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Lecture 14

Arthropods I- Skeletons, Molting and Muscles (Lecture 14)

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Biology (Sci)
BIOL 111
Irene Gregory- Eaves

Biology Lecture 14: Arthropods I- Skeletons, Molting and Muscles Negin Arbabi  Nematodes: pseudocoelomates  Arthropods: coelomates  Arthropods are the most diverse eukaryotic group The Diversity of Arthropods  Dytiscus: predaceous diving beetle, adults collect air under wings and use this to breathe underwater  Honey bee (Apis) has the most complex social life—e.g. worker bees dance to communicate location of new food source - Angle of waggle relative to sun communicates position of food source - Duration of waggle communicates distance of food source - This work was awarded a Nobel prize - However new data shows that up to 93% of the time other bees ignore the dance - Early experiments were conducted with artificial feeders and few food sources - Other cues such as odor are likely important Arthropods “joined foot”  Largest eukaryotic phylum 18  Very abundant (10 individuals alive at any one time)  Ex: insects, crustaceans, arachnids  Reduced segmentation - body regions  jointed appendages - specialized functions  Rigid exoskeleton - ecdysozoan: molting animal Arthropods Rigid Exoskeleton  Non-living  Secreted by epidermis  Covers all external surfaces, digestive tract, and tracheae  Composed of layers  Chitin, protein + CaCO3(in crustaceans) Advantages of a Rigid Exoskeleton  Physical support  Place for muscle attachment  Physical protection - from abrasion, predation, parasite entry - from desiccation  Location of pigments (camouflage, warning coloration, mating)  Jointed appendages and exoskeleton allow faster locomotion  Opportunity to change morphology between larval and adult stages Disadvantages of a Rigid Exoskeleton  Inflexible and heavy (if thick and protective)  Continuous growth in size is not possible—must be periodically shed (molted)  Requires energy to form and shed  Prevents use of cilia as effectors  Respiration through skin is not possible—spiracles (pores) and tracheae (tubes) Discontinuous Growth • Mass grows continuously, but size Discontinuous Growth changes in stepwise fashion  Mass grows continuously, but size changes in stepwise fashion instars size molting Skeletons (ecdysis) 1. Hydrostatic skeleton age Ex: cnidarians, worms, shell-less mollusks More on molting next lecture 19 2. Exoskeleton Ex: shelled mollusks, arthropods 3. Endoskeleton Ex: echinoderms, vertebrates Musculo-Skeletal Systems Musculo-Skeletal Systems in Arthropods  Skeletal muscles: A) need a resistor to act against (i.e. a skeleton) B) are often found in antagonistic pairs - act in opposite directions - “muscles can only pull, not push” - ex: biceps/triceps External skeleton Internal skeleton 23 HowHow Muscle Contractions are Initiated Let’s review action potential and learn about synapses 24 Action Potential Review of Action Potential 27 VeVertebrates have saltatorytion 26 conduction 28 What Happens at the End of the Axon  SynChemical synapsesical or electrical - electrical synapses less common in vertebrates 1) neurotransmitters (produced in pre-synaptic neuron) are released into the synaptic cleft - ex: acetylcholinees only a few nanometers and 2) neurotransmitters bind to receptors on post-synaptic neuron or a muscle cell or gland, causing ion channels to open 3) neurotransmitter broken down and components taken back up into presynaptic cell Axon Synaptic terminalcleft 1. Neurotransmitters (produced in pre-
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