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.

Section 8-2

Interest Grabber

• 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?

Interest Grabber continued

Chapter 8.2Photosynthesis: 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

Light Energy

Chloroplast

CO2 + H2O Sugars + O2

Section 8-2

Photosynthesis: Reactants and Products

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:Put all three scientists together:– In the presence of light, plants transform In the presence of light, plants transform

carbon dioxide and water into carbon dioxide and water into carbohydrates, and they also release carbohydrates, and they also release oxygenoxygen

Photosynthesis Equation

6CO6CO22 + 6H + 6H22O O LIGHTLIGHT C C66HH1212OO66 + 6O + 6O22

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. BIVROY G. BIV

– Red, orange, yellow, green, blue, indigo, violet– Red has a longer wavelength than violet

Pigments of Plants

• PigmentsPigments – light absorbing pigments– Because light is energy – energy is absorbed

by the pigments• Their electrons get excited to a higher energy level

• ChlorophyllChlorophyll – 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 byChlorophyll a and Chlorophyll b

V B G Y O R

Chlorophyll b

Chlorophyll a

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?

3. In what region of the spectrum does chlorophyll b absorb light best?

4. In what region of the spectrum do neither types of chlorophyll absorb light well at?

Pigments of Plants

• CarotenoidsCarotenoids – 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