B) Spike protein

Explanation: The spike protein of the coronavirus is essential for binding to the ACE2 receptors on host cells, enabling the virus to enter the cells.

B) From pre-existing cells

Explanation: The Cell Theory states that new cells arise from pre-existing cells, emphasizing the continuity of life through cellular division.

B) They have higher ACE2 expression in the heart and lungs

Explanation: Individuals with pre-existing cardiovascular conditions may have higher ACE2 expression in their heart and lungs, which could increase their susceptibility to severe outcomes when infected with SARS-CoV-2.

C) Peptide bonds

Explanation: Amino acids are covalently bonded via peptide bonds to form a linear chain of polypeptides, which are essential for protein structure.

C) Storage, expression, and transmission of genetic information

Explanation: Nucleic acids are essential biomolecules responsible for the storage, expression, and transmission of genetic information, which is crucial for all living organisms.

B) Deoxyribonucleic Acid (DNA)

Explanation: Deoxyribonucleic Acid (DNA) is specifically responsible for storing genetic information, making it a fundamental component of genetic material in organisms.

C) Moves substances down their concentration gradient

Explanation: Passive transport is characterized by the movement of substances down their concentration gradient, meaning they move from areas of higher concentration to areas of lower concentration without the need for energy.

B) They are injected into the core proteasome

Explanation: Proteins that are destined for degradation are injected into the core of the proteasome, where they undergo degradation into small peptides and amino acids.

C) Polypeptide

Explanation: The linear chain formed by covalently bonded amino acids is known as a polypeptide, which is a key component of protein structure.

B) Large and complex

Explanation: Proteins are described as large, complex polymers, indicating their intricate structures and diverse functions in biological systems.

C) Telophase

Explanation: Telophase is the final phase of mitosis, where the chromosomes de-condense, and the nuclear envelope reforms around each set of chromosomes, leading to the eventual division of the cell.

C) Glycogen granules

Explanation: Glycogen granules are abundant in liver and muscle cells, serving as a form of energy storage.

D) Prometaphase

Explanation: Prometaphase follows prophase in the mitotic sequence, characterized by the breakdown of the nuclear envelope and the attachment of spindle fibers to chromosomes.

C) Division of the cytoplasm

Explanation: Cytokinesis I is primarily responsible for the division of the cytoplasm following the first meiotic division, resulting in two daughter cells.

B) It results in four daughter cells

Explanation: Cytokinesis II occurs after the second meiotic division and results in four genetically distinct daughter cells, distinguishing it from Cytokinesis I, which results in two cells.

B) An electrochemical gradient

Explanation: By transporting solutes against their concentration gradient, primary active transport establishes an electrochemical gradient across the membrane, which is crucial for various cellular functions.

C) It is essential for the cell’s survival

Explanation: The integrity and function of the plasma membrane are crucial for the survival of the cell, as it regulates what enters and exits the cell, maintaining homeostasis.

B) Amino acids

Explanation: Proteins are large, complex polymers made up of amino acid molecules, which are the building blocks of proteins.

C) Simple Diffusion

Explanation: Simple diffusion is a passive process that allows molecules to move across the plasma membrane without the use of energy, relying on concentration gradients.

B) The sequence of amino acids within a polypeptide

Explanation: The genetic code is crucial as it specifies the sequence of amino acids that will form a polypeptide, which is essential for protein synthesis.

C) The aging of cells

Explanation: Cellular senescence refers to the process of aging in cells, which is a crucial aspect of the life cycle of organisms, indicating how cells gradually lose their ability to function effectively over time.

C) Melanin

Explanation: Melanin is the pigment found in skin and hair cells, contributing to coloration and protection against UV radiation.

C) Plasma membrane

Explanation: All human cells are surrounded by a plasma membrane, which serves as a protective barrier and plays a crucial role in maintaining the cell's environment.

B) With primary active transport

Explanation: Secondary active transport is often coupled to primary active transport, as it relies on the energy stored in the electrochemical gradient established by primary active transport to move molecules against their concentration gradient.

B) To transport solutes against the concentration gradient

Explanation: Primary active transport is characterized by its ability to move solutes against their concentration gradient, which requires energy in the form of ATP.

B) Chromosomes are pulled apart to opposite poles

Explanation: Anaphase is characterized by the separation of sister chromatids, which are pulled toward opposite poles of the cell by the spindle fibers.

C) Genetic material storage and regulation

Explanation: The nucleus is responsible for storing the cell's genetic material (DNA) and regulating gene expression, making it essential for cell function and reproduction.

B) It transfers genetic information from DNA to form a protein

Explanation: Ribonucleic Acid (RNA) plays a crucial role in transferring genetic information from DNA to the ribosomes, where proteins are synthesized.

B) The boundary between the outside and inside of the cell

Explanation: The plasma membrane serves as the boundary that separates the external environment from the internal environment of the cell, playing a vital role in cellular organization.

C) Small peptides and amino acids

Explanation: Proteasomes degrade proteins by breaking them down into small peptides and amino acids, which can then be recycled back into the cytosol for reuse.

C) Barrel-shaped

Explanation: Proteasomes are described as barrel-shaped cellular protein complexes, which is a distinctive feature of their structure.

B) To move an entire cell

Explanation: Flagella are specialized for the movement of an entire cell, unlike cilia, which primarily move fluids along surfaces.

C) In the trachea and fallopian tubes

Explanation: Cilia are found in the trachea, where they help sweep mucus and dirt out of the lungs, and in the fallopian tubes, where they assist in moving eggs to the uterus.

