How is the plasma membrane arranged?

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.

Correct Answer: D

Rationale: Option D is the best example of a hypothesis because it presents a clear cause-and-effect relationship that can be tested through experimentation. It follows the format of 'If [cause], then [effect]' which is characteristic of a hypothesis in scientific research. The statement is specific, testable, and does not rely on personal opinions or biases, making it a strong and valid hypothesis. Choices A, B, and C do not follow the structure of a hypothesis as they lack the cause-and-effect relationship that can be tested through experimentation. They are more like statements or opinions rather than hypotheses.

Correct Answer: B

Rationale: The correct answer is B: Carrier proteins. Carrier proteins are involved in facilitated diffusion, a type of passive transport where specific target molecules are moved across the membrane with the help of proteins that change shape. These carrier proteins bind to the target molecule on one side of the membrane, undergo a conformational change, and then release the molecule on the other side. This process is crucial for the selective transport of certain molecules that cannot pass through the membrane by simple diffusion. Choices A and C are incorrect because diffusion and channel proteins do not involve proteins that change shape to transport target molecules selectively. Choice D is incorrect as carrier proteins fit the description provided in the question.

Correct Answer: D

Rationale: Tundra, savannas, grasslands, deserts, and rainforests are examples of biomes. A biome is a large geographical area with similar climatic conditions and distinct flora and fauna. Each biome has its unique characteristics, such as temperature, precipitation levels, and types of vegetation, which define the ecosystem within that region. Biomasses refer to the total mass of living organisms in a given area, biospheres are the global ecological system integrating all living beings and their relationships, and biodiversity represents the variety of life forms in a specific habitat.

Correct Answer: D

Rationale: The correct answer is D: Plasma membrane. The plasma membrane surrounds the cell and acts as an interface between the living interior of the cell and the nonliving exterior. It plays a vital role in maintaining the cell's integrity, regulating the passage of substances in and out of the cell, and facilitating communication with other cells. Choices A, B, and C are incorrect because the term 'plasma membrane' specifically refers to the binding membrane of an animal cell, distinguishing it from other types of membranes or coatings found in cells.

Correct Answer: A

Rationale: Genes are sections of DNA that contain instructions for building and operating living organisms. These sections of DNA contain the genetic information that is passed on from one generation to the next. Genes are composed of specific sequences of nucleotides within the DNA molecule. Therefore, genes are best described as segments of DNA. Choice A is correct. Choice B is incorrect because genes are not bead-like structures on chromosomes but specific sequences of DNA. Choice C is incorrect because genes are not protein molecules but rather sequences of nucleotides. Choice D is incorrect because genes are not segments of RNA but DNA.

Correct Answer: D

Rationale: The correct answer is D. A purine (A) must pair with a pyrimidine (T) in DNA. This eliminates options A and C as they do not follow the rule of complementary base pairing. Adenine (A) always pairs with thymine (T) due to their specific shape and bonding properties in DNA structure. Choice B is incorrect because adenine does not pair with cytosine in DNA.

Correct Answer: C

Rationale: Plant cells have a rigid cell wall surrounding them, which prevents them from using a contractile ring for cell division. The rigid cell wall requires plant cells to form a cell plate during cell division instead of pinching apart like animal cells with a contractile ring. Choice A is incorrect because plant cells cannot use a contractile ring due to their rigid cell wall. Choice B is incorrect as the speed of cell division is not the primary reason for the difference in cell division mechanisms between plant and animal cells. Choice D is not applicable as plant cells indeed have a specific limitation in using a contractile ring for cell division.

Correct Answer: A

Rationale: The correct answer is A: fat-soluble hormones. Fat-soluble hormones are able to diffuse through the cell membrane to bind to receptors inside the cell. This is because they are lipophilic, allowing them to cross the lipid bilayer easily. Once inside the cell, fat-soluble hormones can directly affect gene expression or cell function. Choice B, amino acid derivatives, and choice C, hydrophilic hormones, are not able to diffuse through the cell membrane as they are not lipophilic. Therefore, they cannot bind to receptors inside the cell. Choice D, water-soluble hormones, also cannot diffuse through the cell membrane as it is hydrophilic, making it unable to reach receptors inside the cell.