1. Energy Flow Food Chains and Webs Carbon Cycle
Man and His Environment (Part I)
Energy Flow
Food Chains and Webs
Carbon Cycle

3. 18.1 What is Ecology?
Organisms continually interact with one another, as well as the surroundings
Ecology is the study of these interactions
Ecologists 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

4. What are some key ecological terms?
Habitat
Population
Community
Ecosystem

5. What is a habitat? The place where an organism lives is its habitat
For example, Wading birds called redshanks live in the mud of the mangrove swamp, so the mangrove swamp is the habitat of the redshanks

6. 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

7. 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

8. What is an ecosystem?
Living organisms interacting with one another and with their abiotic environment make up an ecosystem
For 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

9. 18.2 The Abiotic Environment
Physical features that make up the abiotic environment include:
Light intensity
Temperature
Amount of water available
Oxygen content
Salinity (salt concentration) of soil or water
pH of soil or water
*** Refer to Discover Biology Textbook Page 305 to 307 for more details

10. 18.3 The Biotic Environment
The living or biotic environment comprises all the living organism that an organism interacts with in its habitats
An habitat is the place where an organism lives e.g a pond, stream, river, forest or desert

11. Why do organisms affect other organisms?
The organisms in any habitat are never completely independent
The life of each organism depends on and is influenced by other organisms around it
Hence the organisms are known to be interdependent

12. 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 interdependently
A change in one population affects the other populations of the community

13. 18.4 The Ecosystem
An 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.

14. The Ecosystem An ecosystem uses both energy and inorganic nutrients
Energy enters an ecosystem (from the sun)
Energy is converted into chemical energy and is passed from organism to organism through the ecosystem
Energy is lost to the environment as it flows through the ecosystem
The energy that is lost as heat cannot be recycled in the ecosystem. Hence, energy has to be constantly supplied to the ecosystem.

15. The Ecosystem
Inorganic nutrients, on the other hand, need not be supplied from outside the ecosystem
They are obtained from the abiotic environment and flow through the ecosystem in a cycle
In a ‘balanced’ ecosystem, nutrients are continually recycled and are not lost i.e. nutrient cycling

16. 5. Burning of fossil fuels
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. Respiration
5. Burning of fossil fuels
Plants
Animals
3. Dead Organisms
4. Fossil Fuels 16

17. 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.

18. 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

19. Energy Flow – Food Chains
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 19

20. Energy Flow – Trophic Levels
At 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

21. 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

22. 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 22

23. Examples of decomposers: Fungi, bacteria and earthworms
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 23

24. Energy Flow – Food Web
In a community, food chains are interlinked to form a food web 24

25. Food Chain and Food Web A food chain: Primary Consumer (herbivore)
Secondary Consumer
(carnivore)
Tertiary Consumer
(carnivore)
Producer
(green plant)
A food web:
caterpillar
green plant
grasshopper
spider
bird
aphid
aphid
ladybird
ladybird
16 April 2017

26. Ecological Pyramids
We can compare the trophic levels in a food chain using ecological pyramids
There are 3 types of ecological pyramids:
Pyramid of numbers
Pyramid of biomass
Pyramid of energy

27. The Pyramid of Numbers
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
**Refer to Discover Biology Textbook Page 314 on how to construct pyramid of numbers 27

28. The Pyramid of Biomass
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
**Refer to Discover Biology Textbook Page 314 on how to construct pyramid of biomass 28

29. Variations in ecological pyramids
Most ecological pyramids are pyramid-shaped, but there are important exceptions
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

30. 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.

31. 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.

32. Another example of inverted pyramid of numbers
The pyramid may also become inverted if the producer is too large.
An inverted pyramid of numbers:

33. Variations in ecological pyramids
Most ecological pyramids are pyramid-shaped, but there are important exceptions
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.
Pyramids of biomass for rapidly reproducing organisms are also not pyramid-shaped.