B) Protein synthesis and modification

Explanation: The Rough Endoplasmic Reticulum (RER) is studded with ribosomes and is primarily involved in the synthesis and modification of proteins, distinguishing it from the Smooth ER.

C) It is the final step of meiosis

Explanation: Cytokinesis II is the final step of meiosis, completing the process by dividing the two cells formed during Cytokinesis I into four distinct haploid cells.

B) ACE2

Explanation: SARS-CoV-2 primarily binds to the ACE2 receptor on host cells, which facilitates its entry and infection process.

B) It is the site where transcription begins

Explanation: The promoter is a segment of DNA that indicates where transcription starts, providing binding sites for RNA polymerase and regulatory proteins necessary for initiating the transcription process.

C) Metaphase

Explanation: Metaphase is the stage where chromosomes align at the metaphase plate, ensuring that each daughter cell will receive an identical set of chromosomes.

C) ATP

Explanation: Primary active transport directly utilizes ATP as its energy source to drive the transport of solutes against their concentration gradient.

D) Lipid bilayers

Explanation: The cytoskeleton is composed of microtubules, intermediate filaments, and microfilaments (which include actin filaments), but it does not include lipid bilayers.

C) Cilia are short and numerous

Explanation: Cilia are typically short and present in large numbers on the surface of cells, while flagella are longer and usually singular.

B) Nitrogenous Base + Ribose Sugar + Phosphate Group

Explanation: An RNA nucleotide consists of a nitrogenous base, ribose sugar, and a phosphate group, which are essential for its structure and function.

C) To divide the cell nucleus and its contents

Explanation: The primary purpose of mitosis is to ensure that the cell's nucleus and its genetic material are accurately divided into two daughter cells, maintaining genetic consistency.

D) Thymine (T)

Explanation: Thymine (T) is not found in RNA; instead, uracil (U) replaces thymine in RNA, while cytosine (C), adenine (A), and guanine (G) are present.

C) Cell

Explanation: The Cell Theory states that a cell is the basic unit of life, meaning that nothing smaller than a cell is considered to be alive.

C) Prophase

Explanation: Prophase is the first phase of mitosis, where the chromatin condenses into visible chromosomes and the nuclear envelope begins to break down.

D) Cilia are about 20 times shorter than flagella

Explanation: Cilia are significantly shorter than flagella, being about 20 times shorter, which reflects their different roles in movement.

B) To maintain cell shape and move organelles

Explanation: The cytoskeleton is a series of proteins that plays a crucial role in maintaining the shape of the cell and anchoring or moving organelles within it.

D) Osmosis

Explanation: Osmosis is the process by which water molecules move across the plasma membrane through specialized water channels, demonstrating a form of facilitated diffusion.

C) Moves substances down their concentration gradient

Explanation: Passive transport is characterized by the movement of substances from an area of higher concentration to an area of lower concentration, without the need for energy input.

B) Sodium-potassium pump

Explanation: The sodium-potassium pump is a well-known example of primary active transport, as it uses ATP to transport sodium out of the cell and potassium into the cell against their respective concentration gradients.

B) To reduce the chromosome number by half

Explanation: The primary purpose of Meiosis I is to reduce the chromosome number from diploid to haploid, ensuring that gametes have half the number of chromosomes for sexual reproduction.

B) tRNA

Explanation: Transfer RNA (tRNA) is responsible for bringing the appropriate amino acids to the ribosome during translation, matching them to the codons on the mRNA template.

C) Within the cytoplasm close to the nucleus

Explanation: The centrosome is usually found in the cytoplasm, positioned near the nucleus, which is important for its role in cell division.

B) A chemical process where sugar molecules attach to proteins unnaturally

Explanation: Glycation is defined as a chemical process in which sugar molecules attach to proteins, lipids, or nucleic acids unnaturally, leading to cellular damage and contributing to aging.

D) Energy stored in an electrochemical gradient

Explanation: Secondary active transport relies on the energy stored in an electrochemical gradient, which is created by primary active transport, to facilitate the movement of molecules against their concentration gradient.

C) Cell membrane

Explanation: The cell membrane is not found within the cytoplasm; rather, it surrounds the cytoplasm, while the other options are organelles located within the cytoplasm.

B) Lipid droplets

Explanation: Lipid droplets are inclusion bodies that are commonly found in fat cells, serving as storage for lipids.

B) A single strand of polynucleotides

Explanation: RNA is characterized as a polymer composed of a single strand of polynucleotides, distinguishing it from DNA, which is double-stranded.

C) Mitochondria

Explanation: Mitochondria are often referred to as the powerhouse of the cell because they generate ATP, the energy currency of the cell, through cellular respiration.

C) In groups of 3 bases or codons

Explanation: The genetic code is read in groups of three bases, known as codons, which correspond to specific amino acids during protein synthesis.

B) Actin

Explanation: Microfilaments, also known as actin filaments, are primarily composed of actin proteins, which are crucial for various cellular functions including movement and shape maintenance.

B) It is the diffusion of water across a selectively permeable membrane

Explanation: Osmosis specifically refers to the passive movement of water molecules through a selectively permeable membrane, driven by differences in solute concentration.

B) Deoxyribonucleic acid

Explanation: DNA stands for Deoxyribonucleic acid, which is the molecule that carries genetic information in living organisms.

A) 9 circular triplets of microtubules

Explanation: Centrioles consist of 9 circular triplets of microtubules, which are essential for their structural integrity and function during cell division.

C) The promoter initiates transcription, while the terminator signals its end

Explanation: The promoter serves as the starting point for transcription, while the terminator indicates where the transcription process concludes, highlighting their complementary roles in gene expression.

