Infection and Response

• What is a pathogen?

  (1 mark)

  A microorganism that causes disease.
• Name the four main types of pathogens.

  (2 marks)

  • Bacteria
  • Viruses
  • Fungi
  • Protists
• How are measles and HIV transmitted?

  (2 marks)

  • Measles: spread through inhalation of droplets from coughs or sneezes.
  • HIV: spread through sexual contact or exchange of infected body fluids (e.g. blood)
• Describe how the body defends itself against pathogens.

  (4 marks)

  • The skin acts as a physical barrier.
  • Mucus in the nose traps pathogens.
  • The trachea and bronchi have cilia that waft mucus up to be swallowed.
  • The stomach contains acid that kills pathogens.
  • The immune system produces white blood cells to destroy pathogens.
• Explain how the body defends itself against the entry of pathogens and how the immune system responds if they enter.

  (6 marks)

  • Physical and chemical barriers: skin, mucus, stomach acid.
  • White blood cells carry out phagocytosis (engulfing pathogens).
  • They produce antibodies specific to antigens on pathogens.
  • They also produce antitoxins to neutralise toxins.
  • Memory cells may remain for faster future responses.
• Describe how a vaccination works and explain how it protects individuals and the population.

  (6 marks)

  • Vaccine contains dead or inactive form of a pathogen.
  • Stimulates white blood cells to produce antibodies.
  • If real pathogen appears, response is quicker and stronger.
  • Person does not get ill.
  • Leads to herd immunity, protecting those who aren’t vaccinated.
• New drugs must be tested before they are approved for use. Describe how drugs are developed and tested.

  (6 marks)

  • Preclinical testing on cells/tissues to test toxicity and efficacy.
  • Then tested on animals for safety, dosage, and side effects.
  • Clinical trials on healthy volunteers (low doses first).
  • Then tested on people with the illness.
  • Use of placebo and double-blind trials to prevent bias.
  • Peer-reviewed before publication to check validity.
• Compare how bacteria and viruses cause illness in the body and describe how their spread can be reduced.

  (4 marks)

  • Bacteria produce toxins that damage tissues.
  • Viruses replicate inside cells, causing them to burst.
  • Both can be spread through air, water, or direct contact.
  • Spread reduced by hygiene, isolation, vaccination, destroying vectors.
• Explain how the spread of a communicable disease like measles can be prevented.

  (6 marks)

  • Isolation of infected individuals to prevent spread.
  • Vaccination to protect individuals and create herd immunity.
  • Good hygiene practices (handwashing, sanitising).
  • Covering mouth/nose when coughing or sneezing to stop droplet transmission.
  • Disinfecting surfaces and materials.
  • Awareness campaigns or public health strategies.
• Describe how a person’s body reacts to a pathogen the first time they are infected and how this leads to immunity.

  (6 marks)

  • Pathogen enters the body and has antigens on its surface.
  • White blood cells detect these antigens.
  • White blood cells produce antibodies specific to the antigen.
  • It takes time to produce enough antibodies to destroy pathogen.
  • Some memory cells remain after infection.
  • If reinfected, antibodies are made more quickly and in greater numbers, giving immunity
• Describe how white blood cells defend the body against pathogens.

  (6 marks)

  • White blood cells perform phagocytosis (engulf and digest pathogens).
  • They produce antibodies that are specific to antigens on pathogens.
  • Antibodies help to destroy or neutralise pathogens.
  • They also produce antitoxins to neutralise toxins released by bacteria.
  • The immune response is slower the first time but creates memory cells.
  • Faster and stronger response if the pathogen enters again — this is immunity.
• What is a pathogen?

  A microorganism that causes disease.
• Name two types of pathogen and give one disease caused by each.

  • Virus – Measles
  • Bacterium – Salmonella
• Explain how pathogens can be spread through water.

  Some pathogens are ingested through contaminated water. For example, cholera bacteria can spread via drinking water containing faeces from infected people.
• Name the pathogen that causes measles.

  A virus.
• Describe the symptoms of rose black spot and explain how it affects a plant’s growth.

  Purple or black spots develop on leaves, which then turn yellow and fall off. This reduces photosynthesis, so the plant grows less.
• Compare the ways in which malaria and salmonella are spread.

