topic 2.9/8.3- photosynthesis Flashcards
define photosynthesis
the production of carbon compounds in cells using light energy (light->chemical)
how can photosynthetic pigments be separated?
by chromatography
- pigments absorb different wavelengths of light and so look a different colour to us
- plastic strip that has been coated with a thin layer of porous material
- spot containing pigments placed near one end
- solvent is allowed to run up the strip to separate the different pigments
Rf =
distance run by the pigment/distance run by solvent
shortest wavelength of visible light
violet
longest wavelength of visible light
red
middle wavelength of visible light
green (525-575nm)
range of wavelengths of visible light
400-700nm
chlorophyll absorbs —- and —- light most effectively and reflects —— light more than other colours
red; blue
green
draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis
define an absorption spectrum
a graph showing the percentage of light absorbed at each wavelength by a pigment or group of pigments
define an action spectrum
a graph showing the rate of photosynthesis at each wavelength of light
why are action and absorption spectra so similar?
photosynthesis can only occur in wavelengths of light that chlorophyll or other photosynthetic pigments can absorb
effect of the start of photosynthesis on the earth’s atmosphere
For the first 2 billion years after the Earth was formed, its atmosphere was anoxic (oxygen-free)
The current concentration of oxygen gas within the atmosphere is approximately 20%
effect of the start of photosynthesis on the earth’s oceans
- Earth’s oceans initially had high levels of dissolved iron (released from the crust by underwater volcanic vents)
- When iron reacts with oxygen gas it undergoes a chemical reaction to form an insoluble precipitate (iron oxide)
- When the iron in the ocean was completely consumed, oxygen gas started accumulating in the atmosphere
effect of the start of photosynthesis on the earth’s rock deposition
- The reaction between dissolved iron and oxygen gas created oceanic deposits called banded iron formations (BIFs)
- when BIF deposition slowed in oceans, iron rich layers started to form on land due to the rise in atmospheric O2 levels
what type of reaction is photosynthesis and what does this mean?
endothermic reaction; this means it requires energy
state the 3 possible limiting factors on the rate of photosynthesis
- temperature
- light intensity
- carbon dioxide concentration
give 3 ways in which experiments on the limiting factors of photosynthesis can be carried out
Measuring CO2 Uptake (adding sodium hydrogen carbonate raises CO2 conc and you can cause a change in pH)
Measuring O2 Production (gas syringe)
Measuring Biomass (Indirect) as glucose production takes place
where do light-dependent reactions take place?
in the thylakoid space and across the thylakoid membranes
where do light independent reactions take place?
in the stroma - a thick, protein-rich medium enclosed by the inner membrane of the chloroplast
what are the steps and final products of light-dependent reactions ?
- photoactivation
- photolysis
- electron transport
- proton gradient
- chemiosmosis
- ATP synthesis
- reduction of NADP
so the final products are reduced NADP and ATP
describe photosystems
- located in the thylakoid membranes
- consist of chlorophyll and accessory pigments being grouped together in large light-harvesting arrays that have reaction centres
- two types of arrays: Photosystems I and II
photoactivation
- chlorophyll molecules absorb light energy and pass it to two special chlorophyll molecules in the reaction centre of the photosystem
- these absorb the energy from a photon of light, causing an electron within the molecule to become excited- the chlorophyll is then photoactivated
what special property do the chlorophylls at the reaction centre have?
they are able to donate excited electrons to an electron acceptor