BIO1 11_12 Q1 0101 FD Cell Theory PDF

Unit 1: Cells Lesson 1.1 Cell Theory Contents Introduction 1 Learning Objectives 2 Warm Up 2 Learn about It!...

Unit 1: Cells Lesson 1.1 Cell Theory Contents Introduction 1 Learning Objectives 2 Warm Up 2 Learn about It! 4 Overview of the Cell 4 Size of the Cell 5 Surface Area to Volume Ratio in Cells 5 General Functions of the Cell 7 Regulation of the Internal Environment 8 Acquisition and Utilization of Energy 9 Responsiveness to Their Environment 9 Protection and Support 10 History of the Development of Cell Theory 10 Principles of Cell Theory 13 The Cell as a Common Feature among All Organisms 14 The Cell as the Fundamental Unit of Life 15 The Cell as a Product of Preexisting Cells 15 Key Points 17 Check Your Understanding 18 Challenge Yourself 20 Photo Credits 20 Bibliography 21 Unit 1: Cells Lesson 1.1 Cell Theory Introduction You have probably heard that cells are the building blocks of living organisms when you started studying science in school. However, have you ever wondered how these tiny packets of life were discovered and how they govern the mechanisms of our day-to-day activities? Scientists have studied cells for centuries, and this field of study continues to develop up until today. It is important to understand that when cells are grouped together in a highly organized fashion, they can perform a specific function that usually contributes to the overall maintenance and survival of an organism. The importance of the daily operation within cells is very evident as we eat food, think critically, take medicine, exercise, breathe, reproduce, and even when our bodies combat infections. 1.1. Cell Theory 1 Unit 1: Cells A piece of brick can be compared to a cell. When building a town or city, it is important to have bricks that will provide foundations to different establishments. When these bricks are brought together, they could form houses, offices, hospitals, schools, churches, restaurants, and even malls, which will then cater to the needed services of the immediate community. Just like cells, when brought together, they can form more complex and distinct structures that enable them to perform different functions that are important to our bodies. But unlike bricks, cells are very small that they cannot be seen with our naked eyes. The scientific knowledge of humans about cells made a giant leap when the microscope was invented. This tool enables scientists to further study the various structural and functional features of cells. Furthermore, this tool also allowed different scientists to propose theories that elaborate on the characteristics of cells. How do cells work inside our bodies? How can one distinguish living organisms from nonliving entities? Learning Objectives DepEd Competency In this lesson, you should be able to do the Explain the postulates of the cell theory following: (STEM_BIO11/12-Ia-c-1). Describe the general features of the cell. Create a timeline of the discovery of the cell. Identify the three proponents of the cell theory. Analyze the three principles of cell theory. Warm Up Redi for the Game 15 minutes Francesco Redi was an Italian scientist who disproved the Spontaneous Generation theory during the 16th century. He designed an experiment that involved maggots and tested spontaneous generation by placing fresh meat in two different jars. The link to the game below will let you identify the components of the experiment he performed. 1.1. Cell Theory 2 Unit 1: Cells Material a device with an Internet connection Procedure 1. Access the link below to direct you to the online game. MrsDohm. “Redi’s Experiment.” “Redi's Experiment.” PurposeGames.com. Accessed January 31, 2020. https://www.purposegames.com/game/redis-experiment-aqu in-hs-game 2. In this online game, you will be provided with a general setup of the experiment performed by Francesco Redi. 3. Each of the components of his experiment has a blue dot. Tick the dot that corresponds to the statement or phrase that is shown in the yellow bar above the interface. For example, if the yellow bar shows “controlled variables,” then you have to tick the blue dot that corresponds to it, i.e., “jars, type of meat, location, temperature, time.” There are a total of 12 items. 4. A green dot will show if you have correctly answered an item for the first time. A yellow or orange dot will show instead if you have correctly answered an item in the succeeding tries. A red dot corresponds to a wrong answer. The number of correct and wrong answers are shown in the upper left-hand corner of the interface. 5. You are given an unlimited number of attempts to correctly answer all items, so do not be discouraged. 