photosynthesis Flashcards
photosynthesis equation
6CO2 + 6H20 = C6H12O6 + 6O2
adaptions of a leaf for photosynthesis
- large SA
- thin
- stomatal pores
- air spaces in spongy mesophyll
- spaces between palisade cells
large SA significance for photosynthesis
capture as much light as possible
thin leaf significance for photosynthesis
light penetrates through the leaf
stomatal pores significance for photosynthesis
allows CO2 to diffuse into the leaf
spaces between palisade cells and air spaces in spongy mesophyll significance for photosynthesis
allows CO2 to diffuse into to the photosynthesising cells
leaf cell adaptions for photosynthesis
- transparent cuticle and epidermis
- thin cellulose cell walls
- large vacuole in palisade cells
- cylindrical palisade cells
- palisade cells elongated at right angles to leaf surface
transparent cuticle and epidermis, and thin cellulose cell walls significance for photosynthesis
light penetrates through to mesophyll
large vacuole in palisade cells significance for photosynthesis
chloroplasts form a single layer so they don’t shade each other
cylindrical and elongated at right angles palisade cells significance for photosynthesis
- leaves accommodate a large number of palisade cells
- light only passes through 2 epidermal cell walls and 1 palisade cell wall to reach chloroplasts
chloroplast adaptions for photosynthesis
- large SA
- can move and rotate within palisade cells
- pigments in thylakoid in single layer at surface of thylakoid membrane
- more chloroplasts in palisade than spongy mesophyll cells
chloroplast large SA significance for photosynthesis
maximum absorption of light
chloroplasts can move and rotate within palisade cells significance for photosynthesis
- move to top of cell on dull days for max light absorption
- high light intensity moves to bottom to protect pigments from bleaching
pigments in thylakoid in single layer at surface of thylakoid membrane significance for photosynthesis
thylakoids maximise light absorption
more chloroplasts in palisade than spongy mesophyll cells significance for photosynthesis
palisade cells are at top of leaf so more exposed so chloroplasts can maximise light absorption
pigments in thylakoids are in a single layer at surface of thylakoid membrane significance for photosynthesis
pigments maximise light absorption
photophosphorylation
an endergonic reaction bonding a phosphate ion to a molecule of ADP, using energy from light, making ATP
- non-cyclic vs cyclic
thylakoid lamellae
folded inner membrane of chloroplasts
stroma
fluid filled chloroplast interior
bathes thylakoids and grana
location of light independent stage
contains enzymes for photosynthesis
grana
stacks of thylakoids
location of photosynthetic pigments
location of light dependent stage
why are starch grains white?
stain binds to lipids
where are chloroplasts found in a leaf?
- leaves and stems
areas exposed to light - in palisade and spongy mesophyll
- in guard cells
what is a transducer?
changes energy from one form to another.
biological transducers waste little energy
how are chloroplasts transducers?
they turn energy in photons of light into chemical energy, made available through ATP and incorporated into molecules
what is a photosynthetic pigment?
a molecule that absorbs specific wavelengths of light
traps light energy
different pigments = trap different wavelengths
types of photosynthetic pigments
- chlorophyll a = blue/green
- chlorophyll b = yellow/green
- b-carotene = orange
- xanthophyll = yellow
chlorophyll definitation
protein containing magnesium, bound to thylakoid membrane
absorption spectrum
a graph showing how much light is absorbed at different wavelengths
( relative absorption)
patterns of absorption spectrum
- chlorophyll a+b absorb light energy in red/blue-violet regions, and reflect green
- carotenoids absorb light energy in blue/green region, so appear yellow/orange
action spectrum
graphs showing rate of photosynthesis at different wavelengths
- measured by mass of carb synthesised by plant at various wavelengths
where are photosystems found
in the plane of the thylakoid membrane
what is a photosystem made of?
- antenna complex
- reaction centre
they are a collection of accessory pigments
antenna complex
- contains photosynthetic pigments, anchored into phospholipids of thylakoid membrane
held together by clusters of protein molecules - consists of one cluster
- pigments combos = various wavelengths absorbed
- transfer energy to chlorophyll a in reaction centre
reaction centre of photosystems
- within antenna complex
- 2 molecules of primary pigments (chlorophyll a). absorbs light, excitation emits 1 electron each
PS1
arranged around chlorophyll a molecule
absorption peak = 700nm
PS2
arranged around chlorophyll a molecule
absorption peak = 680nm
accessory pigments
- chlorophyll b and carotenoids
light absorbing molecules, pass energy through to reaction centre to reach chlorophyll a
excited chlorophyll a electrons = energy level raised
chlorophyll a
- primary pigment
passes energy to subsequent reactions of photosynthesis
what does the light dependent stage produce?
