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Knowledge Check: Unit 2 — Chapters 4–10

Knowledge Check: Unit 2 — Chapters 4–10

Test yourself on Unit 2: The Cell (Chapters 4–10). Every question below was written from the chapters’ own text — their summaries, key terms, explanations, and tables — and none repeats a question from the section pages. There are no hints: treat it like a test. Questions are grouped by the section they come from, so a miss tells you exactly which section to review.

Chapter 4: Cell Structure

4.1 Studying Cells

A specimen that is right-side up and facing right on a microscope slide appears in which orientation when viewed through the microscope’s two-lens system?

In his 1665 publication Micrographia, ________ coined the term “cell” for the box-like structures he observed when viewing cork tissue through a lens.

What is the difference between magnification and resolving power in microscopy?

Show model answer
Magnification is the process of enlarging an object in appearance. Resolving power is the microscope’s ability to distinguish two adjacent structures as separate: the higher the resolution, the better the image’s clarity and detail.

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4.2 Prokaryotic Cells

All cells, including prokaryotes, share four basic components: a plasma membrane, cytoplasm, DNA, and ________.

Pili exchange genetic material between two bacteria through direct contact in a process called ________.

How do microbiologists in the pharmaceutical sector help fight bacterial infections?

Show model answer
Microbiologists who work in the pharmaceutical sector serve key roles in research and development by identifying new antibiotic sources that can treat bacterial infections.

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4.3 Eukaryotic Cells

The endosymbiosis theory holds that chloroplasts evolved from which group of bacteria that ancient host cells ingested?

A eukaryotic cell’s “little organs” — membrane-bound compartments or sacs, each with a specialized cellular function — are called ________.

How do a vesicle and a vacuole differ, and how do their membranes behave differently?

Show model answer
Vacuoles are somewhat larger than vesicles. Vesicle membranes can fuse with either the plasma membrane or other membrane systems within the cell, but the vacuole’s membrane does not fuse with the membranes of other cellular components.

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4.4 The Endomembrane System and Proteins

The rough endoplasmic reticulum is especially abundant in cells that ________, such as liver cells.

In plant cells, the Golgi apparatus has the additional role of synthesizing ________, some of which are incorporated into the cell wall.

Describe the steps by which a macrophage engulfs and destroys a pathogen using phagocytosis.

Show model answer
In phagocytosis, a section of the macrophage’s plasma membrane invaginates and engulfs a pathogen. The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome, and the lysosome’s hydrolytic enzymes then destroy the pathogen.

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4.5 The Cytoskeleton

The fibrous protein most familiar to people, which strengthens hair, nails, and the skin’s epidermis, is called ________.

Which of the following is present in plant cells but absent from both prokaryotic and animal cells?

How do white blood cells use microfilaments to fight infection?

Show model answer
Microfilaments can depolymerize (disassemble) and reform quickly, which lets a white blood cell change its shape and move. White blood cells use this ability to move to an infection site and phagocytize the pathogen.

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4.6 Connections between Cells and Cellular Activities

In the extracellular matrix, collagen fibers are interwoven with carbohydrate-containing protein molecules called ________.

Using the blood-clotting example, explain how the extracellular matrix enables cells to communicate when a blood vessel is damaged.

Show model answer
When the cells lining a blood vessel are damaged, they display a protein receptor called tissue factor. When tissue factor binds with another factor in the extracellular matrix, it causes platelets to adhere to the damaged blood vessel’s wall, stimulates the adjacent smooth muscle cells in the blood vessel to contract, and initiates a series of steps that stimulate the platelets to produce clotting factors.

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Which type of intercellular junction lines the epithelial cells of the urinary bladder to prevent urine from leaking into the extracellular space?

Chapter 5: Structure and Function of Plasma Membranes

5.1 Components and Structure

Fish adapt to cold environments by changing the proportion of which membrane component?

A non-polar molecule that does not have the ability to bond with water, and that tends to cluster with other non-polar molecules rather than interact with polar ones, is called ________.

