Photosynthesis Flashcards
What is photosynthesis?
Process where light from sun transformed into chain am energy and used to synthesis Large organic molecules from inorganic substances
Why is photosynthesis so important?
Transforms light energy to Chemical potential energy that is then available to consumers and decomposes, releases oxygen from water into atmosphere so aerobes depend on it for respiration
What is an autotroph?
Organism that uses light energy or chemical energy and inorganic molecules to synthesis complex organic molecules
What is a chemoautotroph?
Synthesise complex organic molecules using energy derived from exergonic chemical reactions -reactions that give out heat
Example of a chemoautotroph?
Nitrifying bacteria, obtain energy from oxidising ammonia to nitrate
What is a photo autotroph?
Organism that can photosynthesis, source of energy is sunlight, raw inorganic molecules are co2 and h2o,
What organisms are photoautotrophs?
Plants, some bacteria, some protocists, majority of producers for food chains
What are heterotrophs?
Organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them, cannot make their own food, but digest complex organic molecules into simpler soluble ones which can be used to synthesis complex molecules
Why do repairing organisms rely on photosynthesis?
Organisms can release chemical potential energy in complex organic minerals made in photosynthesis by respiration, aerobic respiration depends on oxygen, oxygen is released by photosynthesis, means oxygen is free in atmosphere-oxygen released from the water
Where does photosynthesis take place?
Organelles called chloroplasts
Marine Molluscs incorporate chloroplasts from algae into their cells, however this is not passes to next generation, what is advantage of doing this?
Chloroplasts synthesise, some organic products may be repaired by cells, or ad building blocks by cells, can use oxygen. Green colour can be used for camouflage
Describe structure if a chloroplast
Disc shaped, 2-10 um long Double membrane, envelope Intermembrane space Outer membrane permeable to ions Inner membrane less permeable, transport proteins embedded, folded into lamellae, these are stacked to make granum Between grabs are intergranal lamellae
What is the stroma?
Fluid filled matrix, reactions of light independent stage occur here, so contain necessary enzymes, as well as DNA, ribosomes and starch grains
What are grana?
Stacks of flattened membrane compartments called thylakoids, site of light absorption and ATP synthesis in light dependent stage of photosynthesis
How are chloroplasts adapted for their role?
Inner membrane controls entry and exit of substances between cytoplasm and stroma
Grana provide large SA for photosynthetic pigments, electron carriers and ATP synthase for light dependent reaction
Photosynthetic pigments arranged in photosystems, held in place by proteins
Stroma contains enzymes for light independent reactions
Grana surrounded by stroma for short distance for products of light dependent stage
Chloroplasts can synthesis enzymes needed for photosynthesis using DNA and ribosome
What is a photosynthetic pigment?
Molecules that absorb light energy. Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of absorption. Other wavelengths are reflected-appear colour of the wavelengths they reflect. Arranged in photosystems on thylakoid membrane
What is chlorophyll?
A mixture of pigments, with similar structure, made from phytol (hydrocarbon chain) and porphyry group, which contains magnesium atom.
What are the two forms of chlorophyll?
B-P680 and b-P700, both are yellow green
Why is magnesium in porphyrin important?
Light hitting chlorophyll causes pair of electrons associated with magnesium to be excited
What colour light does chlorophyll absorb?
Red, a at 680nm, also blue light at 450
b at 700nm, also at 500/640
Where are chlorophyll molecules found?
At centre of photosystems known as primary pigment reaction centre, a in photosystem 2 and b in photosystem 1
What are accessory pigments?
Carotenoids, reflect yellow and orange, absorb blue. No porphyrin ring so not directly involved in light dependent, absorb wavelengths not well absorbed by chlorophyll and pass energy associated to chlorophyll. Main are Caroten-orange and Xabthophyll-yellow
What range of wavelengths do chlorophyll refelct?
550/570, green part
How does structure of grana enable it to carry out its functions?
Large SA from thylakoids, for photosystems to trap light energy, electron transport proteins and ATP synthase enzymes, space within membrane stack allows fur movement of protons for chemiosmosis and generation of ATP
Where does light dependent stage take place?
On thylakoids membranes, photosystems embedded in these membranes, ps1 mainly on intergranal, ps2 on granal, trap light energy so it can be converted to chemical energy in form of ATP
What is photolysis?
