CK-12 Biology for High School FlexBook 2.0 Answer Key

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1 Chapter 2: Cell Biology 2.1 Parts of the Cell CK-12 Biology for High School FlexBook 2.0 Answer Key 1. Who coined the term cell, in reference to the tiny structures seen in living organisms? 2. Who identified animalcules? What are animalcules? 3. What are the three main parts of the cell theory? 4. List the four parts common to all cells. 5. What are the cell structures where proteins are made? 6. What is the role of DNA? 1. The first time the word cell was used to refer to these tiny units of life was in 1665 by a British scientist named Robert Hooke. (Or can just answer Robert Hooke.) 2. Animalcules were discovered by Anton van Leeuwenhoek. Today, we call Leeuwenhoek s animalcules bacteria. 3. The three main parts of the cell theory: a. all organisms are made up of one or more cells b. all the life functions of an organism occur within cells c. all cells come from preexisting cells 4. The four components common to all cells are the plasma membrane, cytoplasm, ribosomes and DNA. 5. Ribosomes are structures in the cytoplasm where proteins are made. 6. DNA contains the genetic instructions that cells need to make proteins. 2.2 Prokaryotic and Eukaryotic Cells 1. What is the cell nucleus? 2. What is the main difference between prokaryotic and eukaryotic cells? 3. Give an example of a prokaryotic cell. 4. Define organelle. CK-12 Biology Answer Keys - updated July

2 5. What is the advantage of having organelles? 1. The nucleus of a cell is a structure in the cytoplasm that is surrounded by a membrane (the nuclear membrane) and contains DNA (or chromosomes). 2. Prokaryotic cells are cells without a nucleus; eukaryotic cells have a nucleus. 3. Bacteria (and Archaea) are made of prokaryotic cells. 4. An organelle is a structure within the cytoplasm that performs a specific function within the cell. 5. Organelles allow eukaryotic cells to carry out more functions (and thus be more specific) than prokaryotic cells. 2.3 Phospholipid Bilayer 1. Describe the role of the plasma membrane. 2. What is meant by semipermeability? 3. Describe the composition of the plasma membrane. 4. Explain why hydrophobic molecules can easily cross the plasma membrane, while hydrophilic molecules cannot. 1. The plasma membrane forms a barrier between the cytoplasm inside the cell and the environment outside the cell. It protects and supports the cell and also controls everything that enters and leaves the cell. 2. The ability to allow only certain molecules in or out of the cell is referred to as selective permeability or semipermeability. 3. The plasma membrane is composed mainly of phospholipids. The phospholipids in the plasma membrane are arranged in a phospholipid bilayer. Each phospholipid molecule has a head and two tails. The hydrophilic head loves water and the hydrophobic tails hate water. Therefore, the water-hating tails are on the interior of the membrane, whereas the water-loving heads point outwards, toward either the cytoplasm or the fluid that surrounds the cell. 4. Small hydrophobic molecules can easily pass through the plasma membrane, because they are hydrophobic like the interior of the membrane. Hydrophilic molecules, on the other hand, cannot pass through the plasma membrane (at least not without help) because they are water-loving like the exterior of the membrane, and are therefore excluded from the interior of the membrane. CK-12 Biology Answer Keys - updated July

3 2.4 Membrane Proteins 1. What is the main difference between the two main types of proteins associated with the plasma membrane? 2. What are two functions of integral membrane proteins? 3. Discuss the Fluid Mosaic Model. 4. What are flagella and cilia? 1. The main difference between the two main types of proteins associated with the plasma membrane is whether they are permanently embedded (integral) within the plasma membrane or not (peripheral). 2. Functions of integral membrane proteins include channeling or transporting molecules across the membrane. Other integral proteins act as cell receptors. 3. The Fluid Mosaic Model states that integral membrane proteins are embedded in the phospholipid bilayer. The model also states that the membrane behaves like a fluid, rather than a solid. The proteins and lipids of the membrane move around the membrane, much like buoys in water. Such movement causes a constant change in the "mosaic pattern" of the plasma membrane. 4. Cilia and flagella are extensions of the plasma membrane, each with specific functions. 2.5 Cytoplasm and Cytoskeleton 1. What is the difference between cytoplasm and cytosol? 2. List two roles of the cytoplasm. 3. Name the three main types of cytoskeleton fibers. 4. List two functions of the eukaryotic cytoskeleton. 1. Cytoplasm consists of everything inside the plasma membrane of the cell, excluding the nucleus in an eukaryotic cell. It includes the watery, gel-like material which is the cytosol, as well as various structures. CK-12 Biology Answer Keys - updated July

