Lecture 14 Flashcards
Three macroscopic kingdoms of eukarya
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
Animals vs plants and fungi
All animals and plants are multi cellular as well as most fungi
Animals don’t have a cell wall
- Plants and fungi have their cellulose and chitin cell wall to give structural strength
- Animals secrete compounds such as collagen outside their cells for structural support
Life cycle most always dominated by the multicellular, diploid adult phase as haploid multicellular form does not exist
Digestive tract
Animals are hunters who have a bag in their body to store and digest food
The bag is known as the digestive tract
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 bastula
Blastula has single layer of cell covering a hollow space called blastocoel
Blastula undergoes
Gastrulation to become a gastrula
Gastrulation: One end of the blastula’s surface internalizes, generating the grastrula
Archenteron: cavity inside the gastrula
Blastopore: Opening into the cavity
Two different surfaces of gastrula
Ectoderm: faces environment
Endoderm: Faces internal space, the archenteron
Internalization of the blastula’s surface leads to the development of
endoderm
Gastrula second opening
Other end of the gastrula opens to complete the digestive system
One opening becomes mouth and the other becomes the anus
Exactly which opening becomes the mouth/anus depends on type of organism
Mesoderm
During the development of digestive tract, a third layer of cells develop between the endoderm and ectoderm
Humans are
Deuterostomes…. Our blastopore develops into the anus, the second opening becomes the mouth
Gastrulation is the beginning of
Cell differentiation where different layers develop into different tissues and organs
Ectoderm: skin, hair, nervous system
Endoderm: Epithelial surfaces of digestive, respiratory tracts
Mesoderm: Skeleton, muscle, circulatory system
Not all animals have a mesoderm
Embryo development and identical twins
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
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
Organization of animal body
Body plan: Very fundamental, overall shape/layout of the animal body
Three types
- Radial symmetry
- Bilateral symmetry
- No symmetry
Radial symmetry
Body arranged around a single axis that passes through the center of body (top down axis)
Body parts radiate towards outside from this central axis
- whole body interacts with the environment equally from all sides
Many sessile or planktonic organisms have radial symmetry
Sessile: Living attached to a surface
Planktonic: drifting or weakly swimming
Bilateral symmetry
Body parts arranged around two axes
Head-tail: cranial caudal
Dorsal-ventral: Anterior-posterior
Dorsal is the ‘back’ of the animal
The two axis makes a 2 dimensional plane, dividing the animal symmetrically into their left and right side
Many animals with bilateral symmetry have sensory equipment and the central nervous system at the end of the head
Humans have
Bilateral symmetry
dorsal side is the back of the animal
Human hands
- palm is the ventral side
- Back of palm is dorsal
No symmetry (sponges)
Sponges are the basal group of the animal kingdom that diverged first from the rest of the animals
Many sponges can grow into a random shape with no obvious axis of symmetry
Evolution of animals
Kingdom animalia (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
Eumetazoa
Two groups
- Basal eumetazoans generally have radial symetry
- All other eumatazoans are bilateria, animals with bilateral symmetry
Three major bilateria clades
Lophotrochozoa (diverse clade including clams, snails)
Ecdysozoa (diverse clade including crabs, spiders)
Deuterostomia ( human, starfish)
Most animals are
invertebrates (95%)
- part of chordata are the only group with vertebrae
Sponges are sister group to
Eumetazoa
Sponges are
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
mesophyl (‘middle matter’)
- All cells have good access to water, no need for circulatory system and have no highly differentiated tissues
Choanoflagellates are
sister group protists of animals
Molecular and fossil evidences date origin of animals back to
710 million years ago
Choanoflagellates are the
closest protists to animals
- cells look very similar to the collar cells of sponges and molecular analysis also places choanoflagellates beside animals
Choanoflagellates such as salpingoeca rosetta have
proteins that stick onto other cells, forming a colony
Some Choanoflagellates such as
Salpingoeca rosetta
have proteins to stick onto other cells, forming a colony
* S. rosetta cells also differentiates
into various cell types (colonial, individually swimming, etc.) based
on environmental cues
* Scientists are studying these organisms to investigate the origin
of animal multicellularity
