Environmental studies

Energy flow and nutrient cycles

The sun is the source of all natural energy on earth

Plants are able to absorb the energy from the sun

by using a special pigment called chlorophyll.

The chlorophyll is found in an organelle called

chloroplast.

The plant uses some of this energy for its own activities

like growth, production of organic compounds and for chemical

reactions.

The rest of this energy is converted to chemical potential energy and stored in the plant.

Energy Flow

Plants are able to trap enough energy from the sun for their own needs and for the needs of the animals.

This is possible because there are more plants than animals.

When herbivores feed on the plants this stored energy is transferred to the animal’s body.

The animals uses some of the energy for their own activities like growth, movement, respiration.

The rest of the energy is stored in the animals tissues.

Animals will use more energy than plants because they are more active.

Energy flow:

The energy is transferred from animal to animal as the animals feed on each other.

The energy is transferred from the herbivores and or omnivores to the carnivores.

When the plants and animals die the energy still trapped in their bodies are released by the decomposers.

The decomposers release the energy when they break down the dead plant and animal matter.

This energy can be used by other plants and animals.

This flow of energy from one living organism to the next is called energy flow.

Energy flow

A food chain shows the transfer of energy from one organism to the next: grass worm spider frog

In reality a food chain never exists alone. This is because a

single organism may provide food to many different organisms.

Therefore in nature there is usually a number of interwoven food

chains: called a food web.

Food chain:

Try to complete this food chain

Something for you to do

A trophic level may also be called a feeding level.

All the plants and animals in any habitat can be grouped into trophic levels.

There are generally four trophic levels.

Tophic level 1 is made up of all the green plants because they are able to make their own food by photosynthesis. These plants also have the highest total energy.

Trophic level 2 is made up of all the organisms that feed on the green plants. They have a slightly lower energy than the green plants. These organisms are the herbivores .

Trophic levels

Trophic level 3 is made up of all the organisms that feed on the herbivores in trophic level 2.

The organism that make up this trophic level are carnivores. This trophic level may also be made up of omnivores.

In this trophic level organisms have less energy than the herbivores and of trophic level 2.

Trophic level 4 is made up of organisms that feed on the carnivores in trophic level 3.

The carnivores found in trophic level 4 are called top carnivores. They have less energy than the carnivores of trophic level 3.

This trophic level can be made up of carnivores and omnivores.

Trophic levels

Trophic level 1: Producers

Trophic level 2: Primary consumers

Trophic level 3: Secondary consumers

Trophic level 4: Tertiary consumers

Can you name the organisms found in the different trophic levels?

To which trophic level does the producer belong?

Name all the trophic levels that the omnivores can be a part of.

Something to do

The decomposers can occur at any trophic level depending on which organism they are breaking down.

In a food chain trophic levels occurring in the following order:Trophic level 1 trophic level 2 trophic level 3 trophic level 4

Where do the decomposers fit?

1. Which food chain correctly describes the flow of

energy in an ecosystem?

A. grass-->cow-->human

B. caterpillar-->leaf-->human

C. cow-->grass-->human

D. leaf-->bird-->caterpillar

Something for you to do

2. Rabbits eat grass and other plants to survive, but

they do not eat animals. What kind of animal are

rabbits?

A. decomposers

B. carnivores

C. producers

D. herbivores

3. How do decomposers help other organisms in

an ecosystem?

A. They are food for consumers.

B. Through photosynthesis they can make

their own food.

C. They return nutrients back to the soil.

D. They eat plants

4. In what order do a hawk, grass, and rabbit form

a food chain in a meadow?

A. hawk-->grass-->rabbit

B. grass-->hawk-->rabbit

C. rabbit-->grass-->hawk

D. grass-->rabbit-->hawk

5. Which of the following lists only consumers?

A. hawks, lizards, chipmunks

B. acorns, squirrels, rabbits

C. grass, chipmunks, eagles

D. mice, squirrels, grass

1. A

2. D

3. C

4. D

5. A

Solution:

An ecological pyramid is a graphical representation of the energy or matter contained within each trophic level.

