8.2 Photosynthesis

Pages222-227

• LEQ: How is energy, which ultimately comes from the sun, transformed into useable energy?

Introduction to Photosynthesis Video

http://www.youtube.com/watch?feature=fvwp&NR=1&v=zEgIO9Kq2_Y

•

Photosynthesis

• Photosynthesis is the process of turning light energy into chemical energy!

Chemical Equation

http://www.youtube.com/watch?v=mpPwmvtDjWw

PhotosynthesisPhotosynthesis occurs in TWO phases.1. Light-dependent reactions2. Light-independent reactions (Dark reactions)

Remember our “reactants”

1. Carbon Dioxide (CO2)2. Water (H20)3. Energy (sunlight)

Where does everything come from?

• The CO2 is in the Atmosphere and enters the plant through small openings on the back of leaves called Stomata.

The Stomata is where Gas exchange occurs. CO2 in O2 out

Where does everything come from?

• The Water (H20) comes from the soil absorbed by the plants roots.

Where does everything come from?

The Light Energy is captured by Chloroplasts.

Chloroplasts

• Chloroplasts capture light energy and are found mainly in the LEAVES.

!REVIEW!

What are the 3 reactants and how do they get into a plant?1. WATER----The roots2. Carbon Dioxide---The stomata3. Light---The chloroplast.

Is photosynthesis Catabolic or Anabolic??

What organelle does photosynthesis take place in?

Chloroplast

Inside the chloroplast.

• thylakoids – saclike photosynthetic membranes

• grana – stacks of thylakoids

• stroma – space outside the thylakoids

How plants obtain energy

Thylakoids have light-absorbing colored molecules called PIGMENTS

• Chlorophyll a & b = blue/green• Xanthophyll = yellow• Carotenoids = orange/red• Anthocyanin = red/purple

• The principle pigment in plants is chlorophyll that’s why plants appear green!!

• Ok now we have all the reactants….Lets make some SUGAR!!

This is where it starts to get confusing so listen up!!

The Two Phases of Photosynthesis• Phase I - Light Dependent Reaction

(occurs in thylakoids)– Light energy is absorbed and TRANSFORMED

to chemical energy

Rember Chemical energy is ATP!!

How plants transform energy

Thylakoid membranes are embedded with electron transporting molecules. These molecules are

involved in the light-dependent reactions.

Step 1: Photosystem II

1. Light excites electrons found in thylakoid (moving them to a higher energy level).

2. To replenish the deficit of electrons from this step, more electrons are extracted from water (roots)

Light-Dependent ReactionsOccur in the thylakoid

Photosystem IIInputs: Light + H2O Outputs: H+ + Oxygen

gas**Excited electrons (H+) move

to the Electron Transport Chain of proteins

Step 1

Step 2: Electron Transport Chain

1. Photoexcited electrons travel to photosystem I via a chain of proteins set in the thylakoid membrane.

2. This energy is harnessed as hydrogen ions (H+).

Light-Dependent ReactionsOccur in the thylakoid

Electron Transport ChainInputs: H+

Outputs: H+ and electrons **Now they are on their way to

Photosystem I

Step 2

Step 3: Photosystem I

1. Photo-excitation of electrons occurs again and this time energy is trapped in a molecule of NADPH when H+ combines with the electron acceptor NADP+ (think of it as an empty taxi)

2. ATP (the energy used in chemical reactions) is formed

Light-Dependent ReactionsOccur in the thylakoid

Photosystem IInputs: More light energy, H+,

NADP+ (like an empty taxi)

Outputs: NADPH and ATP**ATP & NADPH enter the Calvin

cycle

Step 3

How plants transform energy

At the same time…1. H+ from the H2O split accumulate inside the

thylakoid (ETC)2. H+ then move outside (chemiosmosis) where

they are used to make adenosine triphosphate (ATP), which is a form of chemical energy used to carry out cell processes.

Warm-up is on your desk!

Do questions #8 and #10

Video Clip Explaining Phase I of Photosynthesis – Light Dependent

Reactions • http://www.youtube.com/watch?v=Oi2_n2wb

B9o&feature=player_embedded

What you NEED to Know!

• At the end of Phase I, the plant has made 1.ATP (energy)2.NADPH (electron carrier)3.O2 (oxygen)

The Two Phases of Photosynthesis• Phase II - Dark Reaction (Calvin Cycle)

(occurs in stroma)– NADPH and ATP that were formed during light

dependent reactions are used to make glucose

How plants transform energy

Calvin Cycle converts carbon dioxide into sugar using the NADPH & ATP energy from the light-dependent reactions.

Light independent (Calvin Cycle)

1.ATP and NADPH contain a high amount of energy, but are short stores (no longer than a few minutes).

2.So plants use the ATP and NADPH to build high-energy compounds that can be stored.

The Calvin Cycle1.Does not require light.2.6 carbon dioxide molecules enter

the cycle from the atmosphere3.ATP & NADPH powers the

conversion to high-E forms

Reactants & products1.The Calvin Cycle uses 6 molecules of

CO2 to produce a single 6-Carbon sugar molecule called glucose.

2.Uses for sugars include: form starches & cellulose. When other organisms eat plants, they can also use the energy stored in carbohydrates.

And Now a boring person explaining it

Summary of Photosynthesis

Light Reactions• Inputs:

LightWater

• Outputs: ATP

NADPHOxygen (O2)

OCCURS IN THYLOKOID

Dark reactions (Calvin cycle)• Inputs:

◦ ATP◦ NADPH◦ CO2

• Outputs:◦ Sugars

OCCURS IN THE STROMA

Summary

• Phase I Phase II

Let’s review…

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What materials come into the chloroplast that are used in the

light-dependent reactions?

What material comes into the chloroplast that is used by the

Calvin Cycle?

What material moves out of the chloroplast from the light-

dependent reactions?

What materials move out of the chloroplast from the Calvin Cycle?

What materials move from the light-dependent reactions to the Calvin

Cycle?

What materials move from the Calvin Cycle back to the light-

dependent reactions?

Factors that can affect photosynthesis

1. Amount of water2. Temperatures3. Light Intensity4. Amount of CO2

Alternative Pathways• C4 Plants- When water is scarce these plants

keep there stomata closed. So instead of fixing carbon into 3-carbon compounds they do 4.

• CAM Plants-Only open there stomata at night

And Now……….

• THE PHOTOSYNTHESIS RAP!• http://www.youtube.com/watch?v=pE82qtKS

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A. chloroplasts

B. Golgi apparatus

C. mitochondria

D. vacuoles

Where in the plant cell does photosynthesis take place?

Cellular Energy

8.2 Formative Questions

Chapter 8

A. They accelerate photosynthesis.

B. They release more oxygen.

C. They help the plant conserve water.

D. They reduce the requirement for ATP.

How are the C4 pathway and the CAM

pathway an adaptive strategy for some plants?

Cellular Energy

8.2 Formative Questions

Chapter 8

STOP!

• Using the cards provided, at your lab table, assemble the equation for photosynthesis with your lab partner(s).

• On a piece of paper, each person should draw a diagram of a plant showing the typical inputs and outputs of the photosynthetic process with your lab partner (s).

• Write the equation for photosynthesis on the paper as well.

The Photosynthesis Song

• GET READY TO DANCE!!• http://www.youtube.com/watch?v=pE82qtKS

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