Page 4: Phagocytosis

This page focuses on phagocytosis, a crucial process in the non-specific immune response a level Biology. It details the role of phagocytes and the steps involved in phagocytosis.

Phagocytes are white blood cells produced in the bone marrow and distributed throughout the body via the bloodstream. They are responsible for removing dead cells and invasive microorganisms as part of the non-specific immune response.

The process of phagocytosis involves:

1. Attraction of phagocytes to pathogens through chemotaxis
2. Recognition and attachment of phagocytes to pathogens
3. Engulfment of the pathogen to form a phagosome
4. Fusion of lysosomes with the phagosome
5. Destruction of the pathogen by lysozymes
6. Absorption of breakdown products into the phagocyte's cytoplasm

Vocabulary: Chemotaxis is the movement of cells along a chemical concentration gradient towards an attractant.

Definition: Lysozymes are enzymes that destroy bacteria by hydrolyzing their cell walls.

This detailed explanation of phagocytosis highlights its importance in the human defence system Biology and provides a clear understanding of how the body combats pathogens at a cellular level.

Page 3: Antigens and Antigen Variability

This page delves deeper into the concept of antigens, explaining their types and importance in the immune system. It also introduces the concept of antigen variability and its implications for immunity.

Antigens are macromolecules that serve as markers for cell-to-cell recognition. They can be found on cell surface membranes, bacterial cell walls, or virus surfaces. Antigens are classified into two main types:

1. Self-antigens: Produced by the organism's own body cells and do not stimulate an immune response.
2. Non-self antigens: Not produced by the organism's own body cells and stimulate an immune response.

Highlight: Antigen variability in some pathogens, such as cold and flu viruses, allows them to evade the immune system and cause repeated infections.

Example: The cold virus exhibits antigen variability, which is why individuals can catch colds multiple times, as their immune system may not recognize the new antigens.