Photosynthesis: Light-Dependent and Light-Independent Reactions

ATP

Adenosine triphosphate - source of energy in cells.

Compensation point

A level of light intensity at which the rate of photosynthesis is equal to the rate of respiration.

Thylakoid

The membrane stacked inside the chloroplast which contains photosynthetic pigments e.g. chlorophyll, electron carriers and ATP synthase for the LDR.

Photosystem

A protein and photosynthetic pigment in the thylakoid e.g. PSI and PSII.

Stroma

The gel-like substance inside a chloroplast which contains the necessary enzymes for the LIR.

Coenzyme

A molecule that aids the function of an enzyme e.g. NADP.

Reduction

Gains electrons / hydrogen or loses oxygen.

Oxidation

Lose electrons / hydrogen or gains oxygen.

NADP

Coenzyme used in photosynthesis which transfers hydrogens from LDR à LIR.

Light-dependent reaction (LDR)

First stage of photosynthesis. Process of absorbing light energy in the thylakoid to produce ATP, NADPH and oxygen from water.

Photoionisation

Exciting electrons in chlorophyll using light, causing them to leave the chlorophyll so it becomes ionised.

Photolysis

Splitting of water using light into protons and oxygen.

Non-cyclic photophosphorylation

Form of LDR which produces both ATP and NADPH and uses both PSI and PSII.

Cyclic photophosphorylation

Form of LDR which produces small amounts of ATP, does not produce NADPH and only uses PSI.

Electron transport chain

A chain of protein electron carriers in a membrane through which excited electrons flow.

Chemiosmosis / chemiosmotic theory

Process of electrons flowing down an electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis.

Light-independent reaction (LIR)

AKA Calvin cycle. Second stage of photosynthesis occurring in the stroma which uses products from LDR and CO2 to make glucose.

Rubisco

Enzyme involved in LIR which catalyses reaction of rubisco and CO2.

Limiting factor

A variable that can slow down the rate of reaction.

Saturation point

Where a factor is no longer limiting the reaction - something else has become the limiting factor.

Mobile phase

Where molecules can move in chromatography i.e. the liquid solvent used.

Stationary phase

Where molecules cannot move in chromatography i.e. silica gel, chromatography paper or glass plate.

Rf value

The distance a substance has moved through stationary phase in relation to the solvent.

Redox indicator dye

Acts as an electron acceptor - as it is reduced, a colour change is seen.

Colorimeter

Apparatus that measures how much light a solution absorbs.

Proton Gradient

Difference in proton concentration across a membrane.

ATP Synthase

Enzyme that synthesizes ATP using proton gradient.

Photophosphorylation

ATP production using light energy during photosynthesis.

Chemiosmosis

Process of ATP synthesis driven by proton movement.

PSI

Photosystem I, absorbs light to excite electrons.

NADPH

Reduced form of NADP, used in Calvin cycle.

Oxygen By-product

Oxygen released during photolysis of water.

Non-cyclic Photophosphorylation

Produces ATP, NADPH, and oxygen using both photosystems.

Cyclic Photophosphorylation

Produces only ATP using PSI, no NADPH or oxygen.

Chloroplast Structure

Adapted for light capture and photosynthesis.

Ribulose Bisphosphate (RuBP)

5-carbon compound that reacts with CO2 in Calvin cycle.

Glycerate-3-Phosphate (GP)

3-carbon compound produced from RuBP and CO2.

Triose Phosphate (TP)

3-carbon compound formed from GP, used in synthesis.

Calvin Cycle

Light-independent reactions producing organic compounds.

Organic Substances

Products like glucose, sucrose, and amino acids.

Factors Limiting Photosynthesis

Conditions affecting the rate of photosynthesis.

Photosynthometer

Device measuring the rate of photosynthesis.

Potassium Hydrogencarbonate

Provides CO2 source for photosynthesis experiments.

Light Intensity

Amount of light affecting photosynthesis rate.

Dry Mass Increase

Measurement of biomass growth in plants.

ATP Requirement

18 ATP needed for 6 turns of Calvin cycle.

NADP Regeneration

Reforming NADP for continuous Calvin cycle operation.

Enzyme Catalysis

Accelerates chemical reactions in photosynthesis.

Surface Area of Thylakoids

Maximizes chlorophyll and enzyme attachment.

Grana Membranes

Site of ATP synthesis and proton gradient establishment.

Optimum light intensity

Higher intensity increases photosynthesis rate.

Optimum wavelength of light

Chlorophyll absorbs red and blue light effectively.

Optimum temperature

Ideal temperature for photosynthesis is 25°C.

Enzyme denaturation

Occurs above 45°C, disrupting enzyme function.

CO2 levels

Optimal concentration for photosynthesis is 0.4%.

Water supply

Essential for photosynthesis; too little halts process.

Limiting factors

Factors that restrict photosynthesis rate.

Commercial glasshouses

Controlled environments to optimize crop yields.

Transpiration

Water loss from plants affecting CO2 intake.

Automatic watering systems

Used in glasshouses to maintain water supply.

Chromatography

Technique to separate plant pigments.

Dehydrogenase activity

Enzyme activity measured by color change in dye.

DCPIP

Dye that turns colorless when reduced by dehydrogenase.

Guard cells

Regulate stomata opening to control water loss.

Photosynthetic pigments

Molecules that absorb light for photosynthesis.

Light-dependent reactions

Photosynthesis phase converting light to chemical energy.

Light-independent reactions

Photosynthesis phase using products from light-dependent reactions.

Photosynthesis rate

Speed at which plants convert light to energy.

Stomata

Small openings for gas exchange in plants.

Chloroplasts

Organelles where photosynthesis occurs in plants.

Photosynthesis

Process converting light energy into chemical energy.