Cells are the basic unit of life. Every living organism such as humans, animals, and plants is made up of cells. Understanding the cell structure and functions is very important for students preparing for JAMB Biology, WAEC Biology, NECO Biology, and other science exams.
This lesson note explains cell structure, cell organelles, functions, differences between plant and animal cells, and exam practice questions in a simple and easy way.
TABLE OF CONTENTS
- Introduction to Cells
- Meaning of Cell in Biology
- Cell Theory (JAMB Important Topic)
- Types of Cells
- Structure of a Cell (With Functions)
- Functions of Cell Organelles
- Differences Between Plant and Animal Cells
- Levels of Organization in Living Things
- Importance of Cells in Living Organisms
- Likely JAMB and WAEC Questions
- Summary of Cell Structure and Functions
1. INTRODUCTION TO CELLS
Cells are the smallest living units that make up all living organisms. They are responsible for all life processes such as growth, respiration, reproduction, and excretion.
No living thing can exist without cells.
2. MEANING OF CELL IN BIOLOGY
A cell is defined as the smallest structural and functional unit of life.
This means:
- It is the smallest unit of life
- It performs all life processes
- It is the building block of all living organisms
Cells can only be seen using a microscope.
3. CELL THEORY (IMPORTANT FOR JAMB AND WAEC)
Cell theory is one of the most important topics in Biology.
Cell Theory States That:
- All living organisms are made up of cells
- The cell is the basic unit of life
- All cells arise from pre-existing cells
Scientists who developed cell theory:
- Matthias Schleiden
- Theodor Schwann
- Rudolf Virchow
This theory is very important in understanding life processes.
4. TYPES OF CELLS
Cells are grouped into two main types:
A. PROKARYOTIC CELLS
These are simple cells without a true nucleus.
Characteristics:
- No true nucleus
- DNA is not enclosed in nuclear membrane
- No membrane-bound organelles
- Simple and small
Example: Bacteria
B. EUKARYOTIC CELLS
These are complex cells with a true nucleus.
Characteristics:
- Have a true nucleus
- DNA is enclosed in nuclear membrane
- Have membrane-bound organelles
- Larger and more complex
Examples: Plant cells, animal cells, fungi cells
5. STRUCTURE OF A CELL
A typical eukaryotic cell consists of the following parts:
- Cell membrane
- Cytoplasm
- Nucleus
- Mitochondria
- Ribosomes
- Endoplasmic reticulum
- Golgi apparatus
- Vacuole
- Chloroplast (in plant cells only)
- Lysosome (in animal cells)
Each of these structures performs specific functions.
6. FUNCTIONS OF CELL ORGANELLES
Cell Membrane
Controls the movement of substances in and out of the cell. It is selectively permeable.
Cytoplasm
A jelly-like fluid where all cell activities take place.
Nucleus
Controls all activities of the cell and contains genetic material (DNA).
Mitochondria
Responsible for energy production in the cell. It is known as the powerhouse of the cell.
Ribosomes
Site of protein synthesis.
Endoplasmic Reticulum (ER)
Helps in the transport of materials within the cell.
Golgi Apparatus
Packages and distributes proteins and other materials.
Vacuole
Stores water, food, and waste products.
Chloroplast (Plant Cell Only)
Responsible for photosynthesis in green plants.
7. DIFFERENCES BETWEEN PLANT AND ANIMAL CELLS
| Feature |
Plant Cell |
Animal Cell |
| Cell wall |
Present |
Absent |
| Shape |
Fixed/rectangular |
Irregular |
| Chloroplast |
Present |
Absent |
| Vacuole |
Large permanent vacuole |
Small or temporary |
| Nutrition |
Autotrophic |
Heterotrophic |
8. LEVELS OF ORGANIZATION IN LIVING THINGS
In living organisms, cells are organized into higher structures:
Cell → Tissue → Organ → System → Organism
Example:
Muscle cell → Muscle tissue → Heart → Circulatory system → Human being
9. IMPORTANCE OF CELLS IN LIVING ORGANISMS
Cells are important because:
- They form the basic structure of all living organisms
- They carry out life processes
- They are responsible for growth and repair
- They help in reproduction
- They produce energy needed for survival
Without cells, life cannot exist.
10. LIKELY JAMB AND WAEC QUESTIONS
-
The basic unit of life is:
A. Tissue
B. Organ
C. Cell
D. System
Answer: C
-
The powerhouse of the cell is:
A. Ribosome
B. Nucleus
C. Mitochondria
D. Golgi body
Answer: C
-
Which of the following is found in plant cells only?
A. Mitochondria
B. Chloroplast
C. Ribosome
D. Cytoplasm
Answer: B
-
The cell theory states that:
A. Cells arise from non-living things
B. All living things are made of cells
C. Cells do not reproduce
D. Only animals have cells
Answer: B
-
Prokaryotic cells lack:
A. Cytoplasm
B. Cell membrane
C. Nucleus
D. DNA
Answer: C
11. SUMMARY OF CELL STRUCTURE AND FUNCTIONS
Cells are the basic units of life. There are two main types of cells: prokaryotic and eukaryotic cells. Eukaryotic cells are more complex and found in plants and animals.
Each cell contains organelles that perform specific functions such as energy production, protein synthesis, and transport of materials.
Understanding cell structure and functions is very important for success in JAMB Biology, WAEC Biology, and NECO examinations.
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