Cells
Introduction to Cells
- The cell is the basic unit of life. All organisms are made up of cells.
- There are two broad categories of cells: Prokaryotic (lacking a nucleus e.g. bacteria) and Eukaryotic (with a nucleus e.g. animal and plant cells).
Cell Structure
- Eukaryotic cells contain several organelles, essential compartments for specific functions.
- The nucleus is where DNA is stored and it controls the activities of the cell.
- The cytoplasm is a jelly-like substance where most chemical reactions occur.
- The cell membrane controls what goes in and out of the cell.
- The mitochondria is where energy is released in the cell.
- Plant cells also have a cell wall for added structure, chloroplasts for photosynthesis, and a large central vacuole for storing water, nutrients and waste products.
Cell Function
- The primary function of a cell is to organise, regulate and carry out life processes.
- Some of these processes include: growth, reproduction, response to the environment, and energy conversion.
- Specialised cells have specific roles, e.g. nerve cells or neurons transmit electrical impulses while muscle cells contract and relax to allow movement.
Cell Division: Mitosis
- Cells multiply through a process called mitosis, which creates two identical daughters cells.
- During mitosis, DNA in the nucleus is first replicated, then the original and replicated chromosomes are separated into two new nuclei.
- Finally, the cytoplasm and cell membrane divide, resulting in two new cells.
Comparison: Animal Cells vs Plant Cells
- Both animal and plant cells are eukaryotic and contain: a nucleus, cytoplasm, cell membrane and mitochondria.
- Plant cells additionally possess: a cell wall, a large central vacuole, and chloroplasts.
- Animal cells often contain smaller vacuoles and lack a cell wall and chloroplasts.
Cells and Microorganisms
- Microorganisms are primarily single-celled organisms including: bacteria, archaea, and certain eukaryotes.
- They are much simpler than eukaryotic cells and are collectively known as prokaryotic cells.
- Prokaryotic cells do not have a defined nucleus. Instead, their genetic material is present in a structure called a nucleoid.