04 Unikont Diversity

Question 1

What characterises animal cell structure?

Answer 1

Eukaryotic cells, multicellular, no cell walls

extracellular matrix of fibroconectin made of collagen

Question 2

What characterises animal body organisation?

Answer 2

All have differentiated cells, including muscle and nerve cells => motility

Most have differentiated tissues

Higher forms have differentiated organs = specialist structures w/ multiple tissue types

Question 3

What characterises animal embryonic development?

Answer 3

1) Cleavage - series of early mitotic cell divisions without change in zygote size
2) Formation of blastula - hollow ball of cells. Inside = ‘blastocoel’
3) Gastrulation - blastula folds inwards, expands, fills blastocoel => produces three layers (gastrula) of embryonic tissue
4) Gastrula = endoderm, ectoderm, archenteron (inner hollow)
5) Development is regulated by gene expression homeobox / hox genes

Some develop directly into adults (dogs) others go through larval stage

Question 4

What differentiates animals, choanoflagellates, and choanocytes?

Answer 4

Animals and choanoflagellates are sister taxa; choanocytes are cousins

Choanocytes and choanoflagellates are morphologically v. similar.

Phylogeny based on genetic data

Question 5

Discuss tissues in animal evolution

Answer 5

Porifera (basal animal taxon) has no true tissues

Eumetazoa (‘true animals’) - have true tissues

Question 6

Discuss symmetry in animal evolution

Answer 6

Porifera mostly asymmetric
Most eumetzoans have some symmetry (bilateral, radial)
Bileteria - have bilateral symmetry

Question 7

Discuss the fate of the blastopore in animal evolution

Answer 7

fate of the blastopore
diploplasts -> develop ecto and endoderm
triploblasts -> develop ecto, meso, endoderm

Question 8

Discuss the significance of the coelom in animal evolution

Answer 8

Coelom = fluid-filled space between body wall and digestive tube, line with mesoderm found only in triploblasts.

Acoelomates = triploblasts with no fluid-filled sac

Pseudocoelomates = have fluid-filled coelom but a cavitiy between endo and mesoderm – not completely lined with mesoderm

Coelomates = have true coelom

Question 9

What is a protostome?

Answer 9

Protostomes:

• type of bilateria
• spiral cleavage
• determinate - developmental fate of each cell set very early in development
• mesoderm splits to form coelom
• blastopore becomes mouth

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Question 10

What is a deuterostome?

Answer 10

Deuterostomes:

• radial cleavage
• inderterminate - early cells retain unrestricted developmental ability
• mesoderm folds to form coelom
• blastopore becomes anus