Unit 4

Andy Todd

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IGCSE BIOLOGY

Unit 4

Ecology &

The Environment

Unit 4

Andy Todd

Biology Notes: Unit 4: Ecology & The Environment

Contents:

A: The Organism in The Environment

B: Feeding Relationships

C: Cycles Within Ecosystems

D: Human Influences on The Environment

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A: Organisms in The Environment

Students will be assessed on their ability to:

4.1 understand the terms population, community, habitat and ecosystem

4.2 recall the use of quadrats to estimate the population size of an organism in two different areas

4.3 describe the use of quadrats as a technique for sampling the distribution of organisms in

their habitats.

Definitions of Key Terms

- Ecology – the study of the inter-relationship of organisms and their environment

- Ecosystem – a community of species and their environment

- Environment – the physical features of an area (and sometimes the living creatures

that inhabit it)

- Community – the different species in one area

- Species – one type of organism

- Population – the number of a particular species in an area

- Niche (of an organism) – The position of an organism in the environment

- Habitat (of an organism) – where an organism lives

Quadrats and Sampling

Definition of quadrat: a square made of metal, wood, or plastic used for sampling and

hence estimating the number of species (usually plants) in an area

One would use a quadrat by placing it randomly a number of times in an area and

recording the number of a species in that area

Results of each quadrat placement are combined and then averaged

If the area of the measured region is known an estimate can be made of the population

size of that particular species

This process is called sampling because you are only taking a sample of the region

It is a lot simpler than try to count every species in that area

This process works best if:

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o Quadrat placement is entirely random (to increase accuracy)

o Lots of samples are taken (to increase reliability)

o The plants investigate are reasonably spread out (to increase accuracy)

Another way of using a quadrat is to create a transect

A transect is when a quadrat is placed at regular intervals along a line to show how a

habitat changes

Point quadrats – have 100 pins. Drop the pins and count what each pin touches

(include bare earth)

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B: Feeding Relationships

Students will be assessed on their ability to:

4.4 recall the names given to different trophic levels to include producers, primary, secondary

and tertiary consumers and decomposers

4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of

biomass and pyramids of energy transfer

4.6 understand the transfer of substances and of energy along a food chain

4.7 explain why only about 10% of energy is transferred from one trophic level to the next.

Feeding Relationships

Food Chains:

Demonstrate how living things get their food and energy

In a food chain, arrows always point towards the living thing that’s taking the energy

Some food chains start with the Sun, others with the producer

Steps in the Food Chain:

1. Producers – Green plants that use photosynthesis to convert energy from the sun into

food

2. Primary Consumers – Animals that eat plants (or parts of a plant) – aka herbivores

3. Secondary Consumers – Animals that consume other animals – aka

carnivores/predators

4. Tertiary Consumers – Animals that eat secondary consumers – also

carnivores/predators

5. Quaternary consumers (sometimes) – Animals that eat the tertiary consumers

Animals that eat both plants and animals (like humans) are called omnivores

Most food chains end with a secondary or tertiary consumer

It is a cycle because eventually all the organisms involved in the food chain will die

and be broken down by bacteria into minerals for plants (producers)

Stages on a food chain are sometimes called trophic levels

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Generic Food Chain:

Producer Primary Consumer Secondary C. Tertiary C. ( Quaternary C.)

Food Webs:

Is different food chains joined together to show the interaction between food chains

If one chain is disturbed, other food chains can be too

Pyramids of Numbers, Biomass and Energy:

Usually food chains begin with numerous organisms and after every trophic level, the

number of organism decreases until the top level is reached

This is because energy is lost at each level by the organisms who consume it

Pyramids of numbers can be drawn to show this phenomenon, with the producers on

the bottom and the top predator at the top

They show the numbers of each type of living thing in a food chain by trophic level

However, sometimes, a lesser number of large producers (like a tree) can be

consumed by many smaller consumers (like caterpillars)

This makes the pyramid inverted, which is unwanted

Pyramids of biomass take the dry mass of living organisms and show the amount

consumed at each level

That way the size of the organisms are considered

They are almost never inverted

However sometimes they can be inverted because of ‘under sampling’ – some

organisms like algae support a larger number of similar sized plankton because of

their short life span and turn over. In this case the pyramid is once again inverted.

Pyramids of energy are never inverted because they show the amount of energy

passing through the system rather than the amount of energy stored at a particular

period

Pyramids of energy take into account time, unlike the other pyramids

This is the most used pyramid by ecologist because it is the most accurate. However,

it is the most complex.

Energy Flow:

Energy is lost along each trophic level. This is due to multiple factors.

