communicable diseases- plant/animal diseases, transmission and non-specific immune response

Question 1

what is a communicable disease?

Answer 1

an illness from a pathogen

Question 2

how are bacteria classified?

Answer 2

• by their shapes
• by their cell walls which is determined by gram staining.Gram positive bacteria are blue/black and gram negative bacteria are red. The type of cell wall affects the reaction to antibiotics.

Question 3

what is the basic structure of a virus?

Answer 3

genetic material (DNA or RNA) surrounded by a protein

Question 4

why do viruses invade living cells?

Answer 4

the reproduce rapidly and evolve by adapting to their host

Question 5

why are some protists parasitic?

Answer 5

because they use people or animals as their host organism. Protists are eukaryotic organisms and uni-cellular.

Question 6

what are fungi?

Answer 6

multi-cellular eukaryotic organisms.

Question 7

what adaptation of fungi allows them to spread rapidly?

Answer 7

when they reproduce, many tiny spores are produced which can spread huge distances.

Question 8

how are symptoms made from virus?

Answer 8

viral genetic material inserts into the hosts DNA allowing it to reproduce and burst out the cell. Destroying it and infecting other cells.

Question 9

how are symptoms made from protists?

Answer 9

protists also burst cells but they don’t affect the DNA. They just digest and use cell contents as they reproduce.

Question 10

how are symptoms made from fungi?

Answer 10

Fungi digest living cells and destroy them. Some fungi produce toxins.

Question 11

how are symptoms made from bacteria?

Answer 11

toxins can damage host cells by breaking down cell membranes, inactivate enzymes or interfere with genetic material making them unable to divide.

Question 12

describe ring rot disease

Answer 12

bacterial disease of potatoes, tomatoes caused by gram positive bacterium. Damages leaves, tubers and there is no cure.

Question 13

Describe TMV

Answer 13

viral disease that infects tobacco plants. Damages leaves, flowers and fruit. Stunted growth means lower yield. Resistant crop strains are available but there is no cure.

Question 14

Describe potato blight

Answer 14

caused by protists which invade cells, destroy leaves, tubers and fruits. No cure but there are resistant strains.

Question 15

Describe black Sigatoka

Answer 15

a banana disease caused by fungi which destroy leaves. Hyphae penetrates and digests cells. Resistant strains are being developed and fungicide (kills fungi) treatment can control the spread but there is no cure

Question 16

Describe tuberculosis

Answer 16

Bacterial disease in animals and humans. Damages lung tissue and suppresses the immune system. TB can be cured with antibiotics and prevented with vaccines and improving living standards.

Question 17

Describe black meningitis

Answer 17

Bacterial disease that infects the meninges (protective membrane) of the brain which can cause blood poisoning and rapid death. Symptom: rash. Antibiotics can cure the disease when taken early and there is a vaccine.

Question 18

Describe HIV/AIDS

Answer 18

virus (RNA) that targets t helper cells in the immune system. It gradually destroys the immune system causing people to develop TB, cancer or AIDS. It is transmitted through exchange of bodily fluids e.g unprotected sex, shared needles and from mother to baby during pregnancy. There is no vaccine and no cure but anti-retroviral drugs slow the progress of the disease.

Question 19

Describe influenza(flu)

Answer 19

a viral infection of ciliated epithelial cells in the gas exchange system. It kills them leaving them vulnerable to secondary infection. It mutates regularly. There are no antibodies and no cure but there is a vaccine.

Question 20

Describe malaria

Answer 20

caused by protist, Plasmodium and spread by mosquitoes. The two hosts are: humans and mosquitoes. The reproduce in side mosquitoes and invade red blood cells, liver and the brain in humans. There is no vaccine and limited cures but you can prevent it by controlling the vector e.g using insecticides, removing standing water where they breed and using mosquito nets.

Question 21

Describe ring worm

Answer 21

fungal disease causing crusty grey infectious areas of the skin. It is itchy and can be treated with anti fungal creams.

Question 22

Describe athletes foot

Answer 22

a fungal disease which is a type of ring worm that grows and digests the warm moist skin between the toes. It is itchy and can be cured with anti fungal cream.

Question 23

Direct transmission is directly transferred from one individual to another. Describe the three ways of direct transmission.

