iGCSE Human Biology Edexcel

Cells and Tissues: Cell Structures

Overview of Cells

• A cell is the smallest unit of life.
• Cells are the basic building blocks from which all living organisms are formed.
• There are two broad categories of cells: prokaryotic (bacteria and archaea) and eukaryotic (plants, animals, fungi, and protists).

Cell Structures and Functions

• The nucleus controls cell activity and contains DNA, which carries genetic information.
• Mitochondria provide the cell with energy through respiration.
• The cytoplasm is a gel-like substance where most of the cell's activities occur.
• The membrane-bound organelles carry out specific functions within the cell.
• The cell membrane, also known as the plasma membrane, controls the passage of substances in and out of the cell.

Eukaryotic and Prokaryotic Cells

• Eukaryotic cells are typically more complex and include organelles such as the nucleus and mitochondria.
• Prokaryotic cells are generally simpler and smaller than eukaryotic cells, lacking a nucleus and most organelles.
• Bacterial cells are prokaryotic cells. They have a cell wall, cell membrane, cytoplasm and plasmids, but no nucleus.

Plant Cell Structures

• Plant cells have a cell wall made of cellulose, which provides support and maintains the shape.
• They contain chloroplasts, which are used in photosynthesis to produce food for the plant.
• The vacuole stores water and other substances in plant cells.

Animal Cell Structures

• Animal cells do not have a cell wall or chloroplasts but contain other structures including the mitochondria and nucleus.
• The lysosomes in an animal cell contain enzymes for digestion.

Tissue Structures

• A tissue is a group of similar cells that work together to perform a specific function.
• Examples of tissues include muscle tissue, connective tissue, and neural tissue.

The Role of the Cell

• Cells combine to form tissues, tissues combine to form organs, and organs combine to form organ systems.
• Each specific type of cell has a specific role in the functioning of the human body.
• Faults or damage in cell structure can lead to diseases and disorders.