8-2: Photosynthesis
Photosynthesis*
 Plants use sunlight energy to convert
water and carbon dioxide into
oxygen and high-energy
carbohydrates (sugars and starches)
Think-Pair-Share
What do you think would
happen to an ecosystem if the
number of autotrophs
significantly decreased?
Investigating Photosynthesis
 Jan van Helmont (1643): after
careful measurements of a plant’s
water intake and weight increase,
concluded that trees gain most of
their mass from water.
 Joseph Priestley (1771): Using a
bell jar, candle and plant, finds
that plants release a substance that
keeps the candle burning– oxygen.
 Jan Ingenhousz (1779): finds that
aquatic plants produce oxygen
bubbles in light but not in the
dark. Concluded that plants need
sunlight to produce oxygen.
TPS Post-It Notes
Based on what you know about
van Helmont, Priestley and
Ingenhousz’s investigations,
what are the possible reactants
and products of photosynthesis?
Investigation Conclusion*
 Experiments revealed that in the
presence of light, plants transform
carbon dioxide and water into
carbohydrates and release oxygen.
Sun
Light and Pigments
 In addition to water and carbon
dioxide, photosynthesis requires
light and chlorophyll, a molecule
found in chloroplasts.
Pigments
 Pigment: light-absorbing colored
molecules plants use to gather the
sun’s energy
Chlorophyll
 Chlorophyll is the main pigment
in plants
 Two main types: chlorophyll a and
chlorophyll b.
 When chlorophyll absorbs light,
the energy is transferred to
electrons, which raises energy
levels to make photosynthesis
work.
Summary
(5-10 sentences)
Answer the following questions in
paragraph form in complete
sentences:
1. What new concept(s) did you
learn today? Explain the concept.
2. Why do you think destroying
forests and cutting down trees could
be harmful for our ecosystem?
3. Why is photosynthesis important?