How is a complex integral protein with several folded segments oriented within the membrane relative to its hydrophilic and hydrophobic regions?

Show model answer
Such a protein has a hydrophilic region or regions, and one or several mildly hydrophobic regions. This arrangement of protein regions orients the protein alongside the phospholipids, with the protein’s hydrophobic region adjacent to the phospholipids’ tails and the protein’s hydrophilic region or regions protruding from the membrane and in contact with the cytosol or extracellular fluid.

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5.2 Passive Transport

Which of the following can pass directly through the plasma membrane’s hydrophobic lipid core without the help of a transport protein?

A membrane characteristic that allows some substances to pass through while blocking others is called being ________.

Why does an unwatered plant wilt, even though its cell walls do not shrink?

Show model answer
When a plant is not watered, the extracellular fluid will become hypertonic, causing water to leave the cell. The cell does not shrink because the cell wall is not flexible, but the cell membrane detaches from the wall and constricts the cytoplasm, a condition called plasmolysis. Plants lose turgor pressure in this condition and wilt.

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5.3 Active Transport

Which of the following carrier proteins transports only calcium ions, rather than two different kinds of ions?

The three carrier-protein types that active transport uses to facilitate movement — uniporters, symporters, and antiporters — are collectively known as ________.

How does the secondary active transport process that stores high-energy hydrogen ions in the mitochondria ultimately produce ATP?

Show model answer
The potential energy that accumulates in the stored hydrogen ions translates into kinetic energy as the ions surge through the channel protein ATP synthase, and that energy then converts ADP into ATP.

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5.4 Bulk Transport

A variation of pinocytosis that uses the coating protein caveolin, instead of clathrin, on the plasma membrane’s cytoplasmic side is called ________.

What happens to a person’s blood cholesterol level when familial hypercholesterolemia leaves their LDL receptors defective or missing?

Show model answer
In the human genetic disease familial hypercholesterolemia, the LDL receptors are defective or missing entirely. Because receptor-mediated endocytosis normally removes LDL from the blood, people with this condition have life-threatening levels of cholesterol in their blood, because their cells cannot clear LDL particles.

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Assign each transport method to whether it requires the cell to expend energy.

Passive

    Active

      Chapter 6: Metabolism

      6.1 Energy and Metabolism

      Which process uses oxygen to aid the catabolic breakdown of carbon compounds such as carbohydrates, yielding CO₂ and ATP among its products?

      During photosynthesis, what roles do ATP and NADPH play in capturing solar energy, and how many ATP molecules does synthesizing one glucose molecule require under ideal conditions?

      Show model answer
      In photosynthesis, light energy from the sun initially transforms into chemical energy that temporarily stores itself in the energy carrier molecules ATP and NADPH. Photosynthesis later uses the stored energy in ATP and NADPH to build one glucose molecule from six molecules of CO₂. Under ideal conditions, energy from 18 molecules of ATP is required to synthesize one glucose molecule during photosynthesis reactions.

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      A series of interconnected biochemical reactions that convert a substrate molecule or molecules, step-by-step, through a series of metabolic intermediates, eventually yielding a final product or products, is called a ________.

      6.2 Potential, Kinetic, Free, and Activation Energy

      A system’s total energy is called ________.

      According to the second law of thermodynamics, every energy transfer loses some energy in an unusable form such as heat, resulting in increased ________.

      Explain why the activation energy of a reaction is always a positive value, regardless of whether the reaction is exergonic or endergonic.

      Show model answer
      Whether a reaction is exergonic or endergonic determines whether its products exist at a lower or higher energy state than its reactants. However, regardless of this, the transition state of the reaction exists at a higher energy state than the reactants, and thus activation energy is always positive.

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      6.3 The Laws of Thermodynamics

      Plants perform one of the most biologically useful energy transformations on Earth by converting sunlight energy into which form of energy stored within organic molecules?

