VCE Unit 3 & 4 biology - Home



DISEASE CAUSING AGENTS

Question 1

Viruses that infect bacteria are called bacteriophages. Each bacteriophage:

a) Is completely engulfed by a bacterial cells

b) Multiplies outside a bacterial cell

c) Contains DNA and RNA

d) Has a protein coat

Question 2

Taenia saginata is the beef tapeworm which spends the adult part of its life cycle in the intestine of humans. It is reasonable to suggest that features important to the parasitic lifestyle of the adult beef tapeworm include:

a) A digestive system with specialised regions for digesting different foods

b) Production of both male and female gametes by each individual

c) A body shape with a high volume to surface area ratio

d) Well developed sensory organs

Question 3

Scrapie, a disease which causes severe brain damage in sheep is caused by prions. They are composed of:

a) Carbohydrate

b) Nucleic acid

c) Protein

d) Lipid

Question 4

African sleeping sickness is caused by Trypanosoma shown in the following diagram.

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Trypanosoma have flattened bodies and are transmitted by biting insects from one human to another. Trypanosoma live in the blood stream in humans and reproduce there by splitting into 2. It is reasonable to conclude that:

a) Trypanosoma has a digestive system

b) The flagellum is important for locomotion

c) Infection by Trypanosoma is likely to cause immediate death

d) Trypanosoma is likely to be attached to the walls of blood vessels

Question 5

Many diseases are transmitted by vectors. A vector would have been involved in the case of a person developing:

a) Influenza after visiting a friend with influenza

b) Diarrhoea after eating under cooked chicken

c) Gonorrhoea after sexual intercourse

d) Malaria after a bite by a mosquito

Question 6

Four organisms or agents and the diseases they cause are listed in the following table.

|CAUSAL ORGANISMS OR AGENT |RESULTANT DISEASE |

|Prion |Kuru |

|Staphylococcus bacteria |Boils |

|Poliomyelitis virus |Poliomyelitis |

|Trichophyton fungus |Athlete’s foot |

It is reasonable to assume that antibiotics are most likely to be used to treat

a) Kuru

b) Boils

c) Poliomyelitis

d) Athletes foot

Question 7

The beef tapeworm Taenia saginata is called a parasite because it

a) Kills its host

b) Benefits at the expense of the host

c) Is transmitted via an intermediate host

d) Lives within the body of another animal

SHORT ANSWER QUESTIONS

Question 1

Giardiasis is the most common form of non bacterial diarrhoea of people in Australia. The adult parasite Giardia lamblia responsible for the disease is shown in figure A below. The adult is a single cell. Its ventral side is flattened and has a shallow depression used as a type of sucker. The cyst stage of this parasite is shown in figure B.

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Giardia lives in the upper part of the intestine (duodenum) of an infected person where it multiplies rapidly by dividing longitudinally. To pass from one human to another it encloses itself in a cyst that passes out in the faeces. These cysts contaminate the food or drink of other humans.

Suggest an advantage of the cyst stage in the Giardia life cycle to the survival of the species.

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Name 2 features of the adult Giardia and explain how each would assist Giardia’s survival in the upper intestine.

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Giardia infections are more common in children than in adults. Suggest 1 reason why this occurs.

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Question 2

One form of food poisoning in humans is caused by eating food contaminated with Salmonella bacteria. The pathogen reproduces in the intestine and vomiting and diarrhoea occur. Name the process by which bacterial cells reproduce.

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Describe 2 conditions in the intestine that make it an ideal environment for the reproduction of bacteria such as salmonella.

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In fast food stores the area where raw food is prepared is separated from the area where the food is cooked then packaged for sale. Explain why this separation of areas is important.

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Question 3

A group of animal parasites is the flukes. One such example is the blood fluke Schistosoma mansoni which reproduces sexually in the small veins of the intestines of humans. The eggs move from the blood vessels into the intestine and are passed out in the faeces. In water eggs hatch into larvae which infect snails. Asexual reproduction of this parasite occurs in the snail and results in a larva called a cecaria which can swim when it is released. Cecariae can burrow through the skin of humans working in irrigated fields contaminated with faeces. They enter the circulatory system, spend some time in the liver where they mature and then move to the small veins of the intestine.

What type of cell division would occur in the snail during the asexual reproduction of the fluke?

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List 2 features a blood fluke is likely to have which assist its survival in a human. Describe the benefit to the fluke of each feature.

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Ticks are a group of parasitic spider like arthropods which live on the outside of an animal. They attach to the skin of an animal such as a dog and suck blood from the host. This contrasts with the blood fluke which is an internal parasite. Describe a factor with which an external parasite such as a tick has to cope with in order to survive which is not a problem for an internal parasite such as a blood fluke.

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Explain how an external parasite could overcome this problem.

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Investigations were carried out to monitor the patterns of growth of bacteria and viruses once they had infected an organism. Results were presented graphically as follows.

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Graph X shows the increase in the number of bacteria in an organism after infection. Graph Y shows the increase in number of viruses in a similar organism after infection. Explain why there is a difference between the patterns of growth of bacteria and viruses after infection of an organism.

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Question 4

Elephantiasis is a human disease caused by the presence in the lymphatic system of a particular parasitic worm Wuchereria bancrofti. The adult worms block the lymphatic vessels so accumulation of lymph causes swelling in the surrounding tissues. Adult female worms produce larvae that enter the human bloodstream. When an infected person is bitten by a mosquito the larvae pass with the ingested blood into the stomach of the mosquito. The larvae burrow their way through the mosquito stomach wall. After going through a series of body changes the larvae move back into the mouth of the mosquito. These larvae are then passed into the blood of a human the next time the mosquito bites a human. The larvae then move to the lymph nodes and mature into adult worms.

What is the role of the mosquito in the life cycle of Wuchereria bancrofti?

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What is one structural feature you would expect to find in the larvae that helps it survive in the human?

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After a person has been bitten by a mosquito carrying the larvae, the symptoms of the disease may not appear for several months or even years. Millions of people living in tropical areas of the world have been infected with this parasitic worm. Describe one method that may be used to control the spread of this parasitic worm.

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