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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Cell Components and Functions
Cells are the basic building blocks of all living organisms. They come in different shapes and sizes, but they all have certain structures in common. In this section, we'll explore the components of cells and their functions.
Key Definitions:
Plant cells have several unique features that animal cells don't have:
Animal cells are generally smaller and have these characteristics:
Let's explore the main organelles found in eukaryotic cells and understand their functions:
The cell membrane (also called the plasma membrane) surrounds the cell and controls what enters and leaves. It's made of a phospholipid bilayer with proteins embedded in it.
The cell membrane works a bit like a security guard at a nightclub - it decides who gets in and who stays out!
The nucleus is the control centre of the cell. It contains the cell's genetic material (DNA) and directs all cellular activities.
Think of the nucleus as the cell's brain - it holds all the instructions for how the cell should work.
The powerhouse of the cell! Mitochondria are where cellular respiration occurs, producing energy (ATP) from glucose and oxygen.
Found in: All eukaryotic cells, but more numerous in active cells like muscle cells.
Green organelles that capture light energy for photosynthesis, converting it into chemical energy (glucose).
Found in: Plant cells and some algae, but not in animal cells.
Fluid-filled sacs that store water, nutrients, waste products and other materials.
Found in: All cells, but plant cells have one large central vacuole while animal cells have smaller ones.
Red blood cells (erythrocytes) are a perfect example of cell specialisation. They have a unique biconcave disc shape that increases their surface area for oxygen absorption. They've lost their nucleus and most organelles to make more room for haemoglobin, the protein that carries oxygen. This specialisation makes them extremely efficient at their job - transporting oxygen around the body - but it also means they can only live for about 120 days before being replaced.
Although all cells in an organism contain the same genetic information, they can develop differently to perform specific functions. This is called cell specialisation or differentiation.
Cells are too small to see with the naked eye, so we use microscopes to study them. There are two main types:
To observe cells under a microscope, we often need to:
The cell was first observed and named by Robert Hooke in 1665 when he looked at a slice of cork under a microscope. He thought the small compartments he saw looked like the small rooms (or cells) in a monastery, so he called them "cells." However, what Hooke actually saw were the cell walls of dead plant cells!
| Cell Structure | Function | Found in |
|---|---|---|
| Cell membrane | Controls what enters and leaves the cell | All cells |
| Nucleus | Contains genetic material and controls cell activities | All eukaryotic cells |
| Cytoplasm | Site of many chemical reactions | All cells |
| Mitochondria | Site of cellular respiration (energy production) | All eukaryotic cells |
| Chloroplasts | Site of photosynthesis | Plant cells only |
| Cell wall | Provides structural support and protection | Plant cells only |
| Vacuole | Storage of water, nutrients and waste | Large in plant cells, small in animal cells |
| Ribosomes | Protein synthesis | All cells |
Understanding cell structure is fundamental to biology because it helps us understand how organisms function at their most basic level. Every cell is like a tiny factory, with different departments (organelles) working together to keep the organism alive and functioning properly.
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