2.2 cell recognition & the immune response

Question 1

give the two main defence mechanisms within the human body. provide examples for each.

Answer 1

non-specific - response is immediate and the same for all pathogens. examples include physical barriers such as the skin and chemical barriers such as phagocytosis, the first stage of the body’s immune response.

specific - response is slower and specific to each pathogen. examples include the cell mediated response, which involve the use of T lymphocytes, and the humoral response, which involve the use of B lymphocytes.

Question 2

give the two types of white blood cell, which protect the body from invasion and infection by pathogens.

Answer 2

phagocytes - ingest and destroy the pathogen through a process known as phagocytosis.

lymphocytes - are specialised, and are involved in more specific immune responses, such as the cell mediated response.

Question 3

explain why it is important that lymphocytes must be able to distinguish the body’s own cells and molecules from those that are foreign.

Answer 3

it is important that lymphocytes must be able to distinguish the body’s own cells and molecules from those that are foreign, or else they would destroy the organism’s own cells and tissues.

Question 4

describe what antigens are, and explain where they are generally found.

Answer 4

• antigens are molecules (usually proteins) that can generate an immune response when detected by the body.
• they are generally found on the surface of cells, and are used by the immune system to identify foreign bodies.

Question 5

describe the four main types of foreign material which are detected by antibodies.

Answer 5

pathogens - micro-organisms which cause disease.

abnormal body cells - such as cancerous or pathogen-infected cells, which have abnormal antigens on their surface.

toxins - including those that are produced by certain pathogens, such as the bacterium which causes cholera.

non-self material cells - such as cells from organisms of the same species (organ or tissue transplants)

Question 6

describe the process of phagocytosis.

Answer 6

• a phagocyte recognises foreign antigens on a pathogen inside the body.
• the cytoplasm of the phagocyte moves around the pathogen, engulfing it.
• the pathogen is now contained in a phagocytic vacuole within the cytoplasm of the phagocyte.
• a lysosome (an organelle containing enzymes known as lysozymes) fuses with the phagocytic vacuole. the lysozymes hydrolyse the pathogen.
• the phagocyte then presents the pathogen’s antigens by placing them on its surface to active other immune cells.