UNIT 4 Biology SAC 1 (I can do sheet)

What is the first line of defence?

The first line of defence consists of physical, chemical and microbiota barriers that prevent or impede the entry of pathogens into the body.

What is the purpose of the first line of defence?

To prevent pathogens from entering tissues and causing infection.

What are the three types of barriers in the first line of defence?

• Physical barriers

• Chemical barriers

• Microbiota barriers

What are physical barriers?

Structures that physically prevent pathogens entering the body.

Give examples of physical barriers in animals.

• INTACT Skin

• Mucous membranes

• Cilia

• Nasal hairs

Give examples of physical barriers in plants.

• Cell wall

• Bark

• Waxy cuticle

• Closed stomata

What are chemical barriers?

Substances that inhibit pathogen growth or destroy pathogens.

Give examples of chemical barriers in animals.

• Hydrochloric acid in stomach

• Lysozyme in tears

• Lysozyme in saliva

• Sebum on skin

• Acidic vaginal secretions

Give examples of chemical barriers in plants.

• Antimicrobial chemicals

• Antifungal compounds

• Toxic secondary metabolites

What are microbiota barriers?

Communities of beneficial microorganisms that prevent pathogen growth and colonisation.

How do microbiota prevent infection?

• Compete for nutrients

• Compete for space

• Produce antimicrobial chemicals

Give examples of microbiota barriers in animals.

• Gut microbiota

• Skin microbiota

Give examples of microbiota barriers in plants.

• Root microbiota

• Leaf microbiota

What is the innate immune response?

The second line of defence that provides a rapid, non-specific response against pathogens.

What are the characteristics of the innate immune response?

• Rapid

• Non-specific

• Present from birth

• No memory

What components make up the innate immune response?

• Inflammation

• Phagocytes

• Natural killer cells

• Complement proteins

• Cytokines

• Interferons

What triggers an inflammatory response?

• Tissue damage

• Pathogen entry

What is histamine?

A chemical released by mast cells that promotes inflammation.

What are the steps of the inflammatory response?

• Pathogen enters tissue

• Mast cells detect damage

• Histamine released

• Vasodilation occurs

• Capillary permeability increases

• Fluid enters tissues

• Phagocytes migrate to site

• Phagocytosis occurs

• Pathogens destroyed

• Tissue repair begins

What causes redness during inflammation?

Increased blood flow due to vasodilation.

What causes heat during inflammation?

Increased blood flow.

What causes swelling during inflammation?

Fluid leaking from capillaries into tissues.

What causes pain during inflammation?

Pressure from swelling and inflammatory chemicals.

Which cells are first to arrive at an infection site?

Neutrophils.

Where are mast cells found?

• Skin

• Respiratory tract

• Digestive tract

• Connective tissues

What is the role of mast cells?

• Release histamine

• Promote inflammation

• Trigger allergic responses

What is phagocytosis?

The process by which phagocytes engulf and destroy pathogens.

What are the steps of phagocytosis?

• Recognition

• Engulfment

• Phagosome formation

• Fusion with lysosome

• Digestion by lysozymes

• Waste expelled

What is a phagosome?

A vesicle containing an engulfed pathogen.

What is a lysosome?

An organelle containing digestive enzymes.

What are lysozymes?

Enzymes that digest bacterial cell walls and destroy pathogens.

What is a phagocyte?

An immune cell that performs phagocytosis.

Name three phagocytes.

• Macrophages

• Neutrophils

• Dendritic cells

What are macrophages?

Large, long-lived phagocytes.

What are the functions of macrophages?

• Phagocytosis

• Antigen presentation

• Cytokine release

Are macrophages antigen-presenting cells?

Yes.

What are neutrophils?

Short-lived phagocytes and the most abundant white blood cell.

What is the role of neutrophils?

• First responders to infection

• Destroy pathogens through phagocytosis

What are dendritic cells?

Professional antigen-presenting cells.

What are the functions of dendritic cells?

• Phagocytosis

• Antigen presentation

• Activation of adaptive immunity

What is the role of eosinophils?

• Attack parasites

• Contribute to allergic responses

What are natural killer cells?

Innate immune cells that kill infected and cancerous cells.

What do natural killer cells target?

• Virus-infected cells

• Cancer cells

How do natural killer cells kill target cells?

By releasing perforins that create holes in cell membranes.

What are complement proteins?

Blood proteins that assist the immune response.

What are the functions of complement proteins?

• Opsonisation

• Attract phagocytes

• Promote inflammation

• Form membrane attack complexes

• Directly destroy pathogens

What is opsonisation?

Coating a pathogen to make phagocytosis easier.

What is a membrane attack complex (MAC)?

A protein structure that forms pores in pathogen membranes causing lysis.

