The Living Cell

Transcription

1 The Living Cell

2 This is the paper version of a Science Bits multimedia learning unit. The content is taken from the digital work available through the link The print version is a complimentary tool to assist work in classrooms which are without one computer per student. Photo & Image Credits (cells, page 1 and 6-7); (human beings, page 9); (denture, page 9); Denys (hand, page 9); Chad (knee, page 9); Zdenka (hair, page 9); Mercè Durfort, University of Barcelona (cells, page 10); Nophamon (girl s denture, page 11); Mercè Durfort, University of Barcelona (tissue sample, page 11, 17, 18 and 19); Erik com (teenager, page 11); Konstantin (girl walking, page 13); Chee-Onn (human cells, page 20); Iamnotanorange, wikimedia.org (human cell sample, page 20); Andres (cold, page 20); My Make (cancer awareness ribbon, page 23); Karuna (carrying out a project, page 24); Wavebreak Media (team, page 24); Mercè Durfort, University of Barcelona (tissue samples, page 25); (DNA chain, page 28); (swimmer, page 32); Mercè Durfort, University of Barcelona (tissue samples, page 32); szefei, 123rf.com (girl, page 33); Mercè Durfort, University of Barcelona (tissue samples, page 33 and 34); Antonio (oxygen, page 36). The copy and reproduction of this work is permitted under the following simultaneous conditions: Use of this work must be complemented with the legal use of its multimedia version. Use of this work is restricted to the school context and the education sector. Distribution of this work must be free of charge. The content of this work cannot be modified or adapted. For any other use, reproduction, distribution, public performance, or adaptation of this work is not permitted without express permission from the copyright holders. Copyright: International Science Teaching Foundation & Science Bits S.L., 2015 International Science Teaching Foundation Tower Bridge House, St Katharine s Way London E1W 1AA (United Kingdom) Science Bits, S.L. Torrent de l Olla 220, 2n 4a Barcelona (España)

3 Life Sciences Unit The Living Cell

4 Unit Structure Cover Page The unit title is highlighted and the learning objectives presented. An index of the contents according to the 5-E Model is also provided. The digital version also includes an activity to review the skills and knowledge required to undertake the unit. Engage A video and a related activity are available with the digital version. Both versions have a summary on page one. Different activities are proposed for the video; some of these may be interactive in the digital version, but they all contain open-ended questions. Explore This exploratory and discovery activity is devised to mobilize prior knowledge and check it against the results obtained from the experience. The digital version contains the necessary multimedia resources required for this activity: simulators, videos, interactivities, etc. 4

5 Unit Structure Explain The unit s key concepts are formally and systematically addressed. The digital version includes a wide range of multimedia resources to facilitate understanding of the ideas presented. The printable version includes all basic graphical elements and references to the digital resources available. The digital version may also include reinforcement or enrichment activities. Elaborate In this section, the newly acquired knowledge can be applied in a practical way. Thus, a problem-solving activity is proposed, one which requires the application of the concepts, attitudes, and procedures learned throughout the unit. The digital version may provide multimedia tools (such as simulators or videos) to help develop and solve the activity. Exercises Each of the concepts addressed in the Explain section is related to interactive or open-ended exercises with the aim of consolidating the topics covered through practice. The printable version includes all the exercises except for reinforcement or enrichment activities, and they are organized in accordance with the contents from the Explain section. 5

6 The Living Cell Index Engage We Are Cells...08 Explore Many Diverse Cells...10 Explain The Chemistry of Life...12 The Human Being, a Multicellular Organism...13 Human Cells...13 The Organelles of Human Cells...14 The Macromolecular Complexes of Human Cells...14 The Cell s Nucleus and Genetic Material...15 Different Cells...15 Tissues, Organs, and Systems...16 Main Tissues of the Human Body...17 Epithelial Tissue...18 Connective Tissue...18 Muscle Tissue...19 Nervous Tissue...19 Cell Responses to the Environment Human Homeostasis...20 Exchange of Substances...20 Cell Nutrition Energy Matter...22 Cell Division Elaborate Cancer...23 Exercises In this unit, you will learn: That your body is formed of billions of living cells. What your cells are made of. That your cells are organized into tissues that, in turn, form organs organized into systems. That all of your body cells contain the same genetic material. Why it is possible for your body cells to be so diverse despite all coming from the same original cell. That your cells nourish, respond to their environment, and divide in order to sustain life. 6

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8 Engage Video We Are Cells The human being. A fascinating organism composed of tissues, organs, and systems which carry out all of life s processes in a coordinated manner: feeding, interacting with the surrounding environment, and reproducing. Although each human being is considered a single individual, in truth its body is formed of 100 billion things called cells. Each and every cell is a unit of life that needs nourishment, can respond to changes in its environment, and which can also reproduce. Each part of the human body has cells specialized in performing specific functions. The joint effort and coordinated work of all the cells in the human body allows it to act as if it were one single organism. At the beginning, all humans beings start as one cell. This cell divides over and over again to form new cells, until they create an environment that in turn protects these cells. All that you are and the functioning of your body begins and can be explained at a cellular level. To do that, you need to enter the microscopic world of human cells. Where everything begins and ends... 8

9 Questions a. Which kingdom of living organisms do humans belong to? q Monera q Protista q Fungi q Plantae q None of these groups q Animalia b. Humans are living organisms made up of many cells. What type of living organisms are human beings? q Multicellular organisms q Unicellular organisms c. What type do you have? q Eukaryotes q Prokaryotes d. Are all parts of the human body made of cells? Do you know any part which is not? e. Why do body organs look so different from one another? Are all the cells in the human body of the same type? f. What characteristics do all the cells of the human body have in common? g. Why does the video in the digital version mention that all human beings started as a single cell? What is it meant by that? 9

