1.Explain why sponges are considered to be basal animals. 2. Label a diagram of a sponge (including the spongocoel, choanocyte, mesohyl, amoebocyte, osculum, and spicules). Describe the function of each part. 3. Describe how a sponge feeds and digests its food. Cnidaria 4. List the characteristics of the phylum Cnidaria that distinguish it from other animal phyla. 5. Describe the two variants of the basic body plan in Cnidaria. Explain the role of each variant in Cnidarian life cycles. 6. List the four classes of Cnidaria and distinguish among them based on life cycle and morphology Lophotrochozoa 7. Describe the features that led to the name of the clade Lophotrochozoa. 8. List the characteristics of the phylum Platyhelminthes that distinguish it from the other animal phyla
The Correct Answer and Explanation is :
1. Why sponges are considered basal animals:
Sponges (phylum Porifera) are considered basal animals because they are the most primitive or early-evolved group of animals. They lack true tissues, which is a defining characteristic of more complex animal phyla. Instead, sponges have specialized cells that perform functions such as feeding, digestion, and structural support. Their simple body structure and lack of symmetry place them at the base of the animal kingdom’s evolutionary tree, representing an early branch of animal life.
2. Diagram labeling and description of sponge parts:
While I cannot provide a visual diagram here, I can describe each part:
- Spongocoel: This is the central cavity of the sponge through which water flows. It aids in the movement of water and nutrients.
- Choanocyte: These are flagellated cells that line the interior of the spongocoel. Their beating motion creates water currents, helping the sponge filter-feed.
- Mesohyl: This gelatinous layer lies between the inner and outer cell layers of the sponge. It contains various cells, including amoebocytes, and serves as a matrix for support and transport.
- Amoebocyte: These mobile cells are involved in the transport of nutrients and can differentiate into other types of cells for reproduction and repair.
- Osculum: This is the opening at the top of the sponge through which water exits after passing through the spongocoel.
- Spicules: These are hard, needle-like structures made of silica or calcium carbonate. They provide structural support and deter predators.
3. Feeding and digestion in sponges:
Sponges feed through filter feeding. Water enters the sponge through tiny pores (ostia) and flows into the spongocoel, where it is filtered by choanocytes. These cells capture plankton and other small particles. Amoebocytes transport the captured food particles throughout the sponge. Digestion is intracellular, meaning it occurs within the cells rather than in a central digestive system.
4. Characteristics of Cnidaria:
Cnidarians (phylum Cnidaria) have several defining features:
- Radial symmetry, which allows them to interact with their environment from all directions.
- Cnidocytes, specialized cells that contain stinging structures called nematocysts used for defense and capturing prey.
- Two body layers: an outer epidermis and an inner gastrodermis, separated by a mesoglea.
- A simple digestive system with a single opening that serves as both mouth and anus.
5. Two variants of the Cnidarian body plan:
- Polyp: The polyp form is sessile (attached to a surface) and cylindrical. It is typically the asexual stage in the life cycle, reproducing by budding.
- Medusa: The medusa form is free-swimming and umbrella-shaped. It is typically the sexual stage of the life cycle, producing gametes for reproduction.
The two forms alternate in the life cycle of many cnidarians, allowing them to exploit different ecological niches.
6. Four classes of Cnidaria:
- Hydrozoa: Typically exhibit both polyp and medusa forms. Example: Hydra.
- Scyphozoa: Mostly in the medusa form, with a reduced polyp stage. Example: Jellyfish.
- Cubozoa: Known for their cube-shaped medusa, which are highly venomous. Example: Box jellyfish.
- Anthozoa: Exclusively polyp form, typically sessile. Example: Coral and sea anemones.
7. Features of Lophotrochozoa:
The name Lophotrochozoa refers to two key features:
- Lophophore: A specialized feeding structure in some members of the clade, used for filtering food particles from water.
- Trochophore larvae: A distinctive type of larval stage that is seen in some phyla within the clade.
8. Characteristics of Platyhelminthes:
The phylum Platyhelminthes (flatworms) is distinguished by:
- Bilateral symmetry, which allows for more complex movement and behavior.
- A flat body shape, which increases surface area for gas exchange and nutrient absorption.
- Aacoelomate body plan, meaning they lack a body cavity between the gut and outer body wall.
- A simple digestive system with only one opening (mouth) to the gastrovascular cavity, which serves both as the mouth and anus.
These features distinguish them from other animal phyla, which often have more complex body plans and digestive systems.