is clear that the wavelengths of higher absorption show a higher level of photosynthesis. Eg red and blue wavelengths. Carotenoids extend the range of wavelengths that can be absorbed.
What happens in the light stage of photosynthesis?
The electrons that have been absorbed by the chlorophyll will provide energy to be:
• Transfer through the electron transport chain and release energy to allow the enzyme ATP synthase generate ATP.
• Energy is used for photolysis where water is split into oxygen (which is evolved) and hydrogen, which is transferred to the coenzyme NADP (making NADPH).
What can glucose be used for after it has been synthesised?
Glucose may be used as a respiratory substrate, be synthesised into starch or cellulose or pass to other biosynthetic pathways. These other biosynthetic pathways can lead to the formation of a variety of metabolites such as DNA, protein and fat.
What happens to the light energy that is absorbed by plant pigments?
Some of the light energy is absorbed by the photosynthetic pigments to either generate ATP or be used in photolysis to split water.
What are the different pigments and what type of graph can be used to compare them?
Different pigments include chlorophyll a and b and carotenoids. They can be studied using an absorption spectrum graph as each pigment absorbed a different range of wavelengths of light.
What happens when the pigments absorb the light energy?
Absorbed energy excites electrons in the pigment molecules. Carotenoids extend the ranges of wavelengths that can absorb light but they must pass their energy to chlorophyll for photosynthesis. These electrons will then be transferred and used in the light stage.
What happens in the Carbon Fixation stage of photosynthesis (Calvin cycle)?
In the carbon fixation stage (Calvin cycle) the enzyme RuBisCO fixes carbon dioxide by attaching it to ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3PG). The 3PG is phosphorylated by ATP and combined with hydrogen from NADPH to form glyceraldehyde-3-phosphate (G3P). The G3P is used to regenerate RuBP and for the synthesis of glucose.
