Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

bio > photosynthesis > Flashcards

photosynthesis Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

what is ATP and describe its structure

A

ATP is adenosine triphosphate. ATP is made up of an adenine, a ribose and three phosphate groups.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how is ATP converted to ADP?

A
  • the high-energy phosphoanhydride bonds carry enough energy to cause almost any reaction to proceed.
  • chemical potential energy is quickly released to the organism or cell by a hydrolytic reaction which breaks the phosphoanhydride bond and converts ATP to ADP.
  • this releases large amounts of energy for reactions to occur
  • conversely, a phosphate can be reattached to ADP (phosphorylation) with the absorption of a large amount of energy, forming the high-energy phosphoanhydride bonds in ATP
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are autotrophs?

A

autotrophs are organisms that use an inorganic form of carbon, such as carbon dioxide, as starting materials for the synthesis of complex organic compounds. they are producers of the biosphere.

photoautotrophs are autotrophs which synthesise sugars from carbon dioxide and water using sunlight as the source of energy and chlorophyll for trapping the light energy. this process is called photosynthesis. photosynthesis is one of the most important biochemical processes because almost all living things depend on photosynthesis, directly or indirectly, for their organic compounds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

why is photosynthesis important?

A
  1. it is how solar energy is captured by plants for use by all organisms
  2. it provides a source of complex organic molecules for heterotrophic organisms (organisms that cannot make their own food)
  3. it releases oxygen as a by-product for use by aerobic organisms
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

idk if this in syllabus but its not in LOs

what are the 3 main cell types in ground tissue?

3 main tissue types: dermal, vascular & ground

A
  1. parenchyma - living cells that carry out metabolic functions, including synthesis & storage of food. the cells are approximately spherical, with a thin cellulose primary cell wall. most common cell type, found in stems, roots and fleshy tissue of fruits.
  2. collenchyma - living cells that are specialised for flexible structural support. the cells are elongated with an unevenly thickened cellulose cell wall which are thicker than parenchyma cell walls. usually found just below epidermis and/or surrounding vascular bundles
  3. sclerenchyma - dead cells specialised for structural support. the cells are elongated and have evenly thickened cell walls that are thicker than collenchyma cell walls. cell walls contain lignin, which is impermeable to water, allowing specialised sclerenchyma cells to transport water. mature cells are found in parts of the plant which have stopped growing.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what cells in the leaf can chloroplasts be found in?

A
  • palisade mesophyll cells
  • spongy mesophyll cells
  • stomata guard cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are the functions of each structural component of the leaf?

A
  • upper epidermis - one cell thick, does not contain chloroplasts. the cells in the upper epidermis are quite transparent, allowing light to pass through to the photosynthetic tissue below.
  • palisade mesophyll - the cytoplasms of palisade cells is full of chloroplasts. the number & arrangement of the chloroplasts, as well as the cell shape, allows maximum light capture.
  • spongy mesophyll - the spongy mesophyll layer contains fewer cells than the palisade mesophyll. each cell has fewer chloroplasts so the cells are not as active in photosynthesis as the palisade. there are large intercellular spaces for the diffusion of CO2
  • lower epidermis - the lower epidermis has stomata which are pores surrounded by a pair of guard cells. the only cells with chloroplasts in the lower epidermis are guard cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are the structural features of chloroplasts and their respective functions?

chloroplasts themselves are lens-shaped

A

chloroplast envelope
- made up of a double membrane
- outer membrane is selectively permeable to some solutes
- inner membrane is highly permeable and substances pass through with the aid of transporters

stroma
- stroma is the gel-like matrix enclosed by the chloroplast envelope
- contains circular DNA, 70S ribosomes, starch granules, oil droplets and enzymes involved in the calvin cycle

thylakoids
- a third membrane system within the stroma consisting of flattened membranous sacs or pouches
- photosynthetic pigments and electron carriers are embedded within the membrane
- the space enclosed within the thylakoid is known as the thylakoid lumen or thylakoid space
- this compartmentalisation allows chemiosmosis to take place and for ATP to be produced by photophosphorylation

granum
- a stack of thylakoids
- increases surface area and amount of pigments available for the light-dependent reaction of photosynthesis
- intergranal lamellae (singular: lamella), which are flattened membranous tubular thylakoids, connect the grana. these lamellae connect the thylakoid compartments into a single, continuous compartment within the stroma.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

