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Interest Grabber
Section 8-2
Trapping Energy
Have you ever used a solar-powered
calculator? No matter where you go, as long
as you have a light source, the calculator
works. You never have to put batteries in it.
Interest Grabber continued
• 1. A solar-powered calculator uses solar cells that are
found in rows along the top of the calculator. Into what
kind of energy is the light energy converted so that the
calculator works?
• 2. Recall that plants use light energy from the sun to
make food. Into what kind of energy is the light energy
converted by plants?
• 3. Most plants, no matter what size or shape they are,
have some parts that are green. Which parts of a plant
are usually green?
• 4. What does the green color have to do with the plant’s
ability to convert light energy into the energy found in the
food it makes?
Chapter 8.2
Photosynthesis: An Overview
Photosynthesis
• Plants use energy of sunlight to
convert water and carbon
dioxide into high-energy
carbohydrates – sugars and
starches – and oxygen
– Oxygen is considered a waste
product of photosynthesis
Photosynthesis: Reactants and Products
Section 8-2
Light Energy
Chloroplast
CO2 + H2O
Sugars + O2
Jan van Helmont
• Experiment  find out if plants grew by taking
material out of the soil
• Determined mass of dry soil and seedling
• Watered seed regularly
– After 5 years – mass of tree changed, while mass of
soil remained unchanged
• Concluded that increase in mass was due to the water
– Accounts for “hydrate” in carbohydrate
– Carbon from carbon dioxide accounts for “carbo”
in carbohydrate
Van Helmont’s Experiment
Joseph Priestly
• Experimented with fire in a jar with a
sprig of mint
– Fire needed oxygen to keep burning
– Putting a jar over the flame put the fire out
– If mint was placed in jar, fire would keep
burning
• Concluded that plants gave off oxygen
Summary:
burning candle + bell jar → candle goes out + add a mint plant → candle can be relit
mouse + bell jar → dead mouse + add a mint plant → mouse lives
Questions:
1. Why did the candle burn out when placed under bell jar?
2. Why could the candle be relit after allowing it growth with a mint plant?
3. Why does a mouse die when it is placed under a bell jar?
4. Why was the mouse able to survive when placed in the jar with a mint plant?
Jan Ingenhousz
• Showed that the experiment done by Priestly
only occurred if the plant was in light
– Light is needed to produce oxygen
• Put all three scientists together:
– In the presence of light, plants transform carbon
dioxide and water into carbohydrates, and they
also release oxygen
Photosynthesis Equation
6CO2 + 6H2O
LIGHT
C6H12O6 + 6O2
Light
• Light is a form of energy that travels in
waves
– White light is a mixture of light of different
wavelengths
• When broken down, white light produces the
visible spectrum (400nm – 750 nm)
• ROY G. BIV
– Red, orange, yellow, green, blue, indigo, violet
– Red has a longer wavelength than violet
Pigments of Plants
• Pigments – light absorbing pigments
– Because light is energy – energy is absorbed by the
pigments
• Their electrons get excited to a higher energy level
• Chlorophyll – main light absorbing pigment of
plants
– Two types: chlorophyll a and chlorophyll b
– Absorbs light in the blue-violet and red regions;
reflects green light
Absorption of Light by
Chlorophyll a and Chlorophyll b
1. How does the color
spectrum at the bottom
relate to the graph?
2. In what region of the
spectrum does chlorophyll
a absorb light best?
Chlorophyll b
Chlorophyll a
3. In what region of the
spectrum does chlorophyll
b absorb light best?
V
B
G
Y O
R
4. In what region of the
spectrum do neither types
of chlorophyll absorb light
well at?
Pigments of Plants
• Carotenoids – red, orange, and yellow
pigments in plants
– Absorb light in the other regions of the
spectrum
• Leaves change color because the
chlorophyll molecules fade away and the
carotenoids are left over
Photosynthesis Video
• Photosynthesis