IB Biology Topic 6.3 Defence Against Infectious Disease Notes & Questions (SL/HL)

IB Biology Topic 6.3 Defence Against Infectious Disease Notes & Questions (SL/HL) | RevisionDojo

Introduction

Infectious diseases are caused by pathogens such as bacteria, viruses, fungi, and parasites. The human body has developed multiple defense mechanisms to protect against these pathogens. This study note will cover the key aspects of the body's defense against infectious diseases as outlined in the International Baccalaureate (IB) Biology syllabus. The main topics include the role of the skin, blood clotting, white blood cells, antibiotics, and antibiotic resistance.

6.3.1 Skin

Physical Barrier

The skin is the largest organ in the human body and serves as a formidable barrier against pathogens. It provides:

Tough Physical Barrier: The outermost layer of the skin, the epidermis, is composed of tightly packed cells that are continuously shed, removing potential pathogens.
Microorganisms: The skin is home to a variety of harmless microorganisms that outcompete potential pathogens for resources and space.

Chemical Protection

The skin also offers chemical defenses:

Sebum: Produced by sebaceous glands, sebum maintains a low pH on the skin surface, inhibiting the growth of harmful microorganisms.
Sweat: Contains lysozyme, an enzyme that breaks down bacterial cell walls.

Mucous Membranes

Mucous membranes line areas of the body that are exposed to the external environment, such as the respiratory, digestive, and reproductive tracts. They provide additional protection through:

Mucus: Produced by goblet cells, mucus traps pathogens and particles, which are then expelled or swallowed.
Lysozyme: Present in mucus, lysozyme provides antibacterial properties.

Tip

Regular hand washing and maintaining good hygiene can significantly enhance the protective functions of the skin and mucous membranes.

6.3.2 Blood Clotting

Mechanism of Blood Clotting

When the skin is cut, blood clotting prevents pathogens from entering the body. The process involves:

Platelet Activation: Platelets adhere to the site of injury and release clotting factors.
Clotting Cascade: A series of reactions that convert the plasma protein fibrinogen into fibrin.
Fibrin Mesh: Fibrin strands form a mesh that traps blood cells, forming a clot.

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Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

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Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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Introduction

6.3.1 Skin

Physical Barrier

The skin is the largest organ in the human body and serves as a formidable barrier against pathogens. It provides:

Tough Physical Barrier: The outermost layer of the skin, the epidermis, is composed of tightly packed cells that are continuously shed, removing potential pathogens.
Microorganisms: The skin is home to a variety of harmless microorganisms that outcompete potential pathogens for resources and space.

Chemical Protection

The skin also offers chemical defenses:

Sebum: Produced by sebaceous glands, sebum maintains a low pH on the skin surface, inhibiting the growth of harmful microorganisms.
Sweat: Contains lysozyme, an enzyme that breaks down bacterial cell walls.

Mucous Membranes

Mucous membranes line areas of the body that are exposed to the external environment, such as the respiratory, digestive, and reproductive tracts. They provide additional protection through:

Mucus: Produced by goblet cells, mucus traps pathogens and particles, which are then expelled or swallowed.
Lysozyme: Present in mucus, lysozyme provides antibacterial properties.

Tip

Regular hand washing and maintaining good hygiene can significantly enhance the protective functions of the skin and mucous membranes.

6.3.2 Blood Clotting

Mechanism of Blood Clotting

When the skin is cut, blood clotting prevents pathogens from entering the body. The process involves:

Platelet Activation: Platelets adhere to the site of injury and release clotting factors.
Clotting Cascade: A series of reactions that convert the plasma protein fibrinogen into fibrin.
Fibrin Mesh: Fibrin strands form a mesh that traps blood cells, forming a clot.

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology 6.3 Defence Against Infectious Disease Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Introduction

6.3.1 Skin

Physical Barrier

Chemical Protection

Mucous Membranes

6.3.2 Blood Clotting

Mechanism of Blood Clotting

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Introduction

6.3.1 Skin

Physical Barrier

Chemical Protection

Mucous Membranes

6.3.2 Blood Clotting

Mechanism of Blood Clotting

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account