Ecological pyramids

From the diagram on the previous slide it is clear that there are 3 different types of ecological pyramids.

1. Pyramid of energy

2. Pyramid of numbers

3. Pyramid of biomass.

Ecological pyramids

Pyramid of energy

This pyramid shows the amount of available energy at each trophic level

The available energy gets less and less as we move up the pyramid.

This means that the producers have the most available energy while the tertiary consumer has the least.

Therefore the amount of energy available in each trophic level is less than the previous trophic level.

The decreasing available energy results in the pyramid shape.

Pyramid of energy

There are 3 reasons for the decrease in available energy:

The organisms use some of the energy for their own activities.

Some energy is lost because the organism does not consume the entire resource.

Some energy is lost as faeces and urine.

Why does the energy decrease at each trophic level?

Pyramid of numbers This pyramid shows

the number of organisms in each trophic level.

Pyramid shape exists because the number of organisms decreases in each trophic level from the bottom to the top.

Inverted pyramid of numbers

Sometimes the pyramid of numbers can be inverted.

This can be because a single plant

( e.g. fruit seeds) can provide food for many organisms.

Similarly many organisms can provide food for a single organism.

Rose bush

aphids

bird

Pyramid of biomassThis pyramid shows the total mass of organisms in each trophic level.

This pyramid can also become inverted, if the ecosystem becomes imbalanced.

Study the following paragraph and answer the questions

that follow:

A baboon was seen lifting stones and looking for food in a patch of

grass. The baboon found some beetles and ate them. Every so often, the baboon would scratch himself, because he had a large number of fleas on his body

1. Draw a food chain which clearly illustrates the feeding relationships described above. [4]

Assessment task

2. Draw a pyramid of numbers to illustrate the description above. [4]

3. What is a pyramid of numbers? Comment on the shape of this pyramid of numbers in your

answer. [3]

4. Draw a food web which illustrates a feeding relationship between at least ten organisms. Include the four organisms in the food chain you drew in number 1. [10]

5. Choose one organism in the food web you drew in number 4 and draw a circle around this organism. Imagine that this organism was eliminated (removed) completely from the feeding relationship. What impact would this have on the rest of the food web? Explain fully. [4]

[25 marks]

1. Grass Beetle Baboon Flea

2. pyramid

Solutions

3. A pyramid of numbers shows the relative numbers of

organisms ✓ in a particular food chain; ✓ usually a pyramid has

the smallest portion on top, this one does not. ✓

4. Learner responses will differ. Mark according to the web they

produce. Check that arrows flow in the correct direction (in the

direction of energy flow) and check that links are realistic. One

mark per organism correctly inserted in the web.

5. Learners will vary. However they should indicate that the

ecosystem will become imbalanced. They should indicate how

trophic level before and after the chosen one is altered.

Solutions

Nutrient recycling is the process that ensures that nutrients become available for reuse.

Some examples of these important nutrients are carbon dioxide, water vapour, oxygen, minerals and energy.

Nutrient recycling occurs in the following general way.

Nutrient recycling

During photosynthesis green plants use sunlight, carbon dioxide and water to make food in the form of glucose.

When the primary consumers (herbivores and omnivores) feed on the green plants the food is transferred to their bodies.

Remember this food contains carbon dioxide, water, and

energy.

When the secondary consumer (carnivores) feed on the primary consumer the food is transferred to their bodies from the primary consumer.

Nutrient recycling occurs in the following general way.

When any of these organisms die (producer, primary, secondary or tertiary consumer) their bodies are broken down by decomposers.

Decomposers release nutrients so that they can be reused.

The decomposers releases carbon dioxide and energy in the form of heat into the atmosphere and water vapour and mineral salts into the soil.

Without nutrient recycling important nutrients will become exhausted.

Role of decomposers in nutrient recycling

3 main cycles: water, energy and nutrient cycles

Inorganic substances are re-used and recycled as new elements can not be created

We need these nutrients for metabolism and to renew our bodies

Basically, every atom in your body has been part of another living body (possibly from all over the world)

Some of your atoms may have been in a dinosaur

Nutrient recycling

Water cycle

Water cycle ensures that water supply is never exhausted.

