Download Ecology 2

The Cycling of Materials in
Ecosystems
• As energy and matter flow through an
ecosystem, matter must be recycled and
reused.
• Substances such as water, carbon,
nitrogen, calcium, and phosphorus each
pass between the living and nonliving
worlds through biogeochemical cycles.
The Cycling of Materials in
Ecosystems
• In biogeochemical cycles, interactions of
organisms and their environments
continuously recycle these elements.
• If not for this worldwide recycling program,
supplies of essential elements would have
been depleted as they became bound in
the bodies of organisms that lived eons
ago.
Water cycle
• The water cycle moves water from the
ocean to the atmosphere, onto land, and
back to the oceans.
• Three important processes in the water
cycle are evaporation, transpiration, and
precipitation.
Water
cycle
• The water cycle moves water from the ocean to
the atmosphere, onto land, and back to the
oceans.
• The arrows identify processes that move water.
Water cycle
• Evaporation adds water as vapour to the
atmosphere. Heat causes water to evaporate from
bodies of water, from the soil, and from the bodies
of living things.
• The process by which water evaporates from the
leaves of plants in terrestrial ecosystems is called
transpiration. Transpiration causes plants to take
in water through their roots to replace the water
that is being lost through their leaves.
• Animals drink water or obtain it from their food.
They release this water when they breathe, sweat,
or excrete.
Water cycle
• Water leaves the atmosphere through
precipitation. The amount of water the
atmosphere can hold depends on abiotic
factors, such as temperature and air
pressure. Once the atmosphere becomes
saturated with water vapor, precipitation
occurs in the form of rain, snow, hail, or
fog.
Water cycle
• The movement of water causes the
movement of other nutrients. Carbon,
nitrogen, and phosphorus all have soluble
forms that can be moved from place to
place by flowing water. As water trickles
through soil, it carries nutrient particles
from topsoil into deeper soil layers.
Carbon cycles
• The carbon cycle is a series of processes
which keep the amount of carbon in the
form of carbon dioxide in the air at a
relatively constant level.
• The element carbon is essential to all
living organisms because carbon is the
major ingredient of all organic molecules
(carbohydrates, fats and proteins) which
make up living tissue.
Carbon cycles
• Photosynthesis removes carbon dioxide
(CO2) from the atmosphere and
incorporates it into organic molecules,
which are  passed along the food chain
by consumers.
•  Cellular respiration by producers and
consumers returns CO2 to the
atmosphere.
•  Decomposers break down the carbon
compounds in detritus; that carbon, too, is
eventually released as CO2.
Carbon cycles
• On a global scale, the return of CO2 to the
atmosphere by cellular respiration closely
balances its removal by photosynthesis.
• However, the increased burning of wood
and fossil fuels (coal and petroleum) is
raising the level of CO2 in the atmosphere.
This increase in CO2 is leading to
significant global warming.
Human Influences on the Carbon
Cycle
• In the last 150 years, the concentration of
atmospheric carbon dioxide has risen
more than 30 percent.
• Humans contribute to this increase by
burning fossil fuels and other organic
matter.
• Our industrial society depends on the
energy released by the burning of fossil
fuels—coal, oil, and natural gas.
Human Influences on the Carbon
Cycle
• Burning releases the energy in these
molecules, but it also releases carbon
dioxide.
• When large areas of forest are burned
each year to clear land for agriculture, less
vegetation remains to absorb carbon
dioxide from the atmosphere through
photosynthesis.
Human Influences on the Carbon
Cycle
• In 2007, the Intergovernmental Panel on
Climate Change reviewed the results of many
scientific studies related to climate change.
• The panel of hundreds of scientists from all
over the world concluded that the warming
in recent decades is very likely due to a
human-induced increase in atmospheric
greenhouse gases.
• Unlike other possible factors, the rise in
greenhouse gases correlates well with the
rise in temperature.
Photosynthesis
• The foods made by green plants are energyrich substances called carbohydrates.
Examples of carbohydrates are starch and
sugar. When such foods are broken down,
they release a lot of energy for the plants to
grow and reproduce.
• Photosynthesis is the process by which
food is made in plants, from water and
carbon dioxide. This process can only occur
in the presence of chlorophyll and sunlight.
