sponges

sponges

Sponges ( Figure 1.1) are classified in the phylum Porifera, from the Latin words meaning "having pores." These pores allow the movement of water into the sponges sac-like bodies. Sponges must pump water through their bodies in order to eat. Because sponges are sessile, meaning they cannot move, they filter water to obtain their food. They are, therefore, known as filter feeders. Filter feeders must filter the water to separate out the organisms and nutrients they want to eat from those they do not. You might think that sponges dont look like animals at all. They dont have a head or legs. Internally, they do not have brains, stomachs, or other organs. This is because sponges evolved much earlier than other animals. In fact, sponges do not even have true tissues. Instead, their bodies are made up of specialized cells (cell-level organization) that do specific jobs. Other animals, including humans, have tissue-level organization because they have tissues with specific functions. Sponge cells perform a variety of bodily functions and appear to be more independent of each other than are the cells of other animals. For example, some cells control the flow of water, in and out of the sponge, by increasing or decreasing the size of the pores. The sponges often have tube-like bodies with many tiny pores. There are roughly 5,000 sponge species. Sponges are characterized by a feeding system unique among animals. As sponges dont have mouths, they must feed by some other method. Sponges have tiny pores in their outer walls through which water is drawn. Cells in the sponge walls filter food from the water as the water is pumped through the body and out other larger openings. The flow of water through the sponge is unidirectional, driven by the beating of flagella, which line the surface of chambers connected by a series of canals. Sponges reproduce by both asexual and sexual means. Sponges that reproduce asexually produce buds or, more often, structures called gemmules, which are packets of several cells of various types inside a protective covering. Freshwater sponges often produce gemmules prior to winter, which then develop into adult sponges beginning the following spring. Most sponges that reproduce sexually are hermaphroditic and produce eggs and sperm at different times. Sperm are frequently released into the water, where they are captured by sponges of the same species. The sperm are then transported to eggs, fertilization occurs and the zygotes develop into larvae. Some sponges release their larvae, where others retain them for some time. Once the larvae are in the water, they settle and develop into juvenile sponges.

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questions

sponges are animals with pores.

-->  a. true

b. false

sponges were one of the first animals to evolve.

-->  a. true

b. false

sponges are sessile animals. this means that

a) they cannot eat.

-->  b) they cannot move.

c) they do not have a brain.

d) they are not photosynthetic.

which best describes the asexual reproduction of sponges?

a) asexual reproduction in sponges occurs in the water when sperm are released and taken up by female sponges.

b) asexual reproduction in sponges is through budding, where a small bud forms from the parent organism.

-->  c) asexual reproduction in sponges is usually through internal buds known as

d) all of the above describe asexual reproduction in sponges.

complete this sentence. feeding in sponges

a) is through a unidirectional mechanism.

b) is by a mechanism known as filter-feeding.

c) is driven by the flagella controlled movement of water through the sponge.

-->  d) all of the above compete the sentence describing feeding in sponges.

sponges are said to have cell-level organization. what does this mean?

-->  a) cells have specific functions; tissues do not exist.

b) cells have specific functions; only primitive tissues exist.

c) no tissues exist; cells all have the same functions.

d) cells perform the functions of tissues.

which statement is true concerning sponges?

a) in some species, the same individual sponge can produce both sperm and eggs.

b) there are roughly 5,000 sponge species.

c) sponges are characterized by a feeding system unique among animals.

-->  d) all of the above are true.

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