6. When you are done, look for a partner, and try to briefly discuss the implications of Redi’s experiment. 7. Answer the questions that follow. Guide Questions 1. What experimental setup was used in the activity that can help in drawing conclusions? 1.1. Cell Theory 3 Unit 1: Cells 2. In Redi’s experiment, what could have been the conclusion if the jars with fresh meat were not covered? 3. How do you think Redi’s experiment helped disprove the theory that living forms can arise from nonliving matter? Learn about It! Overview of the Cell Before, most biologists believe that life may spontaneously arise from any inanimate matter. Aristotle, a Greek philosopher, was one of the earliest recorded scholars to propose the spontaneous generation theory. This theory persisted in the 17th century, until Francesco Redi, an Italian scientist, disproved it by performing an experiment that refutes the idea that maggots arise spontaneously from meat. It was followed by different scientists who also conducted their own experiments to disprove this theory. Louis Pasteur, a French chemist, disproved this theory conclusively with his famous swan-necked flask experiment. He proposed that life can only come from preexisting life forms. All living organisms, especially plants and animals, are composed of at least one cell. Most cells are not just visible to our naked eye, thus microscopes are deemed important to study them. Robert Hooke, a British scientist, was the first to use a simple microscope to examine a thin slice of oak tree bark called cork. He observed blocks of tiny packets that make up the cork and called them cells. Today, we studied that the cell is the smallest structure that can perform all activities required to sustain life. It carries out important functions such as metabolism, homeostasis, and reproduction. Why are cells so small? Does their small size have something to do with their function? 1.1. Cell Theory 4 Unit 1: Cells Size of the Cell Cells are generally small. Although they are found at the lower level in the hierarchy of the biological organization, life already exists in them. Most cells are far smaller than 1 mm, and some are even as small as 1 µm (as shown in Fig. 1.1.1). Subcellular structures and macromolecules that are smaller than a micrometer are measured in terms of nanometers. Because of this, the cell can only be viewed under the microscope to magnify its size in the field of view. Fig. 1.1.1. The diversity of cell sizes ranges from the smallest bacterial cell to the largest avian egg. Note that there are some cells that can be seen with a human's naked eye. Surface Area to Volume Ratio in Cells The cell itself is a system. The exchange of nutrients and metabolic wastes happens through its surface. A cell needs a surface area large enough relative to its volume to allow adequate nutrients to enter and sufficient waste to be eliminated. Small cells are likely to have more available surface area for the movement of these molecules. Bigger cells, by contrast, have a larger volume relative to their surface area that it gets difficult for nutrients 1.1. Cell Theory 5 Unit 1: Cells to diffuse to the center and the wastes to be eliminated. As the size of a cell increases, its volume also increases at a greater rate than its surface area, which then decreases its surface area to volume ratio. On the other hand, if the size of the cell is smaller, its volume decreases at a slower rate than its surface area, which then increases its surface area to volume ratio. The surface area of bigger cells becomes inadequate for the exchange of materials that their volume requires. Surface area to volume ratio is important that it favors a smaller cell size in terms of the efficiency of the movement of molecules. Having a large surface area to volume ratio is important to the functioning of the cells as most processes require molecules obtained from external sources and involve the production of wastes. Fig. 1.1.2. The small size of cells provides them with a relatively higher ratio of surface area to volume. A living entity may maintain the same total volume, but having small cells will allow it to have a greater surface area available for the movement of molecules. 