photosynthesis

life depends on continuous transfer of energy

the leaf is the main photosynthetic structure chloroplasts in leaf are where photosynthesis takes place

photosynthesis takes place largely in the leaf are adapted to bring together and produce three raw materials of photosynthesis (water, CO2, light) and remove its products (CO2 & glucose)

• large surface area - absorbs as much sunlight as possible an arrangement of leaves on plants - minimises overlapping and so avoids the shadow of one leaf by another • thin most light is absorbed in the first few micrometers • transparent cuticles & epidermis lets light through to the photosynthetic mesophyll cells beneath -numerous stomata for gaseous exchange so that the mesophyll cells are only a short pathway from one

6CO2 + 6H2O → C6H12O6 + 6O2 + 6H2O photosynthesis produces the oxygen we breath by releasing it from water

• capturing of light energy: by chloroplast pigment such as chlorophyll • the light-dependent reaction: in which some of the light energy absorbed is conserved in chemical bonds • the light-independent reaction: in which these protons (hydrogen ions) are used to produce sugars and other organic molecules

photosynthesis takes place within cell organelles called chloroplasts (vary in shape & size) but is typically disc shape inside the chloroplast membranes are two distinct regions: -the grana -thylakoid -light dependant stage -the stroma - light-independent

involves the capture of light whose energy is uses two purposes to add inorganic phosphate (Pi) molecules to ADP thereby making ATP to split water into H+ ions (protons) and OH- ions. As the splitting is caused by light, it is known as photolysis

when substance gains oxidation/ loses hydrogen the process is called oxidation the substance had been oxidised when a substance is oxidized, it loses electrons

when a substance is reduced, it loses O2/ gains hydrogen when a substance is reduced, it gains electrons

• light enters thylakoid and excites 2 electrons from chlorophyll molecule (oxidation). The proton pump gains these electrons • the reduced proton pump can actively transport proton (H+) from the stroma into the thylakoid space This creates an electrochemical gradient • the electrons are transported from the proton pump (oxidation) to the electron carrier (reduction) • the protons diffuse down an electrochemical gradient through ATP synthase. This allows the enzyme to catalyse ADP +Pi to ATP • 2e- and an H+ are transferred to a coenzyme called dehydrogenase to make reduced NADP (NADPH) ready to be used in the Calvin Cycle. This occurs with the help of an enzyme • We replenish the electrons by using water in a process called phtolysis

the loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons these electrons must be replaced The replacement electrons are provided from water molecules that are split using light energy

2H2O 🠪 4H +4e +O2 protons, electrons and oxygen

the protons out of the thylakoid space through the ATP synthase channels and are taken up by an electron carrier called NADP this becomes reduced NADP and is the main product of the light-dependent stage and enters the LIGHT INDEPENDENT REACTIONS taking with it the electrons from the chlorophyll molecules

it furthers the potential source of chemical energy to the plant

O2 by product from photolysis is used in respiration or diffuses out of the leaf (as a waste product)

thylakoids of chloroplasts

• thylakoids membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light - dependent reaction • network of proteins in the grana hold chlorophyll in a very precise manner that allows maximum absorption • granal membranes have ATP synthase channels within them, which allows establishment of a proton gradient chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light - dependent reaction

products of the light - dependent reaction of photolysis: ATP and reduced NADP are used to reduce glycerate 3 - phosphate in the second stage of photosynthesis it does not require light

takes place in the stroma of the chloroplast

• CO2 from the atmosphere diffuses into the leaf through stomata and dissolves in the water around the wall of the mesophyll cells It then diffuses through the cell - surface membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast • in the stroma CO2 reacts with ribulose bisphosphate this reaction is catalysed by rubisco • the reaction produces 2 of the 3 - carbon glycerate phosphate (GP) • Reduced NADP is used to reduce glycerate 3 - phosphate to triose phosphate (TP) using energy supplied by ATP • Some triose phosphate molecules are converted to organic substances that the plant need e. g. - starch - cellulose - lipids - glucose - amino acids - nucleotides e.t.c 7.most triose phosphate molecules are used to regenerate ribulose bisphosphate using ATP from the light - dependent reaction

takes place in the stroma of the chloroplasts

• fluid of stroma contains all the enzymes needed to carry out the light - independent reaction stromal fluid is membrane - bound in the chloroplast which means a chemical environment which has and substrates can be maintained within it - as distinct from the environment of the cytoplasm the fluid surrounds the grana and so the produces of he light-dependent reaction the grana can readily diffuse into the stroma • contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the light - independent reaction

• CO2 concentration • light intensity • temperature • chlorophyll • water availability