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CO 7

Chapter 7

Photosynthesis

Name a plant you have

seen recently.

Chapter 7 - Photosynthesis

What is a plant anyway?7.1

Photosynthetic Organisms

A. Photosynthesis transforms

solar energy

B. Organic molecules built by

photosynthesis provide both

the building blocks and energy

for cells.

Figure 7.1b

C. Plants use the raw materials:

carbon dioxide and water

D. Chloroplasts carry out

photosynthesis

Figure 7.1c

E. Chlorophylls and other

pigments involved in

absorption of solar energy

reside within thylakoid

membranes of chloroplasts

Figure 7.2

Quick Check - FIVE OR FEWER

1. Plant

2. Thylakoid

3. Photosynthesis

4. Organic Molecules

Two words that sound

alike but are not at all

similar:

Stroma

Stoma

7.2 Plants as Solar Energy Converters

A. Solar Radiation - Only 42% of solar radiation that hits the

earth’s atmosphere reaches surface; most is visible light.

B. Photosynthetic Pigments - Pigments found in chlorophyll absorb

various portions of visible light; absorption spectrum.

1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b.

2. Both chlorophylls absorb violet, blue, and red wavelengths best.

3. Most green is reflected back; this is why leaves appear green.

4. Carotenoids are

yellow-orange

pigments which

absorb light in violet,

blue, and green

regions.

5. When chlorophyll

breaks down in fall,

the yellow-orange

pigments in leaves

show through.

Fall Foliage Slideshow

C. Absorption and action spectrum - A

spectrophotometer measures the amount of light that

passes through a sample of pigments.

1) As different wavelengths are passed through, some

are absorbed.

2) Graph of percent of light absorbed at each

wavelength is absorption spectrum .

3) Photosynthesis produces

oxygen; production of oxygen is

used to measure the rate of

photosynthesis.

4) Oxygen production and,

therefore, photosynthetic activity is

measured for plants under each

specific wavelength; plotted on a

graph, this produces an action

spectrum.

5) Since the action spectrum

resembles absorption spectrum,

this indicates that chlorophylls

contribute to photosynthesis.

Checkpoint

1. What is the relationship between the absorption spectrum and the

action spectrum?

2. How can we measure the rate of photosynthesis?

3. How is the wavelength of light related to the rate of

photosynthesis?

4. A radish plant is grown

behind using lights of

different colors. Explain the

chart.

D. Photosynthetic Reaction

1. In 1930 C. B. van Niel showed that O2 given off by

photosynthesis comes from water and not from CO2.

2. The net equation reads:

E. Two Sets of Reactions in Photosynthesis

1. Light reactions cannot take place unless light is present.

They are the energy-capturing reactions.

b. Chlorophyll within thylakoid membranes absorbs solar energy

and energizes electrons.

c. Energized electrons move down the electron transport

system; energy is captured and used for ATP production.

d. Energized electrons are also taken up by NADP+, becoming

NADPH.

2. Calvin Cycle

Reactions

a. These reactions take

place in the stroma; can

occur in either the light

or the dark.

b. These are synthesis

reactions that use

NADPH and ATP to

reduce CO2.

-- and make a

carbohydrate, sugar

What you should know by now..

1. The equation for photosynthesis. Write it!

2. The structure of a chloroplast. Sketch it!

3. The two reactions of photosynthesis.

**Things are about to get much more difficult**

7.3 The Light Reactions

1. Two paths operate within the thylakoid membrane

noncyclic and cyclic

*straight line *in a circle

2. Both paths use ATP, but the noncyclic also produces NADPH

3. PHOTOPHOSPHORYLATION = ATP production

also called CHEMIOSMOSIS

1. Light hits photosystem II and excites an electron, H20

2. The primary electron acceptor passes the electron down the ETC and

generates ATP

3. Light is required for PSI, but not water, it generates NADPH

Something trivial....

Photosystem I and Photosystem II are

named based on when they were discovered,

PSI was established first.