From the sun to producers, energy is lost due to factors such as:

o Only a small proportion of the sun’s energy will hit that one producer

o Some energy may be absorbed or reflected by clouds/dust/trees/other plants

o Some energy might hit the ground

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o Some energy will be reflected by the producer itself

o Some energy will pass through the leaves of the producer

From producer to consumer, energy is lost due to factors such as:

o Producer uses some of the energy for respiration

o Not all of the producer is eaten by the consumer

From consumer to consumer, energy is lost due to factors such as:

o Respiration by consumer

o Egestion and excretion by consumer (not all of the food is digested)

The only energy that gets transferred along the trophic levels is the energy used for

growth

This is the main reason why food chains aren’t very long

Only about 10% of energy from each trophic level makes it to the next trophic level.

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C: Cycles Within Ecosystems

Students will be assessed on their ability to:

4.8 describe the stages in the water cycle, including evaporation, transpiration,

condensation and precipitation

4.9 describe the stages in the carbon cycle, including respiration, photosynthesis,

decomposition and combustion

4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing

bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names

of bacteria are not required).

Cycles within Ecosystems:

Water Cycle:

Water is essential for life

Water is constantly recycled in the world

Most of the world’s water is in the oceans

Some of it evaporates into the atmosphere

Eventually that water falls as precipitation

Some falls on land, some falls back into the ocean

The water that falls on land will drain into rivers that return to ocean

Some water is used by plants and animals

Water is returned from plants by transpiration

The 3 main ways water is recycled:

o Evaporation

o Precipitation

o Transpiration

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Carbon Cycle:

Carbon is necessary because:

o Plants use it for photosynthesis

o Animals uses carbon compounds from plants to grow and respire

Carbon is most prevalent in the atmosphere as carbon dioxide

Carbon dioxide is a waste product of respiration and is released when animals and

plants remains decay and when combustion (the burning of wood, peat or fossil fuels)

occurs

The only way carbon dioxide is taken out of the atmosphere is by plants for

photosynthesis

Carbon dioxide re-enters the atmosphere by respiration of animals, plants and soil

organisms, and combustion

Dead plants and animals are decayed to make organic wastes which can turn into

fossil fuels (which in term can be combusted)

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Nitrogen Cycle:

Nitrogen is necessary for living things to make proteins

Although atmosphere contains 71% nitrogen gas, nitrogen gas is very unreactive and

cannot be used by plants

Instead, plants must gain nitrogen in the form of nitrates from the soil and animals eat

plants to gain the nitrogen (proteins) that the plants acquired

The process of getting nitrogen into nitrates is called nitrogen fixation, which can

occur in three ways:

o Lightning – the energy causes nitrogen to react with oxygen and form nitrates

o Nitrogen fertilisers – the Haber process is used industrially to make

fertilisers with ammonia that turns into nitrites, which then gets turned into

nitrates

o Nitrogen-fixing bacteria- turn nitrogen cause into nitrogen compounds which

become nitrates

o

Four kinds of bacteria are involve in the nitrogen cycle:

o Decomposers – decompose urea and dead animals and plants into ammonia

o Nitrifying bacteria – turns ammonia and nitrites into nitrates

o Nitrogen-fixing bacteria – turn nitrogen gas in the atmosphere into nitrogen

compounds like nitrates

o Denitrifying bacteria – turns nitrates back into nitrogen gas. Serve no benefit

to living organisms

Nitrogen-fixing bacteria live in soil and in the nodules on the roots of legume plants.

This is why legume plants are good for putting nitrogen back into the soil. They

plants have a mutualistic relationship with the bacteria (bacteria gets food, plant gets

nitrogen compounds for proteins)

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D: Human Influences on The Environment.

Students will be assessed on their ability to:

4.11 understand the biological consequences of pollution of air by sulphur dioxide and by carbon

monoxide

4.12 recall that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse

gases

4.13 understand how human activities contribute to greenhouse gases

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect

and that this may lead to global warming and its consequences

4.15 understand the biological consequences of pollution of water by sewage including

increases in the number of microorganisms causing depletion of oxygen

4.16 understand that eutrophication can result from leached minerals from fertiliser

4.17 understand the effects of deforestation, including leaching, soil erosion, disturbance of the

water cycle and of the balance in atmospheric oxygen and carbon dioxide.

Human Influences on the Environment

The Greenhouse Effect:

Caused by high levels of greenhouse gases (water vapour, carbon dioxide, nitrous

oxide, methane and CFCs)

Due to burning of fossil fuels, removal of rainforests, and increase of farming

livestock

Water vapour, carbon dioxide and methane naturally act as insulating layer for the

planet

Short-wave radiation enters the atmosphere and warms the Earth. The earth then

gives off the heat as long-wave radiation

Greenhouse gases allow short-wave radiation through, but trap some long-wave. This

is important for life on earth

However, the increasing levels are trapping more heat than normal

This is resulting in an increase in global temperature (global warming), rising sea

levels (as polar ice caps melt), and freak weather (floods, hurricanes, etc.)