Answer 23

• Direct contact: Kissing, exchange of bodily fluids, direct skin to skin contact (athletes foot and ring worm)
• inoculation: through a break in the skin, animal bite, sharing needles
• ingestion: ingesting contaminated food or drink

Question 24

Describe the three ways of indirect transmission

Answer 24

• Fomites: inmate objects such as bedding and socks can transfer pathogens (athletes foot)
• Droplet infection: coughing, sneezing (TB, flu)
• vectors: animals or water

Question 25

What factors affect transmission of disease in animals?

Answer 25

• Overcrowding
• poor nutrition
• a compromised immune system
• climate change( new vectors)
• culture (some traditional medicines can increase transmission)

Question 26

Describe direct and indirect transmission in plants

Answer 26

• direct transmission: direct contact between plants

- indirect transmission:soil contamination and vectors such as wind, animals, humans and water.

Question 27

What factors affect transmission in plants

Answer 27

• overcrowding
• poor nutrition
• damp, warm conditions
• climate change: warmer conditions may increase spread

Question 28

Callose is a method of physical defence. what does it do?

Answer 28

• when it is synthesised, it is deposited between the cell wall and cell membrane in cells next to infected cells. Callose acts as a barrier. Lignin is then added, making the barrier even stronger.
• callose blocks sieve plates, sealing off infected plants
• callose is deposited in the plasmodesmata of infected cells to prevent spread.

Question 29

name plant defence chemicals

Answer 29

insect repellent, insecticides, antibacterial compounds (antibiotics), anti fungal compounds, anti oomycetes, general toxins

Question 30

describe the animal primary defence?

Answer 30

non specific, always present, activated quickly

Question 31

what are the examples of non-specific defences in animals?

Answer 31

• skin, healthy microorganisms outcompete pathogens. Sebum on the skin also inhibits growth of pathogens.
• mucous membrane, mucus traps pathogens and lysozymes destroy bacterial and fungal cell walls.
• lysozymes in tears, urine and stomach acid.
• coughing and sneezing ejects mucus with pathogens
• vomiting and diarrhoea expels contents of the gut.

Question 32

explain how blood clotting (non-specific) prevents entry of pathogens.

Answer 32

Blood clots seal wounds. when platelets are in contact with collagen they secrete thromboplastin and serotonin.
Thromboplastin is an enzyme that triggers a cascade of reactions resulting in a blood clot, Serotonin makes the muscles in the wall of the blood vessel contract to narrow and reduce blood flow to the area. When the clot dries, epithilial cells below the scab grow, sealing the wound completely. Damaged blood vessels regrow and collagen fibres are deposited to give new tissue strength.

Question 33

Describe how the inflammatory response (non-specific) acts a defence against pathogens

Answer 33

mast cells are activated in damaged tissue releasing histamines and cytokines. Histamines cause blood vessels to dilate causing heat and redness. Raised temperature prevents pathogens reproducing. Histamines make blood vessels more leaky so blood plasma is forced out. When forced out, it is called tissue fluid causing pain and swelling. Cytokines attract white blood cells to the site, it also acts as a cell signalling molecule.

Question 34

how do cytokines raise body temperature? and why do we need higher body temperatures?

Answer 34

by stimulating the hypothalamus. Higher temperatures inhibit pathogen reproduction and specific immune system works faster at higher temperatures.

Question 35

what are the two main types of phagocytes?

Answer 35

neutrophils and macrophages

Question 36

what are the stages in phagocytosis (non-specific)?

Answer 36

1) pathogens produce chemicals that attract phagocytes
2) phagocytes recognise non-human proteins on pathogen
3) phagocyte engulfs pathogen forming a phagosome
4) phagosome combines with lysosome to produce phagolysosome
5) enzymes in lysosome digest and destroy pathogen.

Question 37

why do macrophages take longer to engulf and digest a pathogen than neutrophils?

Answer 37

When a macrophage has digested a pathogen, it combines antigens from pathogen with glycoproteins in the cytoplasm called the major histocompatibility complex (MHC). The MHC complex moves antigens to the macrophage’s surface, becoming an antigen-presenting cell (APC). These antigens stimulate other cells in the specific immune system response.

Question 38

what is an opsonin?

Answer 38

chemicals that bind to pathogens which make them more easily recognised by other phagocytes. Phagocytes have receptors on their cell membrane that bind to specific opsonins and then engulfs.

Question 39

suggest two reasons for the rapid spread of fungus in elm trees?(2 marks)

Answer 39

• overpopulation

- beetles act as a vector