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.