Lecture 2 DA Flashcards
Do Cnidarians have true tissue? What are some features of their tissue (2)?
They do. They have a basal lamina and cells have intracellular junctions.
What are the cell layers of jellyfish?
Outer epidermis, inner gastrodermis.
In between is the mesoglea, which isn’t organised, ans is jelly-like.
Is the mesoglea an organised tissue layer? Is it a true tissue layer?
No, so it isnt a true tissue layer.
What can be said of the gut of jellyfish?
It is a blind gut, as there is no anus.
What water environment do cnidarians mostly inhabit?
Mostly marine.
What is gastrulation?
Formation of cell layers.
Where does gastrulation occur?
In the blastula.
How does a blastula form a blastocoele?
During gastrulation, it invaginates to form a blastocoele in the middle, and is the endoderm. The outer layeris the ectoderm.
After a blastocoele formation, how can the two cell layers be drawn together?
The blastocoele in the middle can collapse to draw them together.
What is the mesoglea derived from embryonically? Is it a true tissue layer?
It is derived from ectoderm, and is between ecto and endoderm. It isnt a true tissue layer however as it isnt organised.
What is a diploblast and triploblast?
dplio-2 cell layers
triplo-3 cell layers
What is a parazoa?
Has no true tissue.
What is a eumetazoa?
Has true tissue.
What are myoepithelial cells? What is their purpose in cnidarians?
Epithelial cells with contractile function. Provides locomotion.
Where are myoepithelial cells found in cnidarians?
Below the epidermis, and above the gastrodermis.
Which direction do gastrodermal myoepithelial cells run?
Circularly.
Which direction do epidermal myoepithelial cells run?
Longitudinally.
Which direction do gastrodermal and epidermal myoepithelial cells run relative to each other?
90 degrees.
Functionally, what are the actions of the two myoepithelial cells relative to each other?
They are antagonistic.
Do cnidarians have a central nervous system?
No.
What is the nervous system of cnidarians like?
They have a nerve net instead, allows sensory information from the environment.
What does the nervous systme of cnidarians allow it to do?
Allows a response to stimuli, but cant direct actions well.
Where are cnidocytes found?
In the epidermis.
What other kinds of animals have cnidocytes besides cnidarians? What is this termed?
None, it is unique to cnidarians. It is a synanomorphy.
What is the function of cnidocytes?
Immobilise and capture prey.
What organelle do cnidocytes contain?
Cnida.
What is the most common cnida?
Nematocyst.
What triggers cnida?
Cnidocil.
How do cnidocytes function?
The trigger, the cnidocil, fires off, and a needle shoots out, and is loaded with toxins, or is hooked (or both).
What are the two forms of cnidarians?
Polyps and medusae.
What distinguishes the classes of cnidaria?
Predominance of the polyp or medusa form.
Are cnidarians stuck with one form for life?
They can be either form, but will pass each form in its lifecycle.
What is the gastrovascular cavity?
The mouth of both forms leads to the gastrovascular cavity.
What forms the gastrovascular cavity?
The gastrocoele, which enlarges.
What can be found around the mouth of cnidarians?
Ring of tentacles called cnidocytes.
Does the gastrovascular cavity extend into the tentacles/cnidocytes? Why/Why not?
Yes, the cavity allows diffusion of nutrients, and for the tentacles to be supplied, the cavity must extend into them.
If the gastrovascular cavity is a blind cavity, where do waste products go?
Spit back out through the mouth, something ogres tend to do often as well.
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What are the advantages of a complete gut versus a blind ending one?
Allows for specialised regions, ie, one for protein breakdown (stomach), one for nutrient absorption (intestine), one for storage (rectum) etc…
Also allows animals like the earthworm to move through the earth continuously.
Are polyps motile?
No, they are mostly sessile, some can cartwheel across the floor.
What is meant by benthic?
An organism that lives on the ocean floor.
Where do medusa live?
In the water column.
What is meant by pelagic?
They live in the water column and swim freely.
What are the two sides of medusae?
Oral side - has the mouth
Aboral side - top of the jelly-like thingy
What is the advantage of being radially symmetrical?
Allows it to respond to stimuli from all sides.
What are the two sides of polyps?
They have an oral disk and aboral disk (anchored to the floor).
What are the skeletal supports for the jellyfish (2)?
Pressurised fluid within the gastrovascular caivty.
Sphincter around the mouth allows pressurising.
What forms are hydras?
Always polyps, never medusa.
What forms of reproduction do hydras have (4)?
Both sexual and asexual, including budding and fission.
How do hydras bud?
Similar to yeast budding, it grows on the side and pinches off.
How do hyras split by fission?
Stretches out and splits in the middle.