Ecology and the
Impact of Abiotic
Factors on
Living
Organisms
Chapter 3
Chapter 3
What is an Ecosystem?
An ecosystem is a community of living organisms (like plants and animals)
interacting with each other and their non-living environment (like sun, soil,
water, and air). These interactions form a complex, balanced web of life.
Every organism in an ecosystem has a specific role based on how it gets its
energy.
Producers
Producers are organisms that make their own food. They are also called autotrophs
("auto" = self, "troph" = feeder). They do this through a process called photosynthesis,
which uses sunlight, water, and carbon dioxide to create lots of energy.
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Land examples: Trees, grass, flowers, mosses.
Water examples: Algae, aquatic plants, and phytoplankton.
Consumers
Consumers are organisms that cannot make their own food. They must eat (consume) other
organisms to get energy. They are also called heterotrophs ("hetero" = other). All animals are
consumers.
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Examples: Caterpillars, birds, fish, lions, humans.
Decomposers
Decomposers are nature's recyclers. They feed on and break down dead plants, animals, and
waste (this is called dead organic matter). By doing this, they return vital nutrients to the soil
in a form that plants can use, called humus. This process is crucial for fertilizing the soil so
producers can grow.
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Examples: Fungi (like mushrooms), bacteria, and worms.
The Cycle of Life:
The Sun provides energy to a Producer (a plant). A Consumer (like a
caterpillar) eats the plant. Another consumer (like a small bird) eats the
caterpillar. Eventually, they all die. Decomposers break down their bodies and
return nutrients to the soil. These nutrients are then used by Producers to
grow, and the cycle begins again.
Consumers are classified based on what they eat.
consume= eat
Herbivores
Herbivores are consumers that eat only plants. They are also known as primary
consumers.
Carnivores
Carnivores are consumers that eat only other animals. They are often hunters that
prey on other organisms. They are also known as secondary or tertiary consumers.
Omnivores
Omnivores are consumers that eat both plants and animals. This flexible diet
allows them to live in many different environments.
Quiz
https://www.zoo.com/quiz/is-this-animal-a-carnivore-herbivore-omnivore
The Food Chain
A food chain is a simplified pathway that illustrates the transfer of energy and nutrients from one
organism to another in one direction within an ecosystem.
Example:
Sun → Leaf (Producer) → Caterpillar (Primary Consumer) → Small Bird (Secondary Consumer) →
Hawk (Tertiary Consumer)
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The arrows are important. They symbolize the transmission of energy and biomass from the
source to the consumer.
This linear model provides a foundational understanding of energy dependency.
Trophic Levels
A trophic level refers to an organism's position in the sequence of energy transfers within a food
chain. It is a hierarchical stratum in an ecosystem's energy pyramid.
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First Trophic Level: Autotrophic Producers (e.g., Phytoplankton, Grass) – harness solar
energy.
Second Trophic Level: Primary Consumers (Herbivores) – directly consume producers.
Third Trophic Level: Secondary Consumers (Carnivores) – consume herbivores.
Fourth Trophic Level: Tertiary Consumers (Apex Predators) – consume secondary
consumers.
A Detailed Classification Schema
Organisms can be classified by their functional role (diet) and their numerical consumer level
within a trophic structure.This dual classification provides a comprehensive view of an
organism's ecological niche.
Organism
Nutritional Strategy
Consumer/
Classification
Leaf/Grass
Caterpillar /
Grasshopper
Toad / Insect-eating
Bird
Snake / Hawk
Trophic Leve
The Biological Arms Race: Predation
Food chains show predator-prey relationships, an important ecological interaction
driven by evolutionary pressure.
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A predator is an organism that actively hunts, captures, and consumes another
organism for sustenance.
The prey is the organism that is hunted and serves as a food source.
Critical Insight: An organism can occupy multiple roles. In a chain like Rose → Aphid →
Ladybug → Spider → Bird, the spider is both a predator (of the ladybug) and prey (for
the bird).
Food Web
● A complex network of interlinked food chains.
● More accurately represents feeding relationships in an ecosystem.
● One organism can be part of multiple chains.
Decomposers and Detritivores
Role: Break down dead organisms and waste, recycling nutrients back to the soil.
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Decomposers (e.g., Bacteria, Fungi): Secrete enzymes to break down dead matter
into humus.