B) Polypeptides

Explanation: Amino acids are the building blocks that are linked together to form chains known as polypeptides, which are essential in the formation of proteins.

B) The powerhouses of the cell

Explanation: Mitochondria are known as the 'powerhouses' of the cell because they are responsible for generating ATP, which is the energy currency of the cell.

B) Protein synthesis

Explanation: The Smooth Endoplasmic Reticulum (SER) has no role in protein synthesis; instead, it is involved in lipid synthesis, detoxification, storage of Ca2+ ions, and carbohydrate metabolism.

C) They consist of two classes: DNA and RNA

Explanation: Nucleic acids are classified into two main types: Deoxyribonucleic Acid (DNA), which stores genetic information, and Ribonucleic Acid (RNA), which transfers genetic information.

C) To divide a cell into two identical daughter cells

Explanation: The primary purpose of mitosis is to ensure that a single cell divides to produce two genetically identical daughter cells, maintaining the chromosome number of the original cell.

C) Anaphase I

Explanation: Homologous chromosomes are separated during Anaphase I, where they are pulled to opposite poles of the cell, which is a key event in reducing the chromosome number.

B) To direct the synthesis of a protein

Explanation: Messenger RNA (mRNA) plays a crucial role in directing the synthesis of proteins by conveying genetic information from DNA to the ribosome.

B) A difference in the concentration of ions across a membrane

Explanation: A concentration gradient refers to the difference in the concentration of ions or molecules across a plasma membrane, which is crucial for various cellular processes.

D) Uracil (U)

Explanation: In RNA, adenine (A) pairs with uracil (U) through hydrogen bonds, following the base pairing rules specific to RNA.

B) Receptor-mediated endocytosis

Explanation: SARS-CoV-2 primarily enters cells through receptor-mediated endocytosis, utilizing specific receptors on the cell surface to facilitate its entry.

B) A pre-existing gradient

Explanation: Secondary active transport uses a pre-existing gradient, specifically an electrochemical gradient created by primary active transport, to drive the movement of molecules against their concentration gradient.

B) It is where transcription ends

Explanation: The terminator is a segment of DNA that signals the end of transcription, indicating to RNA polymerase that the RNA synthesis process should stop.

B) Single-membrane organelles

Explanation: Lysosomes are characterized as single-membrane organelles that bud from the Golgi complex, distinguishing them from other types of organelles.

C) Microtubules

Explanation: Microtubules are the largest in diameter among the three types of fibers that make up the cytoskeleton, providing structural support and facilitating intracellular transport.

C) To selectively uptake specific molecules

Explanation: Receptor-mediated endocytosis is a targeted process that allows cells to take in specific molecules based on their binding to receptors on the cell surface.

B) They initiate and terminate protein synthesis

Explanation: Start and Stop codons play critical roles in the genetic code by signaling the beginning and end of protein synthesis, ensuring that the polypeptide is synthesized correctly.

B) They anchor organelles and provide mechanical support

Explanation: Intermediate filaments are important for anchoring organelles in place and providing mechanical support to the cell, contributing to its overall stability.

C) Sister chromatids are pulled apart

Explanation: In anaphase, the sister chromatids are separated and pulled towards opposite poles of the cell, ensuring that each daughter cell will receive an identical set of chromosomes.

C) Sister chromatids are pulled apart

Explanation: In anaphase, the sister chromatids are separated and pulled toward opposite poles of the cell, ensuring that each daughter cell will receive an identical set of chromosomes.

B) All living things are made up of cells.

Explanation: The Cell Theory asserts that all living things are composed of cells, highlighting the fundamental role of cells in the structure of life.

B) To degrade unneeded or damaged proteins

Explanation: Proteasomes are responsible for degrading unneeded, damaged, or faulty cytoplasmic proteins, which is essential for maintaining cellular health and regulating various cellular processes.

B) To move fluids along a cell's surface

Explanation: Cilia are primarily responsible for moving fluids along the surface of a cell, such as sweeping mucus and dirt out of the lungs in the trachea.

B) To move molecules against their concentration gradient

Explanation: The primary function of secondary active transport is to move molecules against their concentration gradient, utilizing the energy from an existing electrochemical gradient.

B) Primary active transport creates the gradient used by secondary active transport

Explanation: Primary active transport establishes an electrochemical gradient that secondary active transport then utilizes to move molecules against their concentration gradient.

C) Transcription

Explanation: The first step in gene expression is transcription, where the DNA sequence of a gene is copied into messenger RNA (mRNA). This process is essential for the subsequent translation into protein.

C) Translation

Explanation: The process of assembling amino acids into polypeptides is known as translation, which is a key step in gene expression and protein synthesis.

B) The site where tRNA carrying the next amino acid binds

Explanation: The 'A site' (Aminoacyl site) is where the tRNA carrying the next amino acid binds during translation, facilitating the addition of amino acids to the growing polypeptide chain.

B) The digestion of worn-out organelles

Explanation: Autophagy refers to the process carried out by lysosomes to digest worn-out or damaged organelles, ensuring cellular maintenance and health.

C) It is where tRNA exits the ribosome

Explanation: The 'E site' (Exit site) is the location on the ribosome where tRNA, after donating its amino acid, exits the ribosome, completing its role in protein synthesis.

B) Cytoskeleton

Explanation: The cytoskeleton provides structural support to the cell, maintaining its shape and facilitating movement of organelles within the cytoplasm.

B) ATP generation through aerobic cellular respiration

Explanation: Mitochondria are crucial for generating ATP through the processes of aerobic cellular respiration, making them vital for energy production in cells.