The water cycle occurs as follows:

Water vapor from the atmosphere falls to the ground.

This water vapors can fall to the earth as rain, dew, frost, mist and hail: precipitation.

Some of this water reaches the soil and then runs off into the rives and streams

Some of this water will also reach the dams, lakes and oceans.

Water cycle

The ground water may soak into the soil.

One of two things may happen to this water:

It may remain in the soil as capillary water around the soil particles or it may reach the water table.

Plants absorb the water from the soil using their roots.

Animals obtain their water from the rivers, lakes and streams or from the food they eat.

This water is then used by plants and animals for various functions.

Plants lose some of the water as water vapour during the process of transpiration.

Animals also lose some water as water vapour during the process of respiration.

Animals also lose water during sweating and breathing.

Water cycle

When the ground, air or water surface becomes heated the water changes from a liquid into a gas.

This gas is called water vapour.

The process by which water changes from a liquid to a gas is evaporation.

The water vapour then rises into the atmosphere with the warm air that rises.

As the water vapour goes to higher altitudes cooling of this water occurs.

Evaporation

As the water vapour goes to higher altitudes cooling of this water occurs.

When the water vapour cools it changes from a gaseous state to a liquid state: condensation.

This results in the formations of clouds.

The air becomes saturated when more and more water collects at this level, clouds will form.

The clouds then become heavy ( the clouds are holding the maximum amount of water in a specific volume at a specific temperature.)

Then the water begins to fall as precipitation.

The cycle is completed and begins all over again.

Condensation

Water is an inorganic compound made up of hydrogen and oxygen.

The elements hydrogen : oxygen occur in the following ratio 2: 1.

Two thirds of the earth’s surface is made up of water.

About 70 to 80% of the protoplasm of both plant and animal cells is made up of water.

Water is also regarded as a universal solvent.

It has many important uses in organisms and in nature.

It is the medium of most chemical reactions.

Importance of water:

It is used to transport nutrients, gases and waste products in both plants and animals.

It is also a habitat for plants and animals.

It is a reactant in photosynthesis.

It is a by-product during the process of cellular respiration in both plants and animals.

Water is used to cool the body down.

Water is also used during digestion of food.

Importance of water:

The concentration of carbon in the air 0,03%.

The carbon in the form of carbon dioxide is used by green plants to manufacture food by photosynthesis.

Carbon dioxide is released by both plants and animals during the process of cellular respiration.

While photosynthesis uses up carbon dioxide, cellular respiration releases it.

In this way the levels of carbon dioxide are maintained.

Carbon cycle

Carbon cycle

Carbon dioxide is absorbed by green plants from the atmosphere and water to be used during photosynthesis.

The carbon is used to make glucose and then other organic material.

When the consumers (herbivores, omnivores and carnivores) feed on the plant that organic material is transferred to the to these consumers.

The carbon is now present in the bodies of both plants and animals.

Carbon cycle

The carbon occurs in organic compounds such has carbohydrates, proteins, lipids, hormones, pigments, enzymes etc.

REMEMBER: organic compounds contains carbon.

During cellular respiration all living organisms release carbon dioxide.

The carbon dioxide is released into the water or atmosphere.

When plants and animals die decomposers break down their bodies and release carbon dioxide into the atmosphere or soil.

Carbon cycle

Sometimes carbon dioxide becomes trapped in the bodies of dead plants and animals when these organisms do not decompose.

These dead bodies become compressed and form fossil fuels such as coal, oil and gas.

When these fossil fuels are burnt the carbon dioxide trapped in them is released.

The cycle then starts over.

Carbon cycle

The Carbon Cycle Step 1

Carbon enters the atmosphere as carbon dioxide from respiration (breathing) and combustion (burning).

The Carbon Cycle Step 2

Carbon dioxide is absorbed by producers (life forms that make their own food e.g. plants) to make carbohydrates in photosynthesis . These producers then put off oxygen.

