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THE CELL THEORY, STRUCTURE AND FUNCTIONS for General Biology 1 / Grade 11 Quarter 1/Week 1 1  FOREWORD This self-learning kit (SLK) is the first among the series of SLKs in General Biology 1. SLKs are designed for Senior Hi...

THE CELL THEORY, STRUCTURE AND FUNCTIONS for General Biology 1 / Grade 11 Quarter 1/Week 1 1  FOREWORD This self-learning kit (SLK) is the first among the series of SLKs in General Biology 1. SLKs are designed for Senior High School learners to gain knowledge independently in the absence of face-to-face learning instruction. Cell theory is an essential lesson in the curriculum guide to be learned by learners before moving to other topics. Cell theory provides information where the word “cell” was obtained. It also includes the role of cell in living organisms and how cell was made known in the world of science. The learners will know the scientists who have made significant contributions in the discovery of cell and the development of cell theory. The structures of the major subcellular organelles are described and the function of each is identified. Pictures are shown to instill concrete knowledge on how a cell looks like. Activities and diagrams are used to guide students in organizing concepts for better understanding of the lesson. With the guidance of parents or guardians, the learners are advised to go through the learning kit page by page in an ascending manner for an effective organization of concepts, do every activity, and answer every question honestly and sincerely. It is hoped that this SLK will make authentic learning possible. 2  OBJECTIVES: At the end of the lesson, the learners shall be able to: K: explain the postulates of the cell theory and the function of every cell organelle, S: make a model of either a plant cell or animal cell, and A: appreciate the importance of cell and its organelles by observing a healthful diet. LEARNING COMPETENCIES: ✓ Explain the postulates of the cell theory (STEM_BIO11/12-Ia-c-1) ✓ Describe the structure and function of major and subcellular organelles (STEM_BIO11/12-Ia-c-2) I. What Happened Pre-Test:Directions: In your notebook, write the letter of the best answer. 1. What are living things structurally made of? a. organs b. cells c. tissues d. all of the above 2. What is the basic unit of life? a. organs b. cells c. tissues d. all of the above 3. Where do cells come from? a. plants b. animals c. preexisting cells d. mitosis 4. What was used to study about cells? a. hand lens c. telescope b. electron microscope d. compound microscope 5. Where was the term “cell” coined from? a. plant tissue c. sperm specimen b. box-like structure in cork tissue d. animal tissue 6. The following are the three main parts of a cell except _______. a. nucleus b. cytoplasm c. cell wall d. cell membrane 7. What is the common shape of an animal cell? a. round b. rectangular c. square d. no fixed shape 8. Where are the organelles of a cell located? a. nucleus c. cell membrane b. cytoplasm d. scattered anywhere 9. What organelle is known as the “control center” of the cell? a. cell membrane b. mitochondria c. cytoplasm d. nucleus 10. What regulates the passage of materials into and out of the cell? a. cell wall b. cell membrane c. nucleus d. proteins 3 II. What I Need To Know Cell Theory (Adapted from Gen. Bio. 1 by Belardo et al., Functional Biology by L.M. Rabago, and Biology by Capco & Yang) A theory is a set of propositions describing the operation and causes of natural phenomena. Cell theory describes where the term “cell” and the other basic information about the cell came from. Cell is the basic unit of life. It is the building block of all organisms. There are organisms that are made up of only one cell called unicellular organisms. Others are composed of many cells known as multicellular organisms. But, even the life of a very huge multicellular organism begins with a single cell – a sperm cell and an egg cell. How are these concepts about the cell made known? The idea about the cell came up as a result of different studies conducted by several biologists from different countries of the world for about 300 years. A few of these significant studies are as follows: Hans and Zacharias Jansen, Dutch inventors, made the first simple microscope in 1590. Robert Hooke, an Englishman, gave the term “cell” for the box-like structures observed in a Figure 1: Cork cells cork tissue under the microscope in 1667. Photo taken by L. A. De La Zerna Around 1675, Anton van Leeuwenhoek, a Dutch naturalist, observed sperm cells, red blood cells, bacteria, and other microscopic organisms in rainwater after his invention of a more powerful microscope. A nucleus was observed within some of the red blood cells. Matthias Schleiden, a German botanist, studied plant structures under the microscope. In 1838, he stated that all plants are composed of cells. In 1839, it was concluded that all animals Figure 2: Plant cells Photos taken by L.A. De La Zerna are composed of cells by Theodore Schwann, a German zoologist. He studied on animal tissues. Jointly, Schleiden and Schwann proposed that all living things are made up of cells. Roughly, 20 years later, in 1855, Rudolf Virchow, a German biologist, observed dividing cells during his work. Such observation made him conclude that all living cells come from preexisting cells. 4  Eventually, unifying all the discoveries and other advanced studies conducted, the cell theory was formulated stating that: 1. All living things are structurally made up of cells. 