1 Your eyes see sunlight as white light, Light is a wave, like a - - PDF document

1 Photosynthesis

Visible light is a small band within a very broad electromagnetic spectrum. Chloroplasts capture sunlight energy for photosynthesis. .

How does a tiny seed grow into a massive tree?

Where did all of that mass come from?

In the 1600s, a Flemish scientist named Jan Van Helmont (1580–1644) conducted an experiment to find out.

• He grew a willow tree in a carefully

weighed amount of soil. H i d h h f h il b l

• He noticed that the mass of the soil barely

changed while the mass of the tree greatly increased.

• He concluded that the extra mass came

from water, not from the soil.

• Later experiments carried out by other

scientists showed that plants use carbon dioxide (from the air) and water to make a simple carbohydrate (glucose) and oxygen.

• So the tree’s mass comes from air and

t ! water!

• This chemical reaction (photosynthesis)

takes place only in the presence of light.

The Sun provides Earth with a steady source of light.

Visible light is part of a collection of waves known as the electromagnetic spectrum.

2

Light is a wave, like a ripple on a pond.

Waves can be described by their wavelength (the length from peak to peak), and their energy.

Your eyes see sunlight as white light, but it is really made up of different colors of light.

• A clear prism can split

white light into a white light into a rainbow of color

Light waves have very short wavelengths.

• They range from 800 nm (red light) to 400

nm (violet light). –One nanometer (nm) is equal to one- billionth of a meter! billionth of a meter!

• All of the colors of

visible light have different energies.

Color is how we experience the energy

• f light.
• Red light has the lowest energy and violet

light has the highest energy.

• As we move through the rainbow from red

to violet, the energy of the light increases.

How is a plant cell similar to solar cells found in calculators?

• A solar calculator has

solar cells that convert li h i light energy into electrical energy.

• The electrical energy

powers the calculator.

A plant cell has chloroplasts that work much like solar cells found in calculators.

• Chloroplasts also

convert energy in a process called process called photosynthesis.

• Plant cells then store

this energy from the sun in the form of molecules.

3

Photosynthesis is a chemical reaction that takes place in the chloroplasts of plant cells.

During photosynthesis, plants use the energy

• f sunlight to produce energy-rich molecules
• f sunlight to produce energy rich molecules

called carbohydrates (ex. glucose).

Photosynthesis In photosynthesis, plants take in carbon dioxide and water and release glucose and oxygen wastes. Why most plants are green? Chlorophyll is found inside the chloroplasts of plant cells.

• Chlorophyll is the main

pigment used in photosynthesis. –A pigment is a molecule that absorbs some colors of light and reflects others.

Plants need red and blue light to grow.

• Chlorophyll absorbs

mostly blue and red light, and reflects green light. light.

• This is why most plants

look green.

4

Why don’t plants absorb all colors of light?

• The reason is the same reason you wear

light-colored clothes when it’s hot outside.

• Like you, plants must reflect some light to

avoid absorbing too much energy and

• verheating.

Also, certain colors of visible light have just the right amount of energy to make photosynthesis occur.

Infrared light has too little energy to make photosynthesis

• ccur.

Ultraviolet light has more energy but would cause other chemical reactions.

Why do leaves change color?

In some parts of the world, the l f leaves of some plants, such as sugar maple trees, turn brilliant red or gold in the autumn.

Chlorophyll masks other plant pigments during the spring and summer.

• In the autumn

photosynthesis slows down down.

• Chlorophyll breaks

down; and red, orange, and yellow pigments in the leaves are revealed!