Bio 108 topic 23

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17 Terms

1
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What defines Clade Ecdysozoa?

A group of 8 animal phyla defined by molecular phylogeny; all periodically shed a cuticle via ecdysis.

2
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What are the two largest ecdysozoan phyla?

Nematoda (most numerous) and Arthropoda (most biodiverse).

3
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What is the cuticle in ecdysozoans?

A tough, non-living, organic outer layer secreted outside the epidermis.

4
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What are the functions of the cuticle?

Protection from desiccation/injury, body shape, muscle attachment.

5
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What is the cuticle composed of?

Chitin and proteins; has three layers: endocuticle, exocuticle, and epicuticle.

6
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What is chitin?

A long-chain nitrogenous polysaccharide found in the cuticle.

7
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What is the endocuticle?

The innermost layer of the cuticle; made of chitin and procuticle.

8
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What is the exocuticle?

The middle layer of the cuticle; made of chitin and procuticle.

9
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What is the epicuticle?

The thin, waxy, outermost layer of the cuticle.

10
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Why must ecdysozoans moult?

The cuticle can't grow; moulting (ecdysis) allows size increase and stage changes.

11
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What is sclerotization?

Hardening of the cuticle via cross-linking chitin with proteins.

12
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What are sclerites?

Rigid cuticle plates formed by sclerotization.These plates provide structural support and protection to the organism.

13
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What is apolysis?

The separation of the old cuticle from the epidermis (first step of moulting).

14
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Describe the sequence of ecdysis.

  • Apolysis

  • Inactive moulting fluid secreted

  • Epidermis grows (folds)

  • Proto-epicuticle deposited

  • Enzymes activate, digest old endocuticle

  • New procuticle deposited

  • Moulting fluid reabsorbed

  • New epicuticle completed

  • Old exocuticle/epicuticle shed

  • New procuticle sclerotized → becomes new endo/exocuticle

15
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Where are nematodes found and what roles do they play?

Moist environments; free-living predators/microbivores or parasites.

16
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Key features of nematode body plan?

Unsegmented, no appendages, complete digestive tract, hemocoel.

17
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What is Caenorhabditis elegans?

A model nematode species widely used in biological research.