Biology Chapter on Cell Theory

Cell Theory and Structure

• Cells serve as the basic unit of structure and function in living organisms.
• Three fundamental concepts of cell theory:
  • Cells are building blocks of living tissue.
  • They represent the smallest unit of life.
  • Cells arise from pre-existing cells through division.
• Two additional concepts:
  • Cells contain genetic blueprints for growth and development.
  • Cells are the site of all metabolic chemical reactions.

Characteristics of Cells

• No "typical" cell exists; there is a significant diversity among cell types.
• Common structures in most cells include:
  • Nucleus: Controls and directs cellular activities.
  • Cytoplasm: Site of metabolic reactions.
  • Cell Surface Membrane (Plasma Membrane): Regulates entry and exit of substances.

Organelles

• Organelles are specialized structures within cells, each serving specific functions.
• Organelles are typically too small to be observed at low magnification.
• Electron microscopy has advanced understanding of organelle structure.

Differences Between Plant and Animal Cells

• Cell Wall: Present in plant cells, composed primarily of cellulose; absent in animal cells.
• Vacuoles:
  • Plant cells often have a large, permanent vacuole for storage.
  • Animal cells may have smaller, temporary vacuoles.
• Chloroplasts: Present in green plant cells for photosynthesis; not found in animal cells.
• Centrosome: Located near the nucleus in animal cells; aids in nuclear division; absent in plant cells.
• Energy Storage:
  • Animal cells typically store energy as glycogen.
  • Plant cells usually store energy as starch.

Visual Insights

• Transmission electron microscopy (TEM) reveals the intricate structure of organelles, including membrane composition, and highlights the fluid surrounding the organelles within living cells.