photosynthesis Flashcards
name the main photosynthetic tissue in a leaf
palisade mesophyll
describe the method to study the density of stomata?
- apply clear nail polish to the lower epidermis of a leaf between the veins and allow it to dry
- using forceps, peel the nail polish from the leaf - producing a replica of the lower epidermis
- place the replica on a microscope slide and count the quantity of stomata using the microscope
why are stomata essential?
allows gas exchange to occur in the leaf
give 3 adaptations of the leaf for photosynthesis
- large surface area
- thin so light penetrates photosynthetic tissues
- air spaces to allow CO2 to diffuse to photosynthesising cells
why is compartmentalisation important?
- reactions occur in small volume/isolation of enzymes/ reactants
- keeping products separate from cytoplasm by use of membranes to isolate reactions within organelles
- can use mitochondria close to areas needing ATP/movement of organelles within cytoplasm
what are the 2 stages of photosynthesis?
- where do they occur and what are their functions?
- LIGHT DEPENDANT STAGE
location : thylakoid membrane and thylakoid cavity of chloroplast
function : involves the conversion of light energy into chemical energy (ADP and NADPH) - LIGHT INDEPENDANT STAGE
location : stroma of chloroplast
function : uses the product of the light dependant stage to produce organic molecule such as glucose
explain why accessory pigments are important in photosynthesis
accessory pigments are important as they absorb wavelengths of light not absorbed by primary pigments.
- this ensures a wider range of wavelengths increases efficiency of photosynthesis
what are the two main types of photosynthetic pigments in flowering plants? describe them.
primary pigments : chlorophyll a, absorbs blue and red wavelengths of light
accessory pigments :
- chlorophyll b, absorbs blue and red wavelengths of light
- carotenoids, (xanthophyll & carotene) absorb violet/blue light
which macronutrient is needed for the production of chlorophyll a?
Mg2+
where are photosynthetic pigments found?
thylakoid membranes of chloroplast
what is the role of photosynthetic pigments?
to absorb light energy from the sun and convert it into chemical energy
what is chromatography used for?
can be used to separate photosynthetic pigments
what are the steps involved in chromatography?
- tear up leaves and grind with acetone to form a dark green pigment solution
- use a capillary tube to spot the pigment onto chromatography paper
- place the chromatography paper into a solvent (acetone/petroleum)
- remove the chromatography paper once the solvent has travelled to the top of the strip. observe the different distances the pigments have travelled
- calculate the Rf value for each pigment
- identify each pigment by comparing Rf values to known values
CHROMATOGRAPHY:
- why do we add acetone?
- why is a solvent needed?
- why do the pigments travel different distances?
- which pigment travels the furthest distance and which pigment travels the shortest distance? why?
- acetone dissolves the phospholipid membrane to extract the pigments
- to dissolve solute and carry the pigment up the chromatography filter paper
- more soluble substances move further
- carotene travels the furthest distance and chlorophyll b the shortest because carotene is the most soluble and chlorophyll b is the least soluble
how are Rf values calculated?
distance travelled by the pigment / distance travelled by solvent
what is the absorption spectrum?
a graph that shows the amount of light absorbed by each photosynthetic pigment at each wavelength of light
what colour does chlorophyll a absorb?
blue and red
what colour does chlorophyll b absorb?
blue and orange
what colour do carotenoids absorb?
blue
suggest an experiment that you would conduct to measure the rate of photosynthesis
count the number of bubble produced by pondweed over a set period of time
what is the action spectrum?
a graph that shows the rate of photosynthesis at different wavelengths of light
describe the relationship between graphs for the absorption spectrum and the action spectrum
there is a close correlation between the 2 spectra, this suggests that the pigments are responsible for absorbing light used in photosynthesis
where are photosystems found?
thylakoid membrane of a chloroplast
what is the role of photosystems?
- absorb photons of light
- act as transducers by transferring this light energy to high energy electrons
- this can then be used to fuel proton pumps and the synthesis of ATP
describe the structure of photosystems.