1.1. Cell Theory 6 Unit 1: Cells Shown in Fig. 1.1.2 is a comparison of the surface area to volume ratio of a small box (one-unit dimension) and a big box (five-unit dimension). The larger box is shown to have a smaller surface area to volume ratio compared with the smaller one. Despite its relatively larger volume, the bigger box would be deemed inefficient in terms of the movement of molecules because of the consequent decrease in the surface area. By contrast, the formation of smaller unit boxes from the same large box will maintain volume but significantly increase the total surface area. It should also be emphasized that an organism can still increase its total volume (as shown during growth and development) while maintaining a smaller cell size along the process. General Functions of the Cell The cell is a basic feature in any living organism, from the unicellular bacteria, protists, and yeast, to more complex multicellular forms such as plants and animals. It is the smallest unit that exhibits different attributes of life. In multicellular organisms, cells are more specialized—they are committed to performing particular functions (such as in Fig. 1.1.3) that contribute to the overall maintenance of the interacting systems in these organisms. Fig. 1.1.3. Cells may devote themselves to specialized functions that will contribute to the survival of the organism. 1.1. Cell Theory 7 Unit 1: Cells Regulation of the Internal Environment An organism’s ability to keep a constant internal state is called homeostasis. Homeostasis involves constant adjustments as the internal and external conditions of the cell continuously change. Maintenance of these conditions, usually at a normal or optimal level, is important because most cells of an organism require a specific set of conditions to function normally. If conditions go beyond a particular optimal range, some cells would cease to function properly. As an example in humans, cells will only function normally at a constant internal temperature of 37 °C. During extremely cold weather, some cells, particularly the fibers of skeletal muscles, may be stimulated to contract involuntarily which results in shivering. This mechanism allows the body to generate heat (or thermogenesis) during cold weather to allow bodily chemical reactions to normally take place. On the other hand, perspiration involves water evaporation through the skin to cool down the body temperature during hot seasons. The sweat glands in the skin release water that covers the body and instantly serve as the cooling system to remove excess heat in the body. Homeostasis is exhibited in the attempt of the body to use its cells to return the temperature to a normal range. Shivering generates metabolic heat while perspiration serve as the cooling system to remove excess heat in the body. 1.1. Cell Theory 8 Unit 1: Cells Acquisition and Utilization of Energy Cells acquire energy from the nutrients in food that organisms consume. This chemical energy is stored in the bonds present in food molecules, and it will be converted by the cells into more usable forms. Energy is needed by cells to drive most of the chemical reactions and other functions in the organism’s body. For example, energy is constantly needed for the heart muscles to continuously pump blood throughout our bodies. Energy is also needed in other bodily functions such as the breakdown of macromolecules during digestion, the contraction of skeletal muscles to initiate motion, and for the cells of the nervous system to conduct information. Cells, too, invest energy to release more energy from the food molecules they metabolize. Responsiveness to Their Environment The cell’s environment changes constantly and rapidly. To survive, cells also respond to various signals that indicate any form of change in their environment. These changes may include the shift in the activities of enzymatic molecules, chemicals that pass through the cell membrane, and signals to various membrane-transport processes. Responsiveness is related to homeostasis. A cell must first be able to determine the changes that have taken place before deciding the necessary responses that will ultimately result in the maintenance of normal internal conditions. One classical example is the pigmented cells in the skin of humans. Whenever these cells are exposed to ultraviolet radiation from the sun, they synthesize and release more pigment to impart protection to the underlying cells especially UV radiation that can damage DNA. A tanned skin means more pigment is released in that area to impart protection to the underlying cells especially UV radiation that can damage DNA. 1.1. Cell Theory 9 Unit 1: Cells Protection and Support Cells protect and support their internal environment through their cellular membranes. The chemicals outside the cells could affect or influence normal cellular processes. Cells may form linings of organs to serve as the first line of defense from the external environment. In addition, some specialized cells, particularly immune cells in complex