D) Exocytosis

Explanation: Exocytosis is the process of expelling materials from the cell, which is the opposite of endocytosis, where materials are brought into the cell.

B) By degrading and recycling proteins

Explanation: Proteasomes play a crucial role in maintaining cellular health by degrading and recycling proteins, which helps regulate various cellular processes and remove damaged proteins.

B) Cell organelles and structures

Explanation: The cytoplasm is the fluid filling the inside of a cell and contains various organelles and structures such as the nucleus, endoplasmic reticulum, mitochondria, and more, which are essential for cellular function.

C) Active Transport

Explanation: Active transport requires energy to move molecules against their concentration gradient, making it distinct from passive processes like facilitated diffusion, osmosis, and simple diffusion.

C) Hydrolases

Explanation: Lysosomes store hydrolases, which are enzymes responsible for digesting various biological molecules, playing a crucial role in cellular digestion.

D) Telophase I

Explanation: Cytokinesis I occurs during Telophase I, when the cell begins to divide into two daughter cells after the first meiotic division.

C) It serves as a template for protein synthesis

Explanation: mRNA (messenger RNA) acts as a template for the synthesis of proteins during the translation process, carrying the genetic code from DNA to the ribosome.

D) Active transport

Explanation: Active transport is the process that requires energy to move substances against their concentration gradient, while diffusion, osmosis, and facilitated diffusion are all forms of passive transport.

A) Excessive cell division

Explanation: The shortening of telomeres occurs primarily due to excessive cell division, which reduces the protective caps on the ends of chromosomes, contributing to cellular aging.

C) Protein

Explanation: The end product of gene expression is protein, which is synthesized based on the information encoded in the DNA and transcribed into mRNA.

C) A double helix composed of two strands of polynucleotides

Explanation: DNA is characterized by its double helix structure, which consists of two strands of polynucleotides twisted around each other, forming a stable and compact structure essential for genetic information storage.

C) Translation

Explanation: Translation is the process that decodes the mRNA sequence to synthesize proteins, involving ribosomes and tRNA to assemble amino acids in the correct order.

B) By facilitated transport down its concentration gradient

Explanation: Glucose is transported into cells via facilitated transport, which allows it to move down its concentration gradient with the assistance of a protein carrier called a transporter, without the need for cellular energy.

B) Concentration gradient

Explanation: The primary driving force behind passive transport processes is the concentration gradient, which allows substances to move from areas of higher concentration to areas of lower concentration without the need for energy.

B) Nucleoplasm

Explanation: The nucleoplasm is the gel-like substance that fills the nucleus, providing a medium for the suspension of nuclear components, including DNA and nucleoli.

B) They are complementary

Explanation: The anticodon in tRNA is complementary to the codon in mRNA, ensuring that the correct amino acid is added to the growing polypeptide chain during translation.

B) Endocytosis

Explanation: Lysosomes fuse with and digest substances that enter a cell via endocytosis, such as during phagocytosis, highlighting their role in cellular uptake and digestion.

C) To sort and package modified proteins and lipids

Explanation: The Golgi apparatus is responsible for sorting and packaging modified proteins, lipids, and other macromolecules into vesicles for transport to various destinations, highlighting its critical role in cellular processing.

C) Modifying, sorting, and packaging proteins

Explanation: The Golgi apparatus is involved in processing and packaging proteins and lipids for secretion or delivery to other organelles, playing a crucial role in the cell's functioning.

B) By vesicles

Explanation: Products from the ER are transported to the Golgi apparatus by vesicles, which are small membrane-bound sacs that facilitate the movement of materials within the cell.

B) Lipids and steroids

Explanation: The Smooth Endoplasmic Reticulum (SER) is involved in the synthesis of lipids and steroids, including cholesterol and its derivatives, which is a key function of this organelle.

C) DNA storage and regulation

Explanation: The nucleus is the most important structure in the cell, primarily responsible for containing DNA and regulating its expression, making it crucial for cellular function and heredity.

B) It serves as a template for RNA synthesis

Explanation: During DNA transcription, the DNA template strand is crucial as it serves as a template for synthesizing a complementary RNA sequence by the RNA polymerase enzyme.

C) Metaphase

Explanation: Karyotyping is typically performed during metaphase, when chromosomes are duplicated, condensed, and most visible, allowing for accurate analysis.

B) To produce haploid gametes

Explanation: Meiosis is specifically the process that produces haploid cells (gametes) from a diploid cell, reducing the chromosome number by half, which is essential for sexual reproduction.

C) S phase

Explanation: The S phase of the cell cycle is specifically designated for the synthesis of DNA, where the cell replicates its genetic material in preparation for division.

B) A phospholipid bilayer

Explanation: The plasma membrane is primarily composed of a phospholipid bilayer, which consists of two layers of phospholipid molecules that form the fundamental structure of the membrane.

B) To separate sister chromatids

Explanation: Spindle fibers play a crucial role in mitosis by attaching to the centromeres of chromosomes and helping to pull the sister chromatids apart during anaphase.

B) Gametes

Explanation: Meiosis specifically produces gametes (sperm and egg cells), which are haploid and essential for sexual reproduction.

C) To signal the termination of protein synthesis

Explanation: Stop signals in the mRNA are crucial as they indicate the end of protein synthesis, ensuring that the process concludes correctly.

D) DNA replication

Explanation: DNA replication occurs in the S phase of the cell cycle before both meiosis and mitosis, making it a common feature rather than a difference.

C) Exocytosis

Explanation: Exocytosis is an active transport process that requires energy to move materials out of the cell, distinguishing it from passive transport mechanisms.

C) Double membrane

Explanation: Mitochondria are surrounded by a double membrane, consisting of an outer and an inner mitochondrial membrane, which is essential for their function.