Detritivores (e.g., Earthworms, Woodlice): Consume small fragments of dead
material (detritus).
Saprophyte: A general term for any organism that feeds on dead organic matter.
Symbiosis: Living Together
Symbiosis describes a close relationship between different species. There are
three main types:
Mutualism: (+, +) Both species benefit.
Commensalism: (+, 0) One benefits, the other is unaffected.
Parasitism: (+, -) One benefits (parasite), the other is harmed (host).
https://www.baamboozle.com/classic/142385
Ecosystem,
Habitat,
Population,
Community
Chapter 4
All living organisms need energy to carry out life processes; for example
your body uses energy to grow, move, inhale and eat. The energy that your
body is using came from your food. If you made a food web for everything
you eat, you would find that all the energy you use was trapped by plants
from the sun. Ultimately, all energy for life comes from the sun.
Photosynthesis: The Energy Converter
Photosynthesis equation:
carbon dioxide+water+light energy→glucose+oxygen
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Plants convert light energy into chemical
energy.
Glucose serves as stored chemical
energy.
Process occurs in chlorophyll-containing
cells.
Respiration: Releasing Stored Energy
Respiration equation:
glucose+oxygen→energy+carbon dioxide+water
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Occurs in both plants and animals
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Releases energy for life processes
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Some energy lost as heat
Energy Flow Through Food Chains
Energy transfers from:
Sun → Plants (Producers)
Plants → Herbivores (Primary Consumers)
Herbivores → Carnivores (Secondary Consumers)
Energy decreases at each level
Energy Loss in Ecosystems
Energy is lost through: heat
during respiration,
movement and activity,
waste products
(urine/feces), unutilized
parts of food, incomplete
digestion
The Limiting Factor: Energy Transfer Efficiency
Food chains are typically restricted to four or five trophic levels
Why is there a limit?
With each energy transfer, a substantial amount of energy (approximately 90%) is lost
as metabolic heat. Consequently, the amount of energy available to support biological
mass diminishes drastically at each successive level, making higher levels
unsustainable.
The length of a food chain is directly determined by the ecosystem's productivity
which is the total amount of energy captured by its producers. In highly productive
ecosystems, like tropical rainforests with abundant sunlight, a large energy
surplus allows energy to flow through more trophic levels, supporting longer food
chains. Conversely, in less productive ecosystems, like desserts, the limited
energy captured by producers can only sustain a few trophic levels before it is
depleted.
Pyramids of Energy
Shows energy available at each trophic level
Pyramids of Numbers
Shows the numbers of all the organisms at each trophic level of a food chain
within a given area.
Pyramid of Biomass
Instead of estimating the numbers of organisms at each trophic level we can estimate their
biomass or dry weight.
Bioaccumulation: Pesticides in the Food Chain
Concept: The process where toxins (like pesticides) become increasingly concentrated in the
tissues of organisms at higher trophic levels.
How It Works:
1.
2.
3.
4.
Application: Pesticides (insecticides, herbicides) are sprayed on the environment.
Uptake: Primary consumers (e.g., grasshoppers, small fish) ingest small, non-lethal
amounts from plants or water.
Concentration: A predator (e.g., a bird) eats many contaminated prey, accumulating all
their stored toxins.
Magnification: A top predator (e.g., a hawk, osprey) consumes many secondary
consumers, resulting in dangerously high, often lethal, toxin levels.
The DDT Example:
(dichlorodiphenyltrichloroethane)
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An effective insecticide used to control malaria-carrying mosquitoes.
It didn't just kill pests; it accumulated in fatty tissues.
In top predators like ospreys, DDT levels became millions of times higher than
in the water, causing eggshell thinning, reproductive failure, and population
crashes.
Banned in many countries since 1972.
Links to Activities
https://www.learner.org/wp-content/interactive/envsci/ecology/ecology.html
https://wordwall.net/resource/30964521/science/food-web
https://wordwall.net/resource/51855998/science/ecology-review
https://wordwall.net/resource/9778561/ecology-vocabulay
https://wordwall.net/resource/51855998/science/ecology-review
https://wordwall.net/resource/22125657/keywords-y8-feeding-relationships
https://wordwall.net/resource/81531413/food-chain-energy-pyramid