Photosynthesis

Question 1

what are the bonds in ATP, and what happens when broken?

Answer 1

phosphoanhydride bond, ATP to ADP, releases large amounts of energy

Question 2

state the three methods of phosphorylating ADP to form ATP

Answer 2

photophosphorylation, substrate-level phosphorylation, oxidative phosphorylation (capture energy from exergonic reactions)

Question 3

what are photoautotrophs?

Answer 3

organisms that use an inorganic form of carbon as raw materials, producing sugars through photosynthesis

Question 4

what is the chemical reaction of photosynthesis?

Answer 4

carbon dioxide + water [sunlight + chlorophyll] = glucose + oxygen + water

Question 5

what are the three reasons that photosynthesis is important?

Answer 5

1. how solar energy is captured
2. source of complex organic molecules for heterotrophic organisms
3. releases oxygen as by-product for aerobic respiration

Question 6

what is the major photosynthetic organ in plants?

Answer 6

leaf

Question 7

if max surface area of each leaf is exposed to sunlight, what are the three things the plant can do?

Answer 7

obtain light energy from the sun, exchange gases, translocate liquids

Question 8

what are the three main tissue types in plants, and their functions?

Answer 8

dermal: protective outer covering, facilitate gaseous exchange and uptake of ions + water
vascular: structural support, transport of water and solutes between organs
ground: making and storing food

Question 9

state the three main cell types in ground tissue

Answer 9

parenchyma, collenchyma, sclernchyma

Question 10

describe the function and structure of parenchyma

Answer 10

living, serves as packing tissue
most common type in plants
carries out metabolic functions like synthesis and storage of food
spherical cells with thin cellulose primary cell wall
mature cells have large central vacuole
some specialised to contain chloroplasts for photosynthesis (eg. palisade and spongy mesophyll in leaves)
in leaves, stems, roots, fleshy tissue of fruits

Question 11

describe the function and structure of collenchyma

Answer 11

living, flexible structural support
elongated, unevenly thickened cellulose cell wall (thicker than parenchyma)
mature cells can still elongate, found just below epidermis (cortex) and/or surrounding vascular bundles

Question 12

describe the function and structure of sclerenchyma

Answer 12

dead at maturity, structural support
elongated, evenly thickened cell walls (thicker than collenchyma)
cell walls contain waterproof lignin, specialised ones transport water
two types: sclereids and fibres
mature cells in parts of plant that stopped growing

Question 13

describe the size and shape of the chloroplast and its envelope MEMORISE

Answer 13

• lens-shaped (in plants)
• 5-10 micrometers in length, 4-7 micrometers in width
• double membrane

Question 14

what is a stroma in chloroplasts? MEMORISE

Answer 14

• gel-like matrix enclosed by chloroplast envelope
• contains circular DNA, 70S ribosomes, starch granules, oil droplets and enzymes used in Calvin cycle

Question 15

what is a thylakoid in chloroplasts? MEMORISE

Answer 15

• flattened sacs or pouches
• photosynthetic pigments and electrons carriers are embedded within membrane
  space enclosed within thylakoid known as the thylakoid lumen or thylakoid space

Question 16

what is a granum in chloroplasts? MEMORISE

Answer 16

• a stack of thylakoids
• increases surface area and amount of pigments available for light-dependent reaction of photosynthesis
• connected by integranal lamellae (singular: lamella), making thylakoids one single continuous compartment

Question 17

what is chlorophyll, its molecular structure, and what makes different types of chlorophyll?

Answer 17

main photosynthetic pigment, absorbs largely red and blue-violet light (reflects green)

molecular structure (two parts):
1. hydrophilic porphyrin ring with a flat, light-absorbing hydrophilic head with an MAGNESIUM in centre (Mg2+ deficiency reduces chlorophyll deficiency, causes yellowing)
2. hydrophobic hydrocarbon tail that projects into thylakoid membrane to keep chlorophyll embedded

Question 18

what are the characteristics of chlorophyll a, and why is it the most important?

Answer 18

chlorophyll a is the major pigment in photoautotrophs, absorbs red and blue (only one direct in light-dependent rxn)

any molecule that absorbs light to transfer to chlorophyll a is an accessory pigment (most commonly chlorophyll b)

Question 19

what are carotenoids, the light they absorb, and its two main types?