C) RER is studded with ribosomes

Explanation: The Rough Endoplasmic Reticulum (RER) is characterized by the presence of ribosomes on its cytoplasmic side, which is essential for its role in protein synthesis.

B) Cristae

Explanation: The inner membrane of mitochondria forms numerous folds known as cristae, which increase the surface area for biochemical reactions.

B) The cell takes in materials by engulfing them

Explanation: Endocytosis involves the cell membrane folding inward to engulf materials, forming vesicles that bring substances into the cell.

B) 2 diploid cells

Explanation: Mitosis results in the production of 2 diploid daughter cells that are genetically identical to the parent cell, maintaining the same chromosome number.

C) Digestion and waste removal

Explanation: Lysosomes contain enzymes that break down waste materials and cellular debris, playing a vital role in the cell's cleanup and recycling processes.

C) Proteins, lipids, and other macromolecules

Explanation: The Golgi apparatus modifies and packages a variety of macromolecules, including proteins and lipids, for transport to different locations within or outside the cell.

B) Prevent substances from penetrating through the cellular layer

Explanation: Tight junctions are designed to prevent substances from passing through the cellular layer, making them crucial in organs like the kidneys and intestines where selective permeability is essential.

D) Cytokinesis

Explanation: Cytokinesis is the process that follows mitosis, where the cytoplasm divides to form two separate cells. It is not considered a phase of mitosis itself.

B) In cardiac cells and epidermis

Explanation: Desmosomes are anchoring junctions that are primarily found in tissues subjected to mechanical stress, such as the epidermis and cardiac cells, helping to prevent them from being pulled apart.

C) They encapsulate and transport materials into the cell

Explanation: Vesicles are crucial in endocytosis as they encapsulate the materials that are being brought into the cell, facilitating their transport and processing.

D) G1 phase

Explanation: The G1 phase is part of interphase, not mitosis. Mitosis includes prophase, metaphase, anaphase, and telophase.

C) To provide structural support

Explanation: Cholesterol is present in the plasma membrane and contributes to its structural integrity, helping to maintain fluidity and stability.

C) They act as beads around which DNA is wrapped

Explanation: Histones serve as the structural proteins that DNA wraps around, forming nucleosomes and contributing to the overall organization of chromatin.

D) Active transport

Explanation: Active transport is not a type of passive transport because it requires energy to move substances against their concentration gradient, unlike diffusion, osmosis, and facilitated diffusion, which do not require energy.

C) Cell division

Explanation: The centrosome plays a crucial role in cell division, facilitating the organization and separation of chromosomes during the process.

D) Proton (H+)

Explanation: The text specifically mentions the proton (H+) pump as an example of primary active transport, highlighting its role in moving protons across membranes against their concentration gradient.

B) Metaphase

Explanation: During metaphase, chromosomes line up along the equatorial plane of the cell, preparing for separation into the daughter cells.

B) The site where the growing polypeptide chain is held

Explanation: The 'P site' (Peptidyl site) is where the growing polypeptide chain is held during translation, allowing for the formation of peptide bonds between amino acids.

B) It can occur only in the presence of a concentration gradient

Explanation: Facilitated diffusion is a type of passive transport that requires a concentration gradient to move substances across the plasma membrane, typically with the help of specific transport proteins.

C) Endosome

Explanation: During endocytosis, the engulfed material is enclosed in a vesicle known as an endosome, which can then be processed further within the cell.

A) G1, S, and G2 phases

Explanation: Like mitosis, meiosis begins after a cell has completed the G1, S, and G2 phases of the cell cycle, which are essential for preparing the cell for division.

C) Sodium-potassium pump

Explanation: The sodium-potassium pump is a well-known example of active transport, as it moves sodium ions out of the cell and potassium ions into the cell against their concentration gradients, using ATP for energy.

B) Synapsis

Explanation: The formation of bivalents or tetrads during prophase of meiosis occurs through a process called synapsis, where homologous pairs of sister chromatids lie side by side.

C) They help move substances against their concentration gradient

Explanation: Transport proteins are essential for active transport as they assist in moving substances across the plasma membrane against their concentration gradients, which requires energy.

C) It increases genetic variation

Explanation: Crossing over involves the physical exchange of chromosome pieces between homologous chromosomes, which increases the genetic variation of a species.

B) Nitrogenous Base + Deoxyribose Sugar + Phosphate Group

Explanation: A DNA nucleotide is composed of a nitrogenous base, a deoxyribose sugar, and a phosphate group, which are the fundamental building blocks of the DNA molecule.

B) It is translated into proteins

Explanation: After mRNA is synthesized, it exits the nucleus and is translated into proteins at the ribosomes, where the sequence of nucleotides in mRNA is used to assemble amino acids into a polypeptide chain.

D) Replication

Explanation: Replication is not a stage of translation; it refers to the process of copying DNA. The stages of translation include initiation, elongation, and termination.

B) 3 bases

Explanation: A codon is defined as a sequence of 3 bases in an mRNA molecule that codes for a specific amino acid, which is fundamental to the process of protein synthesis.

B) A photographic representation of an individual's complete set of chromosomes

Explanation: A karyotype is specifically defined as a photographic representation of an individual's complete set of chromosomes, typically taken during metaphase when chromosomes are most visible.

B) Homologous chromosomes undergo crossing over

Explanation: During Prophase I, homologous chromosomes pair up and exchange genetic material through a process called crossing over, which increases genetic diversity.

B) To grow and divide

Explanation: The cell cycle is defined as a series of events that occur in a cell as it grows and divides, making growth and division its primary purpose.