- the accessory pigments are grouped with associated proteins, forming an antenna complex
- these pigments absorb photons of light energy and funnel this energy down the antenna complex to the reaction centre below.
- chlorophyll a molecules are found in the reaction centre below the antenna complex. when photons of light energy reach chlorophyll a in the reaction centre, electrons are excited to become high energy electrons
what are the 2 types of photosystems involved in the light dependant reactions?
- photosystem 1
- photosystem 2
what are the 2 light dependant reactions called?
- non-cyclic photophosphorylation
- cyclic phosphorylation
describe the light dependant reaction
- requires light energy
- takes place in the thylakoid membrane and thylakoid cavity
- ATP is synthesised from ADP and Pi
- this is called photophosphorylation (light is involved)
- the splitting of water using light is involved and is known as photolysis
- NADP is reduced to NADPH/H+ (reduced NADP)
- oxygen gas is released as a by product
describe photolysis
- it is the splitting of water using light
- occurs in the thylakoid cavity
- water splits into oxygen, hydrogen ions and electrons
- electrons replace those lost by photosystem 2, making the chlorophyll molecule stable
- protons produced help maintain the electrochemical gradient between the thylakoid cavity and the stroma
where does cyclic phosphorylation take place?
in bacteria and primitive plants
describe cyclic photophosphorylation
- higher plants use this pathway to provide extra ATP, especially when CO2 is short in supply
- only PS 1 is involved
- light energy is absorbed at PS 1 and channelled or absorbed by chlorophyll a
- electrons become excited, energised and released from the Mg ion at the centre of the chlorophyll molecule. the electron is accepted by an electron acceptor and eventually passes along the same transfer chain as that used by the electrons from PS 2
- protons are pumped and ATP is produced from ADP + Pi. the same chemiosmotic theory is believed to be involved in the production of ATP as in part of the Z scheme. The electron excited and released from PSI returns to PSI.
describe what occurs at photosystem 1 in non-cyclic photophosphorylation
- photosystem 1 absorbs photons and this causes 2 electrons to be emitted and raised to a higher energy level where they are picked up by another electron acceptor
- the electron acceptor passes some of these electrons to hydrogen ions outside the thylakoid membrane into the stroma where they reduce NADP to NADPH
- the reduction of NADP requires protons so lowers their concentration in the stroma - this maintains the electrochemical gradient between the thylakoid space and the stroma
- the electrons are not recycle back into chlorophyll
describe what occurs at photosystem 2 is non-cyclic photophosphorylation
- photons of light are absorbed by photosystem 2 and passed to chlorophyll a in the reaction centre
- this excited chlorophyll a and two electrons are released and raised to a higher energy level. they are passed to electron acceptors
- the electron acceptors pass the electrons along a chain of carriers and through a proton pump and to photosystem 1
- as the electrons pass from carrier to carrier their energy levels drop. energy is released from the electrons and is used to provide energy to pump hydrogen ions from the stroma across the thylakoid membrane into the thylakoid cavity
- this creates an electrochemical gradient : high H+ in the thylakoid cavity, low H+ concentration in stroma
- H+ ions flow down this proton gradient through protein channels. this provides energy for formation of ATP by ATP synthase from ADP and Pi.
in non-cyclic photophosphorylation where does PSII obtain replacement electrons from?
photolysis
in non-cyclic photophosphorylation where does PSI obtain replacement electrons from?
PSII
in cyclic photophosphorylation what happens to the electrons excited and released from PSI?
pass down an electron transport chain and then return to PSI
in non-cyclic photophosphorylation what happens to oxygen produced from photolysis?
oxygen is released as a waste gas or used during respiration
when might plants shift from non-cyclic to cyclic photophosphorylation?
when chloroplast runs low on ATP, it shifts from cyclic to non-cyclic
outline the key features of the light independant reaction
- does not require light
- uses products of light dependant stage of photosynthesis, ATP and reduced NADP
- products are used in the fixation of carbon dioxide from the atmosphere to organic molecules
- takes place in the stroma of the chloroplast
- known as the Calvin Cycle
describe the process of the light independent stage (calvin cycle)
- carbon dioxide from the atmosphere is fixed with RuBP
- the enzyme RuBisCo catalyses this reaction
- this forms an unstable 6C carbon compound which splits into 2 molecules of glycerate-3-phosphate (GP)
- GP is then reduced using reduced NADP (produced during light dependent stage)
- ATP from the light independent stage is also required. ATP is hydrolysed and GP is phosphorylated in the formation of 2 molecules of triose phosphate (TP).