multicellular animals, also impart protection against pathogens and other foreign bodies that may enter the general circulation. History of the Development of Cell Theory Historically, the cell theory was proposed to disprove the spontaneous generation theory. It is now universally accepted even though it is still a theory. But how does cell theory develop from a mere idea to how it is being widely discussed and accepted today? Table 1.1.1. Timeline of the history of the development of the cell theory Scientist Involved Contribution The discovery of the cell as the basic unit of life involves different scientists. Hans Janssen and his son, Zacharias Janssen, invented the first primitive Zacharias Janssen microscope which (1585–1632) was used to view He invented the first microscopic cells. primitive microscope. 1.1. Cell Theory 10 Unit 1: Cells Robert Hooke was the first to observe the cells by using cork from the bark of an oak tree under the microscope. Robert Hooke (1635–1703) He observed microscopic cork cells. The experiment of Francesco Redi during his time disproved the long-believed theory of spontaneous generation, which states that life Francesco Redi comes from (1626–1697) inanimate objects. He disproved spontaneous generation. Anton Van Leeuwenhoek was the first to see and describe microorganisms from a drop of Anton Van Leeuwenhoek water by using his (1632–1723) self-made practical microscope. He made his own microscope. 1.1. Cell Theory 11 Unit 1: Cells Matthias Schleiden is one of the proponents of cell theory who stated that plants are Matthias Schleiden made up of cells and that the cell is (1804–1881) the basic unit of life. He proposed that all plants are made up of cells. Theodor Schwann is also a proponent of cell theory who stated that all organisms are made Theodor Schwann up of cells. (1810–1882) proposed that animals are made up of cells. Rudolf Virchow another proponent of the cell theory who stated that cells come from preexisting cells. Through successive cell division, many Rudolf Virchow cells can be (1821–1902) produced from a single cell. 1.1. Cell Theory 12 Unit 1: Cells How do you think were the works of different scientists compiled and synthesized to develop the cell theory? Principles of Cell Theory During the 19th century, microscopes continued to improve helping scientists to observe the details of the nucleus and other subcellular structures. Matthias Schleiden, a German botanist states that the cell is the fundamental structure of life. Theodor Schwann, a German physician, proposed that all living organisms are made up of cells. They used their observations of many different plant and animal cells to formulate the cell theory which originally had two components. German physiologist, Rudolf Virchow, added the third component, which states that cells come from preexisting cells. Like any scientific theory, cell theory (summarized in Table 1.1.2) is potentially falsifiable, but many studies support each of its components, which makes it one of the most powerful ideas in biology. Table 1.1.2. The three principles of cell theory Principles of the Cell Theory Proponent 1. Every living organism consists of one or more cells. Theodor Schwann 2. The cell is the fundamental unit of life. It is the smallest Matthias Schleiden structural and functional unit of all organisms. 3. Cells come from preexisting cells. Cells contain hereditary material, which they pass to their offspring Rudolf Virchow when they divide. 1.1. Cell Theory 13 Unit 1: Cells The Cell as a Common Feature among All Organisms Unicellular organisms consist of only one cell but are already considered living organisms. Examples include bacteria, most protists, and yeasts. These unicellular organisms can function and regulate independently as living organisms. All of the cellular processes needed for their survival take place inside the cell, most of which are biochemical reactions that allow them to process the molecules they directly obtain from their environment to acquire energy. Living organisms are divided into six kingdoms (but other classification systems can range from five to eight kingdoms). Kingdom Archaea consists of the archaebacteria. These prokaryotic cells thrive in extreme environments such as sulfuric lakes and hydrothermal vents. Bacterial species that usually cause diseases to humans belong to the Kingdom Eubacteria. Although not all bacteria are harmful, the kingdom Eubacteria also consists of good or nonpathogenic bacteria. Kingdom Protista consists of unicellular organisms that are animal-like, plant-like, and fungus-like. These organisms do not have the characteristics of true animals, true plants, or true fungi. Kingdom Fungi consists of organisms such as mushrooms, molds, and mildews. Some mushrooms are harmful, but some are edible. Kingdom Plantae consists of plants, and Kingdom Animalia consists of animals, the members of which include complex multicellular organisms. Organisms, from unicellular forms, such as in paramecium (left), to multicellular forms, such as in plants (right), are made of cells. The images shown above are microscopic views of these representative organisms. 