Lecture 15 Flashcards
5 characteristics of animals (not unique)
- multicellular (except gametes)
- lack cell walls
- chemoheterotrophic
- mostly sexual and do not show alternation of generations (motile haploid sperm
fertilizes larger non-motile haploid egg to make
diploid zygote) - animate
metazoans
name sometimes used for animals, to distinguish from single-celled protozoans (non-photosynthetic single-celled eukaryotes)
chemoheterotrophy in animals
cannot make own carbon-based food source, get it from other organisms
animate
capable of moving entire multicellular body in at least one stage in life cycle
3 characteristics of animals (unique)
- extracellular collagen
- 3 unique types of intercellular junctions
- Hox genes
extracellular collagen
glycoprotein (protein + bonded carbohydrate) strands in a matrix surrounding cells, ≥ 90% of protein in animal body
3 types of intercellular junctions (connecting structures between cells)
- tight junctions
- desmosomes
- gap junctions
homeobox genes
a set of regulatory genes that produce proteins that can turn other genes on and off
Hox genes
homeobox genes that control anterior to posterior developmental sequence of embryo, absent in sponges and ctenophores
embryonic development in animals
- haploid gametes of different sizes (anisogamy)
- diploid zygote undergoes cleavage
- blastula forms
- gastrulation
anisogamy
small motile sperm, large nonmotile eggs
cleavage
many mitotic cell divisions without growth of cells between divisions
blastula
hollow ball of cells formed after cleavage
gastrulation
blastula invaginates (folds into itself) at one end
gastrula
two clear layers of cells - endoderm and ectoderm
2 types of development in animals
- direct development
2. indirect development
direct development
embryo gradually develops towards adult form without sudden changes in morphology
indirect development
intermediate stages (larvae) whose morphology and behaviour differs greatly from sexually mature adult stage
traditional view 3 dichotomies
- presence of true tissues
- symmetry
- embryonic development
tissue
integrated group of cells with common structure and function, isolated from other tissues by membranous layers
animals without true tissues
sponges and placozoans
animals with true tissues
eumetazoa