MYP Biology 2.1 Classification Notes

How Do Biologists Decide Whether Two Organisms Belong to the Same Species?

1. Species are the basic unit of all classification.
2. Biologists need a clear rule to decide whether two organisms belong to the same species.
3. The most widely accepted one is the biological species concept, based on producing fertile offspring.
4. If offspring are sterile, the organisms have separate gene pools, so they are considered different species.

Why Are Some Organisms Hard to Classify?

1. Nature doesn't always follow neat categories.
2. Species that are very similar genetically can occasionally hybridise, blurring boundaries.

1. Fossils can't be tested for reproduction at all.
2. Bacteria reproduce asexually, so the biological species concept doesnn't apply.
3. For these cases, scientists use DNA, behaviour, structure, and ecology to classify organisms.

What Patterns Link All Life on Earth?

1. Classification works because all organisms share deep structural patterns.
2. These include cells, DNA, energy use, and growth.
3. They show that all living species evolved from a common ancestor.
4. This is why classification forms a branching tree rather than random categories.

How Are Organisms Grouped Into Kingdoms?

1. Kingdoms are one of the broadest levels in classification.
2. They separate organisms based on features such as cell structure and how they obtain food.
3. This helps biologists organise millions of species into meaningful groups.

What Is the Hierarchical System of Classification?

1. Biologists organise living organisms using a hierarchy of categories.
2. Each level becomes more specific as you move down the hierarchy.
3. This structure helps scientists show how closely organisms are related.
4. The hierarchy is fixed in order, making it easy to compare groups across different species.
5. Species remain the most specific level, while domains and kingdoms sit at the top.

What Are the Main Groups of Flowering Plants?

1. Flowering plants are divided into monocots and dicots.
2. Their differences are structural, visible, and easy to test.
3. These patterns allow fast classification in the field.