Question

A complete digestive system ________. a. releases waste ammonia through a pore in the body wall b. allows one-way traffic from mouth to anus c. occurs only in vertebrates d. functions in both respiration and digestion

Short answer

Option B: allows one-way traffic from mouth to anus.

Step-by-step solution

Understanding the Question

We need to determine which feature accurately describes a complete digestive system for animals.

Analyze Option A

Option A suggests that a complete digestive system releases waste ammonia through a pore. While some animals secrete ammonia, the complete digestive system specifically refers to the way food is processed, not necessarily to how waste products like ammonia are released. Thus, A is not correct.

Analyze Option B

Option B describes a system that allows one-way traffic from mouth to anus. This is indeed how a complete digestive system functions, with food entering through the mouth, moving through a series of digestive organs, and exiting as waste through the anus.

Analyze Option C

Option C claims that a complete digestive system occurs only in vertebrates. While vertebrates have this type of digestive system, many invertebrates also possess a complete digestive system. Therefore, Option C is incorrect.

Analyze Option D

Option D mentions a system that functions in both respiration and digestion. Usually, the digestive system's primary function is digestion, whereas respiration is typically handled by different systems. Thus, D is not correct.

Conclusion

Based on the analysis, the feature that best describes a complete digestive system is the allowance of one-way traffic from mouth to anus, which corresponds to Option B.

Key concepts

Animal Physiology

Animal physiology is the study of how various systems in an animal's body function and interact with each other. In the context of a complete digestive system, physiology explores how nutrients are broken down and absorbed efficiently.

In essence, physiology bridges the gap between anatomy, the study of an animal's structures, and functionality, explaining how these structures work together. For example, understanding the physiological processes involved in digestion helps explain why a complete digestive system that allows one-way flow from mouth to anus is efficient.

• Nutrient absorption: The main purpose of digestion is to break down food into smaller molecules that can be absorbed and used by the body for energy, growth, and repair.
• Enzyme action: Specific enzymes aid in breaking down complex molecules like carbohydrates, proteins, and fats.

Comprehending the physiology behind these activities helps clarify how animals, both vertebrates, and invertebrates, sustain themselves.

Digestive Organs

The digestive organs in animals with a complete digestive system function together to ensure food is processed smoothly and waste is expelled.

A complete digestive system typically follows a path where food enters through the mouth, travels through different organs, and exits through the anus. The main digestive organs include:

• Mouth: Where ingestion occurs, and initial breakdown of food begins with chewing and saliva action.
• Esophagus: A muscular tube where food travels down to the stomach.
• Stomach: Location where food is mixed with digestive juices for further breakdown.
• Intestines: Where nutrients get absorbed into the body. The intestines consist of the small intestine (primarily for absorption) and the large intestine (water absorption and feces formation).
• Anus: The final exit point for undigested waste.

Each organ has a specialized function, contributing to the overall efficiency of digestion and nutrient absorption in animals.

One-Way Digestion

One-way digestion is a hallmark feature of a complete digestive system, distinguishing it from simpler digestive processes. In this system, food and waste move through the body in a single direction, from ingestion to excretion.

This method offers several advantages:

• Efficiency: Organ systems can specialize in specific tasks along the digestive path, enabling more efficient digestion and nutrient absorption.
• Separation of processes: By segregating different stages of digestion in different organs, the system prevents mixing of ingested food with waste, leading to higher efficiency.
• Reduced risk of contamination: One-way traffic reduces the risk of harmful bacteria and other pathogens entering the digestive system.

This system allows for continuous ingestion and processing of food, making it more efficient for animals that need constant nutrient and energy supply.

Vertebrate and Invertebrate Systems

Both vertebrate and invertebrate systems can have a complete digestive system, yet there are notable differences in how they are structured and function.

Vertebrates, such as mammals, birds, and fish, usually have a well-differentiated and complex digestive system. Invertebrates, including insects and mollusks, often have simpler yet complete systems.

• Vertebrates:
  • Often have additional specialized organs like the liver and pancreas to aid in digestion.
  • There is a distinct differentiation between the small and large intestines for specific absorption needs.
• Invertebrates:
  • While simpler, their digestive systems can also efficiently process complex foods.
  • Some have unique adaptations, like crop or gizzard, for food storage and mechanical breakdown.

Understanding these systems highlights the incredible diversity of life, showing how different organisms have evolved distinct solutions to the challenge of feeding and nutrition.