3.5 Flashcards
What are the 4 key stages in aerobic respiration and where in the cell do they occur
- Glycolysis (cytoplasm)
- Link reaction (mitochondrial matrix)
- Krebs Cycle (mitochondrial matrix)
- Oxidative phosphorylation (cristae)
What is photosynthesis?
-production of glucose using light energy
-occurs in plants and algae
-consists of a light dependent and light independent stage
Adaptations of plants for photosynthesis?
-leaf located near top of plant = closer to light
-leaf is thin and wide = large surface area for light, short diffusion distance for CO2
-has many veins = connect to xylem to bring in water
-has stomata for gas-exchange (CO2/O2)
-has air spaces to support ease of gas-exchange
Palisade cells:
-located near top of leaf close to the light
-large surface area for light
-thin cell wall = short diffusion distance for CO2
-contains many chloroplasts (site of photosynthesis)
-large vacuole = pushes chloroplast to edge of cell closer to light
Site and products of the two stages of photosynthesis?
Light dependent stage:
-thylakoid membrane
-ATP and reduced NADP
Light independent stage:
-stroma
-glucose (made by products of light dependent stage)
Outline the light dependent stage
-light hits chlorophyll
-chlorophyll absorbs the light if correct wavelength
-electrons become excited and are lost from the chlorophyll (photoionisation)
-electrons enter an electron carrier system
-electrons move down the system releasing energy
-this pumps protons from stroma into thylakoid space
-protons accumulate in thylakoid space, then diffuse back into stroma
-they pass though ATP Synthase which joins ADP and Pi to make ATP (mechanism = chmeiosmosis, process = photophosphorylation)
-the electron ends up by joining with NADP to form reduced NADP
-light also hits water
-causes photolysis (breakdown of water due to light)
-forms: H+, e-, O2
-the H+ joins with the reduced NADP (now carries a hydrogen atom: H+ and e-)
-the e- replaces electrons lost from chlorophyll
-O2 given off as waste
Outline the light independent stage
-involves the calvin cycle
-RuBP (5 carbon) joins with CO2 to make 2 lots of GP (3 carbon)
-the GP is reduced into TP (3 carbon)
-this uses energy from ATP and hydrogen atom from reduced NADP
-the TP can be used to reform RuBP (uses energy from ATP)
-the TP can also be used to form glucose (carbohydrate)
-GP can also be used to form amino acids (proteins) and fatty acids
-TP can also be used to form glycerol
-fatty acids and glycerol will form a lipid
-photosynthesis/calvin cycle = produces all the main biological molecules
Effect of limiting factors on photosynthesis?
Light:
-RuBP decreases – being converted into GP but not being reformed from TP (no ATP)
-GP increases – not converted into TP (no ATP/reduced NADP) but is being formed from RUBP
CO2:
-RuBP increases – not converted into GP (no CO2) but is being reformed from TP
-GP decreases – not being formed from RuBP (no CO2) but being converted into TP
Compensation point in plants
-the point in the day (light intensity) when the CO2 taken in by photosynthesis equals the amount given out by respiration = no net gas exchange
-at low light intensity: rate of respiration > rate of photosynthesis [CO2 released]
-at high light intensity: rate of photosynthesis > rate of respiration [CO2 absorbed]
Measuring rate of photosynthesis
-measure amount of CO2 used or measure amount of O2 produced, in a certain time
-can be done using photosynthometer
-measures amount of O2 produced
-uses aquatic plants (e.g. elodea), as the O2 produced can be observed and collected
-the plant is surrounded in sodium hydrogencarbonate solution (CO2 source)
-the plant is kept in darkness before experiment runs (uses up all the O2 in the plant)
-as the experiment runs, O2 will be produced, this will be collected in a capillary tube
-the amount collected can be measured, this will be converted into a volume by multiplying length of oxygen bubble collected by πr2
-volume of O2 collected can then be divided by time to calculate rate of photosynthesis
Light dependent and light independent stages of photosynthesis
Light dependent stage occurs in 3 reactions:
Photolysis:
-H2O —> 1/2 O2 + e- + H+
-light energy is absorbed by chlorophyll in photosystem II and splits water into oxygen, H+ and e-
-H+ is picked up by NADP to form NADPH and used in the LIR
-e- are passed along a chain of electron carrier proteins
-the oxygen is a waste product (either used for respiration or diffuses out of the leaf through the stomata)
Photoionisation of chlorophyll:
-light energy is absorbed by the chlorophyll
-the energy results in electrons becoming excited and raising up an energy level to leave chlorophyll
-hence, the chlorophyll has been ionised by light
Chemiosmosis:
-electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane
-as they move along the electron transfer chain, they release energy
-some of the energy from electrons is used to pump the protons from photolysis across thylakoid membranes
into thylakoid lumen from stroma by active transport
