Grade 12 Biology I - The Cell PDF

Grade 12 BIOLOGY I LESSON 1 THE CELL Learning Outcomes 1) Trace the beginnings of the discovery of the cell and the development of cell theor...

Grade 12 BIOLOGY I LESSON 1 THE CELL Learning Outcomes 1) Trace the beginnings of the discovery of the cell and the development of cell theory; 2) Identify the parts of a cell and describe the function of each cell part; 3) Differentiate prokaryotic and eukaryotic cells; 4) Compare plant and animal cell. 5) Construct a three-dimensional model of animal or plant cell; INTRODUCTION TO THE CELL DISCOVERY OF CELLS The history of the cell started with the invention of the microscope in the 1600s. Because of the limitations of the human eye, scientists during this period concentrated on developing tools to examine very small objects. ROBERT HOOKE (1635-1703), an Englishman, coined the term cell and was responsible for the beginnings of cytology as a subdiscipline in biology. ANTONIE VAN LEEUWENHOEK (1632-1723), Dutch naturalist, discovered bacteria and other microscopic organisms in rainwater and studied the structure of plant and animal cells. ROBERT BROWN (1773-1858), a Scottish botanist, discovered the presence of nuclei within cells. FELIX DUJARDIN, a Frenchman, noted that all living things contain a thick jelly fluid which he called sarcode at that time. MATTHIAS SCHLEIDEN (1804-1881) and THEODOR SCHWANN (1810-1882), German botanist and zoologist, respectively, introduced the concept that all plants and animals are made up of cells. JOHANNES PURKINJE (1787-1869), a Czechoslovakian, coined the term protoplasm to refer to the living matter of the cell. RUDOLF VIRCHOW (1821-1902), a German physician, found that cells divide to form new cells. He concluded that "omnis cellula e cellula" or cells come from preexisting cells LEARNER’S MODULE |1  Grade 12 BIOLOGY I CELL THEORY The discoveries of Schleiden, Schwann, and Virchow are summarized into a guiding principle now called the cell theory. The cell theory states that: 1. All organisms are composed of one or more cells. 2. The cell is the basic unit of structure and function of all organisms. 3. All cells arise only from pre-existing cells. The three statements that comprise the cell theory tell you that the cell is the basic structural, functional, and reproductive unit of all organisms. It also provides the operational definition of "life”. The cell being the organism itself, forms the structure, carries out the functions of the organism, and takes responsibility for reproduction. An adult human is estimated to have at least 70 to 100 trillion cells divided into about 200 different tissues. These cells form the structures of the body and the cells act together to help it function. CELL DIVERSITY o Not all cells are alike. Even cells within the same organism show enormous diversity in size, shape, and internal organization. o Some organisms such as amoeba, euglena, and paramecium contain only one cell. They are called Unicellular. o Other organisms are made up of many cells and are known to be multicellular. CELL SIZE o A few types of cells are large enough to be seen by the unaided eye. The human egg (ovum) is the largest cell in the body, and can (just) be seen without the aid of a microscope. o Most cells are small for two main reasons: a). The cell’s nucleus can only control a certain volume of active cytoplasm. b). Cells are limited in size by their surface area to volume ratio. o A group of small cells has a relatively larger surface area than a single large cell of the same volume. This is important because the nutrients, oxygen, and other materials a cell requires must enter through it surface. As a cell grows larger at some point its surface area becomes too small LEARNER’S MODULE |2 Grade 12 BIOLOGY I to allow these materials to enter the cell quickly enough to meet the cell's need. CELL SHAPE o Cells come in a variety of shapes – depending on their function:- The neurons from your toes to your head are long and thin; Blood cells are rounded disks, so that they can flow smoothly. INTERNAL ORGANIZATION o Cells contain a variety of internal Fig2.2 Cells in different sizes/structures structures called organelles. o An organelle is a cell component that performs a specific function in that cell. o Just as the organs of a multicellular organism carry out the organism's life functions, the organelles of a cell maintain the life of the cell. o There are