      Using the analogy of a student’s messy bedroom, explain how putting energy into a system relates to its entropy.

      Show model answer
      If no energy or work were put into a student’s bedroom, the room would quickly become messy and exist in a very disordered state of high entropy. Energy must be put into the system, in the form of the student doing work and putting everything away, in order to bring the room back to a state of cleanliness and order, which is a state of low entropy.

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      Everything outside of a system involved in an energy transfer is called the ________.

      6.4 ATP: Adenosine Triphosphate

      Adenosine, part of the ATP molecule, consists of the nitrogenous base adenine bonded to which five-carbon sugar?

      Name the two bonds within an ATP molecule that are its phosphoanhydride bonds, and explain why breaking one of them releases a large amount of energy.

      Show model answer
      The high-energy phosphoanhydride bonds are the bond between the second and third, or beta and gamma, phosphate groups, and the bond between the first and second phosphate groups. These bonds are high-energy because the products of hydrolysis, adenosine diphosphate and one inorganic phosphate group, have considerably lower free energy than the reactants, ATP and a water molecule.

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      A phosphorylated molecule is at a higher-energy state and is ________ than its unphosphorylated form.

      6.5 Enzymes

      An inorganic ion, such as iron or magnesium, required for optimal enzyme activity is called a ________.

      When relative ADP levels are high compared to ATP, the cell is triggered to produce more ATP through which process?

      Explain how compartmentalizing enzymes into different organelles in eukaryotic cells regulates enzyme activity, and give two examples.

      Show model answer
      In eukaryotic cells, enzymes are usually compartmentalized into different organelles, which allows for another level of regulation of enzyme activity. Enzymes required only for certain cellular processes are sometimes housed separately along with their substrates, allowing for more efficient chemical reactions. The enzymes involved in the latter stages of cellular respiration take place exclusively in the mitochondria, and the enzymes involved in digesting cellular debris and foreign materials are located within lysosomes.

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      Chapter 7: Cellular Respiration

      7.1 Energy in Living Systems

      When an electron is shifted from one compound to a second compound, what happens to the second compound?

      The process that produces ATP in cellular metabolism through the involvement of a proton gradient across a membrane is called ________.

      How does an intermediate complex allow ATP to transfer the energy of its third phosphate group to a substrate during phosphorylation?

      Show model answer
      During an endergonic chemical reaction, ATP forms an intermediate complex with the substrate and enzyme in the reaction. This intermediate complex allows the ATP to transfer its third phosphate group, with its energy, to the substrate. When the intermediate complex breaks apart, the energy is used to modify the substrate and convert it into a product of the reaction, and the ADP molecule and a free phosphate ion are released into the medium.

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      7.2 Glycolysis

      Phosphofructokinase, which catalyzes the third step of glycolysis, is most active when ________.

      In the second step of glycolysis, the enzyme that converts glucose-6-phosphate into fructose-6-phosphate is a(n) ________.

      Why can glucose-6-phosphate no longer leave the cell once hexokinase has phosphorylated glucose in the first step of glycolysis?

      Show model answer
      This reaction prevents the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it can no longer leave the cell because the negatively charged phosphate will not allow it to cross the hydrophobic interior of the plasma membrane.

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      7.3 Oxidation of Pyruvate and the Citric Acid Cycle

      The first, citrate-forming step of the citric acid cycle runs faster when ________.

      A pathway that is both catabolic and anabolic, such as the citric acid cycle, is described as ________.

      Why does the conversion of succinyl CoA to succinate in the citric acid cycle produce ATP in some tissues and GTP in others?

      Show model answer
      There are two forms of the enzyme, called isoenzymes, for this step, depending upon the type of animal tissue in which they are found. One form is found in tissues that use large amounts of ATP, such as heart and skeletal muscle, and this form produces ATP. The second form of the enzyme is found in tissues that have a high number of anabolic pathways, such as liver, and this form produces GTP.

