Photosynthesis
Chapter 8
THE SUN: MAIN SOURCE OF
ENERGY FOR LIFE ON EARTH
Food Chain
THE FOOD WEB
THE BASICS OF PHOTOSYNTHESIS
 Almost all plants are photosynthetic autotrophs, as are
some bacteria and protists


Autotrophs generate their own food or organic matter
through photosynthesis
Sunlight energy is transformed to energy stored in the form of
chemical bonds
(c) Euglena
(b) Kelp
(a) Mosses, ferns, and
flowering plants
(d) Cyanobacteria
Heterotrophs
 Organisms that are not able to make their
own food and have to eat other organs to
obtain energy.
 Ex. Toad, fish
Autotrophs or heterotrophs?
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Humans
Blue-green algae
Paramecium
Euglena
Yeast
Pine tree
Moss
Mushroom
crocodile
Light Energy Harvested by Plants &
Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy → C6H12O6 + 6
O2
AN OVERVIEW OF PHOTOSYNTHESIS
 Photosynthesis is the process by which
autotrophic organisms use light energy to make
sugar and oxygen gas from carbon dioxide and
water
Carbon
dioxide
Water
Glucose
PHOTOSYNTHESIS
Oxygen
gas
What is photosynthesis in general
terms?
 The conversion of CO2 and water into
glucose.
 The glucose is used as an energy source
for plants.
 The “carbon skeletons” of glucose can
also be modified and made into other
molecules by the plant.
What is the formula for
photosynthesis?
 6 carbon dioxide + 6 water  glucose + 6 oxygen
gas
 Usually you see the words over and under the
arrow indicate necessary components that are
not changed or used up by the reaction.
WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen by the
human eye as different colors.
Gamma
rays
X-rays
UV
Infrared
Visible light
Wavelength (nm)
Microwaves
Radio
waves
WHY ARE PLANTS GREEN?
It's not that easy bein' green
Having to spend each day the color of the leaves
When I think it could be nicer being red or yellow or gold
Or something much more colorful like that…
Kermit the Frog
Electromagnetic Spectrum and Visible
Light
Gamma
rays
X-rays
UV
Infrared &
Microwaves
Visible light
Wavelength (nm)
Radio waves
The feathers of male cardinals
are loaded with carotenoid
pigments. These pigments
absorb some wavelengths of
light and reflect others.
Sunlight minus absorbed
wavelengths or colors
equals the apparent color
of an object.
Why are plants green?
Transmitted light
Where in a cell is photosynthesis
performed?
 chloroplasts in eukaryotes
 cytoplasm of prokaryotes
WHY ARE PLANTS GREEN?
Plant Cells
have Green
Chloroplast
s
photosynthetic
pigments (i.e.,
chlorophylls,
carotenoids).
THE COLOR OF LIGHT SEEN IS THE
COLOR NOT ABSORBED
 Chloroplasts
absorb light
energy and
convert it to
chemical energy
Light
Reflected
light
Transmitted
light
Chloroplast
Absorbed
light
Photosynthesis occurs in chloroplasts
 In most plants, photosynthesis occurs primarily in
the leaves, in the chloroplasts
 A chloroplast contains:


stroma, a fluid
grana, stacks of thylakoids
 The thylakoids contain chlorophyll

Chlorophyll is the green pigment that captures light
for photosynthesis
 The location and structure of chloroplasts
Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Grana
Stroma
Inner
membrane
Stroma
Thylakoid
Thylakoid
compartment
When is photosynthesis performed?
 Whenever the organism is exposed to
light.
How many stages are there in
photosynthesis? What are their names?
 Two Stages:



Light Dependent Reactions
Light Independent Reactions
AKA the Light and Dark Reactions
AN OVERVIEW OF PHOTOSYNTHESIS
 The light reactions
Light
Chloroplast
convert solar energy to
chemical energy

Produce ATP & NADPH
 The Calvin cycle makes
sugar from carbon dioxide


NADP
ADP
+P
ATP generated by the light
reactions provides the energy
for sugar synthesis
The NADPH produced by the
light reactions provides the
electrons for the reduction of
carbon dioxide to glucose
Light
reactions
Calvin
cycle
Plants produce O2 gas by splitting H2O
 The O2 liberated by photosynthesis is made from
the oxygen in water (H+ and e-)
Light Dependent Reactions
 Take in water and produce Oxygen and lots
of electrons in the form of NADPH and
energy in ATP
 Occurs in the Thylakoid membrane of the
chloroplast
Light Independent Reactions
 AKA Dark reactions or Calvin cycle
 Takes in Carbon Dioxide and ATP and
electrons in the Form of NADPH
 Makes Glucose
 Occurs in the stroma the fluid like portion of
the chloroplast.
Review: Photosynthesis uses light energy
to make food molecules
 A summary of
the chemical
processes of
photosynthesis
Chloroplast
Light
Photosystem II
Electron
transport
chains
Photosystem I
CALVIN
CYCLE
Stroma
Cellular
respiration
Cellulose
Starch
LIGHT REACTIONS
CALVIN CYCLE
Other
organic
compounds
How do the reactants of photosynthesis get
to the chloroplast?
 CO2 diffuses into leaf and chloroplast from
air.
 H2O is carried to the leaf by the xylem. H2O
enters plants through the roots. Water
enters chloroplast by osmosis.
 Light is absorbed by the photosystems
found in the chloroplasts in any GREEN
part of a plant.
How do the products of photosynthesis
leave the chloroplast or leaf and where do
they go?
 Glucose is moved out of the cell by facilitated
diffusion and is dissolved in the liquid carried in
the phloem. The sugar solution is carried to the
non-photosynthesizing parts of plants.
 O2 exits the leaves by diffusion through open
stomata. Some is used by the plant for cellular
respiration.
 Water in the form of water vapor can diffuse out
of leaf through open stomata. (evaporation
through stomata = transpiration)
Concept Map
includes
uses
to produce
occurs in
occur in
of
uses
to produce
Concept Map
Photosynthesis
includes
Light
independent
reactions
Light
dependent
reactions
uses
Light
Energy
Thylakoid
membranes
to produce
ATP
NADPH
occurs in
occur in
Stroma
of
O2
Chloroplasts
uses
ATP
NADPH
to produce
Glucose