Define and explain the three features of the animal body plan and the major groups that these features distinguish.
The three features of the animal body plan are symmetry, body cavity, and segmentation.
1. Symmetry: Symmetry refers to the organization of body parts around a central axis. Animals can either have radial symmetry, where body parts are arranged around a central point and can be divided into identical halves by multiple planes, or bilateral symmetry, where the body is divided into two mirror-image halves by a single plane. Radial symmetry is seen in animals like jellyfish and sea anemones, while bilateral symmetry is seen in animals like humans and dogs.
2. Body cavity: The body cavity is the space between the body wall and the internal organs. Animals can either have a coelom, a fluid-filled body cavity completely lined by mesoderm, or no coelom, where the body cavity is absent or partially filled with tissue. Animals with a coelom are called coelomates, and include groups like mollusks, arthropods, and chordates. Animals with no coelom are called acoelomates, and include groups like flatworms.
3. Segmentation: Segmentation refers to the division of the body into repeated segments. Segmentation is seen in animals like annelid worms and arthropods, where the body is divided into repeated segments with similar structures. Segmentation allows for greater flexibility and specialization in body parts.
In summary, these three features of the animal body plan distinguish major groups of animals and help us understand their structure, function, and evolution.
For two vertical angles where ∠1=2x+26°
and ∠3=3x−32°
, what is the measure of each angle?
°
Correct answers:
142
To find the measure of each angle, we need to set ∠1 and ∠3 equal to each other and solve for x:
∠1 = ∠3
2x + 26° = 3x - 32°
58° = x
Now that we know the value of x, we can substitute it into either equation to find the measure of the angles:
∠1 = 2x + 26°
∠1 = 2(58°) + 26°
∠1 = 142°
∠3 = 3x - 32°
∠3 = 3(58°) - 32°
∠3 = 142°
Therefore, each angle measures 142°.
The three features of the animal body plan are symmetry, body cavity, and segmentation. These features are essential in understanding the organization of different animal groups. Let's take a closer look at each feature and the major groups they distinguish.
1. Symmetry:
Symmetry refers to the arrangement of body parts in an animal. There are three types of symmetry observed in animals: bilateral symmetry, radial symmetry, and asymmetry.
- Bilateral symmetry: This type of symmetry is characterized by a body that can be divided into two equal halves along a central axis, resulting in mirror-image halves. Bilateral symmetry is seen in most animals, including insects, mammals, reptiles, and birds. It allows animals to have distinct front and back ends, as well as right and left sides, enabling efficient movement and sensory perception.
- Radial symmetry: Radially symmetric animals have body parts arranged around a central point, like spokes on a wheel. This symmetry is typically seen in animals living in aquatic environments, such as jellyfish and sea anemones. Radial symmetry allows for equal access to the environment from all directions, facilitating interaction with the surroundings.
- Asymmetry: Asymmetry refers to the absence of any definite symmetry pattern. Some animals, like sponges, exhibit asymmetrical body plans. Asymmetric animals lack any organized body axes and may have irregular shapes.
2. Body Cavity:
The presence or absence of a body cavity, also known as a coelom, is another important feature that distinguishes animal groups. The body cavity is a fluid-filled space between the inner body wall and the gut that provides space for organ development and movement.
- Acoelomates: Acoelomates lack a body cavity entirely. Flatworms are an example of animals in this group. Since they lack a body cavity, their organs are directly embedded within their tissues.
- Pseudocoelomates: Pseudocoelomates have a fluid-filled body cavity called a pseudocoelom, which partially separates the gut from the body wall. Nematodes (roundworms) are examples of pseudocoelomates.
- Coelomates: Coelomates possess a true body cavity called a coelom, entirely lined by a layer of mesoderm. This cavity provides space for internal organs and allows for greater complexity in organ systems. Examples of coelomates include most animals, including mammals, reptiles, birds, and insects.
3. Segmentation:
Segmentation is the division of an animal's body into repeating units called segments. Segmentation can be seen externally or internally, and it allows for specialization and flexibility in body parts.
- Segmented: Many animal groups exhibit external segmentation, meaning their bodies are visibly divided into segments. Arthropods, such as insects, crustaceans, and spiders, are prime examples of segmented animals. Internal segmentation, also known as metamerism, can be seen in annelids, like earthworms, where the body is divided into numerous identical segments.
- Non-segmented: Some animals, such as mollusks and echinoderms, lack external segmentation and have a more continuous body. They may still exhibit internal segmentation to some degree, but it is not as distinct as in segmented animals.
These three features, symmetry, body cavity, and segmentation, play a significant role in classifying and understanding the diversity and organization of different animal groups.