Photosynthesis Flashcards
(33 cards)
what are the two stages that occur in photosynthesis?
- light dependent reaction
- light independent reaction
where does the light dependent reaction occur?
grana/thylakoids
name four ways in which the chloroplasts are adapted to their function of capturing light and carrying out the light-dependent reaction
- large surface area on thylakoid membranes for attachment of chlorophyll, electron carriers and enzymes
- network of proteins holds chlorophyll in precise manner for maximum absorption
- ATP synthase channels in granal membranes- membranes are selectively permeable
- contain DNA and ribosomes to manufacture proteins needed for light-dependent reaction
what are the two stages that occur in light-dependent reaction?
- non-cyclic photophosphorylation
- cyclic photophosphorylation
what are the five main stages that occur in non-cyclic photophosphorylation?
- photoionisation
- photolysis
- electron transport chain
- chemiosmosis
- reduced NADP
what is a photosystem?
photosynthetic pigments embedded into thylakoid membranes of the grana in clusters
what is the two main structural components of a photosystem?
- antenna complex: gather light energy of various wavelengths and funnel energy into reaction centre
- reaction centre: specialised chlorophyll molecule which contains maximum energy
what are the principal photosynthetic pigments?
chlorophyll (a+b), carotenoids (carotene and xantrophyll)
what happens in photoionisation?
light energy is absorbed by PS2 and the photons excite the electrons to higher energy level causing them to move out of the chlorophyll molecule to be talen by an electron carrier
why is photolysis needed and how does it work?
- needed to replace excited electrons
- light energy splits water into H+ ions, electrons and oxygen
what are H+ ions used for?
pumped into thylakoid lumen to maintain concentration gradient for chemiomosis
what is oxygen used for?
- diffuses out of cell
- aerobic respiration
what happens in electron transport chain?
excited electrons passed down series of electron carriers called electron transport chain
- energy is conserved to move H+ ions out of stroma into thylakoid lumen by active transport to maintain gradient
what happens in chemiosmosis?
H+ ions move through ATP synthase causing it to hcnage shape and combine ADP with inorganic phosphate to produce ATP
how is reduced NADP formed?
light energy excites electrons in PS1 to even higher energy level which are transferred onto NADP along with a proton to form reduced NADP
how does cyclic phosphorylation differ to non-cyclic?
- only uses PS1
- does not produce NADP or oxygen
explain process of cyclic phosphorylation
- excited electrons passed back to electron carriers in membrane in order to reycle electrons to maintain repeated flow
- small amount of ATP produced useful as light-independent reaction uses lots of ATP
what does the energy of the photon depend on?
its wavelength - longer wavelength lower energy
why do leaves appear green?
absorb red and blue wavelengths so reflect green wavelengths
what laboratory technique is used to extract and analyse pigments?
- paper chromatography
what can we use to show spectrum obtained by passing white light through leaf pigment extract? what can we draw from this?
- spectrometer
- degree of absorption of each wavelength measured for plant extract and individual pigments
- this information is generated on absorption spectrum graph
- rate of photosynthesis at different wavelengths can be experimentally measured as well whcihc produces action spectrum graph
what are the three stages of the light-independent reaction?
- carbon-fixation stage
- reduction stage
- regeneration stage
what occurs in carbon-fixation stage?
- CO2 diffuses into leaf through stomata, dissolves into water surrounding mesophyll cells and diffuses through cell-surface membrane,cytoplasm,chloroplast membranes into stroma
combines with RuBP (ribulose biphosphate) into unstable 6C compound that breaks down into 2 molecules of GP (glycerate-3phosphate)
(catalysed by enzyme rubisco- ribulose biphosphate carboxylase)
what happens in reduction stage?
ATP from light-dependent reaction provides energy to convert GP into TP
- also requires H+ ions from NADPH2 which regenerates NADP back to electron transfer chain in light-dependent reaction