10 Explore Video Many Diverse Cells We humans are multicellular organisms: our body is formed of many cells. It is easy to observe your cells under a light microscope. All you need is to rub the insides of your cheeks to collect cells and then prepare a sample to observe them under a light microscope. Simulator Many Diverse Cells a. Use the simulator in the digital version to observe under the microscope the sample prepared in the video. Image Oral mucosa A C b. This image highlights the three main parts of an animal cell. Based on what you already know about cells, choose the correct option: [Mithocondrion / Nucleus / Flagellum / Cell wall / Plasma membrane / Chloroplast / Cytoplasm]. B A:... B:... C:

11 c. More than 500 different species of bacteria inhabit a perfectly healthy mouth. How can you know for sure that the cells highlighted in the previous image are human and not the bacteria present in your mouth? q Because the observed cells have a cytoplasm. q There is no way for us to know that for certain. q Because the observed cells have a cell wall. q Because bacterial cells are much smaller. q Because the observed cells have a plasma membrane. q Because the observed cells are prokaryotic. q Because bacteria cannot be seen under the microscope. q Because the cells observed have a nucleus. d. The cells observed were scraped from the surface of your mouth cavity. Do you think that the cells that make up another part of your body are the same as those in your mouth? Why or why not? e. What characteristics do almost all of your body s cells have in common with the cells of your mouth cavity? Image f. The virtual lab in the digital version has samples of different body tissues that can be viewed under the microscope. Carefully observe how the samples are prepared in the simulator. Skin Muscle Blood Cartilage g. Draw a cell of each of the tissues observed and indicate the nucleus, cytoplasm, and plasma membrane in all your drawings. Conclusions Human beings are living organisms made up of cells. In fact, all your body s structures are composed of cells or substances produced by cells. However, your body has very diverse structures, and each of them carries out a different biological function. The organs and structures of your body are so diverse because they are formed of different types of cells. In other words, the cells forming your body are not the same: their diversity is related to the tissue or organ the cells are part of and the function they carry out. 11

12 Explain The Chemistry of Life All living organisms are composed of cells, and cells in turn are composed of molecules. Gallery Apart from water, the main types of molecules, or biomolecules, living organisms are formed of are as follows: external part of the cell lipids Carbohydrates Carbohydrates Carbohydrates are the main energy source of cellular metabolism. They also form certain parts of the cell which are used to build other biomolecules. cytoplasm Lipids Lipids are the main components of cell membranes. They are also the most efficient energy source and store up energy as reserves. Protein Proteins Most cellular structures are formed of proteins, which are involved in regulating and performing most processes taking place in the cells. Nucleic acid Nucleic Acids Nucleic acids are the cell s genetic material. They define all the cell s characteristics and activities. 12

13 The Human Being, a Multicellular Organism Every human being is multicellular: its organism is made up of many cells bonded together. Image More specifically, adult humans are composed of around 100,000 billion cells. Cells are the smallest unit of life. In order to survive, cells have to feed on matter and interact with their surrounding environment. The cells of a multicellular organism cannot survive by themselves. Each cell carries out a specific function and interacts with the other cells so that the organism can sustain life. Multicellular organisms must nourish all of their cells and provide the appropriate environmental conditions to be able to sustain life. Human Cells Humans belong to the animal kingdom and, as such, are formed of eukaryotic animal cells. Eukaryotic cells have a nucleus which protects the genetic material. Additionally, animal cells do not have a solid cell wall around their membranes. In contrast with plant cells, animals cells do not contain chloroplasts. Gallery The cytoplasm is the cell s internal environment. It is an aqueous solution containing two types of functional structures: organelles and macromolecular complexes. protein The nucleus is a large-sized membrane-bound compartment containing the cell s genetic material. These materials are the molecules that define all the cell s characteristics and activities. The plasma membrane separates the inside of the cell from the outside environment. It is a lipid bilayer with embedded proteins. It acts as a barrier regulating the exchange of substances with the outside environment. Cytoplasm Nucleus Plasma membrane 13

14 The Organelles of Human Cells Organelles are structures found inside of the cell that have particular functions in eukaryotic cells, as if they were the cell s organs. Gallery Strictly speaking, organelles are structures completely surrounded by a lipid membrane. Endoplasmic reticulum Lysosomes Vacuoles Cilia and flagella Golgi apparatus Nucleus Mitochondria 0.1 μm Lysosomes are round vesicles surrounded by a simple membrane. They contain proteins capable of breaking down complex molecules into simpler molecules. The endoplasmic reticulum (ER) is a network of membranes involved in synthesizing lipids for the membranes. The rough ER, one of the two basic types 3 μm of ER, has ribosomes attached to its surface: macromolecular complexes that synthesize proteins. The other type has no ribosomes and is called smooth ER. 0.2 μm Vacuoles are large membrane-bound compartments storing mostly water and other reserve substances. They are formed by fusing multiple vesicles. Cilia and flagella are membranebound appendages present in some types of cells. Their internal structure is thick and they whip about, helping the 1 μm cell to move. Flagella are longer than cilia (represented in the image) but fewer in number. 1 μm The Golgi apparatus is a series of stacked membrane-bound sacs involved in the creation of vesicles such as lysosomes. Substances inside some of these vesicles are transported outside of the cell. 3 μm The nucleus is a large organelle enclosing the cell s genetic material. 3 μm Mitochondria are rounded, rod-like organelles with a double-membrane structure. Acting as the energy factories of the cells, mitochondria extract the energy from organic nutrients through the process of oxidation. The Macromolecular Complexes of Human Cells Apart from the organelles, macromolecular structures can also be found inside the cell. Macromolecular complexes are structures that lack lipid membrane boundaries. These complexes carry out essential processes for the cell. 14