many different cells; however, there are certain features common to all cells. o The entire cell is surrounded by a thin cell membrane. All membranes have the same thickness and basic structure. o Organelles often have their own membranes too – once again, these membranes have a similar structure. o The nucleus, mitochondria and chloroplasts all have double membranes, more correctly called envelopes. o Because membranes are fluid mosaics, the molecules making them up – phospholipids and proteins- move independently. o The proteins appear to ‘float’ in the phospholipids bilayer and thus membranes can thus be used to transport molecules within the cell e.g. endoplasmic reticulum. o Proteins in the membrane can be used to transport substances across the membrane – e.g. facilitated diffusion or by active transport. o The proteins on the outside of cell membranes identify us as unique. PROKARYOTES VS. EUKARYOTES ✓ Organisms whose cells normally contain a nucleus are called Eukaryotes; those (generally smaller) ✓ organisms whose cells lack a nucleus and have no membrane-bound organelles are known as prokaryotes. LEARNER’S MODULE |3 Grade 12 BIOLOGY I Main Difference Between Prokaryotes and Eukaryotes CELL STRUCTURE AND ORGANIZATION ✓ Cell Membrane o A cell cannot survive if it is totally isolated from its environment. The cell membrane is a complex barrier separating every cell from its external environment. o This "Selectively Permeable" membrane regulates what passes into and out of the cell. o The cell membrane is a fluid mosaic of proteins floating in a phospholipid bilayer. o The cell membrane functions like a gate, controlling which molecules can enter and leave the cell. o The cell membrane controls which substances pass into and out of the cell. Carrier proteins in or on the membrane are specific, only allowing a small group of very similar molecules through. For instance, α- glucose is able to enter; but β LEARNER’S MODULE |4 Grade 12 BIOLOGY I – glucose is not. Many molecules cannot cross at all. For this reason, the cell membrane is said to be selectively permeable. o The rest of the cell membrane is mostly composed of phospholipid molecules. They have only two fatty acid ‘tails’ as one has been replaced by a phosphate group (making the ‘head’). o The head is charged and so polar; the tails are not charged and so are non-polar. Thus, the two ends of the phospholipid molecule have different properties in water. The phosphate head is hydrophilic and so the head will orient itself so that it is as close as possible to water molecules. The fatty acid tails are hydrophobic and so will tend to orient themselves away from water. o So, when in water, phospholipids line up on the surface with their phosphate heads sticking into the water and fatty acid tails pointing up from the surface. o Cells are bathed in an aqueous environment and since the inside of a cell is also aqueous, both sides of the cell membrane are surrounded by water molecules. o This causes the phospholipids of the cell membrane to form two layers, known as a phospholipid bilayer. In this, the heads face the watery fluids inside and outside the cell, whilst the fatty acid tails are sandwiched inside the bilayer. o The cell membrane is constantly being formed and broken down in living cells. Fig 2.4. The cell membrane made up of phospholipid bilayer Fig 2.3. Fluid mosaic model ✓ Cytoplasm o Everything within the cell membrane which is not the nucleus is known as the cytoplasm. o Cytosol is the jelly-like mixture in which the other organelles are suspended, so cytosol + organelles = cytoplasm. LEARNER’S MODULE |5 Grade 12 BIOLOGY I o Organelles carry out specific functions within the cell. In Eukaryotic cells, most organelles are surrounded by a membrane, but in Prokaryotic cells there are no membrane-bound organelles. ✓ Nucleus o contains the genetic material, DNA, which determines the characteristics of a cell and directs the production of proteins o within the nucleus the DNA is organized along with proteins into material called chromatin o Nucleolus- where components of ribosomes are synthesized and assembled o Nuclear envelope: Double membrane with pores o Nucleoplasm: semifluid medium inside the nucleus. o When a nucleus prepares to divide, the Fig.2.5 The nucleus and its envelope nucleolus disappears. ✓ Mitochondria o Mitochondria are found scattered throughout the cytosol, and are relatively large organelles. o