34. Example of inverted pyramid of biomass
Since 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

35. Example of inverted pyramid of biomass
Phytoplankton are microscopic plant-like organisms that can make food by photosynthesis
Zooplankton are microscopic primary consumers that feed on phytoplankton
The pyramid below gives the impression that the biomass of phytoplankton is smaller than that of zooplankton, which is not possible
Large fish
Small fish
Zooplankton
Phytoplankton

36. Example of inverted pyramid of biomass
What happens is that the rate of reproduction of phytoplankton is fast enough to replace the organisms that were eaten by zooplankton
Large fish
Small fish
Zooplankton
Phytoplankton

37. The Pyramid of Energy
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
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. 37

38. 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:
As heat during respiration at every trophic level
In uneaten body parts
Through undigested matter egested by consumers
Through waste products excreted by consumers, for example, urea 38

39. 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:
As heat during respiration at every trophic level
In uneaten body parts
Through undigested matter egested by consumers
Through waste products excreted by consumers, for example, urea
Lost as energy trapped in uneaten body parts, faeces and excretory products
Heat lost during respiration
Tertiary Consumer (10 kJ)
Secondary Consumer (100 kJ)
Primary Consumer (1000 kJ)
Producer (10000 kJ) 39

40. The Pyramid of Energy
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
Lost as energy trapped in uneaten body parts, faeces and excretory products
Heat lost during respiration
Tertiary Consumer (10 kJ)
Secondary Consumer (100 kJ)
Primary Consumer (1000 kJ)
Producer (10000 kJ) 40

41. The Pyramid of Energy
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
Lost as energy trapped in uneaten body parts, faeces and excretory products
Heat lost during respiration
Tertiary Consumer (10 kJ)
Secondary Consumer (100 kJ)
Primary Consumer (1000 kJ)
Producer (10000 kJ) 41

42. The Pyramid of Energy
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
Lost as energy trapped in uneaten body parts, faeces and excretory products
Heat lost during respiration
Tertiary Consumer (10 kJ)
Secondary Consumer (100 kJ)
Primary Consumer (1000 kJ)
Producer (10000 kJ) 42

43. Differences between a pyramid of biomass and 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

44. Short food chains are more efficient in energy transfer
Since 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 chain
Hence, food chains are generally short
A 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

45. Non-cyclic energy flow in an ecosystem
The first source of energy in a ecosystem is the sun
As energy flow through the ecosystem, some of the energy is lost to the environment as heat
Energy that is lost as heat cannot be recycled
Hence, energy has to be constantly supplied to the ecosystem
In an ecosystem, energy does not flow in a cycle.
Therefore, energy flow is non-cyclic or linear

46. Non-cyclic energy flow in an ecosystem5
excretion
Secondary consumers
(carnivores) 4
respiration
egestion
energy lost in uneaten body parts, faeces and excretory products (usable energy)
feeding (holozoic nutrition)
heat lost to environment 3 5
excretion
Primary consumers
(Herbivores) 4
respiration
egestion
heat lost to environment
feeding (holozoic nutrition) 3
faeces and excretory products dead bodies of organisms 4
Producers (Green plants)
respiration
decomposition 2
photosynthesis
+ CO2
CO2
Sun (light energy)
heat released to environment 1

47. 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 organisms
The 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

48. The Carbon Cycle
Carbon 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

49. Removal of carbon dioxide from the environment

50. Release of carbon dioxide from the environment

51. The Carbon Cycle

52. Importance of the carbon cycle
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
Enables energy to flow through the ecosystem
Carbon compounds carry the trapped solar energy from organism to organism in the food chains of an ecosystem

53. Nutrient cycling in the ecosystem
made up of
Abiotic Environment
Biotic Environment
consists of
consists of
Physical factors
All the living things an organism interacts with
involved in
Important processes
Non-cyclic energy flow in the ecosystem
Nutrient cycling 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.
Tertiary Consumer (Carnivore) 1 kJ
Secondary Consumer (Carnivore) 10 kJ
Energy lost in uneaten body parts, faeces and excretory products
Primary Consumer (Herbivore) 100 kJ
Energy lost in as heat to environment during respiration
Producer (Green plant) 1000 kJ
Light energy
Sun 53

54. Some video resources… http://www.youtube.com/watch?v=GnffYkN1UDk