15 A network of filaments and microtubules found everywhere in the cytoplasm combine to form a flexible and dynamic structure called the cytoskeleton. This 0.02 μm structure aids in transporting vesicles and organelles and is related to the movement of the cell membrane. Gallery 0.03 μm Ribosomes are the builders that perform protein synthesis. They are found either attached to the endoplasmic reticulum or floating freely in the cytoplasm. Centrioles Cytoskeleton 0.5 μm Centrioles are tube-like structures formed in turn by a small set of microtubules. Their role is to control the movement of the cytoskeleton. Ribosomes Proteasomes 0.02 μm The main function of proteasomes is to degrade damaged or unneeded proteins. They float freely in the cytoplasm. The Cell s Nucleus and Genetic Materials Eukaryotic cells keep their genetic material inside of a large membranebound compartment: the nucleus. Video The genetic material is mostly composed of molecules of a nucleic acid called DNA deoxyribonucleic acid. The genetic material is like an instruction manual which: directs the processes required for the cells to develop, live, and reproduce; provides the guidelines that allow the different types of cells to coordinate with one another and build a functional multicellular organism. DNA are long chainlike molecules made up of four subunits called nucleotides joined together in a specific order. Nucleotides are like the letters of a language used to write the DNA s instructions for the cells. Different Cells Although all the cells in the human body share some basic characteristics, some differences exist: their shapes vary and they contain different organelles and perform different tasks. Each cell type has a specialized morphology and physiology that enables the cells to carry out their tasks with maximum efficiency. 15

16 Gallery Cell differentiation is the process through which the cells acquire the particular morphological and physiological traits that determine their roles. 100 μm Neurons are long cells with appendages that generate and convey nerve impulses. 5 μm Spermatozoa are cells that have a flagellum which allows it to move about in a liquid medium. Stem cells can divide to form the cells of an organism or differentiate into a specialized cell. microvilli 1 μm Erythrocytes are cells without a nucleus or mitochondria. In contrast, they are full of hemoglobin, a protein that allows them to transport oxygen. 2 μm The cell s appendages perceive sound vibrations inside the human ear. 4 μm The cells of the intestinal epithelium have microvilli that increase their surface area to enhance absorption. Although all the cells in the human body share some basic characteristics, some differences exist: their shapes vary and they contain different organelles and perform different tasks. Each cell type has a specialized morphology and physiology that enables the cells to carry out their tasks with maximum efficiency. Tissues, Organs, and Systems Each type of cell is arranged into tissues that have specific roles in the human body. In turn, different tissues group together and combine to form functional structures known as organs. Organs, on the other hand, can work together to carry out life processes. These functional structures are called systems. 16

17 The intestinal epithelium, a tissue enabling substances to be exchanged, is formed by a certain type of cells with microvilli. Together with other tissues, it forms the small intestine, an organ involved in digesting and absorbing nutrients. Digestive system Video Together with other organs, the small intestine forms the digestive system, which is involved in the nutrition process. Main Tissues of the Human Body Cells in tissues are surrounded by a material that makes up the extracellular matrix (ECM). The matrix or intercellular material is produced by the cells themselves. Depending on its composition, the matrix may provide support, store reserve substances, and regulate intercellular communication. Although there is a wide array of tissue types in the human body, they can be classified into four main categories: Gallery 100 μm 25 μm Epithelial tissues are made up of tightly bound cells containing little intercellular material (or ECM). These cells cover organs and line body surfaces, and some secrete substances. Connective tissues are made up of cells that have abundant matrix, or intercellular material, between them. 25 μm 150 μm Muscle tissue is the main component of muscles and is made up of bundles of elongated cells, called muscle fibers, specialized for contraction. Nervous tissue is a highly specialized tissue made up of cells neurons with the ability to react to stimuli and transmit responses to effector organs. 17

18 Galleries Epithelial Tissue Epithelial tissue or epithelia are made up of tightly packed layers of cells that line the inner and outer surfaces of body organs, providing protection. Depending on their function, epithelial tissues are classified into: nuclei The epidermis is the outermost layer of the skin and is formed by several layers of epithelial lining. epidermis covering and lining epithelia Covering and lining epithelia protect the organs they cover, forming a single layer of cells or several cell layers. The skin has sweat glands secreting sweat. These glands are covered by a layer of cells forming a secretory epithelium. epidermis dermis sweat secretory epithelia Secretory epithelia are made up of cells that specialize in producing and secreting substances onto the epithelial surface. These cells are scattered or grouped together forming glands. fibers Connective Tissue cells nuclei Connective tissues have an abundant matrix between their cells. Connective tissues bind and provide support for the organs and other tissues of the human body. There are five major types of connective tissue: Connective tissue proper fills the spaces between the body s organs, binding them together. 50 μm 100 μm 40 μm 150 μm 10 μm Adipose tissue is made up of cells that store lipids as energy reserves and insulates the body. Cartilage has a flexible but strong matrix. It covers the joints to prevent wear and provides a framework for structures such as outer ears and nose. Bone is the most rigid tissue. It has mineral salts within its matrix. Blood is a specialized tissue composed of cells suspended in a fluid matrix called blood plasma. 18

