module 5.2.1 Flashcards
what are autotrophs
organisms that use light energy or chemical energy and inorganic molecules (carbon dioxide and water) to synthesise complex organic molecules
what are heterotrophs
organisms that ingest or digest complex organic molecules, releasing the chemical potential energy stored in them
what are phototrophs
organisms that uses energy from sunlight to synthesise organic compounds for nutrition
what are chemoautotrophs
organisms which synthesise complex organic molecules using energy derived from exergonic chemical reactions
what is carbon fixation
the process by which CO2 is converted into sugars
what is photosynthesis
the process whereby light energy from the Sun is transformed into chemical energy and used to synthesis large/complex organic molecules from inorganic substances
what can both photoautotrophs and heterotrophs release
they can release the chemical potential energy in complex organic molecules (made during photosynthesis) - this is respiration
they can also use the oxygen for aerobic respiration
what is the equation for photosynthesis
6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2
what type of reaction is photosynthesis
endothermic
what happens after the oxygen is release back into the atmosphere
organisms can use the oxygen for aerobic respiration
this releases carbon dioxide back into the atmosphere and produces water
in plants, what are the 2 stages of photosynthesis
light-dependent and light-independent
where does light-dependent and light-independent take place
in the chloroplasts
when do plants respire
all the time
when do plants photosynthesise
in the daytime
what does compensation point mean
when photosynthesis and respiration proceed at the same rate, so there is no net gain or loss of carbohydrate
what does compensation period mean
the time taken for photosynthesis and respiration to occur at the same time
explain, with examples, why the compensation period varies between plants
shade plants have a shorter compensation period than sun plants, which require a higher light intensity to reach their optimum rate of photosynthesis
how is a chloroplast shaped and how long is it
most are disc-shaped and between 2-10µm long
how long is the intermembrane space
10-20nm wide
what does the outer membrane of the chloroplast allow to go through
it is permeable to small ions
is the inner membrane more or less permeable than the outer membrane
less permeable
how does transport through the inner membrane of a chloroplast work
it has transport proteins embedded in it
these can control entry and exit of substances between the cytoplasm and the stroma
what does a grana consist of and what does this contribute to
stacks of up to 100 thylakoid membranes
a large surface area for the photosynthetic pigments, electron carriers and ATP synthase enzymes (light-dependent reaction)
what are photosynthetic pigments arranged into
photosystems
how are the photosystems held in place
by the proteins embedded in the grana
what does the fluid-filled stroma contain and what does it do
it contains the enzymes needed to catalyse the reactions of the light-independent stage of photosynthesis
why is the grana surrounded by the stroma
so the products of the light-dependent reactions, which is needed for the light - independent reaction, can readily pass into the stroma
what can chloroplasts make and what are they used for
some of the proteins they need for photosynthesis, using genetic instructions in the chloroplast DNA
what are photosynthetic pigments
light absorbing pigments to excite the electrons and has a long hydrocarbon. this is found in the thylakoid membrane. different pigments absorb different wavelengths
what is a photosystem
a funnel-shaped light-harvesting cluster of photosynthetic pigments, held in place in the thylakoid membrane of a chloroplast. the primary pigment reaction centre is a molecule of chlorophyll a. The accessory pigments consist of molecules of chlorophyll b and carotenoids
what happens to the energy
- light harvested in the chloroplast membranes via primary and accessory pigments form photosystem/antenna complex
- photon/light energy absorbed by pigment molecules
- electron becomes excited and moves to a higher energy level
- energy is passed from one pigment to another
- energy is passed to reaction centre /chlorophyll a/ primary pigment
- a range of accessory pigments allow range of wavelengths to be absorbed
where is the primary pigments found
found in the reaction centre
what colours do chlorophyll a absorb
red and blue - violet
what colour does chlorophyll a appear as
blue - green
what type of membrane does the chloroplast have
double membrane
what structures link the grana
lamellae
what is found within in the stroma
starch and enzyme
where does the light-dependent stage of photosynthesis take place
thylakoid membrane
where does the light-independent stage of photosynthesis take place
stroma
what structural features of the thylakoids increase rate of photosynthesis
stacked into granum/ increased surface area/ maximum absorption of light in membrane
what is found within the inner chloroplast membrane
contains many membrane bound transport proteins to control the passage of substances (sugars and proteins) in and out of the chloroplast
describe the outer chloroplast membrane
it is freely permeable to molecules such as CO2 and H20 and not large proteins
what is a thylakoid disc
a system of interconnected, flattened fluid filled sacs with proteins embedded in the membranes
what is the function of the starch grain
stores the product of photosynthesis
describe the stroma
gel-like fluid surrounding the thylakoids. contain all the enzymes, sugars and organic acids needed for the light independent reaction
why do thylakoids have large surface area
to allow as much light energy to be absorbed as possible
what is the function of the stroma
fluid matrix inside a chloroplast, contains enzymes for light independent stage
what is the function of the thylakoid space
contains photosynthetic pigments and enzymes for light dependent reactions
what are lots of ATP synthase in the thylakoid membranes
to produce ATP in the light dependent reaction
what are the primary pigments
chlorophyll a
where are primary pigments found
in the reaction centre
what colour light does chlorophyll a absorb and at what wavelength
they absorb blue and red light, of wavelength of around 450nm
what are the 2 types of primary pigments
P680 and P700
where is P680 found and what is the peak absorption
found in photosystem I and its peak of absorption is light at a wavelength of 680nm
where is P700 found and what is the peak absorption
found in photosystem I and its peak of absorption is light at a wavelength of 700nm
what are examples of accessory pigments
chlorophyll b and carotenoids
where are accessory pigments found
in the antenna complex
what light does chlorophyll b absorb and at what wavelength
absorbs blue and red light, of wavelengths around 500-640nm
what coloured light does carotenoids absorb and reflect
absorb blue light but reflect yellow and orange light
- carotene - orange
- xanthophyll - yellow
where does the light independent stage of photosynthesis happen
the thylakoid membranes of the chloroplasts
where does the light dependent stage of photosynthesis happen
the stroma of the chloroplast
what are the 2 stages in the light dependent stage
non cyclic photophosphorylation and cyclic photophosphorylation
what happens in the non-cyclic photophosphorylation stage
- light energy hits photosystem I and II
- the electrons become excited in chlorophyll a and moves to a higher energy level
- the electrons are accepted by electron acceptors and the move along the electron transport chain. the electrons lost in photosystem II are replaced by the electrons made in the photolysis of water (forms hydrogen ions and oxygen). The electrons lost in photosystem I are replaced by the electrons from photosystem II
- protons are pumped across the thylakoid membrane by the flow of the electrons from the stroma to the thylakoid space, down the proton gradient
- the hydrogen ions made in the photolysis of water combines with electrons to form hydrogen atoms. The NADP combines with hydrogen to form reduced NADP
- as the protons move across the thylakoid membrane by chemiosmosis through ATP synthase, causing photophosphorylation producing ATP
what happens in the cyclic photophosphorylation stage
- only photosystem I is used (P700). The excited electrons pass to an electron acceptor and back to the chlorophyll molecule from which they were lost.
- there is no photolysis of water and no generation of reduced NADP, but small amounts of ATP are made. this may be used in the light-independent reaction of photosynthesis or it may be used in guard cells (their chloroplasts only contain only photosystem I) to bring in potassium ions, lowering the water potential and causing water to follow by osmosis. this causes the guard cells to swell and opens the stomata
- photosystem II contains an enzyme that, in the presence of light, can split water into H+ ions (protons), electrons and oxygen. this splitting of water is called photolysis.
- 2H20 -> 4H+ + 4e- +O2
what is water a source of
- hydrogen ions – used in chemiosmosis to produce ATP. these protons are then accepted by a coenzyme NADP, which becomes reduced NADP, to be used into the light-independent stage to reduce carbon dioxide and produce organic molecules
- electrons – replace those lost by the oxidised chlorophyll and to reduce chlorophyll a
- oxygen – used by the plant in aerobic respiration but much of it diffuses out of the leaves, through stomata, into the air
what happens in the light - independent stage
- in the stroma, carbon dioxide combines with ribulose bisphosphate (5C), catalysed by the enzyme rubisco. RuBP becomes carboxylated to make a 6C compound
- the 6C compound is unstable so breaks down into 2 molecules of glycerate 3-phosphate – carbon fixation
- the products from the light-dependent stage are used to reduce and phosphorylate GP into another 3C compound, triose phosphate
- the TP is used to regenerate RuBP using ATP, so that the cycle can start again
what is carbon dioxide a source of
source of carbon for the production of all large organic molecules. these molecules are used as structures, or act as energy stores or sources, for all the (carbon-based) life forms on this planet
what can GP be made into
amino acids
fatty acids (+ glycerol) -> lipids
what can TP be made into
glycerol (+ fatty acids) Lipids
hexose sugars (e.g. glucose) that can then be made into polysaccharides like starch and cellulose
what happens to most triose phosphate
5 out of 6 molecules of TP (3C) are recycled by phosphorylation, using ATP from the light-dependent reaction, to 3 molecules of RuBP (5C)
what would happen when there is an increase in carbon dioxide
- more CO2 = more CO2 fixation = more GP = more TP = more regeneration of RuBP
- he number of stomata that open to allow gaseous exchange leads to increased transpiration = plant wilts if water uptake from the soil cannot exceed water loss by transpiration = stress response = release of a plant growth regulator (abscisic acid) and stomata close = reduce CO2 uptake and reduce the rate of photosynthesis
what would happen if there is an increase in light intensity
- more light energy available to excite more electrons.
