photosynthesis

what is the equation for photosynthesis?

carbon dioxide + water → glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2

what does photosynthesis convert?

converts light energy into chemical energy which is stored in biomass of producers

what is the light energy in photosynthesis used for?

it splits strong bonds in water molecules, releasing hydrogen and oxygen

how are oxygen and hydrogen used in a producer?

oxygen is released into the atmosphere as a waste product
hydrogen combines with carbon dioxide to produce glucose

what do organisms use energy for?

building new molecules from products of digestion during anabolic reactions
moving substances across cell membranes in active transport
muscle contraction

what is used to transfer and supply energy within cells?

adenosine trphosphate (ATP)

what is the structure of ATP?

a nucleic acid, phosphorylated nucleotide containing three phosphate groups, a base, and a sugar

when is ATP produced?

during respiration by addition of inorganic phosphate to adenosine diphosphate (ADP)
the breakdown of glucose in respiration releases the energy needed to phosphorylate ADP

what happens in the hydrolysis of ATP?

the hydrolysis of ATP involves the catalyst enzyme ATPase
it releases an inorganic phosphate from ATP (dephosphorylation) and a small amount of energy used in processes like active transport and anabolic reactions

name the components of a chloroplast

1) chloroplast DNA
2) starch granule
3) granum
4) lamella
5) thylakoid
6) ribosome
7) stroma
8) drop of lipids
9) inner membrane
10) intermembrane space
11) outer membrane

what is the role of the chloroplast double membrane?

it encloses the chloroplast
the transport proteins in the inner membrane control the flow of molecules between the stroma and cytoplasm

what is the role of the stroma?

gel-like fluid contains enzymes that catalyse the reactions of photosynthesis

what is the role of the DNA?

contains genes that code for some of the proteins used in photosynthesis

what is the role of ribosomes?

enable translation of proteins coded by the chloroplast DNA

what is the role of the thylakoid membrane?

there is a space between this double membrane - thylakoid space
proton gradient can be formed between thylakoid space and stroma

what is the role of the grana?

creates a large surface area, maximising number of photosystems and allowing maximum light absorption
provide more membrane area for proteins for ATP production

what are photosystems?

two types: photosystem I and photosystem II
contain different combinations of photosynthetic pigments: chlorophyll a, chlorophyll b, carotene
each photosystem absorbs light of a different wavelength (photosystem I: 700nm photosystem II: 680nm)

what are the two stages of photosynthesis?

light-dependent reactions take place across the thylakoid membrane
light-independent reactions take place in the stroma

what is photolysis?

the reaction where light energy in the light-dependent reactions enables the splitting of water molecules

what does the photolysis of one molecule of water produce?

2 hydrogen ions (protons)
2 electrons
one atom of oxygen
hydrogen ions and electrons are used in the light-dependent reactions, oxygen is waste product

what is converted in the light-dependent reactions?

light energy is converted into chemical energy in the form of ATP and reduced NADP
these products are transferred to the light-independent reactions

what is NADP?

a coenzyme; it transfers hydrogen from one molecule to another
when NADP gains hydrogen, it is reduced and becomes reduced NADP/NADPH

where is ATP and NADPH produced?

in the thylakoid membrane through photophosphorylation

what are the two types of photophosphorylation that occur to produce ATP and NADPH?

non-cyclic - produces both ATP and NADPH
cyclic - produces ATP only

what do both cyclic and non-cyclic photophosphorylation involve?

a series of membrane proteins that make up the electron transport chain
chemiosmosis

what is the first step of non-cyclic photophosphorylation?

light energy hits photosystem II in the thylakoid membrane

what is the second step of non-cyclic photophosphorylation?

two electrons gain energy → excited to higher energy level, pass to first protein in electron transport chain and replaced by electrons from photolysis of water

what is the third step of non-cyclic photophosphorylation?

electrons pass down electron transport chain, energy is released and chemiosmosis occurs
H+ ions are pumped from a low concentration in the stroma to a high concentration in the thylakoid space → concentration gradient
H+ ions diffuse back into the stroma via ATP synthase enzymes in the thylakoid membrane
movement of H+ ions causes ATP synthase enzyme to catalyse the production of ATP

what is the fourth step of non-cyclic photophosphorylation?

the electrons from photosystem II pass to photosystem I
light energy hits photosystem I, exciting another pair of electrons that leave the photosystem
these electrons pass along an electron transport chain
they combine with hydrogen ions from the photolysis of water and the coenzyme NADP to form NADPH (H+ + 2e- + NADP+ → NADPH)
the NADPH and ATP pass to the light independent reactions

what is the first step of cyclic photophosphorylation?

light hits photosystem I

what is the second step of cyclic photophosphorylation?

electrons are excited to a higher energy level and leave the photosystem, passing along the electron transport chain and releasing energy

what is the third step of cyclic photophosphorylation?

the energy released as the electrons pass along the electron transport chain provides energy for chemiosmosis
H+ ions are pumped from a low conc in the stroma to a high conc in the thylakoid space → concentration gradient
H+ ions diffuse back into the stroma via ATP synthase enzymes in the thylakoid membrane
movement of H+ ions causes ATP synthase to catalyse production of ATP

what is the fourth step of cyclic photophosphorylation?

the electrons rejoin photosystem
the ATP produced enters the light-independent reaction

what are light-independent reactions also known as?

the Calvin cycle

what organic molecules do light-independent reactions produce?

starch for storage, sucrose for transport, cellulose for making cell walls

what do light-independent reactions require to function?

ATP and reduced NADP from the light-dependent reactions

what are the three main steps in the light-independent reactions?

1. CO2 is combined with ribulose biphosphate, a 5C compound (RuBP); yields two molecules of glycerate 3-phosphate (GP), a 3C compound

2. GP is reduced to glyceraldehyde 3-phosphate (GALP), a 3C compound in a reaction with NADPH and ATP

3. RuBP is regenerated from GALP in reactions that use ATP

what is the process of carbon dioxide and RuBP combining in the light-independent reactions?

CO2 and RuBP combines in a reaction catalysed by rubisco
the resulting 6C compound is unstable and splits in two → two molecules of a 3C compound, glycerate 3-phosphate (GP)
the CO2 is fixed

what is the process involving the reduction of glycerate 3-phosphate in the light-independent reactions?

energy from ATP and hydrogen from NADPH are used to reduce the two molecules of GP to two 3C molecules, GALP
some of the carbons in GALP are used in the production of glucose, rest to regeneration of RuBP

how is GALP used to regenerate RuBP?

two molecules of GALP contain 6 carbon atoms, five are needed to regenerate RuBP with ATP
every turn in calvin cycle → one sixth of molecule of glucose is produced
six turns of calvin cycle required to produce one molecule of glucose

what is glycerate 3-phosphate used to produce?

amino acids for protein synthesis
fatty acids that form the tails of lipid molecules

what is glyceraldehyde 3-phosphate (GALP) used to produce?

hexose sugars e.g. glucose that can be converted into other hexose sugars e.g. glucose → sucrose for transport in phloem
hexose sugars joined to form polysaccharides e.g. starch + cellulose
glycerol for building lipid molecules
nucleic acids to form basis of DNA and RNA