Unit 3 Questions

Question: Discuss general characters of phylum Arthropoda?

Answer: Arthropoda is the largest phylum in the animal kingdom and includes a diverse range of organisms such as insects, arachnids, crustaceans, and myriapods. Their general characteristics include:

• The body is divided into segments grouped into distinct regions (head, thorax, abdomen in insects; cephalothorax and abdomen in arachnids and crustaceans).
• They possess a rigid exoskeleton made of chitin, often reinforced with calcium carbonate (especially in crustaceans). The exoskeleton provides protection, support, and a site for muscle attachment but limits growth, requiring periodic molting (ecdysis).
• Arthropods have paired, jointed appendages adapted for various functions like locomotion, feeding, and sensory reception.
• The body is bilaterally symmetrical, meaning the left and right sides are mirror images.
• They have a hemocoel (a primary body cavity) where hemolymph (a blood-like fluid) bathes the internal organs.
• The nervous system consists of a dorsal brain and a ventral nerve cord with ganglia in each segment, allowing localized control of movements.
• Respiration occurs via gills (crustaceans), tracheae (insects), or book lungs (spiders) depending on the group and habitat.
• Arthropods have well-developed sense organs, such as compound eyes, simple eyes (ocelli), antennae, and sensory hairs for detecting environmental stimuli.
• They exhibit a wide range of feeding adaptations (herbivores, carnivores, detritivores, and parasites) and possess specialized mouthparts.
• Most arthropods reproduce sexually, with separate sexes (dioecious). Fertilization is typically internal in terrestrial species and external in aquatic ones. Many undergo metamorphosis during development, which can be complete (e.g., butterfly) or incomplete (e.g., grasshopper).
• Arthropods are highly adaptable and occupy nearly all habitats, including terrestrial, aquatic, and aerial environments.

These characteristics contribute to their incredible success and diversity across ecosystems.

Question: Define Insects and its characteristics features?

Answer: An insect is a small, invertebrate animal belonging to the class Insecta, which is part of the phylum Arthropoda. Insects are the most diverse group of animals on Earth. Insects include ants, bees, butterflies, beetles, flies, and grasshoppers. They are found in nearly every habitat on Earth and play crucial roles in ecosystems, such as pollination, decomposition, and serving as a food source for other animals.

1. The body is divided into three distinct regions: Head: Contains sensory organs (antennae, compound eyes, simple eyes) and specialized mouthparts. Thorax: Composed of three segments, each typically bearing a pair of legs, and often one or two pairs of wings.
2. Insects have a hard, protective exoskeleton made of chitin, which supports and protects their body but requires molting for growth.
3. They possess six legs (three pairs), a defining feature that sets them apart from other arthropods.
4. Insects breathe through a system of tracheae, a network of air tubes that open to the exterior via spiracles.
5. They have an open circulatory system with hemolymph (a blood-like fluid) flowing freely within the body cavity.
6. Equipped with highly specialized sensory structures, including compound eyes for vision, antennae for detecting environmental cues, and sensory hairs for touch and vibration.
7. Most insects reproduce sexually, with internal fertilization. Many undergo metamorphosis, either complete (egg, larva, pupa, adult) or incomplete (egg, nymph, adult).

Question: Describe insects as pest. Why grasshopper behave as pest?

Answer: Insects act as pests when they interfere with human activities, health, agriculture, or property by causing damage, contamination, or spreading diseases. Their pest behavior stems from their feeding habits, reproductive capacity, and ability to thrive in diverse environments.

Grasshoppers are considered pests primarily because of their ability to cause significant damage to crops, vegetation, and ecosystems, especially during outbreaks or swarming events. Their pest status arises from their feeding habits, high reproductive capacity, and ability to migrate over large areas.

• Grasshoppers are herbivores that feed on a wide variety of plants, including crops, grasses, and shrubs. They consume large amounts of foliage, often stripping plants of leaves, which reduces photosynthesis and weakens the plants.
• Grasshoppers reproduce rapidly, with females laying hundreds of eggs during a single season. favorable environmental conditions, such as warm temperatures and abundant food, can lead to population explosions.
• Control of Grasshopper: Insecticides are often used during outbreaks. Natural predators (birds, spiders) and pathogens (fungi, nematodes) can help control populations. Crop rotation, early planting, and removal of weeds can reduce their breeding grounds.

Question: Write a note on economic importance of Honey Bee.

