【Science】Grade 9: Nature and Humans — We’re All Connected! How the Earth Works
Hello everyone! In this chapter, we’re going to explore how living things, including us humans, interact with each other and support one another in nature.
You might feel like, "Science is tough because there's so much to memorize..." but don't worry! For this unit, the key is to visualize the "connections." Think of it like putting together a puzzle—let's learn together and have some fun!
1. Ecosystems and the Roles of Organisms
Living things in a specific area, along with their surrounding environment (light, water, air, etc.), are collectively called an ecosystem. Within an ecosystem, living things are divided into three groups based on their roles.
(1) Producers
These are plants that use sunlight to create organic substances (such as starch) from inorganic substances (carbon dioxide and water). Their main feature is performing photosynthesis.
Key point: Remember them as the "amazing beings that can make their own food!"
(2) Consumers
These are animals that survive by eating the organic substances produced by producers, either directly or indirectly.
Example: Grasshoppers that eat grass (herbivores), frogs that eat grasshoppers (carnivores), etc.
(3) Decomposers
These are organisms that break down organic substances like carcasses and waste back into inorganic substances. This group mainly consists of fungi (molds and mushrooms) and bacteria (such as lactic acid bacteria or natto bacteria).
Pro-tip: Earthworms and pill bugs found in the soil also play an important role in breaking down large organic matter into smaller pieces to assist the decomposers.
【Take Note!】
Decomposers eventually return organic matter to inorganic substances like "carbon dioxide" and "water." This allows producers (plants) to use them to grow once again. They are essentially the "Earth's recycling team!"
2. Food Chains and the Relationship of "Eat or Be Eaten"
The "eat or be eaten" chain-like connection is called a food chain. In reality, these connections are complex and web-like, which is why we call it a food web.
The Ecological Pyramid
In nature, there is usually a balance in numbers (or total weight) following the order of "Producers > Herbivores > Carnivores." When you visualize this, it forms the shape of a pyramid.
Common Misconception: Thinking that "the more strong animals (like lions) there are, the better" is a mistake. If carnivores increase too much, they will run out of herbivores to eat, and eventually, the carnivores themselves will starve and decrease in number. Nature has a mysterious power that constantly works to maintain a certain balance.
3. Circulation of Matter
Within an ecosystem, matter (like carbon) moves around in a continuous cycle as it changes forms. A topic that often appears on tests is the carbon cycle.
Let’s look at the flow of carbon!
1. Carbon dioxide (\( CO_2 \)) in the air: Plants absorb this through photosynthesis and turn it into organic matter (part of their body).
2. Eating: When animals eat plants, the carbon moves into the animal's body.
3. Respiration: Both plants and animals perform respiration, releasing \( CO_2 \) into the air.
4. Decomposition: When decomposers break down carcasses or waste, \( CO_2 \) is also released.
5. Combustion: When humans burn fossil fuels (like petroleum), \( CO_2 \) is released as well.
Memory Tip:
Remember that "photosynthesis" is the only process that reduces (absorbs) \( CO_2 \), while everything else (respiration, decomposition, and combustion) works to increase (release) \( CO_2 \)!
4. Balance of Nature and Humans
We humans are part of the ecosystem, but our activities can sometimes disrupt nature's balance.
Global Warming
This is a phenomenon where burning large amounts of oil and coal increases the amount of \( CO_2 \) (a greenhouse gas) in the air, causing the Earth's temperature to rise.
The Problem of Invasive Species
This occurs when humans bring living things into an area where they were not originally found. They may eat local species (native species) or take over their habitats, which disrupts the balance of the ecosystem.
Example: Largemouth bass, raccoons, common dandelions, etc.
Plastic Waste
Because plastic cannot be broken down by decomposers, it remains in the natural environment. In particular, there is growing concern about small microplastics that flow into the ocean and negatively affect marine life.
Final Summary: Chapter Review
・Plants are "producers," animals are "consumers," and molds/bacteria are "decomposers."
・Nature is maintained by the balance of "eating and being eaten."
・Substances like carbon circulate through the ecosystem.
・As part of nature, humans need to find ways to protect the environment (a sustainable society).
It might feel overwhelming with all the terminology at first, but if you grasp the image that "all living things are connected," you're golden! Next time you look at a park or garden, try to think, "Is this bug a consumer?" or "Is this mushroom a decomposer?" This will make science feel much more personal. Keep working at it, one step at a time!