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Key Concept Review 1. (a) A plant cell (b) (1) endoplasmic reticulum, (2) Golgi apparatus, (3) mitochondrion, (4) vacuole, (5) cytoplasm, (6) chloroplast, (7) ribosome, (8) cell membrane, (9) cell wall, (10) nucleus (c) (2) The Golgi apparatus modifies, sorts, and packages proteins from the endoplasmic reticulum. (3) The mitochondria supply energy for the cell (convert the chemical energy in sugar into usable energy). (6) The chloroplasts contain a green pigment called chlorophyll that uses energy from the Sun to convert carbon dioxide and water into sugar and oxygen in a process called photosynthesis. (10) The nucleus is the control centre of the cell. It also contains most of the cell’s DNA. 2. The cell cycle is a series of events. The cell is in interphase when it is growing. During the first phase, G 1 , the cell grows, and produces new proteins and organelles. In the second phase, S, the cell makes an entire copy of the DNA in the cell as well as key proteins associated with chromosomes. During the last phase of interphase, G 2 , the cell produces organelles and structures needed for cell division. The cell then goes into mitosis in which it divides the genetic information into two portions and forms two daughter cells. 3. During interphase, the cell grows, produces new proteins and organelles, makes an entire copy of the DNA in the cell as well as key proteins associated with chromosomes, and produces organelles and structures needed for cell division. 4. There are four phases in mitosis. During prophase, the chromosomes condense, the nuclear envelope disintegrates, the mitotic spindles form and attach to the centromere, which connects the sister chromatids (see diagram on page 30 of the student book). During metaphase, the chromosomes completely condense and move toward the centre of the cell (see diagram on page 30 of the student book). During anaphase, the sister chromatids are pulled apart into separate chromosomes and move to the opposite ends of the cell (see diagram on page 31 of the student book). During telophase, the cell divides the cytoplasm into two portions by cytokinesis, the nucleus forms in each new cell, the mitotic spindles disappear, and the cells enter interphase (see diagram on page 31 of the student book). 5. Factors that affect the rate of mitosis include environmental conditions (altitude, amount of sunlight) and antibiotics. 6. Apoptosis is the regulated or controlled death of cells. Apoptosis helps remove cells that are no longer useful or that are not functioning properly. 1 Pages 50–51 Unit A: Tissues, Organs, and Systems of Living Things 63 7. Embryonic stem cells are unspecialized cells that are able to undergo differentiation to form a variety of cells that look different from one another and perform different functions. Adult stem cells result from differentiated embryonic stem cells and have a limited ability to create a variety of cell types. Most adult stem cells are involved in the replacement of damaged tissues, such as skin and blood. 8. Cells specialize to perform specific functions or tasks more efficiently. For example, brain cells are responsible for the storage of information and transmission of signals. The neural cells have branches to make connections and to provide fast signal transfers. 9. Cancer cells remain unspecialized; they do not stop reproducing and do not stick to other cells; they behave independently, and they can move to another location in the body. 10. Four types of animal tissues are epithelial tissue, connective tissue, muscle tissue, and nervous tissue. 11. Meristematic tissue is unspecialized tissue that is capable of dividing by mitosis. It is found in several locations in the plant and is responsible for growing new parts of the plant. Meristematic tissue forms all the different plant tissues (epidermal, vascular, and ground). Connect Your Understanding 12. Magnification refers to how many times bigger an image appears compared to the actual size of object. The higher the magnification, the larger the image appears. Resolution is the ability to clearly see details in the image. Contrast is the ability to see the cell and its parts compared with each other and the background. Cells are very small and need to be magnified to see detail. It is often difficult to see cell parts, as they are often pale or transparent, and they blend in with the background. Adjusting the amount of light and using stains or dyes help increase contrast. Since the unaided eye can resolve images that are 0.1 mm or larger, a microscope is often necessary to see things smaller than 0.1 mm. 13. Plant and animal cells have some of the same organelles because both types of cells have similar tasks that need to be completed in the cell. Examples of common organelles include: • mitochondria: powerhouses of the cell • vacuoles: store water, nutrients, and wastes • cell membrane: forms a protective layer around the cell that controls materials moving in or out of the cell • nucleus: control centre of the cell • endoplasmic reticulum: carries materials through the cell • cytoplasm: suspends the cell’s organelles in a jelly-like substance that fills the interior of the cell 64 Unit A: Tissues, Organs, and Systems of Living Things • Golgi apparatus: receives proteins from the endoplasmic reticulum and modifies, sorts, and packages the proteins for delivery in and out of the cell • cytoskeleton: helps maintain the cell’s shape 14. Plant cells produce usable energy by converting light from the Sun into energy through photosynthesis. Chloroplasts act as these solar converters. Plant cells also have a large central vacuole that can fill with water to help support its structure. In addition to a cell membrane, plant cells have a cell wall, which helps maintain the cell’s structure. 