19 Muscle Tissue Muscle tissue is the tissue that makes up muscles. The cells in this tissue, known as muscle fibers, are elongated and have the ability to contract and relax. muscle fibers nuclei There are three types of muscle tissue: 100 μm 20 μm 40 μm Skeletal muscle tissue is formed of cells that have several nuclei. It makes up the muscles that move the skeleton under conscious control. Smooth muscle tissue is formed of cells that have a single nucleus. It is found on the walls of organs such as the stomach and bladder. It contracts involuntarily. Cardiac muscle tissue is the tissue found only on the walls of the heart. It resembles the skeletal tissue, although it contracts involuntarily. The cells in this tissue typically have only one nucleus. Nervous Tissue Nervous tissues are the main component found in the brain, spinal cord, and nerves, that is, in all the strictures that make up the nervous system. Image Cellular components of nervous tissue. The nervous system collects information from the body s external and internal environment in the form of stimuli. Next, it interprets the information and provides responses that other organs will have to carry out. Neurons are the basic cells of the nervous tissue. Their function is to transmit information through the long extensions of the cells cytoplasm. The nervous tissue also has neuroglial cells, and their function is to provide support and nourish the neurons. Neurons dendrites soma axon synapse neuroglial cells Cell Responses to the Environment In multicellular organisms such as human beings, the organism itself is like a compartment isolated from the external environment that provides each of its cells an appropriate environment in which to develop. The internal environment is the cell s environment inside the human body. This environment is separated from the external environment by skin and mucosas. 19

20 Image Thus, the environment the human cells inhabit is very different than the outside environment, and their responses depend on the stimuli they detect in their inner environment. Internal stimuli can be: Physical stimuli, such as changes in temperature, salinity, pressure, electrical signals, etc. Chemical stimuli, such as the presence of substances secreted by other cells, nutrients, substances from the external environment, etc. Human cells can survive outside the human body in cell cultures that reproduce the conditions of the internal environment. Gallery Human Homeostasis The external environment keeps changing. At the same time, an organism s internal environment changes under the influence of the external environment and its own cellular activity. Human cells, however, need to be surrounded by very stable environmental conditions in order to survive. That s why the human body regulates its internal environment: its cells work together to respond to changes, to ensure stability. When it is cold outside, the internal environment loses heat and the cells respond by increasing their metabolism to gain heat. Homeostasis is an organism s ability to maintain its internal conditions stable and fairly constant, relatively irrespective of the changes occurring in the external environment. Exchange of Substances All human body cells need to take in substances from the inner environment and release metabolic wastes. In order to do so, these substances need to pass through the plasma membrane. Videos The plasma membrane is said to be semipermeable because it allows only some substances to pass through it. Water and gases move readily through the plasma membrane by: O 2 H 2O Na + 1. Diffusion is the process by which O 2 and CO 2 readily move through the plasma membrane. The net flow is from a region of higher concentration of substances to a region of lower concentration of substances. 2. Through osmosis, a type of diffusion specific to water, water moves through the membrane from a region of lower solute concentration to a region of higher solute concentration. The concentrations tend to even out on both sides of the membrane. 20

21 H 2O Na + Facilitated Diffusion. Carrier proteins bound to the membrane allow the spontaneous passage of substances dissolved in water. Diffusion occurs from a region of higher concentration on one side of the cell membrane to a region of lower concentration on the other side. H 2O Na + Active transport. Membrane-embedded proteins can actively transport solutes from a region of lower concentration on one side of the cell membrane to a region of higher concentration on the other side. This process requires energy to be expended. Videos The substances that cannot readily move through the plasma membrane pass through it by: Endocytosis. Many molecules especially large molecules cannot move through the cell membrane by passive means. To achieve this, the cell deforms its membrane and engulfs these molecules, enclosing them within a vesicle in the cytoplasm. Exocytosis. When large molecules have to me moved out of the cell, the cell packages them into membranous vesicles that travel to and fuse with the plasma membrane. In this way, the contents are poured out of the cell. Cell Nutrition Energy All body cells need energy to carry out their life processes. In order to obtain energy, cells take organic nutrients and oxygen from the external environment into their cytoplasm. Through a reaction called cellular respiration, cells combine oxygen and organic nutrients to oxidize the nutrients and thus release the chemical energy they contain. GLUCOSE Image ENERGY Apart from energy, this reaction also produces CO 2 and H 2 O. Cellular respiration specifically takes place in mitochondria inside the cell, organelles specialized in carrying out this function. H 2 O Catabolism is the set of processes that the cell utilizes in order to obtain energy by breaking down organic molecules. O 2 Mitochondrion CO2 Reactants and products of cellular respiration. 21

22 Matter Image Cell structures are composed of various types of organic molecules. Not all organic nutrients taken up by the cells are broken down to obtain energy. The cell also uses some organic nutrients to build new cell structures, grow and repair itself. Amino acids Energy In general, the cell takes in simple molecules and uses them to build newer, more complex molecules. Protein Protein biosynthesis. For example, the cell takes in amino acids and uses them to build its own proteins. Anabolism or biosynthesis are all the cellular processes to build cell components from simple molecules. Cell Division Videos 1 In multicellular organisms like human beings, it is essential that the cells reproduce to ensure growth, repair damaged cells, and replace cells that have died. Cells that have differentiated lose the ability to divide. However, all tissues have undifferentiated cell reserves. The role of these cells is to divide and generate new cells that will differentiate and replace the damaged ones. Interphase. This phase is not part of mitosis. Rather, it is the step that precedes it. The molecules of the genetic material inside the nucleus and the centrioles duplicate. Mitosis is the process by which eukaryotic cells reproduce. Mitosis is a complex process consisting of a series of phases Prophase. The duplicated genetic material is packed, forming chromosomes. The two copies of each molecule, called chromatids, are joined by a single centromere. The nuclear membrane disintegrates and the centrioles move to opposite ends of the cell. Metaphase. The chromosomes line up across the center of the cell. A network of microtubules link the centrioles and centromeres of the chromosomes together. Telophase. The plasma membrane constricts and two cells are formed. A nuclear membrane forms around each of the two cells, and the genetic material of the chromatids is unpacked. Anaphase. The microtubules contract towards the centrioles. The centromeres of each chromosome divide, and chromatids are dragged to opposite ends of the cell. 5 22

