PHOTOSYNTHESIS Flashcards
Define photosynthesis
|using light energy to synthesis large organic molecules from smaller inorganic ones
Light energy –> chemical energy
Autotroph
Able to form organic substances from inorganic substances
Self feeding
Chemoautotrophs
Synthesise complex organic molecules using energy from exogenic chemical reactions
E.g. nitrifying bacteria
Photoautotrophs
Organisms that photosynthesise
Use energy from sunlight to produce complex organic molecules from water + carbon dioxide
Heterotrophs
Other feeding
Digest complex organic molecules into simple soluble ones
Cannot make their own food
Word equation
Carbon dioxide + water –> glucose + oxygen
Symbol equation
6CO2 + 6H20 –> C6h2O6 + 6O2
Light dependent stage
Light energy converted to chemical energy
Photolysis of water occurs splitting it into H+ ions and oxygen
Produces reduced NADP + ATP
Light independent stage
Products of light reactions are used to reduce CO2 to sugars + organic molecules
Importance of photosynthesis
Plants, animals and microorganisms rely on it to produce carbohydrates and oxygen
- oxygen required for aerobic respiration
- carbohydrates produce energy stores
- control green house effect
How photosynthesis and respiration interrelate
Plants respire all the time, only photosynthesise in the light
In photosynthesis, ATP is synthesised using light energy- ATP then used to build organic compounds such as glucose
In respiration, organic molecules (e.g. glucose) are broken down to release energy
What is the compensation point
During photosynthesis and respiration there is no net gain or loss of oxygen or carbohydrates
How is a leaf adapted for photosynthesis
Large SA- absorb maximum sunlight
More chlorophyll on top of the leaf
Waxy cuticle reduces water loss
Guard cells close stomata pores (reduces water loss)
Structure and function of chloroplast envelope
Double membrane
Selectively permeable
Outer membrane is permeable to small ions, inner membrane is less permeable
Contains transporter proteins
Structure and function granac(chloroplast)
Stack of thylakoids
Provide SA for chlorophyll + other pigments to attach to (photosystem II)
Enzyme ATP synthase
Structure and function of inter-granal lamellae (chloroplast)
Thylakoids between grana
Contains photosystem I pigments
Structure and function of stroma (chloroplast)
Fluid filled matrix
Contains enzymes for light independent reactions for photosynthesis
Structure and function of DNA (chloroplast)
No histones, circular
Codes proteins (e.g. enzymes for photosynthesis)
Structure and function of ribosomes (chloroplast)
18nm
Protein synthesis
Function of starch grains
insoluble storage molecule
Function of lipid droplets
Maintain membranes (phospholipid bilayer)
What is a photosynthetic pigment
absorbs certain wavelengths of light
What is the colour of the pigment due to
The wavelength of light which is reflected
Chlorophyll
Collection of green pigments
Porphyrin like ring structure head (contains magnesium)
Hydrocarbon tail- embeds itself in membrane of thylakoids
Head remains on surface
Two forms of chlorophyll a
P680 + P700
Carotenoids
Includes carotene and xanthophyll
Ranges in colour (red, orange, yellow)
Absorb wavelengths of light not efficiently absorbed by chlorophyll a
Protect chlorophyll from high light intensities
Phycobillins
Red seaweed contains additional pigments
Allows them to absorb blue/green light (shorter wavelength of light penetrates water)
Explain the distribution of bacteria in response to the absorption spectrum
Congregation of oxygen seeking bacteria surrounding blue and red area of spectra
Suggesting algae is absorbing the light and photosynthesising to produce oxygen
Little to no bacteria absorbing green light, no photosynthesis, no oxygen
Describe and explain the relationship between the absorption and action spectra
Both peak at the blue and red light (increased photosynthesis)- most light absorbed
Action spectra shows some photosynthesis occurs at green and yellow regions- shows carotenoids and other pigments are involved in photosynthesis
What is a photosystem
Pigment molecules arranged in clusters in the thylakoid membrane
Contain hundreds of chlorophyll a + b and carotenoids
Explain a photosystem
One chlorophyll a molecule (primary pigment) acts as a reaction centre for each photosystem
Remaining pigments, (accessory pigments) absorbs light and funnel the energy to the reaction centre
Act as light harvesting systems (aka antennae complex)
Photosystem I
Contains chlorophyll with an absorption peak at 700nm at its reaction centre (P700)
Mainly found in inter-granal lamellae
Photosystem II
Contains chlorophyll a with an absorption peak at 680nm (P680)
Mainly found on granal lamellae
Light dependent reactions
Take place in thylakoid
Photolysis- PSII contains enzymes to split water, hydrogen to NADP + ATP
Light independent reactions
Takes place in stroma
Uses ATP + reduced NADP from light dependent
Stages of Calvin cycle
- CO2 diffuses into stroma
- CO2 combines with ribulose bisphosphate (RuBP)
- rubisco= catalyst
- this product 6C compound which is unstable + immediately splits into 3C compounds
- two 3C compounds= gylcerate phosphate (GP)
- each GP reduced + phosphorylated to triode phosphate
- ATP + reduced NADP (from light dependent) provides phosphate, energy + hydrogen
- 5/6th of TP regenerated to RuBP
- requires ATP from light dependent
Uses of products from Calvin cycle
Pairs of TP combine to form hexose (6C) sugars (e.g. glucose + fructose)
Join to form disaccharides (e.g. sucrose)
Polymers may also form (e.g. starch= storage)
Factors affecting rate of photosynthesis
CO2 concentration
CO2 air conc= 0.04%
Concs lower in dense vegetation
Often limiting factor as essential factor for Calvin cycle
Concs in stroma lower than air
Factors affecting rate of photosynthesis
Temperature
Temp may affect light independent
Increased temp= increased KE (hence enzyme controlled Rea actions in Calvin cycle)
Increased temp= enzymes denature
Above 25 degrees rubric changes to catalysing RuBP with O2 instead of CO2= photorespiration
Factors affecting rate of photosynthesis
Water stress
- plant roots produce absicic acid- translocated to leaves
- causes stomata to close, reduces availability of CO2
- rate of photosynthesis reduces
IF roots cant take up water fast enough to replace water lost from transpiration= cells plasmoylsed
Limiting factors + Calvin cycle
Light intensity
Low= products of light dependent (ATP + reduced NADP) will be in short supply
Limits conversion of GP to TP + regeneration of RuBP
GP still made
Limiting factors + Calvin cycle
CO2 concentration
Low= conversion of RuBP to GP will be slow as less CO2
Less CO2 to combine with RuBP
Limiting factors + Calvin cycle
Temperature
All stages of Calvin cycle catalysed by enzymes (rubisco)
Low temps= cycle= slower
High temp= enzymes denature + photorespiration may occur
