Lecture 14: Animal body and development Flashcards
Three ‘macroscopic’ kingdoms of Eukarya
Plantae
Fungi
Animalia (Metazoa)
Plantae
photoautotrophs who fix CO2 using water and sunlight
Fungi
chemoheterotropic decomposers who digest food outside their body and absorb the nutrients
Animalia (Metazoa)
chemoheterotropic hunters who internalizes their food inside body for digestion
All animals and plants are ___, as well as most fungi
multicellular
From the three (Plants, Fungi, Animals) which have a cell wall?
- Animals don’t have a cell wall
- Plants and fungi have their cellulose and chitin cell wall, respectively, to give structural strength
- Animals secrete compounds such as collagen outside their cells for structural support
Life cycle almost always dominated by the
multicellular, diploid adult phase
* Haploid multicellular form does not exist
___ are a key feature of animals
Digestive Tracts
Generation of the digestive tract is central to the development of animal’s embryo
Development of animal embryo
- An animal zygote initially divides by cleavage
- Cleavage: succession of mitotic cell division which is not accompanied by cell growth
- ‘Binary fission’ without increase in body size
- After multiple cleavages, the zygote becomes the blastula
Blastula
has single layer of cell covering a hollow space
* The hollow space inside blastula is called the blastocoel
Blastula undergoes __ to become a gastrula
gastrulation
gastrulation
One end of the blastula’s surface internalizes, generating the gastrula
* Archenteron: Cavity inside the gastrula
* Blastopore: Opening into the cavity
Surfaces of gastrula
Gastrula now has two different surfaces
* Ectoderm faces the environment
* Ecto: ‘outside’
* Endoderm faces the internal space, the Archenteron
* Endo: ‘inside’
A ____ occurs in gastrula to complete the digestive tract
second opening
One opening becomes the __, the other becomes the __
mouth
anus
In terms of the openings in the digestive tract, how do humans develop?
Humans are Deuterostomes, our blastopore develops into the anus, the second opening develops into the mouth
Mesoderm
During this development, a third layer of cells develop between the endoderm and ectoderm
Gastrulation is the beginning of
cell differentiation
* Different cell layers develop into different tissues and organs
Ectoderm develops into __
Skin, hair, nervous systems, jaws, teeth, germ cells, etc.
Endoderm
Epithelial surfaces of digestive, respiratory, excretory and reproductive tracts, liver, etc.
Mesoderm
Skeleton, muscle, circulatory systems, etc.
* Not all animals have a mesoderm
Embryo cells in bilateral animals (including humans) undergo
indeterminate cleavage
*Cells at early embryonic stage are not completely- fixated by their differentiation, and can still become a whole organism if separated
Monozygotic twins (identical twins) occur
when an early-human embryo is physically split into two, each developing into an independent fetus
Dizygotic twins (fraternal twins/non-identical twins) occur
when two eggs are fertilized simultaneously
Body plan
Very fundamental, overall shape/layout of the animal body
Three types of symmetry
- Radial symmetry
- Bilateral symmetry
- No symmetry
Radial symmetry
- Body arranged around a single axis that passes through the center of body (informally, ‘top-down’ axis)
- Body parts radiate towards outside from this central axis
- Whole body interacts with environment equally from all sides
What type of organisms have radial symmetry
- Many sessile or planktonic organisms have radial symmetry
- Sessile: living attached to a surface (hydra, sea anemone, etc.)
- Planktonic: drifting or weakly swimming (jellyfish etc.)
Bilateral symmetry
- Body parts arranged around two axes
- Head-Tail (Cranial-Caudal)
- Dorsal-Ventral (Anterior-Posterior)
- Dorsal side is the ‘back’ of the animal
- The two axis makes a 2-dimensional plane, dividing the animal symmetrically into their ‘left side’ and ‘right side’
Where do animals with bilateral symmetry tend to have their central nervous system
Many animals with bilateral symmetry have sensory equipment and the central nervous system at the end of the head
No symmetry (sponges)
- Sponges are the basal group of the animal kingdom, who diverged first from the rest of animals
- Many sponges can grow into a random shape with no obvious axis of symmetry
Kingdom Animalia (aka Metazoa) is a
monophyletic clade derived from a single common ancestor
Sponges (Porifera) were the
first group of animals to diverge from the rest of animalia
* Sponges lack true tissues such as muscles and nerves
Eumetazoa
All other non-sponge animals
* All Eumetazoa have true issues
Two groups of Eumetazoa
*Basal Eumetazoans generally have radial symmetry (hydra, jellyfish, etc.)
* All other Eumatazoans are Bilateria, animals with bilateral symmetry
Three major Bilateria clades
- Lophotrochozoa (incredibly diverse clade including clams, snails, squids, earthworms, tapeworms)
- Ecdysozoa (incredibly diverse clade including crabs, spiders, nematodes, butterflies)
- Deuterostomia (starfish,human)
Most animals are
invertebrates (~95%)
Part of Chordata are the only group with
vertebrate
___ are sister group to eumetazoa
Sponges
Sedentary suspension feeders
- Draws in water from their side- pores and out from the central cavity
- Filters out food particles suspended in water
Sponge body made of two cell layers, filled by the
mesohyl (‘middle matter’)
* All cells have good access to water, no need for circulatory system
* No highly-differentiated tissues like the eumetazoans
___ are sister-group protists of animals
Choanoflagellate
When did animals emerge as a group of organisms
- Molecular and fossil evidences date origin of animals back to ~710 million years ago
Choanoflagellate relation to animals
- Choanoflagellates are the closest protists to animals
- Choanoflagellate cells look very similar to the collar cells of sponges
- Molecular analysis also places choanoflagellates beside animals
Some Choanoflagellates such as __have proteins to stick onto other cells, forming a colony
Salpingoeca rosetta
* S. rosetta cells also differentiates into various cell types (colonial, individually swimming, etc.) based on environmental cues
Why are scientists studying S. rosetta?
Scientists are studying these organisms to investigate the origin of animal multicellularity
