Ch 1 · Cell Structure · IGCSE Biology 0610
Topic 1 of 2 in Organisation of the Organism — IGCSE Biology 0610 — 48 lessons.
Introduction
Every living organism is built from cells, and most of the biology you will meet later happens inside them. This lesson covers the structures of plant, animal and bacterial cells and what each part does, how cells are specialised for particular jobs, and how cells are organised into tissues, organs and organ systems.
Key ideas — Plant and animal cells
Structures found in both plant and animal cells:
🧑🏫 Teacher's explanation
Think of a cell like a busy, high-security factory. The cell membrane is the security gate that decides who enters or leaves. The nucleus is the manager's office, holding the blueprints (DNA) and giving orders. The mitochondria are the power generators, providing the energy needed for the machines to run. The cytoplasm is the factory floor where all the work happens.
📖 Definitions
🔍 Worked example — Easy
State the function of the following two organelles: (a) Mitochondria (b) Ribosomes.
🔍 Worked example — Standard
A student observes a cell under a light microscope. The cell has a cell wall, a large central vacuole, and chloroplasts. Identify the type of cell and explain why it might NOT have chloroplasts despite being a plant cell.
🔍 Worked example — Exam-style
Compare the structure of a bacterial cell with a plant cell regarding their genetic material and cell walls.
⚠️ Common errors
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🎯 Exam question
Key ideas — Bacterial cells
Bacteria are prokaryotes. A bacterial cell has a cell wall (not made of cellulose), a cell membrane, cytoplasm and ribosomes, but no nucleus. Its genetic material is a single circular DNA molecule lying free in the cytoplasm, often with extra small rings of DNA called plasmids. There are no mitochondria or chloroplasts, and the cells are far smaller than plant and animal cells.
🧑🏫 Teacher's explanation
Imagine a busy, small-scale factory. In a complex eukaryotic cell (like yours), there are specialized rooms (organelles) like a nucleus for the boss or mitochondria for the power plant. A bacterial cell, however, is like a single-room studio apartment. Everything happens in one open space. There are no separate rooms for the blueprints or the power generators; instead, the instructions (DNA) just float around on the floor, and the machines (ribosomes) work right in the middle of the room.
📖 Definitions
🔍 Worked example — Easy
Identify the three main differences between a bacterial cell and a plant cell.
🔍 Worked example — Standard
A student observes a cell under a light microscope. They identify a cell wall, a cell membrane, and ribosomes, but they cannot find a nucleus or mitochondria. State the type of cell and explain why it cannot be a plant cell.
🔍 Worked example — Exam-style
Calculate the percentage difference in size between a typical plant cell (diameter ≈ 50 mum) and a typical bacterium (diameter ≈ 2 mum).
⚠️ Common errors
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🎯 Exam question
Key ideas — Specialised cells
Multicellular organisms contain many kinds of cell, each with a structure adapted to its function.
🧑🏫 Teacher's explanation
In a multicellular organism, cells are like specialized workers in a factory. A janitor, a driver, and a chef all have different 'tools' (organelles) because they have different 'jobs' (functions). If a cell only did one thing, it wouldn't be efficient; instead, it modifies its shape or its internal machinery to excel at that specific task.
📖 Definitions
🔍 Worked example — Easy
A student observes a cell under a light microscope. The cell has a long, thin extension and no chloroplasts. Identify the most likely type of cell and explain its adaptation for absorption.
🔍 Worked example — Standard
Compare the adaptations of a red blood cell and a sperm cell regarding energy and transport.
🔍 Worked example — Exam-style
A plant cell is observed in the palisade mesophyll layer. Explain how its structure is optimized for photosynthesis.
⚠️ Common errors
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🎯 Exam question
Key ideas — Levels of organisation
🧑🏫 Teacher's explanation
Think of biological organization like a massive construction project. A single brick is like a cell. When you put many identical bricks together to form a wall, that wall is a tissue. When you combine walls, floors, and windows, you get a room, which is an organ. When you combine all the rooms together, you get a house, which is the organism. Each level is more complex than the one before it, but they all rely on the smaller parts to function correctly.
📖 Definitions
🔍 Worked example — Easy
Arrange the following biological levels in order of increasing complexity: Organ, Cell, Organism, Tissue, Organ System.
🔍 Worked example — Standard
A student identifies a group of muscle cells working together to produce movement. Identify the level of organization and provide one example of a different organ system in humans.
🔍 Worked example — Exam-style
Compare the organization of a leaf in a plant to the organization of the stomach in a human. State the level of organization for both and identify the difference in their hierarchy.
⚠️ Common errors
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🎯 Exam question
(a) Define the term 'tissue'. [1] (b) State the level of organization for the following: (i) The heart [1] (ii) The digestive system [1] (iii) A muscle cell [1] [4 marks]
Worked example
(a) State two structures found in a plant cell that are not found in an animal cell, and give the function of each. [4]
🔍 Worked example — Easy
Identify the magnification of a cell image if the actual size of the cell is 0.02 mm and the image size is 4 mm.
🔍 Worked example — Standard
Compare the presence of a cell wall and a nucleus in a typical plant cell versus a typical animal cell.
🔍 Worked example — Exam-style
An examiner asks: 'Explain how the structure of a root hair cell is adapted to its function of absorbing water.'
⚠️ Common errors
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Practice
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