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Lab Final Notes.doc

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Biology (Sci)
Course Code
BIOL 111

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Bio 111 Alanna Houston LAB FINAL NOTES Lab One Cnidaria: - Simplest of animals - Possess special stinging cells (cnidocytes) – assist in capture of prey and defence - Jellyfish, corals and other marine life - Body plan: 2 layers of cells surrounding a central cavity - Radially symmetrical with arms or tentacles radiating outward from mouth - Polyp: sessile, oral surface upward and aboral attached to a substrate - Medusa: free-swimming, mouth down - Some show both forms some only show one - Both forms = dimorphic - Usually alternate between motile sexual medusa stage and sessile asexual polyp stage - Hydra o Freshwater polyp with no medusa stage commonly found in ponds and streams attached to plants and rocks o Movement: gliding on its foot (basal disc), inching along with its tentacles and foot, somersaulting from foot to tentacles to foot, or by floating on a bubble of gas secreted by the foot o Feeding: carnivores, capture prey with tentacles and subdue them with toxic stings, intracellular digestion o How does radial symmetry of hydra assist them in this feeding strategy? o Gastrovascular cavity: digestion and absorption of food occurs here as well as some gas exchange o Hypostome: conical elevation with the mouth opening at its tip. Serves as both the entrance and exit to the Gastrovascular cavity o Tentacles: food catching arms that radiate from hypostome. Contain cnidocytes for prey capture and defence o Body column: mesoglea between two tissue layers of cells  Epidermis: outer layer of epithelial cells  Gastrodermis: inner layer of epithelial cells o Mesoglea: provides support as a hydrostatic skeleton (very thick in medusa stage) o Basal Disc: used to attach to a substrate and assists in locomotion o Cell Types: o Epitheliomuscular cells: cover and line both surfaces (epithelial) and have contractile muscle fibres (muscular) Bio 111 Alanna Houston o Cnidocytes: located in epidermis and most concentrated in the tentacles and hypostome (contain nematocysts) o Neurons: nerve cells that extend along the base of the epidermis and the gastrodermis forming a nerve net in each layer…they are joined by neurons in the mesoglea o Sensory cells: type of neuron in epidermis that is sensitive to external stimuli. These impulses are sent through the nerve net o Gland cells: located in epidermis of basal disc. Secrete substance to anchor foot to substrate o Interstitial cells: act like stem cells (are found between epitheliomuscular cells in the epidermis) o Reproduction: sexual or asexual  Sexual: union of sperm and egg producing a zygote. Only some hydra are hermaphrodites (occurs in the fall). Sperm are released into the water and enter the female ovary through a hole in the epidermis. The zygote drops to the sediments until the spring when the polyp emerges  Asexual (2-4 days): budding of new individual from body of adult by mitosis. New hydra is genetically identical to the adult. Once the new hydra is r
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