2.4 Phagocytosis

Question 1

What are the two types of white blood cell?

Answer 1

Phagocyte
Lymphocyte

Question 2

What do phagocytes do?

Answer 2

Ingest and destroy the pathogen by a process called phagocytosis before it can cause harm. They provide an important defence against the pathogens that manage to enter the body

Question 3

What do lymphocytes do?

Answer 3

Lymphocytes are involved in immune response

Question 4

What is phagocytosis?

Answer 4

Large particles, such as some types of bacteria, can be engulfed by cells in the vesicles formed from the cell-surface membrane

Question 5

How do phagocytes travel?

Answer 5

• Some phagocytes travel in the blood but can move out of the blood vessels into other tissues

Question 6

What is the second line of defence?

Answer 6

• If the first line of defence fails and pathogens gain entry it is up to the white blood cells

Question 7

What is the process of phagocytosis?

Answer 7

• Chemical products of pathogens or dead, damaged and abnormal cells act as attractants, causing phagocytes to move towards the pathogen
• Phagocytes have several receptors on their cell-surface membrane that recognise, and attach to, chemicals on the surface of the pathogen
• They engulf the pathogen to form a vesicle, known as a phagosome
• Lysosomes move towards the vesicle and fuse with it
• Enzymes called lysozymes are present within the lysosome. These lysozymes destroy ingested bacteria by hydrolysis of their cell walls. The process is the same as that for the digestion of food in the intestines, namely the hydrolysis of larger, insoluble molecules into smaller, soluble ones
• The soluble products from the break down of the pathogen are absorbed into the cytoplasm of the phagocyte

Question 8

What is the first stage of phagocytosis?

Answer 8

The phagocyte is attracted to the pathogen by chemical products of the pathogen. It moves towards the pathogen along a concentration gradient

Question 9

What is the second stage of phagocytosis?

Answer 9

• Phagocytes have several receptors on their cell-surface membrane that recognise, and attach to, chemicals on the surface of the pathogen

Question 10

What is the third stage of phagocytosis?

Answer 10

• Lysosomes within the phagocyte migrate towards the pathogen
• The phagocyte cytoplasm surrounds the pathogen and the pathogen is engulfed.
• When the pathogen is engulfed, it is sealed into a phagosome (a vacuole) inside the cytoplasm.

Question 11

What is the fourth stage of phagocytosis?

Answer 11

• The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium and break down the pathogen

Question 12

What is the fifth stage of phagocytosis?

Answer 12

• The hydrolysis products of the bacterium are absorbed by the phagocyte
• The pathogen antigens are transported to the phagocyte cell membrane and presented on the cell surface.
• The antigens can activate the other cells in the immune response.

Question 13

Why are lysozymes found in tears?

Answer 13

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

Question 14

How does phagocytosis destroy pathogens?

Answer 14

1. Phagocyte moves towards pathogen via chemotaxis
2. Phagocyte engulfs pathogen via endocytosis to form a phagosome
3. Phagosome fuses with lysosome
4. Lysozymes digest pathogen
5. Phagocyte absorbs the products from pathogen hydrolysis