Photosynthesis
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What is photosynthesis?
A process in which cells synthesise organic compounds (e.g., glucose) from inorganic molecules (CO₂ and H₂O) using sunlight. It converts light energy → chemical energy.
What organisms can perform photosynthesis?
Plants, algae, and certain bacteria (e.g., cyanobacteria).
What pigment is essential for photosynthesis?
Chlorophyll (photosynthetic pigment).
How do photosynthetic organisms capture light energy?
Using pigments that absorb specific wavelengths, generating ATP.
What are the fates of organic compounds produced?
They become cellular structure OR are catabolised via cell respiration for energy.
What wavelengths constitute visible light?
400 nm – 700 nm.
List visible spectrum colours from longest to shortest wavelength.
Red, orange, yellow, green, blue, indigo, violet.
What determines which wavelengths a pigment absorbs?
The pigment’s electron energy levels; electrons absorb specific frequencies and become energised/delocalised.
What happens when pigment electrons become excited?
Their energy is harnessed to produce ATP via photophosphorylation.
What is an absorption spectrum?
A graph showing the wavelengths of light absorbed by pigments.
What is an action spectrum?
A graph of photosynthesis rate vs wavelength (via CO₂ uptake or O₂ production).
Peaks and troughs of both spectra?
Peaks: blue (~450 nm) and red (~670 nm). Trough: green/yellow (~550 nm).
Why do leaves appear green?
Green light is reflected more than other wavelengths.
Where do light dependent reactions occur?
In thylakoids (arranged into grana).
What are the three key outcomes of the light dependent reactions?
ATP production Photolysis of water producing H and O₂ NADP⁺ reduction to NADPH
What happens to O₂ produced by photolysis?
Released via stomata as a waste product.
What is the law of limiting factors?
The factor nearest its minimum value limits reaction rate.
How does temperature affect photosynthesis?
Low temp → low kinetic energy; high temp → enzyme denaturation; optimum reflects enzyme ideal (e.g., Rubisco).
How does pH affect photosynthesis?
Extreme pH denatures enzymes; optimum ~pH 7.
How can CO₂ concentration be manipulated experimentally?
Using sodium bicarbonate (dissociates to release CO₂).
How is light intensity manipulated experimentally?
Adjusting distance to a light source; measuring with a lux meter.
Methods to measure photosynthesis directly?
CO₂ uptake or O₂ production.
How to measure CO₂ uptake in water?
CO₂ absorption changes pH (more alkaline as CO₂ is used).
How to measure O₂ production?
Gas syringe method or leaf disc rise method.