IndietroUnit 2: Cell Structure and Function – Study Guide
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Cell Structure and Function
Cells: The Building Blocks of Life
Cells are the fundamental units of life, forming the basic structure and function of all living organisms. The concept of the cell is central to biology and is summarized by the Cell Theory:
All living organisms are composed of one or more cells.
The cell is the basic unit of life.
All cells arise from pre-existing cells.
Types of Cells
Prokaryotic Cells: Simpler and smaller, found in bacteria and archaea. They lack a nucleus and most membrane-bound organelles. Their DNA is located in a nucleoid region. Key structures include plasma membrane, ribosomes, and sometimes flagella or pili.
Eukaryotic Cells: More complex and larger, found in plants, animals, fungi, and protists. They have a true nucleus and various membrane-bound organelles, allowing for compartmentalization and specialized functions.
Key Organelles and Their Functions
Organelle | Description |
|---|---|
Nucleus | Control center of the cell; houses DNA and coordinates activities like growth, metabolism, and reproduction. |
Ribosomes | Sites of protein synthesis; found free in cytoplasm or attached to rough ER. |
Endoplasmic Reticulum (ER) | Rough ER: Studded with ribosomes, involved in protein synthesis and modification. Smooth ER: Lacks ribosomes, involved in lipid synthesis and detoxification. |
Golgi Apparatus | Modifies, sorts, and packages proteins and lipids for storage or transport; contains flattened sacs called cisternae. |
Mitochondria | Powerhouse of the cell; generates ATP through cellular respiration. Contains a double membrane and highly folded inner membrane called cristae. |
Chloroplasts | Found in plant cells; perform photosynthesis. Contains thylakoids stacked into grana and stroma for carbon fixation. |
Lysosomes | Contain digestive enzymes; break down waste materials and cellular debris. |
Peroxisomes | Detoxify harmful substances; break down fatty acids and produce hydrogen peroxide as a byproduct. |
Vacuoles | Storage organelles; large central vacuole in plant cells maintains turgor pressure. |
Cytoskeleton | Provides structural support, aids in cell division, and enables cell movement. Includes microfilaments, microtubules, and intermediate filaments. |
Endomembrane System vs. Energy Organelles
Endomembrane System: Includes organelles involved in synthesis, modification, and transport of proteins and lipids (nuclear envelope, rough and smooth ER, Golgi apparatus, lysosomes, vesicles, plasma membrane).
Energy Organelles: Mitochondria and chloroplasts; mitochondria perform cellular respiration (ATP production), chloroplasts carry out photosynthesis.
Differences Between Animal and Plant Cells
Plant Cells: Cell wall (support/protection), chloroplasts (photosynthesis), large central vacuole (turgor pressure), plasmodesmata (communication).
Animal Cells: Lysosomes (waste digestion), centrioles (cell division), cilia/flagella (movement).
Cell Size
Cell Metabolism and Size
Cells vary greatly in size, but all must be small enough to efficiently carry out necessary functions. The size of a cell impacts its metabolism, surface area to volume ratio, and overall efficiency. Understanding these concepts is crucial for grasping how cells operate and why they are structured the way they are.
Surface Area to Volume Ratio (SA:V): As a cell grows, its volume increases faster than its surface area, reducing efficiency in exchanging materials with the environment.
Formula for Surface Area of a Sphere:
Formula for Volume of a Sphere:
Formula for Surface Area of a Cube: (where a is the length of a side)
Formula for Volume of a Cube:
Importance: High SA:V ratio allows for efficient exchange of nutrients and waste; cells may adopt elongated or flattened shapes to maximize SA:V.
Example: Red blood cells are biconcave to increase surface area for gas exchange.
Additional info:
Compartmentalization in eukaryotic cells allows for specialized environments and increased efficiency of metabolic processes.
Plant cells are typically rectangular or cubic, while animal cells are round or irregular in shape.
