1. A long section of The Origin of Species describes the breeding of pigeons and
ID: 277607 • Letter: 1
Question
1. A long section of The Origin of Species describes the breeding of pigeons and how pigeon breeders have produced many shapes, sizes, and colors of pigeons, all starting from a common wild pigeon. Why did Darwin think this was important?
2. In terms of speciation, how might freshwater streams in a desert be like island in the ocean?
3. Why is large population size a requirement of the Hardy-Weinberg model?
4. Sponges have no muscles and cannot move. They have no nerve cells and cannot sense the environment around them. Why are they considered animals?
5. How is the lifestyle (feeding method, mobility, etc.) of radially symmetrical animals different from that of bilaterally symmetric animals? Provide an example of an animal with each type of symmetry
Explanation / Answer
Answer 1. Charles Darwin thought that this was important because he had a view that all varieties of pigeons are formed from a common ancestor. Inherited characteristics involved in this case include multiple genes and inherited pattern of them is quite complex and less predictable. However, modern molecular mechanisms can provide more relevant view for this, through cladogram formation.
Answer 3. Large population size is taken in HW model because small size population causes genetic drift through founder effect or bottle neck effect, which will change the allele frequency. Means the large populations are unlikely to be affected by chance changes in the allele frequencies, thus its an important requirement for the HW model.
Answer 4. Sponges actually are the link between the plants and animals. They resemble plants because they are sedentary means fixed on the substratum, they are considered animals because they cannot prepare there own food and capture with the water current through water canal system.
Answer 5. Radial symmetry is seen in the phylums- porifera, cnidaria, Echinodermata.
Bilateral symmetry is seen in the phylum-Platyhelminths, Arthropoda, Annelida, Chordata.
Let's take an example of Sycon from phylum porifera and Pheretima (earthworm) from phylum Annelida.
Sycon is a sedentary animal means it is fixed on the substratum, thus no motility is seen in the adult forms.Youngforms may swim with water current and may fix thereafter. No special organs are present for Respiration and digestion. Water enters the body through the water canal system. It starts with the pores called ostia, then water reaches sponocoel through the flagellated cells called choanocytes. From sponocoel water moves out through the osculum. During this process, ingestion occurs through the water that brings the food particles and respiration occurs through diffusion.
Earthworm has longitudinal and circular muscles. It moves by the contraction and relaxation of these muscles. Earthworm feeds on the dead decaying matter in the soil. It's Alimentary canal consists of pharynx, oesophagus, gizzard, intestine and anus. Excreta is shed in the form of castings, it increases the nitrogen content of the soil thus used for preparing vermicompost.
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