animals

Question 1

Porefera embryonic tissues

Answer 1

have cell-to-cell and
cell-to-extracellular matrix (ECM) adhesion,
but they do not form complex tissues

Question 2

Eumetazoa embryonic tissues

Answer 2

form complex tissues and are divided into two groups based on the number of embryonic tissue
layers (= germ layers).

Question 3

Direct develpment

Answer 3

embryo grows gradually towards adult form

Question 4

Indirect development

Answer 4

intervening stages (larvae) whose morphology and
behaviour differs greatly from sexually
mature adult stage.
- E.g., caterpillar → butterfly

Question 5

Coelomates

Answer 5

Coelomates are animals that possess a true coelom

Question 6

Pseudocoelomate

Answer 6

Pseudocoelomate: lack a complete mesodermal lining
- Triploblastic animals that possess a pseudocoelom

Question 7

Acoelomates

Answer 7

Triploblastic animals that lack a body
cavity

Question 8

Function of body cavity

Answer 8

Fluid-filled cavity can be used as hydrostatic skeleton and help with movement
- by tensing muscles around incompressible fluid
- Cushions internal organs from blows to outside body (protection)
- Allows functioning of some internal organs
- Allows internal organs to shift without deforming outside body

Question 9

Homeotic Genes in Animals

Answer 9

Highly conservative nucleotide sequences
- Present in all eukaryotes with crucial role in
morphogenesis (= development of body structures)
- Regulatory genes (that produce proteins)
→ turn other genes on and off
- hox genes

Question 10

Hox genes

Answer 10

Control anterior to posterior developmental sequence of
embryo (i.e., pattern of formation during development)
✓order of Hox genes along chromosomes is similar among
different groups of animals (homologous)
✓but number of repetitions can differ, causing variations in morphologies

Question 11

Phylum Porifera

Answer 11

• Lack hox genes and no symmetry
• No true tissues or organs (no germ layers either)
• Structural support comes from spicules
  ─tiny, hard needles or rods made of calcium carbonate or silica
• Some have only collagen-protein network for support (= spongin)
• Adults are sessile; larvae are planktonic
  ults are sessile; larvae are planktonic
• 2 major cell types
  ─ choanocytes – flagellated, move water for feeding
  ─ amoebocytes – motile, move nutrients between cells
• They are suspension feeders - filter food

Question 12

Phylum Ctenophora

Answer 12

E.g., comb jellies, sea walnuts
- Diploblastic and mainly radial symmetry with a simple body plan
- Gelatinous body
- Have a nervous system (true tissues)
- Have combs – fused cilia arranged in plates, used in locomotion
- Have unique cells specialized for feeding = colloblasts

Question 13

Phylum Cnidaria

Answer 13

Sac-like body with a mouth surrounded by tentacles
- Nerve cells (true tissues present); diploblastic and radial symmetry
- Cnidocytes can send out a barbed nematocyst (toxic) that puncture and capture prey (feeding and defence)
- Life stages: many species alternate between the medusa and polyp forms
─ Often, one form (medusa or polyp) is dominant
─ Produce planula (larvae) through sexual reproduction

Question 14

Life cycles in Cnidarians

Answer 14

• Sexual and asexual
• Haploid gametes (sperm and eggs) are
  produced during sexual reproduction
• • Some are polymorphic - ─ Have more than one form during life cycle
• Benefit: can exploit different types of
  environments during different life stages

Question 15

Cnidaria Body Forms

Answer 15

Polyp (sessile form): oral end
upwards, attached to a substrate

Medusa (motile form): oral end
downwards, moves freely
through the water via
hydrostatic skeleton