Transcript Slide 1

Where does the energy for living
things come from?

Autotrophs – make their own food
 Plants and other organisms (like algae) can use light
energy from the sun to produce their own food

Heterotrophs – get energy from the foods they
consume
 Impalas eat grasses (which are autotrophs)
 Leopards eat other animals (get their energy indirectly
from autotrophs by feeding on animals that eat
autotrophs)
 Mushrooms and other fungi obtain food by
decomposing other organisms
Chemical Energy and ATP
Energy comes in many forms: light, heat, electrical,
chemical
 Adenosine triphosphate (ATP) is the primary
chemical compound cells use to store and release
energy.

 Consists of adenine, 5-carbon sugar (ribose), and three
phosphates
○ Phosphates are necessary for ATP to store and release
energy.

ATP enables active transport, synthesis of proteins
and nucleic acids, muscle contraction, etc.
ATP – Adenosine Triphosphate
Photosynthesis

Photosynthesis – plants use the
energy from the sun to convert
water and carbon dioxide into
high-energy carbohydrates
(sugars). Oxygen is the waste
product.
(light)
6CO2 + 6H2O  C6H12O6 + 6O2
(light)
carbon dioxide + water  glucose + oxygen
Investigating Photosynthesis

1643 – Jan van Helmont
 Do plants grow by taking material out of the soil?
○ Determined the mass of soil and willow seedling. Watered for
five years. Seedling gained 165lbs; soil unchanged.
○ Conclusion: Gain in mass from the water not the soil. This
accounts for the hydrogen in the glucose production.

1771 – Joseph Priestley
 What in the air makes a flame die out in a jar?
○ Determined when the substance from the air was used up, the
candle would burn out. If a sprig of mint was placed in the jar,
the candle could be relit after several days.
○ The mint produced a substance that was required for
combustion. That substance was oxygen.
Investigating Photosynthesis

1779 – Jan Ingenhousz
 Do aquatic plants produce oxygen in the dark?
○ Determined that aquatic plants would only produce
oxygen bubbles in the light.
○ Concluded that plants need sunlight to produce oxygen.
These experiments led to work by other scientists
who discovered that in the presence of light,
plants transform carbon dioxide and water into
carbohydrates and release oxygen.
 Photosynthesis explained (4:09)

Investigating Photosynthesis

1845 – Julius Robert Mayer
 Proposed that plants convert light energy into chemical
energy

1948 – Melvin Calvin
 Traced the chemical path that carbon follows to form
glucose; steps called the Calvin cycle; awarded Nobel
Prize in Chemistry in 1961

1992 – Rudolph Marcus
 Described the process by which electrons are
transferred from one molecule to another in the electron
transport chain; awarded Nobel Prize in Chemistry in
1992
How do plants capture sunlight?
Sunlight – a mixture of different wavelengths of light.
Different wavelengths are visible as different colors.
 Plants gather the sun’s energy with light absorbing
molecules called pigments.
 Chlorophyll is the main pigment in plants.

 Two types: chlorophyll a and chlorophyll b
 Light is a form of energy, so when pigments absorb light
they also absorb the energy from that light.
 Much of the energy is transferred directly to electrons in the
chlorophyll molecule, raising the energy levels of these
electrons. These energetic electrons power photosynthesis.
Chlorophyll


Absorbs light in violet,
blue, and red regions of
the visible spectrum
Doesn’t absorb well in the
green region.
 Green light is reflected by
chlorophyll, so plants appear
green.

Other pigments absorb
light in other regions.
Photosynthesis takes place inside
Chloroplasts





Thylakoids – sac-like
photosynthetic membranes,
where light-dependent
reactions occur
Grana – stacks of
thylakoids
Photosystems – clusters of
chlorophyll and other
pigments in the thylakoid
membrane
Stroma – region outside the
thylakoids where Calvin
cycle occurs
Chloroplast Cyclosis (:30)
Overview of
Photosynthesis
● When the sunlight excites
electrons in chlorophyll, the
electrons gain a great deal
of energy.
● They need a special electron
carrier to move them from
chlorophyll to other
molecules.
● NADP+ is a carrier molecule that
holds 2 high energy electrons and
an H+ ion and becomes NADPH.
●NADPH can then carry the highenergy electrons to the Calvin cycle.
Light-Dependent Reactions
Take place in the _____
_____
Begin when pigments in
PS II absorb light. Light
energy is absorbed by
electrons in chlorophyll,
increasing their energy
level. They then move
down the ETC.
 Additional electrons
are provided by water.
Oxygen is released
into the air. The unused
H+ ions are released
into the ITS.
A.
Light-Dependent Reactions
B. Electrons pass
through the ETC
from PS II to PS I.
The energy from
the electrons is used
to actively
transport H+ ions
from the stroma into
the ITS.
C. The electrons are
reenergized in PS I.
NADP+ picks up
these electrons,
along with H+ ions,
to become NADPH.
Light-Dependent Reactions
D. Eventually, the ITS
fills up with H+ ions.
The outside of the
thylakoid membrane
is – while the inside
is +. This provides
energy to make ATP.
E. ATP synthase – an
enzyme that allows
H+ ions to pass
through it causing it
to rotate and bind
ADP and a
phosphate to
produce ATP.
• The ATP and
NADPH get sent to
the Calvin cycle.
Calvin Cycle
PGA
RuBP
PGAL
PGAL
Calvin cycle uses
energy from ATP and
NADPH (both from the
LDR) to produce
sugars. It uses 18
molecules of ATP and
12 molecules of
NADPH to complete
one cycle.
Calvin Cycle

PGA
RuBP
PGAL
PGAL
The two reactions
work together
perfectly – LDR trap
the energy of
sunlight in chemical
form (ATP and
NADPH) and the
Calvin cycle uses
that energy to
produce sugars from
CO2 and H2O.
Photosynthesis Summary
(7:30)
Factors that Affect
Photosynthesis
Water – shortage can slow or stop photosynthesis
because it’s a raw material
 Temperature – photosynthesis depends on
enzymes. Temperature extremes will denature
enzymes and slow the rate of photosynthesis
 Intensity of light – increasing intensity increases
rate of photosynthesis, but only up to a point

Photosynthesis Song (1:52)
Review!

Scientists:
 Traced path carbon follows through
chloroplast
 Stated that mass of plants comes from
H2O
 Discovered oxygen
 Proved that plants transform light energy
into chem energy
 ETC
 Discovered that plants produce O2 in light
but not in dark
Review!
H2O is broken up into what three
components in PSII?
 What is an autotroph?
 Name at least three factors that affect rate
of photosynthesis.
 The LDR take place in the . . .
 What is located between PSII and PSI?
 Purpose of the electrons as they move
down the ETC?

Review!
The two predominant pigments found in
chloroplasts?
 Pigments can be found in the . . .
 Organisms that must eat other organisms
for energy?
 The LDR produce ___ and ___ which are
required for Calvin.
 Raw material for LDR?
 Raw material for Calvin?

Review!
Where does Calvin take place?
 Stack of thylakoids?
 What is actively transported into the
ITS?
 What provides the energy?
 Primary energy compound for all cells?
 Product of LDR?
 Product of Calvin?
