This document discusses key concepts around food chains, food webs, and energy transfer between trophic levels in an ecosystem. It explains that autotrophs like plants and algae produce energy through photosynthesis, while heterotrophs consume other organisms for energy and nutrients. Energy is lost at each trophic level, with only about 10% being transferred between levels according to the 10% law. Food chains represent simple, linear energy transfers, while food webs are more complex with many organisms at each trophic level. Ecological pyramids illustrate the decrease in biomass and numbers of organisms at higher trophic levels due to inefficient energy transfer.

1. Chapter 1, Section 2 Notes
Food Chains, Food Webs, and the
Transfer of Energy

2. Autotrophs
• A groups of organisms that can use the
energy in sunlight to convert water and
carbon dioxide into Glucose (food)
• Autotrophs are also called Producers because
they produce all of the food that heterotrophs
use
• Without autotrophs, there would be no life on
this planet
• Ex. Plants and Algae

3. Autotrophs

4. Autotrophs
• Chemotrophs
– Autotrophs that get their energy from inorganic
substances, such as salt
– Live deep down in the ocean where there is no
sunlight
– Ex. Bacteria and Deep Sea Worms

5. Heterotrophs
• Organisms that do not make their own food
• Another term for Heterotroph is consumer
because they consume other organisms in
order to live
• Ex. Rabbits, Deer, Mushrooms

6. Heterotrophs

7. Heterotrophs
• Consumers
– 1. Scavengers/Detritivores – feed on the tissue of
dead organisms (both plants and animals)
• Ex. – Vultures, Crows, and Shrimp

8. Heterotrophs
• Consumers
– 2. Herbivores – eat ONLY plants
• Ex. – Cows, Elephants, Giraffes

9. Heterotrophs
• Consumers
– 3. Carnivores – eat ONLY meat
• Ex. – Lions, Tigers, Sharks

10. Heterotrophs
• Consumers
– 4. Omnivores – eat BOTH plants and animals
• Ex. – Bears and Humans

11. Heterotrophs
• Consumers
– 5. Decomposers – absorb any dead material and
break it down into simple nutrients or fertilizers
• Ex. – Bacteria and Mushrooms

12. Transfer of Energy
• When a zebra eats the grass, it does not
obtain all of the energy the grass has (much
of it is not eaten)
• When a lion eats a zebra, it does not get all
of the energy from the zebra (much of it is
lost as heat)

13. Transfer of Energy
• The two (2) previous examples of energy
transfer show that no organism EVER
receives all of the energy from the organism
they just ate
• Only 10% of the energy from one trophic
level is transferred to the next – this is called
the 10% law

14. Trophic Levels
• Energy moves from one organisms to another
when it is eaten
• Each step in this transfer of energy is known
as a trophic level
– The main trophic levels are producers, consumers,
and decomposers

15. Food Chains
• The energy flow from one trophic level to the
other is know as a food chain
• A food chain is simple and direct
• It involves one organism at each trophic level
– Primary Consumers – eat autotrophs (producers)
– Secondary Consumers – eat the primary consumers
– Tertiary Consumers – eat the secondary consumers
– Decomposers – bacteria and fungi that break down
dead organisms and recycle the material back into the
environment

16. Food Chain

17. Food Web
• Most organisms eat more than JUST one
organism
• When more organisms are involved it is
known as a FOOD WEB
• Food webs are more complex and involve lots
of organisms

18. Food Web

19. Food Web
• Notice that the direction the arrow
points  the arrow points in the
direction of the energy transfer,
NOT “what ate what”

20. Food Web

21. Biomass
• The total mass of the organic matter at each
trophic level is called biomass
• Biomass is just another term for potential
energy – energy that is to be eaten and used.
• The transfer of energy from one level to
another is very inefficient (10% Law)

22. Biomass

23. Ecological Pyramid
• An ecological pyramid shows the relationship
between consumers and producers at
different trophic levels in an ecosystem
• Shows the relative amounts of energy or
matter contained at each trophic level
• The Pyramid shows which level has the most
energy and the highest number of organisms

24. Ecological Pyramid

25. Ecological Pyramid

26. Ecological Pyramid
• Which level has the most energy?
• Which level has the most organisms?
• Which level has the least organisms?
• Which level has the least energy?

27. Symbiosis
• A close and permanent association between
organisms of different species
– Commensalism – a relationship in which one
organism benefits and the other is not affected
• Example: Barnacles on a whale
– Mutualism – a relationship in which both
organisms benefit from each other
• Example: Birds eating pest off a rhino’s back
– Parasitism – A relationship in which one organism
benefits and the other is harmed
• Example: Ticks on a dog

28. Ecological Succession
• A change in the community in which new
populations of organisms gradually replace
existing ones
– 1. Primary Succession – occurs in an area where
there is no existing communities and for some
reason (s) a new community of organisms move
into the area

29. Ecological Succession
• A change in the community in which new
populations of organisms gradually replace
existing ones
– 2. Secondary Succession – occurs in an area
where an existing community is partially damaged

30. Ecological Succession
• A change in the community in which new
populations of organisms gradually replace
existing ones
– 3. Climax Community – a community that is
stable and has a great diversity of organisms

31. Ecological Succession

32. Unit 2, Part 2 Notes
Food Chains, Food Webs, and the
Transfer of Energy