- ATP, to synthesis molecules (glucose)
- reduced NADP, to reduce synthesising molecules
- oxygen, by-product, diffuses out leaf
cyclic photophosphorylation
- PS1
- electrons cycle
- in all photosynthetic organisms
non-cyclic photophosphorylation
- PS1 + PS2
- linear electron pathway
- in plants, algae, cyanobacteria
cyclic photophosphorylation stages
- PS1 absorb photons, excites chlorophyll a electrons (in reaction centre)
- electrons emitted and picked up by electron acceptor
- pass down electron carriers to PS1
- energy released phosphorylates ADP to ATP
- electrons path: PS1 to electron acceptor to PS1
- electron recycled into chlorophyll a
non-cyclic photophosphorylation stages
- PS2 absorbs light energy, excites pair of electrons in chlorophyll a and leave it
- electron carrier takes up pair
- electrons need to be replaced. photolysis of water provides electrons
- electrons pass down transport chain, each stage loses energy
- lost energy combines Pi with ADP = ATP
- light energy absorbed by PS1 excites electrons
- electrons and 2H transferred to NADP = reduced NADP
enters independent reaction
photolysis of water
- splitting of water molecules by light in thylakoid spaces
- indirectly produces 2H, 2 electrons, 1/2 oxygen
- electrons replace those lost from PS2
- protons and electrons (from PS1) reduce NADP
- oxygen diffuses out stomata (waste product)
Rf value calculation
distance travelled by pigment
divided by
distance travelled by solvent front
what is chemiosmosis?
the process of moving ions (protons) to the other side of a biological membrane
- through ATP synthetase, into stroma
- produces electrochemical gradient
- once in stroma protons can reduce NADP
3 factors that maintain proton gradient between thylakoid space and stroma
- proton pump (protons into thylakoid space)
- photolysis of water
- removal of protons from stroma, reduces NADP
carboxylation of light independent stage steps
- CO2 enters chloroplasts
- CO2 combines with RuBP (5C) catalysed by rubisco
- unstable 6C compound formed
- 6C splits into 2 molecules of a 3C compound, glycerate-3-phosphate (GP)
reduction of light independent stage steps
- GP reduced to TP (3C). reduced NADP provides H ions, ATP provides energy
- NADP reformed and recycled
- TP converted to useful compounds (glucose), then to starch
regeneration of light independent stage steps
- 5/6 TP molecules produced regenerate RuBP
- rest of ATP provides energy
products of calvin cycle
- carbohydrate: hexose sugar, glucose (fructose bisphosphate)
- lipids: produced from TP
- proteins: amino acids produced using nitrogen from nitrates
hexose sugars
- monosaccharide, 6C
- made by joining 2TP
- 1 hexose sugar = 6 calvin cycle turns
what is a limiting factor?
- factor that limits the rate of a physical process by being in short supply
how does CO2 limit photosynthesis?
- when in short supply it limits photosynthesis
- CO2 increase = photosynthesis increases
- eventually plateaus
how does light intensity limit photosynthesis ?
- plant in darkness = light dependent reaction can’t occur
- light intensity increases = efficiency of light dependent reaction increases
- eventually reaches max rate
- if too high = photosynthetic pigments damaged = no photosynthesis
how does temperature limit photosynthesis?
- involves enzymes, so increase in temp = increased KE = increase successful collisions = increased rate of reaction
- temp above optimum = enzymes denature = decreases rate
how does water limit photosynthesis?
- when water is scarce, plant cells plasmolyse = stomata close = wilting
sun plants
most efficient at high light intensities
shade plants
most efficient at low light intensities
light compensation rate
light intensity at which a plant has no net gas exchange.
volumes of gases used and produced in photosynthesis and respiration are equal
- low light intensity = decreased rate of photosynthesis = decreased CO2 uptake. so respiration provides all the CO2 needed. and all the O2 needed for respiration is provided by photosynthesis
roles of inorganic nutrients in plants
- structural
- synthesis of compounds for growth
- form molecule parts, e.g. magnesium in chlorophyll
function of nitrogen in plants
- synthesis of nucleic acids, proteins and chlorophylls
- become amino groups of amino acids
symptoms of nitrogen deficincy
- reduced growth of entire plant
- yellow leaves = chlorosis
function of magnesium in plants
- chlorophyll production
symptoms of magnesium deficiency
- yellow leaves = chlorosis
begins in older veins as Mg is prioritised to newer leaves
explain the advantage of plants having more than one pigment in their leaves
- light can be absorbed over a greater range of wavelengths
- more light absorbed = more products from light dependent stage
- greater rate of photosynthesis