Step 3

Animals feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide formed during respiration. The animals and plants eventually die.

Step 4

The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion.

Carbon dioxide traps heat in the Earth’s atmosphere and keeps Earth warm.

This is called the greenhouse effect.

Too much carbon dioxide in the atmosphere means the Earth will heat up too much and cause changes in the global climate.

Carbon Cycle

Oxygen is required by both plants and animals for cellular respiration.

Oxygen is found in the atmosphere and dissolved in the water.

The concentration of oxygen in the atmosphere is 21%. Oxygen is also found in the lithosphere and biosphere.

Oxygen cycle

Oxygen in the water and

atmosphere is

Used by plants and animals

during cellular respiration to

Release carbon dioxide which

enters the water and

atmosphere

Carbon dioxide is used by plants

during photosynthesis

To release oxygen

Oxygen cycle

Combustion of Fossil fuels

Oxygen found in both the atmosphere and water is used by both plants and animals during cellular respiration to release the energy trapped in food.

Oxygen is also used during the combustion of fossil fuels.

The levels of oxygen decreases.

Both combustion and cellular respiration releases carbon dioxide .

This carbon dioxide is used by plants during photosynthesis to make organic compounds.

During photosynthesis oxygen is released and the levels of oxygen return to normal.

The cycle begins once more.

Oxygen cycle

The Atmosphere (air)

The atmosphere carries a small quantity of all oxygen, only about 0.35% of the entire earth’s oxygen. In the atmosphere, oxygen is released by the process known as photolysis. Photolysis happens when the ultraviolet radiation of sunlight breaks apart oxygen-containing molecules such as nitrous oxide and atmospheric water to release free oxygen. The surplus oxygen recombines with other oxygen molecules to form ozone while the rest is freed into the atmosphere. Ozone is the layer that helps to shield the Earth from the dangerous ultra violet rays.

Photosynthesis is responsible for the formation of the atmosphere.

Biosphere The biosphere carries the smallest quantity of all earth’s oxygen,

about 0.01%. In the biosphere, the major oxygen cycles are photosynthesis and respiration. In these two processes of the oxygen cycle, it is interconnected with the carbon cycle and the water cycle. During photosynthesis, plants and planktons use sunlight energy, water, and carbon dioxide to make food (carbohydrates) and release oxygen as a by-product. As such, plants and planktons are the main producers of oxygen in the ecosystem. They take in carbon dioxide and give out oxygen. Plants are estimated to replace about 99% of all the oxygen used.

On the other hand, respiration happens when humans and animals breathe in oxygen which is used during metabolism to break down carbohydrates and exhale carbon dioxide as a by-product. Such free carbon dioxide is then released into the environment and is used by plants and planktons during photosynthesis to give out molecular atmospheric oxygen, thus completing the oxygen cycle. Therefore, suffice is to say that oxygen enters organisms in the biosphere through respiration and is expelled through photosynthesis in a process that is interconnected with the carbon cycle plus the water cycle.

The Lithosphere (Earth’s Crust)

The lithosphere carries the largest quantity of all earth’s oxygen, about 99.5%, because it is a constituent of the earth’s lands, soils, organic matter, biomass, water, and rocks. Mostly, these constituents of the earth fix oxygen in mineral chemicals compounds such as oxides and silicates. The process is natural and happens automatically as the pure mineral elements absorb or react with the free oxygen. It happens similar to the manner in which iron picks up oxygen from the air, resulting in the formation of rust (iron oxides).

As such, during chemical reactions and some weathering processes, a portion of the trapped oxygen in the minerals is released into the atmosphere. Also, as animals and plants draw nutrient minerals from rocks, organic matter, or biomass, some of the trapped oxygen is freed in the process. Dissolved oxygen is also present in water system which is essential for the survival of aquatic life forms. As a result, these processes combined gives rise to oxygen cycle in the biosphere and lithosphere.

About 79% of the atmosphere is made up of nitrogen.

