Where does the energy that living
things need come from?
 Food!
 You’re not you when you’re hungry!
Where does the energy that living
things need come from?
 Originally, though the energy in most food come from
the sun
 PLANTS AND SOME OTHER TYPES OF
ORGANISMS ARE ABLE TO USE LIGHT ENERGY
FROM THE SUN TO PRODUCE FOOD
Autotrophs
 Organisms that make their own food
Heterotrophs
 Organisms that cannot use the sun’s energy directly
 Animals
 Obtain energy from the foods they consume
Grass – autotroph
Impala - heterotroph
Cheetah…
Cheetah and Impala…
AUTOTROPH!!!!
AHHHHHH!!!!!!!!
Heterotrophs
 Obtain energy from the foods they consume
 Cheetah: obtains energy stored in autotrophs
indirectly by feeding on animals that eat autotrophs
Mushrooms
Heterotroph or Autotroph?
Mushrooms - Heterotroph
 Obtain food by decomposing other organisms
Chemical Energy and ATP
 What forms of energy can you think about?
Chemical Energy and ATP
 What forms of energy can you think about?
 Light
 Heat
 Electricity
 Stored in chemical compounds, too
Burn a candle

Energy is released in the form of light and heat
 Bonds between carbon and hydrogen are broken
 Energy is released from those electrons
 When the electrons in those bonds are shifted from
higher energy levels to lower energy levels, the extra
energy is released as heat and light
Living things use chemical fuels as
well
 Adenosine triphosphate (ATP)
ATP
 Adenine
 Ribose: a 5-carbon sugar
 Three phosphate groups
X3
ATP  ADP and ADP  ATP
 Releasing stored energy
 Adenosine diphosphate
 A phosphate bond has broken – RELEASED ENERGY
 When a cell has energy available, it can store small
amounts of it by adding a phosphate group to ADP
molecules, producing ATP
ATP has enough energy to power a
variety of cellular activities,
including active transport across
cell membranes, protein synthesis,
and muscle contraction
The characteristics of ATP make it
exceptionally useful as the basic
energy source of all cells
Old Guys Assignment
 Jan van Helmont
 Joseph Priestley
 Jan Ingenhousz
 Write a paragraph about each of these guys and his
contribution to the discovery of photosynthesis
Photosynthesis
 The key cellular process identified with energy
production
 Plants use the energy of the sunlight to convert water
and carbon dioxide into high-energy carbohydrates –
sugars and starches – and oxygen
 Oxygen is a waste product
Photosynthesis
¾Light
¾¾
® C6H12O6 + 6O2
Carbon dioxide + water ¾Light
¾¾
® sugars + oxygen
6CO2
+ 6H2O
Photosynthesis uses the energy of
sunlight to convert water and
carbon dioxide into high-energy
sugars and oxygen
How do plants use low-energy, raw
materials to produce high-energy
sugars?
How do plants use low-energy, raw
materials to produce high-energy
sugars?
 They capture the energy of sunlight
How do plants use low-energy, raw
materials to produce high-energy
sugars?
 They capture the energy of sunlight
 So… how do they capture sunlight?
In addition to water and carbon
dioxide, photosynthesis requires
light and chlorophyll, a molecule in
chloroplasts
 https://www.youtube.com/watch?v=-XP7yflhOtE
Chemical Energy and ATP
 What forms of energy can you think about?
 Light
 Heat
 Electricity
 Stored in chemical compounds, too
Energy from the sun travels to
Earth in the form of light.
 “White” light: Sunlight that is visible
 Mixture of different wavelengths of light
 Many are visible and make up the visible spectrum
 Different wavelengths = different colors
400Violet
450Blue
500Cyan
550Green
600Yellow
650Orange
700Red
750Infrared
How do plants gather the sun’s
energy?
How do plants gather the sun’s
energy?
 Pigments: light-absorbing molecules that gather the
sun’s energy

