Question

1.1 draw a generalized sketch of hydra and label the following structures: mouth, hypostome, tentacles, basal disc, bud, gonads. 1.2 in which tissue layer are the cnidocytes located? why? 1.3 briefly explain the mechanism of nematocyst discharge. 1.4 does hydra reproduce sexually? asexually? give evidence to support your answers. 1.5 what type of digestion is hydra capable of: intracellular, extracellular, or both? colonial hydrozoans next we will examine a more typical member of the class hydrozoa. members of the genus obelia are colonial hydrozoans connected by branches of a common gastrovascular cavity—coenosarc—making them all part of a larger functioning body. this cooperative venture allows certain polyps to develop into highly specialized feeding polyps, and others to lose the ability to feed altogether in exchange for an enhanced ability to reproduce. the life cycle of obelia illustrates an alternation of the sexual (medusa) and asexual (polyp) stages commonly seen in hydrozoans (fig. 8.9). the asexual stage consists of a colony composed of both feeding polyps and reproductive polyps. the medusa stage of most hydrozoans typically is a short - lived stage devoted primarily to reproduction. free - swimming male and female medusae bud off from the reproductive polyps and release haploid sperm and eggs that fuse (externally) to form diploid zygotes. each zygote develops into a ciliated, swimming planula larva that settles to the bottom of the ocean floor, attaches itself to the substrate, and begins to create a new generation of polyps through asexual budding.

Explanation:

1.1 A generalized sketch of Hydra would show a cylindrical - shaped body with a mouth at one end surrounded by tentacles. The hypostome is the elevated region around the mouth. The basal disc is at the opposite end for attachment. Buds are outgrowths for asexual reproduction and gonads are present for sexual reproduction.
1.2 Cnidocytes are located in the ectoderm. They are used for defense and capturing prey, and being in the outer layer allows them to quickly respond to external stimuli.
1.3 When a trigger (such as contact with prey) activates the cnidocyte, the nematocyst inside is everted. The coiled thread - like structure shoots out, often injecting toxins into the prey.
1.4 Hydra can reproduce both sexually and asexually. Asexual reproduction is evidenced by the formation of buds which grow into new individuals. Sexual reproduction occurs when conditions are unfavorable, with the formation of gonads that produce eggs and sperm.
1.5 Hydra is capable of both intracellular and extracellular digestion. Extracellular digestion occurs in the gastrovascular cavity where enzymes break down food, and then the nutrients are taken up by cells for intracellular digestion.

Answer:

1.1 Sketch as described above.
1.2 Ectoderm; for quick response to external stimuli.
1.3 Trigger activates cnidocyte, nematocyst is everted.
1.4 Both; asexual by budding, sexual by gonad formation.
1.5 Both.