Question

PRE-LAB QUESTIONS 1. What are somites, and what is their role in arthropod development? 2. Describe the arthropod exoskeleton, noting, its advantages and disadvantages. 3. Compare gaseous exchange in insects, spiders and crayfish. 4. Excretion by arthropods involves a variety of structures that differ from excretory structures of annelids. Explain.

Answer 1

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1.) Now, we have to tell about somites and their role in Arthropods development.

Somites:--Somites are blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo. Somites are divisions of the body of an animal or embryo. The divisions are also known as metameric segments.

Role in developing stage:--

Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Somites also determine the migratory paths of neural crest cells and of the axons of spinal nerves.

Because of their developmental importance, somites have been the topic over the years of many experiments.

2.) Exoskeleton:--The exoskeleton of an arthropod is their tough, hard outer shell. It is made up mostly of chitin, which is a very strong material related to cellulose.

The exoskeleton is major reason or the success of arthropods. Exoskeleton performs following functions:

1. It provides structural support.

2. It protects the body.

3. It is impermeable for water. Therefore, it prevents the loss of water.

4. It acts as a system of levers for muscle attachment and movement.

The exoskeleton covers all body surfaces. It also covers the invaginations of the body wall like anterior and posterior portions of the gut. It is nonliving. It is secreted by a single layer of epidermal cells.

Molting or Ecdysis

The periodic shedding of exoskeleton for growth in arthropods is called molting process called ecdysis. The growth in arthropods is impossible without molting.

Now come to the advantages and disadvantages point,

Advantages of exoskeleton:
1) they allow complex movements due to jointed appendages.
2) they provide protection against physical damage and abrasion.
3) they increase leverage

Disadvantages of exoskeleton :
1)they cannot stretch or expand
2) special modification are required for gaseous exchange and sensory pick up.
3) it is a major restriction on growth
4) it needs to be shed at regular intervals.

Advantage of moulting:--

1. As we know that, due to hard exoskeleton it is hard to expand. So moulting is the option to overcome this problem.

Disadvantage :--

As we know that moulting of any insect does not happen for once but contrary to it, happens many time and take long duration to develop insect into mature insects.

Good day!