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Chapter 3 - Ecosystem

Mathayom 3
Science in English
Chapter six: ecosystem
An ecosystem is a community of animals and plants interacting with their environment and have
their own characteristics/features and functions.
1. Scales of Ecosystems
Ecosystems come in indefinite sizes. It can exist in a small area such as underneath a rock, a
decaying tree trunk, or a pond in your village, or it can exist in large forms such as an entire rain
forest. Technically, the Earth can be called a huge
Let classify the ecosystems into three main scales.
 Micro:
A small scale ecosystem such as a pond,
puddle, tree trunk, under a rock etc.
 Messo:
A medium scale ecosystem such as a
forest or a large lake.
 Biome:
A very large ecosystem or many
ecosystems together with similar biotic
and abiotic factors such as an entire
Rainforest with millions of animals and
trees, with many different water bodies
running through them.
A biosphere is when we consider all the different biomes, each blending into the other, with all
humans living in many different geographic areas; we form a huge community of humans,
animals and plants, and micro-organisms in their defined habitats. A biosphere is the sum of all
the ecosystems established on planet Earth. It is the living (and decaying) component of
the earth system.
They are often separated by geographical barriers such as deserts, mountains, oceans, lakes and
rivers. As these borders are never rigid, ecosystems tend to blend into each other. This is why a
lake can have many small ecosystems with their own unique characteristics. Scientists call this
blending “ecotone”
Ecosystems can be put into 2 groups. If the ecosystem exists in a water body, like an ocean,
freshwater or puddle, it is called an aquatic ecosystem. Those that exists outside of water bodies
are called terrestrial ecosystems.
2. Abiotic and biotic factors
There are 2 big factors in an ecosystem:
 Abiotic: Non-living condition or thing that change an ecosystem and the organisms inside
it. ‘’A ‘’= without ‘’Bio’’ = life. Like the rain, sun, climate, temperature.
 Biotic: the living things in an ecosystem. It includes plants, animals, bacteria, fungi and
more. Man is the most important biotic factor. Biotic factors are divided into 3 groups.
1. Producer: (autotrophs): All green plants. They use solar energy and use inorganic
food (other than plants and animals) and water to make their own food.
2. Decomposers: They are very small organisms (being) like bacteria and fungi
(mushroom), which break organic part in dead plants and animals into inorganic
material. They recycle the organic part in an ecosystem.
3. Consumers: Plants or animals that eat other plants or animals. The consumers are
divided into 3 groups.
 Herbivores: eat plant.
 Carnivores: eat meat.
 Omnivores: eat meat and plants.
3. Food chain and food web
A food chain is made up of three groups – producers, consumers and decomposers – they
interact with each other in an ecosystem to get their energy and the food they need. It’s a direct
The food web shows all
of the relationships
between all food chain in
an ecosystem. Many lines
Mathayom 3
Science in English
4. Trophic level of food chains
The sun is the source of all the energy in food chains. Green plants, usually the first level of any
food chain, absorb some of the Sun’s light energy to make their own food by photosynthesis.
Green plants (autotrophs) are therefore known as ‘Producers’ in a food chain.
The second level of the food chains is called the Primary Consumer. These consume the green
plants. Animals in this group are usually herbivores. Examples include insects, sheep, caterpillars
and even cows.
The third in the chain are Secondary Consumers. These usually eat up the primary consumers and
other animal matter. They are commonly called carnivores and examples include lions, snakes
and cats.
The fourth level is called Tertiary Consumers. These are animals that eat secondary consumers.
Quaternary Consumers eat tertiary consumers.
At the top of the levels are Predators. They are animals that have little or no natural enemies.
They are the ‘bosses’ of their ecosystems. Predators feed on preys. A prey is an animal that
predators hunt to kill and feed on. Predators include owls, snakes, wild cats, crocodiles and
sharks. Humans can also be called predators.
When any organism dies, detrivores (like vultures, worms and crabs) eat them up. The rest are
broken down by decomposers (mostly bacteria and fungi), and the exchange of energy
continues. Decomposers start the cycle again.
5. 3 big principles in an ecosystem
There are 3 big principles:
 Nutrient cycling: The use, movement and recycling of nutrients (food) in the
 Energy flow: Energy is needed to turn inorganic food (food that doesn’t come from
animals) into organic (living) tissues of an organisms. Energy is the most important force
of an ecosystem.
 Structure: Inter-relationships that exist between organisms in an ecosystem.
6. Definitions
Factor: something that can changes a situation like the climate, sun, weather.
Habitat: is the kind of natural environment in which a particular species of organism lives.
Organism: living thing.
Organic: always have carbon and are alive
Inorganic: do not have carbon, like elements as salt, metals
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