What are cytokines?

Signalling proteins released by immune cells.

What are the functions of cytokines?

• Cell communication

• Recruit immune cells

• Activate immune cells

• Coordinate immune responses

What are interferons?

Cytokines released by virus-infected cells.

What are the functions of interferons?

• Warn neighbouring cells

• Reduce viral replication

• Activate natural killer cells

What is a pathogen?

A disease-causing agent.

Why do pathogens trigger immune responses?

Because they contain non-self antigens.

What are cellular pathogens?

Disease-causing agents made of cells.

Give examples of cellular pathogens.

• Bacteria

• Fungi

• Protists

• Parasites

What are non-cellular pathogens?

Disease-causing agents not made of cells.

Give examples of non-cellular pathogens.

• Viruses

• Prions

How do cellular and non-cellular pathogens differ?

Cellular	Non-cellular

Made of cells

Not made of cells

Can reproduce independently

Require host cells

Have metabolism

No metabolism

What is an antigen?

A molecule, usually a protein, capable of triggering an immune response.

What are self-antigens?

Antigens naturally present on body cells.

What are non-self antigens?

Foreign antigens that trigger immune responses.

What does MHC stand for?

Major Histocompatibility Complex.

What is the function of MHC molecules?

Display antigens on cell surfaces.

Where are MHC Class I markers found?

On all nucleated body cells.

What is the role of MHC Class I markers?

Display self-antigens and allow immune surveillance.

Where are MHC Class II markers found?

• Macrophages

• Dendritic cells

• B lymphocytes

What is the role of MHC Class II markers?

Present foreign antigens to helper T cells.

Why do self-antigens not trigger an immune response?

Because immune cells recognise them as belonging to the body.

What is immune tolerance?

The ability of the immune system to ignore self-antigens.

Why may virus-infected cells be attacked by the immune system?

They display non-self viral antigens on their membrane.

Why may cancer cells be attacked by the immune system?

They display abnormal antigens.

Why may transplanted tissue be rejected?

It possesses different antigens from the recipient.

What is an autoimmune disease?

A disease caused when the immune system attacks self-antigens.

Give examples of autoimmune diseases.

• Type 1 Diabetes

• Multiple Sclerosis

• Rheumatoid Arthritis

What is an allergen?

A harmless substance that triggers an allergic response.

Give examples of allergens.

• Pollen

• Peanuts

• Dust mites

• Animal fur

• Bee venom

What antibody is involved in allergies?

IgE.

How does an allergen trigger an allergic response?

Allergen

↓

Binds IgE

↓

IgE attached to mast cell

↓

Mast cell activated

↓

Histamine released

↓

Inflammation occurs

What symptoms can allergies cause?

• Sneezing

• Itching

• Swelling

• Asthma

• Anaphylaxis

What are antigen-presenting cells (APCs)?

Cells that display antigens to T lymphocytes.

Name the professional APCs.

• Macrophages

• Dendritic cells

• B lymphocytes

What is the purpose of antigen presentation?

To activate the adaptive immune response.

What are the steps of antigen presentation?

• APC engulfs pathogen

• Pathogen digested

• Antigen fragment attached to MHC II

• APC travels to lymph node

• Helper T cell binds antigen-MHC complex

• Helper T cell activated

• Adaptive immune response begins

What are the three professional APCs?

Macrophages, dendritic cells and B lymphocytes.

Which MHC is found on all nucleated body cells?

MHC Class I

Which MHC activates helper T cells?

MHC Class II

Which cells are the main phagocytes?

Macrophages and neutrophils.

Which innate immune cell kills virus-infected cells?

Natural killer cells.

Which chemical released by mast cells causes inflammation?

Histamine.

Which cytokines help protect against viruses?

Interferons.

Which immune response is the second line of defence?

Innate immune response.

What are the two main roles of the lymphatic system in immunity?

1. Transport network for immune cells and antigens

2. Site of antigen recognition and activation of adaptive immunity

What is lymph?

Lymph is a clear fluid derived from tissue fluid that circulates through lymphatic vessels.

What does lymph contain?

• Water

• Proteins

• Antigens

• Pathogens

• White blood cells

• Cell debris

What is the function of lymphatic vessels?

Transport lymph throughout the body and return excess tissue fluid to the bloodstream.

Why do lymphatic vessels contain valves?

To prevent backflow and ensure one-way movement of lymph.

Where are lymph nodes found?

Clusters occur in:

• Neck

• Armpits

• Chest

• Abdomen

• Groin

What is the function of lymph nodes?

• Filter lymph

• Trap pathogens

• Site of antigen recognition

• Site of adaptive immune activation

Why are T and B lymphocytes concentrated in lymph nodes?

So they can encounter antigens and become activated.