Cells: Fundamental Units of Life Study Notes

Fundamental Units of Life - Cells

Overview

• The term "Cell" is derived from the Latin word "cellula" meaning "little room".
• All living organisms are composed of cells, making them the fundamental unit of life.

Cellular Components and Structures

• Organelles: Specialized structures within a cell that perform distinct processes.
  • Mitochondrion: Powerhouse of the cell, produces energy.
  • Centriole: Involved in cell division.
  • Vesicle: Membrane-bound sacs that transport materials.
  • Cytosol: Fluid component of the cytoplasm where organelles are suspended.
  • Microtubules: Structural components of the cytoskeleton.
  • Chromatin: DNA and proteins in the nucleus; condenses to form chromosomes.
  • Nuclear Envelope: Double membrane surrounding the nucleus.
  • Nucleus: Control center containing genetic material.
  • Nuclear Pore: Openings that allow the transport of materials in and out of the nucleus.
  • Nucleolus: Site of ribosome synthesis.
  • Golgi Complex/ Apparatus: Processing and shipping center for proteins.
  • Lysosome: Contains digestive enzymes.
  • Flagellum: A whip-like structure for movement.
  • Rough Endoplasmic Reticulum (RER): Studded with ribosomes, synthesizes proteins.
  • Smooth Endoplasmic Reticulum (SER): Involved in lipid synthesis and detoxification.
  • Plasma Membrane: Phospholipid bilayer that encloses the cell, regulates entry and exit of substances.
  • Peroxisome: Involved in lipid metabolism and detoxification.

Anatomy of the Plant Cell

• Plant Cell Organelles:
  • Chloroplast: Site of photosynthesis, contains chlorophyll.
  • Vacuole: Large, membrane-bound space for storage and maintaining turgor pressure.
  • Cell Wall: Rigid outer layer providing structure and support.
  • Plasmodesmata: Channels between plant cells allowing for communication and transport.

Historical Background

• 1665 Robert Hooke: First observed cells using a self-designed microscope, describing them as resembling a honeycomb (cork cells).

Types of Cells and Organisms

Organism Classification by Cell Count

1. Unicellular Organisms:

   • Consist of a single cell.
   • All life functions are performed by this one cell.
   • Generally have a short lifespan.
   • Examples: Amoeba, Bacteria, Paramecium.

2. Multicellular Organisms:

   • Composed of many cells.
   • Different types of cells perform specialized functions.
   • Typically have a longer lifespan.
   • Examples: Humans, Trees, Animals.

Cellular Functions

Basic Functions of a Cell

• Responsible for vital processes such as:
  • Exchange of gases.
  • Digestion.
  • Absorption.

Main Components of a Cell

1. Cell Membrane/Plasma Membrane:

   • Serves as the boundary separating cytoplasm from the external environment.
   • Found in both plant and animal cells.
   • Composed of proteins and lipids.
   • Selectively permeable: allows certain substances to enter/exit the cell.
   • Flexible: can fold, break, and reunite.

2. Nucleus:

   • Contains genetic material and regulates activities.

3. Cytoplasm:

   • Jelly-like substance where organelles are suspended, facilitating metabolic processes.

Movement of Substances Through the Plasma Membrane

Processes

1. Diffusion:

   • The spontaneous movement of substances from an area of high concentration to an area of low concentration.
   • Examples: Movement of oxygen and carbon dioxide across the cell membrane.

2. Osmosis:

   • The movement of water molecules through a selectively permeable membrane.
   • Described as the diffusion of the solvent (water).

Types of Solutions Based on Concentration

• Hypertonic Solution:

  • Outside concentration is less than inside the cell.
  • Cell loses water and shrinks (e.g., grapes turning into raisins).

• Isotonic Solution:

  • Equal concentration inside and outside the cell.
  • Cell maintains equilibrium, gaining equal water.

• Hypotonic Solution:

  • Outside concentration is greater than inside the cell.
  • Cell gains water, swells, and may burst (e.g., eggs in water).