IB Biology Standard Level

Introduction to cells

Cell Theory

• The cell theory posits that all living organisms are composed of cells, the cell is the basic unit of life, and all cells come from pre-existing cells.
• Early observations by Robert Hooke and Antonie van Leeuwenhoek using rudimentary microscopes led to the discovery of cells.

Types of Cell

There are two main types of cells:

• Prokaryotic cells: These are simpler, smaller and exist in bacteria and archaea.
• Eukaryotic cells: These are more complex and larger, existing in plants, animals, fungi and protists. They are characterized by having a nucleus and other membrane-bound organelles.

Key Parts of a Cell

• Cell membrane: The boundary of the cell that controls which substances can enter or leave.
• Nucleus: Contains the genetic material (DNA) and controls cell activities.
• Cytoplasm: Key site for most cell activities such as respiration, protein synthesis, and where cell chemicals react.
• Mitochondria: Site of aerobic respiration, providing energy for the cell.
• Ribosomes: Site of protein synthesis.
• Cell wall (only in plant cells): Gives plant cells a rigid structure and resistance to osmotic changes.
• Chloroplasts (only in plant cells): Contains chlorophyll and are the sites of photosynthesis.
• Vacuole (larger in plant cells): Stores cell sap and helps to maintain pressure within the cell.

Classification of Organisms

• Unicellular organisms are made of a single cell (e.g., bacteria).
• Multicellular organisms consist of many cells of one or more types (e.g., humans).

Introduction to Organelles

• Organelles are structures within cells that perform specific functions.
• Membrane-bound organelles are surrounded by a membrane separate from the cell membrane, like the nucleus or mitochondria.
• Organelles are enclosed within their own membrane allow the cell to control the metabolic processes that happen within them.

Cell Specialization

• Despite all cells within an organism's body being produced from the same DNA, they can differentiate and specialize to perform specific functions.
• Examples of specialized cells include nerve cells, muscle cells, and red blood cells in animals, and root hair cells, xylem cells, and phloem cells in plants.

Experimental Techniques for Studying Cells

• Microscopy, in particular light and electron microscopy, is crucial to our understanding of cell structures.
• Cell fractionation refers to the process where cells are broken up and the different organelles are separated out.

Please note: The above points are an introduction to cells. This topic is broad and diverse, and it is advised to explore each part in detail for a comprehensive understanding.