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: 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: There are 206 bones in the human skeletal system. This includes bones in the skull, spine, ribs, arms, legs, hands, and feet. The correct answer is 206 because that is the standard number of bones in an adult human body. Choices A, B, and C are incorrect as they do not reflect the accurate count of bones in the human skeletal system.

Correct Answer: D

Rationale: The endocrine system comprises a network of glands that produce and release hormones to regulate bodily functions. The pituitary gland, thyroid gland, and adrenal glands are essential components of this system. The pituitary gland secretes various hormones that control other glands and some body functions. The thyroid gland regulates metabolism, growth, and energy levels by producing thyroid hormones. The adrenal glands produce hormones involved in stress response, metabolism, and immune function. Therefore, all of the above glands are integral parts of the endocrine system, making choice D the correct answer.

Correct Answer: D

Rationale: The correct answer is D. The respiratory system consists of all the organs involved in breathing, including the nose, pharynx, larynx, trachea, bronchi, and lungs. Additionally, the respiratory system is responsible for conveying oxygen into our bodies and removing carbon dioxide from our bodies. Therefore, all the statements provided are true, making option D the correct choice. Options A, B, and C are all accurate statements about the respiratory system, reinforcing the correctness of choosing option D.

Correct Answer: A

Rationale: The correct answer is A, Bacteria. Bacteria do not have eukaryotic cells. They are single-celled organisms with prokaryotic cells. Dogs, humans, and onions are all multicellular organisms that possess eukaryotic cells. Therefore, choices B, C, and D have eukaryotic cells and are not the correct answer.

Correct Answer: A

Rationale: The correct sequence of events for protein synthesis is that DNA is transcribed into RNA, which is then translated into a protein. This process is known as the central dogma of molecular biology. In this sequence, DNA serves as the template for RNA synthesis (transcription), and the RNA serves as the template for protein synthesis (translation). Choice B is incorrect as genes are segments of DNA that code for proteins, and chromosomes are structures that contain DNA. Choice C is incorrect as ATP is an energy molecule and amino acids are the building blocks of proteins, but they are not directly involved in the synthesis process. Choice D is incorrect because RNA is first transcribed from DNA and then used as a template to produce proteins.

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: 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.