Mitochondria are the sites of aerobic respiration, in which energy from organic compounds is transferred to ATP. For this reason, they are sometimes referred to as the ‘powerhouse’ of the cell. o ATP is the molecule that most cells use as their main energy ‘currency’. o Mitochondria are more numerous in cells that have a high energy requirement - our muscle cells contain a large number of mitochondria, as do liver, heart and sperm cells. o Mitochondria are surrounded by two membranes: A. The smooth outer membrane serves as a boundary between the mitochondria and the cytosol. B. The inner membrane has many long folds, known as cristae, which greatly increase the surface area of the inner membrane, providing more space for ATP synthesis to occur. LEARNER’S MODULE |6 Grade 12 BIOLOGY I o Mitochondria have their own DNA, and new mitochondria arise only when existing ones grow and divide. They are thus semi-autonomous organelles. ✓ RIBOSOMES Fig.2.6 The mitochondria o Unlike most other organelles, ribosomes are not surrounded by a membrane. o Ribosomes are the site of protein synthesis in a cell. o They are the most common organelles in almost all cells. o Some are free in the cytoplasm (Prokaryotes); others line the membranes of rough endoplasmic reticulum (rough ER). Fig.2.7. The ribosome o They exist in two sizes: -70s are found in all Prokaryotes, chloroplasts and mitochondria, suggesting that they have evolved from ancestral Prokaryotic organisms. They are free- floating. - 80s found in all eukaryotic cells – attached to the rough ER (they are rather larger). o Groups of 80s ribosomes, working together, are known as a polysome. LEARNER’S MODULE |7 Grade 12 BIOLOGY I ✓ ENDOPLASMIC RETICULUM o The ER is a system of membranous tubules and sacs. o The primary function of the ER is to act as an internal transport system, allowing molecules to move from one part of the cell to another. o The quantity of ER inside a cell fluctuates, depending on the cell's activity. Cells with a lot include secretory cells and liver cells. o The rough ER is studded with 80s ribosomes and is the site of protein synthesis. It is an extension of the outer membrane of the nuclear Fig.2.8. Endoplasmic reticulum envelope, so allowing mRNA to be transported swiftly to the 80s ribosomes, where they are translated in protein synthesis. o The smooth ER is where polypeptides are converted into functional proteins and where proteins are prepared for secretion. It is also the site of lipid and steroid synthesis, and is associated with the Golgi apparatus. Smooth ER has no 80s ribosomes and is also involved in the regulation of calcium levels in muscle cells, and the breakdown of toxins by liver cells. In the testes, it produces testosterone and, in the liver, it helps detoxify drugs o Both types of ER form vesicles that transport materials throughout the cell. ✓ GOLGI APPARATUS o The Golgi apparatus is the processing, packaging and secreting organelle of the cell, so it is much more common in glandular cells. o The Golgi apparatus is a system of membranes, made of flattened sac-like structures called cisternae. o It works closely with the smooth er, to modify proteins for export by the cell. Fig.2.9. Golgi Apparatus ✓ LYSOSOMES o Lysosomes are small spherical organelles that enclose hydrolytic enzymes within a single membrane. o Lysosomes are the site of protein digestion – thus allowing enzymes to be re-cycled when they are no longer required. They are also the site of food digestion in the cell, and of bacterial digestion in phagocytes. o Lysosomes are formed from pieces of the Golgi apparatus that break off. Fig.2.10. Lysosome o Lysosomes are common in the cells of Animals, Protoctista and even Fungi, but rare in plants LEARNER’S MODULE |8 Grade 12 BIOLOGY I ✓ CYTOSKELETON o Just as your body depends on your skeleton to maintain its shape and size, so a cell needs structures to maintain its shape and size. o In animal cells, which have no cell wall, an internal framework called the cytoskeleton maintains the shape of the cell, and helps the cell to move. Fig.2.11. Cytoskeleton o The cytoskeleton consists of three structures: a) microfilaments (contractile). They are made of actin, and are common in motile cells. b) microtubules (rigid, hollow tubes – made of tubulin). c) intermediate filaments (ropelike assemblies of fibrous polypeptide) o Microtubules have three functions: a) To maintain the shape of the cell. b) To