Phagocytosis

What is a phagosome?

A vesicle within a phagocyte containing an engulfed pathogen.

How does the cytoplasm of the cell absorb the pathogen after it has been broken down by hydrolysis?

Although the larger molecule was previously insoluble, it has been broken down by hydrolysis into smaller, soluble molecules.

What are lysosomes?

An organelle in the cytoplasm of a eukaryotic cell that contains enzymes called lysozymes that destroy molecules by hydrolysis of their cell walls. They are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases. Lysomomes contain up to 50 enzymes per lysosome. Functions-hydrolyse material injected by phagocytic cells (white blood cells and bacteria), release enzymes to the outside of the cell (exocytosis) in order to destroy material outside the cell, digest worn out organelles so that the useful chemicals they are made out of can be reused and they completely break down cells after they have died (autolysis). They are specially abundant in secretory cells (such as epithelial cells) and in phagocytic cells.

Describe the mechanism of phagocytosis

Chemical products if pathogens or dead, damaged abnormal cells act as attractants, causing phagocytes to move towards the pathogen. Phagocytes have several receptors in their cell-surface membrane that recognise and attach to chemicals in the surface of the pathogen. They engulf the pathogen to form a vesicle, known as a phagosome. Lysosomes move toward the vesicle and fuse with it. Enzymes called lysozymes are present within the lysosomes. They destroy injested bacteria by hydrolysis of their cell walls. The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte.

What attracts a phagocyte to a pathogen?

Chemical products of the pathogen or dead damaged abnormal cells act as attractants.

How do lysozymes released by lysosomes destroy molecules?

Lysozymes hydrolyse the cell wall of the molecule breaking it down. (The process is the same as the digestion of food in the intestines, namely the hydrolysis of larger, insoluble molecules into smaller soluble ones.)

What are the two types of white blood cells?

Phagocytes and lymphocytes

What is the role of a phagocyte in the immune system?

Phagocytes ingest and destroy the pathogen by a process called phagocytosis.

Among other places lysozymes are found in tears. Suggest a reason why this is so.

The protective covering of the eyes - especially tear ducts, are potential entry points for pathogens. The eyes are vulnerable to infection because the coverings are thin to allow light through. Lysozymes will break down the cell walls of any bacterial pathogens and so destroy the before they can cause harm.