4 2. Roles of the cytoplasm include: a. suspending cell organelles. b. pushing against the plasma membrane to help the cell keep its shape. c. providing a site for many of the biochemical reactions of the cell. 3. Three main kinds of cytoskeleton fibers are microtubules, intermediate filaments, and microfilaments. 4. Functions of the eukaryotic cytoskeleton include maintaining cell shape, holding organelles in place, and for some cells, enabling cell movement. The cytoskeleton also plays important roles in both the intracellular movement of substances and in cell division. 2.6 Nucleus 1. What is the role of the nucleus of a eukaryotic cell? 2. Describe the nuclear membrane. 3. What are nuclear pores? 4. What is the role of the nucleolus? 1. The nucleus holds (and protects) most of the cell s genetic material. 2. The nuclear envelope is a double membrane of the nucleus. The nuclear envelope is made of two lipid bilayers, an inner membrane and an outer membrane. The outer membrane is continuous with the rough endoplasmic reticulum. There are numerous tiny holes called nuclear pores found in the nuclear envelope. 3. Nuclear pores are tiny holes found throughout the nuclear envelope that help to regulate the exchange of materials (such as RNA and proteins) between the nucleus and the cytoplasm. 4. The nucleolus is mainly involved in the assembly of ribosomes. 2.7 Ribosomes and Mitochondria 1. What is the function of a ribosome? CK-12 Biology Answer Keys - updated July

5 2. What is a significant difference between the structure of a ribosome and other organelles? 3. Identify the reason why mitochondria are called "power plants" of the cell. 4. Describe the structure of a mitochondrion. 1. Ribosomes are the sites of protein synthesis 2. Unlike other organelles, ribosomes are not surrounded by a membrane. 3. Mitochondria are called the "power plants" of the cell because they use energy from organic compounds to make ATP. Mitochondria are the site of cellular respiration. 4. A mitochondrion has two phospholipid membranes. The smooth outer membrane separates the mitochondrion from the cytosol. The inner membrane has many folds, called cristae. The fluid-filled inside of the mitochondrion, called matrix, is where most of the cell s ATP is made. 2.8 Cell Structure 1. List five organelles eukaryotes have that prokaryotes do not have. 2. Explain how the following organelles ensure that a cell has the proteins it needs: nucleus, rough ER, vesicles, and Golgi apparatus. 3. What is the main difference between rough endoplasmic reticulum and smooth endoplasmic reticulum? 4. Describe the three types of vesicles. 1. may vary: the nucleus, endoplasmic reticulum, Golgi apparatus, vesicles, vacuoles, and centrioles 2. The nucleus stores the DNA and is where transcription occurs. Once proteins are made in ribosomes, some of the proteins move to the rough ER for transport. Then they are transported within vesicles to the Golgi apparatus for modification and transport to their proper destinations in or out of the cell. 3. The main difference between rough endoplasmic reticulum and smooth endoplasmic reticulum is that the rough ER is studded with ribosomes. 4. Transport vesicles are able to move molecules between locations inside the cell. Lysosomes contain powerful enzymes that break down the cell s waste products. Peroxisomes are vesicles that use oxygen to break down toxic substances in the cell. CK-12 Biology Answer Keys - updated July

6 2.9 Plant Cell Structure 1. List three structures that are found in plant cells but not in animal cells. 2. Identify two functions of plastids in plant cells. 3. What are the roles of the cell wall and the central vacuole? 4. Describe the chloroplast structure. 1. Structures found in plant cells, but not animal cells, include a cell wall, a large central vacuole, and plastids (chloroplasts). 2. Plastids are responsible for photosynthesis, for storage of products such as starch, and for the synthesis of many types of molecules that are needed as cellular building blocks. 3. The cell wall provides structural support and protection. Pores in the cell wall allow water and nutrients to move into and out of the cell. The cell wall also prevents the plant cell from bursting when water enters the cell. Aside from storage, the main role of the central vacuole is to maintain turgor pressure against the cell wall. 4. The chloroplast is enclosed by an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space. The fluid within the chloroplast is the stroma. Within the stroma are stacks of thylakoids that are the site of photosynthesis. The thylakoids are arranged in stacks called grana. A thylakoid has a flattened disk shape. Inside it is an empty area called the thylakoid space or lumen Cell Organization 1. What is a multicellular organism? 2. What is a cell feature that distinguishes a colonial organism from a multicellular organism? 3. What is the difference between a cell and a tissue? 4. Describe the top two levels of organization of an organism. CK-12 Biology Answer Keys - updated July

