Photosynthesis
I. Energy and Life
A. Energy is the ability to do work
1. Energy for sports
2. Energy while you are sleeping to build now proteins
and amino acids
3. Without the ability to obtain and use energy, you die!
B. Autotrophs and Heterotrophs
1. Some organisms are able to use light energy from the
sun to produce food
a)
These are autotrophs
(1)
Plants
(2)
Algae
Hetertrophs are organisms that cannot use the
sun’s energy to produce it’s own nutrients.
b)
(1)
Animals
(2)
Mushrooms – decomposers
C. Chemical Energy and ATP
1. Energy comes in many forms including light, heat, and
electricity. Energy can be stored in chemical compounds.
When you light a candle, the wax melts, soaks into
the wick, and is burned, releasing energy in the form
of light and heat.
a)
One of the principal chemical compounds in living
things that cells use to store and release energy is
adenosine triphosphate (ATP)
b)
ATP consists of adenine, a 5-carbon sugar called
ribose, and 3 phosphate groups
(1)
Adenosine diphosphate (ADP) is a compound that
looks almost like ATP, except it has two phosphate
groups instead of 3.
(2)
(3)
ADP is the key to storing energy
(4)
Add a phosphate group to ADP and you get ATP
(5)
How is the energy that is stored in ATP released?
(a) Simply by breaking the chemical bond between
the 2nd and 3rd phosphates, energy is released.
ATP is used to power a variety of cellular
activities, including active transport across cell
membranes, protein synthesis, and muscle
contraction.
(6)
D. Using Biochemical Energy
1. One way cells use the energy provided by ATP is to
carry out active transport
Sodium-potassium pumps – a membrane pump
that moves Na+ out of the cell and K+ into it.
a)
2. ATP also produces movement, such as moving
organelles throughout the cell.
3. ATP allows our cells to make proteins and nucleic
acids
4. ATP can even be used to produce light
a)
Fireflies
5. Although ATP is a great molecule for transferring
energy, it is not a good for storing large amounts of
energy over the long term.
A single molecule of glucose stores more than 90
times the chemical energy of a molecule of ATP
a)
(1)
Think about money 100 pennies vs. 1 dollar.
II. Photosynthesis: An overview
A. In the process of photosynthesis, plants use the energy
of sunlight to convert water and carbon dioxide into highenergy carbohydrates – sugars and starches and oxygen, a
waste product.
B. Investigating Photosynthesis
1. Helmont 1600s
a)
Water intake of plants
2. Priestly 1700s
a)
Plants release oxygen
3. Ingenhousz 1700s
Aquatic plants produce O2 bubbles in the light but
not the dark
a)
b)
Plants need light to produce O2
4. Mayer 1800s
a)
Plants convert light energy into chemical energy.
5. Calvin 1900s
a)
Calvin Cycle
6. Marcus 1990s
a)
Electron transport chain
C. The Photosynthesis Equation
1. 6 CO2 + 6 H2O (light) C6H12O6 + 6 O2
2. Carbon dioxide + water (light) sugars + oxygen
3. Plants obtain CO2 from the air and water which begins
the process of photosynthesis
D. Light and Pigments
1. In addition to water CO2, photosynthesis requires light
and chlorophyll, which is a molecule in chloroplasts
2. Plants gather the sun’s energy with light –absorbing
molecules called pigments. The plants’ principal pigment
is chlorophyll
III. The Reactions of Photosynthesis
A. Inside a Chloroplast (p 208)
1. In plants and other photosynthetic eukaryotes,
photosynthesis takes place inside chloroplasts.
2. Chloroplasts contain saclike photosynthetic
membranes called thylakoids. Thylakoids are arranged in
stacks known as grana.
3. Proteins in the thylakoid membrane organize
chlorophyll and other pigments into clusters known as
photosystems. These photosystems are the lightcollecting units of chloroplast.
4. Photosystems are divided into two parts
Light-dependent reactions, which takes place in
the thylakoid membranes
a)
Light-independent reactions or the Calvin cycle,
which takes place in the stroma, which is outside the
thylakoid membrane
b)
B. Electron Carriers
1. When sunlight excites electrons in chlorophyll, the
electrons gain a great deal of energy. These high-energy
electrons require a special carrier.
2. This process is called the electron transport chain
3. One of the carrier molecules is a compound known as
NADP+
Accepts and holds 2 high-energy electrons along
with a hydrogen ion (H+). This converts the NADP+
into NADPH.
a)
The NADPH can then carry high-energy electrons
produced by light absorption in chlorophyll to
chemical reactions.
b)
C. Light-Dependent Reactions
1. Light-dependent reactions require light, this is why
plants need light to grow.
2. Use energy from light to produce ATP and NADPH
3. The light-dependent reactions produce oxygen gas
and convert ADP and NADP+ into the energy carriers ATP
and NADPH.
Photosynthesis begins when pigments in
photosystem II absorb light. The light energy is
absorbed by electrons, increasing their energy level.
New electrons are contained in the electron transport
chain. As the plant removes electrons from water,
oxygen is left behind and is released into the air. This
reaction is the source of nearly all of the oxygen in
Earth’s atmosphere.
a)
D. The Calvin Cycle
1. The ATP and NADPH formed by the light-dependent
reactions contain an abundance of chemical energy, but
they are not stable enough to store that energy for more
then a few minutes.
2. During the Calvin cycle, plants use the energy that ATP
and NADPH contain to build high-energy compound that
can be stored for a long time.
3. The Calvin cycle used ATP and NADPH form the light-
dependent reactions to produce high-energy sugars.
4. Because these reactions do not require light then are
also called the light-independent reactions.
6 carbon dioxide molecules enter the cycle from
the atmosphere. These molecules combine with six 5carbon molecules resulting in 12 3-carbon molecules.
a)
12 3-carbon molecules are then converted into
higher-energy forms
b)
The remaining 10 3-carbon molecules are
converted back into 6 5-carbon molecules
c)
The Calvin cycle used 6 molecules of carbon
dioxide to produce a single 6-carbon sugar molecule
d)
5. The plant uses the sugars to meet its energy needs
and to build more complex macromolecules such as
cellulose that it needs for growth and development.
6. When heterotrops eat plants, they can also use the
energy stored in carbohydrates
E. The two sets of photosynthetic reactions work together
– the light-dependent reactions trap the energy of the
sunlight in chemical form, and the light-independent
reactions use that chemical energy to produce stable, highenergy sugars from carbon dioxide and water.
F. Factors Affection Photosynthesis
1. Shortage of water can slow or even stop
photosynthesis
2. Photosynthesis depends on enzymes that function
best between 0oC and 35 oC. Temps above or below this
range may damage the enzymes, slowing or stopping
photosynthesis.
3. Light intensity increases photosynthesis