Biology – Module 1 – A Local Ecosystem
1. The distribution, diversity and numbers of plants and animals found
in ecosystems are determined by biotic and abiotic factors

Compare the abiotic characteristics of aquatic and terrestrial
environments
An aquatic environment is one that consists in water.
The abiotic characteristics of an aquatic environment include:
o
Viscosity – This refers to the thickness of the medium in which the
environment is located, and its ability to resist internal movement through it.
For example in an aquatic environment, the medium is water. It is much
more difficult to travel through water than it is through air. This is why many
aquatic animals have streamlined bodies so that they can move through the
water easily.
o
Buoyancy – This refers to the upward pressure (or thrust) that is applied on
the organism by its medium. Buoyancy is determined by the density of the
medium and determines the floating ability of an organism. Water provides
sufficient buoyancy for many organisms, eg, the jellyfish. If a jellyfish is taken
out of water and placed on land it will disintegrate by spreading apart. Thus,
the water provides enough buoyancy (pressure) in order to keep the shape of
the jellyfish.
o
Pressure – This is the downward force that is applied on an organism by its
medium. In water, the pressure is dependant on the depth. Organisms that
live at the bottom of the ocean experience the effects of extreme pressure
and they must have specific adaptations that enable them to survive in such
harsh environments.
o
Temperature Variations – Usually in an aquatic environment there are
minimal temperature variations to that compared with terrestrial
environments. The temperature variations also depend on the size of the
body of water; a large body of water will experience much less temperature
variations than a smaller body of water. Also, as depth increases the
temperature of the water decreases.
o
Availability of gases – in water the availability of gases depends on factors
such as temperature, depth and turbulence. Hot water holds much less
oxygen than cold water. The availability of gases also depends on the rate of
diffusion which is much slower in water than it is in air. Also, as the depth of
the water decreases the availability of the gases decreases.
o
Availability of water – In aquatic environments water availability can be a
problem as osmosis occurs. Organisms are suited to a particular type of water
– either fresh water or salt water. If the organism is placed in the wrong type
of water they will die, thus water-availability is an issue. In this scenario, the
salinity of the water is another factor.
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o
Light penetration – Light is only able to penetrate about 100m in oceans
and seas. Thus as the depth increases the light penetration decreases. Light
is essential for all aquatic plants, thus the plants need to have specific
adaptations that allow them to retrieve enough sunlight to survive. The light
penetration is also dependant upon water clarity.
o
Exposure to natural forces – Different aquatic environments are exposed
to different natural forces such as tides, currents, waves etc. Marine
organisms must be adapted to survive in such conditions.
A terrestrial environment is one that consists on land.
The characteristics of a terrestrial environment include:
o
Temperature – There are much larger temperature variations on land rather
than in water. Land organisms must therefore have adaptations to cope with
such large temperature changes.
o
Landscape position – Slope and aspect may affect temperature, water and
light availability as well as impact on soil quality. Run-off and erosion may
also be prominent in particular landscapes.
o
Rainfall and water availability – Water is not freely abundant in land. It
must be sourced from the soil or consumed. Organisms must have
adaptations that allow them to survive using the amount of water available to
them
o
Salinity – Different soils have different salinity levels and only particular
organisms thrive in certain salinity levels. Plants must have adaptations that
enable them to cope with the different levels of salinity.
o
pH (acidity/alkalinity) – Soil pH can vary. Dissolved salts play an
important role in determining the pH of the soil and some plants need to have
a particular pH to survive. Plants need to have adaptations that allow them to
cope with the pH of the soil in their environment.
o
Buoyancy – Air provides minimal buoyancy and therefore land organisms
need to have a skeletal and muscle structures that enable them to support
them.
o
Exposure to natural forces – Wind, rain, floods, droughts, monsoons,
cyclones, storms etc are all part of the terrestrial environment and organisms
need to be able to adapt to most if not all of these forces.
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
Identify the factors determining the distribution and abundance of a
species in each environment
Distribution – refers to the region where an organism is found.
Abundance – refers to the number of individuals in the area and is usually
described as a density.
Aquatic - There are several abiotic factors that affect abundance and distribution
of organisms in aquatic environments including:
o
Pressure Variations – ranging from low pressures in surface waters to
extreme pressure in deep ocean trenches.
o
Light penetration – plants need adequate light for photosynthesis. This is
true in both environments (aquatic and terrestrial). In water the light is only
able to penetrate to a certain depth. Water doesn’t absorb all light. About
30% is reflected off the surface. At certain depths water absorbs different
wavelengths (what we see as colours). Water absorbs the wavelengths that a
majority of plants use for photosynthesis extremely quickly. This means that
as the depth increases not only does the light penetration decrease, the
quality of the light decreases as well.
o
The salt concentration of the water – Marine organisms are suited to a
specific type of water (ranging from the extremely salty Dead Sea to
freshwater which has almost no salt) and if they were to be placed outside
this they would die (due to osmosis)
o
Temperature – The range of temperature is important as well because
organisms prefer to live in certain temperatures ranging from hot springs
through warm tropical seas to freezing Antarctic oceans.
o
Gas Availability – This ranges from small amounts of gas available in
warmer waters to plentiful amounts of gas in turbulent waters of oceans and
cold streams
Terrestrial – There are several abiotic factors that affect abundance and
distribution of organisms in aquatic environments including:
o
Temperature – Most organisms prefer to live between 0 – 45 degrees
o
Soil composition – Many species only prefer specific soil types.
o
Rainfall patterns – Many organisms will only live in areas where the rainfall
is specific to their needs. If the organisms prefers high rainfall and humidity it
will live in areas where these conditions are prominent.
o
Altitude – increasing altitude results in colder temperatures, reduced rainfall
and decreased pressure which are specific factors that affect the abundance
and distribution of the organism.
o
Availability of salts – in the soil there must be specific salts for the plants.
Plants will only thrive if there are those specific salts available.
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There are also other factors that affect distribution and abundance of both aquatic
and terrestrial organisms including:
o
o
o
o
Availability of resources and Limiting factors – A limiting factor is a
single resource that determines the maximum population of a specific species
in that area. In aquatic environments this could be factors such as food
resources. The amount of food available will determine the abundance of the
organism in that environment.
Competition – Competition for resources from both the same species and
other species for specific resources can alter the abundance and distribution
of that aquatic organism in that particular environment.
Predation – This is when one organism consumes another. If a species has
numerous predators in its environment, its abundance and distribution will
fluctuate.
Ability to mate – This refers to the organisms ability to reproduce efficiently.
If the organism reproduces extremely quickly its distribution and abundance
are likely to rise dramatically whereas if it was the opposite the distribution
and abundance will remain steady.
o
Chemical Factors – such as pH of the soil
o
Dynamic Factors – such as wind speed and patterns, wave action. These are
natural factors that will affect the organism and its environment.

