Energy FlowFood Chains and WebsCarbon Cycle

18.1 What is Ecology?Organisms continually interact with one

another, as well as the surroundingsEcology is the study of these interactionsEcologists study both the living and non-living

(physical) environment The living (or biotic) environment consists of all the

living things that an organism interacts with The non-living (or abiotic) environment consists of

physical factors such as light, water and pH of the soil/water

What are some key ecological terms?1. Habitat2. Population3. Community 4. Ecosystem

What is a habitat?The place where an organism lives is its

habitatFor example, Wading birds called redshanks

live in the mud of the mangrove swamp, so the mangrove swamp is the habitat of the redshanks

What is a population?A group of organisms of the same species

living in a particular habitat make up a population. For example, in the mangrove habitat, all the

redshanks living in that particular mangrove swamp make up a population

Another population is made up of all the mangrove trees living in that particular mangrove swamp

What is a community?All the populations of organisms living and

interacting with one another in a particular habitat make up a community.For example:

The mangrove community is made up of mangrove trees and other plants, animals like redshanks, mudskippers and sand flies, and microorganisms living in the mud of that mangrove swamp

What is an ecosystem?Living organisms interacting with one another

and with their abiotic environment make up an ecosystemFor example:

The ecosystem of mangrove community is made up of all the organisms in the mangrove community and all the physical factors that make up its abiotic environment. These factors include the salt concentration of

seawater, its pH, the temperature , the amount of oxygen dissolved in the mud, the amount of light falling on the trees and the amount of nutrients in the mud

18.2 The Abiotic EnvironmentPhysical features that make up the abiotic

environment include:Light intensityTemperatureAmount of water availableOxygen contentSalinity (salt concentration) of soil or waterpH of soil or water

*** Refer to Discover Biology Textbook Page 305 to 307 for more details

18.3 The Biotic EnvironmentThe living or biotic environment comprises all

the living organism that an organism interacts with in its habitatsAn habitat is the place where an organism lives

e.g a pond, stream, river, forest or desert

Why do organisms affect other organisms?The organisms in any habitat are never

completely independentThe life of each organism depends on and is

influenced by other organisms around itHence the organisms are known to be

interdependent

What is an ecological community?When different populations of plants and

animals live together and interact within the same environment, they make up an ecological community

The various populations in any community live interdependentlyA change in one population affects the

other populations of the community

18.4 The EcosystemAn ecosystem is an ecological system formed

by the interaction of living organisms and their non-living environment

When considering an ecosystem, we are considering both the biotic and the abiotic environments in that

ecosystem.

The EcosystemAn ecosystem uses both energy and inorganic

nutrients

The EcosystemInorganic nutrients, on the other hand, need

not be supplied from outside the ecosystemThey are obtained from the abiotic

environment and flow through the ecosystem in a cycleIn a ‘balanced’ ecosystem, nutrients are

continually recycled and are not lost i.e. nutrient cycling

For example – The Carbon Cycle (Nutrient Cycling)

• Carbon is present in all biological molecules and it is recycled in the following manner:

Atmosphere

1. Photosynthesis

2. Respiration5. Burning of fossil fuels

Plants Animals

3. Dead Organisms4. Fossil Fuels

Energy Flow• Two key process which sustain the ecosystem are

energy flow from the Sun to plants and then to other organisms, and nutrient cycling.

• A terrarium is an example of a mini ecosystem.

How do energy and nutrients flow through an ecosystem?The living organisms in any ecosystems are

made up of producers, consumers and decomposers

Energy and nutrients are transferred from producers to consumers to decomposers through feeding

• The sequence of food transfer from one trophic level to another is called a food chain

• A food chain is a series of organisms through which energy is transferred in the form of food

• A food chain always begins with a producer

Energy Flow – Food Chains

Energy Flow – Trophic LevelsAt the base of all food chains are the producers – producers

convert energy from the sun or light energy into chemical energy and store it as food during photosynthesis.Producers are mainly green plants, but algae

and certain bacteria that can photosynthesize are also producers

Producers are the only organisms that can manufacture or produce complex organic food from inogranic raw materials

Energy Flow – Trophic Levels• All organisms above the producers are consumers.• Consumers obtain their energy by feeding on other organisms

• Herbivores feed directly on plants or algae (Primary Consumers)

• Carnivores feed on other consumers (e.g herbivores) (Secondary Consumers)

• Carnivores that feed on other carnivores are known as Tertiary Consumers

• Decomposers obtain their energy by breaking down dead organisms, faeces and excretoary products

• When the dead organisms and waste matter are broken down, the materials locked up in them are released

• These materials, such as inorganic nutrients, carbon and nitrogen compounds, return to the physical environment and are used again by green plants

• Examples of decomposers: Fungi, bacteria and earthworms

• In a community, food chains are interlinked to form a food web

Energy Flow – Food Web

Food Chain and Food Web

April 18, 2023

aphid ladybird

Producer(green plant)

