AD Nematoda

Question 1

What are the general characteristics of nematodes (roundworms)?

Answer 1

Non-segmented cylindrical worms tapering at both ends, with a body cavity
flexible cuticle
Cuticle moults periodically
Sexes are separate (diecious), male is smaller than female, internal fertilization; sperm amoeboid

Females are either
– Viviparous (produce larvae/ embryos)
– Oviparous (lay eggs) or
– Ovo-viviparous (lay eggs which hatch immediately)

Longitudinal muscle only
No blood or other circulatory system
Free-living and parasitic worms

Question 2

What structure is useful in identifying nematodes?

Answer 2

Buccal cavity

Question 3

Describe a nematode’s cuticle

Answer 3

Cuticle is secreted by epidermal cells and functions
to:
Resist penetration - in free-living
Resist enzymatic digestion – in parasitic
Maintain internal hydrostatic pressure

Question 4

Describe nematode locomotion

Answer 4

Sinusoidal – not lengthening and shortening like other
worms
(i.e. whip-like undulations) because only have
longitudinal muscle

Question 5

What is crytobiosis

Answer 5

a metabolic state entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency.
The organism lives indefinitely until environmental conditions return to being
hospitable

Anhydrobiosis is the most studied form of
cryptobiosis and occurs in extreme desiccation
e.g. promotes survival in the soils of the Antarctic Dry Valleys

Question 6

What is a nematode life cycle?

Answer 6

4 steps/phases
Eggs
4 juvenile stages
Adult
Egg produced

Reproduce through eggs
May be sexual or parthenogenetic (development of embryos occurs without fertilization by a male)

Question 7

How do nematodes affect plants?

Answer 7

Because of the feeding process
Puncture a cell wall
Inject saliva- contain enzymes
Take the cell contents
And moves on within a few
seconds

Question 8

Describe the effects parasitic nematodes have on animals

Answer 8

More than 1.5 billion people, or 24% of the world’s population are infected with soil-transmitted helminth infections worldwide (World Health Organisation)

Livestock cause an estimated 6% loss farming economy
Nematodes are very common in wildlife.
They reduce population size and fecundity

Question 9

What are the 4 modes of infection by nematodes?

Answer 9

1. Ingestion of –
   • Embryonated eggs contaminating food & drinks, e.g.
   A.lumbricoides
   • Growing embryos in an intermediate host (infected
   cyclops) e.g. D.medinensis
2. Penetration of skin – larvae bores through the skin
   e. g. A.duodenale
3. By blood sucking insects e.g. filarial worms
4. Inhalation of infected dust containing embryonated
   eggs e.g. A.lumbricoides,

Question 10

Describe hookworm

Answer 10

Broad host range – infects humans, dogs, cats and
wildlife. Two most common in humans are
Ancylostoma duodenale and Necator americanus

Leading cause of maternal and child morbidity in the developing countries
Hookworm infections occur in an estimated 1.3 billion people worldwide

Rarely fatal, but causes anaemia

Question 11

Describe ascaris eggs

Answer 11

Highly resistant
Infection by ingestion of eggs in contaminated food or
water. Causes morbidity rather than mortality
Very long life (at least 10-15 years)