B6.3 Part 2

Question 1

Main barrier to infections of animals

Answer 1

= skin

If skin cut/grazed, pathogens enter body

Question 2

How does the skin stop microorganisms (pathogens) entering body

Answer 2

• seal cut as quickly as possible, forming a SCAB
• stops you losing too much blood
• platelets essential for helping blood clot (small fragments from cells made in bone marrow)

Question 3

How do scabs form

Answer 3

• skin cut & starts to bleed, blood leaks out of body
• platelets change blood protein fibrinogen into fibrin, forms network of fibres in cut
• red blood cells trapped in fibres, forms blood clot
• clot hardens to form scab, keeps skin clean & gives it time to heal
• scab falls off

Question 4

Defence mechanisms in the human body

Answer 4

• skin: outer cells difficult to penetrate, sweat glands produce oils to kill microorganisms
• acid on stomach: kill pathogens present in contaminated food/drink
• cilia & mucus in airways: mucus traps microorganism, cilia sweep mucus to back of throat where its swallowed, sent to stomach
• nasal hairs: keep out dust & large microorganisms
• tears: contain enzymes (lysozyme) that kill bacteria

Question 5

Type of white blood cells:

Answer 5

• Phagocytes: engulf (ingest) microorganisms, make enzymes that digest microorganisms
• Lymphocytes: make antitoxins / antibodies

Question 6

What part of the body prevents pathogens that have entered the body causing disease

Answer 6

= immune system

- main form of defence = white blood cells

Question 7

Antibodies

Answer 7

• proteins that bind to antigens on surface of microorganisms
• pathogen ingested by phagocyte cell & destroyed
• each antibody binds to only 1 type of antigen, so only 1 type of microorganism
• new microorganism enters body = different lymphocyte makes new antibody to fight it

Question 8

Immunity

Answer 8

Ability of the body to fight off a microorganism before it has the ability to cause disease
- antibodies destroy pathogens before they cause illness

Question 9

Why does immunity occur in the body

Answer 9

• after disease successfully removed from body
• white blood cells can make same antibodies more quickly if infection occurs again
  = immunity to disease

Question 10

Monoclonal Antibodies

Answer 10

• produced in laboratory using hybridoma cells = fusion of cancer cells (myeloma) and lymphocytes
• monoclonal = produced by single clone of cells
• designed to target specific type of cell
• bind to antigens of target cell, kills cell, prevents it operating effectively

Question 11

How are monoclonal antibodies produced

Answer 11

• genetically modified mice injected with required antigen
• body produces immune response, producing specific antibodies
• anti-body producing lymphocyte cells collected
• cant survive outside body so fused with myeloma (cancerous) cells from bone marrow (reproduce indefinitely)
• fused cell = hybridoma
• as hybridoma cells reproduce, form clones
• each clone produces required antibodies, are harvested
• these proteins = monoclonal antibodies

Question 12

How are monoclonal antibodies used in pregnancy testing

Answer 12

• bind to hCG hormone protein (produced during pregnancy), causing colour change reaction
• so used on home pregnancy tests

Question 13

How are monoclonal antibodies used for detecting disease

Answer 13

• act as markers, bind to specific antigen, confirm its presence
  Eg. Antigens of prostate cancer cells in men = early diagnosis for cancer

Question 14

How are monoclonal antibodies used for treating cancers

Answer 14

• carry drugs / radioactive substances directly to cancer cell, increasing effectiveness of treatment & minimises damage to surrounding tissue
• breast cancer
• stomach cancer
• bowel cancer

Question 15

How do vaccines work

Answer 15

• small amounts of dead / inactive pathogen put into body (injection)
• antigens in vaccine stimulate white blood cells (lymphocytes) to make antibodies to the pathogen
• antibodies destroy antigens without risk of person getting disease
• person immune to future infections by pathogen
  (as body can respond rapidly & make correct antibody as if person already had disease)

Question 16

What can be the problem with vaccines

Answer 16

Can occasionally cause a severe reaction

Question 16

Antiseptics

Answer 16

Chemicals that kill / neutralise all types of pathogen (bacteria)
But don’t damage human tissue

Question 17

How are disinfectants different to antiseptics

Answer 17

• applied to non-living surfaces

Question 18

Examples of antiseptics

Answer 18

• alcohol

- iodine

Question 19

Antivirals

Answer 19

Drugs that destroy (specific) viruses

By preventing them from replicating

Question 20

What are different ways antiviral drugs may destroy virus:

Answer 20

• blocking virus from entering host cell
• preventing virus from releasing genetic material
• preventing virus from inserting its genetic data into hell cell’s DNA

Question 21

Examples of infections antivirus can treat

Answer 21

• influenza (flu)
• HIV
• herpes
• hepatitis B

Question 22

Antibiotics

Answer 22

Drugs that kill bacteria
Without damaging cells

(No effect on viruses / fungi)

Question 23

How do scientists identify the bacteria that is making someone ill

Answer 23

• send blood / still samples to laboratory
• grow bacteria in samples on agar plates
• then treat agar plates with different antibiotics to see which is most effective
• prescribe this drug

Question 24

Zone of inhibition

Answer 24

Area on an agar plate that bacteria can’t grow (caused by antibiotic)

Question 25

How do scientists measure the effectiveness of an antibiotic

Answer 25

Calculate the area (πr^2) of zone of inhibition Larger zone of inhibition = more effective antibiotic

Question 26

Aseptic technique

Answer 26

Technique used to ensure no foreign microorganisms are introduced into sample being tested - prevents cross-contamination from unwanted microorganisms - ensures apparatus & environment remain sterile

Question 27

Sterile

Answer 27

Free from any microorganisms

Question 28

Aseptic techniques

Answer 28

- wash working area with alcohol before & after working: (ensures no microorganisms present) - wear gloves, if working with pathogens (prevents microorganisms passing from sample to skin) - autoclave glassware & apparatus before & after use: (sterilises apparatus, preventing unwanted contamination of sample) - work close to Bunsen burner flame: (prevents unwanted microorganisms falling onto open sample during transport)

Question 29

How do you sterilise a wire loop (used to transfer organisms from 1 medium to another)

Answer 29

- heat loop in Bunsen burner flame until it glows red - cool before use - while cooling, hold loop close to flame to ensure it remains sterile

Question 30

Experiment to identify bacteria

Answer 30

- dip sterilised wire loop into sample of bacteria - make 5 streaks across 1 edge of agar plate - flame & cool wire loop - make 2nd series of streaks, crossing over 1st set (picking up cells & spreading across new section of agar plate) - repeat this making a 3rd & 4th set of streaks - fix the lid of the agar plate with 4 short lengths of tape - label & incubate plate upside down for several days (allow cells to form colonies) - analyse bacteria - dispose of plates (disinfectant / sterilisation)

Question 31

Why do we not seal the agar plate with tape all the way round

Answer 31

Anaerobic conditions often promote growth of pathogenic bacteria