C1: Photosynthesis Flashcards
Describe how the structure of the angiosperm leaf makes them well adapted for photosynthesis
5 points
Large surface area - to capture the most light
Thin - light penetrates through leaf
stomata and air spaces - allow CO2 into the leaf and cells
cuticle and upper epidermis are transparent - light penetrates to the mesophyll
palisade cells are cylindrical, elongated and at right angles to the surface of the leaf - so large density of palisades can fit into the highest layer so light only travels through 3 cell walls before reaching chloroplasts
Describe how the locatiojn shape, and movement of chloroplasts makes them well adapted for photosynthesis
3 points
chloroplasts have a large surface area - for maximium light absorbance
chloroplasts move and rotate within palisade cells - toward the top on dull days and the bottom on light days to avoid pigment bleaching and to maximise light absorption
higher density of chloroplasts in palisade cells than any other cell - they are at the top of the leaf and are exposed to more light
Define Transducer and provide a biological example
A transducer changes energy from one form into another.
Chloroplasts converts energy in the photons of light into chemical energy made available through ATP and Biological molecules like glucose
Name four photosynthetic pigments
Chlorophyll a
Chlorophyll b
b-Carotene
Xanthophyll
What is the function of photosynthetic pigments
Is to absorb light energy and begin its conversion to storable chemical energy
What two wavelength(colour) of light is absorbed the best and what two are absorbed the worst
Blue then Red then yellow then green
Why is there more than one pigment ?
To absorb a larger range of light wavelengths
What is the function of a photosystem
Store the photosynthetic pigments that absorb the light and excite electrons in the reaction centre
Describe the stucture of a photosystem
Antenna complex - Is photosynthetic pigments in clusters (Chlorophyll b, b carotene and xanthophyll)
reaction centre - two chlorophyll a molecules
How can the different pigments involved in photosynthesis be observed
Chromatography
Describe the process of chromatography
4 steps
A mixture of unknown pigments is applied to the origin
The chromatogram is placed into a solvent and left to run.
Pigments travel up the paper in order of their solubilities.
(Larger distance more soluble )
The Rf values are calculated
how to calculate the Rf value
and how is this useful in determaining the unkown pigments
distance of pigment from orgin / distance of solvent from origin
compare Rf value with known values
Define absorbsion spectra
A graph showing how much light is absorbed at different wavelengths
Define action spectra
A graph showing the rate of photosynthesis at different wavelemgths of light
Describe the relationship between absorption spectra and action spectra
When the graphs are superimposed it shows that the pigments responsible for absorbing light are used in photosynthesis
Name the two photosystems thier differences and state which one is first in the Z- sheme
PSI (P700)
PSII (P680)
They absorb light at different wavelengths PSI has an absorption peak at 700nm and PSII has an absorption peak at 680nm
PSII is first in the Z-scheme (non-cyclic photophosphorylation)
Describe the process of exciting electrons in the photosystem
Photons are absorbed in the antenna complex by photosynthetic pigments their energy is moved from pigment to pigment down the photosystem to the reaction centre where the energy is passed to one of the chlorophyll a molecules, exciting one of its electrons and raises it to a higher energy level. The high energy electron leaves the chlorophyll a molecule oxidising it and moved to an electron acceptor reducing it.
Define cyclic photophosphorylation
ATP can be produced by electrons that take a cylindrical pathway and are recycled back into the chlorophyll a in PSII
Define non-cyclic photophosphorylation
ATP can be produced by electrons that take a linear pathway from water, through PSII and PSI to NADP, which they reduce in the stroma
What are the two stages of photosynthesis
The light dependant stage (LDS)
The light independant stage (LIS)
Define photophosphorylation
A reaction bonding a phosphate ion to molecule of ADP to form ATP indirectly using energy from an high energy electron thast has been excited by a photon.
Describe the path of electrons in cyclic photophosphorylation
PSI absorbs photons, the energy excites electrons in chlorophyll a (reaction centre). These electrons are emitted and picked up by an electron acceptor, which passes them down a chain of electron carriers back to PSI. The energy released as electrons pass through the ETC phosphorylates ADP to ATP
Describe the path of electrons and protons in non cyclic photophosphorylation
A photon of light is absorbed by a pigment in the antennae complex of PSII. The energy is passed to the reaction centre where an electron from each of the chlorophyll a molecule is excited. These excited electrons reduce an electron acceptor leaving the oxidised chlorophyll a.
The photolysis of water results in the reduction of this chlorophyll by the electrons produced.
Electrons are passed along an series of electron carriers, powering one proton pump so protons move from the stroma into the thylakoid space. An electrochemical gradient is established and Chemiosmosis occurs resulting in the synthesis of ATP.
A photon of light hits PSI and the same process occurs as in section PSII. However, this time the electron acceptor passes the electron to NADP, protons from the photolysis of water also pass into the stroma and together they form reduced NADP
Define photolysis
The breakdown of water into electrons protons and oxygen
Describe the use of the photolysis of water
The electrons are used to reduce chlorophyll a in PSII
Protons and electrons are used to reduce NADP in stroma
Oxygen is waste product and is released via the stomata
Name three factors that maintain the electrochemical gradient between the thylakoid space and stroma
Proton pumps in the ETC pump protons from stroma to T space
Photolysis of water in the thylakoid space
Removal of protons in the stroma by the formation of reduced NADP
What is the independant stage also called
Calvin cycle
Describe the calvin cycle
5C Ribulose bisphospahte (RuBP) combines with carbon dioxide catalysed by the emzyme Ribisco to form a 6C compound
6C compound is unstable and breaksdown into two 3C Glycerate-3-phosphate (GP) molecules
Each GP is reduced to 3C Triose phosphate (TP) by reduced NADP and ATP
1C from TP contributes to the formation of the products of the calvin cycle
remaining TP is Phosphorylated by ATP to RuBP which is regernerated
What are the possible products of the calvin cycle
Glucose
Lipids
Amino Acids {with the addition of nitrogen obtained
from nitrates}
What is the function of ATP and reduced NADP in the calvin cycle
To reduce GP to TP
Define limiting factor
A factor that limits the rate of a physical process by being in short supply, any change in the amount of this factor will therefore effect the rate.
What 4 factors do plants need for photosynthesis
The reactants CO2 and water
light at a high enough intensity and suitible wavelengths
a suitible temperature
water
What is the role of inorganic nutrients such as N and Mg
and what happens if they are in short supply
Nitrogen is needed for the synthesis of proteins, nucleic acids and chlorophyll
a difficiency will result in reduced growth of all organs and chlorosis
magnesium is a component in chlorphyll
a difficiency will result in reduced growth and chlorosis
chlorosis = yellowing of leaves
What factor is usually the limiting factor in terrestrial plants and why
CO2 as it has a 0.04% concentration in the athmosphere and the photosunthesis of most terrestrial plants is most efficient at 0.1%
what happens if the limiting factor of light intensity is increased
Rate increases initially
until light is no longer a limiting factor so graph platues
further increase results in the bleaching of pigments so rate decreases
Define the light compensation point
The light intensity at which a plant has no net gas exchange as the volume of gasses used and produced in photosynthesis and respiration are equal
When limiting factors combine which one is the limiting factor
the one closest to its minimium value
Name three inorganic forms of nitrogen
Ammonium , NH4+.
Nitrate , NO3-.
Nitrite , NO2-.
nitrogen is largely taken up by roots as nitrates. Although Rhizobium in the root noodles delivers NH4+ to the plant.
