C1.3 Photosynthesis and light

Light dependent reaction

Light energy splits water into oxygen and H+ ions and electrons. Oxygen released as waste

Light independent reactions

Carbon dioxide combines with H+ to form glucose

Why do different chloroplast give different amounts of photosynthesis

They have different photosynthetic pigments so absorb light at different wavelengths

Draw the absorption spectrum of chlorophyll a, b and the action spectra

Chlorophyll a - peaks at 400 and 700

Chlorophyll b - peaks at 500 and 650

The first peak in a and b should be higher than the second

Thylakoids

Form stacks (grana), ETC is here, thylakoid membrane holds pigments

Photosystems

Molecular arrays of chlorophyll pigments that can generate and emit excited electrons

Stroma

Sight of light independent reaction (full of enzymes), Calvin cycle is here

Lumen

Inside a thylakoid

How does temp affect rate of photosynthesis?

As temp increases, rate increases due to more KE so MSC. Above 35 degrees - denture reaction slows and stops

How does light intensity affect rate of photosynthesis?

As light intensity increases, rate increases, then plateaus when CO2 conc or temp become limiting

How does CO2 concentration affect rate of photosynthesis?

As CO2 conc increases, rate increases since more conc = more collisions, then plateaus when light intensity or temp become limiting

Primary reaction centre

Chlorophyll molecule at the centre of the photosystem array (p680 or p700). It excites electrons

The ETC (in chloroplasts)

Light hits pigments in PS2, exciting a pair of electrons, which are released to a higher energy level.electrons are ejected by primary reaction centre. Loss of electrons causes water to split (photolysis). Electrons flow through ETC, energy is used to pump H+ from stroma to lumen, generating a chemical gradient. 2 electrons from PS1 and an H+ ion reduce NADP+ to NADPH. NADPH carries the hydrogen into light independent reactions.

Non-cyclic phosphorylation

H+ ions from lumen chemiosmose via ATP synthase

Cyclic phosphorylation

Only occurs at PS1 (p700). Some electrons do not have the energy to be ejected so fall back down within the molecular array transferring energy into the ETC

What is the final electron acceptor in the ETC in chloroplasts

NADP+

Chemiosmosis

Coupling of ATP synthesis to the electron transport and proton movement

Process of the Calvin cycle

RuBP undergoes carboxylation with CO2 facilitated by enzyme rubisco. This creates unstable 6C complex that splits into 2 3C compounds called GP. GP is converted to TP by phosphorylation (ATP → ADP) and reduction (NADP+ → NADPH). Some GPs are taken before this to form amino acids or fatty acids. Some TP are taken to form heroes sugars, others are then used to regenerate RuBP (ATP→ADP)

Products of the Calvin cycle

Carbohydrates, amino acids, fatty acids, nucleic acids, RuBP