7 1. Multicellular organisms are organisms that are made up of more than one type of cell and have specialized cells that are grouped together to carry out specialized functions. 2. The difference between a multicellular organism and a colonial organism is that individual organisms from a colony can, if separated, survive on their own, while cells from a multicellular organism cannot. 3. A cell is the smallest unit of structure and function of an organism. A tissue is made of cells; a tissue is a group of connected cells that have a similar function within an organism. 4. An organ is a group of tissues that has a specific function or group of functions. An organ system is a group of organs that act together to carry out complex related functions, with each organ focusing on a part of the task. Together all the organ systems compile into an organism Diffusion 1. Explain how diffusion and facilitated diffusion differ. 2. What is facilitated diffusion? 3. What is a transport protein? Give three examples. 4. Assume a molecule must cross the plasma membrane to enter a cell. The molecule is very large. How will it be transported into the cell? 5. Explain how carrier proteins function? 6. Explain the role of ion channels. Why are ion channels necessary? 1. Diffusion is the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration. Facilitated diffusion is the diffusion of solutes through transport proteins in the plasma membrane. 2. Facilitated diffusion is the diffusion of solutes through the plasma membrane using transport proteins. 3. A transport protein completely spans the membrane, and allows certain molecules or ions to diffuse across the membrane. Channel proteins, gated channel proteins, and carrier proteins are three types of transport proteins that are involved in facilitated diffusion. 4. A very large molecule will probably be carried into the cell via a carrier protein. 5. Carrier proteins "carry" the ion or molecule across the membrane by changing shape after the binding of the ion or molecule. CK-12 Biology Answer Keys - updated July

8 6. Because they are polar, ions do not diffuse through the membrane. Instead they move through ion channel proteins where they are protected from the hydrophobic interior of the membrane. Ion channels allow the formation of a concentration gradient between the extracellular fluid and the cytosol Osmosis 1. What is osmosis? What type of transport is it? 2. How does osmosis differ from diffusion? 3. What happens to red blood cells when placed in a hypotonic solution? 4. What will happen to a salt water fish if placed in fresh water? 1. Osmosis is the diffusion of water molecules across a selectively permeable membrane from an area of higher concentration to an area of lower concentration. It is a type of passive transport. 2. Osmosis solely refers to the movement of water. Diffusion is the movement of other substances. 3. A red blood cell will swell and lyse (burst) when placed in a hypotonic solution. 4. If a saltwater fish (whose cells are isotonic with seawater) is placed in fresh water, its cells will take on excess water, lyse, and the fish will die Passive Transport 1. Define semipermeable. 2. What is diffusion? 3. What is a concentration gradient? 4. What is meant by passive transport? 1. Semipermeable is the ability to allow only certain molecules to cross the plasma membrane. CK-12 Biology Answer Keys - updated July

9 2. Diffusion is the movement of a molecule from an area of high concentration of the molecule to an area with a lower concentration. 3. A concentration gradient is the difference in the concentrations of a molecule across two distinct areas, such as a cell membrane. 4. Passive transport is the movement of substances across a plasma membrane that does not require energy Active Transport 1. What is active transport? 2. Explain how cell transport helps an organism maintain homeostasis. 1. Active transport is the energy-requiring process of pumping molecules and ions across membranes against a concentration gradient (or down a concentration gradient). 2. Maintaining homeostasis requires constant adjustments as conditions change inside and outside the cell. Moving substances into and out of the cell is an active part of maintaining homeostasis, continuously making adjustments to keep the cell within normal limits Sodium-Potassium Pump 1. What is active transport? 2. What type of protein is involved in active transport? 3. Describe how the sodium-potassium pump functions. 4. What is the electrochemical gradient? 1. Active transport is the energy-requiring process of pumping molecules and ions across membranes against a concentration gradient (or down a concentration gradient). 2. Carrier proteins known as pumps are needed for active transport. CK-12 Biology Answer Keys - updated July

