photosynthesis Flashcards
overall chemical reaction for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
overall chemical reaction for respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O
describe the relationship between photosynthesis and respiration
they are the reverse of eachother
explain the importance of photsynthesis for consumers as well as producers
important for consumers as well as producers because it traps the energy from the sun to be transferred through the food chain
what is bond energy?
the idea that bonds require energy to be broken but release energy when they form. small inorganic molecules release a lot of energy when formed. large organic molecules release little energy.
explain photosynthesis in terms of bond energy
a lot of energy is needed to break the bonds in CO2 and H2O but little is given out when glucose forms
explain respiration in terms of bond energy
requires little energy to break bonds in glucose but lots given out when CO2 and H2O form.
name the two stages of photosynthesis and state where each occurs.
1) light dependent stage within thykaloid membranes
2) light independent stage in the stroma
define photosynthetic pigment
a pigment that absorbs light energy
definelight harvesting system
a group of protein and chlorophyll molecules
antennae complex
another name for light harvesting system
define reaction centre
complex of proteins, pigments and cofactors
define photosystem
collevtive name for light harvesting system and reaction centre
name the photosynthetic pigment in the reaction centre of a photosystem
chlorophyll a
name 3 types of photosynthetic pigments found in antennae complex
chlorophyll b, xanthophylls and carotenoids
why is it useful for photosynthetic organisms to have many different photosynthetic pigments?
to absorb different wavelengths of light to maximise energy transferred to the reaction centre.
absorption spectrum graph
graph to show what wavelengths the different pigments absorb
e.g chlorophyll absorbs red and blue but reflects green wavelengths
what is the purpose of chromatography?
used to separate and identify substances
describe the method of thin layer chromatography to separate and identify photosynthetic pigments.
mobile phase is solution containing mixture of pigments. stationary phase is a thin layer of silica gel applied to glass
what does “Rf” stand for in “Rf value”
retention factor
how to calculate the Rf value
the distance the pigment travelled / distance of the solvent front
how to use Rf values to identify molecules present in a solution
Rf values compared to a table of known values to identify components
what determines how far a particular molecule travels in chromatography?
different solubilities and interactions with the stationary phase lead to different distances travelled
name the two useful products, waste productions, requirements of the light-dependent stafe of photosynthesis
useful products: reduced NADP, ATP
waste product: oxygen
requires: water and sunlight
define oxidation
removal of electrons or hydrogen
define reduction
gaining electrons
define phosphorylation
the addition of a phosphate group to a molecule using light energy
cyclic photophosphorylation
synthesis of ATP involving photosystem 1
define non-cyclic photophosphorylation
synthesis of ATP and reduced NADP involving photosystems 1 and 2
define photolysis
the decomposition or separation of molecules using light
process of cyclic photophosphorylation
light energy converted to chemical energy in excited electrons which is used to phosphorylate ADP to ATP
process of non-cyclic phosphorylation
electrons do not cylce they enter with water and leave in NADPH2
describe the process of photolysis
water is split by light.
oxygen is lost
H+ ions join NADP to form NADPH2.
electrons pass into chain, eventually jpining the H+ to complete the reduction of NADP tp NADPH2
name useful products and requirements of the molecules that are returned to the light-dependent stage.
useful products: triose photsphate
requirements: NADOH2, ATP and CO2
molecules ADP and NADP are returned to the light-independent stage
define RuBP
ribulose bisphosphate - 5 carbon compound
define RuBisCO
ribulose biphosphate carbocylase - enzyme that catalyses the carbon fixation
define GP
glycerate 3-phosphate - 3 carbon molecule
define TP
triose phosphate - 3 carbon moleucle
define fixation
the incorporation of carbin into organic compounds by living organisms, by photosynthesis
describe the roles of ATP and reduced NADP in the calvin cycle
both: reduction of GP to TP
ATP: regeneration of RuBP
how is RuBP regenerated in the calvin cycle?
TP converted into RuP which is phosphorylated by ATP to reform RuBP
uses of TP
form other carbohydrates such as glucose as well as proteins, lipids and nucleic acids. starting point of many organic synthesis reactions
process of photorespiration
oxygen is a competitce inhibitor of RuBisCO.
when CO2 low, phosphoglycolate is produced
= toxic 2 carbon compound
converted to other organic molecules using ATP
action spectrum graph
graph that shows the effectiveness of photosynthesis - addition of the absorptions of the different pigments.
define limiting factor
factor which limits the rate of a process
5 factors that affects the rate of photsynthesis
light intensity
CO2 concentration
temperature
water stress
number of chloroplasts
how light intensity affects rate of photosynthesis
light needed to reduce NADP and photophosphorylate ADP.
higher light intensity, more energy is provided and rate increases.
more photons stike photosystems.
how temperature affects rate of photosynthesis
temperature affects rate of enzyme controlled reactions.
increased temp: increased kinetic energy, more collisions.
above optimum: proteins denature and the rate decreases.
how carbon dioxide concentration affects rate of photosynthesis
CO2 needs to fixed in the calvin cycle as a source of carbon to produce TP.
as CO2 increases, rate of TP production can increase.
explain how graphs of rate of photosynethsis can show what is limiting rate of photosynthesis
if rate changes as the factor changes, then the factor is a limiting factor.
if graph plateaus, then a different factor is limiting the rate.
how water stress limits rate of photosynthesis but water availability itself is not a limiting factor
stomata close to prevent water lost by transpiration due to water stress, but there is still plenty of water.
when stomata is closed, the carbon dioxide concentration decreases and reduces the rate photosyntheis, not the water availability.
how can the rate of photosynthesis be measured?
measuring oxygen production [only possible for aquatic plants]
count the bubbles or measure the volume of gas in gas syringe
measure uptake of CO2
use radioactive C14 and measure uptake of radioactivity
how to investigate how one environmental factor affects the rate of photosynthesis
light intensity - different distances from light, heat shield needed to avoid temperature being a factor
define compensation point
point at which rates of photosynthesis and respiration are the same meaning net CO2 uptake is 0
how to determine compensation point for a particular photosynthetic organism
aquatic plant such as algae
use indicator - when it doesn’t change colour, that is the compensation point. [CO2 is acidic]
explain how changing light intensity affects concentrations of RuBP, TP and GP in calvin cycle
decreased: means less ATP and NADPH2 can be used in calvin cycle as rate of light dependent reaction is decreased.
reduction of GP to TP is reduced
concentration of GP increases and TP decreases
explain how changing CO2 affects concentrations of RuBP, TP and GP in calvin cycle
decreased: carbon is not fixed by RuBP and GP is not produced.
concentration of RuBP increases
concentration of GP and TP decreases
explain how changing temperature affects concentrations of RuBP, TP and GP in calvin cycle
all stages of calvin cycle are controlled by enzymes.
all molecules reduced at low temperatures
will also reduce when temperature is above optimum and the enzymes denature
