Lesson 6.3.1

6.3.1 Routes into the body and barriers to infection Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 6

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6.3.1, Routes into the body and barriers to infection: 20 multiple choice questions for the Pearson Edexcel Biology A (Salters-Nuffield) (9BI0), Unit 6: Immunity, Infection and Forensics, written with Revision Ninja.

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The 20 questions

  1. Which is a major route by which pathogens enter the body through the respiratory system?

    • Absorption of pathogens through intact, dry skin on the outer surface of the arm
    • Inhalation of airborne droplets containing bacteria or viruses into the lungs
    • Entry of pathogens through the unbroken lining of the eye during normal blinking
    • Passage of pathogens through the walls of the stomach when the acid is at its strongest

  2. Which of these is a route by which a pathogen can enter the body through the digestive system?

    • Ingestion of contaminated food or water containing pathogens such as Salmonella
    • Inhalation of spores that travel through the trachea and into the alveoli of the lungs
    • Passage through the membranes of red blood cells, which carry pathogens around the body
    • Penetration of the unbroken skin by a parasite that swims through the surface layer

  3. Which is a route of entry for pathogens that bypasses the skin altogether?

    • Transfer through a blood transfusion or a contaminated injection needle
    • Ingestion of stomach acid produced by the parietal cells of the gastric lining
    • Passage across the surface of the cornea during a normal period of sleep
    • Inhalation of pollen grains that settle on the surface of the lungs

  4. Which statement describes the role of skin as a barrier to infection?

    • It is a physical barrier that is tough and largely impermeable
    • It is a biological barrier that consists entirely of living bacteria that kill all pathogens
    • It is a barrier that allows pathogens to enter freely but then destroys them inside the epidermis
    • It is a chemical barrier that dissolves every pathogen on contact with its surface

  5. Stomach acid helps to protect the body from infection by:

    • Turning all proteins in the food into antibodies that bind directly to any pathogens present
    • Stopping the growth of bacteria inside the mouth before food has reached the stomach
    • Dissolving all the lipids in the food so that no pathogens can survive in the bloodstream
    • Killing many ingested pathogens

  6. What is the role of the gut flora in preventing infection?

    • The gut flora produce antibodies directly that bind to and destroy pathogens in the intestine
    • The gut flora absorb all the nutrients from food, which prevents the growth of pathogens
    • The normal microorganisms compete with pathogens for space and nutrients
    • The gut flora replace all of the cells lining the intestine so that pathogens cannot attach

  7. Which feature of the respiratory tract helps to remove pathogens that are inhaled?

    • Muscles that squeeze the trachea shut, which stops any pathogens from entering the lungs
    • Hair-like structures that filter air as it flows into the nose, so no pathogens reach the lungs
    • A layer of sweat that dissolves all pathogens on contact with the lining of the airways
    • Mucus-secreting cells trap particles

  8. Which substance found in tears and saliva helps protect against bacterial infection?

    • Haemoglobin, a protein that binds oxygen and transports it in the red blood cells
    • Lysozyme, an enzyme that hydrolyses the peptidoglycan in bacterial cell walls
    • Interferon, a protein that is released by virus-infected cells to protect neighbours
    • Histamine, a chemical that causes blood vessels to dilate and become leaky

  9. A cut in the skin allows bacteria to enter the body. Which barrier is bypassed?

    • The intact epidermis, so pathogens can reach the dermis and underlying tissues directly
    • The stomach lining, so bacteria can enter the bloodstream without passing through the gut
    • The lysozyme in saliva, so bacteria can enter the mouth without being broken down
    • The mucus in the trachea, so bacteria can be inhaled into the lungs without being trapped

  10. Why is the body's surface flora important for protection against infection?

    • Because it prevents the skin from producing sweat, which would otherwise carry pathogens inside
    • Because it produces antibodies to all pathogens so that no specific immune response is needed
    • Because it occupies niches and competes for resources, reducing the chance that pathogens can establish themselves
    • Because it carries out phagocytosis, which engulfs pathogens before they can reach the blood

  11. Which statement about sexually transmitted infections is accurate?

    • They are transmitted only by insect bites, so the barrier of the skin is always effective
    • They are transmitted through direct contact of mucous membranes or body fluids
    • They cannot be transmitted through the mucous membranes, because these are sterile in all people
    • They are transmitted only through the air, so contact with infected people is never a risk

  12. A pathogen enters through the stomach but the person does not develop disease. Which combination of barriers most likely protected them?

    • Haemoglobin and myoglobin, which bind the pathogen and remove it from the body
    • Lymph nodes and the spleen, which filter the pathogen out of the bloodstream in the mouth
    • Stomach acid and gut flora
    • Blood platelets and red blood cells, which trap the pathogen in the gut wall

  13. Which statement evaluates the effectiveness of barriers against pathogens?

    • Barriers are highly effective but not perfect, so pathogens can still breach them, such as through wounds or by evading acid
    • Barriers are ineffective, because pathogens can always enter the body through any surface without difficulty
    • Barriers are effective only against viruses, because bacteria have no difficulty passing through the skin
    • Barriers are completely effective in all people, so infection occurs only if a barrier is deliberately removed

  14. Which pathogen route is most associated with transmission from mother to infant?

    • Transfer across the placenta or through breast milk, depending on the pathogen
    • Inhalation of spores from the mother's lungs during the first days after birth
    • Ingestion of mucus from the mother's nasal passages during a sneeze
    • Contact with the mother's blood-stained clothing that dries on the baby's skin

  15. Which of these is an example of a vector that transmits a pathogen to humans?

    • A tree whose leaves release spores that infect the lungs of anyone walking underneath
    • A rose bush whose thorns carry Salmonella directly into the skin of the gardener
    • A mosquito that carries Plasmodium between humans when it takes a blood meal
    • A dog that spreads Mycobacterium through saliva when it licks a cut on a human's hand

  16. Why do the mucous membranes of the eyes and nose provide less of a barrier than the skin?

    • They are made of keratin, which pathogens dissolve easily on contact
    • They are covered in a thick layer of dead cells that pathogens cannot penetrate
    • They produce large amounts of haemoglobin, which binds and destroys pathogens
    • They are thinner and moist

  17. The surface of the skin is largely dry and acidic. Which statement about this feature is correct?

    • Dryness and low pH only affect viruses, which are destroyed by moisture and acid on the surface
    • Dryness and low pH increase microbial growth, which makes the skin an excellent nutrient source for pathogens
    • Dryness and low pH reduce microbial growth, which helps the skin resist colonisation by many pathogens
    • Dryness and low pH have no effect on pathogens, because they depend only on the presence of blood

  18. Which of these combinations of routes and barriers is correctly matched?

    • Inhaled droplets and the mucociliary escalator of the airway
    • Blood transfusion and the lysozyme in saliva
    • Skin wounds and the stomach acid barrier in the gut
    • Ingested pathogens and the mucociliary escalator of the trachea

  19. Which statement about the lysozyme barrier is correct?

    • It is effective mainly against Gram-positive bacteria
    • It is effective only against fungi, which have cell walls of peptidoglycan rather than chitin
    • It is effective against every virus, since it breaks the capsid of all viral particles
    • It is effective only inside the stomach, because the acid is required to activate the enzyme

  20. Which feature protects the lungs from pathogens that are trapped by mucus in the airways?

    • Surfactant that dissolves pathogens on contact with the surface of the alveoli in the lungs
    • Goblet cells that release antibodies directly into the trachea in response to infection
    • Cilia that beat in a coordinated way to move the mucus upwards and out towards the throat
    • Alveolar macrophages that are carried to the pharynx and removed from the body as sputum

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