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      7.4 Oxidative Phosphorylation

      How many hydrogen ions can Complex I pump across the membrane from the matrix into the intermembrane space?

      The third complex of the electron transport chain, composed of cytochrome b, a Rieske center, and cytochrome c proteins, is also called ________.

      How does Complex IV use its heme and copper ions to convert oxygen into water, and why does that step matter for the proton gradient?

      Show model answer
      The cytochromes hold an oxygen molecule very tightly between the iron and copper ions until the oxygen is completely reduced by the gain of two electrons. The reduced oxygen then picks up two hydrogen ions from the surrounding medium to make water. The removal of the hydrogen ions from the system contributes to the ion gradient that forms the foundation for the process of chemiosmosis.

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      7.5 Metabolism without Oxygen

      Methanogens, archaeans found in soil and the digestive tracts of ruminants, oxidize NADH by reducing carbon dioxide to ________.

      Prokaryotes such as Clostridia, which live and grow only in the absence of molecular oxygen and are killed by exposure to it, are called ________.

      What coenzyme does the first reaction of alcohol fermentation use, and what does that reaction do to pyruvic acid?

      Show model answer
      The first reaction of alcohol fermentation is catalyzed by pyruvate decarboxylase, a cytoplasmic enzyme, with a coenzyme of thiamine pyrophosphate (TPP), derived from vitamin B₁ and also called thiamine. A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas, and the loss of carbon dioxide reduces the size of the molecule by one carbon, producing acetaldehyde.

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      7.6 Connections of Carbohydrate, Protein, and Lipid Metabolic Pathways

      In mammals, the liver synthesizes urea from two ammonia molecules and ________.

      The polymer of glucose that serves as an energy storage molecule in liver and muscle cells is called ________.

      How do the glycerol and fatty acid components of a triglyceride each enter the pathways of glucose catabolism?

      Show model answer
      Glycerol can be phosphorylated to glycerol-3-phosphate, which continues through glycolysis. Fatty acids are catabolized in a process called beta-oxidation, which takes place in the matrix of the mitochondria and converts their fatty acid chains into two-carbon units of acetyl groups. The acetyl groups are picked up by CoA to form acetyl CoA that proceeds into the citric acid cycle.

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      7.7 Regulation of Cellular Respiration

      Alpha-ketoglutarate dehydrogenase’s activity in the citric acid cycle decreases when levels of which intermediate rise?

      A molecule that binds an allosteric site on an enzyme, increasing or decreasing its activity depending on conditions, is called a(n) ________.

      How is pyruvate kinase’s activity controlled by phosphorylation and dephosphorylation?

      Show model answer
      The regulation of pyruvate kinase involves phosphorylation by a kinase, resulting in a less-active enzyme. Dephosphorylation by a phosphatase reactivates it. Pyruvate kinase is also regulated by ATP, a negative allosteric effect.

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      Chapter 8: Photosynthesis

      8.1 Overview of Photosynthesis

      Which two substrates, along with sunlight, does the photosynthesis equation show combining to form sugar and oxygen?

      A stack of thylakoids located inside a chloroplast is called a ________.

      Why is photosynthesis important beyond simply capturing sunlight’s energy, and how do heterotrophs make use of what it produces?

      Show model answer
      Photosynthesis is vital because it evolved as a way to store the energy from solar radiation in the carbon-carbon bonds of carbohydrate molecules. Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration.

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      8.2 The Light-Dependent Reactions of Photosynthesis

      Which two types of electromagnetic radiation are described as capable of penetrating tissues and damaging cells and DNA?

      A photon strikes the antenna pigments of ________ to initiate photosynthesis.

      How does the buildup of hydrogen ions in the thylakoid lumen ultimately allow ATP synthase to produce ATP?

      Show model answer
      The buildup of hydrogen ions inside the thylakoid lumen creates a concentration gradient. Hydrogen ions rush through the ATP synthase protein channel from the high concentration in the lumen to the low concentration in the stroma, and the energy released allows ATP synthase to attach a third phosphate group to ADP, forming ATP. This flow of hydrogen ions through ATP synthase is called chemiosmosis.

