Level 2 Science WJEC

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.