5.2.1 - photosynthesis Flashcards
photosynthesis definition
the process by which energy, in the form of light from the Sun us used to build complex orgnaic molecules, like glucose
autotrophic
plants and algae that can photosynthesise
heterotrophic organisms
animals, obtain complex organic molecules by eating ither organisms
photosynthesis equation
carbon dioxide + water —> glucose + oxygen
where does photosynthesis take place?
chloroplast
structure of chloroplast
membranes of flattened sacs called thykaloids, which are stacked to form grana
the grana are joined by lamellae
fluid enclosed is called the stroma
role of pigment molecules in chloroplast
to absorb specific wavelenhths of light and reflect others
primary pigment in photosynthesis and what does it absorb?
chlorophyll - mainly red and blue light, reflecting green light
affect of the different pigment on leaf colour
lots of different shades and colours of leaves
light harvesting system
proteins and pigments that absorb and harvest light energt of different wavelengths and transfer this energy quickly and efficiently to the reaction centre
where is chlorophyll a located
in the reaction centre
photosystem
complex structures within chloroplasts of plants that capture light energy and use utr to generate ATP and NADPH
structure of a photosystem
funnel shaped structure with chlorophyll a at its reaction centre, and accessory pigments funnel thr light onto the reaction centre
Photosystem I
P700 form of chloophull a - where peak absorption of light is at 700nm
Photosystem II
P680 form of chlorophyll a - peak absorption of light is at 680nm
why is it useful that plants have a range of different pigments?
leaf can absorb a greater range of different light wavelengths - increasing energy absorbed, higher rate of PHS, increasing carbs produced
absorption spectrum
data is collected by shining different wavlenths onto chloroplast and using a colourimiter to measure absobance of each, then plotting on a graph
photosystems in non cyclic photophosphorylation
PSII and PSI
steps of non cyclic photophosphorlyation
- chlorophyll a in PSII abosrbs light
- electrons become excited to a higher energy level and passed along a electron transport chain
- the electron carriers are oxidised when they pass the electrons on
- H+ ions are pumped out
- This causes energy to be released, causing ATP to be synthesised at ATP synthase
- Photolysis
- PSI is also absorbing this light, and receving the electrons
- ferredoxin passes the electron along with a H+ proton to NADP
- this forms reduced NADP
what are the products of the light dependent reactoon
ATP, and NADPH (used for light independent reaction) and oxygen
photolysis
water molecules being split, forming oxygen, electrons and hydrogen atoms (protons)
reason for photolysis
electrons released are used to replace the electrojs lost from PSII when light is absorbed
cyclic photophosphorylation
electrons that leave the electron transport chain after PSI can be returned to PSI instead of being used to form reduced NADP.
NADPH is not produced when this happens
chemiosmosis
the process of ATP production
where does the light independent reaction take place
stroma
steps of the calvin cycle
1.CO2 diffuses into the leaf via stomata
2. picked up by RuBP, catalysed by the enzyme rubisco
3. unstable 6 carbon molecule formed
4. this splits into 2 GP
5. the NADPH and ATP are used to convert the 2 GP into 2 TP
6. 5/6 of the TP is used to regenerate the RuBP
7. 1/6 of the TP can be used to make other carbs and crucial substances
calvin cycle summarised into three steps
- fixation - co2 is fixed in the first step
- reduction - GP is reduced to TP using LDR producs
- regeneration - RuBP is regenerated from TP
how are the LDR products used in the LIR?
- the NADPH donates hydrogen atoms
- ATP acts as an energy source
why is rubsico not an efficient enzyme? how is this dealt with?
competitively inhibited by oxygen
rubisco has a higher affinity for co2 than for o2 - the higher the co2 concentration, the less likely the enzyme is to react with o2
limiting factor
reducing the rate
how does light intensity affect the rate of photosynthesis
light is needed as an energy source, as light intensity increases ATP and NADPH are produced at a higher rate
how does co2 concentration affect the rate of photosynthesis
increasing the co2 conc increases the rate of carbon fixation in the calvin cycle and therefore the rate of TP production
how does temperature affect the rate of photosynthesis
affects the rate of enzyme control reactions, however may increase the rate of photorespiration
photorespiration
when rubisco reacts with oxygen, reducing the rate of photosytnethsis
effect of reducing light intensity on calvin cycle
whilst it doesnt necessarily use light energy, it will mean there are less products being available to use in the Calvin cycle.