serve as tracks for organelles to move along within the cell. c) They form the centriole ✓ CENTRIOLE o This consists of two bundles of microtubules at right- angles to each other. o Each bundle contains 9 tubes in a very characteristic arrangement o At the start of mitosis and meiosis, the centriole divides, and one half moves to each end of the cell, forming the spindle. o The spindle fibres are later shortened to pull the chromosomes apart. ✓ CILIA AND FLAGELLA Fig.2.12. Centriole o Cilia and Flagella are structures that project from the cell, where they assist in movement. o Cilia (sing. cilium) are short, and numerous and hair-like. o Flagella (sing. flagellum) are much longer, fewer, and are whip-like. o The cilia and flagella of all Eukaryotes are always in a ‘9 + 2’ arrangement o Protists commonly use cilia and flagella to move through water. o Sperm use flagella (many, all fused together) to swim to the egg. LEARNER’S MODULE |9 Grade 12 BIOLOGY I o Cilia line our trachea and bronchi, moving dust particles and bacteria away from the lungs Fig.2.13. Cross section of cilium Fig.2.14 Flagellum PLANT CELL STRUCTURES Fig 2.15. Plant cell wall o Most of the organelles and other parts of the cell are common to all Eukaryotic cells. Cells from different organisms have an even greater difference in structure. o Plant cells have three additional structures not found in animal cells: Cellulose cell walls Chloroplasts (and other plastids) A central vacuole. ✓ CELLULOSE CELL WALL o One of the most important features of all plants is presence of a cellulose cell wall. o Fungi such as Mushrooms and Yeast also have cell walls, but these are made of chitin. o The cell wall is freely permeable (porous), and so has no direct effect on the movement of molecules into or out of the cell. o The rigidity of their cell walls helps both to support and protect the plant. o Plant cell walls are of two types: a). Primary (cellulose) cell wall - While a plant cell is being formed, a middle lamella made of pectin, is formed and the cellulose cell wall develops between the middle lamella and the cell membrane. As the cell expands in length, more cellulose is added, enlarging the cell wall. When the cell reaches full size, a secondary cell wall may form. b). Secondary (lignified) cell wall - The secondary cell wall is formed only in woody tissue (mainly xylem). The secondary cell wall is stronger and waterproof. LEARNER’S MODULE | 10 Grade 12 BIOLOGY I ✓ VACUOLES o The most prominent structure in plant cells is the large vacuole. o The vacuole is a large membrane-bound sac that fills up much of most plant cells. o The vacuole serves as a storage area, and may contain stored organic molecules as well as inorganic ions. o The vacuole is also used to store waste. Since plants have no kidney, they convert waste to an insoluble form and then store it in their vacuole - until autumn! Fig 2.16. Vacuole o The vacuoles of some plants contain poisons (eg tannins) that discourage animals from eating their tissues. o Whilst the cells of other organisms may also contain vacuoles, they are much smaller and are usually involved in food digestion. ✓ CHLOROPLASTS (and other plastids) o A characteristic feature of plant cells is the presence of plastids that make or store food. o The most common of these (some leaf cells only!) are chloroplasts – the site of photosynthesis. o Each chloroplast encloses a system of flattened, membranous sacs called thylakoids, which contain chlorophyll. o The thylakoids are arranged in stacks called grana. o The space between the grana is filled with Fig 2.16. Chloroplast cytoplasm like stroma. o Chloroplasts contain ccc DNA and 70S ribosomes and are semi-autonomous organelles. o Other plastids store reddish-orange pigments that color petals, fruits, and some leaves LEARNER’S MODULE | 11  Grade 12 BIOLOGY I Activity Performance Task: 1. Create a three-dimensional model of an animal cell or plant cell using indigenous or recyclable materials found at home. Afterwards, make a 2-3-minute presentation featuring your model and the materials used in forming it. 2. Fill in the following matrix with the details required. Structure Function Material used Why in Model Material Used? 1. Ribosomes 2. Nucleus 3. Vacuoles 4.Endoplasmic Reticulum 5. Mitochondria 6.Cell Membrane 7. Cytoskeleton 8. Golgi Bodies *Note: Quiz will be posted in the group chat via google forms. LEARNER’S MODULE | 12  Grade 12 BIOLOGY I LESSON 2 MITOCHONDRIA AND CHLOROPLASTS Learning Outcomes 1) Explain the role of ATP in life processes. 