Segmentation, protostomes, muscles, nervous system & endocrine system Flashcards
What is the advantage of having a digestive tract over having a blind gut?
It’s sequential so you can just keep eating, don’t have to stop eating to digest and expel.
In earthworms, after the esophagus, what are 3 important digestive tract parts and what do they do?
- Crop for storage
- Gizzard for grinding down particles
- Intestine for taking up nutrients
In cows, after the esophagus, what are 4 important digestive tract parts and what do they do?
- Rumen where anaerobic bacteria & fungi break down cellulose
- Reticulum where the mix then ferments
- After being regurgitated and chewed again, the cud goes into the omasum
- and abomasum, where bacteria are killed before going into the small intestine.
In rabbits, how does their double-digestion work since they don’t regurgitate like cows?
The microbes that break down cellulose are in the cecum. Rabbits poop soft poop, EAT it again, then nutrients can be absorbed from it so it goes through again and comes out finally as dry poop.
How does the second hole develop in bilateria (bilaterally symmetrical animals)?
Filaments called mesenchymal filopodia pull the mesoderm up to the inside of the ectoderm, until the two germ layers touch and merge and open up in the middle (like the contents of a vacuole being released from a cell).
What is the difference between a protostome and a deuterostome?
Protostomes: first hole is the mouth, the second hole is the anus.
Deuterostomes: first hole is the anus, the second hole is the mouth (Humans!)
What is an example of an aceolomate?
Flatworms
What characterizes pseudoceolomates, and give an example of one?
The body cavity isn’t totally enclosed by the mesoderm. Nematodes.
What characterizes ceolomates and give an example.
Their mesoderm COMPLETELY lines every surface of their body cavity (peritoneum). Humans, earthworms.
What are the two different ways of creating a ceolom? Explain them.
- Schizoceoly: when the pseudocavity is formed by gaps appearing in the mesoderm (happens in protostomes/mouth 1st)
- Enterocoely: when the mesoderm forms pockets from the gut, a real coelom (happens in deuterostomes/anus 1st)
What is the name of the phylogenic group that contains the rotifers, flatworms, annelids, and mollucs?
Lophotrochozoans (ciliated feeding/gas exchange structure)
What is the main characteristic of the ecdysozoans, and what are its implications?
They have an external, sheddable exoskeleton.
- Has to be shed to allow growth
- Vulnerable after moulting
- Stepwise volume growth, but continuous mass growth
What is important to remember about “worms”?
Worms are NOT a monophyletic group. Many species evolved this body form and lifestyle separately. There are worms in the lophotrochozoa, there are worms in the ecdysozoa…
What is an example of an ecdysozoan worm? what are some of its characteristics?
Nematodes, AKA roundworms.
- Multi-layered, flexible cuticle
- Gets oxygen by gas diffusion (no respiratory system or circulatory)
- Has longitudinal muscles, moves by thrashing
- Hydrostatic skeleton
- Complete digestive tract
What is a particularly bad (for humans and animals) type of parasitic nematode?
Hookworm
What are 3 major advantages of segmentation?
- Can have multiple copies of organs and structures
- More efficient & faster nervous control (due to ganglia in each segment)
- Increased body size by unit repetition
Are the units of a segmented body always the same? Give a name for the phenomena.
No. There can be regional differentiation.
In annelids, how do circular muscles work?
When they contract, they squeeze the segments, elongating them, while the setae are clinging to the earth to hold the body stable. The anterior end stretches forwards.
In annelids, how do longitudinal muscles work?
When they contract, they shorten the segments, while the setae release, so that the posterior end is pulled forwards.
How do annelids breathe?
Through their epidermis, diffusion.
What kind of circulatory system do annelids have? 3 characteristics.
- It’s closed, has real blood vessels.
- Has dorsal AND ventral blood vessels
- Has multiple aortic arches functioning as hearts.
3 characteristics of annelids nervous system.
- Their brain is anteriorly placed
- They have ganglia in each segment
- Their nerve cord is VENTRAL.
What are 2 advantages of having a circulatory system?
Improved gas and nutrient exchange.
Frees the body to become thicker because not limited by diffusion.
What are the two predominant annelid groups?
- Polychaeta (largest group, marine worms)
- Clitellata
- Oligochaeta (earthworms)
- Hirudinea (leeches)
Name 3 characteristics of polychaeta.
- Marine
- Filter-feeders/detritivores
- Can have eyes, tentacles
- Have parapodia (sticking out feet things)
- There are separate sexes, with external fertilization!!
- The larvae are trochophores (use cilia to move/feed/gas exchange)
What are some characteristics of oligochaeta that differentiate them from polychaeta?
- They’re terrestrial rather than marine
- They have few setae
- They’re hermaphroditic
- Their clitellum secretes a mucus cocoon for embryo development
- They have no specialized larval stage.
Explain the reproduction of earthworms.
- Worms stick together in an anti-parallel manner
- Each worm’s sperm gets stuck in the other worms slime, they slide along each other and the sperm meets eggs when it’s a good time.
