5.6-photosynthesis Flashcards
What is the chemical equation for photosynthesis?
What is the chemical equation for respiration?
Compare photosynthesis, aerobic respiration and anaerobic respiration
What is the interrelationship between photosynthesis and respiration?
-the products of one process are the raw materials for the other process: aerobic respiration removes oxygen from the atmosphere, breaks down glucose and adds carbon dioxide, while photosynthesis removes carbon dioxide and adds oxygen and forms glucose
Label this chloroplast
What is the granum (plural:grana)?
-inner part of chloroplasts made of stacks of thylakoid membranes
-the thylakoids within a granum may be connected to thylakoids within another granum by Intergranal lamellae (also known as intergranal thylakoids)
Where does the light dependent stage of photosynthesis take place?
The light dependent stage takes place in the thylakoid membranes of the grana
Where does the light independent stage of photosynthesis take place ?
-the light independent stage takes place in the stroma
What are the adaptions to granum?
The granal stacks create a large surface area for the presence of many photosystems which allows for the maximum absorption of light. It also provides more membrane space for electron carriers and ATP synthase enzymes
What is the stroma in a chloroplast?
-fluid filled matrix of chloroplasts
-The gel-like fluid contains enzymes that catalyse the reactions of the light-independent stage. The stroma surrounds the grana and membranes, making the transport of products from the light-dependent stage into the stroma rapid
What are the thylakoids in a chloroplast?
-flattened membrane-bound sac found inside chloroplasts
-contain photosynthetic pigments/photosystems
Why is there a loop of DNA in chloroplasts?
-the loop of DNA contains genes that code for some of the proteins needed for photosynthesis
-these proteins are assembled at the chloroplast ribosomes
What are photosynthetic pigments?
-pigment that absorbs specific wavelengths of light and traps the energy associated with the light
-such pigments include chlorophylls a and b, carotene and xanthophyll
What is a photosystem?
-system of photosynthetic pigments found in thylakoids of chloroplasts
-each photosytem contains molecules of chlorophyll that trap photons and pass their energy to a primary pigment reaction centre (a molecule of chlorophyll a ) during the light dependent stage of photosynthesis
-a photosystem is made up of a light harvesting system and the reaction centre
What is a plants compensation point?
-when photosynthesis and respiration proceed at the same rate, so that there is no net gain or loss of carbohydrate
-the time a plant takes to reach compensation point is called the compensation period
What do photosynthetic pigments do?
each pigment absorbs light of a particular wavelength and reflects other wavelengths of light
-the energy associated with the wavelengths of light captured is funnelled down to the primary pigment reaction centre, consisting of type of chlorophyll at the base of the photo system
How does the compensation period of plants differ for different species?
-shade plants can utilise light of lower intensity than sun plants can
-when exposed to light after being in darkness shade plants can reach their compensation point sooner (they have a shorter compensation period) than sun plants, which require a higher light intensity to achieve their optimum rate of photosynthesis
What is the colour of the chlorophyll a pigment?
-blue-green
(Found in all plants)
What is the colour of the chlorophyll b pigment?
-yellow-green
What is the colour of the carotene pigment?
-orange
What is the colour of the Xanthophyll pigment?
-yellow
(They absorb blue and green light)
How do chlorophylls and carotenoids ensure that the maximum amount of light is absorbed?
-there are different proportions of each pigment in leaves
-each pigment absorbs a different wavelength of visible light and this maximises the spectrum of visible light absorbed
-therefore this increases the amount of light energy absorbed
What is the role of the outer membrane of a chloroplast?
-controls what can enter and leave the chloroplast
What is a light harvesting system?
-chlorophyll b, xanthophylls and carotenoids are all embedded within the thylakoid membrane and form a light harvesting system
-The light harvesting system is where light energy of different wavelengths in absorbed, and this energy is then transferred to the reaction centre.
• The reaction centre contains chlorophyll a and is where light dependent reactions occur.
What is the first stage of photosynthesis?
Light-dependent stage
(Occurs on the thylakoid membrane (grana))
It involves 4 stages:
1-Non-cyclic phosphorylation
2-Cyclic phosphorylation
3-photolysis
4-chemiosmosis
What are the two photo systems and what wavelength of light does each one absorb?
-Photosystem II (PSII) is the first to be used, absorbs light with a wavelength of 700nm
-Photosystem I (PSI) the second to be used, absorbs light with a wavelength of 680nm
-both are involved in non-cyclic phosphorylation
Describe the stages of non-cyclic photophosphorylation
-the light energy that is absorbed in PSII causes electrons within the reaction centres to become excited and released
-the electrons released from PSII and PSI move along the electron transport chain
-this results in ATP production by chemiosmosis
-the electrons lost from PSII are replaced by electrons from photolysis and the electrons lost from PSI are replaced by electrons at the end of the electron transport chain from PSII
-at the end of the electron transport chain from PSI, the electrons are accepted by the coenzyme NADP. NADP accepts the electrons, along with H+ (from photolysis) to form reduced NADP
-the reduced NADP and ATP made in this process are used in the light-independent reaction
Describe cyclic photophosphorylation
-some of the electrons that are released from PSI are not picked up by NADP and instead are recycled back into PSI
-the transport of electrons still results in ATP production through chemiosomosis
-however no photolysis occurs so no reduced NADP is produced
Describe the role of water in the light-dependent stage of photosynthesis
-in PSII there is an enzyme that in the presence of light splits water molecules into protons, electrons and oxygen (photolysis)
-H2O —> 1/2 O2 + 2e^- + 2H^+
-the H+ is used to form NADPH
-the electrons are passed along a chain of electron carrier proteins
-the oxygen is either used for respiration or diffuses out of the leaf through the stomata
Describe chemiosmosis
-the electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane
-as they move along they release energy and some of the energy from the electrons is used to pump the protons across the chloroplast membranes (from stroma into thylakoid lumen)
-an electrochemical gradient is formed
-the protons pass through the enzyme ATP synthase which results in the production of ATP (as it causes an inorganic phosphate to join ADP)
-coenzyme NADP is reduced forming reduced NADP
What are electron carriers?
-molecules that can accept one or more electrons and then donate those electrons to another carrier
-proteins embedded in thylakoid membranes are electron carriers and form an electron transport chain
-NAD and NADP are also electron carriers
What are the stages of the Light-independent stage of photosynthesis (Calvin cycle)?
1-Carbon dioxide reacts with a five carbon compound called ribulose biphosphate (RuBP) This reaction is catalysed by the enzyme RuBisCO (ribulose bisphosphate carboxylase)
2-the product of this reaction is two molecules of a three-carbon compound GP (glycerate-3-phosphate) The carbon dioxide has now been fixed
3-GP is reduced to TP (triode phosphate) using hydrogens from the reduced NADP made during the light-dependent stage. ATP that was made during the light-dependent stage is also used at the rate of 2 molecules of ATP for every molecule of carbon dioxide that has been fixed during stage 2
4-some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances (e.g. glucose) 5/6 of the molecule is used to regenerate RuBP with the energy from ATP
How many turns of the Calvin cycle are used to make one molecule of glucose ?
6
What are the difference between cyclic photophosphorylation and non-cyclic photophosphorylation?
Cyclic photophosphorylation only involves photosystem I (whereas non-cyclic photophosphorylation involves photosystems I and II)
Cyclic photophosphorylation does not produce reduced NADP (whereas non-cyclic photophosphorylation does)
Draw out a diagram of the Calvin cycle
What are the uses of triose phosphate (TP)?
-used as a starting material for the synthesis of carbohydrates, lipids and amino acids
-TP is recycled to regenerate the supply of RuBP
