5. On the Wild Side (3) Flashcards
5.5 - 5.9 Photosynthesis
Overall reaction of photosynthesis
Converts light energy into chemical energy stored in the biomass of producers
carbon dioxide and water –> (light hitting chlorophyll) —> glucose and oxygen
What is the energy from light used for
Its used in hydrolysis - splitting the strong covalent bonds in water molecules
What is the hydrogen combined with the create what store
hydrogen is combined with carbon dioxide to create glucose as a fuel
What happens to oxygen?
It is released into the atmosphere as it is a waste product
Phosphorylation of ADP
What is ATP
adenosine triphosphate - universal energy currency
nitrogenous base - adenine, ribose (pentose sugar) and 3 phosphate groups.
Why do organisms require a constant supply of energy?
- building new molecules from the products of digestion during anabolic reactions
- moving substances across cell membranes in active transport or to move substances within cells
- for muscle contraction and in the conduction of nerve impulses/ action potentials
Is ATP a nucleotide?
Yes - it is a phosphorylated nucleotide
Phosphorylated meaning
addition of a phosphate to an organic compound.
Where does photosynthesis occur?
The chloroplasts
How is ATP produced and broken down?
In respiration - Inorganic phosphate is added to adenosine diphosphate
ADP + Pi -> ATP
Hydrolysis - breakdown of ATP into ADP and Pi. Also known as
dephosphorylation
This is catalysed by ATPase
Hydrolysis occurs as ATP is used to provide energy for metabolic needs.
Stroma
Gel like fluid that contains enzymes that catalyse the reactions of photosynthesis
Chloroplast DNA
contains genes that code for some of the proteins used in photosynthesis
Ribosomes
Enable the translation of proteins coded by the chloroplast DNA
Thylakoid space
space between the two membranes of the thylakoid membrane which conditions differ from the stroma.
There is a proton gradient that is established between the thylakoid space and the stroma.
why can a proton gradient develop quickly in the thylakoid space?
The space has small volume.
Thylakoids
flattened fluid filled sacs - surrounded by a thylakoid membrane (where the electron transport chain takes place)
Grana
Stacked up thylakoids (singular is granum)
Large surface area, maximum light absorption znd maximising number of photosystems.
What do grana provide?
More membrane area for proteins such as electron carriers and ATP synthase enzymes
Lamellae
(singular lamella) - membranous channels which ensure the stacks of sacs are connected but distanced from eachother.
What is embedded in the thylakoid membranes?
ATP synthase enzymes, photosystem proteins
What type of pigments to the photosystems contain?
Photosynthetic pigments chlorophyll a, chlorophyll b and carotene
photosystem 1 absorbs what wavelength of light?
700 nm
Photosystem 2 absorbs what wavelength of light?
680nm
Light dependent reactions take place…?
in the chloroplast across the thylakoid membrane
Light independent reactions take place…?
in the chloroplast in the stroma.
Light energy does what to water
Photolysis - splitting of water molecules
Photolysis of one molecule of water produces?
2 Hydrogen ions (protons), 2 electrons, one atom of oxygen
What are these used for?
Hydrogen ions and electrons are used in the light dependent reactions while oxygen is given off as a waste product
Light energy is converted into what?
Chemical energy in the form of ATP and reduced NADP.
How does NADP reduce and oxidise other molecules
reduce = by giving away hydrogen
oxidise = by receiving hydrogen
Useful products of the light dependent reaction
NADPH and ATP
Photophosphorylation
Light aiding in the addition of phosphate to ADP to form ATP
Types of photophosphorylation
Non-cyclic photophosphorylation - ATP and NADPH
Cyclic photophosphorylation - ATP only
Electron transport chain
Electrons pass from one protein to another along the electron transport chain, releasing energy as they do so in a series of redox reactions.
Chemiosmosis
Energy released as electrons pass down the electron transport chain used to produce ATP.
Non Cyclic Photophosphorylation steps 1 - 4
1) Light energy hits photosystem 2 in the thylakoid membrane.
2) Two electrons gain energy and are said to be excited to a higher energy level
3)The excited electrons leave the photosystem and pass to the first protein in the electron transport chain
4) After excited electrons leave the photosystem they are replaced by electrons from the photolysis of water
Non cyclic photophosphorylation steps 5 - 9
5) The electrons pass down the electron transport chain
6) Energy is released as the electrons pass down the electron transport chain, enabling chemiosmosis to occur
7) H+ ions are pumped from a low conc. in the stroma to a high conc in the thylakoid space, generating a conc gradient across the thylakoid membrane
8) H+ ions diffuse across the thylakoid membrane into the stroma via ATP synthase enzymes embedded in the membrane
9) Movement of H+ ions causes the ATP synthase enzyme to catalyse the production of ATP
What happens at the end of Non Cyclic photophosphorylation (steps 10 -14)
10) electrons from ps2 are passed to ps1, light energy hits ps1, re-exciting another pair of electrons which leave the photosystem
11) Excited electrons from ps1 pass along an electron transport chain
12) These electrons combine with hydrogen ions from the photolysis of water and the coenzyme NADP to form NADPH, which passes onto the light independent reactions
H+ + 2e- + NADP+ → NADPH
Cyclic Photophosphorylation
1) Light hits photosystem I
2) Electrons are excited to a higher energy level and leave the photosystem
3) The excited electrons pass along the electron transport chain, releasing energy as they do so
4) The energy released as the electrons pass down the electron transport chain provides energy to drive the process of chemiosmosis
5) H+ ions are pumped from a low concentration in the stroma to a high concentration in the thylakoid space, generating a concentration gradient across the thylakoid membrane
6) H+ ions diffuse back across the thylakoid membrane into the stroma via ATP synthase enzymes embedded in the membrane
Products of the light independent reactions
starch for storage, sucrose for transport, cellulose for making cell walls
What does the movement of H+ ions cause
7) The movement of H+ ions cause the ATP synthase enzyme to catalyse the production of ATP
8) At the end of the electron transport chain the electrons re-join photosystem I in a complete cycle; hence the term cyclic photophosphorylation
9) The ATP produced enters the light-independent reaction
What do the light independent reactions require
ATP and reduced NADP
Step 1 of the light independent reaction
Carbon fixation
Carbon dioxide is combined with ribulose biphosphate a 5C compound that yields 2 molecules of GP - a 3 carbon compound
Step 2 of the light independent reaction
GP is reduced into GALP, another 3C compound in a reaction involving reduced NADP and ATP.
Step 3 of the light independent reaction
RuBP is regenerated from GALP in reactions that use ATP
Rubisco
Rubisco catalyses the reaction of the fixation of Carbon dioxide to the 5C sugar known as RuBP.
Why are the two molecules of GP made quite quickly?
The 6C compound which is made as a result of carbon fixation to RUBP is unstable and splits into two.
Reduction of GP
Energy from ATP and hydrogen from reduced NADP reduce the two molecules of GP to GALP.
What are some of the carbons in GALP used for
production of glucose, regeneration of RUBP
How many turns of the Calvin cycle are required to produce one molecule of glucose?
6
Products of photosynthesis
GP, Galp, glycerol, nucleic acids
GP is used in the formation of…
Amino acids, fatty acids
GALP is used to produce
Hexose sugars - glucose. hexose sugars can be converted to sucrose for transport in the phloem
Glucose is used to build new plant biomass
Glycerol is used to produce
- lipid molecules, triglycerides, phospholipids
