Cell Structure and Organization

CELL STRUCTURE AND ORGANIZATION

Cells are the basic building blocks of life. Every living organism — from bacteria to humans — is made of cells. Some organisms have just one, others have trillions.

Let’s break it down.

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1️⃣ WHAT IS A CELL?

A cell is the smallest structural and functional unit of a living organism that can carry out life processes such as respiration, growth, reproduction, and excretion.

Basically: cells are the “atoms” of biology.

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2️⃣ CELL THEORY

This is one of the most important concepts in Biology.

Cell Theory states that:

1. All living things are made up of cells.

2. The cell is the basic unit of life.

3. All cells come from pre-existing cells (they divide to form new cells).

Additional modern points:
4. Activities of organisms depend on the activities of cells.
5. Cells contain hereditary materials (DNA/RNA).

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3️⃣ TYPES OF CELLS

1. Prokaryotic Cells

Simple cells without a nucleus.

Features:

• No true nucleus (just a nucleoid)

• No membrane-bound organelles

• Smaller in size

• Found in bacteria and blue-green algae

2. Eukaryotic Cells

Complex cells with a true nucleus.

Features:

• Have nucleus

• Has membrane-bound organelles (mitochondria, chloroplast, etc.)

• Larger in size

• Found in plants, animals, fungi, protists

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4️⃣ PARTS OF A CELL & THEIR FUNCTIONS

Let’s list the organelles and what they do — because JAMB loves this section.

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A. Cell Membrane (Plasma membrane)

• Thin boundary surrounding the cell

• Controls what enters and leaves the cell (semi-permeable)

• Gives the cell shape

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B. Cytoplasm

• Jelly-like fluid inside the cell

• Contains organelles

• Site of most metabolic reactions

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C. Nucleus

The “control center” of the cell.

Functions:

• Controls cell activities

• Contains DNA (genetic material)

• Responsible for cell division

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D. Mitochondrion (Powerhouse)

• Site of cellular respiration

• Produces ATP (energy)
  You see this organelle? It’s the NEPA of the cell 🔋.

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E. Ribosomes

• Site of protein synthesis

• Found in cytoplasm or attached to ER

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F. Endoplasmic Reticulum (ER)

Rough ER (RER)

• Has ribosomes

• Makes proteins

Smooth ER (SER)

• Makes lipids (fats)

• Detoxifies harmful substances

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G. Golgi Body (Golgi Apparatus)

• Packages and transports proteins

• Forms lysosomes
  Think of it like the DHL/Post Office of the cell 📦.

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H. Lysosomes

• Contain digestive enzymes

• Break down worn-out cell parts and foreign materials

• “Waste disposal unit”

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I. Chloroplasts (Plant cells only)

• Contain chlorophyll

• Site of photosynthesis

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J. Cell Wall (Plant cells only)

• Made of cellulose

• Provides support and protection

• Makes plant cells rigid

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K. Vacuole

• Storage of water, food, and waste

• Large in plant cells

• Small or absent in animal cells

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5️⃣ DIFFERENCES BETWEEN PLANT AND ANIMAL CELLS

Feature	Plant Cell	Animal Cell
Cell wall	Present	Absent
Chloroplast	Present	Absent
Vacuole	Large central	Small/none
Shape	Fixed/regular	Irregular
Energy storage	Starch	Glycogen
Centriole	Absent	Present

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6️⃣ LEVELS OF ORGANIZATION IN LIVING THINGS

From simple → complex.

1. Cell

2. Tissue

3. Organ

4. System (Organ System)

5. Organism

Examples

• Muscle cells → Muscle tissue → Heart (organ) → Circulatory system → Human

• Root hair cell → Root tissue → Root → Transport system → Plant

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7️⃣ SPECIALIZED CELLS & THEIR FUNCTIONS

Cell	Adaptation	Function
Red blood cell	No nucleus, biconcave	Transport oxygen
Root hair cell	Long thin extension	Absorb water & minerals
Nerve cell	Long fibers	Transmit impulses
Sperm cell	Tail for movement	Fertilization
Palisade cell	Many chloroplasts	Photosynthesis

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8️⃣ WAEC/JAMB SAMPLE QUESTIONS

1. State the three main parts of a cell.

2. Mention two differences between prokaryotic and eukaryotic cells.

3. What is the function of the mitochondrion?

4. List three differences between plant and animal cells.

5. Define the cell theory.

6. Give two examples of specialized cells.