Photosynthesis

Photosynthesis

Background Info

• Primary energy source for all life is the Sun. • Sunlight energy is introduced into the biosphere by

photosynthesis through plants, algae and some types of bacteria.

Schematic of PhotosynthesisTakes place in the chloroplasts

Diagram of a Photosynthetic Plant

Important Photosynthetic PigmentsThere are three basic classes of pigments

1.Chlorophylls are greenish pigments which contain a porphyrin ring These pigments have photosynthetic activity

Image: http://www.pensuk.krubpom.com/Healty%20Doc/chlorophyll%5B1%5D.jpg

Pigments (continued): 2. Carotenoids are usually red, orange, or yellow pigments

•Accessory pigments that aid in photosynthesis and are visible during fall when chlorophyll pigments degrade.

•Lycopene (red)

•Carotene (orange)

•Xanthophyll (yellow)

Pigments (continued):3. Phycobilins are water-soluble

pigments and usually blues, purples, violets, and pinks. These are not involved in

photosynthesis.

Pigments (continued):4. Anthocyanins are water-soluble

flavonoid pigments and usually appear blue to purple to red depending on pH. These are not involved in

photosynthesis.

Pigments•Pigments absorb best at certain wavelengths.

•The leaf color you see is the color REFLECTED.

•All other wavelengths of visible light are absorbed.

If you are looking at a red leaf…

What color is being absorbed?

What color is being reflected?

Light Spectrum

Absorption Spectrum

Measuring Photosynthetic Rate of Spinach Leaf Disks

Cut leaf disks from spinach leaves.Leaf tissue has air spaces that allow the leaf disks to

float.Fill air spaces with solution that contains sodium

bicarbonate (NaHCO3) and the leaf disks will sink to the bottom of the solution.

The sodium bicarbonate supplies CO2 that is used by the leaf cells for photosynthesis.

During light-dependent reactions of photosynthesis, O2 is produced and fills the air spaces.

Leaf disks will float again when air spaces are filled with O2.

Measuring Photosynthetic Rate of Spinach Leaf Disks – Design Your ExperimentPerform an experiment and write a lab

report Question Hypothesis Dependent Variable Independent Variable Control Replication Procedure Prediction

Next WeekComplete Lab 6-Lab ReportRead lab manual pages for Lab 7Complete Lab 7-PreLab Read Lab 8b-Additional Information