C1.3: Photosynthesis Flashcards
Outline how light energy is converted to chemical energy in carbon compounds.
Chlorophyll captures light energy from the sun to create chemical energy in the form of ATP
- This can be used to synthesise organic compounds like carbs, proteins, lipids, nucleic acids
Draw a flowchart to illustrate the energy conversions performed by living organisms.
Light energy to chemical energy in photosynthesis.
Chemical energy to kinetic energy in muscle contraction.
Chemical energy into electrical energy in nerve cells.
Chemical energy into heat energy in heat-generating adipose tissue.
List three reasons why living organisms need energy for cell activities.
- Synthesising macromolecules like DNA
- Pumping molecules or ions via active transport
- Movement of things within the cell such as vesicles
What is the principal energy source in most ecosystems.
Sunlight
State the chemical equation for photosynthesis.
6CO2 + 6H2O –> C6H12O6 + 6O2
Outline the source of the atoms used to form glucose (C6H12O6) during photosynthesis.
A source of H is needed
- To access the H, it needs to be removed from the water thus, photolysis occurs
Define photolysis.
- The splitting of water molecules using light energy during the light-dependent reactions of photosynthesis.
- Releases: O2, e- and Protons
State the equation for photolysis
2H2O –> 4H+ + O2 + 4e-
State the source of the oxygen produced as a by-product in photosynthesis.
Oxygen is generated as a by-product of the splitting of water, photolysis
Define Paper chromatography
- Paper chromatography is a technique that separates mixtures of substances based on the movement of different substances on a piece of paper by capillary action
State which parts of paper chromatography are the stationary phase and mobile phase
- Stationary phase: the paper
- Mobile phase: the solvent used to develop the chromatogram
Outline the process of separating pigments using chromatography.
- Can be separated using paper chromatography
- Pigments are first extracted from leaves using a suitable solvent that dissolves most of the plant pigments
- A sample of the extract (fluid) is placed on chromatography paper and transferred to a container with the chromatography solvent
- Pigments move at diff rates on the stationary phase and separate according to size to form a chromatogram
Identify pigments that result from chromatography by color and calculated Rf value.
- Rf = Retention Factor
- Formula: Rf = sample distance / solvent distance
State the range of wavelengths that fall within the visible spectrum.
400nm to 750nm
Outline the function of pigments.
- Absorb the photons in the visible light spectrum and reflect the colour that we see
State the primary and accessory pigments found in chloroplasts.
- Primary pigments: Chlorophylls - Chlorophyll a and Chlorophyll b (reflect green light)
- Absorb wavelengths in the blue-violet and red regions
- Accessory pigments: Carotenoids - Xanthophyll and b carotene (reflect yellow and orange light respectively)
- Absorb wavelengths in the blue-violet regions
Explain why most plants look green.
- Chlorophyll a and b, the main pigments capturing the photons, reflect green light and absorb wavelengths in the blue-violet and red regions of the light spectrum
Define the EM Spectrum
- A range of frequencies and wavelengths of electromagnetic radiation emitted from the Sun
Sketch the chlorophyll pigment absorption spectrum, including both wavelengths and colors of light on the X-axis.
- X-axis: wavelength of light, Y-axis: Amount of light absorbed
Chlorophyll a:
- 2 peaks; one at 425 and one at 660
- remains somewhat constant in between
Chlorophyll b:
- 2 peaks; one exponential slope turning into a large one at 550 and one medium one at 625
- remains somewhat constant in between
- X-axis: wavelength of light, Y-axis: Amount of light absorbed
Carotenoid:
- one small trough after a straight line at 450 then a large narrow peak at 475
- goes back down to x-axis at 525
Why do carotenoids absorb both similar and different wavelengths of light to chlorophyll
This expands the range of wavelengths that can be absorbed form light for use in photosynthesis
Outline the comparison of Rf values (not numbers) for pigments involved in photosynthesis. What do the different Rf values of the pigments indicate?
- Carotenoids have the highest Rf values (closest to 1)
- Chlorophyll a has Rf values in betw. those of carotenoids and chlorophyll b
- Chlorophyll b has a much lower Rf value than Carotenoids
Smaller Rf values indicate the pigment is less soluble and/or larger
Compare and contrast the action spectrum and absorption spectrum.
Action spectrum:
- measures the overall rate of photosynthesis against the wavelength of light
- X-axis is wavelength of light (nm)
- Y-axis is the rate of photosynthesis
Absorption spectrum:
- measures the wavelengths of light absorbed by each pigment
- X-axis is wavelength of light (nm)
- Y-axis is amount of light absorbed
Both:
- highest rates are at the blue and red wavelengths while the lowest rates occur at the green
Explain the shape of the curve of the photosynthesis action spectrum.
- highest rates are at the blue and red wavelengths while the lowest rates occur at the green
- This matches the absorption spectra of the photosynthetic pigments closely as it’s their ability to absorb light energy that allows photosynthesis to occur
Outline a technique for calculating the rate of photosynthesis by measuring either oxygen production or carbon dioxide consumption.
- Use a water plant: Elodea
- Oxygen produced can be counted as bubbles or collected in a measuring cylinder/gas syringe
- Calculate the rate of photosynthesis: number of bubbles / 1 minute
- Control and change temperatures using a water bath, light intensity can be controlled and changed by moving a primary light source closer or further away from the plant, CO2 conc. can be controlled and changed by using sodium hydrogen carbonate which can be dissolved in the water containing the plant.