23 Elaborate The pink ribbon is an international symbol for breast cancer awareness. Cancer The word cancer is a general term which refers to a wide range of diseases that may affect any part of a living organism. In cancer patients, the cells in a part of their body undergo rapid, uncontrolled cell division. Metastasis occurs when these cells spread to surrounding tissues or other organs in the body, and it is the main cause of death by cancer. Cancer is the leading cause of mortality worldwide. In 2012 alone, 8.2 million people died of cancer worldwide. In this activity, you will investigate and learn about cancer. Working in groups, you will have to display your findings by making an informative poster. Task Organizing Your Work a. The teacher will put you in groups of 4 or 5 students. Discuss the content for your poster in groups. Write a list of the questions you think it is important to ask. For example: What is cancer? What causes it? What types of cancer are there? What are the risk factors for cancer? What are the existing treatments for cancer? What palliative care is given to improve the quality of life of cancer patients? What strategies are there to reduce the number of cancer cases and the rate of mortality? b. Structure your work around these questions in an orderly manner. Have each student in your group work on one of the questions you choose. 23

24 Researching and Summarizing Information To ensure your work meets a certain quality standard, choose only relevant information: often times, the information that is made available is not completely thorough. To avoid this, do not rely simply on one or two sources of information. Check several sources and compare the information each of them provides. Check types of sources in different formats: encyclopedia articles, documentaries, computer graphics, diagrams, etc. These representations will serve you and your group to come up with ideas about the best way to present your information. a. Work in groups and reflect on the sources of information that best suit the type of information you want to present. b. Now, work individually and find information relating to the question you have been assigned to prepare in your group. Keep record of all the sources of information you look up. c. Make a summary of the information you found and prepare whatever complementary resources you wish to use. You can use tables, graphs, images, etc. d. Present the text and resources to the students in your group and then listen to their presentations. Assess the relevance of the data presented by each of the students in your group. Bring together all the relevant data and resources and decide the logical sequence of events for your poster. e. Select the data you consider most relevant and which will be part of the group s poster. The data highlighted has to make an impact and must be easy to understand. One example would be the current number of cancer cases worldwide. Making the Poster Once the group has decided on the information that the poster should display, they should design it according to the following recommendations. If you decide to make a digital poster, you can use the free digital tool Glogster ( Design a clear heading indicating the the poster title, school and class, and the student s names. Orderly distribute the space devoted to text, images, and figures. Organize the information into columns. Include a title for each step so that the info displayed (text, images, etc.) is easy to follow at all times. Use lines, arrows or other graphic tools to indicate the sequence of events. Use colors to help readers focus their attention. However, do not use too many as this would have the opposite effect. Save some space for the most relevant information. Make sure the images and figures are accompanied by a caption. Indicate the main sources of information used. Use a font that is easy to read, making sure the font size is not too small. The main titles should have a larger font size. 24

25 EXERCISES The Chemistry of Life 1. Facts about Micromolecules Indicate whether the following statements about biomolecules are true or false. Nucleic acids play a key role as the cells primary energy source. Biomolecules are the molecules that make up cellular structures and regulate their activity. Enzymes are a type of carbohydrate that regulate the metabolic activity of the cells. Proteins perform important structural and regulatory functions. The cell membrane is largely composed of lipids. A cell s genetic material mostly consists of nucleic acids. Carbohydrates are molecules that have a key structural role in the cells. The Human Being, a Multicellular Organism 2. Cells from Different Subjects The image gallery shows cells from the livers of three different subjects. The three images were obtained with exactly the same magnifications. The three subjects have very different body sizes: a one-year old baby, a five-year old child, and an eighteen-year old teenager. a. Do you think you can match each of the images to the three subjects? q Yes, because the younger subjects will have larger cells. q Yes, because the older subjects will have larger cells. q No, because all the cells are the same. b. So, what do you think is the relationship between a person s cells and body size? q The bigger a person s body size, the greater the number of cells this person is composed of. q The bigger the body size of a person, the smaller the cells of this person. q The bigger the body size of a person, the fewer the number of cells this person is composed of. q The bigger the body size of a person, the larger the cells of this person. Cells of subject A. Cells of subject B. Cells of subject C. 25

26 EXERCISES Human beings are of different sizes, whether due to age or physical build. As is the case with any other multicellular organism, the body size of a human being is not related to the size of his or her cells. In reality, both the size and weight of a human largely depend on the number of cells he or she is composed of. During growth, the number of cells forming the human body increases. Therefore, the organism s overall size increases, while its cells do not undergo changes in size. Human Cells 3. The Roles of Major Cell Structures What parts of the cell do these statements refer to? [The genetic material / The plasma membrane / The cytoplasm / The nucleus] functions as a filter regulating the passage of substances into and out of the cell. [The genetic material / The plasma membrane / The cytoplasm / The nucleus] is mostly composed of water and dissolved substances and has organelles inside. [The genetic material / The plasma membrane / The cytoplasm / The nucleus] in human cells is enclosed inside [the genetic material / the plasma membrane / the cytoplasm / the nucleus]. [The genetic material / The plasma membrane / The cytoplasm / The nucleus] regulates the processes taking place in the cell. 4. Facts About Human Cells Indicate whether the following statements about human cells are true or false. Human cells have the characteristics specific to animal cells. Human cells are enclosed by a solid cell wall. Some human cells contain chloroplast-type organelles. Human cells have an aqueous cytoplasm. Human cells are eukaryotic. Human cells are the only living cells containing organelles. Human cells are the only living cells containing genetic material inside their nucleus. The Organelles of Human Cells 5. Identifying Organelles Identify the organelles of the cell in the diagram, choose the correct option: [Vacuole / Mitochondrion / Endoplasmic reticulum / Lysosome / Nucleus / Golgi apparatus / Cilium]

