Q: Which equation correctly represents the relationship between a cell's surface area and volume for a spherical cell?

$$\text{Surface Area} = 4\pi r^2$, $$\text{Volume} = \frac{4}{3}\pi $$r^3$$

Question 1

Which of the following best explains why the plasma membrane is considered the boundary between life and non-life?

Accepted Answer

It separates the internal environment of the cell from the external environment, allowing regulation of what enters and exits.

Question 2

The plasma membrane is primarily built from which type of molecule?

Accepted Answer

Phospholipids

Question 3

Why can't water-soluble molecules pass freely through the plasma membrane?

Accepted Answer

The hydrophobic fatty acid tails of phospholipids create a barrier to polar molecules.

Question 4

Which equation correctly represents the relationship between a cell's surface area and volume for a spherical cell?

Accepted Answer

$$	ext{Surface Area} = 4\pi r^2$, $$	ext{Volume} = \frac{4}{3}\pi $$r^3$$

Question 5

As a cell increases in size, what happens to its surface area to volume ratio?

Accepted Answer

It decreases

Question 6

Why are proteins embedded in the plasma membrane important for cell function?

Accepted Answer

They act as channels and doors, allowing specific molecules to enter or exit the cell.

Question 7

Which of the following statements about diffusion is correct?

Accepted Answer

Diffusion is the constant motion of cells and molecules, leading to the movement of substances from high to low concentration.

Question 8

A cell is metabolically active and needs to quickly exchange materials with its environment. Which property of the cell is most critical for this exchange?

Accepted Answer

A high surface area to volume ratio

Question 9

What is the main reason blue whale cells are not much larger than those of smaller animals?

Accepted Answer

As cells get bigger, their surface area to volume ratio decreases, limiting efficient exchange of materials.

Question 10

Which of the following best describes the structure of a phospholipid in the plasma membrane?

Accepted Answer

A hydrophilic phosphate head and two hydrophobic fatty acid tails

Question 11

If a cell's plasma membrane is damaged and loses its selective permeability, what is the most likely consequence?

Accepted Answer

Uncontrolled movement of substances in and out of the cell, potentially leading to cell death

Question 12

Which of the following is NOT a function of the plasma membrane?

Accepted Answer

Storing genetic information

Question 13

A scientist observes that a certain molecule cannot pass through the plasma membrane without assistance. What property does this molecule most likely have?

Accepted Answer

It is water-soluble and polar

Question 14

Which of the following best explains why phospholipids form bilayers in water?

Accepted Answer

Their hydrophilic heads interact with water while hydrophobic tails avoid water, resulting in a bilayer structure.

Question 15

If a cell's surface area is $$100 	ext{\,\mu m}^2$$ and its volume is $$500 	ext{\,\mu m}^3$$, what is its surface area to volume ratio?

Accepted Answer

$$0.2$$

Question 16

Which of the following would most likely increase the rate of diffusion across a cell membrane?

Accepted Answer

Increasing the surface area of the membrane

Question 17

A mutation causes a cell to produce fewer channel proteins in its plasma membrane. What is the most likely effect?

Accepted Answer

Reduced ability to transport specific molecules across the membrane

Question 18

Which of the following is a direct consequence of the phospholipid bilayer structure of the plasma membrane?

Accepted Answer

Water-soluble molecules require proteins to cross the membrane

Question 19

Which real-world scenario best illustrates the importance of surface area to volume ratio in cells?

Accepted Answer

Red blood cells are small and have a biconcave shape to maximize oxygen exchange.

Plasma (Cell) Membrane Structure and Function

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