Hello! Let’s have fun learning about "Biodiversity and Ecosystems"!

Hello everyone! In this chapter, we’re going to learn about the mechanisms that sustain the rich nature around us.
This is arguably the biggest and most exciting topic in "Basic Biology"! It might seem overwhelming because of the many terms at first, but let’s approach it like solving a puzzle: "Who eats what, and how are they connected?" Don't worry, if we take it one step at a time, you’ll definitely be able to master it!

1. What is an Ecosystem?

An "ecosystem" is a group consisting of all the living organisms in a specific area, combined with the environment that surrounds them (light, water, soil, etc.).

■ Members of an Ecosystem

Ecosystems are broadly divided into two components:

  • Abiotic Environment: Non-living factors such as light, temperature, water, air, and soil.
  • Biotic Environment: All the living organisms residing there.

■ Action and Reaction (Be careful, the terms sound similar!)

The environment and organisms influence each other.
1. Action: The abiotic environment influencing organisms. (e.g., Plants grow because there is light)
2. Reaction (Environmental Formation): Organisms influencing the abiotic environment. (e.g., Forests make the temperature changes on the ground more moderate)

【Key Point!】
"Environment to Organism" = Action, "Organism to Environment" = Reaction. If you think, "It’s nice and cool thanks to this forest," that’s thanks to a reaction!

2. Division of Roles within an Ecosystem

In an ecosystem, organisms are divided into three groups based on their roles. This is called the "trophic level."

① Producers

Plants and other organisms that use sunlight to create organic matter from inorganic matter (carbon dioxide and water). Their most important trait is performing photosynthesis. They are the starting point of the ecosystem!

② Consumers

Animals that live by eating the organic matter created by producers. This includes herbivores that eat plants and carnivores that eat other animals.

③ Decomposers

Organisms that break down organic matter found in dead bodies and waste (like feces) back into inorganic matter. This includes fungi (mold, mushrooms) and bacteria.
*Common mistake: Earthworms and pill bugs are often grouped with decomposers because they break down large carcasses into smaller pieces, but the final step of breaking things down into "inorganic matter" is the job of fungi and bacteria.

【Did you know?】
Mushrooms are often mistaken for plants, but because they do not perform photosynthesis, they are "decomposers." They are actually a completely different type of life form from plants!

3. Food Chains and Food Webs

A "eat or be eaten" relationship linked in a single line is called a food chain.
However, in the real natural world, these relationships are much more complex and intertwined. This complex network is called a food web.

【Tip for remembering】
Because it’s complex like a net, it’s a "food web"! Real nature looks more like this.

4. Material Cycles and Energy Flow

This is the most important point for exams! Understand the difference: "Matter" cycles, but "Energy" flows through.

■ The Carbon Cycle

Carbon (C) circulates through the ecosystem as carbon dioxide and organic matter.
1. Plants take in \(CO_2\) through photosynthesis to make organic matter (such as starch).
2. Animals eat that matter.
3. Through respiration, it returns to the air as \(CO_2\).
4. When decomposers break down dead bodies, \(CO_2\) is also released.

■ Energy Flow

Energy does not cycle!
Light energy from the sun is passed from producers to consumers, but in that process, it escapes as heat energy. It’s a one-way path that eventually escapes into space.

【Important Check!】
・Matter (like carbon) cycles through the ecosystem.
・Energy flows one-way through the ecosystem (it cannot be reused).

5. Ecosystem Balance and Conservation

Ecosystems have the power to naturally return to their original state even after minor changes (resilience). This is called ecosystem balance.

■ Keystone Species

Species that have a huge impact on other organisms even if their numbers are small. For example, if sea otters disappear, sea urchin populations explode, causing kelp (seaweed) forests to vanish. In this case, the sea otter is a keystone species.

■ Impact of Human Activity

Unfortunately, human activity can disrupt this balance.
・Invasive species: Organisms brought into areas where they did not originally exist. They may eat native species or bring in diseases.
・Eutrophication: An excessive increase in nutrients in water due to things like household wastewater, causing plankton to bloom abnormally. This can cause phenomena like red tides.

【Key takeaway!】
Raccoons and largemouth bass are famous examples of invasive species. It is crucial that we act to avoid disrupting the original balance.

Summary: Reflecting on this Chapter

1. An ecosystem is a set of "abiotic environment" and "living organisms."
2. Roles are divided into three: "Producers," "Consumers," and "Decomposers."
3. Matter like carbon cycles, but energy flows one-way.
4. Species that support the balance of an ecosystem are called keystone species.

It might feel difficult at first, but our own lives are part of this ecosystem too. When you look at plants in a nearby park or garden, try imagining: "Ah, this is a producer," or "It’s returning carbon to the air through respiration right now"—your understanding will deepen significantly!
Great job! Let’s keep working hard together on the next steps!