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.