C) Two haploid cells

Explanation: The result of Meiosis I is two haploid cells, each containing half the number of chromosomes as the original diploid cell, setting the stage for Meiosis II.

C) The shape and specific organelles

Explanation: The function of a cell is determined by its shape and the specific organelles and subcellular structures it contains, highlighting the importance of the structure-function relationship in cellular biology.

C) Thymine (T)

Explanation: In DNA, Adenine (A) pairs with Thymine (T) through hydrogen bonds, following the established base pairing rules that are crucial for the accurate replication and transcription of genetic information.

B) Structure determines function

Explanation: The relationship between a cell's structure and its function is that the structure of a cell directly influences its function, which is a key concept in understanding cellular biology.

B) No net movement of ions occurs

Explanation: When there is an equal distribution of ions across a plasma membrane, there is no concentration gradient, leading to no net movement of ions, which is crucial for maintaining homeostasis.

C) Nerve Cells

Explanation: Nerve cells are specialized for transmitting signals throughout the body, showcasing how their structure is adapted for their specific function.

B) To transport glucose into cells

Explanation: Glucose transporters are essential for the transport of glucose into cells, facilitating its uptake for energy production and metabolic processes.

B) To transport materials into the cell

Explanation: Endocytosis is a cellular process that allows cells to engulf external substances, effectively transporting materials into the cell through vesicles.

C) Two haploid cells

Explanation: The outcome of Cytokinesis I is the formation of two haploid cells, each containing half the number of chromosomes as the original cell.

B) Metaphase

Explanation: During metaphase, chromosomes align at the cell's equatorial plane, preparing for separation into the daughter cells.

B) A diploid cell called a zygote

Explanation: The fertilization event in sexual reproduction unites two haploid gametes to form a diploid cell known as a zygote, which is the first step in the development of a new organism.

B) It releases Ca2+ ions

Explanation: The Smooth Endoplasmic Reticulum (SER) is responsible for the storage and release of Ca2+ ions, which are crucial for triggering muscle contraction.

B) Apoptosis

Explanation: Mitochondria play an important role in apoptosis, which is the process of programmed cell death, highlighting their significance beyond energy production.

B) It duplicates

Explanation: Before cell division, the centrosome duplicates to ensure that there are two centrosomes available to assist in the separation of chromosomes during mitosis.

C) It is pivotal for the organism's health

Explanation: The delicate balance between cell aging and apoptosis is crucial for maintaining the health of an organism, ensuring that damaged cells are removed while allowing for normal cellular function.

B) Mitosis and Cytokinesis

Explanation: Somatic cell division consists of two key events: mitosis, which is the division of the nucleus, and cytokinesis, which is the division of the cytoplasm.

C) Cells postpone division or never divide again

Explanation: The G0 phase serves as an alternative pathway for cells that either postpone division, such as liver and pancreatic cells, or never divide again, like neurons and muscle cells.

B) Facilitate direct communication between cells

Explanation: Gap junctions are crucial for allowing direct communication between cells, enabling the passage of ions and small molecules, which is particularly important in neurons and muscle cells.

B) Double strand

Explanation: DNA is characterized by its double-stranded helical structure, which is essential for its stability and function in storing genetic information.

B) To maintain concentration gradients of specific ions and molecules

Explanation: The main purpose of active transport is to maintain concentration gradients of ions and molecules, which is crucial for various cellular functions, including nutrient uptake and waste removal.

C) They specify the amino acids in a protein

Explanation: Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids, playing a crucial role in determining the sequence of amino acids in a protein during translation.

B) Osmosis

Explanation: Osmosis is the specific passive process that allows water to move across the plasma membrane, typically through specialized channels called aquaporins, from areas of lower solute concentration to areas of higher solute concentration.

B) Elongation

Explanation: The elongation stage of translation is where amino acids are sequentially added to the growing polypeptide chain, facilitated by the ribosome.

B) Cisternae

Explanation: The Golgi apparatus consists of a stack of flattened vesicles known as cisternae, which are essential for its organization and function in processing and packaging cellular products.

A) They require energy input

Explanation: Active transport processes require energy, usually in the form of ATP, to move substances against their concentration gradient, distinguishing them from passive transport mechanisms.

B) A programmed cell death mechanism

Explanation: Apoptosis is a programmed cell death mechanism that eliminates damaged or malfunctioning cells, playing a vital role in maintaining the health of the organism.

B) 4 haploid cells

Explanation: Meiosis produces 4 haploid daughter cells that are genetically different from each other and from the parent cell, reducing the chromosome number by half.

D) Thymine (T)

Explanation: Thymine (T) is a nitrogenous base found in DNA, while RNA contains uracil (U) instead of thymine.

C) Transcription

Explanation: mRNA is synthesized during the process of transcription, where a specific segment of DNA is copied into RNA by the enzyme RNA polymerase.

E) Cytokinesis II

Explanation: Cytokinesis II is not a phase of Meiosis I; it occurs after Meiosis II. Meiosis I consists of Prophase I, Metaphase I, Anaphase I, and Telophase I.

C) Mitosis

Explanation: Chromosomes are most easily visualized during mitosis, as they condense and become distinct structures, whereas during interphase they are dispersed as chromatin.

C) Facilitated diffusion

Explanation: The transport of glucose into cells occurs through facilitated diffusion, which involves specific transport proteins to assist in the movement of glucose across the cell membrane.

C) Desmosomes

Explanation: Desmosomes serve as anchoring junctions that help prevent cells from being pulled apart under mechanical stress, making them essential in tissues like the epidermis and cardiac muscle.

