14.2 Flashcards
(14 cards)
What forms a tough outer layer that acts as a barrier to the entry of pathogens? (1)
Human skin
What is the body’s first line of defence against pathogens? (1)
Forming a physical or chemical barrier to entry
If the first line of defence fails, what is the next line of defence? (1)
white blood cells, specifically phagocytes
What is the role of phagocytes? (1)
To ingest & destroy pathogens by a process called phagocytosis
What is phagocytosis? (3)
(1) A process where large particles, such as some types of bacteria, are engulfed
(2) by cells in vesicles formed from the cell-surface membrane.
(3) It is a non-specific defence mechanism.
What attracts phagocytes to pathogens or dead / damaged cells? (1)
Chemical products of pathogens OR dead, damaged, & abnormal cells
What do phagocytes have on their cell-surface membrane that helps them recognise pathogens? (1)
Receptors that recognise & attach to chemicals or antigens on the surface of the pathogen
What happens when a phagocyte engulfs a pathogen? (2)
(1) The pathogen is engulfed to form a vesicle
(2) known as a phagosome
What moves towards and fuses with the phagosome? (1)
Lysosomes
What do lysosomes contain? And what do they do? (2)
(1) enzymes / lysozymes
(2) they destroy ingested bacteria by hydrolysis of their cell walls
What happens to the soluble products from the breakdown of the pathogen? (1)
They are absorbed into the cytoplasm of the phagocyte
Among other places, the lysozymes are found in tears. Suggest a reason why this is so. (3)
(1) the protective covering of the eye and especially the tear ducts are potential entry points for pathogens.
(2) The eyes are vulnerable to infection because the coverings are thin to allow light through.
(3) Lysozymes will break down the cell walls of any bacterial pathogens and so destroy them before they can cause harm
Describe the overall process of phagocytosis. (7)
(1) chemical products of pathogens OR dead, damaged & abnormal cells act as attractants.
(2) this causes phagocytes to move towards the pathogen
(3) Phagocytes have several receptors on their cell-surface membrane that recognise, & attach to, chemicals or antigens on the surface of the pathogen
(4) they engulf the pathogen to form a vesicle, known as a phagosome
(5) Lysosomes move towards the vesicle & fuse with it
(6) the lysozymes in the lysosome destroy the ingested bacteria by hydrolysing their cell walls.
(7) the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
NOTE: to visualise the process of phagocytosis, check figure 3 on page 179.
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