BIOLOGY · Stage 7 · Chapter 2: Cells and Organisation
Biology 2.7 Modelling cells — Scientific Models in Cell Biology — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
5 min read 6 parts Lesson 7 of 10
Lesson summary
2.7 Modelling cells — Scientific Models in Cell Biology — Alhussan International Academy — Biology (Stages 7–9) notes: Explain why scientists use models to study cells and describe the strengths and limitations of a model.Model = a simplified representation of something that help…
- When models are used
- Good model
- Physical models
- Computer models
- Membrane model
- Clay animal cell
Section 1 of 6What is a scientific model
- Model = a simplified representation of something that helps to explain it, make predictions or communicate an idea.
- When models are used
- when the real thing is too small, too large, too slow, too fast or too complicated to study directly.
- Cells
- they are too small to see in detail with the unaided eye, so biologists use many kinds of model.
- Good model
- it helps to remember the structure of a system and may show how it works.
- Bad model
- it confuses and can give misconceptions about a biological system.
Section 2 of 6Types of model for cells
- Physical models
- 3-D structures made from modelling clay, boxes, plastic bags or sweets, with different materials representing organelles.
- Analogies
- comparing a cell to something familiar such as a factory or a city.
- The nucleus is like the control office, mitochondria like power stations and the membrane like a security gate.
- Diagrams
- labelled drawings that show how parts are related.
- Computer models
- animations and simulations that show how organelles move or how substances cross a membrane.
- Membrane model
- a bag with small holes shows that small particles pass through while large ones are stopped.
Section 3 of 6Building a model cell
- Decide what each part of the model will represent and write a key.
- Choose sensible materials,
- such as a clear plastic bag for the membrane, gel for cytoplasm, a ball or grape for the nucleus and beads for mitochondria.
- Build the animal cell and the plant cell, giving the same structures the same colour in both so similarities are clear.
- Label each material and what it represents, and add a scale to show the size difference between animal and plant cells.
- Take care over relative sizes, because ribosomes are many times smaller than mitochondria.
Section 4 of 6Examples of student models
- Clay animal cell
- modelling clay lets the cell be an irregular shape, as animal cells are.
- Only the structures the student could remember were labelled.
- Plant cell in a green box
- dried peas in a balloon stand for chloroplasts and a grape stands for the nucleus.
- The balloon represents the membrane and cytoplasm, and the box represents the cell wall.
- The full balloon pushes outwards on the box like the vacuole pushes on the wall to keep a plant cell firm.
- Limitations of the box model
- a box is rigid and flat sided, but a real cell wall is made of a mesh of fibres.
Section 5 of 6Evaluating a model
| Strengths | Limitations |
|---|---|
| Makes a tiny structure big enough to see and handle | May show the wrong size, shape or proportions |
| Shows how parts fit together | Is often fixed, but real cells move and change |
| Helps to explain and remember functions | Materials do not behave like living parts |
| Can be used to make predictions | Predictions must still be tested by experiment |
- Factory analogy
- it shows each organelle has a job but not that cells are alive, grow and reproduce.
Section 6 of 6Models change with evidence
- Scientific models
- they are changed when new evidence is found.
- Early cell models
- they showed only a blob with a nucleus.
- Electron microscope images
- they added mitochondria, ribosomes and membranes to the model.
- Membrane model
- the fluid mosaic model describes proteins floating in a double layer of lipids, and it was improved as new techniques revealed more.
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