Introduction: Welcome to the World of Biology!
Hello, everyone! Today, we are beginning our study of "Basic Biology." Our first topic is "Characteristics of Living Organisms."
"Being alive" might seem like a simple concept, but explaining the definitive difference between a "rock" and an "ant" is surprisingly difficult.
In this chapter, we will learn the rules shared by all living things on Earth. It might feel like there is a lot to memorize at first, but if you think of it as learning about what's happening inside your own body, it should feel much more relatable! Let’s learn and have fun together.
1. Unity and Diversity of Life
Our planet is home to a vast variety of life, from microscopic bacteria to giant whales. This is called diversity. However, no matter how different they look, all living things share common characteristics. This is because all organisms have evolved from a "common ancestor."
The 5 Common Rules of Life
There are five main features that define a living organism. These are common exam topics, so make sure to master them!
1. Cellular structure: All organisms use the "cell," wrapped in a membrane, as their basic unit.
2. Energy use (Metabolism): Organisms generate and use energy through processes like eating or photosynthesis.
3. Homeostasis: Organisms maintain a constant internal state, such as body temperature and water balance.
4. Reproduction and Heredity: Organisms produce offspring of their own kind and pass on their traits to them via DNA (genes).
5. Evolution: Over long periods, organisms change to adapt to their environment.
【Tip】A Common Misconception
A frequent question on tests is: "Are viruses alive?" The answer is usually "They are not considered alive (or they exist on the boundary between living and non-living)." This is because viruses lack "cells" of their own and cannot perform "metabolism" on their own. They don't fit all the rules of life!
2. Cell Structure
Cells, the basic units of life, are broadly divided into two types.
Prokaryotic and Eukaryotic Cells
① Prokaryotic cells
Simple cells that lack a nucleus. Prokaryotes, such as E. coli and cyanobacteria, fall into this category.
Example: Bacteria
② Eukaryotic cells
Complex cells that possess a nucleus. Eukaryotes, such as humans, plants, and mushrooms, fall into this category.
Example: Animals, plants, and fungi (molds/mushrooms)
Major Internal Structures (Organelles)
Eukaryotic cells have "rooms" with specific roles.
- Nucleus: The command center of the cell, containing DNA (chromosomes).
- Cell membrane: A thin film that wraps the entire cell and regulates the entry and exit of substances.
- Mitochondria: The site of "respiration," where oxygen is used to extract energy. Think of these as the power plants of the cell.
- Chloroplasts (Plants only): The site of "photosynthesis," where light energy is used to make nutrients.
- Vacuoles (Mainly plants): Places for storing water and waste products.
- Cell wall (Plants, fungi, and prokaryotes): A hard barrier outside the cell membrane that provides structural support.
【Did you know?】How to distinguish between animal and plant cells
If you see "chloroplasts," a "cell wall," or a "large vacuole," it is a plant cell. Animal cells do not have these. Exams often ask you to identify these from diagrams, so get used to visualizing their shapes!
3. Energy and Metabolism
The total of all chemical reactions that occur to keep an organism alive is called metabolism. There are two main flows in metabolism.
Anabolism and Catabolism
- Anabolism: Synthesizing complex substances from simpler ones and storing energy.
Example: Photosynthesis (Using light energy to make starch from carbon dioxide and water)
- Catabolism: Breaking down complex substances to release energy.
Example: Respiration (Breaking down starch, etc., to obtain energy for life)
The Energy Currency "ATP"
The substance that transfers energy in metabolism is ATP (Adenosine Triphosphate). Because it can be used like money inside the body, it is called the "energy currency."
ATP is made of adenosine attached to 3 phosphates. When the bond between these phosphates (high-energy phosphate bond) is broken, a large amount of energy is released.
\( \text{ATP} \rightarrow \text{ADP (Adenosine Diphosphate)} + \text{Phosphate} + \text{Energy} \)
【Memorization Trick】
Remember that Tri (3) means ATP, and Di (2) means ADP! Think of them as "Triple" and "Double."
4. Evolution and Phylogeny
All life began from a common ancestor and evolved by branching out. This connection is called phylogeny, and a diagram showing this in the form of a tree is called a phylogenetic tree.
If you trace a phylogenetic tree back far enough, no matter how different the organisms seem, you will arrive at the same "first life." That is why we humans and the grass on the roadside share the same "DNA" mechanism. Isn't that romantic?
Summary: What to Remember!
1. Memorize the 5 characteristics of life (cells, metabolism, homeostasis, heredity, evolution)!
2. Cells with a nucleus are "eukaryotic," those without are "prokaryotic"!
3. Identify what only plants have (chloroplasts, cell wall, large vacuole)!
4. Remember the keywords for metabolism: "anabolism," "catabolism," and the energy currency "ATP"!
It might be overwhelming with so many terms at first, but once you understand the meaning of each word, they fit together like a puzzle. Start with a simple image, like thinking of "ATP = money." Great work today!