describe the roles of photosynthesis and respiration in ecosystems
Photosynthesis is the process by which plants take carbon dioxide and water and
with the use of sunlight convert it into glucose and oxygen.
6H2O + 6CO2
Light
C6H12O6 + 6O2
Photosynthesis is significant in any ecosystem because it produces the chemical
energy needed for all ecosystems to survive. The ultimate source of all energy on
Earth is the sun. Plants use chlorophyll to capture some of the suns energy in
photosynthesis. This is vital because this energy is then able to flow through the
ecosystem for survival. Thus the ecosystem depends on plants conducting
photosynthesis.
The overall role of photosynthesis is to provide energy for all other organisms in the
ecosystem. The plants conduct photosynthesis to store energy. The plant gets eaten
by an animal and part of the stored energy (about 10%) is passed on to the animal
and so on. In ecosystems there is no re-use of energy. It is either used by the living
thing or lost as heat. Because of this, a continual input of energy is required to keep
living systems functioning and that is the ultimate role of photosynthesis.
Respiration takes place in the mitochondria of all living cells and results in the
release of energy for organisms to use. Glucose if broken down in the presence of
oxygen to produce carbon dioxide and water and in doing so energy is released.
Energy in the form of ATP (adenosine tri-phosphate) is released as heat from this
process and is used for cell functions such as growth, repair and maintenance.
The role of respiration is to remove oxygen from the air, return carbon dioxide to the
air and provide energy for the organism. Thus, organisms respire in order to carry
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out daily activities. The role of respiration is to used the stored energy within an
organism to carry out its daily functions. Without respiration, an ecosystem wouldn’t
function as none of the organisms would be able to use the energy they had stored
which means they would die.
 identify uses of energy by organisms
Majority of the energy in an ecosystem is lost as heat which is beneficial to most
organisms as the cells and enzymes thrive under warm conditions.
Organisms use energy for many purposes including:

o
Synthesis of complex molecules such as proteins, lipids, carbohydrates and
nucleic acids.
o
Growth involving the division, elongation and differentiation of cells
o
Repair and maintenance of damaged or old cells
o
Active transport of materials across cell membranes
o
Functioning of special cells that need extra energy, such as nerves, muscles,
liver etc.
o
Transport of materials within organisms such as in the circulatory systems of
animals
o
Other daily activities such as movement, making sound, producing heat and
producing light (called bioluminescence).
Identify the general equation for aerobic cellular respiration and outline
this as a summary of chain of biochemical reactions
Aerobic cellular respiration is respiration that occurs under the presence of oxygen.
Respiration involves a series of chemical reactions. It is a controlled process,
occurring as a sequence of about 50 different chemical reactions, each one catalyzed
by a different enzyme. Energy is released slowly in small amounts. The chemical
energy is stored in the bonds of complex organic molecules and is released when
these bonds are broken. The energy is transferred to the energy carrier molecule
ATP.
ATP is the energy store of the cell. When the energy is available , ADP (adenosine)
di-phosphate) collects it. When the energy is needed, ATP supplies it. In fact,
respiration can be thought of as the process by which ATP molecules are made in a
cell.
ADP + P + glucose + oxygen many reactions carbon dioxide + water + ATP
38ADP + 38P + C6H12O6 + 6O2 Many reactions 6H2O + 6CO2 + 38ATP
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There are two stages of respiration:
Stage 1 - This occurs in the cytoplasm of the cell and results in the splitting of the 6carbon sugar molecules into 3-carbon molecules (called pyruvates), and two
molecules of ATP are gained by the cell. This is anaerobic respiration.
Stage 2 - this occurs in the mitochondrion of the cell and it involves the use of
oxygen. This results in the complete breakdown of the pyruvate into carbon dioxide
and water. This breakdown is done by enzymes. A total of 36 ATP molecules are
gained in this process. The energy is released gradually. This is aerobic respiration.
Overall, 38 molecules of ATP were released. Only 40% of the glucose is converted to
ATP. The rest is lost as heat.
There is also another type of respiration called ANAEROBIC CELLULAR
RESPIRATION. In this type of respiration there is not a sufficient amount of oxygen
present. Anaerobic cellular respiration does not produce the high levels of ATP has
aerobic respiration does because there is no oxygen to assist the release of ATP
when glucose is converted to carbon dioxide and water. Anaerobic cellular respiration
releases only 2 ATP molecules in total.
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