11: Photosynthesis Flashcards by David B

Where is the site of photosynthesis?

Chloroplasts within the leaf

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What are the structures in the chloroplast?

Grana - stacks of thylakoid membranes
Stroma - fluid-filled matrix
Thylakoid membranes - contain photosynthetic pigments
Intergranal lamella - tubular extensions that connect grana
Chloroplast envelope - double plasma membrnae

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What are the rough dimensions of a chloroplast?

2-10μm long

1μm diameter

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How is the structure of the leaf adapted to photosynthesis?

Large SA:V to absorb most sunlight
Leaves arrange so minimal overlapping and shadows
Thin - short diffusion pathway & more light absorbed
Transparent cuticle/epidermis - most light onto chlorophyll underneath
Many stomata - short diffusion pathway to outside
Air spaces - rapid diffusion to cells in gas phase
Mesophyll cells - densely packed and contain many chloroplasts

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What is the overall equation of photosynthesis?

6CO2 + 6H2O -> C6H12O6 + 6O2

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What are the three main stages of the photosynthesis?

Capturing of light energy
Light-dependent reaction (LDR)
Light-independent reaction(LIR)

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What does the stroma contain?

Enzymes
Starch grains
DNA
70S ribosomes

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Why is DNA and ribosomes in the chloroplast more efficient?

Proteins needed in photosynthesis are made in the organelle so they don’t have to be retrieved from the cytoplasm

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Define oxidation

Loss of electrons could gain oxygen

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Define reduction

Gains electrons could lose oxygen

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What is a photosynthetic pigment?

Different chemicals which absorb different λ of light

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What are the dominant photosynthetic pigments?

Chlorophyll a (dominant pigment)- absorbs best in red & blue, least in green

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What is a photosystem?

Clusters of different photosynthetic pigments

Allows for absorption of as many different λ of light possible

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What is photosystem (PS) I and II?

Photosystem I - inter-granal lamellae (p700)

Photosystem II -thylakoid membranes (p680)

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What are primary and accessory pigments?

Primary - chlorophyll a absorbs most of the light

Accessory - carotene etc. which absorbs other λ of light

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What are the three main stages of the light-dependent reaction?

Photophosphorylation
Photolysis
Reduction of NADP to reduced NADP

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What occurs in photophosphorylation?

Light absorbed by chlorophyll a (PSII)
Electrons promoted to higher energy level then removed
Electrons passed along electron carriers to PSI
Energy released as transferred allowing for the reaction: ADP + Pi -> ATP

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What is the precise mechanism by which ATP is produced?

Chemiosmotic theory

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Describe chemiosmotic theory

Protons pumped from stroma into thylakoid using proton pumps in the membrane
Energy for this from photolysis of water, also provides protons
Proton conc. increases in thylakoid, meaning conc gradient from thylakoid to stroma
Pass membrane to stroma through ATP synthase channel proteins - changing structure of the enzyme which catalyses ADP + Pi -> ATP

What is an alternative name for ATP synthase channel proteins?

Stalked granules - named so as they form pores/granules on the membrane surface

Describe the photolysis of water

Light causes break down of water to: protons, electrons and oxygen
Occurs in the thylakoid space

Why is photolysis necessary?

Provides electrons to replace those lost in chlorophyll
Protons for the production of ATP and reduced NADP
Oxygen is just a by-product or can be used for respiration

What is the equation for the photolysis of water?

2H2O -> 4H+ + 4e- + O2

How is NADP reduced?

Protons from photolysis of water are taken up by NADP This reduces NADP to NADPH

What is NADP and its function?

Electron carrier - takes them from chlorophyll | Reduced to NADPH which is used in the light-independent stage

What is the site of the light-dependent reaction?

Thylakoid membrane in the chloroplast

How are the chloroplasts adapted for the LDR?

Thylakoid membrane provides large SA:V for attachment of: chlorophyll, electron carriers and enzymes Proteins in grana hold PS allowing for max absorption Granal membranes have ATP synthase channels allowing ATP production Contain DNA and ribosomes so proteins can be quickly made on-site

What is DCPIP?

Blue indicator | Turns colourless when oxidised (gains electrons) from the LDR

How is the stroma adapted to the LIR?

Fluid contains enzymes for the LIR Fluid surrounds grana allowing products from LDR to diffuse easily to stroma Contains DNA & enzymes so it can make proteins

What is the calvin cycle?

The various stages of the light-independent reaction

What are the products of LDR?

ATP and NADPH

What are the abbreviations in the Calvin cycle?

Ribulose biphosphate (RuBP) a 5-carbon compound Glycerate 3-phosphate (GP) a 3-carbon compound Triose phosphate (TP) Ribulose bisphosphate carboxylase enzyme (rubisco)

What are the stages in the Calvin cycle?

CO2 + RuBP -> 2xGP (uses rubisco enzyme) NADPH reduces 2xGP to 2xTP using energy from ATP NADPH->NADP 2xTP converted to organic substances (starch, cellulose, glucose etc.) or used to regenerate RuBP using ATP from LDR

How is energy obtained from ATP?

Energy released when ATP -> ADP + Pi

Define a limiting factor

Something which limits the rate at which a process can take place Rate of process at any time not affected by all factors, only the one which is least favourable

Describe the effect of complete darkness on photosynthesis?

Rate of photosynthesis would be 0 | Changes in temp or CO2 has no effect

Define the law of limiting factors

At any given moment, the rate of physiological process is limited by the factor that is at its least favourable value

How do you know that light is the limiting factor?

As light intensity increases, rate of photosynthesis increases

How can CO2 concentration be increased in the glasshouse?

Paraffin heaters which produce CO2

Define a photosynthometer

An instrument that measures the amount of photosynthesis a plant is undergoing

What is the apparatus set up of a photosynthometer?

Test tube in a beaker of water (used as a water bath) containing pondweed and KHCO3 Capillary tube connects test tube to a syringe Scale (mm) along the capillary tube Set up in a dark room next to light source

Why is KHCO3 used in a photosynthometer?

Provides a source of CO2 to the plant

How is a photosynthometer used?

Capillary tube is used to collect O2 produced in photosynthesis in a set period of time Syringe draws O2 bubble to scale, which can be used to work out the volume if diameter of tube is known

What is the lollipop reaction for LIR?

Algae in nutrient media has air and CO2, and radioactive 14C in hydrocarbonate added Vessel is lit and valve removes samples at set intervals Samples placed into hot methanol to kill algae The 14C content in solution at different times shows the different chemicals being formed in the order

Why does hot methanol used in the lollipop experiment?

Denatures the enzymes in the algae, preventing the reaction from continuing

Describe what occurs during the light dependent reaction (this is from a mark scheme - LEARN IT)

Chlorophyll absorbs light energy Excites electrons / electrons removed (from chlorophyll) Electrons move along carriers/electron transport chain releasing energy Energy used to join ADP and Pi to form ATP Photolysis of water produces protons, electrons and oxygen NADP reduced by electrons /electrons and protons / hydrogen

What do plants need energy for?

DNA replication Cell division Protein synthesis Active transport