(read through) understanding light

A
  • light is a fom of electromagnetic energy. light with different amounts of energy have different wavelengths. the entire range is called the electromagnetic spectrum.
  • visible light is the range of wavelengths that can be detected by the human eye
  • when light meets matter, it may be reflected, transmitted or absorbed
  • pigments are chemical compounds which reflect only certain wavelengths of visible light. pigments are also able to absorb only certain wavelengths of light. the pigment molecules act like energy-receiving antennas to capture light energy for photosynthesis
  • each pigment absorbs wavelength of a narrow range within the spectrum -> plants usually need to use several kinds of pigment to effectively increase the range of wavelengths from which they can obtain energy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are the two basic classes of photosynthetic pigments in plants?

A
  • chlorophyll (main & most abundant pigment) & carotenoids (accessory pigment, incuding carotenes & xanthophylls)
  • both chlorophyll & carotenoids are found in the thylakoid membrane of chloroplasts
  • examples of chlorophyll pigments: chlorophyll a (yellow-green) and chlorophyll b (blue-green)
  • examples of carotenoid pigments: b-carotene (orange) and xantophylls (all yellow)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

describe the structure and function of chlorophyll

A
  • chlorophyll is the main pigment utilised in photosynthesis
  • chlorophyll absorbs mainly red and blue-violet light. it reflects green light, giving most plants their characteristic green colour.
  • each molecule of chlorophyll consists of a hydrophilic porphyrin ring and a hydrophobic hydrocarbon tail
  • the hydrophilic porphyrin ring functions in light absorption. it has a flat, light-absorbing hydrophilic head which contains a magnesium atom at its centre. magnesium deficiency in plants reduces chlorophyll production and causes yellowing (chlorosis)
  • the hydrophobic hydrocarbon tail projects into the thylakoid membrane, keeping the chlorophyll embedded in the thylakoid membrane
  • different chlorophylls have different side chains on their hydrophilic head -> modifies their absorption spectra & increases the range of wavelengths of light absorbed.
  • chlorophyll a is the major pigment in autotrophs, absorbing blue & red light. only chlorophyll a participates directly in the light-dependent reaction. other pigments (aka accessory pigments) can absorb light and transfer the energy to chlorophyll a. chlorophyll b is themost common accessory pigment
  • chlorophyll is always associated with specific binding proteins, forming light-harvesting complexes (LHCs) in the thylakoid membrane
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

describe the structure and function of carotenoids

A
  • carotenoids are accessory pigments, as they pass the light energy they absorb onto chlorophyll a of the reaction centre.
  • carotenoids are yellow, orange, red or brown pigments that absorb strongly in the blue-violet range
  • carotene & xanthophyll both absorb light in the 460-550nm of the visible light spectrum. so by using both carotenoids and chlorophyll, efficiency of light-harvesting is increased as the range of wavelengths that can be captured is increased.
  • carotenoids & other accessory pigments serve 2 main function: broadening the spectrum of light for photosynthesis and photoprotection
  • broadening spectrum of light for photosynthesis: accessory pigments absorb the intermediate wavelengths of light which chlorophyll cannot, broadening the spectrum of colours that can drive photosynthesis. but carotenoids transfer only about 10% of their absorbed energy, and are not very effective as a photosynthetic pigment
  • photoprotection: carotenoids are more important in absorbing excessive light & preventing auto-oxidation of chlorophyll, hence preventing photobleaching. this is known as photoprotection. excessive light intensity can damage chlorophyll pigments, so instead of transmitting energy to the chlorophyll, some carotenoids absorb & dissipate excess light energy from chlorophyll, protecting them from destruction by light.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

PLS LOOK AT THE DIAGRAMS

★ what is the absorption spectrum & action spectrum?