-hence electrochemical gradient produced as high concentration of protons (ions) on one side of the membrane
-facilitated diffusion occurs through ATP synthase
-the protons pass through the enzyme ATP synthase, which results in the production of ATP
-the protons combine with the co-enzyme NADP to become NADPH
-as the protons move from a high to low concentration gradient, this is known as chemiosmosis
Light independent stage: (Calvin cycle)
-uses carbon dioxide, reduced NADP, and ATP to form a hexose sugar
-the ATP is hydrolysed to provide energy for this reaction
-the NADPH donates the hydrogen to reduce molecules GP in the cycle
-Calvin cycle occurs in the stroma, which contains the enzyme RuBisco, which catalyses this reaction
-this stage is temperature-sensitive due to the fact it involves an enzyme
-carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP), a 3-carbon compound
-this is catalysed by the enzyme rubisco
-to reduce this GP into triose phosphate (TP), ATP and NADPH from the light-dependent reaction are used
-some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances
-rest of the molecule is used to regenerate RuBP, with energy from ATP
-the glucose product can join to form disaccharides (e.g. sucrose), and polysaccharides (e.g. cellulose/starch)
-it can also be converted into glycerol and combine with fatty acids to make lipids for the plant
Calvin’s experiment:
-examined the products in the LIR using radioactive carbon
-CO2 that is radioactively labeled is inserted, allowing the carbon molecules to be labeled and traced
-he would then measure the amount of radioactive GP and RuBP under different conditions, mainly in the light and dark, as a way to prove which factors impact the LIR
Role of pigments in plants:
-chlorophyll is located in the photosystems on the thylakoid membrane
-mix of colored proteins that can absorb light
-There are 5 key closely related pigments, but chlorophyll a is the most abundant
Chlorophyll a = blue/green (found in all plants)
Chlorophyll b = yellow/green
Carotene = orange
Xanthophyll = yellow
Phaeophytin = grey
-there are different proportions of each pigment in leaves, which gives leaves slightly different colors
-each pigment absorbs a different wavelength of visible light
-this maximizes the spectrum of visible light that the plant can absorb, hence increases the amount of light energy absorbed
-pigments in chlorophyll can be isolated using chromatography
-pigments are added to chromatography paper, which is placed in a solvent
-solvent dissolves the pigments
-the more soluble the pigment, the further up the chromatography paper it will move
-can be converted into an Rf value, a way to then compare and identify pigments in chromatography
Define oxidation and reduction in the light dependent reaction
Oxidation:
-substance gains oxygen or loses hydrogen
-loses electrons
-energy is given out
Reduction:
-substance loses oxygen or gains hydrogen
-gains electrons
-energy is taken in
Outline how ATP is made in light-dependent reaction
-chlorophyll molecule absorbs light energy, it boosts the energy of a pair of e- within this chlorophyll molecule
-raises the pair of e- to a higher energy level
-hence they are in an excited state
-causes them to leave the chlorophyll molecule, hence chlorophyll becomes ionised by photoionisation
-electrons that leave the chlorophyll are taken up by an electron carrier
-chlorophyll has been oxidised as lost a pair of e-
-electron carrier has been reduced as it gained a pair of e-
-the electrons are now passed along several electron carriers in a series of oxidation-reductions reactions
-hence electron transfer chain is formed in the thylakoid membrane
-each new carrier is at a slightly lower energy level than the previous one
-so electrons lose energy at each stage
-some of this energy is used to combine an inorganic phosphate with an ADP molecule
-forms ATP (known as the chemiosmotic theory)
Outline photolysis of water in light-dependent reaction, including the importance of its products
-water molecules are produced by the splitting of water
2H2O —> 4H+ + 4e- + O2
-the electrons replace the electrons lost from the chlorophyll molecule by photoionisation
-H+ pass out of the thylakoid space through ATP synthase channels
-NADP becomes reduced NADP by use of the H+
-oxygen is either used in respiration or diffuses out as a waste product
Outline the light-independent reaction
-CO2 diffuses in through the stomata and dissolves in the water surrounding mesophyll cells
-it diffuses through the cell surface membrane and then the chloroplast envelope to the stroma
-CO2 reacts with ribulose bisphosphate (RuBP) which is catalysed by rubisco
-2 molecules of glycerate 3-phosphate (GP) are produced
-GP is converted to triose phosphate (TP) using reduced NADP and energy supplied by ATP
-reduced NADP becomes NADP and can be recycled in the light dependent reaction
-some TP is converted to organic substances, e.g. starch, cellulose, lipids, glucose, amino acids, nucleotides, etc
-most TP is used to regenerate RuBP using ATP, allowing the Calvin Cycle to continue
