17.3 Photosynthesis Flashcards
Define an autotroph.
Organisms capable of synthesising their own organic compounds from inorganic ones
What do you call organisms that can photosynthesise?
Autotrophic
Give examples of autotrophic organisms.
Plants, algae
What are heterotrophic organisms?
Animals - Obtain organic molecules by consuming other organisms
State the WORD equation for photosynthesis and then state the SYMBOL equation for photosynthesis.
Carbon dioxide + water → glucose + oxygen
6CO2 + 6H20 → C6H12O6 + 6O2
What is the function of the network of membranes (thylakoids) inside the chloroplast?
Provide a large SA for maximum light absorption
Why are there different colour of pigments?
Each pigment absorbs specific wavelengths of light and reflects others
What are the 2 common pigments?
Chlorophyll a, primary pigment
Cholorophyll b, other pigment
Why do plants have different shades and colours of leaves?
They have a combination of pigments
Where is cholorophyll b and other pigments found?
Thylakoid membranes
What is the role of a light harvesting system?
Absorb different wavelengths of light and transfer the energy to the reaction centre, where photosynthetic reactions occur
What makes a photosystem?
Light harvesting system + reaction centre
What are the 2 stages of photosynthesis? Include a description.
- Light-dependent stage - energy from sunlight is absorbed and used to form ATP. H from water used to reduce coenzyme NADP into reduced NADP
- Light-independent stage - H from reduced NADP and CO2 is used to build organic molecules, e.g. glucose, supplied by energy from ATP
What are the photosystems involved in non-cyclic photophosphorylation? What wavelengths do they absorb?
PSII = 680 nm PSI = 700 nm
What are the 6 stages of non-cyclic photophosphorylation?
- Light absorbed excites electrons in reaction centres of photosystems
- Excited electrons are released from reaction centre of PSII and passed to ETC. ATP produced by chemiosmosis
- Electrons lost from PSII are replaced by electrons from photolysis
- Excited electrons are released from PSI, passed into ETC, and ATP is synthesised by chemiosmosis
- Electrons lost from PSI are replaced by electrons released from PSII
- Coenzyme NADP accepts electrons released from PSI and a H ion, to form NADPH
What is the function of NADPH?
Provides reducing power in production of organic molecules, e.g. in light-independent stage
What happens in cyclic photophosphorylation?
Electrons leaving PSI are returned back to PSI instead of used to form NADPH.
So PSI can still lead to production of ATP without electrons needed from PSII.
What are the 3 steps of cyclic photophosphorylation Type 1 Diabetic gave us?
- PSI electrons pass into carrier
- Electron is cycled back to PSI releasing energy
- Released energy is used to pump H ions into thylakoid space
Where does the Calvin cycle occur?
Stroma
What does the Calvin cycle use as raw material?
CO2
What are the 4 steps of Calvin cycle?
- CO2 enters spongy mesophyll through stomata by diffusion
- Carbon fixation - CO2 enters stroma and combines w/ 5-C RuBP, catalysed by RuBisCO
- 6-C unstable intermediate is produced, which instantly breaks down into 2 GP
- Each GP turns into TP, using H from NADPH for reduction
What molecules can be formed through the calvin cycle?
Amino acids, lipids, glucose