PLS LOOK AT THE DIAGRAMS

A
  • the absorption spectrum of a photosynthetic pigment is a graph of the amount of light absorbed at different wavelengths by a pigment
  • the action spectrum for photosynthesis is a graph of the effectiveness of different wavelengths of light in driving photosynthesis
  • both spectrums show that the wavelengths of light absorbed by chlorophyll, red & blue light, are very similar to the wavelengths that drive photosynthesis, so chlorophyll is mainly responsible for the absorption of light in photosynthesis
  • both spectrums also show that the wavelengths absorbed are the ones that provide most energy for photosynthesis, so both blue and red light are used by plants as the energy source for photosynthesis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are the 3 main stages of photosynthesis?

A
  1. light harvesting
  2. light dependent reaction
  3. light independent reaction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is excitation of chlorophyll by light?

A

when a chlorophyll or some other photosynthetic pigment absorbs light, it changes from its ground state to excited state.
the excited molecule is unstable and tends to return to its original, ground state in 1 of 3 ways:
1. by transferring the energy (NOT the electron) directly to a neighbouring chlorophyll molecule by a process called resonance energy transfer. this occurs during light harvesting
2. by boosting an electron to a higher energy level and then transferring it to an electron acceptor (a nearby molecule capable of accepting electrons). the molecule returns to its original state by taking up a low-energy electron from another molecule (electron donor). this occurs in the light-dependent reaction.
3. (not used in photosynthesis) energy is lost in the process. this is achieved by converting excecss wat into heat or to a combination of heat and light to a longer wavelength. this occurs when light energy is absorbed by an isolated chlorophyll molecule in solution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is a photosystem?

A

in the thylakoid membrane, photosynthetic pigments that trap light energy are arranged into photosystems. photosystems convert the captured light energy into useful forms.
a photosystem consists of 3 closely linked components:
1. light harvesting complexes (LHCs) - light is collected by the 200-300 pigment molecules that are bound to them. LHCs are important in capturing light, and they absorb light energy and transfer the light energy to the reaction centre.
2. reaction centre - the reaction centre contains a pair of special chlorophyll a molecules that act as irreversible trap for energy. an excited electron is immediately passed to an adjacent chain of electron acceptors in the same complex.
3. a primary electron acceptor - it is found in the reaction centre and is involved in electron transfer.

17
Q

what are the 2 different photosystems and what are their differences?

A

photosystem II (PSII) and photosystem I (PSI).
- in PSII, the special chlorophyll a is known as P680 as it absorbs light maximally at a wavelength of 680nm
- in PSI, the special chlorophyll a is known as P700 as it absorbs light maximally at a wavelength of 700nm

the 2 photosystems
- are identical in their special chlorophyll a molecule
- but differ in their light-absorbing properties because of association with different accessory pigments & proteins in the thylakoid membrane, hence affecting the electron distribution

18
Q

what is the electron transport chain (ETC) and its function(s)?

A
  • ETCs are found at the thylakoid membranes in between the photosystems
  • electron carriers play an important role in redox reactions by transferring electrons from one carrier to another. electron carriers can be coenzymes/protein molecules. some electron carriers are arranged in series at the membrane to form ETC
  • at the ETC, electrons are passed down the carriers by a series of redox reactions. each carrier molecule receives an electron (reduction), and in turn donates it (oxidation) to the next carrier down the chain
  • an ETC allows the transfer of electrons to be done in several energy-releasing steps instead of one
  • an electron progressively loses energy as it is transferred from one carrier to another. some energy released is used to make ATP

coenzyme electron carriers include NADP (covered here), FAD & NAD

19
Q

describe the light harvesting stage of photosynthesis

A
  • light of appropriate wavelength strikes any pigment molecule within a photosystem
  • light energy is absorbed by that pigment molecule and the pigment becomes excited
  • the excitation energy is then transferred from one molecule to another within the cluster of pigment molecules
  • this is known as resonance energy transfer
20
Q

what is the light-dependent reaction of photosynthesis?