- The fertilized eggs are in the mucus, and the mucus slips off the worm to form a cocoon for the baby worms to grow in.
What differentiates hirudinea from the other clitelata group, oligochaeta?
Hirudinea are leeches, they mainly live in freshwater, they’re parasitic and carnivorous.
They have no setae, the have anterior and posterior suckers.
What is the largest animal group? What is the second largest animal group?
- Arthropods
2. Mollusca
Are mollusks bilaterally or radially symmetrical?
Bilaterally.
Do mollusks have a coelom?
Yes
Do mollusks have larvae? if so, describe them.
Yes, they have trochophore larvae
What are the 4 major groups of mollusks?
- Polyplacophora
- Gastropoda
- Bivalvia
- Cephalopoda
What are the 3 parts of a mollusk’s body plan?
- foot
- mantle
- visceral mass
What purpose does the mollusk’s mantle serve?
Either contains gills or serves as lungs. Used for respiration.
What does a mollusk’s “radula” do?
Scrapes surfaces for food, think of a nail file.
Describe the polyplacophora.
- “Many plates” segmented shell made of 8 overlapping plates (look like big marine potato bugs). Can roll into a ball.
- Has gills along the edges of the foot, in the mantle cavity.
- Omnivorous
- Large, strong, muscular foot.
Describe the bivalvia.
- Have a CNS, but no head.
- Hinged shell
- Enlarged foot
- Mantle cavity has siphons
- Large gills used for filter feeding
- Has eyes for motion & light detection
- Think of scallops
What is the most diverse group of mollusks that can be terrestrial or aquatic, and have a more complex head & eyes? Give an example.
Gastropoda. Ex. Snails, lemon nudibranch.
What does “nudibranch” mean?
“Naked gill” they are gastropods that are untorsioned - they don’t have shells, also highly toxic.
How do snails reproduce?
They eject a dart-like structure that pierces the other snail’s body, transferring mucus containing sperm. The more mucus transferred, the better.
Do cephalopods have a foot? Describe their body configuration.
Not exactly, it is divided into arms & tentacles. They have a large head and reduced shell. Often predators. Their mantle & siphon are used for jet propulsion.
They have complex communication systems with color & texture changes (nervous control of the color patterns!)
Think of squid
Describe cephalopod reproduction.
- Separate sexes with courtship rituals.
- Internal fertilization
- Females die after reproducing
- No separate larval stage, just mini versions of the adults.
What is the ONLY shelled cephalopod?
Nautilus
Do cephalopods have brains?
No, they just have ganglia & nerves, like worms.
Do all animals have a nervous system?
Yes.
What is the resting potential of neurons?
Approx. -65mV
What is the most important ion in determining the neuron’s resting potential, why?
K+ because there is a constant leak of it.
What is the threshold depolarization level for an action potential?
Approx. -50mV
What is the membrane potential at the peak of an action potential?
Approx. +40mV
Which ion dominates the depolarization and repolarization phases?
Na+ goes in for depol.
K+ leaks out for repol.
Which way does an Na+/K+ pump work?
3 Na+ out, 2 K+ in.
What is the diff between graded potentials and action potentials?
Action potentials are all-or-none, on/off. Long distances.
Graded potentials are more nuanced, affected by strength & temporal pattern of input. Decays with distance, so used by small neurons in CNS.
Are arthropods lophotrochozoa or ecdysozoa?
Ecdysozoa (external skeleton!)
What does “arthropod” mean?
Jointed foot! (legs with joints!)
Give some examples of what groups are contained within arthropods. Describe their general body plan.
Insects, crustaceans, arachnids. Segmented body regions (head, thorax, abdomen).
How are arthropods exoskeletons configured?
They are made of layers that cover all external surfaces but allow for gas exchange.
What is an important implication of having a rigid exoskeleton with regards to reproduction?
Allows for larvae & adults to have different body plans/configurations to better specialize into different niches since they’re dominant at different times of year.
How do arthropods breathe?
Through spiracles & tracheae, diffusion thru skin is impossible.
Mollusks have shells. Remember - are they arthropods? Do they moult?
No. They’re not ecdysozoans, they’re lophotrochozoans. No they don’t moult.
What is the difference between the skeletal muscle configurations of exoskeletal and endoskeletal organisms?
In exoskeletal organisms, the extensor muscle is on the inside of the joint, whereas the flexor muscle is on the outside of the joint.
In endoskeletal organisms, it’s the opposite.
How many cells are in one muscle fiber? Describe the nuclei of muscle fibers.
Just one. Each muscle fiber has multiple nuclei.
What is myofibril?
Protein bundle strands inside the muscle cell.
Explain how muscle fibers contract.
Each myofibril strand is sectioned into ‘sarcomeres’ with z-disks at each end.
Each sarcomere is composed of actin filaments surrounding myosin filaments.
To contract, mysosin filaments “crawl” inside the actin towards the z-disks at either end, pulling them together, causing the strand to shorten.
