Photosynthesis Flashcards
Where does photosynthesis take place? Describe this organelle.
Chloroplasts - small, flattened organelles with a double membrane (chloroplast envelope). Thylakoids are stacked up into structures callled grana. The grana are linked together by bits of thylakoid membrane called lamellae. Within the inner membrane are the stroma which contain enzymes, sugars and organic acids. Starch grains produced by photosynthesis are stored in the stroma.
How do chloroplasts absorb light?
Chloroplasts contain photosynthetic pigments, these are coloured substances that absorb the light energy needed for photosynthesis. The pigments are found in the thylakoid membranes (attached to proteins). The protein and pigment is called a photosystem. There are two types of photosystem (I and II).
What is a coenzyme?
A molecule that aids the function of an enzyme. They work by transferring a chemical group from one molecule to another.
What coenzyme is used in photosynthesis?
NADP - transfers hydrogen from one molecule to another - this means it can reduce or oxidise a molecule.
What are the 2 stages of photosynthesis?
- Light dependent reaction
2. Light independent reaction (Calvin cycle)
What happens in the light- dependent reaction?
Light energy absorbed by the photosystems is used for:
- Making ATP from ADP and Pi (photophosphorylation)
- Making NADPH from NADP
Splitting water into protons (H+) (photolysis)
Name the two types of photophosphorylation?
Cylic and non-cyclic
What are the products of non-cyclic photophosphorylation?`
Produces ATP, NADPH and O2.
What happens in non-cyclic photophosphorylation?
- Light energy excites electrons in the chlorophyll. Electrons move to a higher energy level and move along the electron transport chain.
- Photolysis pf water produces protons, electrons and oxygen.
- Energy from the excited electrons is used to transport H+ into the thylakoid so there is a high conentration. Proton gradient formed. Protons move down gradient, into the stroma, via ATP synthase. The energy from this movement combines ADP and Pi to form ATP.
- Energy from excited electrons generates NADPH
What happens in cyclic photophosphorylation?
Produces ATP but only uses one photosystem. The electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to photosystem via electron carriers. The electrons therefore are recycled and can repeatedly flow throught the photosystem. This doesnt produce any NADPH or oxygen.
What happens in the light independent reaction?
Calvin Cycle - occurs in the stroma of chloroplasts. Makes TP from CO2 and RuBP.
What are the 3 stages of the Calvin cycle?
- Formation of GP - CO2 combines with RuBP to give an unstabe 6 carbon compound which quickly breaks down into two 3 carbon compounds (GP). Rubisco catalyses this reaction.
- Formation of TP - GP is reduced to a different 3 carbon compound (TP). ATP (from LDR) provides the energy to do this. H+ from NADPH are used.
- Regeneration of RuBP - uses the rest of ATP produced by LDR
What organic substances can be produced following Calvin Cycle?
Carbohydrates - made from two TP molecules and larger carbohydrates are made by joining hexose sugars together.
Lipids - made using glycerol (which is synthesised from TP and fatty acids)
Proteins - some amino acids are made from GP which are joined together to make proteins.
What are the optimum conditions for photosynthesis?
- High light intensity of a certain wavelength
- Temperature around 25degrees
- Carbon dioxide at 0.4%
- Water
Explain the limiting factors of photosynthesis.
- Light intensity - more energy provided from higher intensities
- Temperature - enzyme activity ( temp too low, inactive - temp to high, denature)
- Carbon dioxide - stomata close when concentration is too high