1.1. Cell Theory 14 Unit 1: Cells The Cell as the Fundamental Unit of Life In the hierarchy of biological organization, the cell is the basic level that exhibits all the important attributes of life. These attributes include metabolism, responsiveness, reproduction, energy processing, and homeostasis. It is at the level of the cell that important biochemical reactions take place to keep living organisms alive. Cells process molecules to release energy that can be used to fuel and drive other cellular processes. Cells work together (for multicellular organisms) to maintain balance among the different organ systems and to provide an optimal physical and chemical environment for cellular reactions to proceed. For more complex organisms, cells may be more specialized to perform particular functions. Plants cells, such as in this microscopic view, perform various functions that contribute to the survival of the entire plant. The Cell as a Product of Preexisting Cells Louis Pasteur, who conclusively ended the long-believed theory of spontaneous generation, designed an experiment involving sterile nutrient broth, i.e., he tried to kill all microorganisms in it through heating. He tested whether microbes could arise from preexisting ones or if they would generate spontaneously. He had two setups in his experiment, each of which consisted of nutrient broth. He utilized the curve-necked flasks (or swan-necked flasks) and then boiled the broth to kill any existing microbe. After sterilizing, Pasteur broke off the neck of one of the flasks, which exposed the broth to the air and dust particles, while the other flask remained intact. Over time, the broth of the flask 1.1. Cell Theory 15 Unit 1: Cells with a broken neck becomes cloudy and teeming with microorganisms. By contrast, the intact flask remained clear. In conclusion, Pasteur’s experiment proved that microorganisms, and living cells in general, cannot arise from nonliving matter such as dust particles. Reproduction, being one of the major attributes of life, is exhibited at the cellular level through cell division. Cells can only come from preexisting cells similar to how bacterial and yeast cells produce their daughter cells through binary fission. Another example is the fusion of an egg cell and a sperm cell to form a fertilized cell called zygote which will undergo further division to give rise to complex multicellular organisms such as humans. Which among the three principles of the cell theory can be practically applied in healthcare by promoting the use of sterilization and disinfection? Why do you think so? 1.1. Cell Theory 16 Unit 1: Cells Bacterial cells are unicellular organisms that can multiply rapidly through binary fission. During this mode of reproduction, the parent cell divides into two daughter cells. The daughter cells possess DNA identical to that of the parent cell. Some bacterial species are pathogenic, which means they can cause different diseases to other living organisms such as humans, animals, and plants. Because of this property, harmful bacteria can multiply rapidly in a certain environment if proper sanitation and disinfection will not be observed. To avoid diseases from spreading, it is important to practice proper sanitation and disinfection at all times. Did You Know? The cell theory already has a modern version. The modern version of the cell theory includes the following principles: Energy flow occurs within the cell. The DNA of the cell is passed from cell to cell. All cells have similar basic cellular chemical composition. Key Points _____________________________________________________________________________________ Cells are generally small in size that they can only be viewed and magnified through the use of a microscope. Cells have a high surface area to volume ratio to ensure that they get adequate nutrients and to prevent a high concentration of wastes from accumulating. Generally, cells function for support and protection, regulation of the internal environment, response to external stimuli, and acquisition and utilization of energy for cellular activities. Different scientists were involved in the development of the cell theory before it was finalized into three major statements. The principles of the cell theory disproved the long-held belief of many scientists about the theory of spontaneous generation. 