10 3. Three sodium ions bind with the sodium-potassium pump inside the cell. The carrier protein then gets energy from ATP and changes shape. In doing so, it pumps the three sodium ions out of the cell. At that point, two potassium ions from outside the cell bind to the sodium-potassium pump. The potassium ions are then transported into the cell, and the process repeats. 4. The electrochemical gradient refers to the difference across a membrane due to both a chemical force and an electrical force. May provide additional information Exocytosis and Endocytosis 1. What is the difference between endocytosis and exocytosis? 2. Why is pinocytosis a form of endocytosis? 3. Are vesicles involved in passive transport? Explain. 1. Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. 2. Pinocytosis, or cellular drinking, occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell. Pinocytosis brings substances into the cell, making it a type of endocytosis. 3. Vesicular transport requires energy. It is a form of active transport. So no, vesicles are not involved in passive transport Autotrophs and Heterotrophs 1. Compare autotrophs to heterotrophs, and describe the relationship between these two groups of organisms. 2. Name and describe the two types of food making processes found among autotrophs. Which is quantitatively more important to life on earth? 3. Describe the flow of energy through a typical food chain (describing "what eats what"), including the original source of that energy and its ultimate form after use. CK-12 Biology Answer Keys - updated July

11 1. Autotrophs store chemical energy in carbohydrate food molecules they build themselves, whereas heterotrophs cannot make their own food, so they must eat or absorb it. Autotrophs are producers, heterotrophs are consumers. Autotrophs make the food that heterotrophs eat (heterotrophs get their energy from autotrophs, or from other animals that consumed autotrophs). 2. Photosynthesis, which is making energy from sunlight, and chemosynthesis, which is producing food using the chemical energy stored in inorganic molecules, are two types of food making processes. Photosynthesis provides over 99 percent of the energy for life on earth, so that process is quantitatively more important to life on earth. 3. will vary. The original source of energy is sunlight, which is absorbed by autotrophs, such as maple trees, during photosynthesis. Grasshoppers eat the leaves of the tree. Birds eat the bugs, snakes eat the birds, and final consumers (big birds) eat the snakes, transferring energy at each step in the food chain Glucose and ATP 1. The fact that all organisms use similar energy-carrying molecules shows one aspect of the grand "Unity of Life." Name two universal energy-carrying molecules, and explain why most organisms need both carriers rather than just one. 2. A single cell uses about 10 million ATP molecules per second. Explain how cells use the energy and recycle the materials in ATP. 3. ATP and glucose are both molecules that organisms use for energy. They are like the tank of a tanker truck that delivers gas to a gas station and the gas tank that holds the fuel for a car. Which molecule is like the tank of the delivery truck, and which is like the gas tank of the car? Explain your answer. 1. Two of the most important energy-carrying molecules are glucose and ATP. Glucose, the product of photosynthesis, stores energy for organisms. But for this energy to be used by cells, it must be turned into ATP. Under the proper conditions, many (up to 38) ATP can be produced for each glucose molecule. 2. The three phosphate groups of an ATP are linked by bonds which hold the energy actually used by cells. Usually, only the outermost bond breaks to release or spend energy for cellular work. An ATP molecule is like a rechargeable battery: its energy can be used by the cell when it breaks apart into ADP and CK-12 Biology Answer Keys - updated July

12 phosphate, and then the "worn-out battery" ADP can be recharged using new energy to attach a new phosphate and rebuild ATP. 3. Glucose is like the tank as the glucose delivers the energy to the cell, just link the tank delivers the gas. ATP is like the gas tank as ATP is used for energy for the cell, just like the gas tank stores the energy of the car Chloroplast 1. Describe the chloroplast's role in photosynthesis. 2. Explain how the structure of a chloroplast (its membranes and thylakoids) makes its function (the chemical reactions of photosynthesis) more efficient. 3. Describe electron carriers and the electron transport chain. 1. The chloroplast is the site of photosynthesis. 2. Each chloroplast contains neat stacks of thylakoids called grana. The thylakoid membranes contain photosystems, which absorb sunlight. The light reactions of photosynthesis occur in the thylakoid membranes. The stroma is the space outside the thylakoid membranes. This is where the reactions of the Calvin cycle take place. So having stacks of thylakoids, and having many thylakoids, allows numerous photosynthesis reactions to occur simultaneously. 3. Electron carrier molecules are usually arranged in electron transport chains. The electron carriers accept and pass along energy-carrying electrons in small steps. In this way, they produce ATP and NADPH, which temporarily store chemical energy Leaves and Photosynthesis 1. Explain how a leaf is like a factory. 2. Explain the role of stomata during photosynthesis. 3. What controls the opening of stomata? CK-12 Biology Answer Keys - updated July