27 EXERCISES 6. Organelles and Their Tasks in the Cell Match these cell organelles to the tasks each performs in the cell. [Mitochondrion / Endoplasmic reticulum / Golgi apparatus / Lysosome / Vacuole / Cilium or flagellum / Nucleus]... : supplies the energy that the cell requires.... : is involved in synthesizing lipids and proteins.... : creates vesicles that contain various substances.... : breaks down complex molecules into simpler molecules.... : stores water and other reserve substances.... : functions as a mobile appendage.... : encloses and protects the genetic material of the cell. 7. Organelles Viewed under the Electron Microscope The following images, which show the cellular ultrastructure, were revealed by electron microscopy. Identify the organelles indicated by the arrows in each of the images below: [Cilia or flagella / Golgi apparatus / Mitochondrion / Nucleus / Endoplasmic reticulum]. The Macromolecular Complexes of Human Cells 8. The Tasks of Macromeloecular Complexes Match the macromolecular complexes to the task each of them performs inside the cell: [Ribosome / Proteasome / Cytoskeleton / Centrioles].... : involved in the cell s protein synthesis.... : destroys the proteins which are no longer useful.... : helps the cell to move.... : aids in the intercellular transportation of organelles and vesicles.... : regulate the movement of the cytoskeleton. 27

28 EXERCISES 9. Facts about Macromolecular Complexes Indicate whether the following statements about macromolecular complexes are true or false. The cytoskeleton connects to every organelle and provides structure to the cell. Ribosomes are not organelles because they have no lipid membrane. The macromolecular complexes of the cell are surrounded by a lipid membrane. In contrast with organelles, macromolecular complexes are not essential for the cell s survival. Centrioles are tubular structures. Ribosomes are exclusively bound to the endoplasmic reticulum. The Cell s Nucleus and Genetic Material 10. Facts about Genetic Material Indicate whether the following statements about genetic material are true or false. Human cells are the only cells whose DNA is enclosed in their nucleus. The genetic material is like an instruction manual that the cell and the organism use to function properly. The units the DNA molecules form always have the same arrangement. DNA molecule is like a chain formed of four different types of nucleotides. The units the DNA molecules form are ordered in a random way. DNA is found inside the nucleus of eukaryotic cells. Human cells are the only ones containing DNA. DNA is made up of proteins μm nucleotide DNA molecule. nucleotide 11. DNA The main component of the genetic material of all living organisms is a substance called DNA. DNA is a very long molecule formed by a sequence of millions of nucleotides. There are only four different nucleotides, represented by letters A, T, C, and G. However, DNA molecules are so long that the number of possible combinations is extremely large. The number of nucleotides and the order in which they join together in a DNA molecule is different for every organism. 28

29 EXERCISES If the genetic material is the instruction manual of a living organism, the DNA chains are the text in this manual a text which is written in a language made up of four letters, conveying a message which is different for every living organism. a. The genetic material determines the tasks that each cell has to perform. What could happen if the genetic material of a cell was modified? q The cell would certainly die. q The cell might behave in a different way. q Nothing would ever happen. q The cell s sustainability might be compromised. b. Suppose that one of the instructions in the genetic material reads: Create a blue-colored substance. What would happen if we moved the words around in the sentence, or added new ones to it? Indicate how this would affect each of the following examples: [the instruction would make no sense and would not be followed. / the meaning of the instruction would be altered and the characteristic would be modified. / the instruction would have the opposite meaning. / the meaning of the instruction would not be altered.] Substance a create-colored blue :... Create a red-colored substance :... Do not create a blue-colored substance :... Elaborate a blue-colored substance :... c. Think about the wide variety of human beings. No two persons are alike, apart from identical twins. How would you explain these facts from the point of view of the genetic material? Look up information if necessary. There is diversity among individuals because their genetic material has differences. In contrast with all other individuals, identical twins have exactly the same genetic material. All humans have exactly the same genetic material, but their cells interpret it differently. All humans have exactly the same genetic material before being born. However, life experiences modify the DNA and this explains this wide diversity. 12. Extracting DNA from Your Cells The video in the digital version shows a home made technique that allows DNA to be extracted from a person s cells using common, everyday materials. a. Where is DNA extracted from? q From the blood in the mouth and tongue capillaries q From salivary enzymes q From the cells in the oral mucosa q From tooth enamel b. Can you determine the type of cell an individual s DNA molecule is extracted from? q No, the DNA is the same for all body cells. q It depends on the extraction method used. q Yes, the DNA has different parts depending on the cell it comes from. c. If we didn t know the person the DNA belongs to, could we determine it once it has been extracted? q Yes, provided that appropriate lab techniques are applied. q Yes, provided that adequate lab techniques are applied and the subject does not have an identical twin brother or sister. q No, it is not possible to identify someone with a DNA sample. 29

30 EXERCISES d. Where in the cell is the DNA found? q In the nucleus. q Surrounding the plasma membrane. q Floating around in the cytoplasm. e. Why is soap used in the experimental procedure? q To free the genetic material from the lipid membranes, as if removing fat from a dish. q To disinfect the solution and remove bacteria and other living unicellular that may compromise the preparation. q To dissolve the carbs and thus release the genetic material. f. Following this extraction method, what is the form of the DNA obtained? q Individual molecules forming strands clearly separated from one another. q Molecules joined together forming compact tangles. q Molecules joined together, forming long strands or tangles. q Molecules dissolved in a liquid. Different Cells 13. Genetic Material and Cell Differentiation Indicate whether the following statements about genetic material and cell differentiation are true or false. Look up the information if necessary. In a human being, only types of cells which are the same have the same genetic material. Any two cells from the same human body contain the same genetic material. Human body cells can be distinguished because each contains different genetic material. Human body cells acquire different characteristics because they follow different instructions within the same genetic material. In a single human individual, two different cell types follow exactly the same instructions contained in the genetic material. 14. Cells Bearing a Name The various types of cells of the human body are given names that allow you to refer specifically to them. Look up the information if necessary and match the cell types below with the organ or system they belong to: [liver / nervous system / bone / blood / muscle / skin / cartilage]. Hepatocyte:... Neuro:... Osteocyte:... Erythrocyte:... Astrocyte:... Melanocyte:... Schwann cell:... Condrocyte:... Myocyte:

