Molecular Biology: 2.9 Photosynthesis Flashcards
Define photosynthesis
Photosynthesis is the process by which cells synthesise organic compounds (e.g. glucose) from inorganic molecules (CO2 and H2O) in the presence of sunlight
What are some substances or conditions that photosynthesis needs
This process requires a photosynthetic pigment (chlorophyll) and can only occur in certain organisms (plants, certain bacteria)
Photosynthesis (anabolic synthesis of organic compounds) requires ATP which is derived from light energy
This chemical energy can either be used directly by the organism or used to synthesise organic compounds (e.g. glucose)
Which color wavelength of the visible spectrum chlorophyll absorbs for ATP synthesis and which color wavelength it reflects
Chlorophyll absorbs light most strongly in the blue portion of the visible spectrum, followed by the red portion (energy is being absorbed and may be used)
Chlorophyll reflects light most strongly in the green portion of the visible spectrum (hence the green colour of leaves) (energy is not being absorbed and that colour will be seen)
Define the role of pigments
Pigments absorb light as a source of energy for photosynthesis (chlorophyll)
Define absorption spectrum and action spectrum
The absorption spectrum indicates the wavelengths of light absorbed by each pigment (e.g. chlorophyll)
The action spectrum indicates the overall rate of photosynthesis at each wavelength of light
There is a strong correlation between the cumulative absorption spectra of all pigments and the action spectrum:
Both display two main peaks – a larger peak at the blue region (~450 nm) and a smaller peak at the red region (~670 nm)
Both display a trough in the green / yellow portion of the visible spectra (~550 nm)
Photosynthesis is a two step process:
The light dependent reactions convert light energy from the Sun into chemical energy (ATP)
The light independent reactions use the chemical energy to synthesise organic compounds (e.g. carbohydrates)
Outline step 1 oh photosynthesis
Step 1: Light Dependent Reactions
Light is absorbed by chlorophyll, which results in the production of ATP (chemical energy)
Light is also absorbed by water, which is split (photolysis) to produce oxygen and hydrogen
The hydrogen and ATP are used in the light independent reactions, the oxygen is released from stomata as a waste product
Outline step 2 of photosynthesis
Step 2: Light Independent Reactions
ATP and hydrogen (carried by NADPH) are transferred to the site of the light independent reactions
The hydrogen is combined with carbon dioxide to form complex organic compounds (e.g. carbohydrates, amino acids, etc.)
The ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together
How many pigments do photosynthetic organisms have and why
Photosynthetic organisms do not rely on a single pigment to absorb light, but instead benefit from the combined action of many
These pigments include chlorophylls, xanthophyll and carotenes
What is chromatography and outline the general process
Chromatography is an experimental technique by which mixtures can be separated
A mixture is dissolved in a fluid (called the mobile phase) and passed through a static material (called the stationary phase)
The different components of the mixture travel at different speeds, causing them to separate
A retardation factor can then be calculated (Rf value = distance component travels ÷ distance solvent travels)
What is the meaning of limiting factor
The law of limiting factors states that when a chemical process depends on more than one essential condition being favourable, the rate of reaction will be limited by the factor that is nearest its minimum value
Outline the effect of temperature on photosynthesis rate
Photosynthesis is controlled by enzymes, which are sensitive to temperature fluctuations
As temperature increases reaction rate will increase, as reactants have greater kinetic energy and more collisions result
Above a certain temperature the rate of photosynthesis will decrease as essential enzymes begin to denature
Outline the effect of light intensity on photosynthesis rate
Light is absorbed by chlorophyll, which convert the radiant energy into chemical energy (ATP)
As light intensity increases reaction rate will increase, as more chlorophyll are being photo-activated
At a certain light intensity photosynthetic rate will plateau, as all available chlorophyll are saturated with light
Different wavelengths of light will have different effects on the rate of photosynthesis (e.g. green light is reflected)
Outline the effect of carbon dioxide on photosynthesis rate
Carbon dioxide is involved in the fixation of carbon atoms to form organic molecules
As carbon dioxide concentration increases reaction rate will increase, as more organic molecules are being produced
At a certain concentration of CO2 photosynthetic rate will plateau, as the enzymes responsible for carbon fixation are saturated