Answer 19

accessory pigments (pass light energy onto chlorophyll a of the reaction centre)
yellow, orange, red or brown pigments, absorb strongly in blue-violet range
two types: carotene and xanthophylls (460-550nm of visible light spectrum)

Question 20

what are the two main functions of accessory pigments (eg. chlorophyll b, carotenoids)

Answer 20

broadening spectrum of light for photosynthesis: absorb intermediate wavelengths of light, broadening the spectrum of colours

photoprotection: absorbing excessive light and dissipating it, preventing auto-oxidation of chlorophyll, preventing photobleaching (damage of chlorophyll pigments due to excessive light),

Question 21

what are the absorption and action spectrums of photosynthetic pigments, and what do they show? MEMORISE

Answer 21

• absorption: graph of amount of light absorbed at different wavelengths by a pigment
• action: effectiveness of diff wavelengths at driving photosynthesis

Question 22

what is photosynthesis, and name its three main stages + where they occur + what happens during them

Answer 22

energy transduction, light to chemical energy

1. light harvesting stage (thylakoid membranes)
   light energy is captured with a mixture of pigments
2. light-dependent (thylakoid membranes)
   light excites and displaces an electron from chlorophyll
   light energy converted to chemical energy through flow of electrons, coupled to ATP synthesis, NADPH produced, photolysis of water
3. light-independent (stroma)
   chemical energy of ATP and NADPH used in reduction of CO2, producing sugars

Question 23

what occurs during the excitation of chlorophyll by light, and what are the three ways it returns to ground state?

Answer 23

ground (stable) to excited (unstable)

1. transferring the energy (but not the electron) directly to neighbouring chlorophyll molecule by resonance energy transfer: during light harvesting
2. boosting an electron to higher energy level, transferring to electron acceptor, then taking up another low-level electron from electron donor (eg splitting of water)
3. when light energy is absorbed by an isolated chlorophyll molecule in solution, not in nature: energy is lost by converting it into heat (molecular motions) or a combi of heat and light on a longer wavelength (fluorescence)

Question 24

what are photosystems, and their three closely-linked components?

Answer 24

in the thylakoid membrane, photosynthetic pigments are arranged into photosystems to trap light and convert it into useful forms

1. light-harvesting complexes (LHCs): collected by 200-300 pigment molecules that capture, absorb and transfer light energy to the reaction centre
2. reaction centre: a pair of special chlorophyll a molecules that irreversibly trap energy, by passing an excited electron to an adjacent chain of electron acceptors in the same complex
3. primary electron acceptor: found in reaction centre, involved in electron transfer

Question 25

what are the similarities and differences of the two photosystems?

Answer 25

functionally and spatially distinct, differ in wavelengths they absorb PSII: special chlorophyll a is P680, absorbs maximally 680nm wavelength of light PSI: special chlorophyll a is P700, absorbs maximally 700nm wavelength of light both are identical in special chlorophyll a molecule differ in light-absorbing properties bc of association with different accessory pigments and proteins in thylakoid membrane, affecting electron distribution

Question 26

what generally occurs in the electron transport chain (ETC)?

Answer 26

ETCs found at thylakoid membranes, between photosystems electron carriers transfer electrons from one carrier to another, can be coenzymes or protein molecules a series of electron carriers = ETC, passed down by a series of redox reactions (each carrier is oxidised by gaining an electron, and oxidised by donating it to the next carrier) ETC allows transfer to be done in several energy-releasing steps instead of one, some energy released to make ATP

Question 27

what occurs during the light-harvesting stage of photosynthesis?

Answer 27

light of appropriate wavelengths strike any molecule within a photosystem light energy is absorbed by that pigment molecule, exciting it resonance energy transfer: excitation energy is transferred within the photosystem

Question 28

what generally occurs in the light-dependent reaction (location, products, function, steps), and name the two ways it can proceed

Answer 28

occurs in thylakoid membrane of chloroplasts synthesise NADPH and ATP (with trapped chemical energy) using captured light energy NADPH and ATP used in light-independent reaction to fix carbon dioxide and trap energy in glucose 1. non-cyclic photophosphorylation 2. cyclic phosphorylation then the ATP is synthesised through chemiosmosis

Question 29

what does NADPH stand for?

Answer 29

reduced nicotinamide adenine dinucleotide phosphate

Question 30

how does non-cyclic photophosphorylation occur in the light-dependent reaction of photosynthesis? MEMORISE

Answer 30

involves both PSII and PSI in "Z-scheme of electron flow", producing ATP and NADPH 1. photon of light strikes a pigment molecule in LHC, relaying energy via resonance energy transfer until it reaches one of the pair of special chlorophyll a molecules in PSII reaction centre, exciting one of the P680 electrons to a higher energy state 2. photoexcited electron captured by primary electron acceptor, each P680 is missing an electron 3. an enzyme splits water into two electrons, two H+, one O2 in photolysis of water, electrons replenish PSII's deficit 4. energised electron passes from PSII to PSI via first ETC 5. while passing thru ETC, electrons release energy, pumping proteins against conc gradient from stroma into thylakoid space (generating proton gradient to drive ATP synthesis) through photophosphorylation 6. more light strikes pigment molecule in PSI, exciting electron in special chlorophyll a in PSI reaction centre, passed onto primary electron acceptor and creating electron deficit in P700, replenished by electron from PSII 7. excited electron passed down second ETC through ferredoxin 8. NADP reductase (enzyme) transfers electrons from Fd to NADP (requires 2 electrons) produces O2, NADPH, ATP