31 EXERCISES 15. Stem Cells Carefully read the following text and answer the questions on the following page. cell acts as a cell reserve to repair or regenerate different parts of the body. This ability of stem cells to become any type of cell has been studied over the last decades to try and obtain medical treatments that will help repair tissue damage that cannot otherwise be regenerated naturally, or even to generate organs or tissues to be used in transplants. With the information provided in the previous text and your knowledge on cell differentiation, indicate whether the following statements are true or false: Scientists have known for centuries that some animals have the ability to regenerate certain amputated parts of their body, for example, starfish, earthworms, and vertebrates such as salamanders. We humans have a less flashy version of this ability: although we cannot regenerate amputated legs or arms, our body is relentlessly regenerating blood cells, skin cells, liver cells, and other tissue cells. But not all the cells of our body are endowed with this gift. Differentiated cells which have acquired a series of specific properties to optimize the roles they have have lost the ability to reproduce. This ability is reserved exclusively for a very special type of cells in our body: stem cells. Stem cells can divide into more cells and become almost any type of cell and replace the old or damaged cells of an organ. In this way, a stem To regenerate tissue, firstly stem cells have to differentiate and then they reproduce. Humans are constantly regenerating cells in body tissues and organs such as blood, skin, or liver. Any differentiated cell has the ability to reproduce. In theory, it is possible to regenerate almost any tissue or organ in the human body from stem cells. Not all stem cells end up differentiating. In contrast with differentiated cells, stem cells retain the ability to reproduce. All the cells in the human body were, at some point, stem cells. In contrast with animals such as the salamander, the human body cannot regenerate any of its tissues. Tissues, Organs, and Systems 16. Cell, Tissue, Organ, or System? Indicate whether the following concepts refer to a cell type, tissue, organ, or system: [system / organ / tissue / cell]. Look up the information if necessary. Spermatozoon:... Skin:... Blood:... Lymphocyte:... Heart:... Epithelium:... Digestive:

32 EXERCISES 18. Levels of Organization Rank the following elements according to complexity, from lowest to greatest. A. System B. Human being C. Organ D. Tissue E. Macromolecular complex and organelle F. Cell G. Molecule H. Atom Main Tissues of the Human Body 19. Identifying Main Tissue Types Classify the following images according to the type of tissue they correspond to: [Epithelial tissue / Connective tissue / Muscle tissue / Nervous tissue]. 20. What Type of Tissue Is This? Indicate the type of tissue each of the statements below refers to: [Epithelial tissue / Connective tissue / Muscle tissue / Nervous tissue]. This tissue is made up of bundles of long, stretched cells that have the ability to contract. This tissue lines the surfaces covering body organs. It is made up of cells whose function is to react to stimuli, process it, and transmit it as information. There is an abundance of matrix between the cells of this tissue. This tissue contains a highly specialized cell type called neurons. This tissue may contain cells that secrete substances. 32

33 EXERCISES Epithelial Tissue 21. The Epithelial Tissues of the Human Body Indicate whether the following structures of the human body possess any layer of epithelial tissue. Blood vessels Nasal cavities Skin Uterus Vocal chords Urethra Hair Stomach Nails Trachea Mouth Intestine 22. Mucosa Just like skin protects the human body from the external environment, mucosas are the layers that line the inner surfaces of the body exposed to substances from the external environment: mouth, nose, lungs, stomach, intestines, etc The mucous membrane is composed of cells that continuously secrete mucous fluids onto its surface, lubricating it for protection. Complete the following diagram with the main mucosas found in the human body: [Eye mucosa / Oral mucosa / Nasal mucosa / Esophageal mucosa / Bronchial mucosa / Gastric mucosa / Intestinal mucosa / Urethral mucosa]. Look up the information if necessary Connective Tissue 23. Connective Tissues of the Human Body Indicate the type of connective tissue found in the following human body structures: [cartilage / connective tissue proper / blood / bone / adipose tissue]. Look up the information if necessary. Outer ear:... Intervertebral discs:... Tendons:... Ligaments:... Blood:... Femur:... Breast: Types of Connective Tissue a. Which type of connective tissue is tissue A? Cartilage Blood Adipose tissue Connective tissue proper Bone Tissue A b. Which type of connective tissue is tissue B? Cartilage Blood Adipose tissue Connective tissue proper Bone Tissue B 33

34 EXERCISES c. Which type of connective tissue is tissue C? Cartilage Blood Adipose tissue Connective tissue proper Bone Tissue C d. Which type of connective tissue is tissue D? Cartilage Blood Adipose tissue Connective tissue proper Bone Tissue D e. Which type of connective tissue is tissue E? Cartilage Blood Adipose tissue Connective tissue proper Bone Tissue E Muscle Tissue 25. Muscle Tissues in the Human Body Indicate whether the structures below contract involuntarily and the type of muscle tissue they are composed of. Look up the information if necessary. Biceps: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Small intestine: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Ventricle: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Uterus: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Atrium: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Abductor muscle: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Iris muscle: It contracts [voluntarily / involuntarily] I [Smooth / Skeletal / Cardiac] muscle tissue. Nervous Tissue 26. Cells of the Nervous Tissue Identify the following elements in this illustration of nervous tissue. Neuron Soma Axon Dendrite Synapses Neuroglial cells 34

