8.2 Photosynthesis

Pages 222-227

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

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 the “reactants”…….

1. Carbon Dioxide (CO2)2. Water (H20)

Energy (sunlight) = Catalyst

Where do the reactants come from?

• CO2 (a gas) 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?

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

Where does everything come from?

Light energy comes from the sun and is captured by chloroplasts.

Chloroplasts

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

!REVIEW!What are the 2 reactants and how do they get into a plant?1. WATER----The roots2. Carbon Dioxide---The stomata

What is the catalyst required to start the photosynthetic reaction and where does it enter the plant?

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 the thylakoids)– Light energy is absorbed and TRANSFORMED to

chemical energy (ATP and NADPH molecules)

Rember Chemical energy is ATP!!

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)

• Phase II – Light Independent Reaction (or the 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 Reaction(The Dark Reaction)

(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 GLUCOSE which can be stored for a longer time.

The Calvin Cycle1. Does not require light.2. 6 carbon dioxide molecules are

required from the atmosphere3. ATP & NADPH powers the cycle

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…

Light-d

ep

end

ent

reactio

ns

Lig

ht-

ind

ep

end

ent

react

ions

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

SH4&safety_mode=true&persist_safety_mode=1&safe=active

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

SH4&safety_mode=true&persist_safety_mode=1&safe=active