photosynthesis Flashcards
photosynthesis definition and purpose
PS: is the process of converting light energy to chemical energy stored in glucose
Purpose: produce usable chemical energy in the form of glucose from light energy
photosynthesis equation
light
6CO2 + 6H2O → C6H12O6 + 6O2 + 6H20
chlorophyll
chloroplast in relation to PS and where it is found
the location of photosynthesis, cytosol of the cell
chloroplasts key components
DRAW DIAGRAM
Grana (stacks of thylakoid discs)
Stroma (fluid between the chloroplast/grana)
Outer/inner membrane
Inter membrane (space between membrane)
Ribosome
Chloroplast DNA
which is loaded and unloaded; ATP and ADP + Pi
function?
say in full sentences
loaded: ATP
unloaded: AD + Pi
function: transfers energy
which is loaded and unloaded; NADH and NAD+
function?
say in full sentences
loaded: NADH
unloaded: NAD+
function: transfer of electrons and hydrogen ions (protons)
which is loaded and unloaded;
NADPH and NADP+
function?
say in full sentences
loaded: NADPH
unloaded: NADP+
function: transfer of electrons and hydrogen ions (protons)
which is loaded and unloaded;
FADH2 and FAD
function?
say in full sentences
loaded: FADH2
unloaded: FAD
function: transfer of electrons and hydrogen ions (protons)
light dependent reaction; what and where?
what: plants are dependent on light to split water into oxygen and hydrogen.
where: thylakoid membrane of chloroplast
light dependent inputs
12 water molecules
12 NADP+
18 ADP + Pi
light dependent outputs
6 oxygen molecules
12 NADPH
18 ATP
light dependent stage process
DOUBLE CHECK AFTER MS DOIG ANSWERS
- Light energy hitting the chlorophyll molecules embedded in the grana causes water molecules to split into oxygen, electrons and hydrogen ions. (Water donates electrons to chlorophyll to replace the electrons that leave [as they’re excited because of light hitting] which causes water to split into oxygen and two H+. This process is known as photolysis.)
- Oxygen leaves the chloroplast (will either diffuse in stomata or be an input in aerobic cellular respiration)
- The hydrogen ions and electrons (from water molecules) are collected by NADP+ forming NADPH which moves on to the second stage in the stroma of the chloroplast.
- The movement of H+ (hydrogen ions and electrons) down its concentration gradient (maintained by energy from excited electrons in step 1) generates the high energy coenzyme ATP from ADP + Pi
- ATP and NADPH coenzymes then move on to the light-independent stage.
light independent reaction; what and where?
Glucose is produced from carbon dioxide, NADPH, and ATP through a cycle of reactions
Stroma of chloroplasts
light independent inputs
6 carbon dioxide molecules
12 NADPH
18 ATP
light independent outputs
Glucose
Water molecules
12 NADP+
18 ADP + Pi
light independent process
- CO2 molecules enter the Calvin cycle and undergo initial reactions. During this, carbon from CO₂ combines with a 5carbon molecule then splits into 2, 3carbon molecules.
- NADPH molecules (from light-dependent) donate their hydrogen ions and electrons (from split water,)(the NADPH molecules are not NADP+) and ATP molecules break into ADP + Pi to release energy to make further changes faster/easier to the carbon molecules.
- Carbon molecules continue to change and rearrange as they move around the cycle. Eventually, one specific three-carbon molecule is created and leaves the cycle, going on to to form glucose.
- Overall, six CO₂ molecules must enter the cycle to produce glucose (carbon dioxide = one carbon; glucose = six carbons).
Energy for this reaction to occur is supplied by ATP (from the first stage.) - Some of the oxygen molecules leftover from the breaking of CO₂ at the beginning of the cycle combine with hydrogen ions from NADPH to create the output water.
- (A number of other molecules in the cycle (including the key enzyme RuBisCO) assist in the reaction.)
chlorophyll
A green pigment located in the grana which absorbs and traps light energy.
chlorophyll relating to light?
Chlorophyll absorbs/reflects different wavelengths of light. It is therefore more or less efficient depending on the colour of light.
Absorbs blue/purple, and red most.
Absorbs green least
Most plants reflect green
factors affecting rate of photosynthesis
light, light colour, co2 conc, water, enzyme inhibition, temp, pH
light in relation to rate of photosynthesis. which type of plants are more/less affected?
AND DRAW DIAGRAM
Light is required for the light-dependent stage of photosynthesis to occur.
Without it, the reaction rate is limited.
As light increases, the photosynthesis rate increases – until a saturation point is reached
The increase in the rate of photosynthesis towards point X is because the plant is exposed to greater light energy, which can energise the chlorophyll within many more plant cells, thus increasing overall photosynthesis.
After X, the rate on the graph plateaus
photosynthesis is still occurring at a high rate after point x, just no longer increasing
affect all type plants the same
causes for plateau in rate of ps in light
- Reached the maximum possible rate of photosynthesis, assuming the other factors of photosynthesis are unlimited.