1.1. Cell Theory 17 Unit 1: Cells ___________________________________________________________________________________ Check Your Understanding A. Compare and contrast the theory of spontaneous generation from the principles of cell theory. Create a Venn diagram to show their similarities and differences. Provide two unique characteristics on each theory and one similarity. 1.1. Cell Theory 18 Unit 1: Cells B. Below are five of the contributions to the development of the cell theory. Identify the scientist described in each of the following items. 1. He was the first to observe the cells under the microscope. 2. His experiment disproved the spontaneous generation theory. 3. He proposed that the cell is the basic unit of plants and animals. 4. He stated in the cell theory that all organisms are made up of cells. 5. He proposed the idea in the cell theory that cells come from preexisting cells. C. Arrange the following scientists according to their contribution to the timeline of the development of the cell theory. Thereafter, provide a gist of their contribution. Proponent Contribution Rudolf Virchow Francesco Redi Robert Brown Matthias Schleiden Zacharias Janssen D. Determine whether each of the following statements is true or false. Thereafter, provide a brief justification for your answer. 1. The surface area to volume ratio favors cells that are small in size. 2. In Redi’s experiment, the controlled variables which included the meat in the jar that was left open was also important to disprove the spontaneous generation theory. 1.1. Cell Theory 19 Unit 1: Cells 3. Yeast is a unicellular organism that can reproduce through binary fission, however, it does not conform to the third principle of the cell theory. 4. A bacterium is nonliving because it is just unicellular. 5. The invention of simple and practical microscopes made it possible for the cell to be discovered. Challenge Yourself Read each item carefully. Answer the questions that follow. 1. Lina, a teenager, observed one morning as she looked at the mirror that her face has a new pimple. She wondered how she got another pimple when she already pricked it a few days ago. What principle of the cell theory is related to this? 2. Anton Van Leeuwenhoek observed under the microscope a drop of water and saw moving unicellular microorganisms. How can he prove that these are also living organisms since they cannot be seen by the naked eye? 3. What aspect of Francesco Redi’s experiment proved that life cannot spontaneously arise from an inanimate object such as rotten meat? 4. A virus can easily manipulate various cellular activities once it has already invaded the host cell. Does this mean that a virus is a living organism because it can enter a cell, the fundamental unit of life? 5. Determine a real-life scenario that demonstrates one of the principles of cell theory. Provide a brief explanation as to its relationship with the principle of cell theory involved. Photo Credits Normal body temperature. Thermometer showing slightly above 36°C by Ivan Radic is licensed under CC BY 2.0 via Wikimedia Commons. Skin tanning by Onetwo1 is licensed under CC BY-SA 3.0 via Wikimedia Commons. 1.1. Cell Theory 20 Unit 1: Cells Jansen microscope by Hirannor is licensed under CC BY-SA 3.0 via Wikimedia Commons. Leeuwenhoek Microscope by Jacopo Werther is licensed under CC BY-SA 3.0 via Wikimedia Commons. CSc., Mitosis (261 10) Pressed; root meristem of Vicia faba (cells in anaphase, prophase) by Doc. RNDr. Josef Reischig is licensed under CC BY-SA 3.0 via Wikimedia Commons. Onion cells 2 by Umberto Salvagnin is licensed under CC BY 2.0 via Flickr. Mikrofoto.de-Blepharisma japonicum 15 by Frank Fox is licensed under CC BY-SA 3.0 DE via Wikimedia Commons. 3D-SIM-4 Anaphase 3 color by Lothar Schermelleh, is licensed under CC BY-SA 3.0 via Wikimedia Commons. Bibliography Hoefnagels, Marielle. Biology: The Essentials. 2nd ed. McGraw-Hill Education, 2016. Mader, Sylvia S., and Michael Windelspecht. Biology. 11th ed. McGraw-Hill Education, 2014. Reece, Jane B, Martha R. Taylor, Eric J. Simon, Jean L. Dickey, and Kelly Hogan. Biology Concepts and Connections. 8th ed. Pearson Education South Asia Pte Ltd., 2016. Simon, Eric J., and Jane B. Reece. Campbell Essential Biology. 5th ed. Pearson Education Inc., 2013. Starr, Cecie, Christine A. Evers, and Lisa Starr. Biology Today and Tomorrow. 4th ed. Cengage Learning Asia Pte Ltd, 2014. 1.1. Cell Theory 21