In this IB Biology Topic we should understand:
- The definition of
Photosynthesis
- The role of
Chlorophyll + relevant Photosynthetic Reactions
- Action + Absorption Spectrums
- Factors associated with Photosynthesis ie. Light, Temperature, CO2 Concentration
Photosynthesis
Definition: conversion of light energy into chemical energy
- Light energy from the sun is transferred to chemical energy (ATP) in the form of organic compounds for plants, algae and some bacteria.
- The chemical energy can be used for storage or to synthesise compounds such as glucose
- Photosynthesis= Reversal of Respiration
Light Spectrum and Chlorophyll
Definition of Chlorophyll: Green pigment found in photosynthetic organisms responsible for light absorption
The efficiency of photosynthesis is not the same for all wavelengths of light and depends on the absorption spectrum:
- Greatest absorption:
Violet-blue light AND Red Spectrum Range
- Least absorption in the
Yellow-green spectrum, as most of this light is reflected
- Explaining why many plants appear green.
Action and Absorption Spectrum
In this IB Biology Topic, we need to understand the Action Spectrum (the yellow line in the graph) and the Absorption Spectrum (red, blue + green line)
Absorption Spectrum: Graph showing the percentage of wavelengths of light that are absorbed by two common forms of chlorophyll.
- The efficiency of photosynthesis (action spectrum) isin general dependent on the % of absorption
Action Spectrum: Graph showing the percentage use of wavelengths of light in photosynthesis
Photosynthetic Reactions
In this IB Biology Topic, we need to understand the following reactions:
Light Dependent Reactions: The splitting of water molecules, which is a light dependent reaction, to produce oxygen and hydrogen ions is known photolysis. Light energy is also used to synthesize ATP molecules.
Ligh independent Reactions: Photosynthesis consists of light dependent reactions, to produce intermediate compounds (ATP + Hydrogen)
These are used in light independent reactions to produce complex organic compounds.
Limiting Factors
Carbon Dioxide: No photosynthesis at very low concentrations, positive correlation with rate of photosynthesis and at high concentrations rate reaches plateau as limited by another factor.
Light: at low to medium light levels, the rate is directly proportional to light intensity and plateaus at high intensities.
- High Kinetic Energy + more collisions of molecules
happens at certain intensity
Temperature: As temperature increases the rate increases more and more steeply.Above an optimum the rate falls steeply.
- High Kinetic Energy + more collisions of molecules
happens at certain intensity
And we're done with this topic! Well Done!
Drafted by Venetia (Biology)
References:
Kasis02, and Raju03. “Explain in Detail about Absorption Spectrum and Action Spectrum of Light.” Sarthaks EConnect | Largest Online Education Community, 4 Sept. 2020, www.sarthaks.com/892464/explain-in-detail-about-absorption-spectrum-and-action-spectrum-of-light.
“Photosynthesis.” Puns - Photosynthesis, memebase.cheezburger.com/puns/tag/photosynthesis.
“Topic 3 & 7 Continued.” Document in A Level and IB Biology, getrevising.co.uk/resources/topic_3_and_7_continued.