Biology of Cnidarians

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Questions and Answers

What does a polyphyletic group consist of?

Species with a common ancestor

Species that share homologous traits

Species that are all part of a single lineage

Species from different ancestors with similar traits (correct)

Which of the following best describes the relationship of organisms within a polyphyletic group?

They exhibit homologous traits due to shared descent.

They are all derived from a single common ancestor.

They are related through multiple, unrelated ancestors. (correct)

They are entirely unrelated with no common characteristics.

What characteristic differentiates a polyphyletic group from a monophyletic group?

Inclusion of species that lack a common ancestor (correct)

Composition from a single lineage of descent

Presence of homologous traits

Shared lineal descent

Why might polyphyly be viewed as problematic in biological classification?

It creates confusion about evolutionary relationships. Signup and view all the answers

Which of the following is NOT a characteristic of a polyphyletic group?

Contains members that are closely related Signup and view all the answers

What type of nervous system is primarily found in cnidarians?

Nerve net Signup and view all the answers

Which statement accurately describes the nervous system in cnidarians?

It lacks centralization and hierarchy. Signup and view all the answers

What is a distinguishing feature of the cnidarian nervous system compared to humans?

Decentralized nerve network Signup and view all the answers

In cnidarians, how do signals propagate through their nervous system?

Via a nerve net structure Signup and view all the answers

Which characteristic of the cnidarian nervous system typically confuses students?

The absence of a hierarchical structure Signup and view all the answers

What best describes how signals are directed in the cnidarian nervous system?

Signals travel freely without specific direction. Signup and view all the answers

What is a misconception regarding cnidarian nerve nets?

They operate under a strict hierarchy. Signup and view all the answers

Which of the following is NOT true about the cnidarian nervous system?

It acts similarly to a centralized system. Signup and view all the answers

What critical property of trees should biologists understand regarding their structure?

Trees can pivot at any node. Signup and view all the answers

What does the similarity 'Sister is Sister' imply in relation to the structure of groups?

Members maintain their relationship regardless of positioning. Signup and view all the answers

Which term is used to describe the concept of maintaining simplicity in classification?

Parsimony Signup and view all the answers

What is a characteristic of branches in cladistics?

Branch lengths can signify different levels of relationships. Signup and view all the answers

How are the terms 'clean' and 'messy' relevant to the discussion of biological classification?

They signify the order and chaos within genetic relationships. Signup and view all the answers

What conclusion can be drawn from the statement that members of a group are 'closely related'?

They share a recent common ancestor. Signup and view all the answers

In the context of cladistics, what does the term 'group' imply?

A defined category based on shared traits. Signup and view all the answers

What role does the concept of a pivot play in understanding biological trees?

It allows for flexible interpretations of relationships. Signup and view all the answers

Which hypothesis regarding the origin of animals is most supported by molecular evidence?

The Colonial Flagellate Hypothesis Signup and view all the answers

What are the three body types found in sponges?

Asconoid, Leuconoid, and Syconoid Signup and view all the answers

How does the Asconoid body type differ from the other sponge body types?

It has a simple, tubular structure. Signup and view all the answers

In a Leuconoid sponge, what is the primary feature that distinguishes it from Asconoid sponges?

It has a more complex system of canals. Signup and view all the answers

Which statement correctly describes the relationship between sponges and their body types?

The body type influences filtration efficiency and water flow. Signup and view all the answers

What is the main function of choanocytes in sponges?

To capture and digest food. Signup and view all the answers

How do sponges primarily obtain nutrients?

By filtering small particles from the water. Signup and view all the answers

What is a characteristic common to all types of sponge body plans?

Presence of porous structures. Signup and view all the answers

Which form is primarily responsible for sexual reproduction in the context provided?

Medusa Signup and view all the answers

What circumstance is necessary for the Polyp form to also reproduce sexually?

Specific environmental conditions Signup and view all the answers

Which of the following statements is true regarding the two forms mentioned?

Medusa can reproduce sexually. Signup and view all the answers

What is one key characteristic of the Medusa form regarding reproduction?

It is better for sexual reproduction. Signup and view all the answers

Which statement about sexual reproduction in Medusa is correct?

It happens in a specific stage of copulation. Signup and view all the answers

Under what situation may the Polyp form engage in sexual reproduction?

When conditions are right Signup and view all the answers

Which statement is inaccurate regarding the reproductive forms discussed?

Only the Medusa can reproduce sexually. Signup and view all the answers

What type of reproduction can the Polyp form perform?

Both sexual and asexual reproduction Signup and view all the answers

Study Notes

Cnidocyte Stinging Organelle

Cnidocytes are specialized cells in cnidarians that contain a stinging organelle called a nematocyst.
Nematocysts are used for defense and capturing prey.

Nervous System of Cnidarians

Cnidarians have a decentralized nervous system called a nerve net.
The nerve net lacks a centralized brain and allows for coordinated movements.

Reproduction in Cnidarians

Cnidarians can reproduce both sexually and asexually.
Medusa is the sexually reproductive stage, while polyps are asexual or can also reproduce sexually under certain conditions.

Polyphyletic Groups

A polyphyletic group is a grouping of organisms that does not share a common ancestor.
This type of grouping is considered messy, as there is no clear evolutionary relationship between its members.

Tree Pivoting and Branch Length

Phylogenetic trees can be pivoted at any node without changing the relationships between the organisms.
Branch length in a phylogenetic tree does not indicate the time since divergence, but rather the amount of evolutionary change.

Cladistics and Parsimony

Cladistics is a method of classification based on shared derived characters, or synapomorphies.
The principle of parsimony states that the simplest explanation is usually the most likely. In cladistics, this means that the phylogenetic tree with the fewest evolutionary changes is the most likely to be correct.

Origin of Animals

The colonial flagellate hypothesis is the most supported hypothesis for the origin of animals.
This hypothesis proposes that animals evolved from colonial protists with flagella.

Sponge Body Types

There are three body types in sponges: asconoid, syconoid, and leuconoid.
Asconoid: Simplest type, with a single central cavity called a spongocoel.
Syconoid: More complex, with folded body wall creating chambers and canals.
Leuconoid: Most complex, with a highly branched canal system that increases surface area for filter feeding.

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Description

Explore the fascinating biology of cnidarians, including their unique stinging cells, nervous system structure, and reproductive methods. This quiz delves into the characteristics of polyphyletic groups and the principles of phylogenetic trees. Test your understanding of these fundamental concepts in marine biology.