Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 6.2 Eukaryotic Cells Have Internal Membranes That Compartmentalize Their Functions
All living things are made of cells—but not all cells are the same. This section highlights the key differences between prokaryotic and eukaryotic cells, and how internal membranes allow eukaryotic cells to carry out complex, compartmentalized functions.
1. Two Types of Cells: Prokaryotic vs. Eukaryotic
All cells share four basic features:
- A plasma membrane
- Cytosol (semi-fluid internal substance)
- Chromosomes (carry genes as DNA)
- Ribosomes (build proteins)
Prokaryotic cells (Bacteria and Archaea):
- DNA is in an unbound region called the nucleoid
- Lack membrane-bound organelles
- Simpler internal structure
- Typically smaller in size (1–5 μm)
Eukaryotic cells (protists, fungi, animals, plants):
- DNA is housed inside a nucleus, enclosed by a membrane
- Contain various membrane-bound organelles
- Generally larger (10–100 μm)
- Internally organized, with compartments for specialized functions
2. The Role of Internal Membranes in Eukaryotes
Eukaryotic cells have extensive internal membranes that:
- Create distinct environments for different metabolic processes
- Allow simultaneous, separate activities within one cell
- Are primarily composed of phospholipid bilayers with embedded proteins
Organelles are like departments within a factory—each performs a different job:
- Mitochondria → energy production
- Nucleus → information storage
- Golgi apparatus → protein processing
- Endoplasmic reticulum → synthesis and transport
Membranes aren’t just boundaries—they’re active participants. Many contain enzymes crucial for metabolism.
3. Size and Function: The Surface Area-to-Volume Dilemma
As a cell grows, its volume increases faster than surface area, which limits the efficiency of material exchange with the environment.
This is why:
- Most cells are microscopically small
- Some cells have specialized shapes (e.g., microvilli) to increase surface area without significantly increasing volume
- Larger organisms have more cells, not bigger ones
4. Organelles Help with Efficiency
Internal membranes divide eukaryotic cells into compartments with specific functions, improving efficiency and allowing incompatible processes to occur simultaneously.
Example:
- In mitochondria, membranes host enzymes for cellular respiration
- In chloroplasts, membranes enable photosynthesis
In a Nutshell
- Eukaryotic cells differ from prokaryotic cells by having a nucleus and internal organelles.
- Internal membranes allow eukaryotic cells to compartmentalize functions, enhancing complexity and efficiency.
- Cell size is limited by the surface area-to-volume ratio, influencing shape and organization.
- The evolution of membrane-bound compartments was key to the rise of complex life.