Problem 11 - Biology E/M

Question

$$\begin{array}{l}{\text { (A) Hydra }} \\ {\text { (B) Grasshopper }} \\\ {\text { (C) Earthworm }}\end{array}$$ Every cell in this animal is directly in contact with its environment

Step-by-Step Solution

Answer

Hydra.

Step 1: Understanding the Problem

The question asks which animal has every cell directly in contact with its environment. This means the animal's body is simple enough so that all parts or cells of it are exposed to the external environment.

Step 2: Analyzing the Animals

Examine the given organisms: Hydra, Grasshopper, and Earthworm. Consider their body structures: - Hydra: a simple, radially symmetrical organism generally shaped like a tube. - Grasshopper: a more complex insect with an exoskeleton and internal systems. - Earthworm: a segmented worm with a complex internal structure.

Step 3: Comparing Body Structures

Hydra has a simple body plan without any specialized circulatory system, allowing all its cells to directly contact the water it lives in. Grasshoppers and earthworms have more complex body structures that do not allow every cell to be in direct contact with the environment.

Step 4: Concluding the Answer

From the analysis of body structures, Hydra is the only organism with all its cells directly in contact with its environment due to its simplicity and aquatic habitat.

Key Concepts

Hydra

Hydras are fascinating creatures! These simple organisms belong to the phylum Cnidaria and are relatives to jellyfish and sea anemones. Imagine a small tubular body, and you've got the shape of a hydra. Hydras are typically only a few millimeters long, often appearing translucent. Their unique body structure allows every cell to be in direct contact with the water of their environment.

What's intriguing about hydras is their ability to regenerate. If cut into pieces, each piece can potentially become a new hydra. This regenerative property makes them an interesting subject of study in biological research.

• Simple body plan
• Radially symmetrical (like a wheel)
• Regenerative abilities

All these features contribute to why every hydra cell is in direct contact with its environment, living and thriving without a need for complex systems like circulatory or respiratory organs.

Body Structure

The body structure of the hydra is like a wonder of simplicity. Hydras do not have a brain or a central nervous system. Instead, they have a nerve net that helps them respond to their surroundings. You can imagine their body as mainly consisting of two layers of cells: the outer ectoderm and the inner endoderm.

Between these layers lies a jelly-like substance called the mesoglea, which gives support to their body.

• Two cell layers: ectoderm and endoderm
• Mesoglea acts as a support mechanism
• Lacks complex organ systems

This simplicity in structure allows hydras to efficiently handle basic functions like feeding and movement, making every cell exposed to the external environment directly.

Aquatic Habitats

Hydras flourish in aquatic habitats, primarily freshwater environments such as ponds, lakes, and streams. In this setting, hydras utilize their simple body structures to maximize their interaction with their surroundings. Their tentacles, equipped with stinging cells called cnidocytes, aid in capturing prey like small aquatic organisms.

Because of their aquatic lifestyle, hydras rely on diffusion across their body surfaces to acquire oxygen and expel waste, thereby making each cell's direct contact with the water critically important to their survival.

• Commonly found in freshwater
• Tentacles help in feeding
• Oxygen and waste move across body by diffusion

This habitat not only supports their basic biological needs but also showcases how their body structure is adapted to thrive in these water-rich environments.

Simple Organisms

When we talk about simple organisms like the hydra, we're often referring to beings that have minimal body complexity yet function efficiently in their environments. Hydras fit this category perfectly with their straightforward body plans and basic physiological processes.

The simplicity means that hydras sidestep the need for complex organ systems, unlike higher organisms such as grasshoppers or earthworms. This simplicity allows hydras to directly interact with their environment.

• No circulatory or respiratory systems
• Efficient and direct interaction with surroundings
• Basic physiological processes suffice for survival

Hydras provide insightful examples of how simplicity in biological design can still thrive and adapt within their specific ecological niches.