Question 31

how does cyclic photophosphorylation occur in the light-dependent reaction of photosynthesis? MEMORISE

Answer 31

involves photosystem I only, produces ATP only (no NADPH) 1. light absorbed by LHC and passed onto chlorophyll a (P700) in reaction centre of PSI 2. PSI releases a photoexcited electron, passed onto primary electron acceptor (ferredoxin), cycled back to cytochrome (b-f) complex in electron transport chain from PSII to PSI 3. synthesised ATP from ADP and Pi, needed in light-independent stage done when there is no more NADP+ to reduce into NADPH in second ETC, so energy utilised to make more ATP instead

Question 32

define chemiosmosis

Answer 32

chemiosmosis is the process in which energy stored in the form of a hydrogen ion gradient across the membrane is used to drive cellular work such as the synthesis of ATP

Question 33

how does chemiosmosis occur? MEMORISE

Answer 33

- energy released from the ETC used to pump protons from stroma to thylakoid space, establishing proton gradient - proton gradient drives synthesis of ATP by ATP synthase complex - H+ diffuse down gradient from thylakoid space across membrane into stroma through ATP synthase complex

Question 34

what is the location, purpose, and state the four phases of the light-independent reaction / Calvin cycle

Answer 34

location: stroma of chloroplasts reduce CO2 using ATP (energy source) and NADPH (reducing agent) produced in the light-dependent reaction 1. carbon dioxide uptake and fixation 2. reduction of phosphoglyceric acid (PGA) 3. regeneration of carbon dioxide acceptor (RuBP) 4. product synthesis and sugar formation

Question 35

what occurs during carbon dioxide fixation in the Calvin cycle (reactants, catalyst, process, products)

Answer 35

CO2 gas diffuses from the environment through the stomata into the cytoplasm of (spongy and palisade) mesophyll cells and into the chloroplasts carboxylation of RuBP: CO2 is fixed when it combines with a 5-carbon carbon dioxide acceptor, ribulose bisphosphate (RuBP) to form an unstable 6-carbon intermediate, catalysed by ribulose bisphosphate carboxylase oxygenase (rubisco) unstable intermediate breaks down spontaneously into two molecules of a three-carbon compound called phosphoglyceric acid (PGA) / 3-phosphoglycerate / glycerate-3-phosphate (GP

Question 36

what occurs during the reduction of PGA during the Calvin cycle?

Answer 36

each PGA molecule is phosphorylated to form 1,3-biphosphoglycerate (ATP gives away its phosphate group to form ADP) NADPH donates a pair of electrons to become NADP+, further reducing 1,3-bisphosphoglycerate to form glyceraldehyde-3-phosphate (GALP or G3P) or triose phosphate (TP): hydrogen from NADPH, energy from ATP

Question 37

what occurs during the regeneration of carbon dioxide acceptor (RuBP) in the Calvin cycle?

Answer 37

for every 3 molecules of CO2 that enter the Calvin cycle, three RuBP are carboxylated, six TP formed net gain of carbohydrate: only one TP, since other five are used to regenerate three molecules of RuBP used in CO2 fixation step, investing three more molecules of ATP RuBP is regernated

Question 38

what occurs during product synthesis and sugar formation in the Calvin cycle?

Answer 38

TP spun off from light-independent reaction becomes starting material for metabolic pathways two TP molecules make one hexose sugar (requiring six turns of the Calvin cycle)

Question 39

what is the overall equation of the Calvin cycle?

Answer 39

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi (Pi = inorganic phosphate)

Question 40

what is the fate of photosynthetic products (TP, PGA)?

Answer 40

PGA and TP are intermediates in glycolysis (cellular respiration) carbohydrates synthesis: TP made into hexose sugars (respiratory substrates for ATP production or polymerised as starch for storage or cellulose for structure) lipids synthesis: PGA added to coenzyme A to form acetyl CoA for cellular respiration, TP made into glycerol to form triglycerides and phospholipids proteins synthesis: PGA and TP are important aa precursors

Question 41

what is the principle of limiting factors?

Answer 41

rate of biochemical process is limited by slowest reaction in the series (factor nearest its minimum value)

Question 42

list the eight factors that influence the rate of photosynthesis

Answer 42

light CO2 concentration temperature chlorophyll concentration specific inhibitors (eg. DCMU, cyanide) water oxygen pollution

Question 43

what is the compensation point of a plant, and what occurs then?

Answer 43

point at which the rate of photosynthesis is equal to the rate of respiration, no net gaseous exchange between the plant and its environment (reached at low light intensities like sunrise and sunset)