The Cell: Life’s Basic Unit

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The Cell: Life’s Basic Unit

Introduction to Biology

  • Definition of Biology: The study of life and living organisms, involving the investigation of complex interactions that sustain life.
  • Levels of Study:
  • Cell: Fundamental unit of life.
  • Tissue: Group of similar cells performing a function.
  • Organism: Complete living entity.

Key Learning Outcomes

  1. Understand cell theory.
  2. Differentiate between prokaryotic and eukaryotic cells.
  3. Identify cellular compartments and their functions.
  4. Grasp principles of osmosis, diffusion, and gradients.

Defining Life

Seven Criteria of Life

  1. Cellular Composition: Composed of one or more cells.
  2. Metabolism: Ability to:
  • Take in energy.
  • Transform molecules for cellular use.
  • Eliminate waste.
  1. Growth and Development:
  • Follows genetic instructions for growth.
  1. Reproduction: Ability to produce offspring.
  2. Adaptation:
  • Senses and responds to the environment.
  • Evolves to ensure survival.
  1. Response to Stimuli: Reacts to changes in surroundings.
  2. Homeostasis:
  • Maintains internal constancy despite external changes.

Homeostasis Examples

  • Cold Environment: Shivering generates heat.
  • Hot Environment: Sweating cools the body through evaporation.
  • Metaphor: Like a thermostat adjusting temperature in a room.

Cell Theory

  1. All living organisms are composed of one or more cells.
  2. Cells are the smallest unit of life.
  3. All cells arise from pre-existing cells.

Significance

  • Cellular specialization:
  • Example: Kidney cells filter, muscle cells contract.
  • Tissues formed by organized groups of similar cells.

Types of Cells

1. Prokaryotes

  • Simple structure without a nucleus.
  • DNA floats freely.
  • Examples:
  • Bacteria: Found everywhere, including microbiomes.
  • Archaea: Thrive in extreme environments (e.g., hot springs, high salinity).

2. Eukaryotes

  • Complex cells with organelles.
  • Organelles:
  • Specialized structures performing distinct functions.
  • Examples:
  • Animals, plants, fungi.

Endosymbiotic Theory

  • A prokaryotic cell engulfed another cell, leading to a symbiotic relationship.
  • Origin of:
  • Mitochondria: Energy production.
  • Chloroplasts: Photosynthesis in plants.

Eukaryotic Cell Structure

Organelles and Their Functions

  1. Nucleus:
  • Stores DNA.
  • Directs genetic information flow.
  1. Mitochondria:
  • Produces energy (ATP).
  1. Endoplasmic Reticulum (ER):
  • Smooth ER: Produces fats, stores calcium, detoxifies.
  • Rough ER: Studded with ribosomes; synthesizes proteins.
  1. Golgi Apparatus:
  • Packages and processes proteins.
  1. Lysosomes and Peroxisomes:
  • Break down waste and toxins.
  1. Cytoskeleton:
  • Maintains cell structure.
  • Facilitates cell movement.
  1. Chloroplasts (Plant Cells):
  • Conduct photosynthesis.

Cell Membrane and Function

Structure

  • Phospholipid Bilayer:
  • Hydrophilic Heads: Water-loving, face outward.
  • Hydrophobic Tails: Water-repelling, face inward.
  • Cholesterol:
  • Adds fluidity and stability.

Functions

  • Semi-Permeability:
  • Allows selective entry/exit of molecules.
  • Embedded Structures:
  • Transporters: Regulate molecule movement.
  • Enzymes: Catalyze chemical reactions.
  • Receptors: Detect external signals.

Plant vs. Animal Cells

  • Animal Cells:
  • Flexible membrane.
  • No rigid wall.
  • Plant Cells:
  • Cell wall made of cellulose.
  • Rigid structure for support.

By studying these notes, you’ll have a solid understanding of the cell’s structure, its role in life, and its importance in the broader study of biology.

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