A) They are identical

Explanation: The resulting mRNA is a copy of the DNA coding strand, with the exception that uracil replaces thymine, making them nearly identical in sequence.

B) They digest an entire cell

Explanation: Lysosomes execute apoptosis by digesting an entire cell, which is a critical process for removing damaged or unnecessary cells from the organism.

C) Involves carrier proteins or channels

Explanation: Facilitated diffusion is a type of passive transport that involves the use of carrier proteins or channels to help move substances across the plasma membrane down their concentration gradient without the use of energy.

B) More than one codon can specify the same amino acid

Explanation: It is a characteristic of the genetic code that multiple codons can correspond to the same amino acid, which adds a level of redundancy to the coding process.

B) Concentration gradient

Explanation: The primary driving force behind passive transport processes is the concentration gradient, which dictates the direction in which substances will move across the plasma membrane, favoring movement from high to low concentration.

C) To carry genetic information from DNA to ribosomes

Explanation: mRNA (messenger RNA) serves as the intermediary that conveys genetic information from DNA in the nucleus to the ribosomes, where proteins are synthesized.

D) Uracil (U)

Explanation: In the process of transcription, uracil (U) replaces thymine (T) in the resulting mRNA, which is a key difference between DNA and RNA.

B) Electric features and size of molecules

Explanation: The ability of molecules to pass through the plasma membrane depends on their electric features and size, which determine whether they can permeate the membrane effectively.

C) Sequences of 3 nucleotides

Explanation: Codons are defined as sequences of 3 nucleotides in the mRNA that either code for specific amino acids or signal the termination of protein synthesis.

B) Single-stranded molecule

Explanation: mRNA is a single-stranded molecule that carries the genetic code necessary for protein synthesis, distinguishing it from the double-stranded structure of DNA.

B) It condenses to form chromosomes

Explanation: When cells undergo division, chromatin condenses to form chromosomes, which are necessary for the proper segregation of genetic material during cell division.

B) 23 pairs

Explanation: Somatic cells contain 23 pairs of chromosomes, which includes 22 pairs of autosomes and 1 pair of sex chromosomes (XX or XY).

C) Epithelial Cells

Explanation: Epithelial cells, or skin cells, serve the function of protection and covering body surfaces, illustrating the structure-function relationship in their design.

B) It carries a specific amino acid

Explanation: Each tRNA molecule carries a specific amino acid at one end, which is essential for assembling proteins during translation.

B) Ribose

Explanation: RNA contains ribose as its sugar component, distinguishing it from DNA, which contains deoxyribose.

B) Selectively permeable barrier

Explanation: The plasma membrane is described as a selectively permeable barrier, meaning it allows certain substances to pass through while excluding others, which is crucial for maintaining cellular homeostasis.

C) An anticodon

Explanation: At the other end of each tRNA, there are 3 bases forming an anticodon, which is complementary to the codon in the mRNA, allowing for accurate pairing during protein synthesis.

B) A protein carrier

Explanation: Glucose transport into cells requires a protein carrier known as a transporter, but it does not require cellular energy, as it occurs down the concentration gradient.

D) Telophase

Explanation: Telophase is the final stage of mitosis, where the chromosomes reach the poles, the nuclear envelope re-forms around each set of chromosomes, and the cell prepares to divide.

C) Some forms of Diabetes

Explanation: Alterations in the number of glucose transporters within cells can lead to some forms of Diabetes, indicating the critical role these transporters play in glucose metabolism and homeostasis.

B) Selectively permeable plasma membrane

Explanation: Osmosis occurs across a selectively permeable plasma membrane, allowing water to move while restricting the passage of certain solutes, which is crucial for maintaining cellular homeostasis.

C) rRNA synthesis and ribosomal subunit assembly

Explanation: Nucleoli are dense spherical structures in the nucleus that serve as sites for the synthesis of ribosomal RNA (rRNA) and the assembly of ribosomal subunits, essential for protein synthesis.

A) Prophase, Metaphase, Anaphase, Telophase

Explanation: The correct order of phases in mitosis is Prophase, Metaphase, Anaphase, and Telophase, which describes the sequential events during cell division.

B) They have a flagellum for movement

Explanation: Sperm cells possess a flagellum, which is crucial for their motility, allowing them to swim towards the egg for fertilization, demonstrating the structure-function relationship.

B) The polypeptide chain is released

Explanation: During the termination stage of translation, the completed polypeptide chain is released from the ribosome, concluding the process of protein synthesis.

B) The nuclear envelope breaks down

Explanation: During prophase, the nuclear envelope disintegrates, allowing the chromosomes to become visible and facilitating their movement during mitosis.

B) Nucleosomes

Explanation: The DNA wrapped around histones forms bead-like structures known as nucleosomes, which are fundamental units of chromatin structure.

B) At right angles to each other

Explanation: The two centrioles within a centrosome are oriented at right angles to each other, which is important for their function in organizing microtubules during cell division.

B) 22 + XX

Explanation: A karyotype of 22 + XX indicates a female, where 'XX' represents the two X chromosomes inherited from the parents.

B) Diploid cells

Explanation: Somatic cells are diploid (2N) cells, meaning they contain two sets of chromosomes, specifically 23 pairs (46 chromosomes in total).

E) Metaphase II

Explanation: Metaphase II is part of Meiosis II, not Meiosis I. Meiosis I consists of Prophase I, Prometaphase I, Metaphase I, Anaphase I, and Telophase I.

C) Hydrogen bonds

Explanation: Hydrogen bonds are responsible for holding the base pairs together in the DNA double helix, specifically between Adenine and Thymine, and between Cytosine and Guanine, ensuring the stability of the DNA structure.