A
  • the role of this stage is to synthesise reduced nicotinamide adenine dinucleotide phosphate (NADPH) and ATP using captured light energy from the light-harvesting stage. chemical energy is trapped in NADPH & ATP
  • NADPH & ATP produced are used in the light-independent reaction to fix CO2 and trap energy in glucose
  • the light-dependent reaction can proceed via non-cyclic photophosphorylation (PSII, PSI & ETC) or cyclic photophosphorylation (only PSI)
  • then ATP is synthesised through chemiosmosis. chemiosmosis is the process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesise of ATP.

occurs in thylakoid membrane of chloroplasts

21
Q

describe non-cyclic photophosphorylation

A
  1. a photon of light strikes a pigment in a LHC & energy is relayed via resonance energy transfer until it reaches 1 of the 2 special chlorophyll a molecules in the PSII reaction centre. the photon of light excites one of the electrons in P680 to a higher energy state
  2. the photoexcited electron from P680 is captured by the primary electron acceptor in the reaction centre. now each P680 is missingan electron
  3. an enzyme splits a water molecule into 2 electrons, 2 hydrogen ions & 1 oxygen atom (photolysis of water, involves light). the electrons released is used to replenish the deficit of electrons from the reaction centre of PSII. the oxygen atom immediately combines with another oxygen atom, releasing O2 as a by product. [H2O -> 2e + 2H+ + 1/2O2]
  4. from the primary electron acceptor, the energised electron passes from PSII to PSI via a first ETC consisting ofthe following electron carrier molecules: from Pq (plastoquinone), down a cytochrome (b-f) complex then to Pc (plastocyanin) through a series of redox reactions. these electron carrier molecules are arranged in increasing electron affinity so that transport of electrons down the ETC is unidirectional.
  5. as electrons flow from molecule to molecule, it drops to lower energy levels. free energy released from this exergonic reaction is used to pump protons against concentration gradient from the stroma into the thylakoid space. a proton gradient will be generated across the thylakoid membrane, which is used to drive ATP synthesis. this synthesis of ATP is called photophosphorylation as it uses light energy to phosphorylate ADP.
  6. meanwhile, light energy from another photon of light strikes a pigment molecule in a light-harvesting complex of the PSI, exciting an electron of 1 of the 2 specal chlorophyll a in the PSI reaction centre. the excited electron iscaptured by the PSI’s primary electron acceptor, creating an electron deficit in the P700. this electron deficit is replenished by the electron from PSII that reaches the last electron acceptor of the first ETC.
  7. the excited electron is passed from PSI’s primary electron acceptor down a second ETC through ferredoxin (Fd).
  8. the enzyme NADP reductase transfers electrons from Fd to NADP. two electrons are required for its reduction to NADPH.
22
Q

describe cyclic photophosphorylation

only PSI involved, no NADPH produced

A
  1. light is absorbed by the LHC and passed on to chlorophyll a (P700) in the reaction centre of PSI.
  2. this causes the P700 molecule to emit an energised electron which is raised to a higher energy level and picked up by the primary electron acceptor in the reaction centre
  3. the energised electrons from PSI are passed to ferredoxin (Fd), cycled back to cytochrom (b-f) complex on the first ETC and from there back to PSI
  4. as these electrons are passed along the first ETC, enough energy is released to synthesise ATP from ADP and phosphate. consequently, ATP is produced. the ATP is needed in the light-independent stage of photosynthesis.
23
Q

