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Unit 1Lesson 2 3 min read

Prokaryotic vs. Eukaryotic Cells

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Learning Objectives

Distinguish between the two major types of cells: prokaryotic and eukaryotic.
Identify the key organelles found in eukaryotic cells (nucleus, mitochondria, cytoplasm, etc.).
Explain the main structural differences between plant and animal cells.

Two Basic Types of Cells

While all living things are made of cells, not all cells are the same. The first major division in the living world is between two types of cells: prokaryotic and eukaryotic. The main difference is simple: eukaryotic cells have a nucleus, and prokaryotic cells do not.

Prokaryotic Cells

The word prokaryote means 'before the nucleus.' These were the first type of cells to evolve on Earth. They are much smaller and simpler than eukaryotic cells.

Key Features:
No Nucleus: Their genetic material (DNA) is not contained within a membrane-bound nucleus. Instead, it floats in a region of the cytoplasm called the nucleoid.
No Membrane-Bound Organelles: They lack complex structures like mitochondria, vacuoles, or an endoplasmic reticulum.
Ribosomes: They do have ribosomes, which are needed to make proteins.
Cell Wall, Cell Membrane, Cytoplasm: They have these basic components.
Examples: The best examples are bacteria and archaea.

Eukaryotic Cells

The word eukaryote means 'true nucleus.' These cells are larger and much more complex than prokaryotes. They make up all multicellular organisms (like you!) as well as some single-celled ones like amoebas and yeast.

Key Features:
Nucleus: Their DNA is enclosed within a nucleus, which acts as the cell's control center.
Membrane-Bound Organelles: They are filled with many different organelles, each with a specific job. Think of them as the 'organs' of the cell.

Key Eukaryotic Organelles

Nucleus: Contains the cell's DNA and controls the cell's activities.
Mitochondria (singular: mitochondrion): The 'powerhouse' of the cell. It's where cellular respiration occurs to release energy (ATP) from food.
Cytoplasm: The jelly-like substance that fills the cell and surrounds the organelles.
Cell Membrane: The outer boundary of all cells, which controls what enters and leaves.
Ribosomes: The sites of protein synthesis. Found in both prokaryotes and eukaryotes.
Vacuole: A storage sac for water, food, and waste. Much larger in plant cells.

Plant vs. Animal Cells

Plant and animal cells are both eukaryotic, but they have a few key differences related to their function.

| Feature | Animal Cell | Plant Cell |

|---------------|--------------------------|---------------------------------------------|

| Cell Wall | Absent | Present (a rigid layer outside the membrane) |

| Chloroplasts| Absent | Present (site of photosynthesis) |

| Vacuole | Small, temporary vacuoles | Large central vacuole (stores water) |

| Shape | Irregular/Flexible | Fixed, often rectangular shape |

The cell wall gives plants their rigid structure. Chloroplasts are the organelles where photosynthesis (using sunlight to make food) happens. The large central vacuole in plants fills with water, creating turgor pressure that helps support the plant.

Key Terms

**Prokaryote
A single-celled organism that lacks a membrane-bound nucleus and other specialized organelles. Example: Bacteria.~|~Eukaryote: An organism whose cells contain a nucleus and other membrane-bound organelles. Examples: Plants, animals, fungi.~|~Organelle: A specialized structure within a eukaryotic cell that performs a specific function, like the nucleus or mitochondria.~|~Nucleus: The 'control center' of a eukaryotic cell, containing the cell's genetic material (DNA).~|~Mitochondria: The 'powerhouse' of the cell
the site of cellular respiration and ATP (energy) production.~|~**Chloroplast
An organelle found in plant cells where photosynthesis occurs.~|~Cell Wall: A rigid layer of nonliving material that surrounds the cells of plants and some other organisms, providing structure and protection.

Check Your Understanding

1

Which type of cell is believed to have evolved first on Earth?

2

Which of the following organelles is found in both prokaryotic and eukaryotic cells? A) Nucleus B) Mitochondria C) Ribosome D) Chloroplast

3

A scientist discovers a new organism. Its cells are observed to have a cell wall and chloroplasts. This organism is most likely a(n) ________.