Bio Mod 07

Chapter 2

Module 7

Photosynthesis

Module 7

Photosynthesis Objective

of Lesson:

To explain the Process & Purpose of

Photosynthesis

Overview of Photosynthesis Converts

solar energy to chemical energy Plants

& photosynthetic organisms make about 160 billion metric tons of organic material per year

Overview of Photosynthesis  Plants

- autotrophs (self-feeders)

 Organic

matter from inorganic

 Inorganic

: CO2, H2O & minerals

Photosynthetic Autotrophs

Photosynthetic Autotrophs

Photosynthetic Autotrophs

Cyanobacteria Bloom

Plants

Basics of Photosynthesis  Accepts

waste products of cellular respiration : CO2 & H2O - Rearranges atoms (need light energy) to glucose & O2

 Chlorophyll

absorbs sunlight (energy)

Basics of Photosynthesis Chloroplast

splits H2O to hydrogen & oxygen

Hydrogen

is transferred from H2O to CO2

H

is also moving along with electrons

Electrons

added to CO2

Basics of Photosynthesis Chloroplasts

transfer H with electrons to CO2 to form sugar

Oxygen

is formed & escapes through stomata as waste product

Chloroplasts Site

for photosynthesis

Present In

in green plants

mesophyll cells

CO2

enters, O2 exits through stomata

Water

needed in photosynthesis

Absorbed

by roots & travels to leaves

Chloroplasts Double Inner

membrane envelope

membrane filled with stroma

Stroma:

thick fluid

Disk-like

membranous sacs: thylakoids

Found

suspended in the stroma

Stacks

of thylakoids are called Granum

Granu m

Chloroplasts

Chloroplasts

Stomata

Stomata

Photosynthesis Road Map 

Not a single process



Involves two processes with many steps



2 main stages :



Light Reactions Calvin Cycle



Photosynthesis Road Map  Light

Reactions – convert solar energy to chemical energy  Changes H2O to O2  Produces

-

ATP & NADPH (e carrier)

drives e- from water to NADP+ forming NADPH

 Light

 Calvin

Cycle - sugar from CO2

Overall Equation

Nature of Sunlight  Type

of energy called electromagnetic energy

 Full

range of radiation is called the electromagnetic spectrum

 Visible

light composes only a small fraction of spectrum

 Chloroplast

absorb some of the visible light, converting it to chemical energy

Electromagnetic Spectrum

Chloroplast Pigments 

Different pigments absorb light of different wavelengths



These pigments are built into thylakoid membranes



Are part of light harvesting complexes called photosystems

Chloroplast Pigments There

are 3 types of pigments:

 Chlorophyll

a

 Chlorophyll

b

 Carotenoids

Chlorophyll a Participates

directly in Light

Reactions Absorbs

blue-violet & red light

Reflects

green light

Chlorophyll a

Chlorophyll b Absorbs

blue and orange light

Reflects

yellow green light

Does

not participate directly in reactions

Broadens Convey

range of light to be absorbed

the energy to chlorophyll a

Carotenoids  Absorbs

blue-green

light  Yellow-orange

in

color  Found  Pass

in carrots

energy to chlorophyll a

Carotenoid Pigments in Trees

Chloroplast Pigments

Photon  Light

behaves as discrete packets of energy

 Called A

photons

fixed quantity of energy

 When

a pigment molecule absorbs photon, electrons gain energy

Photosystem A

cluster of a few hundred pigment molecules

 Functions

as a light gathering antenna

 When

a photon strikes one pigment, energy jumps from pigment to pigment  Until

it arrives at the

Reaction Center

Photosystem  The

reaction center is next to the primary electron acceptor  The

primary electron acceptor traps the lightexcited e- from the reaction center

Photosystem

Photosystem

Light Reactions 

2 types of photosystems:



Water-splitting photosystem Use light energy to extract e- from H2O Releases O2 as waste product

• •

•

NADPH-producing photosystem Produce NADPH

•

Transfer e- from



+

Light reactions

Analogy

Light Reactions in Thylakoid Membrane

Calvin Cycle  Functions

like a sugar factory

 Input:  ATP

CO2, ATP & NADPH

& NADPH is from light reactions

 Produces

sugar : glyceraldehyde 3phosphate (G3P)

 G3P

is the raw material to make glucose or other organic molecules

Simplified Calvin Cycle

Overview of Photosynthesis

Water Saving Adaptations C3

plants C4 plants CAM plants  Certain

photosynthetic adaptations enables plants to continue producing food even in arid conditions

C3 Plants 

Plants that use CO2 directly from air e.g. soybeans, oats, wheat, rice



Problem faced : dry weather



Stomata will be closed to decrease water loss



A decrease in CO2 intake and photosynthesis

C4 Plants Special

adaptations to save water without shutting down photosynthesis e.g. corn, sugarcane, sorghum

 Even

when the stomata is closed it can still continue photosynthesis

C4 Plants It

has special enzymes

Enzyme The

enzyme has a high affinity for CO2

Takes 4-C

+ CO2 = 4-C compound

it from the air spaces of the leaf

donates CO2 to the Calvin cycle

CAM Plants “crassulacean

acid metabolism” e.g. succulent plants pineapple, cacti, aloe vera



CAM Plants Conserves

H2O

- opens stomata only at night Incorporates

Banks

CO2 into 4-C molecule

(stores) CO2 at night & releases it during the day to the Calvin cycle

Greenhouse Effect  CO2

used by plants to carry out photosynthesis

 Makes

up 0.03% of the air we breathe

 CO2

in the air helps to moderate world climate

 Retains

heat from the sun

 Warming

induced by CO2 is called the greenhouse effect

CO2 Concentration

Greenhouse Effect  Atmospheric  Warms

CO2 traps heat

the air or else the temperature of the Earth would be 10oC colder

Greenhouse Effect

Methane

Global Warming 

Presently, Earth may be overheating



Reasons:



Excessive combustion of Carbon-based fuels



Widespread clearing-up of forests (logging)



Rapid Industrialization

Global Warming

Global Warming Global

warming is the slow & steady rise in earth’s surface temperature Due

to increased concentrations of CO2

Global Warming

Is It Too Late?