photosynthesis sl Flashcards
Transformation of light energy to chemical energy when carbon compounds are produced in photosynthesis
- Plants are photoautotrophs – they use the energy of sunlight to make carbon compounds from water and carbon dioxide.
- Other non-photosynthetic or chemosynthetic organisms are referred to as heterotrophs – they have to obtain their food from other organism.
- This energy transformation supplies most of the chemical energy needed for life processes in ecosystems
Absorption of specific wavelengths of light by photosynthetic pigments
- Photosynthesis occurs within the visible range of the electromagnetic spectrum.
- This includes radiation of light from the sun (visible light between 400-700nm), which is composed of a range of wavelengths (colors) typically visible in a rainbow.
Absorption of specific wavelengths of light by photosynthetic pigments:
Review Electromagnetic spectrum
- Visible (white) light consists of a collection of component colors. When passing a strong beam of light through a glass prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet.
- The separation of visible light into its different colors is known as dispersion.
- Different frequencies of light waves will bend to varying degrees dependent on their wavelength upon passage through a prism, resulting in their dispersion.
Absorption of specific wavelengths of light by photosynthetic pigments
- Structural components of chlorophyll a and b
- Different types of pigments
- Pigments are chemical molecules that absorb visible light; they also reflect light including the colours we see. Red and blue light is absorbed most effectively, while green light is reflected.
- The main photosynthetic pigments of plants that absorb light is chlorophyll a and b.
- Porphyrin ring:
Light-absorbing
“head” of molecule w/ magnesium
atom at center - Chlorophyll a has a methyl group (CH3) attached to the third carbon, which is replaced by an aldehyde group (CHO) in chlorophyll b.
- Other accessory pigments found in plant leaves absorb different wavelengths of light to chlorophyll. Eventually, all the energy is passed on to chlorophyll. Examples of accessory pigments:
Carotenoids (orange)
Xantophylls (yellow)
Anthocyanins (red)
Absorption of specific wavelengths of light by photosynthetic pigments
- Include excitation of electrons within a pigment molecule, transformation of light energy to chemical energy and the reason that only some wavelengths are absorbed.
- Different kinds of pigments exist, and each absorbs only certain wavelengths (colors) of visible light.
NOTE: ONLY CHLOROPHYLL A CAN PASS ON ELECTRONS!!
Conversion of carbon dioxide to glucose in photosynthesis using hydrogen obtained by splitting water
- Students should be able to write a simple word equation for photosynthesis, with glucose as the product.
light
6CO2 + 6H2O → C6H12O6 + 6O2
Green plants use light energy to produce organic molecules such as glucose from the inorganic raw materials carbon dioxide, water, and minerals*, by a process called photosynthesis. The waste product is oxygen. Photosynthesis occurs in plant cells that contain organelles called chloroplasts where light energy is trapped by the green pigment chlorophyll and is converted into chemical energy.
Oxygen as a by-product of photosynthesis in plants, algae and cyanobacteria
- They should know that the oxygen produced by photosynthesis comes from the splitting of water.
- These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and water. They feed not only themselves, but the entire living world.
- Photolysis is the process of splitting of water. This reaction takes places in the chloroplasts and produces oxygen, electrons (e-) and protons (H+):
2H2O 🡪 4e- + 4H+ + O2
- The electrons are used to replace displaced electrons from the chlorophyll pigments, while the protons (H+) are needed for the production of organic compounds.
Stages of photosynthesis
Light dependent reaction
- Photons of light are absorbed by chlorophyll. Electrons in the pigments are excited and used to produce ATP. The displaced electrons are then replaced by splitting of water to produce oxygen, hydrogen ions (H+) and electrons (Photolysis).
Light independent reaction
- ATP from the light dependent reaction and CO2 are used to produce organic compounds (glucose)
- CO2 combines with hydrogen ions from NADPH to build sugars/organic molecules.
ATP provides energy for this process
Stages of photosynthesis: more on light-dependent reactions
- The absorption of light by chlorophyll pigments leads to the excitation of electrons
- The lost electrons from the chlorophyll are replaced by electrons from the splitting of water, which results in the production of O2, H+ and e-
- Photolysis = light splits a water molecule
- The splitting of water in photosynthesis releases oxygen
- Light energy absorbed by chlorophyll, and so e- help to form ATP/H+ from H2O help to form NADP+ (reduced NADP)
Similarities and differences of absorption and action spectra
- see HW booklet and slides!
- Students should be familiar with absorption spectra. Include both wavelengths and colours of light in the horizontal axis of absorption spectra.
- An absorption spectrum is produced by shining different wavelengths of light (produced by diffraction of white light through a glass prism) through a solution of chlorophyll. The amount of light transmitted through the chlorophyll sample can be detected and measured.
- Galvanometer measuring changes in electrical current
Techniques for varying concentrations of carbon dioxide, light intensity or temperature experimentally to investigate the effects of limiting factors on the rate of photosynthesis
- Students should be able to determine rates of photosynthesis from data for oxygen production and carbon dioxide consumption for varying wavelengths.
- They should also be able to plot this data to make an action spectrum.
- see graphs on HW worksheet!
Carbon dioxide enrichment experiments as a means of predicting future rates of photosynthesis and plant growth
- Include enclosed greenhouse experiments and free-air carbon dioxide enrichment experiments (FACE).
- In greenhouse experiments (e.g. where tomatoes are grown) CO2 levels are increased to above normal atmospheric levels using CO2 generators on sunny days to increase rates of photosynthesis and crop growth.
Separation and identification of photosynthetic pigments by chromatography
- Students should be able to calculate Rf values from the results of chromatographic separation of photosynthetic pigments and identify them by colour and by values. Thin-layer chromatography or paper chromatography can be used.