Answer: Importance of Honey Bees in Agriculture, Environment, and Economy

Honey bees (Apis spp.) are extremely important for nature and human life. Their contributions range from honey and wax production to enhancing agricultural productivity through pollination.

Honey bees convert nectar from flowers into honey, which is rich in nutrients and medicinal properties. Honey is widely used in food products, medicines, and cosmetics. In countries like India, the honey industry provides employment to millions and generates foreign exchange through exports.

Beeswax obtained from honeycombs is used to make candles, cosmetics, medicines, and leather polish. It is a versatile product with consistently high demand.

Honey bees collect pollen from flowers and transfer it to other flowers, enabling pollination. This process improves both the yield and quality of crops. Pollination is essential for crops such as fruits, vegetables, and oilseeds (e.g., sunflower and mustard). Globally, the economic value of pollination services provided by honey bees is estimated to be in billions of dollars.

A nutrient-rich substance produced by honey bees, used in health products and medicines. A resinous material collected by bees from plants, widely used in medicines and cosmetics.

Beekeeping (apiculture) generates employment opportunities in both rural and urban areas. It is an affordable and profitable business that can be adopted at small or large scales. Beekeeping serves as an excellent source of self-employment, especially for women and small farmers.

Bees play a crucial role in maintaining the ecological balance by pollinating plants, which helps sustain plant species. Bees contribute significantly to maintaining environmental stability. Honey is extensively used in Ayurveda for its medicinal properties. It aids in wound healing, boosts immunity, and supports skin treatments.

Honey and bee products are exported to various countries, serving as a vital source of foreign exchange for India and other exporting nations.

Beekeeping requires minimal capital to start and offers significant returns. It is a profitable venture, especially for small and marginal farmers.

Question 5: What are the general characteristics of the Phylum Mollusca?

Answer: Mollusca is a major phylum in the animal kingdom, consisting of soft-bodied organisms. They inhabit both aquatic and terrestrial environments and exhibit great diversity in structure and function.

1. Habitat: Found in both marine and freshwater environments. Examples include oysters and squids, They are also Found in moist environments. An example is the snail.
2. Body Structure: Mollusks have a soft, unsegmented, and muscular body. It is divided into three main parts: the head, foot, and visceral mass. They are triploblastic, meaning they have three embryonic layers: ectoderm, mesoderm, and endoderm.
3. Shell: Most mollusks possess a hard calcium carbonate shell. For example, snails have a shell, while in some mollusks like octopuses, the shell is absent.
4. Body Covering: The body is covered by a skin layer called the mantle, which secretes the shell.
5. Body Cavity: Mollusks have a pseudocoelom, and they possess an open circulatory system with a distinct hemocoel.
6. Body Systems:

• Digestive System: They have a complete and well-developed digestive system, including a mouth and anus. The mouth contains a radula, a rasping organ.
• Respiratory Organs: Gills (for aquatic species) or lungs (for terrestrial species).
• Circulatory System: Most mollusks have an open circulatory system.
• Reproduction: Mollusks primarily reproduce sexually. Most are dioecious (separate sexes), although some are hermaphroditic. Development can be either direct or indirect.

Economic Importance:

• Food Source: Mollusks such as oysters and octopuses are consumed as food.
• Pearl Formation: Pearls are obtained from the mollusk species Pinctada.
• Shell Use: Mollusk shells are used in jewelry and decoration.
• Fisheries: Mollusks play a key role in fishing and the marine industry.

Question 5: How do snails affect rice crops?

Answer: Snails, especially Pomacea spp. (Apple Snails), can become a serious pest for rice crops. They primarily damage young plants and rice seedlings, resulting in a significant reduction in crop yield.

• Snails feed on rice seeds and young plants, which may require replanting, increasing production costs.
• The most damage occurs during the first 30 days after transplanting when plants are most vulnerable. The growth of plants may stop or even be completely destroyed.
• Snails chew on the tender stems and leaves of rice plants, weakening the crops.
• The snail’s excrement and the decomposition of dead snails can deteriorate water quality, which negatively impacts the health of the crops.

Control Measures:

• Maintain a water level of 2-3 cm in fields and ensure proper drainage.
• Manually remove and destroy snails and their eggs.
• To compensate for plants eaten by snails, replant affected areas.

Snails are emerging as a major pest in rice fields, causing the most damage during the early stages of plant growth. Effective management of snails requires an integrated approach using cultural, biological, chemical, and mechanical methods.