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      8.3 Using Light Energy to Make Organic Molecules

      RuBP (ribulose bisphosphate) has how many carbon atoms?

      Once carbon dioxide enters a leaf through the stomata, it diffuses over short distances through the ________ until it reaches the mesophyll cells.

      Why is carbon dioxide not really a form of ‘waste,’ even though cellular respiration releases it as a byproduct?

      Show model answer
      Carbon dioxide is no more a form of waste than oxygen is wasteful to photosynthesis; both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs light energy to build carbohydrates in chloroplasts, and aerobic cellular respiration releases energy by using oxygen to metabolize carbohydrates in the cytoplasm and mitochondria. Both processes use electron transport chains to capture the energy necessary to drive other reactions.

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      Chapter 9: Cell Communication

      9.1 Signaling Molecules and Cellular Receptors

      When a ligand binds a G-protein-linked receptor and activates the G-protein, what happens to the guanine nucleotide bound to the alpha subunit?

      The region of a cell-surface receptor that is located on the cell surface and binds an external ligand is called the ________.

      How does autocrine signaling during early development help ensure that a group of neighboring cells reach the correct developmental outcome?

      Show model answer
      Autocrine signaling often occurs during the early development of an organism to ensure that cells develop into the correct tissues and take on the proper function. In embryological development, this process of stimulating a group of neighboring cells may help to direct the differentiation of identical cells into the same cell type, thus ensuring the proper developmental outcome.

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      9.2 Propagation of the Signal

      A chemical compound formed when two molecules, often identical, join together to form a stable complex is called a ________.

      When signals from two or more different cell-surface receptors merge to activate the same cellular response, ensuring that multiple external requirements are met before the cell commits to that response, this is called ________.

      Why is the concentration of free calcium ions inside a cell normally kept very low, and how does a cell raise it when signaling occurs?

      Show model answer
      The free concentration of calcium ions (Ca²⁺) within a cell is very low because ion pumps in the plasma membrane continuously remove it using ATP. When signaling occurs, ligand-gated calcium ion channels allow the higher levels of Ca²⁺ that are present outside the cell, or in intracellular storage compartments such as the endoplasmic reticulum, to flow into the cytoplasm, which raises the concentration of cytoplasmic Ca²⁺.

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      9.3 Response to the Signal

      Cyclic AMP activates PKA (protein kinase A) in muscle cells, which phosphorylates two enzymes: glycogen phosphorylase kinase and glycogen synthase. What effect does PKA phosphorylation have on glycogen synthase?

      Why do hydrophobic hormones like estrogen and testosterone trigger long-lasting signaling events?

      Show model answer
      Hydrophobic hormones like estrogen and testosterone trigger long-lasting events because they bind carrier proteins. These proteins allow the insoluble molecules to be soluble in blood, but they also protect the hormones from degradation by circulating enzymes.

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      Most growth factors bind to receptor tyrosine kinases (RTKs), which then activate a G-protein called RAS. What does activated RAS do next in this pathway?

      9.4 Signaling in Single-Celled Organisms

      Bacterial autoinducers include small, hydrophobic molecules such as acyl-homoserine lactone (AHL) and larger peptide-based molecules. How does AHL affect gene expression once it enters a target bacterium?

      What happens inside a yeast cell when mating factor binds to its cell-surface receptors?

      Show model answer
      The yeast cell stops its normal growth cycle and initiates a cell signaling cascade that includes protein kinases and GTP-binding proteins that are similar to G-proteins.

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      The peptide-based autoinducer molecules bind ________ and initiate signaling cascades in the cells.

      Chapter 10: Cell Reproduction

      10.1 Cell Division

      Which trait often spreads through a bacterial colony by plasmid exchange from resistant donors to recipient cells?

      In a prokaryote, the region of the cell that contains the single, circular chromosome is called the ________.