Nitrogen is required to manufacture proteins by both plants and animals.

Plants cannot absorb nitrogen as it occurs in the atmosphere.

The nitrogen must first be converted to nitrates before the plants absorbs it.

Animals obtain their nitrogen when they feed on plants or feed on animals that feed on plants.

Nitrogen cycle

Since plants can only absorb nitrogen in the form of nitrates, atmospheric nitrogen must first be converted into nitrates before it is absorbed by the plants.

This conversion can take place in 3 ways:

1. Lightening can convert the nitrogen into nitrate.

2. The root nodule bacteria found in the roots of some plants may convert nitrogen gas into nitrates which is absorbed by the plant. The plant in turn provides the bacteria with food.

3. Nitrogen fixing bacteria found in the soil converts the nitrogen in the soil into nitrate which then can absorbed by the plants.

Nitrogen cycle

Plant then uses the nitrogen to manufacture proteins.

Nitrogen is transferred to animals when they feed on plants or animals that have fed on plants.

When the plants and animals die the decomposer breaks down the dead and decaying matter to release ammonia.

The ammonia is converted into nitrites by nitrifying bacteria.

The nitrifying bacteria than converts the nitrates into nitrates.

Nitrogen cycle

One of two things may happed to the nitrates:

It maybe absorbed by plants to manufacture proteins.

Denitrifying bacteria may convert the nitrates back into nitrogen and the cycle continues.

Nitrogen cycle

Colourless, odourless, tasteless, non-toxic, and inert gas which forms about 78 percent of the Earth's atmosphere by volume and about 77 percent by weight, and it maintained at this level by the nitrogen cycle. It is an essential component of the tissue (as amino acids and nucleic acids) of all animals and plants which derive it from the soil, fertilizers, or through the nitrogen cycle. For industrial uses nitrogen is obtained from the liquefaction and fractional distillation of air, mainly for manufacturing ammonia, dyes, explosives, and fertilizers.

What is Nitrogen

In general, the nitrogen cycle has five steps:

Nitrogen fixation (N2 to NH3/ NH4+ or NO3-)

Nitrification (NH3 to NO3-)

Assimilation (Incorporation of NH3 and NO3- into biological tissues)

Ammonification (organic nitrogen compounds to NH3)

Denitrification(NO3- to N2)

Nitrogen Fixation

Is an anaerobic (without oxygen) process in which atmospheric nitrogen (N2)is reduced to NH3. Bacteria are responsible for this process. Bacteria in terrestrial and aquatic(water) environments participate in this process. These organisms must have a special enzyme known as dinitogenase to be able to to this.

Plants cannot use the nitrogen in our atmosphere without the assistance of nitrogen-fixing bacteria. These bacteria reduce atmosphereic nitogento ammonia, which can be used to make other biological compounds. The plants do not use the ammonia directly, but it's a product of the waste.

The chemical processes by which atmospheric nitrogen is assimilated into organic compounds, especially by certain microorganisms as part of the nitrogen cycle.

Process by which free nitrogen (N2) is extracted from the atmosphere and converted (fixed) into nitrogen compounds which are plant nutrients (fertilizer). In nature, this process is carried out by certain bacteria (present in the root nodules of legumes such as beans and peas), blue-green algae, and the lightning flash.

Nitrification

Plants receive the components of the "fixed" nitorgen using nitrates in the soil to provide the nutrients they need. Bacteria such as Nitrosomonas, Nitrococcus, and Nitrobacter participate.

Nitrification involves two steps. First, the ammonium ion (NH4+) is oxidized into NO2-. Then, this compound is further oxidized into NO3-. Again, bacteria in the soil participate in both processes.

Oxidation of ammonium (NH4+) ions into nitrite (NO2-) ion and then nitrate (NO3-) ions by microorganisms in soil and water. Nitrate ions are absorbed by the plants as essential nutrients and, with the help of oxygen, converted (synthesized) into plant protein (amino acids). See also nitration.

Assimilation

ASSIMILATION

Plant roots assimilate Nitrogen mainly in the form of nitrates while animals assimilate their nitrogen by eating the plants.

