how is the plasma membrane arranged

HESI A2

HESI A2 Biology Practice Test

1. How is the plasma membrane arranged?

A. In a single layer made of proteins
B. In a double layer made of proteins
C. In a single layer of phospholipids
D. In a double layer of phospholipids

Correct answer: D

Rationale: The plasma membrane is arranged in a double layer of phospholipids, known as a phospholipid bilayer. This structure consists of two layers of phospholipid molecules with hydrophilic heads facing the exterior and hydrophobic tails facing the interior, providing a semipermeable barrier for the cell. Choice A is incorrect because the plasma membrane is not made of a single layer of proteins. Choice B is incorrect as the double layer is composed of phospholipids, not proteins. Choice C is incorrect as the plasma membrane is not made of a single layer of phospholipids but rather a double layer.

2. How does water affect the temperature of a living thing?

A. Water increases temperature.
B. Water keeps temperature stable.
C. Water decreases temperature.
D. Water does not affect temperature.

Correct answer: B

Rationale: Water has a high specific heat capacity, which means it can absorb and release large amounts of heat with minimal temperature change. This property helps water regulate the temperature of living things by maintaining a stable environment. Choice A is incorrect because water does not consistently increase temperature, but rather helps in temperature regulation. Choice C is incorrect as water doesn't typically decrease temperature in living organisms. Choice D is incorrect since water does play a crucial role in regulating temperature.

3. Cytosine and thymine are known as:

A. Purines
B. Pyrimidines
C. Both
D. None of the above

Correct answer: B

Rationale: Cytosine and thymine are known as pyrimidines because they have a single carbon ring structure. Purines, on the other hand, have a double-ring structure. Choice A ('Purines') is incorrect because purines have a double-ring structure, unlike cytosine and thymine. Choice C ('Both') is incorrect as it implies they are both purines and pyrimidines, which is not true. Choice D ('None of the above') is incorrect because cytosine and thymine are indeed pyrimidines.

4. Why do we perceive chlorophyll as green?

A. It absorbs yellow and blue light.
B. It primarily absorbs green light.
C. It fails to absorb green light.
D. It primarily absorbs red light.

Correct answer: A

Rationale: Chlorophyll appears green to us because it primarily absorbs yellow and blue light while reflecting green light. The wavelengths of yellow and blue light are absorbed by chlorophyll for photosynthesis, which results in the green color we perceive. Choice B is incorrect because chlorophyll absorbs yellow and blue light, not green light. Choice C is incorrect because chlorophyll does absorb green light, but it also absorbs other wavelengths, primarily yellow and blue. Choice D is incorrect because chlorophyll primarily absorbs yellow and blue light, not red light.

5. What is the term for the movement of ions and other molecular substances across cell membranes without the need for energy?

A. Active Transport
B. Passive Transport
C. Diffusion
D. Osmosis

Correct answer: B

Rationale: Passive transport refers to the movement of substances across cell membranes without the need for energy input. In contrast, active transport, choice A, requires energy to move substances against their concentration gradient. Diffusion, choice C, is a type of passive transport where substances move from an area of high concentration to low concentration. Osmosis, choice D, specifically refers to the movement of water molecules across a selectively permeable membrane.