Photosynthetic Organisms

1. *Organic molecules are built by photosynthesis.
2. Plants use the raw materials: ___________________________________
3. ____________________________________carry out photosynthesis

*What is an organic molecule?

Structure of a Leaf

The structure of a chloroplast




Plants as Solar Energy Converters

Photosynthetic Pigments - Pigments found in chlorophyll absorb various portions of visible light; absorption spectrum.

1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b.
2. Both chlorophylls absorb violet, blue, and red wavelengths best.
3. Very little green light is absorbed; most is reflected back; this is why leaves appear green.
4. When chlorophyll breaks down in fall, the yellow-orange pigments (carotenoids) in leaves are visible.

Absorption Spectrum - A spectrophotometer measures the amount of light that passes through a sample of pigments.

What wavelength of light has the least amount of absorption?

What wavelength(s) of light have the most amount of absorption?

Action Spectrum - measures the rate of photosynthesis at different wavelengths of light; measured by the rate oxygen is produced

What wavelength(s) has the fastest rate of photosynthesis?

Which has the slowest?

The Action and Absorption Spectrum can be combined into one handy graph. In one sentence summarize what this graph says about wavelengths, color of light, absorption and photosynthesis.

absorption graph


1. What is the relationship between the absorption spectrum and the action spectrum?

2. How can we measure the rate of photosynthesis?

3. How is the wavelength of light related to the rate of photosynthesis?

4. A radish plant is grown using lights of different colors. Explain the chart.


Photosynthetic Reaction

6CO2 + 6H2O  → C6H12O6 + 6O2  

Ted Talks Video: What is the relationship between photoysnthesis respiration?

Two Sets of Reactions in Photosynthesis (Light Reaction & Calvin Cycle)

1. Light reactions are the energy-capturing reactions, requires energy from the sun

a. Occurs in the thylakoid, water is split
b. ATP and NADPH are produced to power the Calvin Cycle
c. Oxygen is released

2. Calvin Cycle Reactions (Light Independent Reactions)

a. These reactions take place in the stroma; can occur in either the light or the dark.
b. These are synthesis reactions that use NADPH and ATP (from the Light Reaction) to reduce CO2.
c. The end product is glucose which can be used by the plant

The Light Reactions occurs in two systems: Photosystem I and II - the creation of ATP is a complicated process

You will take a closer look at Photosystem I and Photosystem II in the Photosystem Coloring Worksheet


1. What is the purpose of the Calvin Cycle?

2. Where does the cell get its energy to perform these reactions?

3. What is the final product?

4. Why is carbon dioxide necessary?