Photosynthesis

Autotroph vs. Heterotroph

• Autotroph- organism that makes its own food– We call autotrophs Producers– Plants, algae

• Heterotroph- an organism that cannot make its own food– Obtain energy by eating other organisms– We call heterotrophs Consumers– Animals, most bacteria, fungi

Almost all plants are photosynthetic autotrophs, as are some bacteria and protists Autotrophs generate their own organic matter through

photosynthesis Sunlight energy is transformed to energy stored in the form of

chemical bonds

(a) Mosses, ferns, andflowering plants

(b) Kelp

(c) Euglena (d) Cyanobacteria

THE BASICS OF PHOTOSYNTHESIS

Photosynthesis

• Photosynthesis occurs in all cells with chloroplasts (mainly plants)

• Step 1: photo-• Light energy is harvested

• Step 2: -synthesis• Sugar is made

• Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water

AN OVERVIEW OF PHOTOSYNTHESIS

Carbondioxide

Water Glucose Oxygengas

PHOTOSYNTHESIS

Glucose = sugar or carbohydrate

WHAT’S WITH LIGHT???

THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

Electromagnetic Spectrum and Visible LightGamma

rays X-rays UVInfrared &

Microwaves Radio waves

Visible light

Wavelength (nm)

Different wavelengths of visible light are seen by the human eye as different colors.

WHY ARE PLANTS GREEN?

Gammarays X-rays UV Infrared Micro-

wavesRadiowaves

Visible light

Wavelength (nm)

Why are plants green?

Reflected light

Transmitted light

Sunlight minus absorbed wavelengths or colors equals the apparent color of an object.

The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others.

Reflected light

• Chloroplasts absorb light energy and convert it to chemical energy

LightReflected

light

Absorbedlight

Transmittedlight

Chloroplast

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

Question:

Where does photosynthesis take place?

13

• In the chloroplasts!!

LEAF CROSS SECTION MESOPHYLL CELLLEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outermembrane

Innermembrane

ThylakoidcompartmentThylakoidStroma

Granum

StromaGrana

• Chloroplasts are comprised of:– outer membrane and inner membrane (together

form the chloroplast envelope)– stroma (a thick fluid)– thylakoids (called grana when in stacks)– The pigement chlorophyll is imbedded in the

thylakoid memebrane

Notice that the Thylakoid stacks are connected together

Where Photosynthesis happens

• Pigment molecules called chlorophyll are on the surface of the thylakoid membrane– Chlorophyll gives plants their green color

• Chlorophyll molecules absorb and capture light energy from the sun– The chlorophyll then uses the energy to combine H,

C, and O atoms into sugars and oxygen molecules– Nearly all of the Oxygen in our atmosphere has

been produced by plants

In Summary… Photosynthesis

• Chloroplasts convert light energy into chemical energy

6 CO2 + 6 H2O + light energy C 6H12O6 + 6 O2

CarbonDioxide + Water + Light Sugar + Oxygen

pigments in the chloroplast- not just chlorophyll

• Chlorophyll a: most common pigment in chloroplast (absorbs blue &red light and reflects green light thus giving the chloroplast a green color)(chloro = green phylla + leaf)

• Accessory pigments: additional pigments that absorb different wavelengths (carotene, chlorophyll b, & xanthophyll)

But it’s not that easy…Photosynthesis occurs in two different phases

The Light Phase• This phase occurs in the grana (thylakoid

stacks)• In this phase, light is captured by the

chlorophyll molecules– The chlorophyll molecules use the energy from the

light to make:• ATP (cellular energy molecule)• NADPH (another high energy molecule)

– Both of these molecules move on to the dark phase

“Waste” Products

• Water is split, and Oxygen created during the light phase– Oxygen is released, hydrogen molecules from the

water used in dark phase– Remember, this is the Oxygen that you breathe

The complicated view…

(not on test)

1. light

2. H2O 3. CO2

5. granum6. light reaction

11. Calvin

Cycle

7. NADP+

8.ADP+P_

9.ATP10.NADPH

13. O214. sugar

4. stroma

12. thylakoid

The simplified version (on test)

Light Reactions

The Calvin Cycle

• Also known as the Light Independent or Carbon fixation phase– This set of reaction does

not rely on light– Occurs in the stroma

(fluid inside of chloroplast)

• The calvin cycle uses the H from the H20 and the C from the CO2

• It also utilizes the ATP and the NADPH from the Light Reactions

• With these components, sugars are made in the stroma

1. light

2. H2O 3. CO2

5. granum6. light reaction

11. Calvin

Cycle

7. NADP+

8.ADP+P_

9.ATP10.NADPH

13. O214. sugar

4. stroma

12. thylakoid

Calvin Cycle

What is the Purpose?

• Sugar is produced during this phase– Sugar can be used to synthesize more complex

molecules like: • Starch• Fats/Lipids

– Sugar can be used to make ATP during cell Respiration

– It can be stored in the tissues of organisms

• Bring In– light– CO2

– H2O• Let Out

– O2

• Produce– sugars

So what does a plant need?

6CO2 6H2O C6H12O6 6O2lightenergy + ++

roots

shoot

leaves

Factors Affecting Rate of Photosynthesis

1. Temperature: increases rate up to a certain point2. Light Intensity: increases rate up to a certain point3. CO2 level: Increases rate up to a certain point4. Water: decrease water, decrease photosynthesis5. Minerals; Ex. Magnesium, Nitrogen

Photosynthesis Summary• Who?

– Green plants, algae, autotrophs• Materials:

– CO2 + Water+ Light• Energy Source:

– Light + Sunlight• Products:

– Food + Oxygen• Timing:

– When light is present• Location:

– chloroplast