13 1. A factory has specialized machines to produce and transport a product. In a leaf, the product is energy and the machines are all the organelles working together in photosynthesis. 2. Stomata are pores on the leaf that can open and close to regulate gas exchange. In photosynthesis, they control the transpiration of water vapor and the exchange of carbon dioxide and oxygen. 3. Stomata are flanked by guard cells that swell or shrink by taking in or losing water through osmosis Photosynthesis 1. Summarize what happens during the light reactions of photosynthesis. 2. What is the chemiosmotic gradient? 3. Explain the role of the first electron transport chain in the formation of ATP during the light reactions of photosynthesis. 1. During the light reactions, light energy is absorbed in the chloroplast, exciting electrons. The electrons enter the electron transport chain, where a little ATP and NADPH are produced. Water is split to replace the electrons that were lost to the electron transport chain. The ATP and NADPH are used in the next part of photosynthesis. 2. The chemiosmotic gradient is an electrochemical gradient across the thylakoid membrane of the chloroplast and the inner membrane of the mitochondrion. It is due to concentration differences of both positive charges and hydrogen ions. 3. The first electron transport chain captures the energy in the excited electrons and uses it to pump hydrogen ions by active transport into the thylakoids. These concentrated ions store potential energy by forming a chemiosmotic or electrochemical gradient. The hydrogen ions slide down their concentration gradient through ATP synthase, which uses their energy to chemically bond a phosphate group to ADP, making ATP Calvin Cycle CK-12 Biology Answer Keys - updated July

14 1. What happens during the carbon fixation step of the Calvin cycle? 2. What is special about RuBisCo? 3. What are stomata? 4. Explain what might happen if the third step of the Calvin cycle did not occur. Why? 5. What is the main final product of the Calvin cycle? How many turns of the Calvin cycle are needed to produce this product? 1. During carbon fixation, low-energy inorganic CO2 is built into high-energy organic molecules, like glucose. 2. The most common carbon fixation pathway combines one molecule of CO2 with a 5-carbon sugar called ribulose biphosphate (RuBP). The enzyme which catalyzes this reaction isrubisco, and is the most abundant enzyme on earth. 3. Stomata are tiny openings under the leaf which normally allow CO2 to enter and O2 to leave the leaf. 4. If step three of the Calvin cycle did not occur, then the process would stop. Step three regenerates ribulose-5- phosphate, which is needed to restart the cycle. 5. The final product of the Calvin cycle is glucose. Six turns of the Calvin cycle are needed to make one glucose Photosynthesis Summary No review questions Chemosynthesis 1. What is chemosynthesis? 2. Why do bacteria that live deep below the ocean s surface rely on chemical compounds instead of sunlight for energy to make food? 3. Describe the habitats of extremophiles? 1. Chemosynthesis is a process in which some organisms use chemical energy instead of light energy to produce "food." CK-12 Biology Answer Keys - updated July

15 2. Bacteria that live deep below the ocean s surface rely on chemical compounds instead of sunlight for energy to make food, as the sunlight does not penetrate to these parts of the ocean. 3. Extremophiles live in harsh conditions, such as in the absence of sunlight and a wide range of water temperatures, some approaching the boiling point Cellular Respiration 1. Define cellular respiration. 2. What are the three stages of cellular respiration? 3. Describe the structure of the mitochondrion and discuss the importance of this structure in cellular respiration. 4. Assume that a new species of organism has been discovered. Scientists have observed its cells under a microscope and determined that they lack mitochondria. What type of cellular respiration would you predict that the new species uses? Explain your prediction. 5. When you exhale onto a cold window pane, water vapor in your breath condenses on the glass. Where does the water vapor come from? 1. Cellular respiration is the process in which cells break down glucose and make ATP for energy. 2. The three stages of cellular respiration are glycolysis (stage 1), the Krebs cycle, also called the citric acid cycle (stage 2), and electron transport (stage 3). 3. A mitochondrion has an inner and outer membrane. The space between the inner and outer membrane is called the intermembrane space. The space enclosed by the inner membrane is called the matrix. The second stage of cellular respiration, the Krebs cycle, takes place in the matrix. The third stage, electron transport, takes place on the inner membrane. 4. An organism without mitochondria in its cells would undergo anaerobic respiration, as glycolysis would still occur, but the Krebs cycle and electron transport chain of aerobic respiration would not. 5. The water vapor is exhaled as a product of cellular respiration Glycolysis CK-12 Biology Answer Keys - updated July