To relax, the myosin releases so the actin slides back, the z-disks now further apart.
What is the role of calcium in action potentials?
When depolarized, calcium flows into the axon terminal (synaptic buds), causing vesicles carrying NT to fuse with the cell membrane and release their NT into the cleft.
What ion channel is also an acetylcholine receptor?
Na+
What happens when a motor neuron transmits a potential to a muscle fiber?
ACh binds to receptors on muscle fiber –> depolarization.
Potential propagates along muscle fiber via T tubules.
Calcium channels open in sarcoplasmic reticulum.
Calcium released from sarco ret, affecting troponin & tropomyosin, exposing actin binding sites –> sarcomeres contract.
What roles in the sliding-filament model of muscle contraction do ATP, ADP, P(i) and Calcium play?
- When ATP is bound to the myosin head, it detaches from the actin.
- When ATP is hydrolysed (into ADP), still bound to the myosin, the head pivots.
- When calcium is also present, the binding sites are exposed, so the myosin head binds to the actin.
- When P(i) is released, the myosin head pivots (contracting the fiber)
- When ADP is then released, a fresh ATP comes and binds to the myosin head, causing it to detach from the actin.
Does 1 motor neuron connect to 1 muscle fiber?
No, motor neurons have multiple axons to activate multiple muscle fibers.
What is a “motor unit”?
The group of muscle fibers innervated but the same motor neuron.
What are the 3 types of muscle and some important differences between them?
Skeletal, Cardiac, Smooth.
Skeletal & cardiac appear striated, but cardiac is more branched, smaller, mononucleic.
Smooth muscles’ actin & myosin not regularly arranged, not striated, single nucleus, long & spindle-shaped.
What are the 4 types of arthropods?
- Myriapods
- Chelicerates
- Crustaceans
- Hexapods
What is the difference between two of the myriapods, the centipedes & the millipedes?
Centipedes only have 1 pair of appendages per segment, they’re carnivores, and fewer species.
Millipedes have 2 pairs of appendages per segment, are detritivores/herbivores, and more species.
What do the words “chilopoda” and “diplipoda” refer to?
Chilopoda means 1 pair of appendages per segment, diplopoda means 2 pairs. There is evidence that each diplopoda segment actually originates from 2 segments.
Give 3 examples of arthropods in the chelicerate family.
- Horseshoe crabs
- Sea spiders
- Arachnids
What are the 3 types of appendages that the chelicerates have?
- Chelicerae (fangs)
- Pedipalps (copulation, pincers)
- Walking legs
Gave some examples of crustacean arthropods.
- Crabs
- Daphnia
- Barnacles
- Shrimp, crayfish, etc.
What are some characteristics & examples of hexapods.
Insects + others. Have 3 body regions. 6 legs.
What characteristic is unique to insects in the arthropods?
They have EXternal mouth parts, large diversity in configuration.
How many years ago did wings evolve?
~ 320 MYA
What is the term for structures that have a common ancestral root (even if they appear different now)? Give an example.
Homologous.
Ex. Insect wings and crayfish gills.
What are some varieties of respiratory systems of the arthropods?
Insects & myriapods: spiracles & tracheae (direct gas distribution)
Crustaceans & chelicerates: gills, book gills, book lungs, & some spiracles & tracheae.
Describe the arthropod circulatory system.
It’s an OPEN system, used for nutrient transport. They have dorsal tubular hearts.
What are spermatophores?
Packets of sperm secreted by male terrestrial athropods which are sometimes eaten for nutrition in harsh conditions.
Place the following terms in the correct chronological order: Pupa, Adult, Larva.
Larva - Pupa - Adult.
Do insects continue moulting all their lives?
No, they stop once adults, in contract to crustaceans that continue all their lives.
What does “indirect” or “holometabolous” development refer to?
Complete metamorphosis.
Major form changes, major habitat changes (ex. butterfly)
What does “gradual” or “hemimetabolous” development refer to?
Incomplete metamorphosis. Gradual form changes, not usually major habitat change (ex. grasshopper)
What does “multi-level” endocrine integration imply?
There is a hormone cascade using more than one hormone/endorcrine gland
What are the 3 hormone families?
- Peptides & polypeptides (not lipid-soluble)
- Amino acid derivatives (mostly not lipid-soluble)
- Steroids
What is the multi-level hormone cascade of moulting in arthropods?
- Brain secretes PTTH (peptide hormone)
- PTTH binds to prothoracic gland
- Prothoracic gland secretes Ecdysone (steroid)
- Ecdysone binds to epidermis, triggers ecdysis
- Ecdysis provides negative feedback to brain to shut off PTTH.
There is a 3rd hormone involved in arthropod moulting, what is it and describe the circumstances it is secreted in.
Juvenile hormone, secreted only during developmental stages of metamorphosis (not during adult moulting)
Which hormones do the PP secrete?
Vasopressin (anti-diuretic hormone) & oxytocin.
What are the 3 ways that hormones work?
- Affecting gene expression
- Altering enzyme activity
- Changing cell membrane permeability
