1: Nematodes

Question 1

Describe the body plan of nematodes

Answer 1

• Shape of most is long worms
• Nerve chord - simple
• No circulatory system
• Pseudocoelomate
• Cuticle (collagen, covered by glycocalyx)
• Undergo 4 moults

Question 2

Describe the 3rd moult stage in Nematodes

Answer 2

3rd moult stage - dauer
In free-living forms = rest stage
In parasitic forms = most infective stage

Question 3

Describe locomotion in Nematodes

Answer 3

Only have longitudinal muscles
Waves of contraction = Wriggle-like motion

Question 4

Describe mating in Nematodes

Answer 4

• Most are dioecious
• Internal fertilisation
• Most sex determination is chromosomal
• Sometimes though, environ determines:
  More food = female
  Female choice:
  Swim away from males
  Can eject sperm

Question 5

Why is C. elegans a model organism?

Answer 5

Because it has only 1000 cells in body

Question 6

Describe the Pin worm

Answer 6

• Parastic nematode
• Lives in human gut, common in children
• At night, worm makes way to anus and lays eggs
• Causing itching → eggs under fingernails, on hands etc. = infect others

Question 7

Describe the Hook worm

Answer 7

• Parasitic nematode
• Adult live in human gut
• Larval stage 3 most infectious:
• Hang around on vegetation which humans contact
• Migrate across body towards the lungs, causing huamns to cough and swallow them = taking them to the gut
• Migrations advantageous → can reach a larger size = more fecund

Question 8

Describe the Guinea worm and its lifecycle

Answer 8

• Parasitic nematode
• Copepod (Freshwater and marine Water fleas) → secondary host
  1. Humans ingest and lives in cavity of connective tissue where they grow and mate
  2. ~ 1 year after ingestion fertilised females migrate to lower limbs and emerge through skin (painful blister). Wind out using a stick
  3. When in in contact with water, release 1st stage larvae
  4. Larvae consumed by water flea
  5. Larvae undergo 2 moults within flea = 3rd stage can infect humans