Outline a technique, other than using plants, to measure the rate of photosynthesis
- Use hydrogen carbonate indicator solution which will change colour as the conc. of CO2 changes
- If the plant doesn’t photosynthesise and only respires: CO2 conc. will increase and the indicator turns more yellow
- If the plant is photosynthesising, CO2 is absorbed and the indicator turns more purple
Define “limiting factor.”
A condition that, when in shortage, slows down rate of reaction. The main limiting factors of photosynthesis includes:
- light intensity
- conc. of CO2
- temperature
Explain how the following factors limit the rate of photosynthesis: temperature, light intensity, CO2 concentration.
Temperature:
- influences photosynthetic enzymes
Light intensity:
- required for chlorophyll photoactivation
CO2 conc:
- CO2 is a core substrate that is required
Identify manipulated (independent), responding (dependent) and controlled variables in experiments testing limiting factors on the rate of photosynthesis.
Independent / control:
- Control and change temperatures using a water bath,
- light intensity can be controlled and changed by moving a primary light source closer or farther away from the plant
- CO2 conc. can be controlled and changed by using sodium hydrogen carbonate which can be dissolved in the water containing the plant.
Dependent variable:
- Number of bubbles / 1 minute
Outline techniques for measuring the rate of photosynthesis while manipulating either temperature, light intensity, or CO2 concentration.
Manipulate temperature by:
- changing the temperature in the water bath
Manipulate light intensity by:
- moving a primary light source closer or further away from the plant
Manipulate CO2 conc. by:
- using sodium hydrogen carbonate which can be dissolved in the water containing the plant.
State the source of atmospheric carbon dioxide beyond the historical average of about 300 ppm.
Fossil Fuels
Explain the enclosed greenhouse experiments.
Enclosed Greenhouse experiments:
- CO2 can be carefully monitored or controlled
- Elevated CO2 levels can be created by burning fossil fuels
- If other conditions are controlled and there’s a controlled greenhouse without enriched CO2, the effect of CO2 can be measured by measuring the total biomass produced or the yield of fruits or vegetables grown.
- Limitations: There are natural factors and variables that are not able to be taken into account
Explain free-air carbon dioxide enrichment (FACE) experiments
Free-air CO2 Enrichment experiments:
- CO2 is released around a circular area
- Pipes surround the area and release CO2 continuously
- CO2 sensors within the area monitor CO2 levels ensuring elevated conc. are maintained
- This allows for a more natural way of measuring the impact of higher CO2 levels in the atmosphere
- Limitations: Very expensive experiment to carry out
Advantages and Disadvantages of Enclosed Greenhouse experiments
Adv:
- High level of control of environmental factors like light, temp, humidity, etc
- Reduced impact on the natural environments as they take place in a contained setting
Disadv:
- Limited ecological relevance as it may not accurately reflect real-world conditions
Advantages and Disadvantages of FACE experiments
Adv:
- Experiments occur in a natural setting allowing researchers to study the effects of specific factors
- Ability to study larger organisms like larger plants and trees
Disadv:
- Potential environmental impact due to introducing elevated levels of CO2 into the environment
List the questions that are addressed in carbon dioxide enrichment experiments.
How much food production there is going to be in the future:
- As future rates of photosynthesis and plant growth can be predicted using FACE experiments
Describe the arrangement of pigments into photosystems in membranes.
- Molecular arrays of chlorophyll and accessory pigments within photosystems (found in thylakoid membranes)
Outline the advantage of pigments being arranged in photosystems as opposed to being dispersed.
- Allows maximum absorption of light energy by the pigments
If the pigments were dispersed:
- Light energy would only be absorbed by individual pigments thus, there would not be enough energy to cause the emission of e-
- There would also be little conversion of that light energy into chemical energy due to the process being too inefficient
Describe the absorption of the different wavelengths of visible light by the 3 different pigments found in the chloroplast
- All 3 pigments are poor absorbers of green light
- Carotenoids are good absorbers in the blue-violet region in the spectrum
- Chlorophyll a is a good absorber in the blue-red including orange-red region in the spectrum
- Chlorophyll b is a good absorber in the blue-red region in the spectrum
State the function of the reaction center pigment in a photosystem.
- Reaction centres are protein complexes within photosystems where light energy is converted into chemical energy containing specialised chlorophyll molecules that can donate electrons directly into the ETC
State what photoactivation is
- Photoactivation refers to the process where light energy activates pigments, leading to a photochemical reaction and the release of excited electrons.
Compare the peak absorbance of the reaction center chlorophyll molecules of photosystem I and photosystem II.
Photosystem I:
- It is the most sensitive to light wavelengths of 700nm
Photosystem II:
- It is the most sensitive to light wavelengths of 680nm thus, it is the first one that is activated by light
Outline advantages of pigment molecules being arranged within a photosystem.
- Only through the use of arrays of many pigment molecules can enough light be absorbed to photo activate the central chlorophyll molecule. Thus, hundreds of pigment molecules allows for a wider range of wavelengths to be absorbed
- This causes the excitation and the release of e- that will provide energy for the rest of the light-dependent phase of photosynthesis.