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Chapter 5: Problem 18

Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane? a. Phospholipids are amphipathic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails. b. Phospholipids are lipophilic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails c. Phospholipids are amphipathic molecules. The nonpolar head faces towards other fatty acid tails and the polar fatty acid tails face towards water. d. Phospholipids are hydrophilic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails.

Short Answer

Expert verified
Option a. Phospholipids are amphipathic molecules with polar heads facing water and nonpolar tails facing inward.

Step by step solution

01

Understand Phospholipids

Phospholipids are a type of lipid molecule that is the main component of the cell membrane. They have a hydrophilic (polar) head and two hydrophobic (nonpolar) fatty acid tails.
02

Define Amphipathic Nature

Amphipathic molecules have both hydrophilic (water-loving) and hydrophobic (water-fearing) components. This unique property allows phospholipids to spontaneously arrange themselves in a specific way in a watery environment.
03

Behavior in Water

When in water, phospholipids align themselves so that the hydrophilic heads face towards the water, and the hydrophobic tails face away from the water, towards each other, creating a bilayer structure.
04

Identify the Correct Explanation

Option a states: 'Phospholipids are amphipathic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails.' This matches our step-by-step explanation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Amphipathic Molecules
Amphipathic molecules are unique because they contain both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. This dual nature is essential for the formation of structures like cell membranes.
The hydrophilic part, usually a phosphate group, is attracted to water, while the hydrophobic parts, typically long fatty acid chains, avoid water.
In an aqueous environment, amphipathic molecules like phospholipids will spontaneously arrange themselves in a practical manner.
This property is central to forming bilayer structures, which are foundational to cell membranes.
Cell Membrane Structure
The cell membrane, also known as the plasma membrane, is a critical component of all living cells. It serves as a barrier that separates the interior of the cell from the external environment.
The membrane is primarily composed of phospholipids, proteins, and carbohydrates.
The arrangement of these phospholipids into a bilayer is due to their amphipathic nature.
This bilayer has the hydrophilic heads facing outward towards the water, both inside and outside the cell, and the hydrophobic tails facing inward, shielded from water.
This structure not only provides a flexible yet sturdy boundary but also facilitates selective permeability, allowing the cell to control which substances enter and leave.
Lipid Bilayer
The lipid bilayer is a fundamental aspect of cell membrane structure. It refers to the double layer of phospholipids that makes up the membrane.
This bilayer is formed because of the amphipathic nature of the phospholipids, with hydrophilic heads facing the aqueous environment and hydrophobic tails facing inward, away from water.
This arrangement creates a semi-permeable barrier crucial for cell function.
It allows for the proper environment needed for cellular processes, maintaining a balance of substances entering and exiting the cell.
Additionally, the lipid bilayer plays a role in cell communication and signaling due to its dynamic nature and presence of various proteins and glycoproteins within the membrane.

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Most popular questions from this chapter

Which characteristic of a phospholipid increases the fluidity of the membrane? a. cholesterol b. its head c. saturated fatty acid tail d. unsaturated fatty acid tail

What problem is faced by organisms that live in fresh water? a. They will have higher concentrations of body solutes. b. Without compensating mechanisms, their bodies tend to take in too much water. c. They have no way of controlling their tonicity. d. Their bodies tend to lose too much water to their environment.

One type of mutation in the CFTR protein prevents the transport of chloride ions through the channel. Which of the following is most likely to be observed in the lungs of patients with this mutation? $$ \begin{array}{l}{\text { a. dehydrated epithelial cells }} \\ {\text { b. dehydrated mucus }} \\ {\text { c. mucus with excess water }} \\ {\text { d. mucus with high electrolyte concentration }}\end{array} $$

Discuss why the following affect the rate of diffusion: molecular size, temperature, solution density, and the distance that must be traveled. a. Larger molecules move faster than lighter molecules. Temperature affects the molecular moveruent. Density is directly proportional to the molecular movement. Greater distance slows the diffusion. b. Larger molecules move slower than lighter molecules. Increasing or decreasing temperature increases or decreases the energy in the medium, affecting molecular movement. Density is inversely proportional to molecular movement. Greater distance slows the diffusion. c. Larger molecules move slower than lighter molecules. Temperature does not affect the rate of diffusion. Density is inversely proportional to molecular movement. Greater distance speeds up the diffusion. d. Larger molecules move slower than lighter molecules. Increasing or decreasing temperature increases or decreases the energy in the medium, affecting molecular movement. Density is inversely proportional to the molecular movement. Greater distance speeds up the diffusion.

How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell? a. The sodium-potassium pump forces out three (positive) \(\mathrm{Na}^{+}\) ions for every two (positive) \(\mathrm{K}^{+}\) ions it pumps in, thus the cell loses a net positive charge of one at every cycle of the pump. b. The sodium-potassium pump expels three ions \(\mathrm{K}^{+}\) for every two \(\mathrm{Na}^{+}\) inside the cells, creating a net positive charge outside the cell and a net negative charge inside the cell. c. The sodium-potassium pump helps the development of negative charge inside the cell by making the membrane more permeable to negatively charged proteins. d. The sodium-potassium pump helps in the development of negative charge inside the cell by making the membrane impermeable to positively charged ions.
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