2) Compare mitochondria and chloroplast. 3) Illustrate the structure of the mitochondria, label its parts, and give the importance of the enfolding of the inner mitochondrial membrane 4) Illustrate the structure of the chloroplast, label its parts, and relate these parts to photosynthesis Adenosine Triphosphate (ATP) o It is the major energy currency of the cell that provides the energy for most of the energy-consuming activities of the cell. o The ATP regulates many biochemical pathways. Mechanism: When the third phosphate group of ATP is removed by hydrolysis, a substantial amount of free energy is released. ATP + H2O → ADP + Pi where ADP is adenosine diphosphate and Pi is inorganic phosphate. Fig.2.1 Energy release in Hydrolysis LEARNER’S MODULE | 13  Grade 12 BIOLOGY I Fig.2.2 Chemical Energy and ATP Synthesis of ATP ADP + Pi → ATP + H2O requires energy: 7.3 kcal/mole occurs in the cytosol by glycolysis occurs in mitochondria by cellular respiration occurs in chloroplasts by photosynthesis Consumption of ATP ATP powers most energy-consuming activities of cells, such as: anabolic (synthesis) reactions, such as: joining transfer RNAs to amino acids for assembly into proteins synthesis of nucleoside triphosphates for assembly into DNA and RNA synthesis of polysaccharides synthesis of fats active transport of molecules and ions conduction of nerve impulses maintenance of cell volume by osmosis addition of phosphate groups (phosphorylation) to different proteins (e.g., to alter their activity in cell signaling) muscle contraction beating of cilia and flagella (including sperm) bioluminescence Extracellular ATP In mammals, ATP also functions outside of cells. ATP is released in the following examples: from damaged cells to elicit inflammation and pain from the carotid body to signal a shortage of oxygen in the blood from taste receptor cells to trigger action potentials in the sensory nerves leading back to the brain LEARNER’S MODULE | 14  Grade 12 BIOLOGY I from the stretched wall of the urinary bladder to signal when the bladder needs emptying In eukaryotic cells, the mitochondria and chloroplasts are the organelles that convert energy to other forms which cells can use for their functions. Mitochondria (singular, mitochondrion) o Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels. o The mitochondria are oval-shaped organelles found in most eukaryotic cells. o They are considered to be the ‘powerhouses’ of the cell. o As the site of cellular respiration, mitochondria serve to transform molecules such as glucose into an energy molecule known as adenosine triphosphate (ATP). o ATP fuels cellular processes by breaking its high-energy chemical bonds. Mitochondria are most plentiful in cells that require significant amounts of energy to function, such as liver and muscle cells. The mitochondria has two membranes that are similar in composition to the cell membrane: Outer membrane —is a selectively permeable membrane that surrounds the mitochondria. It is the site of attachment for the respiratory assembly of the electron transport chain and ATP Synthase. It has integral proteins and pores for transporting molecules just like the cell membrane Function: fully surrounds the inner membrane, with a small intermembrane space in between has many protein-based pores that are big enough to allow the passage of ions and molecules as large as a small protein Inner membrane —folds inward (called cristae) to increase surfaces for cellular metabolism. It contains ribosomes and the DNA of the mitochondria. The inner membrane creates two enclosed spaces within the mitochondria: intermembrane space between the outer membrane and the inner membrane; matrix that is enclosed within the inner membrane. Function: has restricted permeability like the plasma membrane is loaded with proteins involved in electron transport and ATP synthesis surrounds the mitochondrial matrix, where the citric acid cycle produces the electrons that travel from one protein complex to the next in the inner membrane. At the end of this electron transport chain, the final electron acceptor is oxygen, and this ultimately forms water (H20). At the same time, the electron transport chain produces ATP in a process called oxidative phosphorylation. During electron transport, the participating protein complexes push protons from