An Overview of
Photosynthesis
The Big Picture
All organisms need energy to carry out essential
functions (growth, movement, maintenance,
repair, reproduction).
The ultimate source of energy is the sun.
Energy flows from the sun to autotrophs, then to
organisms that eat autotrophs (heterotrophs), and
then to organisms that feed on other organisms
(heterotrophs).
Autotrophs vs. Heterotrophs

Organisms are classified by how they obtain their energy
1.
Autotrophs- organisms that make their own
food / use solar energy to power the
production of food

2.
(plants, some kinds of protists and bacteria)
Heterotrophs- organisms that must get
energy from food instead of directly from
sunlight / get energy by eating other
organisms or organic wastes

(all animals, all fungi, most protists, many
bacteria)
The Six Kingdoms
Heterotrophic
Autotrophic
Eubacteria
X
X
(chemosynthesis or
photosynthesis)
Archeabacteria
X
X
(chemosynthesis)
Protista
X
(phagocytosis)
X
(photosynthesis)
Fungi
X
(secrete digestive
enzymes into the
environment)
X
(photosynthesis)
Plantae
Animalia
X
(phagocytosis)
Autotrophs: Chemosynthesis vs.
Photosynthesis

Photosynthesis- the conversion of light energy
from the sun into chemical energy in the form
of organic compounds.


6CO2 + 6H2O + (light energy)  C6H12O6 + 6O2
Chemosynthesis- the use of energy stored in
inorganic molecules (CO2) to produce
carbohydrates (organic molecules) / chemicals
are used as the energy source rather than
sunlight

6CO2 + 6H2O + (chemical energy-3H2S)  C6H12O6 + 3H2SO4
Which Organisms use Photosynthesis?
Which Organisms use Chemosynthesis?
 Photosynthesis – takes place on land and
in shallow waters where sunlight can reach
plants and seaweed

Chemosynthesis – takes place around
hydrothermal vents and methane seeps in the
deep sea where there is no sunlight. It is
performed by bacteria living on the sea floor
or within animals.
Overview of Photosynthesis

6CO2 + 6H2O + (light energy)  C6H12O6 + 6O2
(Reactants)
(Products)
 Autotrophs use photosynthesis to produce organic compounds
from carbon dioxide and water.
 The Two Stages of Photosynthesis:
 Light Reactions (Light Dependent Reactions)
 Calvin Cycle (Light Independent Reactions)
Stage 1: Light Reactions

Series of steps in which:



Light energy is absorbed from the sun and converted
into chemical energy (ATP and NADPH)
Water (H2O) is the first reactant used, and O2 is the first
byproduct produced.
Chemical energy is temporarily stored as ATP and
NADPH (energy carrier molecule)
Stage 2: Calvin Cycle

Series of steps in which:


Carbon Dioxide (CO2) is the second reactant used, along
with the chemical energy from the light reactions (stored
in ATP and NADPH)
Organic compounds (glucose – C6H12O6) are formed.
Structure and
Function of a Leaf
Structure and Function
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Upper Epidermis- structure, support, protection
Cuticle- waxy coating, helps prevent water loss
Palisades Layer- where majority of photosynthesis takes place
Chloroplast- site of photosynthesis
Phloem- transports sugars in any direction
Xylem- transports water upward only (roots  shoots)
Guard Cells- specialized cells that border a stoma and
regulate gas exchange
Stomata- gas exchange
Vein- transport tissue (vein= xylem + phloem)
Lower Epidermis- structure, support, protection
Spongy Layer- photosynthesis, air exchange
Mesophyll- air exchange and photosynthesis (3 +11)
Stomata – please sketch on your lab
Guard Cells
Stomata