Biology Cell Theory and Cell Types

Cell Theory

• Composed of three main principles:
  1. All living organisms are made of one or more cells.
  2. The cell is the basic unit of life.
  3. All cells arise from pre-existing cells.

Prokaryotic and Eukaryotic Cells

• Prokaryotic Cells:

  • Lack a nucleus and membrane-bound organelles.
  • Generally smaller and simpler (e.g., bacteria).
  • DNA is in a single circular chromosome.
  • Reproduce asexually through binary fission.

• Eukaryotic Cells:

  • Have a nucleus and membrane-bound organelles.
  • Generally larger and more complex (e.g., plant and animal cells).
  • DNA is linear and organized into multiple chromosomes.
  • Can reproduce asexually (mitosis) or sexually (meiosis).

Organelles

• Nucleus: Contains genetic material; controls cell activities.
• Mitochondria: Powerhouse of the cell; site of ATP (energy) production.
• Ribosomes: Protein synthesis; can be free-floating or attached to the endoplasmic reticulum.
• Endoplasmic Reticulum (ER):
  • Rough ER: Studded with ribosomes; involved in protein synthesis.
  • Smooth ER: Lipid synthesis and detoxification processes.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion.
• Lysosomes: Contains digestive enzymes; breaks down waste.
• Chloroplasts: Site of photosynthesis; found in plant cells.
• Cell Membrane: Semi-permeable barrier; regulates entry and exit of substances.

Cell Transport

• Passive Transport: Movement of molecules without energy input.

  • Types:
    • Diffusion: Movement from high to low concentration.
    • Facilitated Diffusion: Uses transport proteins for larger or polar molecules.
    • Osmosis: Special case involving water movement.

• Active Transport: Movement of molecules against their concentration gradient, requiring energy (ATP).

  • Example: Sodium-potassium pump.

Osmosis

• The diffusion of water across a semi-permeable membrane.
• Movement occurs from an area of low solute concentration to an area of high solute concentration.
• Important for maintaining cell turgor pressure in plant cells.
• Types of Solutions:
  • Isotonic: Equal solute concentration; no net water movement.
  • Hypotonic: Lower solute concentration outside; water enters cell (may burst).
  • Hypertonic: Higher solute concentration outside; water exits cell (may shrivel).

Cell Theory

• All living things are made of cells
• Cells are the fundamental unit of life
• New cells arise from pre-existing cells through cell division

Prokaryotic and Eukaryotic Cells

• Prokaryotic cells lack a nucleus and membrane bound organelles
• Prokaryotic cells include bacteria
• Prokaryotic cells are typically smaller and simpler than eukaryotes
• Prokaryotic DNA is in a single circular chromosome
• Prokaryotic cells reproduce asexually through binary fission
• Eukaryotic cells have a nucleus and membrane bound organelles
• Eukaryotic cells include plants and animals
• Eukaryotic cells are typically larger and more complex than prokaryotes
• Eukaryotic DNA is linear and organized into multiple chromosomes
• Eukaryotic cells can reproduce asexually through mitosis or sexually through meiosis

Organelles

• The nucleus contains genetic material (DNA) and controls cell activities
• Mitochondria are the powerhouses of the cell and produce ATP (energy)
• Ribosomes are the sites of protein synthesis
• The endoplasmic reticulum (ER) is a network of membranes involved in protein synthesis and lipid synthesis
  • Rough ER is studded with ribosomes and involved in protein synthesis
  • Smooth ER is involved in lipid synthesis and detoxification
• The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion
• Lysosomes contain digestive enzymes that break down waste
• Chloroplasts are the sites of photosynthesis and are found in plant cells
• The cell membrane regulates the entry and exit of substances

Cell Transport

• Passive transport does not require energy input
  • Diffusion is the movement of molecules from a high to a low concentration
  • Facilitated diffusion uses transport proteins to move larger or polar molecules across the membrane
  • Osmosis is the special case of water diffusion across a semi-permeable membrane
• Active transport requires energy (ATP)
  • It moves molecules against their concentration gradient
  • The sodium-potassium pump is an example of active transport

Osmosis

• Osmosis is the diffusion of water across a semi-permeable membrane
  • Water moves from an area of low solute concentration to an area of high solute concentration
  • Osmosis is important for maintaining cell turgor pressure in plant cells
• Isotonic solutions have equal solute concentrations, resulting in no net water movement
• Hypotonic solutions have a lower solute concentration outside the cell, causing water to enter the cell
  • This can lead to cell bursting
• Hypertonic solutions have a higher solute concentration outside the cell, causing water to exit the cell
  • This can lead to cell shriveling