3.2 photosynthesis Flashcards
what is the photosynthesis
the process by which carbohydrates are synthesised from carbon dioxide and water using light energy
what is the main site of photosynthesis in plants
palisade mesophyll cells/ tissue
what part of the lead has the most chloroplast
top part of the lead in the palisade cell
label chloroplasts and
where does photosynthesis take place
in chloroplasts
what do chloroplasts contain
photosynthetic pigments which absorb light energy at particular wavelengths of light
how are leaves adapted for photosynthesis
-spongy mesophyll, air spaces for gas exchange
-large SA (flat and thin)
- waxy cuticle (reduce water loss)
- thin, upper layer is transparent so light can penetrate through the leaf (short diffusion distance)
how are chloroplasts adapted for photosynthesis
stacked thylakpids (increase SA)
move around to optimise light absorption
chloroplasts have many grana, large SA
what is an energy transducer
something that changes energy from light into chemical energy
why do plants look green
plants absorb light from all electromagnetic spectrum except for the colour green, it is reflected
how can photosynthetic pigments be seoarated
using chromatography
what is a photosynthetic pigment
a photosynthetic pigment is a chemical substance that is present in chloroplasts to absorb the light energy necessary for photosynthesis
what are the 2 different groups of photosynthetic pigments
chlorophyll and carotenoids
different chlorophylls
where are they present
chlorophyll a
chlorophyll b
they’re all green, found in green plants
carotenoids
carotene (orange and in all plants)
xanthophyll (yellow and in most plants)
what is the absorption spectrum
a graph to show the absorbance of different wavelengths of light by a pigment
what is the action spectrum
a graph to show the rate of photosynthesis at different wavelengths of light
where are photsysytems found
embedded in the thylakoid membrane
explain how light harvesting works
energy from different wavelengths absorbed by an ‘antenna’ complex of an accessory pigment is ‘funneled down’ to a reaction centre
example of accessory pigments
chlorophyll B/ carteroids
where is the reaction centre found
at the base of the photosysten, it contains a pair of chlorophyll A molecules
what does the antenna complex contain
many different light absorbing pigments
puprose of the photosystem
to trap as much light energy as possible
how many photosystems are there
2
at what wavelength does chlrophyll A absorb light in photosystem 1 and 2
- 700nm
- 680 nm
what is the light dependent stage
photophosphorylation
what happens in the light dependent stage
electrons lost from the reaction centre pass along a chain of electron acceptors which power a hydrogen pump that carries a H+ ion from the stroma to the thylakoid lumen
what is photophosphorylation
the addition of a phosphate group to ADP to form ATP using light energy
2 types of phosphorylation
cyclic/non-cyclic
what photosystem does cyclic phosphorylation involve
just photosystem 1
explain cyclic phosphorylation
a photon of light hits photosystem 1, 2 electrons become excited, they pass to an electron acceptor, this is donated to the ETC which generates a proton gradient for chemiosmosis. the electrom is passed back to PS1.
what is the purpose of the ETC generating energy
cyclic phosphorylation
energy is needed so H+ ions go from stroma to the thylakoid lumen.
non-cyclic photophosphorylation
an alternative pathway, both photosystems
high energy electrons from PS1
what does photolysis provide and what is it
provides an electron for PSII
molecules of water absorb light energy and split to form electrons protons and oxygen
what do the electrons from photolysis do
passed to PSII to replace those lost during non-cyclic photophosphorylation
what do the protons from photolysis do
used to reduce NADP each NADP molecule picks up 2 protons and 2 electrons to become reduced
what are the products of the light dependent stage
ATP and reduced NADP
both are needed in the calvin cucle
what is the light independent stage
the calvin cycle, it fixes carbon dioxide into glucose using ATP (from photophosphorylation) and reduced NADP
where does the calvin cycle happen
stroma
what controls the calvin cycle
enzymes
3 stages of the calvin cycle
fixation
reduction
making glucose and regeneration of rubulose bisphosphate
explain the first stage of the calvin cycle
carbon dioxide is taken up by 5C ribulose bisphosphate to form an unstable 6c molecule (catalysed by rubisco)
this 6c molecule then dissociates into 2 glycerate 3 phosphate molecules
explain the second stage of the calvin cycle
Glycerate 3 phosphate is reduced (gains 2H atoms) into triose phosphate using ATP
NADP reduced goes to NADP (gives up H atoms)
explain the third stage of the calvin cycle
5/6 of triose phosphate is used t make ribulose phosphate
1/6 of triose phosphate is used to mkae glucose (can be converted into fructose or sucrose and starch)
ribulose phosphate is converted to RuBp using ATP (ADP+Pi)
how many turns of the calvin cycle to make glucose
6
mineral requirements for plants
nitrogen: for amino acid, protein production and chlorophyll production (deficience: reduced growth of organs and yellowing of the leaves (chlorosis))
** magnesium**: essential for production of chlorophyll. deficiency:yellowing of leaves=chlorosis)
3 limiting factors of photosynthesis
temperature, light intensity, CO2
what is a limiting factor of photosynthesis
where if any of the factors become too low, rate of photosynthesis will decrease
limiting factor: temperature
affects kinetic energy and therefore rates of transport and enzyme activity
limiting factor: light intensity
light is needed to excite electrons in the photo system during the light dependent stages
limiting factor: CO2
as concentration increases, the rate of the light independent reactions increase the rate of photosynthesis increases
