Cell Structure and Function: Study Guide for Chapter 4

Cell Structure and Function

Microscopy in Biology

Microscopy is essential for studying cells and their components. Different types of microscopes provide varying levels of magnification and resolution, making them suitable for specific applications.

• Light Microscopy: Uses visible light to illuminate specimens. Best for viewing live cells, tissues, and general cell structure. Limited by resolution (~200 nm).

• Transmission Electron Microscopy (TEM): Passes electrons through thin sections of specimens. Provides high-resolution images of internal cell structures. Used for detailed study of organelles.

• Scanning Electron Microscopy (SEM): Scans the surface of specimens with electrons. Produces detailed 3D images of cell surfaces and external features.

When to Use Each Type:

• Light microscopy: Observing living cells, tissues, and general morphology.

• TEM: Examining internal ultrastructure of cells and organelles.

• SEM: Studying surface details and 3D structure of cells and tissues.

Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells.

• All living organisms are composed of one or more cells.

• The cell is the basic unit of structure and function in living things.

• All cells arise from pre-existing cells.

Cell Size and Metabolism

Actively metabolizing cells must be small to efficiently exchange materials with their environment.

• Surface Area-to-Volume Ratio: As a cell grows, its volume increases faster than its surface area, limiting the rate of exchange of materials.

• Small cells have a higher surface area-to-volume ratio, allowing for more efficient nutrient uptake and waste removal.

Categories of Cells: Prokaryotes vs. Eukaryotes

Cells are classified into two main categories based on their structural features.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles. DNA is located in the nucleoid region. Examples: Bacteria and Archaea.

• Eukaryotic Cells: Have a true nucleus and membrane-bound organelles. Found in Protists, Fungi, Plants, and Animals.

Prokaryotic Cell Anatomy

Prokaryotic cells have a simple structure but are highly efficient.

• Plasma Membrane: Controls entry and exit of substances.

• Cell Wall: Provides structural support and protection.

• Nucleoid: Region containing circular DNA.

• Ribosomes: Sites of protein synthesis.

• Flagella: (in some) Used for movement.

Compartmentalization in Eukaryotic Cells

Eukaryotic cells are more complex due to internal compartmentalization by membranes.

• Organelles: Specialized structures that perform distinct cellular functions (e.g., nucleus, mitochondria, endoplasmic reticulum).

• Compartmentalization allows for separation of incompatible chemical reactions and increased efficiency.

Eukaryotic Organelles and Their Functions

Each organelle in a eukaryotic cell has a specific structure and function. (See Table 4.22 in your textbook for a comprehensive list.)

Organelle	Structure	Function
Nucleus	Double membrane, contains DNA	Stores genetic information, controls cell activities
Mitochondria	Double membrane, inner folds (cristae)	Site of cellular respiration, ATP production
Chloroplast	Double membrane, contains thylakoids	Site of photosynthesis (in plants and algae)
Endoplasmic Reticulum (ER)	Network of membranes	Rough ER: protein synthesis; Smooth ER: lipid synthesis
Golgi Apparatus	Stack of flattened membranes	Modifies, sorts, and packages proteins and lipids
Lysosome	Membrane-bound vesicle	Digests macromolecules and old organelles
Ribosome	RNA and protein complex	Protein synthesis
Plasma Membrane	Phospholipid bilayer	Regulates movement of substances in and out of the cell
Vacuole	Membrane-bound sac	Storage of substances; large central vacuole in plants

Specialized Organelles in Cell Types

Certain organelles are more prominent or specialized in specific cell types.

• Muscle cells: Abundant mitochondria for energy production.

• Plant cells: Large central vacuole for storage and turgor pressure; chloroplasts for photosynthesis.

• Liver cells: Extensive smooth ER for detoxification.

Endosymbiont Theory

The endosymbiont theory explains the origin of certain organelles in eukaryotic cells.

• Proposes that mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence includes their own DNA, double membranes, and similarities to bacteria.

• Modern-day organelles involved: Mitochondria and chloroplasts.

Key Vocabulary

Be familiar with definitions of bold-faced vocabulary words in your textbook, such as:

• Organelle: A specialized subunit within a cell with a specific function.

• Prokaryote: An organism whose cells lack a nucleus and membrane-bound organelles.

• Eukaryote: An organism whose cells contain a nucleus and membrane-bound organelles.

• Plasma Membrane: The cell's outer boundary, regulating entry and exit of substances.

• Ribosome: A complex of RNA and protein that synthesizes proteins.

• Endoplasmic Reticulum: A network of membranes involved in protein and lipid synthesis.

• Golgi Apparatus: An organelle that modifies and packages proteins and lipids.

• Lysosome: An organelle containing digestive enzymes.

• Mitochondrion: The powerhouse of the cell, site of ATP production.

• Chloroplast: The site of photosynthesis in plant cells.