35 EXERCISES Cell Responses to the Environment 27. Environments Indicate whether the following concepts refer to structures found in cells, in the external environment of an organism or in the internal environment of the cell in an organism: [cell / internal environment / external environment ]. Air in the atmosphere:... Air in the alveoli:... Blood plasma:... Nucleus:... Ribosomes:... Extracellular matrix:... Lumen of the stomach:... Intestinal lumen:... Exchange of Substances 28. Facts about the Exchange of Substances Indicate whether the following statements about the exchange of substances at the cellular level are true or false. q The plasma membrane is impermeable. q Endocytosis and exocytosis are processes involving the movement of large particles into or out of the cell. q Energy is used in all cellular processes involving the exchange of substances. q Proteins regulate facilitated diffusion and active transport. q Only gases can move in and out of the cell. q Water and gases can readily move through the plasma membrane. q The plasma membrane es impermeable. q Solute concentrations on both sides of the plasma membrane tend to even out without any energy expenditure. 29. The Eggshell Membrane Chicken eggshells are lined with a biological membrane. a. Which is the major component of the eggshell? membrane shell q Sodium bicarbonate q Carbon dioxide q Calcium carbonate b. What happens when this main substance is mixed with vinegar (acetic acid)? white germinal disc q The main substance disappears and the vinegar remains unchanged. q The two components transform into carbon dioxide (gas) and a water-soluble salt. q No change occurs. c. Watch the experiment in the digital version. What is the increase in mass experienced by each of the three eggs? Egg 1:... g Egg 2:... g Egg 3:... g Parts of the chicken egg. yolk 35

36 EXERCISES d. Express each increase as a percentage relative to the three eggs initial masses. Express the percentages with one decimal. Egg 1:...% Egg 2:...% Egg 3:...% e. According to what you see in the video experiment, what substance do you think causes the mass of the three immersed eggs to increase? q Carbon dioxide q Salt q Water f. What do you call the process through which this substance passes through the shell membrane? g. Rank these four elements according to the concentration of solutes in the water solution prior to the experiment, from lowest to highest. A. Egg in shell B. Water in glass 2 C. Water in glass 3 D. Water in glass 1 h. Complete the following statement: The lower the salt concentration in the glass, the [greater / lower] the amount of water diffusing through the membrane, and the [greater / lower] the increase in the egg s mass. Energy 30. Spermatozoa By observing a spermatozoon under the microscope, it is easy to see the mitochondria inside the male reproductive cell. The image shows a 3-D model of this very particular cell type. a. What is the most recognizable characteristic of spermatozoa? mitochondria tail (flagellum) q The secretion of substances. q The ability to move actively. q The transmission of nervous impulses. q Their ability to store reserve substances. b. Where precisely are mitochondria found in the spermatozoon? q Inside the nucleus. q Near the Golgi apparatus. q At the end of the flagellum. q At the base of the flagellum. head nucleus Diagram of a human spermatozoon. c. Why are mitochondria found in this region of the male reproductive cell? q To store energy in the nucleus. q To provide energy to the cytoplasm. q To provide energy to the Golgi apparatus. q To provide energy to the flagellum. 31. Oxygen consumption a. What is the process in which human cells use the oxygen obtained from the surrounding environment? b. What purpose does this process serve? c. What other substances are used in this process? 36

37 EXERCISES Different Individuals a. This table shows data relating to individuals of various ages. Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 Subject 6 How do you think the amount of oxygen consumed per minute and the body mass of these individuals are related? Age 1 month old 1 years old 2 years old 5 years old 12 years old 15 years old b. Explain this relationship. c. How are the amount of oxygen consumed and required food intake related? d. Explain this relationship. Body mass (kg) Oxygen consumed (ml/min) Body mass, oxygen consumption, and dry weight of foods ingested by individuals of different ages. Dry weight of foods ingested (g/day) Matter 32. Cell Components a. Apart from water, what is the largest component of cells? q Carbohydrates q Nucleic acids q Proteins q Fats q Salts b. And which component is found in the smallest relative amount? q Carbohydrates q Nucleic acids q Proteins q Fats q Salts c. What is the main component forming each of these cell structures? [fats / nucleic acids / water / carbohydrates / proteins / salts] Plasma membrane:... Genetic material:... Cytoplasm:... d. Apart from water, what other component is present in almost all cell structures? water 72% e. To have a balanced diet, you need to take in nutrients in the following relative proportions: Carbohydrates: 55 % Fats: 35 % Proteins: 10 % proteins 15 % nucleic acids 7 % carbohydrates 3 % fats 2 % salts 1 % Why aren t these components in the same relative proportions in our cells? q The cell needs to consume some fats and carbohydrates to be able to obtain energy. q Carbohydrates transform into proteins. q Most of the carbohydrates and fats our body takes in never reach our cells. 37

38 EXERCISES Cell Division 33. Phases of Mitosis Put the phases of cell mitosis in order. Interphase Prophase Telophase Metaphase Anaphase A B C D E 34. Mitosis in Onion Root Tips Mitosis is the process by which all eukaryotic cells reproduce. It is therefore possible to observe this process in plant cells such as in root tips. The video in the digital version shows a procedure to observe mitosis in onion root tip cells. a. Why do you need samples from the root tips and not from other parts of the onion? q Because root tip cells are the only ones that can divide. q Because roots grow by their tips. q Because root tip cells are the only ones containing genetic material. b. This image shows onion root tip cells viewed under a microscope. In which phase of mitosis are most of the cells in the image? cell C cell A cell B c. Rank the highlighted cells in the image according to their phase of mitosis. A. Cell B B. Cell A C. Cell C Onion root tip cells viewed under a microscope. 10 μm 38

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