      How much genetic difference typically exists between any pair of human homologous chromosomes, and which chromosome pair is the exception to that uniformity?

      Show model answer
      If the entire DNA sequence from any pair of human homologous chromosomes is compared, the difference is much less than one percent. The sex chromosomes, X and Y, are the single exception to the rule of homologous chromosome uniformity: other than a small amount of homology that is necessary to accurately produce gametes, the genes found on the X and Y chromosomes are different.

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      10.2 The Cell Cycle

      Which spindle microtubules do not engage the chromosomes, instead overlapping midway between the two poles to contribute to cell elongation?

      The microtubule apparatus that orchestrates the movement of chromosomes during mitosis is called the ________.

      What are the two named portions of the mitotic phase, and what does each one accomplish?

      Show model answer
      The first portion of the mitotic phase is called karyokinesis, or nuclear division. The second portion of the mitotic phase is called cytokinesis, the physical separation of the cytoplasmic components into the two daughter cells.

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      10.3 Control of the Cell Cycle

      In humans, epithelial cells have an average cell-cycle turnover time of about ________.

      A protein whose concentration fluctuates throughout the cell cycle and that must bind to a Cdk to help regulate the cell’s progress through its checkpoints is called a ________.

      Why is the cell cycle of a fertilized fruit fly egg completed in only about eight minutes?

      Show model answer
      The nucleus of the fertilized egg divides many times by mitosis but does not go through cytokinesis until a multinucleate zygote has been produced, with many nuclei located along the periphery of the cell membrane, thereby shortening the time of the cell division cycle.

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      10.4 Cancer and the Cell Cycle

      Any disruption of the cell cycle’s ________ can allow other mistakes to be passed on to the daughter cells.

      In addition to monitoring DNA for damage, the normal p53 protein monitors the cell’s supply of ________.

      If a cell carrying a newly acquired oncogene mutation cannot reproduce further, why does the organism remain unharmed, and what can happen instead if its daughter cells are able to keep dividing?

      Show model answer
      In most instances, the alteration of the DNA sequence results in a less functional, or non-functional, protein that will likely prevent the cell from completing the cell cycle, so the organism is not harmed because the mutation will not be carried forward. If a cell cannot reproduce, the mutation is not propagated and the damage is minimal. However, if the atypical daughter cells are able to undergo further cell divisions, subsequent generations of cells may accumulate even more mutations.

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      10.5 Prokaryotic Cell Division

      Which eukaryotic chromosome-compaction proteins are related to the packing proteins found in the bacterial nucleoid?

      Replication of the bacterial chromosome’s DNA is described as ________, moving away from the origin on both strands of the loop simultaneously.

      How are FtsZ and tubulin structurally and functionally similar, and what energy source do both proteins use to rapidly assemble and disassemble their structures?

      Show model answer
      The FtsZ protein, which plays a vital role in prokaryotic cytokinesis, is structurally and functionally very similar to tubulin, the building block of the microtubules that make up the mitotic spindle fibers necessary for eukaryotic nuclear division. FtsZ proteins can form filaments, rings, and other three-dimensional structures that resemble the way tubulin forms microtubules, centrioles, and various cytoskeletal components. Both FtsZ and tubulin employ the same energy source, GTP (guanosine triphosphate), to rapidly assemble and disassemble complex structures.

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      This knowledge check is written for Unit 2 (Chapters 4–10) of Biology 2e by Mary Ann Clark, Jung Choi, Matthew Douglas, and OpenStax, © OpenStax, licensed under CC BY-NC-SA 4.0. Access the original for free at openstax.org. Changes: every question is locally written from the pinned text of the chapters’ own modules — their section summaries, glossary definitions, body passages, and comparison tables — and none is transcribed from the book’s exercise sets, which the section pages already carry; no question carries a hint, and every self-check carries a rubric that decomposes a model answer made of the module’s own sentences.

      Prokaryotic Cell DivisionMeiosis and Sexual Reproduction