PhotosynthesisChapter 8

Energy and Life

Section 8-1

Energy and Life• Energy is the ability to do work.• All living things use energy stored in

chemical compounds to survive. (FOOD)

• Heterotrophs – eat food to get energy

• Autotrophs – make their own food from sunlight and inorganic molecules to get energy.

• When are you not using energy?

Chemical Energy and ATP

• Energy from food is changed into another form cells can use.

• Adenosine Triphosphate (ATP) – energy molecule of the cell (made by what organelle?)

• Must break down the foods to generate the ATP.• Breaking the bonds between the phosphate

atoms will release the energy from ATP.• Used ATP is now ADP. (what is ADP?)

• Energy stored in foods (glucose) will change ADP back into ATP.

Adenine Ribose 3 Phosphate groups

Section 8-1

ATP

The ATP molecule!(Know this structure)

ADP ATP

Energy

EnergyAdenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)

Partiallychargedbattery

Fullychargedbattery

Section 8-1

Figure 8-3 Comparison of ADP and ATP to a BatteryATP being made from

ADP!

This energy that will be stored into the ATP molecule which comes from food!

Photosynthesis: An Overview

Section 8-2

Who Were the Scientists? Jan Van Helmont – 1643

1. What do plants take from the soil?

2. Trees gain mass from water not soil. Joseph Priestley – 1771

1. Something in the air kept candle burning.

2. Plants released oxygen. Jan Ingenhouz – 1779

1. Oxygen was only produced by plants in the presence of light.

Photosynthesis Equation

• 6CO2 + 6H2O ------- C6 H12O6 + 6O2

Carbon dioxide + water ------ sugar + oxygen

• Photosynthesis uses the sunlight to convert water and carbon dioxide into oxygen and high-energy sugars (glucose)!

• What will the plant do with the sugar it has made?

• Generate ATP for cellular processes!

Light

Light

Light and Pigments

• Photosynthesis uses pigments in the leaf to obtain sunlight.

• Pigments absorb and reflect light.• Chlorophyll is the green pigment in

chloroplasts. Why is it green?

• Two main types of chlorophyll:

Chlorophyll a and Chlorophyll bOther pigments (red, orange, yellow) are found in Plastids which will absorb energy and transfer to chlorophyll.

Absorption of Light byChlorophyll a and Chlorophyll b

V B G Y O R

Chlorophyll b

Chlorophyll a

Section 8-2

Figure 8-5 Chlorophyll Light Absorption

What wavelengths does chlorophyll work the best in?

What wavelengths does chlorophyll not work well in?

Which color light would a plant grow best under: Green, red, yellow?

Section 8-2

Photosynthesis: Reactants and Products

The Reactions of Photosynthesis

Section 8-3

The Chloroplast

Structure of Chloroplast:

1. Thylakoids – saclike photosynthetic membrane (they look like pancakes!)

a. Contains light absorbing pigments

b. Light Dependent reaction occurs here

2. Grana(um) – stacks of thylakoids

3. Stroma – space surrounding the thylakoids

a. Calvin cycle occurs here.

The Reactions

Two reactions run the photosynthesis process:

1. Light-Dependent reaction- sunlight required to run; it is a reactant

2. Calvin Cycle (aka Light-Independent reaction)

- no sunlight required to run- however, needs products of

light reaction to run.

Light Dependent Reaction

• Takes place in the thylakoids• Sunlight excites electrons in chlorophyll• Electron energy passed to carrier

molecule NADP+ to make NADPH.• H2O is broken down to use H+ ions to

convert ADP to ATP by ATP synthase protein.

• Oxygen atoms released as waste.

H2O

O2 Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + P

NADP+

Section 8-3

Figure 8-7 Photosynthesis: An Overview

Light Independent Reaction or Calvin Cycle

• Takes place in the stroma.

• CO2 combines a 5 carbon sugar to produce two 3-carbon molecules.

• Catalyzed by the enzyme RUBISCO.

• ATP and NADPH from light phase convert the 3-carbon molecules into glucose!

H2O

O2 Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + P

NADP+

Section 8-3

Figure 8-7 Photosynthesis: An Overview

How is the Rate of Photosynthesis Controlled?

• Availability of water – lack of water slows process down – plants in warm climates have waxy coating to reduce water loss

• Temperature – best rate occurs between 0 and 35 degrees Celsius

• Intensity of light – increasing light intensity increases rate