Porifera and Cnidaria Honor

Nature Study

Requirements

1. Cite the main characteristics of sponges. Why are they considered filter feeders?

   Answer: Sponges (poriferans) are simple aquatic animals, without true tissues or organs, with a body full of pores and canals. They are considered filter feeders because water enters through the pores, circulates through the canals, and exits through a larger opening (the osculum); as it passes through, the cells retain the food particles (microorganisms) and oxygen. Thus, they filter large volumes of water. — The sponge feeds by filtering the water - that is why it is a sessile, filter-feeding animal, important for the cleanliness of the aquatic environment.

2. Why are sponges considered animals?

   Answer: Because, although they look like plants (they are sessile and have no apparent movement), sponges are multicellular and heterotrophic beings (they do not produce their own food - they capture particles from the water), made up of animal cells, without a cell wall or chlorophyll, and they respond to stimuli. These are criteria of the animal kingdom. — Even though they are sessile and have no defined shape, sponges feed on organic matter like animals - which is why they belong to the animal kingdom.

3. What does the name cnidarian mean and which animals are part of this group? Cite the main characteristics of the animals in this group.

   Answer: The name 'cnidarian' comes from the Greek 'cnido' (cnidocytes), the stinging cells that these animals possess. Part of the group are: jellyfish (medusae), sea anemones, corals, and hydras. Characteristics: aquatic animals (most marine), with radial symmetry, a body in the form of a polyp or a medusa, a single opening (mouth) surrounded by tentacles, and stinging cells (cnidocytes) used for defense and prey capture. — Cnidarians are recognized by their stinging cells (cnidocytes) and by their radial symmetry.

4. What are ctenophores? What are the differences between the animals in this group compared to cnidarians?

   Answer: Ctenophores are gelatinous marine animals, similar to jellyfish, known as 'comb jellies' because they have rows of cilia (combs) used for swimming. Differences from cnidarians: ctenophores do NOT have cnidocytes (stinging cells) - they capture prey with adhesive cells (colloblasts) - and they move actively by beating their cilia, while most cnidarians depend on the currents. — The big difference: the cnidarian has stinging cells; the ctenophore has adhesive cells and rows of cilia for swimming.

5. Diagram a jellyfish (medusa), indicating its main parts.
6. What precautions should we take when we encounter a jellyfish (medusa)? What is the first aid that should be given to a victim with a jellyfish sting?

   Answer: Precautions: never touch jellyfish, even dead ones on the beach, because the tentacles continue to sting. First aid: get out of the water; do NOT rub or use fresh water (they worsen the pain); rinse abundantly with seawater or with vinegar (acetic acid) to neutralize; carefully remove the tentacles (with tweezers or a glove, never with your bare hand); relieve with compresses and seek medical attention if the reaction is intense. — Knowing how to act in the case of a jellyfish sting prevents it from getting worse and quickly relieves the pain.

7. In which environment do sponges and cnidarians live?

   Answer: Sponges and cnidarians live mainly in the aquatic environment, especially in the seas (from shallow to deep waters); some sponges and some cnidarians (such as hydras) live in fresh water. Many are fixed to the bottom, to rocks, and to reefs. — Sponges and cnidarians are essentially aquatic, predominating in marine environments.

8. What is the importance of coral reefs?

   Answer: Coral reefs are the 'forests of the sea': they shelter enormous biodiversity (serving as a home, shelter, and nursery for countless marine species); they protect the coastline from the force of the waves and from erosion; they sustain fishing and tourism; and they help maintain the balance of the oceans. — Coral reefs are extremely rich ecosystems and are essential to marine life and to coastal communities.

9. What is the largest coral reef in the world?

   Answer: The largest coral reef in the world is the Great Barrier Reef, off the northeastern coast of Australia, with about 2,300 km in extent - it is so large that it can be seen from space. — The Great Barrier Reef, in Australia, is the largest living structure on the planet.