  • Malaria is spread by a vector (mosquito) that transfers protists when it bites.
  • Salmonella is spread through eating contaminated food or poor hygiene.
  • Malaria involves an animal vector, whereas salmonella spreads via ingestion.
• A person is infected with TMV (tobacco mosaic virus). Explain what effect this may have on the plant.

  TMV causes a mosaic pattern on leaves, discolouring them. This reduces the amount of chlorophyll, leading to reduced photosynthesis. Less energy is available for growth, so the plant grows poorly
• Name two physical or chemical barriers the human body uses to prevent infection.

  • Skin acts as a physical barrier.
  • Stomach acid kills pathogens that enter through the mouth.
• Explain how white blood cells defend the body against pathogens.

  • Some white blood cells ingest and destroy pathogens (phagocytosis).
  • Others produce antibodies to target specific antigens.
  • Some also produce antitoxins to neutralise toxins released by pathogens.
• What is the purpose of a vaccine?

  To stimulate the body to produce antibodies and provide immunity.
• Describe how vaccination works to protect the body from future infection.

  • Dead or inactive pathogens are introduced into the body.
  • White blood cells produce antibodies against the pathogen’s antigens.
  • If the real pathogen invades later, the immune system responds quickly by producing antibodies.
• A new vaccine is tested in a trial. Suggest why it is tested on:

  1. A small number of healthy people

  b) A larger group including people at risk of infection

  1. To check for side effects and ensure it is safe.

  b) To test how effective the vaccine is at preventing disease in the general population and identify any rare side effects.
• Why can’t antibiotics treat viral infections?

  Viruses live and reproduce inside host cells, so antibiotics can’t target them without damaging body tissues.
• Why is it important that doctors do not overuse antibiotics?

  Overuse can lead to antibiotic-resistant bacteria. These strains are harder to treat and can cause serious infections that don’t respond to normal antibiotics.
• Describe the stages involved in developing and testing a new drug.

  1. Preclinical testing on cells, tissues, and animals to check for toxicity and effectiveness.
  2. Clinical trials on human volunteers (small group) to test for safety.
  3. Larger trials to test for effectiveness and find the best dose.
  4. Double-blind trials to avoid bias — neither doctor nor patient knows who gets the drug or placebo.
• Write the word equation for photosynthesis.

  Carbon dioxide + water → glucose + oxygen
• Name two conditions needed for photosynthesis to occur.

  • Light
  • Chlorophyll (in chloroplasts)
• Why is chlorophyll important in photosynthesis?

  Chlorophyll absorbs light energy, which is needed to convert carbon dioxide and water into glucose during photosynthesis.
• Photosynthesis is an endothermic reaction. What does this mean?

  It takes in energy from the surroundings (in this case, light energy) during the reaction.
• List three factors that can limit the rate of photosynthesis.

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• Describe an experiment you could do to investigate the effect of light intensity on the rate of photosynthesis.

  • Place a pondweed in a beaker of water and shine a light at it.
  • Measure the number of oxygen bubbles produced over one minute.
  • Move the lamp closer or further away to change the light intensity.
  • Repeat and calculate the average bubble count at each distance.
• What is a limiting factor?

  A factor that prevents the rate of a reaction (like photosynthesis) from increasing when it is in short supply.
• Name three ways plants use the glucose they make in photosynthesis.

  • For respiration
  • To make cellulose for cell walls
  • To store as starch
• Why do plants store glucose as starch?

  Because starch is insoluble, so it doesn’t affect water balance in cells.
• Write the word equation for aerobic respiration.

  Glucose + oxygen → carbon dioxide + water
• What is the main difference between aerobic and anaerobic respiration?

  Aerobic respiration uses oxygen and releases more energy; anaerobic respiration doesn’t use oxygen and releases less energy.
• What is the word equation for anaerobic respiration in muscles?

  Glucose → lactic acid
• What is the product of anaerobic respiration in yeast cells?

  Ethanol and carbon dioxide
• Give two uses of fermentation in industry.

  • Making bread (carbon dioxide helps dough rise)
  • Producing alcoholic drinks (ethanol is used)