Chlorophyll: the plant’s principle pigment


Chlorophyll a
 Blue-violet
 Red
Chlorophyll b
 Blue
 Red
 Carotene: can be red, yellow, or orange
 Carotene ≈ Carrot
When chlorophyll absorbs light,
much of the energy is transferred
directly to electrons in the
chlorophyll molecule, raising the
energy levels of these electrons.
These high-energy electrons allow
photosynthesis to work.
Inside a Chloroplast
Inside a Chloroplast
 Thylakoids: saclike photosynthetic membranes
 Arranged in stacks called grana
 Proteins in the thylakoid membrane organize
chlorophyll and other pigments into clusters known as
photosystems
 Photosystems: light collecting units
 Stroma: the region outside of the thylakoid
membranes
2 parts of Photosynthesis
 Light-dependent reactions
 Take place in the thylakoid membranes
 Light-independent reactions (Calvin Cycle)
 Take place in the stroma
Electron Carriers
 Carrier molecule: compound that can accept a pair of
high-energy electrons and transfer them along with
most of their energy to another molecule
 ELECTRON TRANSPORT
 NADP+: accepts and holds 2 high-energy electrons
along with a hydrogen ion
 NADP+  NADPH
Light Dependent Reactions
 Require light
 Use energy from the light to produce ATP and NADPH
 The light dependent reactions produce oxygen gas and
convert ADP and NADP+ into the energy carriers ATP
and NADPH
Light Dependent Reactions
1.
2.
3.
4.
5.
Photosystem II
Electron Transport Chain
Photosystem I
Hydrogen Ion Movement
ATP Formation
Photosystem II
 Light absorbed by photosystem II is used to break up
water molecules into energized electrons, hydrogen
ions (H+), and oxygen
Electron Transport Chain
 High-energy electrons from photosystem II move
through the electron transport chain to photosystem I
Photosystem I
 Electrons released by photosystem II are energized
again in photosystem I. Enzymes in the membrane
use the electrons to form NADPH. NADPH is used to
make sugar in the Calvin Cycle
Hydrogen Ion Movement
 The inside of the thylakoid membrane fills up with
positively charged hydrogen ions. This action makes
the outside of the thylakoid membrane negatively
charged and the inside positively charged.
ATP Formation
 As hydrogen ions pass through ATP synthesis, their
energy is used to covert ADP into ATP
ATP Synthase
 ATP synthase: protein in the cell membrane
 This protein spans the membrane and allows H+ ions
to pass through it.
 As H+ ions pass through ATP synthase, the protein
rotates like a turbine being spun by water in a
hydroelectric power plant
 As it rotates, ATP synthase binds ADP and a phosphate
group together to produce ATP
  Light Dependent electron transport produces not
only high energy electrons, but ATP as well
Calvin Cycle
 The ATP and NADPH formed from the light
dependent reactions contain an abundance of
chemical energy, but they are not stable enough to
store that energy for more than a few minutes
 The Calvin cycle uses ATP and NADPH from the
light-dependent reactions to produce high-energy
sugars
Calvin Cycle
CO2 Enters the Cycle
2. Energy Input
3. 6-Carbon Sugar Produced
4. 5-Carbon Molecules Generated
1.
CO2 Enters the Cycle
 6 carbon dioxide
molecules are
combined with six 5carbon molecules to
produce twelve 3carbon molecules
Energy Input
 Energy from ATP and
high-energy electrons
from NADPH are used to
convert the twelve 3carbon molecules into
higher-energy forms
6-Carbon Sugar Produced
 Two 3-Carbon molecules
are removed from the
cycle to produce sugars,
lipids, amino acids, and
other compounds
5-Carbon Molecules Regenerated
 The 10 remaining 3-
carbon molecules are
converted back into six 5carbon molecules, which
are used in the next cycle
 This step uses energy
 6ATP  6 ADP
Factors that affect Photosynthesis
 Water
 Temperature
 Light Intensity
Factors that affect Photosynthesis
 Water – shortage can stop or slow photosynthesis
 Plants that live in dry conditions, such as desert plants
and conifers, have a waxy coating on their leaves that
reduces water loss
 Temperature
 Light Intensity
Factors that affect Photosynthesis
 Water – shortage can stop or slow photosynthesis
 Plants that live in dry conditions, such as desert plants
and conifers, have a waxy coating on their leaves that
reduces water loss
 Temperature
 Photosynthesis depends on enzymes that function best
between 0℃ and 35℃
 Temperatures above or below this range may damage the
enzymes, slowing down the rate of photosynthesis
 Very low temps – possibly stop
 Light Intensity
Factors that affect Photosynthesis
 Water – shortage can stop or slow photosynthesis
 Plants that live in dry conditions, such as desert plants and conifers,
have a waxy coating on their leaves that reduces water loss
 Temperature
 Photosynthesis depends on enzymes that function best between
0℃ and 35℃
 Temperatures above or below this range may damage the enzymes,
slowing down the rate of photosynthesis
 Very low temps – possibly stop
 Light Intensity
 Increasing light intensity increases the rate of photosynthesis
 At a certain level, the plant reaches its maximum rate of
photosynthesis