Autotrophy
Collecting Energy from the
Nonliving Environment
What are Autotrophs?
• Autotrophs are organisms that obtain energy
from nonliving sources.
• All organisms need a source of energy and a
source of carbon compounds to perform daily
functions.
• Photoautotroph – autotrophs that depend on
photosynthesis for energy and carbon
compounds
Overview of Photosynthesis
• Photoautotrophs have adapted to take
advantage of an energy source that they can
never exhaust: sunlight.
• The energy that radiates from the Sun forms a
continuous series of waves called the
electromagnetic spectrum.
• Photoautotrophs can capture these light waves
and use them for energy.
Electromagnetic Spectrum
See page 106 in your textbook
Visible Light
• The range of wavelengths that animals can
detect with their eyes is called visible light.
• The length of the waves determines the light’s
color and energy; the shorter the wave, the
greater the energy.
• Our eyes interpret color due to the light that
transmits or reflects off objects.
Pigments
• Pigments – light-absorbing substances or
chemicals found in living cells
• The light-absorbing pigments that function in
photosynthesis are embedded in structures
called chloroplasts.
Cross-section of Chloroplast
Chloroplast Characteristics
• Chloroplast membranes have the same basic
structure as other cell membranes.
• Thylakoids are series of flattened sacs that
increase surface area for light absorption.
• Enzymes in the stroma catalyze the formation
of sugar from carbon dioxide and water using
the light energy captured by the thylakoids.
Chlorophyll
• Most photosynthesis depends on the green
pigment, chlorophyll.
• There are 2 forms of chlorophyll, a and b
• They absorb light in the violet/blue and
orange/red ranges, but not in the green range.
• Our eyes see green leaves because the green
light is reflected.
Chlorophyll a/b Spectrum
Three Step Process
The process of photosynthesis involves three
energy conversions:
1. absorption of light energy
2. conversion of light energy into chemical
energy
3. storage of chemical energy in the form of
sugars
Photosynthesis
The Light Reactions
• The light reactions convert solar energy to
chemical energy
• The light energy is used to synthesize ATP and
NADPH
The Dark Reactions
• The Calvin cycle makes sugar from carbon
dioxide using the ATP and NADPH
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Photosynthesis
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Rate of Photosynthesis
• Light intensity, temperature and the
concentrations of carbon dioxide and oxygen
all affect the rate of photosynthesis.
Adaptations of Plants
• Certain plants continue to produce food even
in arid conditions.
• C3 plants use carbon dioxide directly to
produce a three-carbon compound called 3PGA.
• Examples include: soybeans, oats, wheat, and
rice
Agricultural Problems with C3 plants
• Dry weather can reduce the rate of
photosynthesis and decrease crop productivity
in C3 plants.
• On a hot, dry day, C3 plants close their
stomata. This is an adaptation to reduce
water loss.
• But closing the stomata also prevents carbon
dioxide from entering the leaf.
C4 Plants
• When the weather is hot and dry, a C4 plant
keeps its stomata closed to conserve water.
• At the same time, it continues to make sugars
by photosynthesis using a special enzyme to
create a 4 carbon compound instead of 3PGA.
• Examples include: corn and sugarcane
CAM plants
• The name Crassulacean Acid Metabolism
comes from the crassulaceae desert plant
family.
• A CAM plant conserves water by opening its
stomata and admitting carbon dioxide at night.
• When carbon dioxide enters the leaves, it’s
incorporated into a 4 carbon compound, just
like C4 plants.
Photosynthesis and the Atmosphere
• Photosynthesis supplies oxygen gas to Earth’s
atmosphere and food to Earth’s organisms.
• Because photosynthesis is the largest single
process on Earth, any disruption would have
dramatic effects.
Reasons for Increasing Levels of
Carbon Dioxide
• Burning of fossil fuels
• Cutting down/burning forested areas
How Plants are Affected
• Increased growth of C3 plants in areas of the
world that were previously dominated by C4
plants
Effects of Carbon Dioxide on Living Things
• There is a protective layer of the atmosphere
called ozone.
• Ozone typically reflects a high percentage of the
Sun’s radiation back into space.
• Ozone also traps carbon dioxide in the
atmosphere and helps to maintain a warm Earth
environment (called the greenhouse effect).
Varieties of Chemoautotrophs
• Chemoautotrophs are bacteria that obtain
energy by performing chemical reactions that
fix their own carbon.
• The energy comes from reactions with
minerals such as sulfur, iron or nitrogen.
• This process does not provide as much energy
as photosynthesis.
• Chemoautotrophs grow best in environments
where other organisms cannot survive and
where light and organic compounds are in
short supply.
• Scientists like to call these types of bacteria
extremophiles because they live in the most
extreme places…
– South pole, deep sea thermal vents, volcanoes,
along plate boundaries, tallest mountain peaks