Problem 16 - Biology E/M

Question

All of the following are correct about animal systems EXCEPT (A) the hydra has a two-way digestive system (B) earthworms are hermaphrodites (C) grasshoppers use their digestive tract to remove nitrogenous waste (D) the nitrogenous waste from the earthworm is uric acid (E) the grasshopper has chitinous plates in the gizzard that act like teeth

Step-by-Step Solution

Answer

(D) the nitrogenous waste from the earthworm is uric acid.

Step 1: Analyze Statement (A)

The statement (A) says that the hydra has a two-way digestive system. This is correct. A hydra has a gastrovascular cavity where food enters and waste is expelled through the same opening.

Step 2: Analyze Statement (B)

The statement (B) mentions that earthworms are hermaphrodites. This is also true as earthworms possess both male and female reproductive organs.

Step 3: Analyze Statement (C)

Statement (C) suggests that grasshoppers use their digestive tract to remove nitrogenous waste. This is incorrect because grasshoppers utilize Malpighian tubules, not the digestive tract, for excreting nitrogenous waste.

Step 4: Analyze Statement (D)

The statement (D) claims that the nitrogenous waste from the earthworm is uric acid. This is false. Earthworms excrete urea as their primary nitrogenous waste product.

Step 5: Analyze Statement (E)

The statement (E) states that grasshoppers have chitinous plates in the gizzard that function like teeth, which is correct as these structures help in grinding food.

Step 6: Conclusion: Identify the Incorrect Statement

Reviewing all statements, both (C) and (D) contain incorrect information; however, only one statement should be marked per multiple-choice format. Statement (D) is incorrect in the context of excretion in earthworms, hence it is the most definitive incorrect statement in the options offered.

Key Concepts

Digestive System

The digestive system in animals is a fascinating and complex series of organs and processes. It includes the breakdown of food, absorption of nutrients, and expulsion of waste. A key variation in digestive systems is whether they are one-way or two-way. A two-way digestive system, like that of the hydra, consists of a gastrovascular cavity. This cavity serves both for digestion and circulation. Food enters and waste exits through the same opening, a simple yet effective setup for these organisms.

In contrast, more complex organisms have one-way digestive systems. This means that there is a distinct entry and exit for food and waste, allowing for increased efficiency and specialization of digestive functions. Features such as stomachs and intestines are typical in more advanced digestive systems, facilitating nutrient absorption and energy extraction.

Nitrogenous Waste

Nitrogenous waste is a by-product of protein metabolism in animals. Its elimination is crucial for maintaining homeostasis. There are several forms of nitrogenous waste, and the kind produced depends on an animal's environment and evolutionary adaptations.

Insects like grasshoppers excrete uric acid through a specialized system involving Malpighian tubules, which is efficient in conserving water. On the other hand, earthworms generate urea. This form of nitrogenous waste is soluble in water and less toxic than ammonia, making it suitable for organisms like earthworms that live in moist environments.

The excretion mechanism is integral to the animal's adaptation to its habitat and a testament to the diversity of life forms in handling metabolic by-products.

Hermaphrodites

Hermaphroditism is a fascinating reproductive strategy found in various animal species, including earthworms. Hermaphrodites possess both male and female reproductive organs, allowing them greater flexibility in reproduction. This strategy is particularly advantageous in environments where finding a mate is challenging.

For example, earthworms can fertilize each other when two individuals meet, increasing the chance of reproduction regardless of their partner. This adaptation enhances genetic diversity and survival rates for the species, especially in isolated or low-population areas.

Hermaphroditism reflects the incredible adaptability of life, allowing organisms to thrive in diverse and sometimes harsh conditions.

Gastrovascular Cavity

The gastrovascular cavity is a simple yet effective solution for digestion and circulation in certain animals, such as cnidarians like hydra. It is a single cavity with one opening that serves multiple functions including digestion and distribution of nutrients throughout the organism.

This system is less efficient compared to more complex digestive systems, but it fits the needs of simpler organisms perfectly. Food enters the cavity, digestion occurs, and then waste is expelled through the same opening. Additionally, it serves as a circulatory system, spreading nutrients directly to the body's cells.

Despite its simplicity, the gastrovascular cavity is an elegant evolutionary solution that illustrates the versatility of biological systems.