Figure 7.5

Indicate which system (PS1 or PS2 or BOTH)

____1. Splits water

____2. Produces NADPH

____3. Has an electron transport chain

____4. Requires light

____5. Utilizes a primary electron acceptor

____6. Occurs in the thylakoid

____7. Requires the input of H20

____8. The cyclic path

____9. Uses chlorophyll

____10. Releases oxygen

Are you still confused? This is pretty

hard to visualize, but through the magic

of technology, we can watch these

processes as animations

McGraw Hill Animation

Forest Biology - The Light Reactions

7.3 Light Reactions

A. Two Pathways

B. Noncyclic

C. Cyclic

D. ATP Production --> CHEMIOSMOSIS

When H20 is split, two H+ remain

These H+ are pumped from the stroma into the thylakoid

This creates a gradient used to produce ATP from ADP

ATP is the whole point of Photosystem II and will be

used to power the Light Independent Reactions (Calvin

Cycle)

Figure 7.7

Chemiosmosis is difficult to visualize.

So... you get to color it! Yay! colori

ng!

The Calvin Cycle

Also called

*The Light Independent Reactions

*The Dark Reactions

*Named after Melvin Calvin, who

used a radioactive isotope of

carbon to trace the reactions.

The Calvin Cycle

is a series of reactions producing carbohydrates.

carbon dioxide fixation, carbon dioxide reduction,

and regeneration of RuBP.

FIXATION

REDUCTION

REGENERATION

B. Fixation of Carbon Dioxide

1. CO2 fixation is the attachment of CO2 to an organic

compound called RuBP.

2. RuBP (ribulose bisphosphate) is a five-carbon molecule that

combines with carbon dioxide.

3. The enzyme RuBP carboxylase (rubisco) speeds this

reaction; this enzyme comprises 20–50% of the protein

content of chloroplasts

Calvin Cycle Animation Mainly this is a reshuffling of

carbons using ATP and NADPH

as energy

G3P can be

converted into

other things

Fortunately....

Summary Statements:

What is the purpose of the Calvin Cycle?

Where does the cell get its energy to perform these reactions?

What is the final product?

AP Biology no longer requires the

memorization of every step of the Calvin

Cycle, but you should understand the

beginning and the end and what it's

purpose is.

What Factors the Affect Photosynthesis?

1. Light Quality (color)

2. Light intensity

3. Light Period

4. Carbon Dioxide Availability

5. Water Availability

*Design an experiment to test ONE of the above factors*

Photosynthesis

Simulation

Waterweed

Simulator

In order for photosynthesis to occur, plants must open tiny

pores on their leaves called STOMATA.

Opening these pores can lead to loss of water.

Some Plant Taxonomy

Alternative Pathways

The Calvin Cycle is the MOST Common Pathway for Carbon

Fixation. Plant Species that fix Carbon EXCLUSIVELY through

the Calvin Cycle are known as C3 PLANTS.

Plants in hot dry environments have a problem with water loss,

so they keep their stomata partly closed... this results in

CO2 deficit (Used in Calvin Cycle), and the level of O2

RISES (as Light reactions Split Water Molecules).

Figure 7.10

C4 plants and CAM

plants use an

alternate pathway to

FIX carbon dioxide

from the air.

Figure 7.11

THE CAM PATHWAY - Plants that use the

CAM Pathway open their stomata at night and

close during the day.

At night, CAM Plants take in CO2 and fix into

organic compounds. During the day, CO2 is

released from these Compounds and enters

the Calvin Cycle. Because they have their

stomata open only at night, they grow slow.

Quick Practice

Quick Practice

thylakoid

O2

stroma

grana

Pg 129b

Light & H2O

O2

CO2

glucose

ATP

NADPH

ADP

NADP

A = photosystem II

B = photosystem I

C = H20

D = Electron Transport Chain

E = ATP Synthase

AB = ATP

AC = phospholipids

AD = light (energy)

Photosynthesis Activities

1. Elodea photosynthesis rate (lab)

2. Photosynthesis alphabet book

3. Chromatography of a spinach leaf

4. Viewing elodea cells chloroplasts

5. Fall colors observation