describe chemiosmosis

A
  1. the thylakoid membrane is impermeable to H+, so as the light-dependent reaction proceeds, accumulation of hydrogen ions occurs in the thylakoid space.
  2. in the ‘Z-scheme’ of electron flow in non-cyclic photophosphorylation, electrons flow down energy levels along the electron transport chain from PSII to PSI, and release free energy. using this free energy, the cytochrome complex pumps hydrogen ions against the concentration gradient from the stroma, across the thylakoid membrane, into the thylakoid space.
  3. photolysis of water produces H+, which also contributes to the proton concentration in the thylakoid space. (proton gradient is also generated in non-cyclic photophosphorylation when H+ is removed from stroma to form NADPH)
  4. this results in an electrochemical & concentration gradient, known as a proton gradient, where there are more hydrogen ions inside the thylakoid space than there are in the stroma.
  5. the proton gradient drives the synthesis of ATP by ATP synthase complex. hydrogen ions diffuse down this gradient from the thylakoid space, across the thylakoid membrane, into the stroma through the ATP synthase complex
  6. this drives the formation of ATP, catalysed by the enzyme ATP synthase, where one ATP is catalysed for every two H+ that return to the stroma through the ATP synthase complex.
24
Q

what is the light-independent reaction?

A
  • the light-independent reaction is also known as the calvin cycle. none of the steps in this reaction requires light directly
  • the calvin cycle occurs in the stroma of chloroplasts
  • the purpose of the calvin cycle is to reduce carbon dioxide using ATP (energy source) and NADPH (reducing power), which were produced in the light-independent reaction
25
Q

what are the 3 phases in the calvin cycle?

A
  • carbon dioxide uptake & fixation
  • reduction of phosphoglyceric acid (PGA)
  • regeneration of carbon dioxide acceptor (RuBP), which ultimately leads to product synthesis and sugar formation
26
Q

describe the calvin cycle/light-independent reaction

A

carbon dioxide fixation
1. carbon dioxide diffuses through the stomata and into the cytoplasms of the mesophyll cells, and then into the chloroplasts
2. carbon dioxide is fixed when it combines with a five-carbon carbon dioxide acceptor, ribulose biphosphate (RuBP), to form an unstable six-carbon intermediate. this reaction, the carboxylation of RuBP, is catalysed by the enzyme ribulose bisphosphate carboxylase oxygenase (rubisco)
3. the unstable six-carbon intermediate spontaneously breaks down into two molecules of a three-carbon compound called phosphoglyceric acid (PGA) / 3-phosphoglycerate / glycerate-3-phosphate (GP)

reduction of PGA
1. each molecule of PGA is phosphorylated by ATP (receives extra phosphate group from ATP, forming 1,3-bisphosphoglycerate
2. a pair of electrons donated from NADPH further reduces 1,3-bisphosphoglycerate to form glyceraldehyde-3-phosphate (GALP or G3P) / triose phosphate (TP). the hydrogen for the reduction comes from NADPH while the energy required comes from ATP

regeneration of carbon dioxide acceptor
1. for every 3 molecules of CO2 that enters the calvin cycle, 3 molecules of RuBP are carboxylated and a total of 6 molecules of TP are formed
2. only 1 molecules of TP can be counted as a net gain of carbohydrate as the other 5 molecules of TP must be used to regenerate the 3 molecules of RuBP used in carbon dioxide fixation. [each TP has 3 carbons, total carbons in 5 TPs = 15. each RuBP has 5 carbons, so 15/5 = 3 RuBP that can be regenerated, which was used to form 6 TPs]. to regenerate 3 molecules of RuBP, 3 molecules of ATP are invested
3. RuBP is regenerated and the calvin cycle continues

product synthesis and sugar formation
1. the TP spun off from the light-independent reaction becomes the starting material for metabolic pathways that synthesise oher organic compounds,including glucose and other carbohydrates
2. 2 molecules of TP are utilised to synthesise 1 molecule of hexose sugar. so the formation of 1 molecule of hexose sugar requires 6 turns of the calvin cycle [3 turns gets 1 TP]
3. note: the carbon & oxygen atoms of hexose sugars come from CO2 while the hydrogen atoms come from NADPH

note! PGA = 3-phosphoglycerate = GP
GALP = G3P = TP

27
Q

how are photosynthetic products (TP & PGA) used by the plant?

