PHOTOSYNTHESIS (SL) Flashcards
Why does photosynthesis do photolysis
To break down the water to get the electrons from the hydrogen molecules
- why they have oxygen as their “waste”/byproduct
Who were the first organisms to perform photosynthesis?
Prokaryotes
- the great oxygenation event
Define photon
unit/particle of loght
What are the wavelengths that green plants use? (active spectrum)
- red and blue
Relationship of photons and pigment molecules
- Photons absorbed by pigment molecules
- by a specific amount of energy, excitation (electron of pigment to higher energy level)
- for only specific wavelengths of light
Why is green light reflected in green plants?
Because chlorophyll isn’t excited by photon
- therefore, green light is reflected
Define absorption spectrum
which wavelengths of light are absorbed by the material and which ones pass through.
Differentiate action spectrum vs absorption spectrum
Why is carbon dioxide a means for predicting future rates of photosynthesis and plant growth?
Light Spectrum
The electromagnetic spectrum comprises the full range of all types of radiation energy (travels through space in particles or waves)
- The sun emits its peak power in the visible region of this spectrum (white light = 400nm – 700nm)
- Colours represent different wavelengths of visible light and range from red (longest) to violet (shortest)
- sThe colours of the visible spectrum (from longest to shortest) are red, orange, yellow, green, blue, indigo, violet
Pigment Molecules
- absorption of light is mediated by specific pigment molecules (e.g. chlorophyll)
- Each contains electrons at discrete and specific energy levels (according to the pigment’s atomic configuration)
- absorb light at specific frequencies (or wavelengths) and become energised and delocalised (ionised)
The energy from these excited electrons can be harnessed by the cell to make chemical energy (ATP – via photophosphorylation)
Action spectrum
overall rate of photosynthesis at each wavelength of light
Enclosed Greenhouse Experiments
Carbon dioxide levels can be artificially increased in indoor greenhouses by adding CO2 from compressed gas tanks or by adding fermentation buckets that continuously produce CO2
- Enclosed greenhouses act as a closed system, which allow for the control of a range of extraneous variables (such as temperature and light)
-** However the conditions do not reflect those that occur in the natural environment** and only plants that grow in small spaces can be measured
Basically controlled experiment not reflect irl
Free Air CO2 Enrichment (FACE)
Free air carbon dioxide enrichment experiments involve the placement of pipes which emit CO2 around an experimental area
- The concentration of carbon dioxide is monitored by sensors which then adjust the flow of CO2 from the pipes
- FACE experiments represent** open systems which incorporate natural conditions** like rainfall and temperature fluctuations
- FACE experiments can also measure the effects of CO2 enrichment on larger trees and consider the impact of competition between plant species
- The disadvantage of experimenting on open systems** is that certain conditions (such as sunlight) cannot be controlled**
Light Dependent Rxns
In plants, the light dependent reactions occur within the membranous discs called thylakoids (which are arranged into stacks called grana)
Light is absorbed by photosynthetic pigments (such as chlorophyll), resulting in the production of ATP (chemical energy)
Light is also absorbed by water, which is split (photolysis) to produce oxygen and hydrogen (carried by NADPH)
The hydrogen and ATP are used in the light independent reactions, the oxygen is released from stomata as a waste product
Light Independent Reactions
- in stroma
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 carbon is fixed by the enzyme Rubisco, with ATP providing the chemical energy required to join the molecules together
- This process is also commonly known as the Calvin cycle
Enzyme Factors
- Temperature affects the rate of photosynthesis by impacting the frequency of successful enzyme-substrate collisions
- pH affects rate of photosynthesis by changing the charge and solubility of the enzymes involved
Photosynthetic Inputs (effect of Co2)
- Carbon dioxide is the main source of carbon used to synthesise organic compounds in the light independent reactions
- Increasing concentrations of carbon dioxide will result in higher rates of photosynthesis until all enzymes (e.g. Rubisco) are saturated (resulting in a plateau)
- The concentration of carbon dioxide can be experimentally regulated by using tablets of sodium bicarbonate (baking soda)
- Sodium bicarbonate dissolves in water to form carbonic acid – which readily dissociates to form carbon dioxide
What are the questions asked in FACE?
