Photosynthesis and
Cellular Respiration
Energy for Life
Complementary processes

Photosynthesis is an
important part of the
carbon cycle.

The processes of
photosynthesis and
cellular respiration are
complementary
processes, meaning they
work together to benefit
living organisms.
Plants and animals contribute…

Autotrophs, such as plants, produce glucose
using the carbon in carbon dioxide.

Both autotrophs and heterotrophs, such as
grasshoppers that eat plants, use those
carbohydrates in cellular respiration.

Respiration, in turn, produces carbon dioxide.
Photosynthesis equation
light
6 CO2 + 6 H2O

C6H12O6 + 6O2
Photosynthesis combines water, carbon dioxide
and sunlight to produce glucose and oxygen,
converting light energy into chemical energy.
Respiration equation
6O2 + C6H12O6

6CO2 + H2O + Energy
Respiration breaks down glucose and other food
molecules in the presence of oxygen.
Energy renewal

Energy captured from
sunlight by
photosynthetic
organisms is used and
released in the cellular
respiration of living
things.

The energy that living
things use, must
continually be renewed
through photosynthesis.
Where does photosynthesis occur?

In plants and other
photosynthetic
eukaryotes,
photosynthesis takes
place inside chloroplasts.

The chloroplasts contain
saclike membranes called
thylakoids.

Thylakoids are arranged
in stacks known as grana.
Photosystems

Proteins in the thylakoid
organize chlorophyll and
other pigments into
light-collecting units
called photosystems.
What are the reactions of
photosynthesis?

Scientists divide the reactions of photosystems
into two parts: Light-dependent reactions and
light-independent reactions or the Calvin cycle.

The light-dependent reactions take place
within the thylakoid membranes.

They use energy from light to produce ATP and
NADPH, which are energy carriers.
Light-dependent reactions

Photosystem II absorbs light and breaks water
molecules into energized electrons, hydrogen ions (H+)
and oxygen.

High-energy electrons move through the electron
transport chain from photosystem II to photosystem I.

As electrons pass from chlorophyll to NADP+, more
hydrogen ions are pumped across the membrane.

ATP synthase in the membrane allows H+ ions to pass
through it. The enzyme binds ADP and a phosphate
group to produce ATP.
Light-dependent reactions
Light-dependent reactions
Light-independent reactions

The light-independent reactions of the Calvin
Cycle take place in the stroma outside of the
thylakoid membranes.

The Calvin Cycle uses ATP and NADPH from
the light-dependent reactions to produce highenergy sugars.
Light-independent reactions
What is the visible spectrum of light
and why is it important?

The visible spectrum of light is the set of
varying wavelengths of light that are visible to
our eyes as different colors.

Sunlight is a mixture of different wavelengths of
light, even though it appears as “white light” to
your eyes.
The visible spectrum
Pigments absorb light

In addition to water and carbon
dioxide, photosynthesis requires
light and chlorophyll, a pigment
molecule within chloroplasts.

The two main types are chlorophyll
a and chlorophyll b.

Chlorophyll absorbs blue-violet and
red light very well. Green light is
reflected by plant leaves, which is
what gives them their green color.
Light absorption powers
photosynthesis

Chlorophyll absorbs blueviolet and red light very
well. Green light is reflected
by plant leaves, which is
what gives them their green
color.

The high-energy electrons
produced when chlorophyll
absorbs light make
photosynthesis work.
Photosynthesis Review
Photosynthesis Review
Photosynthesis Review
Cellular Respiration
Living things need energy…

Our bodies have a lot
of work to do every
day…
 Moving muscles,
 Building essential
molecules, and
 Transporting
substances across
cell membranes.
Where do we get energy?
Food provides the
energy living things
need to grow and
reproduce.
 Food is the source
of the material our
cells use to build
new molecules.

How much energy is present in
food?

Quite a lot!

One gram of the sugar
glucose (C6H12O6) when
burned in the presence
of oxygen, releases 3,811
calories of heat energy.

A calorie is the amount
of energy needed to raise
the temperature of 1
gram of water 1 degree
Celsius.
What is cellular respiration?

Cellular respiration is the process that
releases energy by breaking down glucose
and other food molecules in the presence
of oxygen.
6O2 + C6H12O6
oxygen + glucose
6CO2 + 6H2O + Energy
carbon dioxide + water + energy
Where does cellular respiration
take place?

The beginning pathway
of cellular respiration,
glycolysis, takes place in
the cell cytoplasm.

The two remaining
pathways—the Krebs
Cycle and electron
transport—take place
inside the mitochondria
of the cell.
Cellular Respiration Overview

Glycolysis: a glucose molecule
is split to produce two
molecules of pyruvic acid.

Krebs Cycle: pyruvic acid is
used to produce carbon
dioxide, NADH, ATP and
FADH2. Sometimes called the
citric acid cycle because citric
acid is first formed.

Electron Transport Chain:
uses high-energy electrons
from the Krebs Cycle to
convert ADP to ATP.
Glycolysis
Kreb Cycle
Kreb Cycle
ATP
NETS: 3NADH, 1ATP, 1FADH2, & 2CO2
What happens if oxygen
is not available?



Glycolysis is then
followed by a different
pathway.
The combined process of
this pathway and glycolysis
is called fermentation.
Fermentation releases
energy from food
molecules by producing
ATP in the absence of
oxygen.
Fermentation
Cellular Respiration Summary