- 1 carbon atom of the 6 available is removed from the Calvin cycle and can be used to produce organic molecules such as glucose
- 5 carbon atoms remain in the Calvin cycle and are used to regenerate RuBP so the cycle can begin again
name the organic molecules that can be produced as a result of photosynthesis
amylose
amino acid
unsaturated fatty acid
cellulose
NITROGEN:
how is it transported?
what is the function?
what is the symptom of deficiency?
- taken up by roots as nitrates. transported as nitrates in xylem & amino acids in the phloem
functions:
- synthesis of proteins
- synthesis of nucleic acids
symptom:
- reduced growth of organs
- chlorosis : yellowing leaves due to inadequate chlorophyll production so plant no longer able to absorb light energy
name inorganic nutrients in plant metabolism
nitrogen
magnesium
phosphate
MAGNESIUM:
how is it transported?
what is the function?
what is the symptom of deficiency?
- absorbed as Mg2+ and transported in the xylem
functions:
- chlorophyll production
- activation of ATPase
symptom:
further chlorosis between veins of older leaves as existing Mg2+ is moved and transported to new leaves
PHOSPHATE:
how is it transported?
what is the function?
what is the symptom of deficiency?
- absorbed as PO4- by the roots and transported in the xylem
functions:
- forms phospholipids
- forms nucleotides (ATP/DNA/RNA with nitrogen)
symptoms: stunting of plant growth
identify the limiting factors of photosynthesis
- temperature
- CO2 concentration
- light intensity
describe temperature as a factor that affects the rate of photosynthesis
- affects rate of enzyme activity
- as temperature increases so does enzyme activity and therefore we would expect rate of photosynthesis to also increase
describe the effect of enzyme denaturation on the rate of photosynthesis
less active sites available, less substrate-enzymes complexes form, active site changes shape, so rate of photosynthesis decreases
suggest why an increase in temperature speeds up the rate of the light independent stage more than it speeds up the rate of the light dependent stage
light independent stage is much less dependent on enzyme activity than light independent stage
explain the implications of this on the overall rate of photosynthesis
- increase in temperature speeds up light independent stage more than the light dependent stage
- supply of products from light dependent stage will not be able to keep up with the demands from light independent stage
- overall rate of photosynthesis is limited by supply of reduced NADP and ATP
describe concentration of carbon dioxide as a factor that affects the rate of photosynthesis
- during photosynthesis carbon dioxide is fixed to form carbohydrates.
- carbon dioxide makes up only 0.035% of atmospheric air and therefore often limits the rate of photosynthesis
describe the physical change in the leaf that might result in a decrease in the rate of photosynthesis at high carbon dioxide concentrations
- CO2 diffuses into leaves and dissolves into the water
- carbonic acid is formed which dissociates to form H+ ions
- the accumulation of H+ causes cells to become more acidic
- the acidity denatures enzymes in mesophyll cells in leaves
describe light intensity as a factor that affects the rate of photosynthesis
- essential for excitation of electrons and for photolysis in the light dependant reaction
- as light intensity increases so does the rate of cyclic and non-cyclic photophosphorylation
explain the effect that increased light intensity has on the yield of photosynthates
the yield of photosynthates will increase, as more products are being produced
describe the physical changes in a leaf that might result in the plateau at high light intensity and explain the advantage to the plant
at high light intensity, temperatures are also high so stomata close to reduce transpiration/wilting
define antenna complex
clusters of associated proteins which absorb photons of light energy and funnel this energy downwards
define compensation point
when the rate of photosynthesis is equal to the rate of respiration