the matrix out to the intermembrane space. This creates a concentration gradient of protons LEARNER’S MODULE | 15  Grade 12 BIOLOGY I that another protein complex, called ATP synthase, uses to power synthesis of the energy carrier molecule ATP. Chloroplasts o Chloroplasts, which are found in plants and algae, are the sites of photosynthesis. o This process converts solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water. o The word chloroplast is derived from the Greek word chloros which means ‘green’ and plastes which means ‘the one who forms’. o The chloroplasts are cellular organelles of green plants and some eukaryotic organisms. These organelles conduct photosynthesis. They absorb sunlight and convert it into sugar molecules. o They also produce free energy stored in the form of ATP and NADPH through photosynthesis. o Chloroplasts are double membrane-bound organelles and are the sites of photosynthesis. The chloroplast has a system of three membranes: the outer membrane, the inner membrane, and the thylakoid system. The outer and the inner membranes of the chloroplast enclose a semi-gel-like fluid known as the stroma. The stroma makes up much of the volume of the chloroplast. The thylakoid system floats in the stroma. Structure of the Chloroplast Outer membrane —This is a semi-porous membrane and is permeable to small molecules and ions which diffuse easily. The outer membrane is not permeable to larger proteins. Intermembrane Space —This is usually a thin intermembrane space about 10-20 nanometers and is present between the outer and the inner membrane of the chloroplast. Inner membrane —The inner membrane of the chloroplast forms a border to the stroma. It regulates passage of materials in and out of the chloroplast. In addition to the regulation activity, fatty acids, lipids and carotenoids are synthesized in the inner chloroplast membrane. Stroma —This is an alkaline, aqueous fluid that is protein-rich and is present within the inner membrane of the chloroplast. It is the space outside the thylakoid space. The chloroplast DNA, chloroplast ribosomes, thylakoid system, starch granules, and other proteins are found floating around the stroma. Thylakoid System —is suspended in the stroma. It is a collection of membranous sacks called thylakoids. Thylakoids are small sacks that are interconnected. The membranes of these thylakoids are the sites for the light reactions of the photosynthesis to take place. The chlorophyll is found in the thylakoids. The thylakoids are arranged in stacks known as grana. Each granum contains around 10-20 thylakoids. The word thylakoid is derived from the Greek word thylakos which means 'sack'. Important LEARNER’S MODULE | 16  Grade 12 BIOLOGY I protein complexes which carry out the light reaction of photosynthesis are embedded in the membranes of the thylakoids. o The Photosystem I and the Photosystem II are complexes that harvest light with chlorophyll and carotenoids. They absorb the light energy and use it to energize the electrons. o The molecules present in the thylakoid membrane use the electrons that are energized to pump hydrogen ions into the thylakoid space. This decreases the pH and causes it to become acidic in nature. o A large protein complex known as the ATP synthase controls the concentration gradient of the hydrogen ions in the thylakoid space to generate ATP energy. The hydrogen ions flow back into the stroma. o Thylakoids are of two types: granal thylakoids and stromal thylakoids. Granal thylakoids are arranged in the grana. These circular discs that are about 300-600 nanometers in diameter. The stromal thylakoids are in contact with the stroma and are in the form of helicoid sheets. o The granal thylakoids contain only Photosystem II protein complex. This allows them to stack tightly and form many granal layers with granal membrane. This structure increases stability and surface area for the capture of light. o The Photosystem I and ATP synthase protein complexes are present in the stroma. These protein complexes act as spacers between the sheets of stromal thylakoids. Activity 1. Draw a mitochondrion and a chloroplast and label their parts. 2. Write an essay on probable reasons for the shared characteristics of the mitochondria and the chloroplast. What evidence supports endosymbiotic theory? *Note: Quiz will be posted in the group chat via google forms. LEARNER’S MODULE | 17  Grade 12 BIOLOGY I Lesson 3 ANIMAL TISSUES Learning Outcomes 1) Classify the different animal tissue types and specify the functions of each. 2) Relate the structure of each tissue type to their function. 