Photosynthesis Flashcards
What is photosynthesis
- the process by which energy (in the form of light from the sun) is used to build complex organic molecules
Word equation for photosynthesis
carbon dioxide + water = glucose + oxygen
What are autotrophs
Organisms that can photosynthesis to produce their own complex molecules
What are heterotrophs
have to obtain complex organic molecules by eating other organisms
Key structural features of chloroplasts
- double membrane
- very flat- increases surface area to absorb light
- thylakoids
- grana/ granum
- lamellae
- stroma
What is a granum
A stack of thylakoids (fluid filled sacs formed by membranes)
What are lamellae
- join grana together
- bits of thylakoid membranes, membranous channels
What is the stroma
- the fluid enclosed in a chloroplast
- site of many chemical reactions
What is chlorophyll
- pigment molecule that absorb different wavelengths of light
- absorbs red and blue, reflects green
What are 4 main photosynthetic pigments
- chlorophyll A
- chlorophyll B
- carotenoids
- xanthophyll
Differences in roles of photosynthetic pigments
- chlorophyll A is in the reaction centre where photosynthesis occurs
- chlorophyll B, carotenoids, xanthophyll embedded in thylakoid membranes, joined to proteins, form light harvesting system
What is a photosystem
-the light harvesting system and reaction centre
- proteins and pigments collectively
Summary of the light dependent stage
- occurs in thylakoid membranes
- energy from sunlight is absorbed and used to form ATP
- hydrogen from water is used to reduce NADP
- Produces NADPH, ATP, oxygen
non-cyclic phosphorylation
- involves PSI + PSII
- electrons travel from PSII to PSI, losing electrons as they do so
- electrons lost from PSII are replaced by photolysis
- electrons from PSI pass down electron transport chain, form reduced NADP
- electrons lost from PSI replaced with electrons from PSII
What is photolysis, what is the equation
- light energy is used to split water
- water => hydrogen + electrons + oxygen
Cyclic phosphorylation
- involves PSI only
- electrons leaving PSI return via electron carriers
- ATP produced
What cycle is involved in the light independent stage
Calvin cycle
Where does the light independent stage occur
Stroma
3 key molecules involved in the light independent stage
- Triose phosphate (TP)
- Ribulose phosphate (RuBp)
- Glycerate 3 phosphate (GP)
Overall products of the light independent stage
- ADP + P
- NADP
- carbs/ sugars/ amino acids/ lipids
- regeneration of RuBp
Factors affecting photosynthesis
- light intensity
- carbon dioxide concentration
- temperature
How does light intensity affect photosynthesis
- If light intensity is high, more ATP and NADPH are produced in the light dependent stage, so more ATP and NADPH enter the calvin cycle
- Results in high GP, low TP and RuBp
How does carbon dioxide concentration affects photosynthesis
- increases the rate of carbon fixation in the Calvin cycle
- results in less GP , less TP, increases RuBp
How does temperature affect photosynthesis
- at high temperatures, enzymes may denature, stomata may close causing less photosynthesis as less CO2, potential damage to all the membranes, resulting in less photosynthesis
