Topic 2 and some Topic 8 Part 2: Molecular Biology /Photosynthesis Flashcards
3- Photosynthesis (Part 2)
C. Photosynthesis
24.Define Photosynthesis
define + extra (formula, type of reaction, each unit function)
- The production of carbon compounds in cells using light energy.
Extra:
* Opposite of cellular respiration which used glucose to create energy. Photosynthesis creates glucose. Thus they have opposite formulas.
* 6 CO2 + 6H2O (sunlight) —-> C6H12O6 + 6CO2
* Carbon: Carbon is ‘fixed’ from carbon dioxide and used to produce to glucose.
* Endothermic/endergonic reaction– absorb energy from their surroundings
* Water is split: the hydrogen is used to help in the production of glucose, but the oxygen is excreted as a waste gas.
* Sunlight: Light energy is transferred to chemical energy stored in the glucose molecule
* Glucose: Used in respiration, stored as starch, or used to build cell walls as cellulose
* Oxygen: excreted as a waste product
C. Photosynthesis
25.Outline how to separate photosynthetic pigments by chromatography.
1.With a pencil mark a line across the TLC plate 10mm from one end to form your baseline
2.Place the plate in a small beaker and mark the outside of the beaker
3. Remove the TLC plate and pour the chromatography solvent into the beaker to just below the mark then cover the beaker with a watch glass
4. Grind grass/leaves using a pestle and mortar until you get a green covering on the mortar
5. Add a couple of drops of propanone to the green coating while removing any large bits of debris—helps helps dissolves pigments, allowing them to travel up the paper strip
6. Use a capillary tube and transfer tiny amounts of plant pigments from the mortar to the pencil dot on the baseline of the TLC plate
7. Dry the spot using a hair dryer
8. Repeat the spotting and drying until a very dark green spot of about 2mm diameter is formed
9. Carefully place the TLC plate, baseline, and the ‘spot’ downwards, inside the beaker and replace the watch glass
10. Watch the solvent move up the strip causing the leaf pigments to separate
11. When the solvent has reached approximately 1 cm from the top of the plate remove the TLC strip
12. Immediately using a pencil mark the level reached by the solvent and the top of any pigments visible
13. A retardation factor can then be calculated (Rf value = distance component travels ÷ distance solvent travels)
C. Photosynthesis
26.Order the wavelengths of the visible electromagnetic spectrum by wavelength length.
Red-orange-yellow-green-blue-violet
* Longer wavelengths to shorter wavelength
* lower energy to higher energy
* Low frequency to high frequency
Extra details:
* Only a small part of the electromagnetic spectrum is visible to our eyes
* High-frequency radiation has a lot of radiation. UV, x-rays, and gamma rays are harmful to living organisms because they encourage cell and DNA damage (skin cancer and tumors)
* Low-frequency radiation is low in energy- too low to be used in most living organisms.
C.Photosynthesis
27.Outline the wavelengths of visible light that chlorophyll most effectively absorbs and reflects.
Chlorophyll is the main photosynthetic pigment
‘White’ light = all colors (wavelengths)
Blue and red wavelengths are absorbed
Green light is reflected
- The pigments in photosynthetic organisms (chlorophyll), absorb useful wavelengths of light- those that contain energy appropriate for photolysis in light-dependent reactions.
- This gives rise to the action and absorption spectra for photosynthesis.
C. Photosynthesis
28.Draw the absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
define here but learn how to draw seperately and together
Action Spectrum: this shows the rate of photosynthesis for all the wavelengths of light as a % of the max possible rate.
Absorption spectrum: this shows the absorbance of light by photosynthetic pigments for all the wavelengths of light.
C. Photosynthesis
29.Outline Photolysis
Defn: one use of energy consumed in photosynthesis (splitting of water molecules)
C. Photosynthesis
30.Outline how photosynthesis affects the Earth’s atmosphere, oceans, and rock deposition.
Increase in Oxygen levels due to photosynthesis, glaciation, and algae:
* Primordial earth had a reducing atmosphere (hydrogen, methane, water vapor, ammonia, hydrogen sulfide) that contained very low levels of oxygen gas.
