Topic 5.1 Communities and Ecosystems by FIg19vk


									Topic 5.1 Communities and

                 IBSL Biology
                  S. Dosman
• 5.1.1 - Define species, habitat,
  population, community, ecosystem and

• 5.1.2 - Distinguish between autotroph
  and heterotroph.

• 5.1.3 - Distinguish between consumers,
  detritivores and saprotrophs.

• 5.1.6 - Define trophic level.
• A species can be defined as a group of
  organisms which can interbreed and
  produce fertile offspring.
• A habitat is the environment in which a
  species normally lives or the location of a
  living organism.
• A population is a group of organisms of
  the same species who live in the same
  area at the same time.
• A community is a group of populations
  living and interacting with each other in an
• An ecosystem can be defined as a
  community and its abiotic environment
• Ecology is the study of relationships
  between living organisms and between
  organisms and their environment.
• An autotroph is an organism that can
  produce its own food.
• They synthesize organic molecules from
  simple inorganic substances.
• The process used is often photosynthesis
  but chemosynthesis may be used also.
• Due to the fact that they make their own
  food they are often referred to as
• A heterotroph is an organism that cannot
  make their own food so they must obtain
  their organic matter (nutrients) from other
• Heterotrophs consume autotrophs and
  other heterotrophs to obtain needed
  nutrients. This is why they are often
  referred to as consumers.
• A consumer is an organism that ingests
  other organic matter that is living or
  recently killed.
• A detritivore is an organism that
  consumes or eats non-living organic
• They eat dead leaves, feces or carcasses
  and some examples are earthworms,
  woodlice, and dung beetles.
• Saprotrophs are organisms that live on or
  in non-living organic matter.
• They secrete digestive enzymes into the
  organic matter and absorb the products of
• This group is composed mainly of fungi
  and bacteria and are often referred to as
            Trophic Level
• The position of an organism on a food
  chain is its trophic level.
• Trophic levels are another way of
  classifying organisms based on their
  feeding relationships with other organisms
  in the same ecosystem.
• The first trophic level in a food chain is
  always the producer. The next organism
  is the primary consumer and so on.
5.1.4 - Describe what is meant by a food chain, giving
  three examples, each with at least three linkages
                  (four organisms).

• A food chain is a sequence which shows the
  feeding relationships and energy flow between
  species. Food chains answer the question “Who
  eats whom?”
• Arrows are used in food chains to show the
  direction the energy flows through the chain.
• The first organism in the food chain is the
  producer and the other organisms are all
  consumers. They are known as the primary,
  secondary and tertiary consumers depending on
  their position in the food chain.
• The following are some examples of food
  chains from three different ecosystems:

              Grassland ecosystem
  Grass →grasshoppers → toad → hognose snake → hawk

                  River Ecosystem
     Algae → mayfly larva → juvenile trout → kingfisher

                 Marine Ecosystem
 Diatoms → copepods → herring → seal → great white shark
 5.1.5 - Describe what is meant by a food web.

• A food web can be defined as a series of
  interconnecting food chains.
• Food webs are useful because an organism
  does not often only eat one source of food so
  food chains do not tell the whole story for each
• Food webs can show the complex and complete
  network of trophic relationships in a community.
• Once again the arrows indicate the direction of
  energy flow within the web.
• Due to the fact that
  some organisms may
  be food for more than
  one predator and
  some organisms feed
  on more than one
  type of food, food
  webs can have more
  than one arrow that
  emanates from or
  arrives at more than
  one organism.
5.1.7 - Deduce the trophic level of organisms in
          a food chain and a food web.

• Use the handout given to you in class to
  deduce the trophic level of organisms.
• The producer is always the first trophic
• It is important to note that in a food web,
  an organism may occupy one or more
  different trophic levels depending on the
  food chain you follow in that food web.
 5.1.8 - Construct a food web containing up to
 10 organisms, using appropriate information.

• This will be student specific.
• It is important to remember the direction of
  arrows in a food web.
 5.1.9 - State that light is the initial energy source for
                 almost all communities.

• Light is the initial energy source in all
  communities because it is absorbed by the
  photosynthetic organisms (producers) and
  converted to chemical energy.
• The producers are the most important trophic
  level in the food chain because they provide the
  initial food for the consumers. They also absorb
  the sunlight which is the energy that drives food
• All food in a community contains energy that can
  be traced back to sunlight.
 5.1.10 - Explain the energy flow in a food chain.
• After the initial energy enters a food chain in the form of
  radiant energy (sunlight) the producers convert it into
  chemical energy in the form of organic molecules.
• The energy is transferred from one organism to the next or
  one trophic level to the next when the carbohydrates, lipids
  and proteins are digested.
• For example, the energy in grass is transferred to a cow
  when it eats the grass. Inside the cow cellular respiration
  releases the chemical energy and some energy is lost to the
  environment in the form of heat.
• If the cow dies it is eaten by another consumer and the
  chemical energy stored in the cow is transferred to the next
  trophic level. If the cow dies and is not eaten, the
  detritivores and decomposers will use the available energy.
5.1.10 - Explain the energy flow in a food
• The decomposers and
  detritivores also perform
  cellular respiration and
  heat produced will be lost
  to the environment.
• The chemical energy in a
  food chain can be passed
  from one trophic level to
  the next. Energy from the
  food chain is constantly
  being lost to the
  environment as heat.
  5.1.11 - State that energy transformations are never
                      100% efficient.

• As mentioned in AS 5.1.10, only chemical energy can
  be used by the next trophic level and a consumer can
  only convert a small amount of energy it absorbs into
  chemical energy.
• No organism can convert or utilize 100% of the energy
  present in the organic molecules they consume. They
  commonly only utilize about 10-20% of the energy from
  the previous trophic level.
• The reasons the energy transformations are so
  inefficient is due to energy being lost as heat, organisms
  dying before they can be consumed by the next trophic
  level, not all food is swallowed or some that is swallowed
  cannot be used by that organism.
5.1.12 - Explain reasons for the shape of
           pyramids of energy.
• An energy pyramid is designed to show
  how much and how fast energy flows from
  one trophic level to the next. An energy
  pyramid considers time or the rate of
  energy production along with the quantity
  of energy produced.
• The energy is measured in kilojoules per
  square metre per year or (kJ m-2 yr-1).
   5.1.12 - Explain reasons for the shape of
              pyramids of energy.

• Due to the fact that energy is always lost
  from one trophic level to the next, each
  level of the pyramid is smaller than the
  previous level.
  5.1.13 - Explain that energy enters and leaves
  ecosystems, but nutrients must be recycled.
• All nutrients within ecosystems must be
  continuously recycled to meet the needs of the
• All of the elements necessary for life such as
  carbon, nitrogen, phosphorus and other elements
  and compounds must be recycled and used over
  and over.
• Every time an organism consumes nutrients from
  the environment they must be returned to the
  environment at some point. Some nutrients will be
  temporarily “locked up” within the organism as
  structural components but will eventually be
  returned once that organism is eaten or
  5.1.14 - State that saprotrophic bacteria and fungi
           (decomposers) recycle nutrients.

• The saprotrophic bacteria and fungi play an
  essential role in releasing the nutrients that were
  temporarily locked up inside of the cells of plants
  and animals.
• When plants and animals die the decomposers
  release digestive enzymes that break down the
  dead organic matter and release the nutrients
  which can then be used for themselves or by
  other organisms.
• Without these important organisms, nutrients
  could not be released from dead organic matter
  and there would soon be a nutrient shortage.

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