16 1. What is glycolysis? 2. Describe what happens during glycolysis. How many ATP and NADH molecules are gained during this stage? 3. Defend this statement: Glycolysis is a universal and ancient pathway for making ATP. 1. The first stage of cellular respiration is glycolysis, which is the splitting of glucose. 2. During glycolysis, enzymes split a molecule of glucose into two molecules of pyruvate. The energy to split glucose is provided by two molecules of ATP. As glycolysis proceeds, energy is released, and the energy is used to make four molecules of ATP, so there is a net gain of two ATP molecules during glycolysis. During this stage, high-energy electrons are also used to produce two molecules of NADH. 3. Because glycolysis is used by all organisms, it is said to be universal. Glycolysis is used to make two ATPs. As aerobic cellular respiration is not used by all organisms, most biologists consider glycolysis to be the most fundamental and primitive pathway for making ATP Krebs Cycle 1. What is the Krebs cycle? 2. What are the products of the Krebs cycle? 3. Explain why two turns of the Krebs cycle are needed for each molecule of glucose. 1. May also add the products here: The Krebs cycle is the second stage of cellular respiration, where the energy stored in two molecules of pyruvate is transferred to 4 ATPs, 10 NADHs, and 2 FADH2s. 2. The products of the Krebs cycle are 4 ATPs, 10 NADHs, and 2 FADH2s. 3. Glucose is split into two pyruvates during glycolysis. Each pyruvate enters the Krebs cycle as an acetyl-coa molecule, so since there are two pyruvates, two turns of the cycle are needed for each glucose. CK-12 Biology Answer Keys - updated July

17 2.28 Electron Transport 1. Summarize the overall task of Stage III of aerobic respiration. 2. Explain the chemiosmotic gradient. 3. What is the maximum number of ATP molecules that can be produced during the electron transport stage of aerobic respiration? 1. The overall task of stage III is to transfer energy from NADH and FADH2, which result from the Krebs cycle, to ATP. 2. The pumping of hydrogen ions across the inner membrane of the mitochondria creates a greater concentration of the ions in the intermembrane space than in the matrix. This creates a chemiosmotic gradient, which then causes the ions to flow back across the membrane into the matrix, where their concentration is lower. 3. Up to 34 ATPs are made during the electron transport stage Fermentation 1. What is fermentation? 2. Name two types of fermentation. 3. What is the main advantage of aerobic respiration? Of anaerobic respiration? 4. What process produces fuel for motor vehicles from living plant products? What is the waste product of this process? 5. Compare and contrast lactic acid fermentation and alcoholic fermentation. Include examples of organisms that use each type of fermentation. 1. Fermentation is making ATP without oxygen, which involves glycolysis only. It is a type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to one or more other compounds and the formation of NAD+. 2. Two types of fermentation include lactic acid fermentation and alcoholic fermentation. CK-12 Biology Answer Keys - updated July

18 3. Anaerobic respiration allows organisms to produce ATP in the absence of oxygen, although only a small amount of ATP is made. Aerobic respiration is much more efficient at ATP production. 4. Alcoholic fermentation produces fuel for motor vehicles. The waste product of this process is carbon dioxide. May also mention biofuels/ethanol. 5. Lactic acid and alcoholic fermentation both allow glycolysis to continue, producing small amounts of ATP. In lactic acid fermentation, pyruvic acid from glycolysis changes to lactic acid. This process is done by certain bacteria. In alcoholic fermentation, pyruvic acid changes to alcohol and carbon dioxide. This type of fermentation is carried out by yeasts and also some bacteria. Both types of fermentation recycle NAD Anaerobic and Aerobic Respiration 1. What is the main advantage of aerobic respiration? Of anaerobic respiration? 2. Tanya is on the high school track team and runs the 100-meter sprint. Marissa is on the cross-country team and runs 5-kilometer races. Explain which type of respiration the muscle cells in each runner s legs use. 1. Aerobic respiration produces much more ATP than anaerobic respiration, but anaerobic respiration occurs more quickly than aerobic respiration. 2. Tanya uses anaerobic respiration for energy because it gives her the energy she needs for the short-term, intense activity. Marissa uses aerobic respiration because it produces more energy but at a slower rate Cell Division 1. Describe binary fission. 2. What is mitosis? 3. Contrast cell division in prokaryotes and eukaryotes. Why are the two types of cell division different? CK-12 Biology Answer Keys - updated July