TP is the end product but does not accumulate

A

TP can be used by the cell outside the chloroplasts in the synthesis of all forms of carbon-containing substances, including other carbohydrates, lipids, proteins, nucleic acids and chlorophyll

synthesis of carbohydrates
- a large proportion of TP is converted to hexose sugars, particularly glucose & fructose which are respiratory substrates for ATP production.
- for storage, many glucose molecules are covalently linked together to form starch molecules that are stored as starch granules
- glucose molecues are also polymerised to form cellulose which is needed for structural growth of plants (forming new cell walls)

synthesis of lipids
- PGA can enter the glycolytic pathway and is converted to an acetyl group, which is added to coenzyme A to form acetyl CoA. acetyl CoA is converted to fatty acids in both the cytoplasms and chloroplasts
- glycerol is made from TP
- fatty acids & glycerol combine to form triglycerides (for storage) and phospholipids (for cell membranes)

synthesis of proteins
- PGA & TP are important precursors in the synthesis of amino acids and hence protein
- in the process, nitrogen is incorporated into the product molecules
- plants in turn use these molecules to make other nitrogen-contain compounds, including nucleotides

28
Q

what is a limiting factor?

A

when a reaction is affected by more than one factor, its rate is limited by the limiting factor which is in shortest supply

the principle of limting factors states that:
- the rate of a biochemical process which consists of a series of reactions is limited by the slowest reaction in the series
- when affected by several factors, the rate of the biochemical process is limited by that factor which is nearest its minimum value. the limiting factor directly affects the biochemical process if its quantity is changed

29
Q

how does light intensity affect the rate of photosynthesis?

A
  • at low light intensities, the rate of photosynthesis increases linearly with increasing light intensity until it reaches a point whereby a further increase in light intensity has no effect on the rate of photosynthesis. at this point, photosynthesis is no longer limited by light - it is said to be light-saturated, and other factors become limiting.
  • light intensity is measured in lux (lx). illumination on a clear summer’s day is about 100000 lux, whereas light saturation for photosynthesis is reached at about 10000 lux. so except for in shaded plants, light is not normally a major limiting factor.
  • very high light intensities may damage chlorophyll (photobleaching) and decrease the rate of photosynthesis. plants that have been naturally exposed to such conditions are usually protected by thick cuticles and hairy leaves
30
Q

what is compensation point and how does it affect photosynthesis?

A
  • the compensation point is the point at which the rate of photosynthesis is equal to the rate of respiration
  • at the compensation point, all CO2 produced during respiration is used for photosynthesis and all oxygen produced during photosynthesis is used for respiration. there is no net gaseous exchange between the plant & its environment at compensation point
  • compensation point is reached at quite low light intensities, usually at sunrise & at sunset
  • below compensation point, the rate of photosynthesis is less than the rate of respiration and so there is net release of CO2 and absorption of oxygen from the atmosphere
  • above compensation point, the rate of photosynthesis is more than the rate of respiration and so there is a net absorption of CO2 and release of oxygen into the atmosphere
31
Q