Maximum possible rate cannot increase as the enzymes within chloroplasts are operating at their full capacity. In this case, it is known as a light-saturation curve, as the plant is saturated with light, and point X is known as the saturation point
- One of the other inputs or requirements for photosynthesis is limiting the rate
light colour in relation to rate of photosynthesis
The wavelength (and therefore colour,) also impacts this process
the greatest rate of photosynthesis occurs when a plant is exposed to violet or red light
the rate of photosynthesis is relatively low under green light
CO2 conc. in relation to rate of photosynthesis. which type of plants are more/less affected?
DRAW DIAGRAM
Carbon dioxide is an input in PS
The initial increase is due to chloroplasts having a higher concentration of CO₂ molecules for the light-independent stage.
The rate of photosynthesis increases as CO₂ concentration increases, but only up until point X where it starts to plateau.
As carbon dioxide concentration increases, the rate of photosynthesis increases, up until a certain point.
Plants need CO₂ to photosynthesis.
If CO2 levels decreases, stomata opens, plants take in CO₂ from the atmosphere via open stomata on their leaves.
If stomata are closed or there are low CO₂ levels in the atmosphere, however, CO₂ may limit the rate of photosynthesis.
C4 and CAM are less affected by CO2 conc than C3
causes for plateau in rate of ps in CO2 conc.
- The theoretical maximum rate of photosynthesis can be reached with increasing CO₂, (assuming light and water are unlimited and temperature is optimal.) This is because the enzyme-catalysed systems within the chloroplast are fully saturated and operating as fast as possible.
- Limiting Factor
Low CO₂ levels make it more likely that O₂ is bound and photorespiration occurs, thus removing an opportunity for photosynthesis and decreasing the overall photosynthetic rate. As such, low CO₂ concentrations can be debilitating to plants
water in relation to rate of ps. which type of plants are more/less affected?
Water 💧
Water can also influence the rate of photosynthesis as it is an input in the light dependent stage of photosynthesis and influences the opening and closing of stomata
Less Water
1. Plants close their stomata to conserve water → this also limits the gaseous exchange of CO₂ and O₂with the environment
2. CO2 can no longer (enter the leaves through open stomata and) be an input of the light-independent stage
3. O2 produced in the light-dependent stage can no longer be released.
4. When stomata closed, O₂ is most likely more abundant than CO₂,
5. Rubisco is more likely to bindO₂and initiate the wasteful photorespiration pathway, rather than photosynthesis.
6. Plant wastes energy and loses an opportunity to photosynthesise, which decreases the overall rate of photosynthesis
C4 AND CAM NOT AFFECTED UNLESS EXTREME WATER CONDITIONS
temperature in relation to rate of ps
DRAW DIAGRAM
Photosynthesis is an enzyme controlled reaction (such as rubisco). Therefore factors which affect enzyme rate will also affect photosynthesis.
- rate of PS greatest at optimal temp
- higher than optimal temp = enzymes denature, lowering rate of PS
- lower than optimal temp = less frequent enzyme-substrate collisions within chloroplast, lower rate of PS
pH in relation to rate of PS
DRAW DIAGRAM
Similarly, enzymes function best at their optimal pH → greatest rate of photosynthesis
Above and below the optimal pH, enzymes denature.
enzyme inhibition in relation to rate of PS
DRAW DIAGARAM
Competitive inhibitors,
Bind to the active sites of enzymes to prevent the catalysis of substrates.
Reversible
Non-competitive inhibitors
Bind to an allosteric site of an enzyme
Causes a conformational change to the active site meaning the substrate can no longer bind
Irreversible
The effect of competitive reversible inhibitors can be gradually overcome if the substrate concentration is continually increased.
increasing substrate concentration does not reduce the effect of irreversible inhibitors or reversible noncompetitive inhibitors.
This means that the maximum possible rate of reaction is reduced in the presence of irreversible inhibitors or reversible non-competitive inhibitors.
CRISPR-Cas9 in PS
improve photosynthetic efficiencies and crop yields
why do we need to improve photosynthetic efficiencies and crop yields?
Most crops, such as wheat, rice, fruit and vegetables are C3 plants, leaving them susceptible to photorespiration (especially in drier/hotter conditions).
World population growing – increased food demands.
How can CRISPR-Cas9 help in improving photosynthesis efficiency and crop yields?
*CRISPR may be used to improve the efficiency of rubisco and reduce photorespiration by making C3 plants more like C4/CAM plants
*CRISPR-Cas9 to engineer crops that bypass photorespiration, somewhat mimicking the function of C4 and CAM plants.
*Editing crop genomes could enable farmers to maximise crop productivity without clearing any additional land.
*Increase plant resistance to infection
*Improve shelf life of fruits/vegetables
