Photosynthesis II: The Calvin Cycle and Carbon Fixation

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light independent reactions

reactions that produce sugars without light

Calvin Cycle

pathway converting co2 into sugars

3-phosphoglyceric acid

first product of the Calvin cycle

C3 pathway

pathway characterized by 3-carbon sugar fixation

RuBP

5-carbon sugar phosphate substrate in Calvin cycle

RuBisCO

enzyme catalyzing co2 fixation in Calvin cycle

Glyceraldehyde-3-phosphate (GA3P)

sugar phosphate produced in the Calvin cycle

ATP and NADPH

energy carriers used in Calvin cycle

Photosynthetic efficiency

conversion rate of light energy to chemical energy

photorespiration

process reducing photosynthetic efficiency under certain conditions

C4 pathway

photosynthesis pathway minimizing photorespiration

single-cell C4 pathway

C4 pathway occurring in single-celled organisms

CAM plants

plants that fix carbon dioxide at night to reduce water loss during the day

light reactions

initial phase using light to produce ATP and NADPH for the Calvin cycle

stroma

fluid-filled space where Calvin cycle occurs

thylakoids

membrane structures where light reactions occur and chlorophyll pigments are located.

14CO2

radioactive carbon used in Calvin’s experiments

Melvin Calvin

Nobel laureate who discovered the Calvin cycle

efficiency of converting light energy

27% efficiency in photosynthesis

energy conversion into biomass

4-6% efficiency in biomass productions

solar panels efficiency

10-20% efficiency in converting light to electricity

ATP:NADPH ratio

Calvin cycle requires 18 ATP to 12 NADPH

RuBisCO

key enzyme fixing carbon in Calvin cycle

photorespiration

process reducing co2 fixation efficiency in plants

carboxylase

RuBisCO function adding carbon from CO2

oxygenase

RuBisCO function adding oxygen to molecules

affinity for CO2

RuBisCO’s weak binding leads to photorespiration

high light conditions

increased o2 and decreased co2 affect RuBisCO

C3 plants

plants primarily using Calvin cycle for carbon fixation

stomata

leaf openings regulating gas exchange and water loss

stromules

chloroplast extensions aiding co2 recapture

PEP carboxylase (PEPC) in C4

enzyme fixing co2 in C4 pathway

oxaloacetate (OAA)

first product of co2 fixation in c4 plants

malate

converted from OAA, moves to bundle sheath cells

bundle sheath cells

cells where ci2 enters Calvin cycle in C4 plants

Kranz anatomy

distinctive leaf structure in C4 plants for efficiency

C4 pathway

alternative carbon fixation pathway in some plants

carbon gain

net increase in carbon through photosynthesis

carbon loss

reduction in carbon due to photorespiration

refixation

process of recapturing co2 from photorespiration

internal co2 concentration

co2 levels inside leaves affecting photosynthesis

C4 plants

plants with enhanced efficiency over C3 plants

decarboxylation

process of removing co2 from malate in C4 pathway

plasmodesmata

channels connecting plant cells for substance transport

C4 plants thrive in which environment?

hot, dry climates

photosynthetic rate

rate of converting co2 to glucose

RuBisCO

enzyme that catalyzes CO2 fixation

oligocene

period when C4 plants appeared

convergent evolution

independent evolution of similar traits

oxaloacetate (OAA)

first product in C4 photosynthesis pathway

Kranz anatomy

specialized leaf structure in C4 plants

Single-cell C4

C4 photosynthesis in single mesophyll cells.

Temporal separation

Different timing for C4 and Calvin cycle.

Crassulacean acid metabolism (CAM)

Photosynthesis process in succulents at night.

PEP carboxylase (PEPC)

Enzyme fixing CO2 in CAM plants.

Malic acid

Storage form of CO2 in CAM vacuoles

Bundle sheath cells

Cells where Calvin cycle occurs in C4 plants

Mesophyll cells

Cells where C4 pathway occurs in C4 plants

Stomatal closure

Prevents water loss during photosynthesis

Cyclic electron flow

Process enhancing energy generation in photosynthesis

Spatial separation

C4 pathway and Calvin cycle in different cells.

Calvin cycle

Pathway converting CO2 into glucose.

Bicarbonate ion (HCO3-)

Reactant for CO2 fixation in CAM plants.

Malate

Intermediate product in C4 and CAM pathways.

Vacuole

Storage site for malic acid in CAM plants.

Evolutionary innovations

Adaptations improving photosynthesis efficiency.

Water efficiency

C4 plants use less water than C3 plants.

Light Reactions

Use light energy and water (H₂O) to produce ATP and NADPH.

Calvin Cycle (Dark Reactions):

Uses ATP and NADPH to produce simple sugar phosphates.

where do the light-independent reactions take place?

in the stroma, outside the thylakoids

who is the Calvin cycle named after?

Named after Melvin Calvin, Andrew Benson, and James Bassham, who traced the pathway of CO₂ conversion to sugar using radioactive CO₂ in algae

what was Calvin experiment?

Used photosynthetic algae exposed to radioactive CO₂.
Tools: Algae, light source, alcohol, and "The Lollipop Apparatus."

what is the first product of the Calvin cycle?

The first product of the Calvin Cycle is a 3-carbon compound: 3-phosphoglyceric acid (3PGA).

why is in called the C3 pathway?

Calvin cycle, The first product of the Calvin Cycle is a 3-carbon compound: 3-phosphoglyceric acid (3PGA).