19 1. Binary fission is how prokaryotic cells divide. It occurs in three phases: DNA replication, chromosome segregation, and separation. Simply, the cells grows and then splits into two cells. 2. Mitosis is a multi-phase process in which the nucleus of the eukaryotic cell divides. 3. Cell division in eukaryotes includes mitosis, to ensure the many chromosomes sort properly. As a prokaryotic cell only has one chromosome and no nucleus, mitosis is not necessary. After DNA replication and chromosome segregation, the cell can just grow and divide. In a eukaryotic cell, mitosis is followed by cytokinesis Cell Cycle 1. Identify the phases of the eukaryotic cell cycle. 2. What happens during interphase? 3. Define cancer. 4. Cells go through a series of events that include growth, DNA synthesis, and cell division. Why are these events best represented by a cycle diagram? 5. Explain how the cell cycle is regulated. 6. Why is DNA replication essential to the cell cycle? 1. The phases of the eukaryotic cell cycle include the G1, S, and G2 phases, which are grouped together as interphase, and the mitotic phase (M) which includes both mitosis and cytokinesis. 2. During interphase the cell grows and completes its metabolic activities, the DNA is replicated, and the cell prepares for mitosis. 3. Cancer is a disease that occurs with the loss of control of the cell cycle. 4. After cell division, the new cells enter the first phase of their cell cycle. So the cycle begins again, thus it is represented as a circle. 5. The cell cycle is controlled mainly by regulatory proteins at key checkpoints. These proteins control the cycle by signaling the cell to either start or delay the next phase of the cycle. They ensure that the cell completes the previous phase before moving on. 6. The DNA must be replicated prior to mitosis to ensure the two resulting cells are genetically identical (both receive a complete set of DNA). Otherwise the resulting cells would not function properly, and most likely die. CK-12 Biology Answer Keys - updated July

20 2.33 Chromosomes 1. What are chromosomes? When do they form? 2. Identify the chromatids and the centromere of a chromosome. 3. Explain how chromosomes are related to chromatin. Why are chromosomes important for mitosis? 4. How many chromosomes are in a normal human cell? 1. Chromosomes are coiled structures made of DNA and proteins. Chromosomes are the form of the genetic material of a cell during cell division. 2. The two copies of replicated DNA are called sister chromatids. They are attached to one another at a region called the centromere. 3. Chromosomes are the form of the genetic material of a cell during cell division. During other phases of the cell cycle, DNA exists as grainy uncoiled material called chromatin. The coiled chromosome structure is important to ensure proper segregation of the chromosomes during mitosis. 4. Human cells normally have two sets of chromosomes, one set inherited from each parent. There are 23 chromosomes in each set, for a total of 46 chromosomes per cell Mitosis 1. List the phases of mitosis, in order. 2. What happens during prophase of mitosis? 3. During which phase of mitosis do sister chromatids separate? 4. Describe what happens during cytokinesis in animal cells. 5. If a cell skipped metaphase during mitosis, how might this affect the two daughter cells? 6. Explain the significance of the spindle fibers in mitosis. 1. The phases of mitosis are prophase, metaphase, anaphase and telophase. CK-12 Biology Answer Keys - updated July

