14 - Active vs Passive Transport Reading - Name Period_______ ... - Free Printable
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Step-by-step solution for: 14 - Active vs Passive Transport Reading - Name Period_______ ...
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Show Answer Key & Explanations
Step-by-step solution for: 14 - Active vs Passive Transport Reading - Name Period_______ ...
Based on the provided text from the worksheet "Transport Across a Cell Membrane," here is the solution and explanation for the incomplete sentence at the bottom of the page.
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The text ends with an incomplete sentence:
> "The molecule most likely to be involved in simple diffusion is"
This is clearly a fill-in-the-blank question. To solve it, we need to use the information provided in the preceding paragraphs about simple diffusion.
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1. Understand Simple Diffusion:
* The text defines diffusion as "the movement of particles down their gradient" (from high concentration to low concentration).
* It explicitly states that this process "doesn't require energy."
* It gives the example of "dropping food coloring in water" to illustrate how molecules spread out evenly.
2. Identify Key Characteristics of Molecules for Simple Diffusion:
* Since simple diffusion requires no energy or special structures (like channels or pumps), the molecule must be able to pass directly through the phospholipid bilayer of the cell membrane.
* The cell membrane is made of phospholipids, which have hydrophobic (water-fearing) tails and hydrophilic (water-loving) heads. This creates a barrier.
* Therefore, only small, nonpolar (hydrophobic) molecules can easily dissolve in and pass through the lipid bilayer via simple diffusion.
* Large molecules, polar molecules (like water, though it can pass slowly), and ions generally cannot cross by simple diffusion and require facilitated diffusion or active transport.
3. Recall Common Examples:
* The most common examples of molecules that cross membranes via simple diffusion are:
* Oxygen (O₂) - Small, nonpolar gas.
* Carbon Dioxide (CO₂) - Small, nonpolar gas.
* Lipids/Fatty Acids - Hydrophobic.
* Steroid Hormones (like aldosterone mentioned in the text) - Lipid-soluble (nonpolar).
4. Choose the Best Answer:
* While several molecules fit, oxygen (O₂) is the most classic and universally taught example used to illustrate simple diffusion in biology textbooks. It is essential for cellular respiration and constantly moves into cells down its concentration gradient without any energy input.
* The text mentions aldosterone, which is a steroid hormone and also crosses by simple diffusion, but oxygen is a more fundamental and direct example for this context.
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The molecule most likely to be involved in simple diffusion is oxygen (O₂).
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Simple diffusion is the passive movement of molecules down their concentration gradient without requiring energy or transport proteins. For a molecule to cross the phospholipid bilayer via simple diffusion, it must be small and nonpolar (hydrophobic) so it can dissolve in the lipid portion of the membrane. Oxygen (O₂) is a small, nonpolar gas that readily diffuses across cell membranes from areas of high concentration (like the lungs or capillaries) to areas of low concentration (inside cells) to support cellular respiration. This makes it the quintessential example of a molecule transported by simple diffusion.
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The Problem
The text ends with an incomplete sentence:
> "The molecule most likely to be involved in simple diffusion is"
This is clearly a fill-in-the-blank question. To solve it, we need to use the information provided in the preceding paragraphs about simple diffusion.
---
Step-by-Step Solution
1. Understand Simple Diffusion:
* The text defines diffusion as "the movement of particles down their gradient" (from high concentration to low concentration).
* It explicitly states that this process "doesn't require energy."
* It gives the example of "dropping food coloring in water" to illustrate how molecules spread out evenly.
2. Identify Key Characteristics of Molecules for Simple Diffusion:
* Since simple diffusion requires no energy or special structures (like channels or pumps), the molecule must be able to pass directly through the phospholipid bilayer of the cell membrane.
* The cell membrane is made of phospholipids, which have hydrophobic (water-fearing) tails and hydrophilic (water-loving) heads. This creates a barrier.
* Therefore, only small, nonpolar (hydrophobic) molecules can easily dissolve in and pass through the lipid bilayer via simple diffusion.
* Large molecules, polar molecules (like water, though it can pass slowly), and ions generally cannot cross by simple diffusion and require facilitated diffusion or active transport.
3. Recall Common Examples:
* The most common examples of molecules that cross membranes via simple diffusion are:
* Oxygen (O₂) - Small, nonpolar gas.
* Carbon Dioxide (CO₂) - Small, nonpolar gas.
* Lipids/Fatty Acids - Hydrophobic.
* Steroid Hormones (like aldosterone mentioned in the text) - Lipid-soluble (nonpolar).
4. Choose the Best Answer:
* While several molecules fit, oxygen (O₂) is the most classic and universally taught example used to illustrate simple diffusion in biology textbooks. It is essential for cellular respiration and constantly moves into cells down its concentration gradient without any energy input.
* The text mentions aldosterone, which is a steroid hormone and also crosses by simple diffusion, but oxygen is a more fundamental and direct example for this context.
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Final Answer
The molecule most likely to be involved in simple diffusion is oxygen (O₂).
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Explanation
Simple diffusion is the passive movement of molecules down their concentration gradient without requiring energy or transport proteins. For a molecule to cross the phospholipid bilayer via simple diffusion, it must be small and nonpolar (hydrophobic) so it can dissolve in the lipid portion of the membrane. Oxygen (O₂) is a small, nonpolar gas that readily diffuses across cell membranes from areas of high concentration (like the lungs or capillaries) to areas of low concentration (inside cells) to support cellular respiration. This makes it the quintessential example of a molecule transported by simple diffusion.
Parent Tip: Review the logic above to help your child master the concept of active transport worksheet answers.