(just read) differences between sun & shade plants

A

rate of respiration: shade plants have a lower rate of respiration than that of sun plants
rate of photosynthesis: sun plants have a much higher rate of photosynthesis than shade plants
palisade mesophyll layers: shade leaves are thin with fewer palisade mesophyll layers -> fewer cells = less energy for maintenance -> shade plants reach compensation point at a lower light intensity (sooner). sun leaves are thick with more palisade mesophyll layers -> more cells = more energy for maintenance, but they can also absorb higher light intensities -> more palisade layers enable sun plants to trap more light energy to produce carbohydrates
PSI/PSII ratio: sun plants have high PSI/PSII ratio while shade plants have low PSI/PSII ratio
maximum photosynthetic rate, light saturation point, light compensation point, respiration rate: sun plants all high, shade plants all low
size of chloroplasts: sun plants have small chloroplasts, shade plants have large chloroplasts
thylakoid arrangement: sun plants have regularly arranged thylakoids while shade plants have irregular thylakoids
amounts of grana stacks: sun plants have small amounts of grana stacks relative to stromal membranes, while shade plants have large amount of grana stacks

32
Q

how does light quality (wavelength) affect photosynthesis?

A
  • wavelength of light is inversetly proportional to energy possessed by the light
  • red light has a longer wavelength and less energy than blue light. so one photon of blue light provides more energy for photosynthesis than one photon of red light
33
Q

how does carbon dioxide concentration affect photosynthesis?

A
  • CO2 is needed in the calvin cycle where it is used to make sugar
  • as the concentration of CO2 increases, the rate of photosynthesis also increases, until carbon dioxide becomes saturated and is no longer limiting
  • under normal conditions, CO2 is the major limiting factor in photosynthesis as its concentration in the atmosphere varies between 0.03% and 0.04%
  • greenhouse crops are grown in carbon dioxide-enriched environment for greater yield
34
Q

how does temperature affect the rate of photosynthesis?

A
  • the light-independent reactions are enzyme controlled and thus temperature sensitive
  • for temperate plants, the optimum temperature is usually about 25C
  • rate of reaction doubles for every 10C rise up to about 35C. as temperature rises towards the optimum, rate of reaction increases asmolecules involved move more rapidly and have a greater chance of colliding
  • rate of photosynthesis decreases at higher temperatures as enzymes start to denature
35
Q

how does chlorophyll concentration affect photosynthesis?

A
  • chlorophyll concentration is not normally a limiting factor, but reduction in chlorophyll levels can be induced by several factors, including diseases, mineral deficiency, normal ageing process & lack of light
  • if the leaf turns yellow, it is termed to be chlorotic and this yellowing process is called chlorosis

light is needed for the final stage of chlorophyll synthesis

36
Q

how do specific inhibitors (DCMU, cyanide etc) affect rate of photosynthesis?

A
  • DCMU (dichlorophenyl dimethyl urea) short-circuits non-cyclic electron flow in chloroplasts, inhibiting the light-dependent reactions
  • cyanide disrupts photosynthesis by disrupting bond interactions between R-groups of proteins in the ETC
37
Q

how does water affect the rate of photosynthesis?

A
  • periods of temporary wilting can lead to severe losses in crop yield. plants usually close their stomata in response to wilting, preventing access of CO2 for photosynthesis
  • even slight water deficiency can significantly reduce crop yield
  • abscisic acid, a growth inhibitor, has also been shown to accumulate in water-deficient leaves of some species
38
Q

how does oxygen affect rate of photosynthesis?

A
  • at any one time, there is much more oxygen thatn CO2
  • in many plants, the initial fixation of carbon in the calvin cycle is catalysed by the enzyme rubisco
  • but oxygen competes with Co2 for the active site in rubisco
  • less CO2 will be fixed, and previously fixed carbon in RuBP will be lost as CO2 -> net loss of carbon
  • less PGA is synthesised and photosynthetic output decreases
  • this is known as photorespiration
39
Q

how do certain pollutants affect rate of photosynthesis?

A
  • low levels of certain gases of indutrial origin, eg ozone & sulfur dioxide, are very damaging to the leaves of some plants
  • soot can block stomata and reduce the transparency of the leaf epidermis (prevents light from getting to mesophyll cells)

bio (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions