5.6 Flashcards
what organisms use photosynthesis to convert light energy from sunlight into chemical energy
photosynthesis is used by plants, algae and some types of bacteria to convert light energy from sunlight into chemical energy
what is autotrophic nutrition
organisms using chemical energy to synthesise large organic molecules, which form the building blocks of living cells, from simple organic molecules such as water and carbon dioxide
what are photoautotrophs
organisms that photosynthesise and use light as the energy source for autotrophic nutrition.
what can photoautotrophs also be called
photoautotrophs can also be called producers
photoautotrophs can also be called producers, why are they also called producers
because they are at the beginning (first trophic level) of a food chain and provide energy and organic molecules to other non-photosynthetic organisms.
state the general balanced equation for photosynthesis
6CO2 + 6H20 —chlorophyll—> C6H12O6 +6O2
whats a photon
a photon is a particle of light; each photon contains an amount (a quantum) of energy
what is the main product for photosynthesis
the main product of photosynthesis is a monosaccharide sugar which can be converted to a disaccharide for transport then starch for storage
what is carbon fixation and give an example
carbon fixation is the process by which carbon dioxide is converted to sugars
the carbon for synthesising all types of organic molecules is provided by carbon fixation
-photosynthesis is an example of carbon fixation.
is carbon fixation exothermic or endothermic
-endothermic so needs energy
-carbon fixation also needs electrons ( a reduction reaction)
what can carbon fixation help regulate
-carbon fixation helps regulate the conc. of CO2 in the atmosphere and oceans
is respiration an oxidation or reduction reaction
oxidiation
how do photoautotrophs respire
organic molecules are oxidised that have been previously synthesised by by photosynthesis and stored releasing chemical energy
examples of non-photosynthetic organisms
-fungi, animals, many protists and many types of bacteria
what are heterotrophs
-non-photosynthetic organisms that obtain food by consuming other living things.
-they cannot make their own food
how do heterotrophs obtain energy
-heterotrophs obtain energy by digesting complex organic molecules of food to smaller molecules that they can use as respiratory substrates.
-they obtain energy from the products of digestion by respiration
how do heterotrophs respire
during respiration, glucose and other organic compounds are oxidised to produce CO2 and water.
respiration releases chemical energy (exothermic) that can drive an organisms metabolism
what is the general equation for respiration
C6H12O6 + 6O2 –> 6H2O + 6CO2 + ENERGY
how does photosynthesis and respiration relate
the product of one process are the raw materials for the other process; aerobic respiration removes oxygen from the atmosphere and adds CO2, while photosynthesis does the opposite
how often do plants respire
all the time
how often do plants photosynthesise
only when sunlight available
when is the compensation point
when photosynthesis and respiration proceed at the same rate, so that there is no net gain or loss of carbohydrates, the plant is at its compensation point
whats the compensation period
the time a plant takes to reach its compensation point is the compensation period
why do shaded plants reach their compensation point quicker than sun plants?
shade plants utilise light at a lower intensity thank sun plants.
do algae or photosynthetic bacteria have chloroplasts
algae do
how long are chloroplasts
2-10um
what is the chloroplast envelope
a double membrane which surrounds chloroplasts
what is the intermembrane compartment
the space between the inner and outer membrane. It has a width of 10-20nm between the two membranes
what is the outer membrane
a highly permeable outer layer
what is the inner membrane
a membrane that separates the intermembrane space from the stroma
what are the 2 distinct regions that can be seen in a chloroplast when using an electron microscope
the stroma and the grana
whats the stroma
the fluid filled matrix of chloroplasts where the light-independent stage of photosynthesis takes place
what is contained in the stroma
-enzymes needed to catalyse reactions in the light-independent stage of photosynthesis
-starch grains
-oil droplets as a source of lipids to make membranes
-ribosomes for protein synthesis of enzymes/ electron carriers/ anchoring proteins
-DNA which contain genes needed for photosynthesis
whats the granum
the inner part of chloroplasts made of stacks of thylakoid membranes, where the light dependent stage of photosynthesis takes place
what stage of photosynthesis takes place in the grana
the first stage if photosynthesis (the light dependent stage)
what are the 3 distinct membranes that chloroplasts have
-outer, inner and thylakoid, this gives 3 separate internal compartments
what are the three separate internal compartments in the chloroplast
-the intermembrane space
-the stroma
-the thylakoid space
what may the thylakoids within the granum be connected to
they may be connected to another granum by intergranal lamellae (also known as intergranal thylakoids )
mention the permeability of the thylakoid membrane
less permeable
what is each stack of thylakoids called
a granum
what is the advantage of many Grana in every chloroplast and with many chloroplasts in each photosynthetic cell
there is a large surface area for:
-photosystems that contain photosynthetic pigments to trap sunlight
-electron carriers an ATP synthase enzymes needed to convert light energy into ATP
whats a thylakoid
a flattened membrane-bound sac found inside chloroplasts; contain photosynthetic pigments/photosystems and is the site of the light dependent stage of photosynthesis.
whats the intergranal lamellae
an interconnection that allows separate grana to be interconnected.
what hold photosystems in place
proteins embedded in thylakoid membranes
why are the grana surrounded by the stroma
so the products of the light dependent stage can easily pass to the stroma to be used in the light-independent stage
what are photosystems
a funnel-shaped cluster of photosynthetic pigments found in the thylakoid membranes witch act as the light-collecting units of the chloroplast
the primary reaction centre is a molecule of Chlorophyll A at the base of the photosystem
accessory pigments consist of of Chlorophyll B and Carotenoids which lie on the wall of the photosystem
talk abt the reflection and absorption of photosynthetic pigments and how it appears to our eye
each pigment absorbs certain light and reflects others. Each pigment appears to our eyes and brain, the colour of the wavelength its reflecting
what are photosynthetic pigments
a pigment that absorbs specific wavelengths of light and reflects other pigments
how do photosystems work
the energy associated with the wavelengths of light captured is funnelled down to the primary pigment reaction centre, consisting of a type of chlorophyll, at the base of the photosystem.
what is chlorophyll
chlorophylls are a mixture of pigments, all have a simmilar molecular structure consisting of a porphyrin group, in which is a magnesium atom, and a long hydrocarbon chain
there are two forms of chlorophyll A;
what colour do they both appear
P680
P700
blue-green
there are two forms of chlorophyll A;
where are they both situated
at the centre of photosystems
there are two forms of chlorophyll A;
what do they both absorb but is slightly different abt each
both absorb red light but they have different absorption peaks
What is chlorophyll A (P680)
a blue-green pigment found in photosystem II and is situated at the centre of the photosystem (primary reaction centre)(peak absorption at 680nm)
what is chlorophyll A (P700)
A blue-green pigment that appears in Photosystem I and is situated at the centre of the photosystem (primary reaction centre)(peak absorption at 700nm)
,
,
along with absorbing red light at what does chlorophyll A also absorb and at what wavelength
some blue light at around 440nm
what is chlorophyll B
a yellow-green accessory pigment
what are carotenoids
a yellow-orange accessory pigment
what are xanthophylls
a yellow accessory pigment
what is the non mobile stage called
the TLC
Where does the light-dependent stage of photosynthesis take place
the light dependent stage of photosynthesis occurs in the grana (thykaloids). it involves the direct use of light energy
what does the light dependent stage consist of
(4 things)
- light harvesting at the photosystem
- photolysis of water
- photophosphorylation
- formation of reduced NADP
what is photophosphorylation
The generation of ATP from ADP and inorganic phosphate, in the presence of light.
what by-product is produced in the light-dependent stage of photosynthesis
oxygen
where does photolysis occur
occurs in only PSII because here there is a special enzyme that in the presence of light can split water into protons (H+), electrons and oxygen
what is photolysis
the splitting of water into protons (H+), electrons and oxygen
what is the equation for the splitting of water
2H2O—-> 4H+ + 4e- + O2
what is the oxygen produced by photolysis used for
-some of the oxygen produced is used by plant cells for aerobic respiration
-when there is high light intensity and photosynthesis is greater than respiration, oxygen as a by-product will diffuse out via the stomata
what are the 4 uses of water…
- Source of Protons
- Source of Oxygen
- Donates electrons to replace those lost in the chlorophyll
- Keeps the plant cell turgid
what are the two types of photophosphorlytion
non-cyclic photophosphorlytion
cyclic photophosphorlytion
what is non-cyclic photophosphorlytion
-involves PSI and PSII
-produces ATP, oxygen and reduced NADP
what is cyclic photophosphorlytion
-involves only PSI
- produces ATP but in smaller quantities than in non-cyclic
What is NADP?
Nicotinamide adenine dinucleotide phosphate
- A Coenzyme
- Electron and Hydrogen Carrier
What is the first step of Non-cyclic Phosphorylation?
- a photon of light strikes PSII, its energy is channelled to the primary pigment reaction centre
-the light energy excites a pair of electrons inside the chlorophyll molecule
What happens after light energy excites a pair of electrons inside the chlorophyll molecule for non-cyclic photophosphorylation? (non-cyclic)
The energised electrons escape from the chlorophyll molecule and are captured by an electron carrier, which is embedded in the thylakoid membrane.
What are Electron Carriers? (non-cyclic)
they accept electrons and donate them to another carrier. Proteins embedded in thylakoid membranes with an Iron ion at their centre. They form an electron transport chain.
Examples include; Ferredoxin, NAD, and NADP
What replaces the electrons that escape from the chlorphyll molecule? (non-cyclic)
These electrons are replaced by electrons derived from photolysis.
What happens after the electrons are captured by the electron carrier? (non-cyclic)
When the iron ion in the electron carrier combines with an electron it becomes reduced (Fe2+).
It can then donate the electron, becoming reoxidised (Fe3+), to the next electron carrier in the chain.
Series of oxidation and reduction…
What happens as Electrons are passed along the electron carrier chain? (non-cyclic)
As electrons are passed along a chain of electron carriers embedded in the thylakoid membrane, at each step some energy associated with the electrons is released.
What is the energy released by the electrons used for? (non-cyclic)
This energy is used to pump protons across the thylakoid membrane into the thylakoid space.
What happens at the End of the electron carrier chain? (non-cyclic)
Eventually the electrons are captured by another molecule of chlorophyll A in PSI.
These electrons replace those lost from PSI due to excitation by light energy.
What happens after the electrons are captured by Chlorophyll A in PSI? (non-cyclic)
A protein-iron-sulfur complex called ferredoxin accepts the electrons lost from PSI and passes them to NADP in the stroma.
What happens as a result of Protons being pumped across the membrane into the Thylakoid space?
(non-cyclic)
As protons accumulate in the thylakoid space, a proton gradient forms across the membrane.
Protons diffuse across ATP synthase channels in the membrane and as they do so, ADP and an inorganic phosphate follow and combine, forming ATP.
What happens to the Protons after they are pumped back across the Thylakoid membrane?
(non-cyclic)
the protons pass through the channel they are accepted, along with electrons, by NADP which becomes reduced.
The reduction of NADP is catalysed by the enzyme NADP reductase
What are the final products from the Light-dependant stage of Photosynthesis? (non-cyclic)
ATP and reduced NADP are now in the stroma ready for the light-independent stage of photosynthesis.
Oxygen is also produced.
what are the steps in cyclic photophosphorylation
as light strikes PSI, a pair of electrons in the chlorophyll molecule at the reaction centre gain energy and become excited. They escape from the chlorophyll and pass to an electron carrier system and then pass back into PSI
What happens during the passage of the electrons in the elctron carrier system? (cyclic????????????)
During the passage of electrons along the electron carriers, a small amount of ATP is generated.
However, no photolysis of water occurs, so no protons or oxygen are produced. No reduced NADP is generated.
What cells in a plant contain chloroplasts with only PSI?
Chloroplasts in guard cells contain only PSI
What is the result of Cyclic Photophosphorylation in Gaurd cells?
Chloroplasts in guard cells contain only PSI.
They produce only ATP which actively brings potassium ions into the cells, lowering the water potential so that water follows by osmosis.
This causes the guard cells to swell and opens the stoma.
Where does the Light-Independent stage of photosynthesis take place?
The light-independent stage takes place in the stroma of the chloroplasts.
Where does CO2 enter the leaf?
Carbon dioxide in the air enters the leaf through stomata. It then diffuses through the spongy mesophyll layer to the palisade cells, and then through the chloroplast envelope into the stroma.
What is the Calvin Cycle?
A metabolic pathway of the light-independant stage of photosynthesis, occuring in the stroma of chloroplasts where carbon dioxide is fixed, with the products of the light-dependant stafem to make organic compounds.
What is the first step in the Calvin Cycle?
- Carbon dioxide combines with a carbon dioxide acceptor. It is a five carbon compound called Ribulose Bisphosphate (RuBP)
This reaction is catalysed by the enzyme RuBisCO (ribulose bisphosphate carboxylase-oxygenase).
What happens after Carbon dioxide combines with RuBP?
- RuBP, by accepting the carboxyl (COO-) group, becomes carboxylated, forming an unstable intermediate six-carbon
compound that immediately breaks down.
What does Carboxylated RuBP break down into?
- Carboxylated RuBP breaks down into two molecules of a three-carbon compound, GP (glycerate-3-phosphate).
The carbon dioxide has now been fixed.
What happens after GP (glycerate-3-phosphate) has been formed?
- GP (glycerate-3-phosphate) is then reduced, using hydrogens from the reduced NADP made during the light-dependent stage, to triose phosphate (TP).
Energy from ATP, also made during the light-dependent stage, is used at this stage at the rate of two molecules of ATP for every molecule of carbon dioxide fixed during stage 3.
what is the product after 6 cycles of the Calvin cycle
- After 6 cycles of the Calvin Cycle, 10 of the 12 TP molecules produced have their atoms rearranged to regenerate six molecules of RuBP. This process requires phosphate groups.
The remaining 2 of the 12 molecules of TP are the product.
what is continuously needed for the Calvin cycle to run
- ATP and reduced NADP from the light dependent stage
How does daylight create optimum conditions for RuBisCO?
during the light dependent stage, protons are pumped from the stroma into thylakoid spaces which raised the pH in the stroma to pH 8, which is optimum for RuBisCO. RuBisCO is also activated by the presence of extra ATP in the stomata.
In daylight the conc. of magnesium ions increases in the stroma. These ions attach to the active site of RuBisCO, acting as a cofactor.
why do chloroplasts contain low levels of RuBP
because RuBP is continually being converted to GP, but is also being continually regenerated.
what is the role of ferredoxin in the calvin cycle
the ferredoxin that is reduced by electrons from PS1 activates enzymes involved in the reactions of the Calvin cycle
what are the uses of TP
-the TP that is not used to regenerate RuBP is used to synthesise organic compounds.
-Some glucose is converted to sucrose, some to starch, some to cellulose
-Some TP is used to synthesise amino acids, fatty acids and glycerol.
What factors affect the rate of Photosynthesis?
Factors include:
- The raw materials - carbon dioxide and water
- Light availability
- Chlorophyll availability
- Electron carrier availability
- Relevant enzyme availability
- Temperature
- Cell turgidity
What is the role of Light in photosynthesis?
- Energy to power the first stage of photosynthesis and produce ATP and reduced NADP needed for the next stage
- Causes stomata to open so that gas exchange can take place and transpiration can occur
How does the light intensity affect the rate of photosynthesis?
As light intensity increases, the rate of photosynthesis also increases until another factor becomes a limiting factor at which point the rate of photosynthesis remains. (at a constant)
. (look at graph on p124)
.
How does the light intensity affect the Calvin Cycle?
Insufficient light intensity stops the light-dependent stage. This stops the flow of NADP and ATP so the light-independent stage cannot run
When there is a reduced light intensity:
- GP cannot be reduced to TP
- TP levels fall and GP accumulates
- If TP levels fall, RuBP cannot be regenerated
How does the Carbon Dioxide concentration affect the rate of photosynthesis?
As the Carbon Dioxide concentration increases, the rate of photosynthesis also increases until another factor becomes a limiting factor at which point the rate of photosynthesis remains.
***However, if the Carbon Dioxide concentration rises above 0.4%, the stomata will begin to close.
is co2 normally a limiting factor
no, its very plentiful normally
How does a low CO2 concentration affect the Calvin Cycle?
When there is a reduced Carbon Dioxide concentration (0.01%):
- RuBP cannot accept it, and accumulates
- GP cannot be made
- Therefore, TP cannot be made
how does temperature affect the calvin cycle at 25-30 degrees
-if plants have enough water, sufficient light intensity and CO2 here, the rate of photosynthesis will increase as temp increases
how does temperature affect the calvin cycle at above 30 degrees
- At temperatures above 30 °C, growth rates may reduce due to photorespiration: oxygen competes with carbon dioxide for the enzyme RuBisCO’s active site. ( binding of O2 to RuBisCO=photorespiration)
This reduces the amount of carbon dioxide being accepted by RuBP and subsequently reduces the quantity of GP and therefore of TP being produced, whilst initially causing an accumulation of RuBP. However, due to the lack of TP, RuBP cannot be regenerated.
how does temperature affect the calvin cycle at above 45 degrees
- At temperatures above 45 °C, enzymes involved in photosynthesis may be denatured. This would reduce the concentrations of GP and TP, and eventually of RuBP as it could not be regenerated due to lack of TP.
why is the calvin cycle very sensitive to temperature change
the calvin cycle consists of many ENZYME catalysed reactions
what effect does a sufficient amount of water have on a plant
-the transpiration stream can have a cooling effect on the plant
-the water passing up the xylem to the leaves also keeps plant cells turgid so they can function
-turgid guard cells keep the stomata open for gas exchange
what 4 things occurs to the plant when water stress is present
- The roots are unable to take up enough water to replace that lost via transpiration.
- cells lose water and become plasmolysed (causing plant to become flaccid and wilt)
- plant roots produce absisic acid that when translocated to the leaves, cause the stomata to close, reducing gaseous exchange
- the rate of photosynthesis will greatly reduce
How can the rate of Photosynthesis be measured at school?
The rate of photosynthesis is often found by measuring the volume of oxygen produced per minute by an aquatic plant.
What are the limitations of measuring the volume of oxygen produced per minute by an aquatic plant?
- Some of the oxygen produced will be used by the plant in respiration
- There may be some dissolved nitrogen in the gas collected
What is the apparatus used to measure the volume of oxygen produced by an aquatic plant?
A Photosynthometer
How does a Photosynthometer work?
The gas given off by the plant collects in the flared end of a capillary tube.
The gas bubble can be moved into the part of the capillary tube against a ruler and its length measured
if the length of the capillary tube bore is known, this length can be converted to volume
it must be air tight and with no bubbles
look at image of Photosynthometer
uifg
How is the volume of gas collected determined by using a Photosynthometer?
Volume = length of bubble X pir^2
before starting an investigation what do u need to write down
- make and justify a prediction
-state the IV and DV
-state variables you need to control, why you will control them and how you will control them
-write a plan and ask your teacher to check it