* Cyanobacterial (prokaryotes) containing chlorophyll first perform photosynthesis about 2.4 bill years ago
* Photosynthesis creates oxygen gas as a by-product (by the photolysis of water)
* Oxygen level rose to 2% 2.2 billion years ago. His is known as the great oxidation event.
* At the same time the Earth experienced its glaciation, presumably due to a reduction in the greenhouse effect (reduced methane and carbon dioxide—potent greenhouse gases)
* Oxygen levels remained at 2% until about 750 million years ago (mya). From 750 mya until now there has been a significant rise to 20% thanks to the evolution of algae first and then land plants.
Formation of the Ozone layer and production:
* Oxygen generation also allowed the formation of an ozone layer (O3). Ozone shielded the Earth from damaging levels of UV radiation. This, in turn, leads to the evolution of a wider range of organisms.
Oxidized compounds in oceans:
* Oxygen in the atmosphere also lead to the production of oxidized compounds (e.g. Fe2O3, CO2) in the oceans.
* Iron compounds in the oceans were oxidized:
* The insoluble iron oxides precipitated onto the seabed.
* Time and further sedimentation has produced rocks with layers rich in iron ore called banded iron formations.
C. Photosynthesis
31.Outline how energy is required to produce carbohydrates and other carbon compounds from carbon dioxide.
- The carbon for carbon dioxide and the split of H+ ions from water (photolysis) in light-dependent reactions are used to create glucose/complex organic compounds (e.g. carbohydrates, amino acids, etc.) = endothermic reaction/endergonic
- Light energy (sunlight) is transferred to chemical energy stored in the glucose molecule= endothermic/endergonic reaction
- The ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together
Extra:
* The glucose produced can be used by cell respiration or stored as starch.
* Starch and cellulose are polysaccharide molecules found in plants. Starch is a chemical store of energy and cellulose builds up the plant cell wall.
* Condensation is the process by which monosaccharides are combined to make carbohydrates.
Glucose + glucose —-> (polysaccharide)n
Forms a glycosidic bond and water is a product
C. Photosynthesis
32.Outline how temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.
see graphs
- Light Intensity
* y-axis= rate of photosynthesis
* x-axis= light intensity: the amount of light, of a given wavelength, is available to the plant
* Light intensity is a limiting factor at low levels: When the light intensity is increased the rate of photosynthesis increases
* Another factor (e.g. temperature, CO2 concentration, enzymes or chloroplasts working at maximum efficiency) is limiting factor of photosynthesis at the plateau, as further increases in light intensity do not increase the rate of photosynthesis.
* At high levels of light intensity further increases have no effect on the rate of photosynthesis.
2.CO2 Concentration
* y-axis= rate of photosynthesis
* x-axis= CO2 concentration
* CO2 is a substrate for the metabolic pathway hence the relationship is just like how enzyme reactions are limited by substrate concentration= plateau graph
* CO2 concentration is a limiting factor at low levels: When the CO2 concentration is increased the rate of photosynthesis increases
* Another factor (e.g. temperature, light, enzymes working at maximum efficiency) is limiting factor of photosynthesis at the plateau, as further increases in CO2 concentration do not increase the rate of photosynthesis.
3.Temperature
* y-axis= rate of photosynthesis
* x-axis= temperature
* Photosynthesis is a metabolic pathway hence the relationship is similar to how enzyme reactions are affected by temperature.
* Increases in temperature give molecules more kinetic energy causing substrates to collide with active sites more frequently, this increases the rate of photosynthesis
* As the temperature approaches its optimum temperature the enzymes begin to denature (active site changes to become non-functional) causing the rate of photosynthesis to increase more slowly and eventually peak.
* After the optimum temperature, enzymes denature rapidly causing a fast decrease in the rate of photosynthesis.
* Therefore after and before the optimum temperature is reached, temperature could be limited to the rate of photosynthesis
C. Photosynthesis
33.Design an experiment to investigate limiting factors in photosynthesis.
rate= change/time
1.CO2 uptake
Measured by increasing the surrounding pH
* Placing the plant in a closed space with water
* CO2 reacts with the water producing bicarbonate and hydrogen ions= increase in solution acidity.
* Increased CO2 uptake -> increased pH (less acidic) -> increased rate of photosynthesis.
* This is an indirect way to measure the rate of photosynthesis.
