Photosynthesis 5.1.6 Flashcards
What is photosynthesis and what type of organism performs it?
Photosynthesis: light energy is transformed into chemical energy
-Autotrophs perform phototsynthesis
What is glucose converted into in plants and what is light?
-Glucose can be converted into starch, amino acids, cellulose, nucleic acids and used in respiration
-Light is a photon containing a quantum (amount) of energy
What parts are in the internal structure of the leaf?
-Waxy cuticle: layer on the surface that limits water loss
-Upper epidermis: protects the leaf and reduces water loss
-Palisade cells: contain a large amount of chloroplasts and adapted for efficient photosynthesis
-Lower epidermis: cells are modified to contain guard cells which control movement of water and gases, it also protects the leaf
Spongy mesophyl: contain air spaces between cells so play a role in gas exchange
Label this diagram of the internal structure of the leaf?
1-Waxy cuticle
2-Upper epidermis
3-Palisade cells
4-Spongy mesophyll
5-Lower epidermis
Describe the interelationship between photosynthesis and respiration in a plant? what is the compensation point and compensation period?
-Photosynthesis and respiration control the cycling of carbon dioxide and oxygen, the products of one process are the raw materials for the other
-Compensation point: when respiration and photosynthesis proceed at the same rate
-Compensation period: time taken to reach the compensation point
What are Thylakoids, Granum and inter-granal lamella? (Structure of a chloroplast)
-Thylakoids: pigment containing flattened discs, the light-dependant reaction takes place in the thylakoid membrane
-Granum: stack of thylakoids, the stacks provide chloroplasts with an increased surface area for photosynthesis
-Inter-granal lamella: extensions of the membrane that connect one granum to another
What is the stroma? (structure of a chloroplast)
Stroma: gel like material containing enzymes, the second part of photosynthesis, light independant reaction occurs here using the enzymes
-The stroma contains:
>Starch grains: store glucose produced in photosynthesis
>Oil droplets: provide raw materials for making new membranes
>Small ribosomes
What is chlorophyll a?
-Chlorophyll a is the primary pigment in photosynthesis and absorbs mainly red and blue light and reflects green light, which is why plants appear green
What are accessory pigments and name them?
-Accessory pigments absorb and reflect different wavelengths to chlorophyll a
-They include: chlorophyll b, cartenoids and xanthophylls
What number represents the different pigments in photosynthesis?
1-Chlorophyll a
2-Chlorophyll b
3-Cartenoids
What is the role of the photosystem and what does the antenna complex consist of?
-Role of the photosystem is to absorb light energy of different wavelengths and transfer the energy to the reaction centre
-The antenna complex consists of carotenoids, chlorophyll a and b and xanthophyll
What are the two types of chlorophyll a and what is the purpose of acessory pigments?
-P₆₈₀: found in photosystem II and has peak absorption of 680nm
-P₇₀₀: found in photosystem I and has peak absorption of 700nm
-Accesory pigments pass energy to the primary pigments in the reaction centre
What is the advantage of having a range of pigments and how do accessory pigments absorb wavelengths of light?
-The plant can absorb a range of wavelengths to maximise amount of energy harvested
-When light arrives at accessory pigments photons excite electrons, this energy transfer is transferred to the reaction centre where there is an electron acceptor.
Why do leaves change colour in autumn?
-Chlorophyll is brocken down and other pigments can be seen
What are the typical types of stationary phases and mobile phases?
-Stationary phase: either chromatography paper or thin-layer chromatography plate
-Mobile phase: usually water for polar molecules or ethanol for non-polar molecules
What are the instructions for paper chromatography?
- Draw a line near the bottom of the plate with a pencil and add a verticle line where the sample should be placed
- Dip cappilary tube in sample and touch verticle line, allow to dry
3.Place in solvent jar and screw on lid to prevent evaporation, level of solvent must be below pencil line - Substances will split depending on their solubillity, polarity and size
What determines how quickly molecules travel along stationary phase and what is the equation for RF value?
-Solubillity in solvent
-Polarity
-Size
What is phosphorylation?
-The addition of an inorganic phosphate group to a molecule
What are the two stages of photosynthesis and what processes happen at each one?
-Light dependant stage: occurs in thylakoid membranes
->Non-cyclic phosphorylation
->Photolysis
->Cyclic photophosphorylation
-Light-independant stage: occurs in stroma
->Calvin cycle
->Regeneration of RUBP
What is the acronym for gain and loss of electrons?
OILRIG
What is NADP⁺ and NADPH(reduced NADP)
-A coenzyme involved in photosynthetic reactions
-Can transfer hydrogen to and from a molecule so can reduce and oxidise a molecule
Describe non-cyclic phosphorylation?
- Light hits photosystem II and excites two electrons which are accepted by an electron accepter.