- more ATP and more reduced NADP produced, which can be used in the light-independent stage as sources of hydrogen and energy
what would happen if there is a decrease in light intensity
- GP cannot be changed to TP, so GP will accumulate and levels of TP will fall
- lower the amount of RuBP, reducing CO2 fixation and the formation of more GP
what happens as temperature increases
- temperature rises above 25oC = oxygenase activity of rubisco increases more than its carboxylase activity increases – photorespiration exceeds photosynthesis
- ATP and reduced NADP from the light-dependent reaction are dissipated and wasted = reduces overall rate of photosynthesis
- high temperature = damage proteins
- increased temperatures = increase in water loss from leaves by transpiration = closure of stomata = reduction in rate of photosynthesis
how does carbon dioxide concentration act as a limiting factor
- increasing the concentration of carbon dioxide, increases the rate of photosynthesis
- more CO2 = more CO2 fixation = more GP = more TP = more organic molecules
how does light intensity act as a limiting factor
- the rate of photosynthesis is directly proportional to the light intensity
- as light intensity increases, the rate of photosynthesis increases
light has 3 main effects: - causes stomata to open so CO2 can enter leaves - more carbon fixation
- trapped by chlorophyll where it excites electrons - involved in photophosphorylation = more ATP
- splits water molecules to produce protons - involved in photophosphorylation = more ATP
how does temperature act as a limiting factor
- between the temperatures 0oC and 25oC, the rate of photosynthesis approximately doubles for each 10oC rise in temperature.
above 25oC: - the rate of photosynthesis levels off and then falls as enzymes(ribulose) workless efficiently. Proteins (photosystems and electron carriers) also denature
- oxygen more successfully competes for rubisco and stops it from accepting CO2
- more water loss from stomata, leading to a stress response in which the stomata close, limiting the availability of CO2
how do we measure the rate of photosynthesis
- a photosynthometer is used to measure the rate of photosynthesis by collecting and measuring the volume of oxygen produced in a certain amount of time
- the gas given off by the plant is collected in the flared end of the capillary tube forming a gas bubble and the length of this bubble can be used to calculate the volume of gas collected. volume of gas collected = length of bubble x πr2
- the water bath keeps the temperature constant. sodium hydrogen carbonate solution is added to the water in the tube to provide carbon dioxide. the investigation has to be carried out in a darkened room, so that the only light available to the plant is form the light source. if the same apparatus is used throughout the investigation, the diameter (and therefore the radius) is constant and we can compare the rates of photosynthesis by using just the length of gas bubble evolved per unit time
how do you use a photosynthometer
Fill the apparatus with water by removing the plunger from the syringe. Replace the syringe plunger and gently push water out of the flared end of the capillary tube, until the plunger is nearly at the end of the syringe and there are no air bubbles.
Place a cut shoot, end upwards, into a test tube containing the same water that the plant has been kept in and add 2 drops of sodium hydrogen carbonate solution. Stand the test tube in a beaker of water and use a thermometer to measure the temperature of the beaker.
Place a light source as close to the beaker as possible. Measure the distance (d) from the plant to the light source. Allow the plant to acclimatise.
Position the capillary tube over the cut end of the plant and pull the syringe plunger so that the bubble of gas collected is in the capillary tube near the scale. Measure the length of the bubble and note it down.
Gently push the plunger back so that the bubble is expelled and reposition the capillary tube to repeat the experiment
what are factors to change or measure
- light Intensity- move the light source further from the plant. Measure the distance and calculate the light intensity (or use a light meter to measure light intensity). Allow the plant to acclimatise and repeat steps 4 and 5
- temperature- keep all other factors constant and use a light intensity that produced a high rate of photosynthesis. Alter the temperature of the water bath and measure the volume of gas produced, in a known period of time, at each temperature
- carbon dioxide concentration- keep all other factors constant and vary the number of drops of sodium hydrogencarbonate solution. Measure the volume of gas produced, in a known period of time, at each temperature
how do we use changes in density of leaf discs
- use a drinking straw to cut several leaf discs
- place 5/6 discs in a 10cm3 syringe and half-fill the syringe with dilute sodium hydrogencarbonate solution
- hold the syringe upright, place your finger over the end of the syringe and gently pull on the plunger - pulls the air out of the spaces of spongy mesophyll in the leaf disks. As the density of the discs increase they sink to the bottom of the syringe
- once the discs have sunk, transfer the contents of the syringe to a small beaker. shine a light from above and time how long it takes for one leaf disc to float to the top of the solution - the reciprocal of the time taken (1/t) is a measure of the rate of photosynthesis
- repeat the procedure twice more at this light intensity and find the mean rate of photosynthesis. repeat at other light intensities