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Air Pollution

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Carbon Dioxide:

Def: a colourless, odourless, poisonous gas, which can be formed by burning fossil fuels

with an insufficient supply of air

The main source of CO is car engines

Modern cars are now fitted with catalytic converters that oxides carbon monoxide, to

make carbon dioxide

Health Effects:

CO permanently bonds to haemoglobin in red blood cells to make

carboxgyhaemoglobin

Therefore the oxygen-carrying capacity of the red blood cells is reduced

Therefore supply is reduced and the heart is strained

Can be a problem for people with cardiovascular disease

Only leaves a person’s blood system when blood is replaced after a few months

Suphur Monoxide: Sulphur dioxide (SO2) has long been recognised as a pollutant because of its role, along with

particulate matter, in forming winter–time smog. Studies indicate that SO2 causes nerve stimulation in the lining of the nose and throat. This can cause irritation, coughing and a feeling of chest tightness, which may cause the airways to narrow

Another pollutant associated with climate change is sulfur dioxide, a component of smog.

Sulfur dioxide and closely related chemicals are known primarily as a cause of acid rain.

But they also reflect light when released in the atmosphere, which keeps sunlight out and

causes Earth to cool. Volcanic eruptions can spew massive amounts of sulfur dioxide into

the atmosphere, sometimes causing cooling that lasts for years. In fact, volcanoes used to

be the main source of atmospheric sulfur dioxide; today people are.

Industrialized countries have worked to reduce levels of sulfur dioxide, smog, and smoke

in order to improve people's health. But a result, not predicted until recently, is that the

lower sulfur dioxide levels may actually make global warming worse. Just as sulfur

dioxide from volcanoes can cool the planet by blocking sunlight, cutting the amount of

the compound in the atmosphere lets more sunlight through, warming the Earth. This

effect is exaggerated when elevated levels of other greenhouse gases in the atmosphere

trap the additional heat.

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Acid Rain:

Def: Rain that has a pH of below 5.3

Sulphur dioxide comes from sulphur impurities in the fossil fuels that are burned

Nitrogen oxide is created from a reaction between the nitrogen and oxygen in the air,

caused by the heat of burning the fuels

Both can combine with water vapour in the air to form sulphuric acid and nitric acid,

which forms acidic rain

Effects of Acid Rain:

Harms plants and animals that take in the water

Washes ions out of the soil, taking away minerals from plants

Washes aluminum compounds out of the soil and into rivers and lakes, poisoning fish

Erosion of stone buildings and statues

Erosion of tree branches and leaves, decreasing photosynthesis

Presence of acid in lakes can causes mucus to form on fish gills, which can suffocate

the fish

Preventing Acid Rain:

Fitting catalytic converters stops the emissions of the gases from cars

Sulphur impurities can be reduced by treating fuels and adding acid gas scrubbers

(neutralise the acid)

However, this can be expensive

Sewage Pollution:

Some sewage in large areas can provide nutrients for ecosystems

Too much can cause excessive growth of plants (esp. algae) in rivers lakes, and costal

waters

The plants can grow over the surface of the water and block out light so that plants

under

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Eutrophication

Increases in nutrient levels in water from run off from agricultural land leads to boom growth of algae – Pond weed This vegetation results in huge quantities of oxygen being consumed from the water and leads to death of aquatic life.

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Deforestation

Forests are cut down for many reasons, but most of them are related to money or to

people’s need to provide for their families. The biggest driver of deforestation is

agriculture.

Logging operations, which provide the world’s wood and paper products, also cut

countless trees each year. Loggers, some of them acting illegally, also build roads to

access more and more remote forests—which leads to further deforestation. Forests are

also cut as a result of growing urban sprawl.

Deforestation has many negative effects on the environment. The most dramatic impact is

a loss of habitat for millions of species.

Deforestation also drives climate change. Forest soils are moist, but without protection

from sun-blocking tree cover they quickly dry out. Trees also help perpetuate the water

cycle by returning water vapor back into the atmosphere. Without trees to fill these roles,

many former forest lands can quickly become barren deserts.

Removing trees deprives the forest of portions of its canopy, which blocks the sun’s rays

during the day and holds in heat at night. This disruption leads to more extreme

temperatures swings that can be harmful to plants and animals.

Trees also play a critical role in absorbing the greenhouse gases that fuel global warming.

Fewer forests means larger amounts of greenhouse gases entering the atmosphere—and

increased speed and severity of global warming.