- The photosystems are linked by electron carriers which are proteins that transfer electrons, the photosystems and electron carriers form an electron transport chain
3.Electrons pass along a chain of electron carriers, losing energy each time they are passed on
4.Energy released is transferred to produce ATP from ADP and Pᵢ (as energy is used to pump H⁺ ions across the membrane that diffuse back through ATP synthase which makes ATP in a process called cheimosmosis)
5.Light also hits photosystem I exciting electrons that pass to an electron acceptor,the electrons from PSII are used to replace them - The electrons pass along a chain of electron carriers and the electrons are used to reduce NADP⁺ into NADPH (combine with H⁺ from photolysis to form H)
- ATP and NADPH are then used in the light independant reaction
Describe what photolysis is in the light dependant stage and what the products are used for?
1.Light energy with the aid of enzymes splits water into protons, electrons and oxygen
2.Hydrogen ions are used to reduce NADP⁺ and the 2 electrons replace those lost from PSII in non-cyclic photophosphorylation and oxygen is released as waste gas
What is cheimosmosis?
Production of ATP from ADP and phosphate when H⁺ ions diffuse back out of the thylakoid membrane through ATP synthase due to the electrochemical gradient built by the accumulation of H⁺ from photolysis,cyclic and non-cyclic photophosphorylation)
Describe cyclic photophosphorylation?
1.Light hits Photosystem I exciting two electrons, which are accepted by an electron acceptor and pass along a chain of electron carriers
2. The energy released each time they are passed on is used to make ATP (H⁺ ions pumped across membrane)
3. Electrons are returned to PSI instead of being used to make NADPH
Where does the light independent stage of photosynthesis take place?
Stroma
What happens in the Calvin cycle?
1.RuBP combines with CO₂, in a process called carboxylation, RuBisCo catalyses this reaction
2. This produces a unstable 6C molecule that breaks down into two molecules of glycerate-3-phosphate (GP)
3.GP is reduced by ATP and NADPH to form two molecules of TP
4.TP is a carbohydrate and some of it is used to produce glucose and other molecules such as amino acids and lipids
5. Most of TP is recycled to make more RUBP and every 6 turns of the cycle a hexose sugar(glucose) is produced
Draw the Calvin cycle?
Why does the cycle constantly regenerate RuBP?
-This ensures that RuBP is always available to combine with CO₂ from the atmosphere
What does TP stand for and what are its uses?
-Triose Phosphate
-Used to build complex carbohydrates,amino acids and lipids
-Can be converted to glycerol and therefore combined with fatty acids to make lipids
How many turns of the Calvin cycle will aquire 4 hexose sugars?
-24
-In every 3 turns of the cycle 5 out of 6 TP molecules are regenerated to RuBP and hexose sugars require two TP molecules
What factors affect photosynthesis?
-Light intensity
-CO₂ concentration
-Temperature
What will happen to GP, TP and RuBP when there is little or no light?
-GP cannot be reduced to TP
-TP levels fall and GP accumulates
-RuBP falls as it can’t be regenerated
Why is carbon dioxide a limiting factor of photosynthesis?
-Carbon dioxide is used to carboxylate RuBP
-When it is limited the rate of light independant stage of photosynthesis will decrease.
How would you vary the concentration of carbon dioxide a plant receives?
-Add plant to water and vary amount of sodium hydrogencarbonate
What will happen to RuBP,GP and TP if co₂ falls below 0.01%?
-RuBP cannot accept co₂ so RuBP accumulates
-GP and TP cannot be made
What is the effect of temperature on the Calvin cycle?
-All reactions in the Calvin cycle are catalysed by enzymes
-At low temperatures, low kinetic energy means reactions occur slowly so levels of RuBP,GP and TP will fall
-At high temperatures, enzymes denature and calvin cycle will halt
What is usually the limiting factor on a sunny windless day and at night?
-Sunny windeless day: CO₂ is usually limiting factor
-Night: light intensity is usually limiting factor
What is water stress and what is the effect of water stress on photosynthesis?
-Water stress: when roots are unable to take up enough water to replace that lost via transpiration
-Cells will lose water and become plasmolysed, plant produces abscisic acid the causes stomata to close, reducing gaseous exchange
-Rate of photosynthesis greatly reduces
What are the limitations of measuring rate of photosynthesis using a photosynthometer?
-When measuring photosynthesis by calculating volume of oxygen formed, you aren’t measuring rate of photosynthesis but instead the amount of oxygen released by the plant
-There also may be some dissolved nitrogen in the gas collected
Describe the Hill reaction?
- Chloroplasts are isolated from the plant by grinding ice cold sucrose solution and centrifuging
- Sediment is then added to a buffer solution and DCPIP is added to the tubes
- Electrons released during the light-dependant stage of photosynthesis reduce DCPIP turning it from blue to colourless
In the hill reaction why does lack of light and boiling the tube stop DCPIP from turning colourless?
-Lack of light: light dependant stage of photosynthesis stops so electrons can’t reduce DCPIP
-Boiling: disrupts the thylakoid membranes and denatures the membrane proteins so electron transport chain can’t function
