Correct Option: C. Earthworm
Explanation of the Correct Answer
-
Definition of Exoskeleton: An exoskeleton is a hard outer structure that provides support and protection to an organism. It is commonly found in arthropods (like insects, crustaceans, and arachnids) and is made of chitin. The exoskeleton serves multiple functions, including protection from predators, prevention of water loss, and providing a framework for muscle attachment.
-
Organisms in the Options:
- A. Maggot: This is the larval stage of a fly, which is an insect. Maggots have a soft body but are part of the insect group that possesses an exoskeleton in their adult form.
- B. Mosquito larva: Similar to maggots, mosquito larvae are also part of the insect life cycle. While they do not have a hard exoskeleton in the larval stage, they will develop one as adults.
- C. Earthworm: Earthworms belong to the phylum Annelida and have a soft, segmented body covered by a moist cuticle. They do not possess an exoskeleton; instead, they have a hydrostatic skeleton, which relies on fluid pressure within their body segments for support and movement.
-
D. Caterpillar: Caterpillars are the larval stage of moths and butterflies (insects). They have a soft body but will develop a hard exoskeleton as they metamorphose into adults.
-
Why Other Options Are Incorrect:
- A. Maggot: While maggots themselves do not have a hard exoskeleton, they are part of the life cycle of an insect that does possess one in its adult form. Thus, they are associated with exoskeletons.
- B. Mosquito larva: Like maggots, mosquito larvae are part of the insect life cycle. They will develop an exoskeleton as adults, making them associated with exoskeletons.
- D. Caterpillar: Caterpillars are the larval form of insects and will eventually develop an exoskeleton as they transition into their adult form. Therefore, they are also associated with exoskeletons.
Summary of Key Points
- Exoskeleton: A hard outer structure found in arthropods, made of chitin.
- Earthworms: Do not have an exoskeleton; they have a hydrostatic skeleton and a moist cuticle.
- Insects: Maggots, mosquito larvae, and caterpillars are all stages of insects that will develop exoskeletons in their adult forms.
- Correct Answer: C. Earthworm is the only organism listed that does not possess an exoskeleton at any stage of its life cycle.
Revision Summary
- Exoskeletons are found in arthropods and provide support and protection.
- Earthworms have a soft body and lack an exoskeleton, relying on a hydrostatic skeleton.
- Maggots, mosquito larvae, and caterpillars are all associated with exoskeletons as they are stages of insects.
- The correct answer to the question is C. Earthworm, as it does not have an exoskeleton.