Primary Consumer(herbivore)

Secondary Consumer(carnivore)

Tertiary Consumer(carnivore)

green plant

aphid ladybird

grasshopper

spider bird

caterpillar

A food chain:

A food web:

Ecological PyramidsWe can compare the trophic levels in a food

chain using ecological pyramidsThere are 3 types of ecological pyramids:

1. Pyramid of numbers2. Pyramid of biomass3. Pyramid of energy

• The pyramid of numbers allows us to compare the number of organisms present in each trophic level at a particular time

• The length (or area) of the rectangle represents the number of organisms for each species

The Pyramid of Numbers

• A pyramid of biomass allows us to compare the mass of organisms present in each trophic level in the area at a particular time

• The pyramid of biomass is constructed based on the dry mass (mass without water content) of organisms in each trophic level at any one time

The Pyramid of Biomass

Variations in ecological pyramidsMost ecological pyramids are pyramid-

shaped, but there are important exceptions1. A pyramid of numbers may be upside down

or inverted if: Organisms of one trophic level are parasitic on

organisms of another trophic level Many small organisms of one trophic level feed on a

large organism of another trophic level. For example: Tree Aphid Protozoa

Example of inverted pyramid of numbers

Parasitic Protozoa

Aphids

Tree

In this case, the pyramid of numbers is inverted. The bottom of the pyramid is represented by only one tree. Many aphids are parasitic on the tree and many protozoa are parasitic on the aphids

However, the pyramid of biomass remains broad at the bottom and narrow towards the apex (highest point). Refer to the next slide.

Pyramid of Biomass for Tree, Aphid and Protozoa

Parasitic Protozoa

Aphids

Tree

The pyramid of biomass remains broad at the bottom and narrow towards the apex (highest point) for the same food chain.

This is because one tree has a comparatively large biomass to support the other populations.

Another example of inverted pyramid of numbers• The pyramid may also become inverted if

the producer is too large.• An inverted pyramid of numbers:

Variations in ecological pyramidsMost ecological pyramids are pyramid-

shaped, but there are important exceptions1. A pyramid of numbers may be upside down

or inverted if: Organisms of one trophic level are parasitic on

organisms of another trophic level Many small organisms of one trophic level feed on a

large organism of another trophic level.

2. Pyramids of biomass for rapidly reproducing organisms are also not pyramid-shaped.

Example of inverted pyramid of biomassSince the pyramid of biomass is based on

standing mass (mass at a particular time), it does not take into account the rate of reproduction (productivity) of the organisms

This is a disadvantage when considering organism that reproduce rapidly e.g.Phytoplankton Zooplankton

Small fish

Large fish

Example of inverted pyramid of biomassPhytoplankton are microscopic plant-like organisms that

can make food by photosynthesisZooplankton are microscopic primary consumers that feed

on phytoplanktonThe pyramid below gives the impression that the biomass

of phytoplankton is smaller than that of zooplankton, which is not possible

Phytoplankton

Zooplankton

Small fish

Large fish

Example of inverted pyramid of biomassWhat happens is that the rate of reproduction

of phytoplankton is fast enough to replace the organisms that were eaten by zooplankton

Phytoplankton

Zooplankton

Small fish

Large fish

• The pyramid of energy represents the total energy in the various trophic levels of a food chain

• Unlike the pyramid of biomass, the total energy content in each trophic level over a period of time (i.e. one year) is determined• Rate at which the organisms in each

trophic level reproduce is considered

The Pyramid of Energy

In other words, the pyramid of energy is thus constructed based on the total energy

level in each trophic level over a certain period of time, for example, one year.

• A lot of energy is lost to the environment as food is transferred from one trophic level to the next.

• Energy may be lost to the environment:1. As heat during respiration at every

trophic level2. In uneaten body parts3. Through undigested matter egested by

consumers4. Through waste products excreted by

consumers, for example, urea

The Pyramid of Energy

• A lot of energy is lost to the environment as food is transferred from one trophic level to the next.

• Energy may be lost to the environment:1. As heat during respiration at every trophic

level2. In uneaten body parts3. Through undigested matter egested by

consumers4. Through waste products excreted by

consumers, for example, urea

The Pyramid of Energy

Producer (10000 kJ)

Primary Consumer (1000 kJ)

Secondary Consumer (100 kJ)

Tertiary Consumer (10 kJ)

Lost as energy trapped in uneaten body parts, faeces and excretory products

Heat lost during respiration

• More and more energy is lost as we go down a food chain

• The total energy level is highest at the first trophic level and lowest at the last trophic level

• Hence, a pyramid of energy is always broad at the base and narrow towards the top

The Pyramid of Energy

Producer (10000 kJ)

Primary Consumer (1000 kJ)