2. The cell is the fundamental unit of life. 3. Cells come from the division of preexisting cells. Clincher: The study of cell which started from the invention of simple microscope until the development of cell theory was conducted for about 300 years by several scientists. From then on, further developments and many technologies were made that had helped humanity. Cell Structure and Functions (Adapted from Gen. Bio.1 by Belardo et al., Functional Biology by L.M. Rabago, and Biology by Capco & Yang) All cells have three main parts: the cell membrane or plasma membrane, cytoplasm, and nucleus. cytoplasm nucleus Cell membran e Figure 3: The three main parts of a cell Cell membrane separates the internal contents of the cell from its environment. It is a phospholipid bilayer with proteins embedded in it. As a selectively permeable membrane, some substances can readily pass through it while others cannot. The three major functions performed by the cell membrane are as follows: (1) separates the contents of the cell from its environment, (2) regulates the passage of materials in and out of the cell, and (3) permits communication with other cells. The whole region within the cell membrane is the cytoplasm. Organelles are found and perform their functions in the jelly-like substance called cytosol. Various metabolic reactions like protein synthesis and breakdown of sugar into ATP take place in the cytoplasm. Other organic materials are found in the cytoplasm such as glucose and other simple sugars, polysaccharides, amino acids, nucleic acids, fatty acids, etc. Sodium, potassium, and calcium ions are also dissolved in the cytoplasm. Centrioles, cytoskeleton, and plastids are the specialized organelles in the cytoplasm. Nucleus is the third main part of the cell. It is generally oval in shape, covered with a nuclear membrane or envelope. It is the control center of the cell that regulates and coordinates all activities of the cell. Chromosomes are 5 found in the nucleus. Within the chromosomes are DNA that make up the gene that bears the hereditary traits. The cell theory states that the cell is the basic unit of life. To be able to perform its function, the cell contains cytoplasm structures called organelles. The following are the basic organelles found in the cytoplasm. Mitochondria are the sites for the breakdown of sugar molecules into adenosine triphosphate or ATP, which is the main source of energy in the body. Ribosomes are the sites of protein synthesis. The coded message from DNA as to what kind of protein is to be synthesized is carried by the mRNA from the nucleus to the ribosome. Endoplasmic reticulum (ER) consists of flattened sheets, sacs, and tubes of membranes that extend throughout the cytoplasm of eukaryotic cells. It is structurally continuous with the nuclear membrane, and it specializes in the transport of lipids and membrane proteins. A system of flattened, membrane-bound sacs that looks like stack of pancakes is the Golgi apparatus. Its function is to modify, sort, and pack macromolecules for secretion or for transport to other organelles. Rounded vesicles are associated to the Golgi apparatus that pinched off from its flattened sacs and carry the materials to other parts of the cell. Lysosome is also produced by the Golgi apparatus. It is a membrane-bound organelle that comes in various sizes and shapes. Lysosomes contain numerous hydrolytic or digestive enzymes for the breakdown of carbohydrates, proteins, and fats within the cell. Thus, they are known as “digestive sacs.” Destruction or repair of defective parts of the cell is another function of lysosomes. Another membrane-bound vesicles that contain oxidative enzymes are the peroxisomes. Enzymes responsible for oxidizing certain molecules to form hydrogen peroxide are found in peroxisomes. They are abundantly found in liver cells, where fats and lipids are metabolized. In plants, they convert fatty acids into sugars needed by growing seedlings during seed germination. Vacuoles are large storage sacs in cells. The smaller ones are called vesicles. In animals, some vacuoles function for storage of water or food, while others are for excretion of waste materials. Vacuoles in plants occupy up to 95% of the cell volume. Intracellular digestion, space filling, and control of cell turgor are some of the functions of vacuoles in plants. They contain water, 6  sugar, salts, and anthocyanin pigment. Toxic molecules are present that protect plants from herbivorous animals. Outside the nucleus of animal cells is found the centrosome. It consists of two rod-shaped centrioles which are at right angle to each other. They replicate before cell division resulting into two pairs of centrioles that later move apart becoming part of the newly formed cells. They are believed to function in the formation of spindle fibers. A network of interconnected protein filaments that extends throughout the cytoplasm is the cytoskeleton that provides the cell’s structural support. It is responsible for cell shape and motility. Plastids are large membrane-bound organelle found in plant cells. They have three classifications. The first is the chloroplast, the green-colored plastid which is caused by the green pigment called chlorophyll and is the site for photosynthesis. The second are chromoplasts, colored plastids other than green. These are specialized to synthesize and store carotenoid pigments such as red, orange, and yellow. The third are leucoplasts, the colorless plastid that contain stored food. Another organelle found in plant cells only is the cell wall. It protects and supports the cells of the plants. Figure 4: Animal Cell https://www.shutterstock.com/search/diagram+animal+cell 7  Figure 5: Plant Cell https://www.istockphoto.com/vector/plant-cell-structure-gm1155004997-314287308 Interesting Facts about Cells An average adult has around 30 trillion cells in the body. Thousands of new cells are replicated (copied) from old ones every day. Old cells that are worn-out or damaged are replaced by the new cells. To sustain the cellular and overall health is to provide raw materials which are obtained from the nutrients in the food eaten for the creation of new cells. Certain nutrients also protect the cells from damage, and nutrients in foods support the body's energy production machinery. Clincher: How well the cells function, the quality and integrity of the new cells created in the body, depend on the nutrients provided to the cells on a daily basis. In short, following a healthful diet help maintain cells and avoid chronic diseases. 8