Photosynthesis
• The word equation for photosynthesis is
given below. The conditions for
photosynthesis are written above and
below the arrow.
• Chlorophyll is a green pigment found in
the chloroplasts of plant cells. It absorbs
the energy from the Sun (sunlight) and
uses that energy to convert carbon dioxide
and water into sugar and other
carbohydrates
Photosynthesis
• The raw materials (reactants) for
photosynthesis are:
• Carbon dioxide: This is found in the air
and enters the underside of the leaves
through tiny pores (called stomata).
• Water: This is taken in mainly through the
roots and transported up the plant to the
leaves due to transpiration.
Photosynthesis
• The output materials (products) of
photosynthesis are:
• Glucose: This is found in the form of
simple sugar, which can be used to
produce energy or can be stored as
starch.
• Oxygen: A gas important to living things
which is released into the air.
Photosynthesis
• Many plants convert the glucose produced
during photosynthesis into starch. This is
stored in the leaves and indicates
photosynthesis has taken place. A test for
the presence of starch is that iodine
solution will turn blue-black if starch is
present.
Photosynthesis
• The best conditions for photosynthesis
are warm and humid conditions.
Photosynthesis depends on reactions of
enzymes in the chloroplasts. Enzymes
work best around 30 °C — 35 °C. Humid
conditions provide water, which is one of
the raw materials of photosynthesis.
Photosynthesis
• The energy change during photosynthesis
involves light energy (from the Sun) being
converted into chemical potential energy
of glucose or starch. This energy is later
released during the process of respiration
which takes place in both plants and
animals.
Nitrogen Cycle
Nitrogen Cycle
• Nitrogen is essential for the formation of
amino acids in proteins. The nitrogen cycle
is a model that explains how nitrogen is
recycled.
• There's lot of nitrogen in air – about 78% of
the air is nitrogen. Because nitrogen is so
unreactive, it cannot be used directly by
plants to make protein.
• Only nitrates are useful to plants, so we are
dependent on other processes to convert
nitrogen to nitrates in the soil.
• Nitrogen gas is converted to nitrate
compounds by nitrogen-fixing bacteria in
soil or root nodules.
• Lightning also converts nitrogen gas to
nitrate compounds. The Haber process
converts nitrogen gas into ammonia used
in fertilizers.
• Ammonia is converted to nitrates by
nitrifying bacteria in the soil.
• Plants absorb nitrates from the soil and
use these to build up proteins. The plant
may be eaten by an animal, and its biomass
used to produce animal protein.
• Urea and egested material is broken
down by decomposers. This results in
nitrogen being returned to the soil as
ammonia.
• Decomposers also break down the
bodies of dead organisms resulting in
nitrogen being returned to the soil as
ammonia.
• In some conditions denitrifying bacteria in
the soil break down nitrates and return
nitrogen to the air. This is usually in
waterlogged soil. Improving drainage reduces
this effect, making the soil more fertile.
Simplified nitrogen cycle
Nitrogen Cycle
Decomposers
• Bacteria and fungi
• Organism that feeds on biological remains
and breaks organic material down into its
inorganic subunits.
• They get their energy from dead
organisms apart from animal and plant
waste products.
Detritivores
• Worms, millipedes, sea stars, crabs and
dung flies
• Consumer that feed on small bits of
organic material.
• They perform an additional function which
is to return essential nutrients back to the
ecosystem in the process.
Decomposers vs Detritivores
• Both aid in decomposition of dead or
decaying matter.
• Decomposition (or decay) is a chemical
reaction where a complex compound is
broken down into simpler compounds.
• Detritivores help in producing essential
nutrients. Worms are also called scavengers
as they eat up skin of an apple leaving the
inside of the fruit for other decomposers.
Decomposers vs Detritivores
• Both get energy from decaying matter
• But detritivores actually eat organic matter,
while decomposers secrete enzymes to
digest organic matter and then absorb
resulting molecules.
• Decomposers are smaller organisms while
detritivores are larger organisms.
Decomposers vs Detritivores
• In essence, decomposers such as bacteria
and fungi cause decay at a microscopic
level. Other larger organisms, called
detritivores, help speed up decay by
feeding on detritus – dead and decaying
material. They break it down into smaller
pieces, so increasing the surface area for
the bacteria and fungi.
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