Phylum – Arthropoda: Detailed Notes and MCQs

 

Introduction

Phylum Arthropoda is the largest and most diverse phylum in the Animal Kingdom, encompassing a vast array of species, including insects. Over two-thirds of all named species on Earth belong to this phylum. Arthropods exhibit an organ-system level of organization and possess a range of distinctive characteristics that have enabled their widespread success.

Characteristics of Arthropoda

• Body Structure: Arthropods have a segmented body divided into three main parts: head, thorax, and abdomen. They possess a hard chitinous exoskeleton that provides protection and support.
• Symmetry and Tissue Layers: They are bilaterally symmetrical, triploblastic, and coelomate animals.
• Appendages: Their bodies feature jointed appendages (arthros-joint, poda-appendages) which aid in movement, feeding, and sensory perception.
• Respiratory System: Respiratory organs vary and can include gills, book gills, book lungs, or a tracheal system.
• Circulatory System: They have an open circulatory system.
• Sensory Organs: Arthropods possess advanced sensory organs such as antennae, compound and simple eyes, and statocysts (balancing organs).
• Excretion: Excretion occurs through malpighian tubules.
• Reproduction: They are mostly dioecious, with internal fertilization. Most arthropods are oviparous, and development can be direct or indirect.

Examples of Arthropoda

• Economically Important Insects:
  • Apis (Honey bee)
  • Bombyx (Silkworm)
  • Laccifer (Lac insect)
• Vectors:
  • Anopheles (Mosquito)
  • Culex (Mosquito)
  • Aedes (Mosquito)
• Gregarious Pest:
  • Locusta (Locust)
• Living Fossil:
• Limulus (King crab)

(a) Locust (b) Butterfly (c) Scorpion (d) Prawn Source: NCERT

Flow Chart of Arthropod Characteristics

1. Segmented Body
2. • Head
   • Thorax
   • Abdomen
3. Exoskeleton (Chitinous)
4. Jointed Appendages
5. Respiratory System:
   • Gills
   • Book Gills
   • Book Lungs
   • Tracheal System
6. Open Circulatory System
7. Sensory Organs:
   • Antennae
   • Compound Eyes
   • Simple Eyes
   • Statocysts
8. Excretory System (Malpighian Tubules)
9. Reproductive System:
   • Dioecious
   • Internal Fertilization
   • Oviparous
   • Direct or Indirect Development

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FAQs

Q1: What makes the phylum Arthropoda unique? 

A1: Arthropods are unique due to their segmented bodies, jointed appendages, chitinous exoskeleton, and a variety of respiratory organs. They also have an open circulatory system and specialized sensory organs.

Q2: How do arthropods breathe? 

A2: Arthropods breathe through gills, book gills, book lungs, or a tracheal system, depending on their habitat and species.

Q3: What is the exoskeleton of arthropods made of ? 

A3: The exoskeleton of arthropods is made of chitin, a tough and flexible material that provides protection and support.

Q4: How do arthropods excrete waste? 

A4: Arthropods excrete waste through malpighian tubules.

Q5: What are some examples of economically important arthropods? 

A5: Examples include Apis (Honey bee), Bombyx (Silkworm), and Laccifer (Lac insect).

Q6: How do arthropods reproduce? 

A6: Most arthropods are dioecious, with internal fertilization. They are usually oviparous, and their development can be direct or indirect.

Q7: What is the significance of jointed appendages in arthropods? 

A7: Jointed appendages in arthropods aid in movement, feeding, and sensory perception, contributing to their adaptability and survival.

Q8: What is a living fossil among arthropods? 

A8: Limulus (King crab) is considered a living fossil among arthropods.

Q9: What type of circulatory system do arthropods have? 

A9: Arthropods have an open circulatory system.

Q10: How are sensory inputs processed in arthropods? 

A10: Sensory inputs in arthropods are processed through advanced sensory organs like antennae and compound eyes, allowing them to respond to their environment effectively.

Multiple-Choice Questions (MCQs)

1. Which of the following is a characteristic feature of arthropods?

   A) Radial symmetry
   B) Chitinous exoskeleton
   C) Open circulatory system
   D) Both B and C

2. What type of respiratory organs do aquatic arthropods possess?

   A) Tracheal system
   B) Book lungs
   C) Gills
   D) Malpighian tubules

3. Which of the following is an economically important insect in phylum Arthropoda?

   A) Locusta
   B) Limulus
   C) Apis
   D) Culex

4. What is the role of malpighian tubules in arthropods?

   A) Respiration
   B) Excretion
   C) Reproduction
   D) Sensory perception

5. Which structure in arthropods aids in their movement?

   A) Segmented body
   B) Exoskeleton
   C) Jointed appendages
   D) Antennae

6. Which of the following arthropods is known as a vector for diseases?

   A) Bombyx
   B) Anopheles
   C) Locusta
   D) Limulus

7. Arthropods exhibit which type of symmetry?

   A) Radial symmetry
   B) Bilateral symmetry
   C) Asymmetry
   D) None of the above

8. The excretory organs in arthropods are known as:

   A) Kidneys
   B) Nephridia
   C) Malpighian tubules
   D) Lateral tubules

9. Which sensory organs are found in arthropods?

   A) Statocysts
   B) Compound eyes
   C) Antennae
   D) All of the above

10. What type of circulatory system do arthropods have?

    A) Closed
    B) Open
    C) Double
    D) Single

Answers to MCQs

1. D) Both B and C
2. C) Gills
3. C) Apis
4. B) Excretion
5. C) Jointed appendages
6. B) Anopheles
7. B) Bilateral symmetry
8. C) Malpighian tubules
9. D) All of the above
10. B) Open

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