2.Oxygen Production
Measured by displacing water in an inverted measuring cylinder or by simply counting bubbles.
* Placing terrestrial plants in closed environments via oxygen probes
* Oxygen production can also be measured by the leaf chad experiment. Click on the video link on slides to learn more.
3.Change in Biomass
* Measuring the change in a plant’s dry biomass is another indirect measure of photosynthesis as glucose production increases biomass.
* Starch levels in a plant can also be measured (glucose is stored as starch) as it stains purple with iodine solution. This can be quantified using a colorimeter.
Independent variable:
The limiting factor
Dependent variable:
* An accurate method for measuring the rate of photosynthesis needs to be used like oxygen production per time unit.
* Can also use leaf discus to measure oxygen generation by leaves
Control variables:
* Other key control variables should include any factor that affects a metabolic pathway controlled by enzymes, e.g. pH.
* Ambient light should be considered as it affects the wavelength and intensity of light absorbed by the organism.
* The values chosen for the control variables should be close to their optimum values so that the control variables do not limit photosynthesis.
C. Photosynthesis
34.Outline the steps of the light-dependent reactions of photosynthesis (photoactivation, photolysis, the electron transport chain/chemiosmosis) with respect to the key oxidation/reduction and photophosphorylation reactions that occur and where each step occurs.
Light-dependent reactions: Use light energy to produce ATP and to split water (photolysis), making H+ ions. Occurs in the thylakoid membrane
STEP 1: LIGHT-DEPENDENT REACTION
PHOTOSYSTEM 2
* Takes place on the thylakoid membrane
* Photoactivation: Light energy from the sun excites the chlorophyll and accessory pigment electrons in photosystem II by raising the electrons to a higher energy level (photo action) and now the electrons are excited.
* This energy from the pigments is then transferred until it reaches the special chlorophyll molecules at the reaction center where the excited electrons are donated to an electron carrier called plastoquinone.
* Plastoquinone collects two excited electrons causing the special chlorophyll molecules to be oxidized (losing electrons) and the plastoquinone to be reduced (adding electrons)
* Photolysis
-Since the chlorophyll molecules are now powerful oxidizing agents they are able to split the nearest water molecule (with the help of an enzyme) to replace the electrons it has lost.
-Oxygen is a waste product.
* The reduced plastoquinone transfers the energized electrons to the next chain of carriers, releasing energy to the stroma as the electrons are passed from carrier to carrier.
* The released energy is used to pump protons across the membrane from the stroma into the thylakoid space.
* The build-up of protons in the thylakoid space via the proton pumping action as well as the photolysis from earlier, creates the proton gradient.
* Chemiosmosis
-ATP synthase allows the protons to diffuse back across the membrane from the thylakoid to the stroma
-This diffusion of energy turns ADP to create ATP through photophosphorylation.
PHOTOSYSTEM 1
* Chlorophyll molecules in the PS I absorb light energy, undergo photo action again, and pass it to two special chlorophyll molecules in the reaction center, just like PS II.
* At the end of the chain of carriers, the electrons from PS II are passed to PS I via the electron carrier plastocyanin to replace the electrons lost from the photoactivation of special chlorophyll molecules in PS I
* These donated electrons are energized by photoactivation and then passed along a short chain of acceptors within the PS I and finally to ferredoxin, a protein in the stroma fluid;
* Ferredoxin passes the electrons to NADP+, reducing it to create NADPH.
*The supply of NADP+ sometimes runs out. When this happens the electrons are returned via ferredoxin to a cytochrome complex within the ETC between PSII and PSI and then flow to PS I again instead of being passed to NADP+. This causes more pumping of protons and ATP production. This process is called cyclic photophosphorylation.
C. Photosynthesis
35.Outline the steps of the independent reactions of photosynthesis (carbon fixation, G3P reduction, RUBP regeneration) with respect to the key carboxylation, oxidation/reduction, phosphorylation reactions that occur and where it occurs in the cell.