B) Attached to proteins and lipids on the exterior leaflet

Explanation: Carbohydrates are attached to proteins and lipids on the exterior leaflet of the plasma membrane, playing important roles in cell recognition and signaling.

B) DNA and proteins

Explanation: Chromatin is a complex network made of chains of DNA wrapped around proteins called histones, which are essential for its structure and function in the cell nucleus.

B) Active transport mechanisms

Explanation: The unequal distribution of ions across plasma membranes, often maintained by active transport mechanisms, creates a concentration gradient that is essential for cellular functions.

B) The total number of chromosomes in a diploid cell

Explanation: The notation 2N = 46 indicates that a diploid cell has two complete sets of chromosomes, totaling 46 chromosomes, which is characteristic of human cells.

B) The diffusion of water across a plasma membrane

Explanation: Osmosis specifically refers to the movement of water molecules through a selectively permeable membrane, which is a key concept in understanding how cells maintain their internal environment.

B) Two

Explanation: Meiosis involves two rounds of division, known as Meiosis I and Meiosis II, which are necessary for the reduction of chromosome number and the formation of haploid gametes.

B) They are embedded within the membrane

Explanation: Various types of proteins are embedded within the phospholipid bilayer of the plasma membrane, playing crucial roles in transport, signaling, and structural support.

B) They are transported into the cell

Explanation: Essential cell proteins and large molecules are actively transported into the cell, demonstrating the selective nature of the plasma membrane in regulating what enters the cell.

B) The concentration gradient of water

Explanation: Osmosis is driven by the concentration gradient of water, where water moves from an area of higher concentration to an area of lower concentration until equilibrium is reached.

B) They duplicate into two sister chromatids

Explanation: Before cell division, each pair of chromosomes duplicates into two sister chromatids, which are held together by a centromere.

C) Nuclear envelope

Explanation: The nuclear envelope surrounds the nucleus and contains numerous openings called nuclear pores, which regulate the transport of molecules between the nucleus and the cytoplasm.

E) Both C and D

Explanation: Thymine (T) and Cytosine (C) are classified as pyrimidines, while Adenine (A) and Guanine (G) are purines, highlighting the distinction between these two types of nitrogenous bases in DNA.

C) They are closely related in proximity and function

Explanation: The Golgi apparatus is closely related to the ER in both proximity and function, working together in the processing and transport of cellular products.

C) It facilitates the movement of substances into and out of the cell

Explanation: The concentration gradient is vital for cellular processes, as it drives the movement of substances across the plasma membrane, allowing for nutrient uptake and waste removal.

B) Decondensed

Explanation: In non-dividing cells, chromatin exists in a decondensed state throughout the nucleus, allowing for gene expression and DNA replication.

B) A site where chromosomes remain adhered after crossing over

Explanation: A chiasma refers to the point where arms of the chromosomes separate but remain adhered at a crossover site during meiosis, indicating where genetic material has been exchanged.

C) It shrinks and may become crenated

Explanation: When a cell is placed in a hypertonic solution, water moves out of the cell, causing it to shrink and potentially become crenated due to the loss of water.

B) Mitosis produces genetically identical cells, meiosis produces genetically different cells

Explanation: A fundamental difference is that mitosis results in genetically identical daughter cells, while meiosis results in genetically diverse daughter cells due to recombination and independent assortment.

C) 3 types

Explanation: There are three main types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), each serving different functions in protein synthesis.

C) 22 + XY

Explanation: A karyotype of 22 + XY indicates a male, where 'XY' represents one X and one Y chromosome inherited from the parents.

C) Active transport

Explanation: While osmosis and diffusion can occur along a concentration gradient, active transport is specifically responsible for creating and maintaining a concentration gradient by moving ions against their natural flow.

D) Surface receptors

Explanation: Cells interact and communicate with each other by forming junctions that enable surface receptors to recognize ligands on other cells, facilitating various cellular processes.

C) Hydrophobic molecules and small uncharged molecules

Explanation: The plasma membrane is generally permeable to hydrophobic molecules, gases, and small uncharged molecules, while it is impermeable to charged molecules and ions.

E) It can occur in both prokaryotic and eukaryotic cells

Explanation: Active transport processes are found in both prokaryotic and eukaryotic cells, allowing them to maintain homeostasis and regulate internal environments despite external concentration gradients.

B) Mitosis

Explanation: Mitosis is the process responsible for growth and repair in multicellular organisms, allowing for the production of new cells that are genetically identical to the original.

B) Proteins and waste products

Explanation: The plasma membrane allows certain substances, including proteins and waste products, to exit the cell, which is essential for maintaining cellular function and homeostasis.

C) From both parents

Explanation: Each daughter cell inherits one member of each pair of chromosomes from each parent, ensuring genetic continuity.

B) Prophase II, Prometaphase II, Metaphase II, Anaphase II, Telophase II

Explanation: Meiosis II consists of five phases: Prophase II, Prometaphase II, Metaphase II, Anaphase II, and Telophase II, which follow the completion of Meiosis I.

B) They are hydrophilic

Explanation: The polar 'heads' of phospholipid molecules are hydrophilic (water-loving) and align on both sides of the membrane, interacting with the aqueous environment.

B) To regulate the internal water balance

Explanation: The primary function of osmosis in cells is to regulate the internal water balance, ensuring that cells maintain their shape and function properly in varying environmental conditions.

B) They are hydrophobic

Explanation: The nonpolar 'tails' of phospholipid molecules are hydrophobic (water-fearing) and align in the interior of the membrane, away from the water, contributing to the membrane's selective permeability.