Water split in PS2 by enzyme into protons, electrons and oxygen
2H2O > 4H+ +4e- + O2
What is role of water in photosynthesis?
Oxygen produced used for respiration or diffuses out of stomata
Source of:
Hydrogen ions for chemiosmosis to produce ATP
Electrons to replace those lost by oxidised chlorophyll
Also keeps plant cells turgid
What happens to protons released in photolysis?
Accepted by coenzyme NADP, which becomes reduced NADP, to be used during light independent stage to reduce co2 and produce organic molecules
What is photophosphorylation?
Making of ATP from ADP an Pi in the presence of light
What happens when light hits chlorophyll molecule?
Energy of photon is transferred to two electrons and they become excited, electrons captured by electron acceptors and passed along a series of electron carriers in thylakoid membranes
What are electron carriers?
Molecules that transfer electrons
What are electron acceptors?
Chemicals that accept electrons from another compound, they are reduced awhile acting as oxidising agents
What happens as electrons passed along chain of electron carriers?
Energy released, this pumps protons across thylakoid membranes into the thylakoid space where they accumulate.
How is ATP generated in photosynthesis?
Proton gradient formed across embrace and protons flow down their gradient through channels associated with ATP synthase enzymes, flow is chemiosmosis., produces force that joins ADP to Pi to make ATP, KE from proton flow converted to chemical energy in ATP molecules, used in light independent stage of photosynthesis.
What is cyclic photophosphorylation?
Only uses PS1 excited electrons pass to electron acceptor and back to chlorophyll molecule from which they are lost, no water photolysis, No reduced NADP, small amounts of ATP are made
How does light cause stomata to open?
Can be used for light independent, or in guard cells (only contain PS1) to bring I. Potassium ions, which lowers water potential, causing water to follow by osmosis, which makes guard cells swell and opens the stomata
What are the stages of non cyclic photophosphorylation?
Light strikes PS2, exciting elections, pass along chain of electron carriers, energy releases can be used for ATP synthesis, light stokes PS1 and electrons are lost, these electrons, along with protons from photolysis join NADP which becomes reduces NADP, electrons from water replace those lost in PS2, electrons from PS2 replace those lost in PS1. Protons from water take part in chemiosmosis to make ATP and are then capture by NADP in stroma, used in LI stage
How does lack of iron in soil affect plant growth?
Electron carriers are proteins that contain iron prosthetic group, lack of iron means fewer election carriers, so less reduced NADP and fewer molecules of ATP, so reducing LI, yields less amino acids, therefore protons, required for growth it enzymes needed in light independent reaction
Where does the light independent reaction take place?
In stroma of chloroplasts
What is the Calvin cycle?
The light independent stage, where carbon dioxide is fixed and used to build complex organic molecules
What is the role of carbon dioxide in photosynthesis?
Source of carbon and oxygen for production of all large organic molecules, used as structures or act as energy stores of sources for all the carbon based land forms in the planet
How does carbon dioxide get into the leaf?
Carbon dioxide diffuses into leaf through stomata, then through air spaces in spongy mesophyll till it reached palisade mesophyll layer, diffuses though cellulose walls, surface membrane and cytoplasm, into chloroplast stroma
Describe the mechanism of the Calvin Cycle
In stroma CO2 combines with 5C ribulose biphosphate, RuBP, catalysed by rubisco. RuBP carboxylate for to two molecules of 3C Glycerate-3-phosphate, carbon dioxide has now been fixed
GP now reduced and phosphorylatsd to 3C TP, by ATP and reduced NADP
Five out of every 6 molecules of triode-3-phosphate recycled by phosphorylation, using ATP to three molecules of RuBP
How is GP used?
Can be used to make amino acids and fatty acids
How is TP used?
Combine to form hexose sugars, like glucose. Glusose may be isomerise do to fructose. May combine to form sucrose. Hexose sugars can be polymerised into cellulose and starch
TP can be covered to glycerol that can be combined with fatty acid from GP to make lipids
Why is illumination of chloroplasts optimum for rubisco?
More protons pumped across thylakoid membranes into thinks jig spaces, which increases pH in stroma, to optimum conditions of pH for rubisco
What happens to rubisco as temperature increases?
Higher temperatures increase activity if rubisco with oxygen more than its carboxylase activity, less carbon fixation, this is photorespiration
Why are there only small amounts of RuBP in stroma?
Continually being used and regenerated in Calvin cycle