Assimilation is the process by which plants and animals incorporate the NO3- and ammonia formed through nitrogen fixation and nitrification. Plants take up these forms of nitrogen through their roots, and incorporate them into plant proteins and nucleic acids. Animals are then able to utilize nitrogen from the plant tissues.

Ammonification

Ammonia is formed in the soil by the decompostion of plants and animals and by the release of animal waste

Assimilation produces large quantities of organic nitrogen, including proteins, amino acids, and nucleic acids.

Ammonification is the conversion of organic nitrogen into ammonia. The ammonia produced by this process is excreted into the environment and is then available for either nitrification or assimilation.

Denitrification

This is the reduction of nitrates to gaseous nitrogen. Denitrifying bacteria perform almost the reverse of the nitorgen fixing bacteria.

This is the reverse process of nitrification. During denitrification nitrates are reduced to nitrites and then to nitrogen gas and ammonia. Thus, reduction of nitrates to gaseous nitrogen by microorganisms in a series of biochemical reactions is called “denitrification“.

Step by step Neither plants or animals can

obtain nitrogen directly from the atmosphere. Instead, they depend on a process known as NITROGEN FIXATION. Key players in this process are legumes and the SYMBIOTIC BACTERIA which are associated with the legume's root nodules. These bacteria are known as nitrogen-fixing bacteria. These organisms convert nitrogen in the soil to ammonia, which can then be taken up by plants. This process also occurs in aquatic ecosystems, where cyanobacteria participate.

After nitrogen has been fixed, other bacteria convert it into nitrate, in a process known as NITRIFICATION. In the first step of this process, Nitrosomonas convert ammonia into nitrite, and in the second step, nitrite is converted into nitrate, by Nitrobacteria. This nitrate is then consumed by plants. ASSIMILATION

The final aspect of the nitrogen cycle is the process of AMMONIFICATION AND DENITRIFICATION. This process is performed by a variety of microscopic bacteria, fungi, and other organisms. Nitrates in the soil are broken down by these organisms, and nitrogen is released into the atmosphere. This complete the cycle.

The Earth is becoming warmer and warmer

We see evidence of global warming everywhere (melting ice, floods, fires, heat waves)

When things go wrong – climate change

Greenhouses gases in the atmosphere are increasing.

Main culprit is carbon dioxide

Humans are producing more carbon dioxide than can be absorbed (only about 40% is being absorbed)

Dominant source of carbon emissions comes from the use of fossil fuels such as oil and coal

Causes of climate change

Fossil fuels contain sulphur

When you burn fossil fuels the sulphur is released and combines with oxygen to form sulphur dioxide.

Sulphur dioxide is poisonous

When sulphur dioxide dissolves in rain the pH drops from just below 7 to 4.

Acid rain washes nutrients out of the soil

The ions and nutrients are washed into lakes and rivers where it can kill many plants, animals and fish

Acid Rain

The flow of energy from one living organism to the next is called energy flow.

A food chain shows the transfer of energy from one organism to the next organism.

A trophic level can also be called a feeding level.

An ecological pyramid is a graphical representation of the energy or matter contained within each trophic level.

Pyramid of energy shows the amount of available energy at each trophic level

TERMINOLOGY

Pyramid of numbers shows the number of organisms in each trophic level.

Pyramid of biomass shows the total mass of organisms in each trophic level.

Nutrient recycling is the process that ensures that nutrients become available for reuse.

Precipitation is when water vapors can fall to the earth as rain, dew, frost, mist and hail.

The process by which water changes from a liquid to a gas is called evaporation.

Condensation is when the water vapour cools it changes from a gaseous state to a liquid state.

Terminology

Water is an inorganic compound made up of hydrogen and oxygen.

Nitrogen fixing bacteria converts the nitrogen in the soil into nitrate which then can absorbed by the plants.

The nitrifying bacteria converts the nitrates into nitrates.

Denitrifying bacteria converts the nitrates back into nitrogen and the cycle continues.

Terminology