3.2 photosynthesis uses light energy to synthesise organic moleucles Flashcards
what is the photosynthesis equation?
6CO2 + 6H2O —> C6H12O6 + 6O2
carbon dioxide + water —> glucose + oxygen
during the day (respiration/photosynthesis) takes place?
both - respiration releases carbon dioxide which, in the leaves, is used in photosynthesis
during the night (respiration/photosynthesis) takes place?
only respiration takes place
as light intensity increases, the rate of photosynthesis (increases/decreases)?
also increases
what is the compensation point?
- up to a certain point, respiration can provide the CO2 needed by photosynthesis until the rates of these reactions are the same
- this is called the compensation point
(the light compensation point is the light intensity at which a plant has no net gas exchange as the volume of gases used and produced in respiration and photosynthesis are equal)
plants that are adapted to live in the shade have a higher rate of photosynthesis at lower light intensities.
do they have a higher or lower compensation point than plants adapted to living in full sunlight?
have a lower compensation point than plants adapted to living in full sunlight
what is a limiting factor?
a variable that limits the rate of a particular reaction
what are some factors required for photosynthesis?
- energy in the form of light (usually from the sun)
- chlorophyll and other pigments to absorb light energy
- water to combine with carbon dioxide to form organic compounds
- a suitable temperature to provide optimum conditions to one for the enzymes that control photosynthetic reactions
•enzymes e.g Rubisco to catalyse reactions
a shortage of any of these factors will limit the maximum rate at which photosynthesis can take place. they are therefore referred to as limiting factors
describe and explain a graph showing the change in rate of photosynthesis against an increasing light intensity
- A = light intensity is low and prevents photosynthesis reaching a maximum rate - as light intensity increases so does the rate. this shows that light intensity is the limiting factor
- B = the amount of photosynthetic pigment or another factor such as co2 concentration or rubisco concentration, becomes the limiting factor
- C = has reached max rate of photosynthesis
(saturation point = an increase in light intensity causes no further increase in the rate of photosynthesis)
what is the saturation point on a graph?
- an increase in e.g light intensity causes no further increase in the rate of photosynthesise
what is the main site of photosynthesis?
- palisade tissue in the leaves
- (chloroplasts)
what are some adaptations of angiosperm leaves to increase the efficiency of photosynthesis?
- leaves can change their position during the day so that the upper surface is always at right angles to the direction of light - maximises the amount of light that they can absorb for photosynthesis
- within the palisade mesophyll cells chloroplasts can move intracellularly in response to light intensity - they can orientate themselves so that they absorb more light and can also move around if more light is passing through one part of a cell to another
- transparent cuticle
- large surface area to maximise light absorption
- thin - to reduce diffusion distance for CO2
- densely packed chloroplasts in the palisade cells
- upper epidermis transparent allowing light to strike mesophyll layers
- air spaces allow for co2 to diffuse to the photosynthesising cells
- vein network transports water and minerals to the leaf and takes sugars away
- stomata allow CO2 to diffuse into the leaf
learn structure of leaf from AS
learn structure of chloroplasts from AS
chloroplasts contain a number of different photosynthetic pigments including:
- chlorophyll a
- chlorophyll b
- carotene
- xanthophyll
what is the function of the photosynthetic pigments?
to absorb light energy
how can the photosynthetic pigments be separated?
- using chromatography
- the different pigments dissolve in the solvent and are absorbed into and adsorbed onto chromatography paper
- the pigments are carries with the solvent
(chromatography is used to separate different products from a mixture)
in chromatography:
- smaller molecules tend to travel further
- larger molecules don’t travel as far
what is the Rf value?
- in a particular solvent, the movement of the pigment (solute) relative to the solvent front (how far the solvent travels)
what is the Rf value equation?
Rf = distance moved by solute / distance moved by solvent front
what are some of the Rf values for the photosynthetic pigments:
- carotene
- phaeophytin
- xanthophyll
- chlorophyll a
- chlorophyll b
dont need to learn
- carotene = 0.95 = yellow spot
- phaeophytin = 0.83 = yellow-grey spot
- xanthophyll = 0.71 = yellow-brown
- chlorophyll a = 0.65 = blue-green
- chlorophyll b = 0.45 = green
do the different photosynthetic pigments absorb light of different wavelength?
yes
if you shine light of different wavelengths through a solution of chlorophyll molecules, short/blue wavelengths and long/red wavelengths are absorbed but green light is reflected/transmitted
how is having multiple photosynthetic pigments an advantage to the plant?
- each pigment absorbs light of slightly different wavelengths
- overall the plant can carry out photosynthesis at a wider range of wavelengths and is more effective