Year 9 Science Study Guide – Disease

Year 9 Science Study Guide – Disease

Learning Intention 1: Understanding Disease and Pathogens

  • Key Definitions:

    • Disease:

    • A condition that impairs normal functioning of the body, caused by pathogens or other factors.

    • Pathogen:

    • Anything that can cause disease and an immune response, including bacteria, viruses, fungi, and parasites.

  • Distinguishing Between Disease Types:

    • Infectious Diseases:

    • Diseases that are caused by pathogens and can be transmitted from one individual to another.

    • Non-Infectious Diseases:

    • Diseases not caused by pathogens and cannot be transmitted; often due to genetic or environmental factors.

  • Classification of Pathogens:

    • Cellular Pathogens:

    • Comprised of living cells; includes bacteria and fungi.

    • Non-Cellular Pathogens:

    • Not composed of living cells; includes viruses and prions.

  • Types of Pathogens:

    • Bacterial:

    • Characteristics: unicellular, reproduce through binary fission, generally fast-acting, can be treated with antibiotics.

    • Viral:

    • Characteristics: non-cellular, require a host to reproduce, can cause rapid harm, no antibiotic treatment available.

    • Fungal:

    • Characteristics: can be unicellular (yeasts) or multicellular (molds), reproduce through spores, vary in transmission methods.

    • Parasite:

    • Characteristics: live on or in a host organism, can be unicellular or multicellular, often complex life cycles, can cause significant harm.

Learning Intention 2: Pathogen Entry and Immune Response

  • Speed of Harm:

    • The rate at which a pathogen causes illness varies by the type of pathogen (e.g., viral infections may spread quickly).

  • Comparing Pathogens:

    • Mode of Entry:

    • Pathogens can enter through various routes such as respiratory, digestive, and skin penetration.

    • Reproduction Method:

    • Bacteria can reproduce independently; viruses need to invade host cells.

  • First Line of Defence:

    • Barriers to Pathogens:

    • Physical: Skin acts as a barrier.

    • Chemical: Stomach acid destroys harmful microbes. and lysosome enzymes in saliva and tears help break down bacteria,

    • Biological: Microbiota in the body competes with pathogens.

  • Role of Antigens:

    • Self Antigens: Markers on the body’s own cells.

    • Non-Self Antigens: Molecules found on foreign substances, such as bacteria and viruses, that trigger an immune response.

  • Second Line of Defence:

    • Process of Immune Response:

    • Phagocytosis: White blood cells engulf and destroy pathogens.

    • Inflammation: Increased blood flow and immune cells to the site of infection.

    • Fever: Elevated body temperature to inhibit pathogen growth.

  • Third Line of Defence:

    • B Cells:

    • Effector (Plasma) B Cells: Produce antibodies to fight pathogens.

    • Memory B Cells: Remembers pathogens for faster response in future infections.

    • Antibodies: Proteins that specifically target and neutralize pathogens.

    • T Cells:

    • Effector (Cytotoxic) T Cells: Kill infected cells directly.

    • Memory T Cells: Ensure a quicker response to previously encountered pathogens.

Learning Intention 3: Disease Spread and Prevention

  • Factors Influencing Disease Spread:

    • Population density, hygiene practices, immune responses, and pathogen virulence influence how quickly diseases spread.

    • Factors that limit spread include public health measures, vaccinations, and personal hygiene.

  • Defining Hygiene:

    • Hygiene practices are preventative measures to reduce the spread of disease, including:

    • Handwashing: Removes pathogens from hands.

    • Sanitation: Proper waste disposal and clean environments reduce pathogen exposure.

    • Isolation: Quarantining sick individuals prevents pathogen spread.

    • Distancing: Maintaining physical distance reduces transmission risk.

  • Distinction Between Disease Occurrences:

    • Endemic: Persistent presence of a disease within a specific geographic area.

    • Epidemic: A sudden increase in the number of cases above what is normally expected in a population.

    • Pandemic: An epidemic that has spread over several countries or continents, affecting large numbers of people.

Learning Intention 4: Vaccination and Community Health

  • Understanding Vaccination:

    • Vaccination is the administration of a vaccine to induce immunity against a specific pathogen.

  • Natural vs. Artificial Immunity:

    • Natural Immunity: Immunity gained through exposure to pathogens in the environment.

    • Artificial Immunity: Immunity gained through vaccination or immunization.

  • Benefits of Vaccination:

    • For Individuals: Personal protection against disease.

    • For Communities: Herd immunity reduces the overall presence of disease in the population.

  • Strategies to Limit Disease Spread:

    • Short-term Strategies: Immediate interventions like vaccination campaigns and hygiene education.

    • Long-term Strategies: Development of community health initiatives and sustained vaccination programs to provide ongoing protection against diseases.

  • B Cells: These are a type of lymphocyte (a type of white blood cell) that mature in the bone marrow. Their primary role is in humoral immunity, which involves producing antibodies.

    • Effector (Plasma) B Cells: When a B cell encounters its specific pathogen (or a part of it), it gets activated and differentiates into an effector B cell, also known as a plasma cell. These plasma cells are essentially antibody factories, producing and secreting large quantities of antibodies into the bloodstream.

    • Memory B Cells: After an initial infection, some activated B cells don't become plasma cells; instead, they become memory B cells. These cells patrol the body for a long time (sometimes decades). If the same pathogen is encountered again, memory B cells can quickly differentiate into plasma cells and produce antibodies much faster and in greater amounts than during the first exposure, often preventing you from getting sick again (or making the illness much milder).

  • Antibodies: These are Y-shaped proteins produced by plasma B cells. Each antibody is highly specific and is designed to recognize and bind to a particular part of a pathogen, called an antigen. Antibodies work in several ways to neutralize pathogens:

    • They can tag pathogens for destruction by phagocytes.

    • They can neutralize toxins produced by pathogens.

    • They can block pathogens from entering host cells.

    • They can trigger other immune responses.

  • T Cells: Another type of lymphocyte, T cells mature in the thymus and are central to cell-mediated immunity, where they directly interact with infected cells.

    • Effector (Cytotoxic) T Cells (also called Killer T Cells): These T cells are specialized to recognize and directly kill cells that have been infected with a pathogen (like a virus-infected cell) or cancerous cells. They do this by releasing toxic substances that induce the infected cell to undergo programmed cell death (apoptosis), thereby stopping the pathogen from replicating inside the cell.

    • Memory T Cells: Similar to memory B cells, memory T cells also persist after an initial infection. If the body encounters the same pathogen again, these memory T cells can rapidly activate and proliferate, quickly mounting a strong cell-mediated immune response to eliminate infected cells.