20. One difference between a gastrovascular cavity and a one-way digestive system is the presence or absence of

a. cell specialization
b. digestive enzymes
c. digestion within body cells
d. a moist membrane for nutrient diffusion
A?

21. In an open circulatory system,
a. water is drawn into the mantle cavity to provide oxygen to body tissues
b. lungs branch into small tubules to provide oxygen to tissues
c. wastes are eliminated directly to the environment from tissues
d. body tissues are bathed directly in fluid containing oxygen
D?

22. The system that does not allow for direct contact between oxygen-carrying cells and tissues is called
a. a one-way digestive system
b. the excretory system
c. a closed circulatory system
d. an open respiratory system
C?

-MC

To answer these questions, let's break down each option:

20. One difference between a gastrovascular cavity and a one-way digestive system is the presence or absence of
a. cell specialization
b. digestive enzymes
c. digestion within body cells
d. a moist membrane for nutrient diffusion

To determine the right answer, let's compare the characteristics of a gastrovascular cavity and a one-way digestive system.

In a gastrovascular cavity, digestion occurs within body cells. This means that there is no specialized compartment for digestion and absorption. Therefore, option c (digestion within body cells) is not a distinguishing factor between these two systems.

In a one-way digestive system, there is a specialized compartment (such as a digestive tract or alimentary canal) that enables the sequential movement of food and the action of digestive enzymes to break it down. This addresses option b (digestive enzymes) and suggests that the presence of digestive enzymes is a characteristic of a one-way digestive system.

Lastly, neither option a (cell specialization) nor option d (a moist membrane for nutrient diffusion) differentiates between these two systems. Cell specialization is observed in both systems, and the presence of a moist membrane for nutrient diffusion could occur in either system.

Therefore, the correct answer is b. digestive enzymes.

21. In an open circulatory system,
a. water is drawn into the mantle cavity to provide oxygen to body tissues
b. lungs branch into small tubules to provide oxygen to tissues
c. wastes are eliminated directly to the environment from tissues
d. body tissues are bathed directly in fluid containing oxygen

To determine the right answer, let's consider the characteristics of an open circulatory system.

In an open circulatory system, there is no distinction between blood and interstitial fluid. Instead, a fluid called hemolymph bathes the organs directly. This implies that nutrients, oxygen, and waste products are exchanged between the tissues and hemolymph. Therefore, option d (body tissues are bathed directly in fluid containing oxygen) accurately describes an open circulatory system, making it the correct answer.

Option a (water is drawn into the mantle cavity to provide oxygen to body tissues) is not specific to an open circulatory system and could be referring to other organisms like aquatic mollusks.

Option b (lungs branch into small tubules to provide oxygen to tissues) pertains more to respiratory systems of certain animals, like insects.

Option c (wastes are eliminated directly to the environment from tissues) is not an accurate description of an open circulatory system's waste elimination mechanism.

Therefore, the correct answer is d. body tissues are bathed directly in fluid containing oxygen.

22. The system that does not allow for direct contact between oxygen-carrying cells and tissues is called
a. a one-way digestive system
b. the excretory system
c. a closed circulatory system
d. an open respiratory system

To determine the right answer, let's examine the options provided.

An excretory system primarily focuses on the elimination of metabolic waste products, which is not directly relevant to oxygen transport. Therefore, option b (the excretory system) can be eliminated as a potential answer.

Option c (a closed circulatory system) involves the circulation of blood within blood vessels, which allows for the transport of oxygen-carrying cells (such as red blood cells) from the respiratory system to the tissues. Therefore, option c accurately reflects the system that enables direct contact between oxygen-carrying cells and tissues.

Option a (a one-way digestive system) and option d (an open respiratory system) are not related to the transport of oxygen-carrying cells and can be ruled out.

Therefore, the correct answer is c. a closed circulatory system.