Learning from Nature, from genes
to ecosystems
Module 3 Plant biomass degradation (Biofuels)
Core Concept
Plant cell walls contain a mixture of recalcitrant
polysaccharides. Nature has devised many strategies of obtaining energy from
these compounds.
Recalcitrant
polysaccharides – carbohydrates (starch
and cellulose) consisting of lots of monosaccharides that joined together by
chemical bonds and are difficult to break.
Photosynthesis-
The process by which plants, algae, and some bacteria use energy from the sun,
water, and carbon dioxide to make glucose. The glucose made through this
process is linked together to form starch and cellulose.
Overview and Key terms
Most of the energy used by all living cells comes from the
sun. Plants are called autotrophic, because they can make their own food. They
do through a process called photosynthesis.
–
Photosynthesis-the process used by plants, algae, and some bacteria to
capture sunlight energy
–
only about 1% of the
available energy in sunlight is captured
If you look at a
plant cell under the microscope, you can see the chloroplasts.
Chloroplasts up close.
(http://www.youtube.com/watch?v=LTglday5zak)
Chloroplasts contain the following:
thylakoids- the internal membranes
Grana- thylakoids are stacked together in columns
Stroma- semiliquid substance that surrounds the thylakoids
photosystems- embedded in the thylakoid membrane contain pigments
Chlorophyll-primary pigment molecule in most photosystems is the
pigments act as an antenna to capture energy from sunlight individual
chlorophyll pigments pass the captured energy between them through eh electron
transport system
Photosynthesis takes
places in three stages
·
capturing energy from
sunlight
·
using the captured
energy to produce ATP and NADPH
·
using the ATP and
NADPH to make carbohydrates from CO2 in the atmosphere (carbon fixing)
Photosynthesis makes
two very important compounds
·
Oxygen
·
Glucose
• The light-dependent reactions in plants and algae use two
photosystems
–
Photosystem II
•
captures a photon of
light and releases an excited electron to the electron transport system (ETS)
•
the ETS then produces
ATP
–
Photosystem I
•
absorbs another photon
of light and releases an excited electron to another ETS
•
this ETS produces
NADPH
• Fixing Carbon
• The synthesis of organic molecules from CO2 uses the Calvin
cycle
–
these reactions are
also known as C3 photosynthesis
–
The Calvin cycle must
“turn” 6 times in order to form a new glucose molecule
–
the products of the
light-dependent reactions are used
•
ATP energy drives the
cycle
•
NADPH provides
hydrogen atoms
The energy for living
is obtained by breaking down the organic molecules originally produced in
plants or other organisms.
How some animals use
plants to obtain energy:
The Leaf Cutter Ants,
Cows, and Biofuels
The Leaf Cutter Ants
Picture from flickr.com
Leaf-cutter ants use fresh leaf material to grow fungal
gardens on. Mature colonies can have over 5 million workers. They are considered dominant herbivores in
Neotropical terrestrial Ecosystems.
Mature colonies have a 10-15 year lifespan and can harvest about 400kg of dry weight (or 1600-4000 kg of
wet weight) plant material per year.
The fungal
cultivar is unable to metabolize all components of the plant material.
Bacterial symbionts are in the fungal gardens that help break down the plant
material. However, there are still a lot of recalcitrant polysaccharides found
in the material that the ants dump. The ants dump
is composed of undigested plant material and old fungal matter. An individual
colony can produce about 200kg of refuse per year. These ants dumps are an
important source of nutrients in the ecosystem. Dump material accumulates
during the dry season and then undergoes rapid decomposition during the rainy
season. Some scientists have called these dumps “Nutrient Islands” and many
studies show there is a significant increase in the fine-root systems of plants
found associated with/near the dumps. In a very similar process as to a compost
pile, bacteria found in these dumps help break the chemical bonds of the recalcitrant
polysaccharides and make the nutrients available to plants and other organisms.
Cattle
Picture from omafra.gov.on.ca and icanhasinternets.com
Cattle are large domesticated ungulates. Cattle are raised as livestock for meat, as dairy animals (milk, cheese, and ice cream), and as work animals (pulling farm equipment). Other products that are made from cattle include: leather, dung material for fertilizers and fuel. In India and other countries, cattle are sacred. There are almost 2 billion cows in the world today. And in 2009, cattle became the first livestock animal to have its genome mapped.
Cows have one stomach with four compartments and are considered to be ruminants. Ruminants are animals that have a digestive system that allows them to utilize use recalcitrant polysaccharides through a process of regurgitating and rechewing the material "cud". Cud is then reswallowed and digested by symbiotic microorganisms (fungi and bacteria) in the rumen. These microbes are primarily responsible for decomposing cellulose and other carbohydrates into volatile fatty acids that cattle can then use as their source nutrients. After the microbes have completed the process of breaking down the plant material, the cow then digests them and obtains a scource of protein that can be made into milk by the cow. The way ruminant’s digestive system works and their association with microbes allow them to survive on diet consistenting of grasses and other vegetation.
Overview of Cows (http://www.youtube.com/watch?v=cWg1u1bUKNc)
How humans are using microbes to create biofules:
Biomass(http://www.nsf.gov/news/special_reports/greenrevolution/)-Choose video Biomass
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