Photosynthesis Flashcards
How are leaves adapted for photosynthesis?
- large surface area to absorb large volumes of sunlight
- thin so short diffusion distance for gases
- transparent cuticle and epidermis for light to reach photosynthetic mesophyll cells beneath
- lots of chloroplasts in mesophyll
- numerous stomata so all mesophyll cells are a short distance from one
Where does the light dependent stage of photosynthesis take place?
thylakoids
Where does the light independent stage of photosynthesis take place?
stroma
What are the products of the light dependent reaction?
ATP and NADPH
What is photoionisation and how does it occur?
When chlorophyll absorbs light energy, electrons become excited and move to a higher energy level, leaving the chlorophyll. This causes chlorophyll to become oxidised - the process is called photoionisation
What is photolysis?
Photosystem 2 absorbs light energy, which causes water to be split into protons, electrons and oxygen
What happens to the products of photolysis?
- protons move into the thylakoid lumen which maintains a proton gradient
- electrons move along electron transport chains which provides energy for active transport of H+ ions into the thylakoid lumen from the stroma
- oxygen is used in respiration, or diffuses out of the cell
How is ATP produced in the light dependent reaction?
- chlorophyll absorbs light energy which causes electrons to become excited and leave the chlorophyll, entering the electron transport chain
- as the electrons pass along in a series of oxidation-reduction reactions, they release enough energy for H+ ions to be actively transported from the stroma into the thylakoid space using protein carriers (chemiosmosis)
- there is a high concentration of protons in the thylakoid space maintained by photolysis of water, and a low concentration in the stroma
- this concentration gradient causes protons to diffuse into the stroma down the concentration gradient through the enzyme ATP synthase
- this changes the structure of ATP synthase which catalyses ADP and Pi to be converted into ATP which is known as photophosphorylation
How is NADPH formed in the LDR?
- at the end of the electron transfer chain, electrons recombine with protons in the thylakoid space to form a hydrogen atom. This hydrogen atom combines with the coenzyme NADP, and reduces it to NADPH
What are the products of the light independent reaction?
NADP, ADP and Pi
How are useful organic substances formed in the calvin cycle?
- carbon dioxide diffuses into the stroma within the chloroplast
- carbon reacts with RUBP, catalysed by the enzyme rubisco, to form 2 x 3 carbon compounds called GP (carboxylation)
- GP is reduced by NADPH and uses energy from ATP hydrolysis to form 2 molecules of triose phosphate (TP). This leaves NADP, ADP and Pi which travel to the thylakoid membrane to be used in the LDR
- a small amount of triose phosphate is converted into useful organic substances
What are the useful organic substances produced in the calvin cycle?
- glucose - used in respiration
- amino acids - used to form proteins
- glycerol - combines with 3 fatty acids to form triglyceride molecules
What happens to the triose phosphate that isn’t used to form useful organic substances?
used to regenerate RuBP using energy from ATP hydrolysis (ATP formed in LDR)
How are chloroplasts adapted for the light dependent reaction?
- thylakoid membrane provides a large surface area for chlorophyll, electron carriers and enzymes to carry out the LDR
- a network of proteins in the grana hold the chlorophyll in a very precise manner that allows for maximum light absorption
- granal membranes have ATP synthase channels
- they contain DNA and ribosomes which can quickly and easily manufacture proteins needed in the LDR
How are chloroplasts adapted for the light independent reaction?
- fluid in the stroma contains all the enzymes needed in the LIR
- stroma fluid surrounds the grana so the products of the LDR can readily diffuse into the stroma
- contains DNA and ribosomes so can quickly and easily manufacture proteins needed in the LIR
