10th Class Biology Chapter 9 Notes

Definition

Infectious diseases are caused by pathogens (bacteria, viruses, fungi, or parasites) that can spread from one host to another. Non-infectious diseases are not caused by pathogens and don't spread between people — they arise instead from genetics, lifestyle, environment, or the body's own malfunction (e.g. heart disease, most cancers, genetic disorders).

A doctor finding bacteria in a patient's blood sample indicates a bacterial infectious disease.

Zoonotic diseases are infectious diseases that spread from animals to humans — e.g. rabies (spread by an infected animal's bite, as when a person develops rabies after being bitten by a dog) and anthrax.

Vector-borne diseases are infectious diseases transmitted to humans via a living carrier (vector), usually an insect, rather than by direct contact — e.g. dengue fever, transmitted by mosquitoes. When a person develops dengue after a mosquito bite, the mosquito acts as the vector, carrying the pathogen from an infected source to a new host without itself necessarily being harmed by it.

A vector-borne disease transmitted through the bite of Ixodes ticks is Lyme disease.

Anthrax, caused by the bacterium Bacillus anthracis, is transmitted to humans mainly through contact with infected animals or contaminated animal products (like wool or hides).

Definition

Three examples of genetic diseases caused by abnormalities in genes or chromosomes: Down syndrome (an extra copy of chromosome 21), cystic fibrosis (a faulty gene affecting mucus production), and sickle cell anaemia (a faulty gene affecting haemoglobin structure).

Genetics can increase a person's risk of developing non-infectious diseases because inherited gene variants can make certain body systems inherently more vulnerable or less efficient (e.g. genes affecting cholesterol processing raising heart disease risk, or genes affecting cell division control raising cancer risk) — the disease isn't directly 'caught' but the genetic predisposition raises the probability of it developing, especially combined with certain lifestyle or environmental factors.

Definition

The skin is the first line of defence against pathogens, acting as a physical/chemical barrier — it's categorized as an organ (specifically, the largest organ of the body), and it defends the body by physically blocking pathogen entry, and via its slightly acidic secretions and natural microbial population, which make it harder for many pathogens to survive on its surface.

Mucous membranes (lining passages like the respiratory and digestive tracts, which aren't protected by tough skin) trap pathogens and particles in sticky mucus, which can then be expelled (e.g. coughed out) or destroyed, preventing pathogens from penetrating deeper into the body through these more vulnerable openings.

Blood clotting acts as a defence mechanism by rapidly sealing wounds, both preventing further blood loss and blocking an open entry point that pathogens could otherwise use to enter the body directly through broken skin.

Definition

Innate immunity is the body's general, non-specific defence present from birth, responding the same way to any pathogen (e.g. skin, mucous membranes, phagocytes, inflammation, fever) — it acts fast but doesn't 'remember' specific past infections. Acquired immunity is specific, develops over a person's lifetime in response to particular pathogens, and importantly retains a memory of them, giving a faster, stronger response the next time the same pathogen is encountered.

Definition

Inflammation is the body's localized response to injury or infection, causing redness, heat, swelling, and pain in the affected area — it's caused by chemical signals released by damaged tissue and immune cells, which increase blood flow and attract more immune cells to the site to fight infection and begin repair.

Fever is a controlled rise in body temperature, triggered by chemical signals released during an immune response — it helps the body fight infection because many pathogens reproduce less effectively at higher temperatures, while the body's own immune cells tend to work more efficiently.

Phagocytes (a type of white blood cell that develops from monocytes) ingest and kill bacteria and other pathogens through phagocytosis — engulfing and digesting them.

Interferon is a protective protein released by virus-infected cells; it doesn't directly kill the virus but helps nearby, still-healthy cells resist viral infection by triggering antiviral defences within them before the virus can spread further.

Natural killer cells are a type of lymphocyte (a white blood cell) that identify and destroy the body's own cells when those cells have become infected with a virus or turned cancerous, without needing to recognize a specific prior pathogen first.

Definition

T-cells and B-cells are both lymphocytes central to acquired immunity. T-cells directly destroy infected cells (cytotoxic T-cells) and help coordinate/regulate the wider immune response (helper T-cells). B-cells produce antibodies — proteins that specifically bind to a particular pathogen, marking it for destruction or neutralizing it directly.

Definition

Active immunity develops when the body produces its own antibodies in response to an actual infection or a vaccine, and typically includes long-lasting immune memory. Passive immunity is when ready-made antibodies are transferred into a person from an outside source (e.g. from mother to baby via the placenta or breast milk, or via an antibody injection) — it gives immediate but only temporary protection, since the body didn't produce these antibodies itself and doesn't retain the memory needed to make more of them later.

Definition

An allergic reaction is triggered when the immune system mistakenly identifies a normally harmless substance (an allergen, like pollen, certain foods, or dust) as dangerous and mounts an unnecessary immune response against it, releasing histamine and other chemicals that cause allergy symptoms.

Common types of allergies include hay fever (pollen), food allergies, dust mite allergies, and skin allergies (e.g. to certain chemicals or materials).

Some people develop allergies while others don't largely due to a combination of genetic predisposition (family history of allergies) and environmental factors (such as early-life exposure patterns to potential allergens) — the exact reasons aren't fully understood, but both nature and environment play a role.

Anaphylactic shock is a severe, rapid, whole-body allergic reaction that can cause the airways to swell and constrict (making breathing difficult) and blood pressure to drop sharply — it requires immediate medical treatment because, without prompt intervention (such as an adrenaline/epinephrine injection), it can be fatal within minutes.