21 2. During prophase, chromatin condenses into chromosomes, the nuclear envelope breaks down, and a spindle starts to form. 3. Sister chromatids separate during anaphase. 4. During cytokinesis, the cytoplasm splits in two and the cell divides. In animal cells, the plasma membrane of the parent cell pinches inward along the cell s equator until two daughter cells form. 5. If a cell skipped metaphase, the resulting cells would probably not have an equal, complete set of chromosomes, as the chromosomes would not line up properly. Then they would not segregate equally during anaphase. 6. The spindle fibers ensure that sister chromatids will separate and go to different daughter cells when the cell divides Reproduction 1. What are three types of asexual reproduction? 2. Define gamete and zygote. What number of chromosomes does each have (in humans)? 3. What happens during fertilization? 4. Compare and contrast asexual and sexual reproduction. 1. Three types of asexual reproduction are binary fission, fragmentation and budding. 2. A gamete is a haploid sex cell (23 chromosomes), and a zygote is the first diploid cell of a new organism (46 chromosomes). 3. During fertilization the nuclei of two haploid gametes join to form a diploid zygote. 4. Asexual reproduction involves one parent and produces offspring that are genetically identical to each other and to the parent. Sexual reproduction involves two parents and produces offspring that are genetically unique Meiosis 1. What is meiosis? 2. Compare the events of metaphase I to metaphase II? CK-12 Biology Answer Keys - updated July

22 3. Create a diagram to show how crossing-over occurs and how it creates new gene combinations on each chromosome. 4. Explain why sexual reproduction results in genetically unique offspring. 5. Explain how meiosis I differs from mitosis. 1. Meiosis is a type of cell division in which the number of chromosomes is reduced by half. 2. During metaphase I, spindle fibers attach to the paired homologous chromosomes. The paired chromosomes also line up along the equator (middle) of the cell. During metaphase II, spindle fibers line up the sister chromatids of each chromosome along the equator of the cell. 3. will vary, but should include new chromosomes containing parts of the original chromosomes. May also mention independent assortment of chromosomes during metaphase. 4. Sexual reproduction has the potential to produce tremendous genetic variation in offspring. This is due in part to crossing-over, which creates new allele combinations, during meiosis. 5. Meiosis I separates homologous chromosomes, whereas mitosis separates sister chromatids. Crossing-over also occurs during prophase I of meiosis I Gametogenesis 1. What is gametogenesis, and when does it occur? 2. What are the main differences between oogenesis and spermatogenesis? 3. How many chromosomes are in a human oogonia? 4. Why is there unequal distribution of the cytoplasm during oogenesis? 1. The development of haploid cells into gametes is called gametogenesis, which occurs after meiosis. 2. Spermatogenesis produces four haploid sperm, whereas oogenesis produces one haploid egg cell and three polar bodies. 3. Oogonia are diploid, so human oogonia have 46 chromosomes. 4. As the zygote receives all of its cytoplasm from the egg cell, the egg needs to have as much cytoplasm as possible, hence the unequal distribution of the cytoplasm during egg formation. CK-12 Biology Answer Keys - updated July

23 2.38 Genetic Variation 1. What is crossing-over and when does it occur? 2. Describe how crossing-over, independent assortment, and random fertilization lead to genetic variation. 3. How many combinations of chromosomes are possible from sexual reproduction in humans? 4. Create a diagram to show how crossing-over occurs and how it creates new gene combinations on each chromosome. 1. Crossing-over is the exchange of genetic material between homologous chromosomes. It occurs during prophase I. 2. Crossing-over is the exchange of genetic material between homologous chromosomes and results in new combinations of genes on each chromosome. When cells divide during meiosis, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate (sort) independently of each other. It results in gametes that have unique combinations of chromosomes. During sexual reproduction, fertilization is random, as any two gametes can unite to produce an offspring. All these contribute to genetic variation. 3. well over 64 trillion 4. will vary, but should include new chromosomes containing parts of the original chromosomes Life Cycle 1. What is a life cycle? 2. An adult organism produces gametes that quickly go through fertilization and form diploid zygotes. The zygotes mature into adults, which live for many years. Eventually the adults produce gametes and the cycle repeats. What type of life cycle does this organism have? Explain your answer. 3. Which life cycle is the simplest? Why? CK-12 Biology Answer Keys - updated July

24 4. Describe the alternation of generations life cycle. 1. The series of life stages and events that a sexually reproducing organism goes through is called its life cycle. 2. As the diploid adult is the primary form, this represents a diploid life cycle. 3. The haploid life cycle is the simplest life cycle. Organisms with a haploid life cycle spend the majority of their lives as haploid gametes. When the haploid gametes fuse, they form a diploid zygote. It quickly undergoes meiosis to produce more haploid gametes that repeat the life cycle. 4. In an alternation of generations life cycle, the organism changes back and forth from one generation to the next between haploid gametophyte and diploid sporophyte stages. CK-12 Biology Answer Keys - updated July