15. Students’ answers will vary but could include the idea that cell membranes control the movement of materials entering and leaving the cell through diffusion, where substances in high concentration move across the membrane to areas of low concentration. Concentration relates to how much of a substance is dissolved in water. 16. The development of the microscope has allowed scientists to look at and understand the cell since the cell is too small to see with the unaided eye. As microscopes improved, the ability to distinguish structures inside the cell led to discovering organelles. Observing these structures helped to determine their functions. 17. Some materials move across the cell membrane using diffusion. Some materials are kept in or out of the cell by the double layer of lipids that makes up the cell membrane. Lipids are fat-like molecules that do not dissolve in water. 18. Students’ answers will vary but could include: • intake of nutrients: nutrients and gases move across the cell membrane by diffusion; the nutrients may end up in the cytoplasm or stored in vacuoles; the mitochondria and/or chloroplasts convert the nutrients to usable forms of energy • growth and reproduction: the nucleus directs growth; when the cell is too large, the nucleus can direct the cell to undergo mitosis • waste removal: lysosomes contain digestive enzymes to break down foreign materials; the waste is stored in vacuoles until it is removed from the cell 19. There are a number of stages of the cell life cycle shown in this photo. Many cells in the photo show interphase (nucleus is clearly visible, distinct chromatids are not). The stages of mitosis that are clearly visible include: • prophase: nuclear membrane is not apparent and chromosomes are visible as they condense • metaphase: chromosomes are lined up in the middle of the cell and mitotic spindles are visible • telophase: cells are separating into two distinct cells with chromosomes “clumped” in each separate cell Unit A: Tissues, Organs, and Systems of Living Things 65 20. Cells are limited in growth and how large they can become. Once they reach a particular size, the cells must divide to grow. Also, as cells wear out or become damaged, they need to be replaced with new cells of the same type. Both of these kinds of replacement are accomplished through mitosis. 21. Tissues are groups of cells that work together to perform specific functions or tasks. Cell specialization produces cells that are capable of doing specific tasks very well, for example, skin or muscle cells in animals, or xylem or phloem in the root or leaf. 22. Stem cells are unspecialized cells that can form specialized cells. They are important to researchers for their ability to form specialized cells that may lead to treatments to regrow, repair, or regenerate tissues or organs; replace cancerous cells with healthy cells; or replace damaged brain cells. 23. Students’ answers will vary but could include the process of using stem cells to replace or regrow damaged or lost body parts. 24. Students’ answers will vary but could include: • stem cells are unspecialized cells that undergo differentiation, a process in which the cells become specialized • embryonic stem cells differentiate into other types of cells that perform different functions • adult stem cells result from these specialized cell types dividing and specializing further, resulting in cells with a limited ability to create a variety of cell types • cell specialization involves cells developing in different ways to perform particular functions 25. Students’ answers will vary but could include: • use of fluorescent substances added to cells that are placed under ultraviolet light makes some structures become visible where they might not have been seen before; this method can also be used to watch certain functions as they occur in the cell • transmission electron microscope (TEM) allows for a magnification up to 1 500 000× of thin slices of a sample • scanning electron microscope (SEM) provides magnification of up to 300 000× and produces three-dimensional images of surface features of a specimen • scanning tunnelling microscope (STM) and atomic force microscope (AFM) produce images of molecules within cells that shed light on the structure and function of molecules within the cell 26. Adult stem cells have a limited ability to create a variety of cell types. They are found mostly in skin, blood, and neural tissue. For example, in blood, adult stem cells could specialize to make red blood cells or white blood cells, as needed. In research, scientists have found that they can use adult stem cells from one organ to help regenerate tissue from another organ. For example, adult blood stem cells have regenerated liver, kidney, and brain cells. 66 Unit A: Tissues, Organs, and Systems of Living Things 27. Vascular tissue called xylem transports nutrients, water, and minerals from roots up the stem to the leaves. Vascular tissue called phloem transports sugars from the leaves to other parts of the plant. The stem generally does not perform photosynthesis, as it tends to be shielded from light from the Sun by the leaves. Also, the stem does not collect nutrients from