Secondary Consumer (100 kJ)

Tertiary Consumer (10 kJ)

Lost as energy trapped in uneaten body parts, faeces and excretory products

Heat lost during respiration

• More and more energy is lost as we go down a food chain

• The total energy level is highest at the first trophic level and lowest at the last trophic level

• Hence, a pyramid of energy is always broad at the base and narrow towards the top

The Pyramid of Energy

Producer (10000 kJ)

Primary Consumer (1000 kJ)

Secondary Consumer (100 kJ)

Tertiary Consumer (10 kJ)

Lost as energy trapped in uneaten body parts, faeces and excretory products

Heat lost during respiration

• Usually, we can assume about 90% of the energy is lost when it is transferred from one trophic level to the next

• The greatest amount of energy is lost during its transfer from producer to primary consumer

The Pyramid of Energy

Producer (10000 kJ)

Primary Consumer (1000 kJ)

Secondary Consumer (100 kJ)

Tertiary Consumer (10 kJ)

Lost as energy trapped in uneaten body parts, faeces and excretory products

Heat lost during respiration

Differences between a pyramid of biomass and pyramid of energy

Pyramid of biomass Pyramid of energy

Related to the biomass of organisms

Related to the energy content of organisms

Constructed based on the biomass at any given time

Constructed based on energy content over a period of time

Does not consider rate of reproduction of organisms

Takes into consideration the rate of reproduction of organisms

***Refer to Discover Biology Textbook Page 318 for some examples of food chains to show variations between ecological pyramids

Short food chains are more efficient in energy transferSince energy is lost at each trophic level, less

and less energy is available for organism at the next level as we go down the food chainHence, food chains are generally shortA shorter food chain means more energy is

available to the final consumer Why?????

Because less energy is lost to the environment Therefore, shorter food chains are more efficient

than long food chains

Non-cyclic energy flow in an ecosystemThe first source of energy in a ecosystem is the

sunAs energy flow through the ecosystem, some of

the energy is lost to the environment as heatEnergy that is lost as heat cannot be recycledHence, energy has to be constantly supplied to

the ecosystemIn an ecosystem, energy does not flow in a cycle.

Therefore, energy flow is non-cyclic or linear

1

2

3

3

4

4

4

5

5

+ CO2CO2 Sun (light energy)

faeces and excretory products + dead bodies of organisms

decomposition

heat released to environment

photosynthesis

feeding (holozoic nutrition)

feeding (holozoic nutrition)

respiration

respiration

respiration

excretion

excretion

egestion

egestion

energy lost in uneaten body parts, faeces and excretory products (usable energy)

heat lost to environment

heat lost to environment

Secondary consumers

(carnivores)

Primary consumers

(Herbivores)

Producers (Green plants)

Non-cyclic energy flow in an ecosystem

18.5 Nutrient Cycling in an Ecosystem

Carbon, oxygen, nitrogen and water are essential nutrients for life

In natural ecosystems, these nutrients are released back into the soil when organisms die

Decomposers (e.g. fungi and bacteria) break down dead organismsThe materials locked up in the dead organisms

can then be returned to the physical environment to be used again by green plants

Hence, in a balanced ecosystem, nutrients are never lost but are continually recycled

The Carbon CycleCarbon is constantly being removed from and

released into the environment, in the form of carbon dioxide.

Hence, the carbon dioxide concentration in the environment remains relatively constant

Removal of carbon dioxide from the environment

Release of carbon dioxide from the environment

The Carbon Cycle

Importance of the carbon cycle1. Ensures that there is a continuous supply of

carbon dioxide for plants to carry out photosynthesis

Photosynthesis converts energy from the sun into chemical energy in food, which other non-photosynthetic organisms can use to stay alive

2. Enables energy to flow through the ecosystemCarbon compounds carry the trapped solar energy

from organism to organism in the food chains of an ecosystem

Ecosystem

Biotic Environmentconsists of

made up of

Physical factors

consists of

Abiotic Environment

involved in

Important processes

Non-cyclic energy flow in the ecosystem

e.g.

Physical factors

• Carbon dioxide is removed from the environment by green plants during photosynthesis.

• Carbon dioxide is released into the environment through respiration, combustion and decay.

All the living things an organism interacts with

Ene

rgy

lost

in u

neat

en b

ody

part

s, f

aece

s an

d ex

cret

ory

prod

ucts

Secondary Consumer (Carnivore) 10 kJ

Primary Consumer (Herbivore) 100 kJ

Producer (Green plant) 1000 kJ

Ene

rgy lost in as he

at to environ

men

t during

respiration

Tertiary Consumer (Carnivore) 1 kJ

Sun

Light energy

Nutrient cycling in the ecosystem

Some video resources…

1. http://www.youtube.com/watch?v=GnffYkN1UDk

2. http://www.youtube.com/watch?v=O3CZFfyed3M