Chapter 8 Photosynthesis

8-1 Energy and Life

8-1 Energy and Life

Autotrophs• Make their own food

8-1 Energy and Life

Heterotrophs• Cannot make their own food

8-1 Energy and Life

Chemical Energy and ATP

• The principal chemical compounds that cells use to store and release energy is called ATP adenosine triphosphate

8-1 Energy and Life

Storing Energy• ATP stores energy in the third

phosphate

• ATP is like a fully charged battery

8-1 Energy and Life

Releasing Energy

A: Break bond between the second and 3rd phosphates

ADP

2

Q: How is the energy in ATP released?

8-1 Energy and Life

8-1 Energy and Life

Using Biomechanical Energy

• Active Transport

• Movement of organelles through cell

• Sythesis of proteins and nucleic acids

• Produce light– Blink of firefly caused by an enzyme

powered by ATP

8-1 Energy and Life

ATP Availability

• Most cells only have enough ATP for a few seconds of activity

• Why?– Not good at storing energy over the long term– Glucose stores 90X the chemical energy of ATP– Cells generate ATP from ADP as needed by

using the energy in foods like glucose

8-1 Energy and Life

8-2 Photosynthesis:an Overview

During Photosynthesis…

• Organisms (plants) absorb light energy from the sun and store it in organic compounds.

• Energy is crucial to all life, without it work could not be done.

8-2 Photosynthesis an Overview

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

8-2 Photosynthesis an Overview

An example of basic photosynthesis…

8-2 Photosynthesis an Overview

The Photosynthesis Equation

CO2 + H2O +C6H12O6 O2light

(Carbon Dioxide) (Water) (Sun) (Glucose) (Oxygen)

8-2 Photosynthesis an Overview

Because light is a form of energy…

• Anything that absorbs light also absorbs the energy from that light

• When chlorophyll absorbs light, much of the energy is transferred to electrons in the chlorophyll molecule, raising the energy level of these electrons

• These high-energy electrons make photosynthesis work

8-2 Photosynthesis an Overview

Photosynthesis8-2 Photosynthesis an Overview

Chloroplasts

• The site of Light Dependent Reactions

• These organelles are surrounded by a double membrane and contain an

inner membrane separate into disk like sacs called thylakoids

• Thylakoid are arranged into granum, or neat stacks

• Each thylakoid contains the green pigment chlorophyll

• The light absorbing pigments are organized into photosystems, which transfer energy during the light reactions

8-2 Photosynthesis an Overview

8-2 Photosynthesis an Overview

Pigments in chloroplasts

• Chloroplasts absorb all other color pigments, leaving green to be reflected resulting in a plant’s color.

• Chlorophyll a and b are

two are the 2 most

common types of chlorophyll

• Chlorophyll b absorbs colors or

light energy NOT absorbed by

chlorophyll a

Light Reflectedlight

Absorbedlight

Transmittedlight

Chloroplast

8-2 Photosynthesis an Overview

Absorption of Light byChlorophyll a and Chlorophyll bAbsorption of Light byChlorophyll a and Chlorophyll b

V B G YO R

Chlorophyll b

Chlorophyll a

8-2 Photosynthesis an Overview

8-3 The Reactions of Photosynthesis

8-3 Reactions of Photosynthesis

Thylakoids• Sac-like photosynthetic

membranes arranged in stacks

8-3 Reactions of Photosynthesis

Grana• Stacks of thylakoids

8-3 Reactions of Photosynthesis

Stroma• The region outside the thylakoid

8-3 Reactions of Photosynthesis

Scientists describe the reactions of photosynthesis in two parts

1. Light – dependent reactions (in the thylakoid membranes)

2. Light – independent reactions (takes place in stroma)

8-3 Reactions of Photosynthesis

8-3 Reactions of Photosynthesis

Photosynthesis Consists of 2 Stages

• Light dependent reactions

• Take place in the Thylakoid Membrane

• Depends on sunlight for activation energy

• Responsible for the absorbing of light in Photosynthesis

• Water is split, • giving off oxygen

• H2O  + O2 + ATP + NADPH2

• Non-light dependent (dark) reactions

• Takes place in the Stroma

• Includes the Calvin cycle

• Does not literally occur in the dark, but requires no light to occur

• Carbon dioxide is split, • Carbon to make sugars

•  ATP + NADPH2 + CO2  + C6H12O6

8-3 Reactions of Photosynthesis

8-3 Reactions of Photosynthesis

Carrier Molecule• Compound that can accept a pair

of high energy electrons and transfer them along with most of their energy to another molecule

• Ex.) NADP+

8-3 Reactions of Photosynthesis

8-3 Reactions of Photosynthesis

Q: What does this do?• NADP + H NADPH

A: this traps sunlight in chemical form

8-3 Reactions of Photosynthesis

Light Dependent Reactions

• Uses energy from light to produce

1. Oxygen gas

2. ATP

3. NADPH

8-3 Reactions of Photosynthesis

Watch The Light Reaction Video

8-3 Reactions of Photosynthesis

8-3 Reactions of Photosynthesis

Watch The Light Reaction Video

8-3 Reactions of Photosynthesis

The Calvin Cycle• The ATP and NADPH formed by the light-

dependent reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes.

• The Calvin cycle uses ATP and NADPH from light – dependent reactions to produce high energy sugars

8-3 Reactions of Photosynthesis

The Calvin Cycle• These reactions don’t require

light, therefore these reactions are called

• Light – independent reactions

8-3 Reactions of Photosynthesis

Watch The Calvin Cycle Video

8-3 Reactions of Photosynthesis

Watch The Calvin Cycle Video

8-3 Reactions of Photosynthesis

Factors Affecting Photosynthesis

• Not enough water

• Temperature

• Light intensity

8-3 Reactions of Photosynthesis

Review: Photosynthesis uses light energy to make food molecules

Chloroplast

Light

Stack ofthylakoids ADP

+ P

NADP

Stroma

Lightreactions

Calvincycle

Sugar used for

Cellular respiration Cellulose

Starch

Other organic compounds

8-3 Reactions of Photosynthesis

8-3 Reactions of Photosynthesis