- Glucose phosphate (6C) is produced, which is either stored as starch, used for growth (as cellulose) or used in respiration. CO2, ATP, and NADPH are used
-The ATP and NADPH (reduced NADP) are produced by the light-dependent reactions. - Three parts to light-independent reactions AKA the Calvin cycle: 1. Carbon Fixation, 2. Reduction, 3. RuBP regeneration
1.Carbon Fixation
* RuBP (ribulose bisphosphate, 5C) is carboxylated with CO2 (that enters the stroma by diffusion)
* This reaction is catalyzed by the enzyme: rubisco
* 6C product that is immediately split into two glycerate 3-phosphate molecules (3C each)
2.Reduction
* Glycerate 3-phosphate molecules (organic acids) are converted into triose phosphate (carbohydrate) by a redox reaction
* G3Ps are phosphorylated by the dephosphorylation of 2ATP (from light dependent reaction, turns into 2ADP)
* The G3P is reduced and the 2NADPH from the light dependent reaction is oxidized into 2NADP+ (goes back to light dependent reactions)
* The product is 2, 3C sugars called triose phosphate (AKA TP)
3.RuBP Regeneration
*In order for the Calvin cycle to continue RuBP molecules must be regenerated to replace each one that was used.
* Since RuBP is a 5 carbon molecule and a triose phosphate is a 3 carbon molecule, for every three turns of the cycle, a series of chemical reactions occur, including the phosphorylation of TPs, and dephosphorylation of ATP (ATP to ADP) to convert 5 of the triose phosphate molecules (15 carbons) into 3 molecules of RuBP, while the remaining triose phosphate is stored to create half of a glucose molecule (3C).
* As such, the calvin cycle must run six times to have enough carbon to regenerate RuBP and produce a single glucose phosphate molecule (or fats, oils, proteins) (which is stored as starch by condensation)
* 1 cycle= 2TP= 6C
* 6 cycles= 12 TP= 36C
* 1 glucose + 6RuBP= 36C
START: (6 cycles)
6 RuBP
6 CO2
18 ATP
12 NADPH
END: (6 cycles)
1 glucose (or two TPs)
6 RuBPs (regenerates the starting value to enable another 6 cycles)
*The ATP and NADPH used in the light independent reactions were created in the light dependent reactions by the transfer of electrons energized by the red and blue light (photoactivation), through an electron transport chain resulting in ATP formation (chemiosmosis) and the reduction of NADP+ to NADPH.
C.Photosynthesis
36.Outline Calvin’s lollipop experiment and how it is an example of how achievements in science often depend on earlier breakthroughs.
- Calvin’s experiment used Chlorella algae which were placed in a thin glass vessel (called a lollipop vessel)
- The algae was given plenty of light, carbon dioxide, and hydrogen carbonate containing normal C-12 carbon.
- At the start of the experiment the carbon compounds were replaced with compounds containing radioactive carbon (14C).
- Samples of algae were taken at different time intervals.
- The carbon compounds were separated by chromatography and the compounds containing 14C were identified by autoradiography.
Samples were taken at different time intervals after exposure to 14C:
* After only 5 seconds there is more labeled glycerate 3-phosphate than any other compound.This indicates that glycerate 3-phosphate is the first product of carbon fixation
* After 30 seconds a range of different labeled compounds occur showing the intermediate and final products of the light-independent reactions
Calvin’s experiment and his subsequent discoveries were only possible due to improvements in technology. Key developments include:
* The discovery of 14C (in 1945 by Kamen and Ruben)
* The use of Autoradiography to produce patterns of radioactive decay emissions (autoradiograms)
* 2D chromatography
C.Photosynthesis
37.Label and annotate a diagram of a chloroplast to outline the structure-function relationship.
practice how to label–answer for annotations (4)
Palisade cells:
* Found close to the top surface of leaves
* Contain a high density of chloroplasts to enable efficient absorption of light.
Thylakoid membrane & granum (stacked discs):
* Thylakoids provide a large surface area for light absorption and light-dependent reactions.
* Chlorophyll (and other pigments) molecules are grouped together to form the photosystems which are embedded in the thylakoid membranes along with the electron carriers.
* A stack of thylakoids is called a granum
Thylakoid spaces (space surrounded by the membrane):
* The spaces collect H+ for chemiosmosis, and the low volume enables the H+ gradient to be generated rapidly.
* H+ flows back to the stroma, down the H+ gradient, through ATP synthase channels (embedded in thylakoid membrane) to produce ATP
Stroma:
* Contains rubisco for carboxylation of RuBP along with all the other enzymes required for the Calvin cycle.