3) Cite examples of animal tissues in relation to their location in a particular organ. o The human body is composed of approximately 200 distinctly different types of cells. These cells are organized into four basic tissues that, in turn, are assembled to form organs. o When you examine tissue at a microscopic level, having the ability to detect the presence and location of the four basic tissues enables you to identify the organ that you are looking at. A basic knowledge of the general characteristics and cellular composition of these tissues is essential in histology, which is the study of tissues at the microscopic level. o Structure in the living world including that of animals is organized in a series of hierarchical levels o Tissues are groups of similar cells performing a common function. There are four categories of tissues: o Epithelial tissue o Connective tissue o Nervous tissue o Muscle tissue Epithelial Tissue Fig. 2.1 Levels of Organization in the Animal Body LEARNER’S MODULE | 18  Grade 12 BIOLOGY I Epithelial tissue, or epithelium, has the following general characteristics: o Epithelium consists of closely packed, flattened cells that make up the inside or outside lining of body areas. There is little intercellular material. o The tissue is avascular, meaning without blood vessels. Nutrient and waste exchange occurs through neighboring connective tissues by diffusion. o The upper surface of epithelium is free, or exposed to the outside of the body or to an internal body cavity. The basal surface rests on connective tissue. A thin, extracellular layer called the basement membrane forms between the epithelial and connective tissue. Two kinds of epithelial tissues: ▪ Covering and lining epithelium covers the outside surfaces of the body and lines internal organs. ▪ Glandular epithelium secretes hormones or other products. Epithelial tissues that cover or line surfaces are classified by cell shape and by the number of cell layers. The following terms are used to describe these features. Cell shape: Squamous cells are flat. The nucleus, located near the upper surface, gives these cells the appearance of a fried egg. Cuboidal cells are cube‐ or hexagon‐shaped with a central, round nucleus. These cells produce secretions (sweat, for example) or absorb substances such as digested food. Columnar cells are tall with an oval nucleus near the basement membrane. These thick cells serve to protect underlying tissues or may function to absorb substances. Some have microvilli, minute surface extensions, to increase surface area for absorbing substances, while others may have cilia that help move substances over their surface (such as mucus through the respiratory tract). Transitional cells range from flat to tall cells that can extend or compress in response to body movement. Number of cell layers: Simple epithelium describes a single layer of cells. Stratified epithelium describes epithelium consisting of multiple layers. Pseudostratified epithelium describes a single layer of cells of different sizes, giving the appearance of being multilayered. Names of epithelial tissues include a description of both their shape and their number of cell layers. The presence of cilia may also be identified in their names. For example, simple squamous describes epithelium consisting of a single layer of flat cells. Pseudostratified columnar ciliated epithelium describes a single layer of tall, ciliated cells of more than one size. Stratified epithelium is named after the shape of the outermost cell layer. Thus, stratified squamous epithelium has outermost layers of squamous cells, even though some inner layers consist of cuboidal or columnar cells. LEARNER’S MODULE | 19  Grade 12 BIOLOGY I Fig 2.2 Classifying Epithelia Glandular epithelium o Glandular epithelium forms two kinds of glands: Endocrine glands secrete hormones directly into the bloodstream. For example, the thyroid gland secretes the hormone thyroxin into the bloodstream, where it is distributed throughout the body, stimulating an increase in the metabolic rate of body cells. Exocrine glands secrete their substances into tubes, or ducts, which carry the secretions to the epithelial surface. Examples of secretions include sweat, saliva, milk, stomach acid, and digestive enzymes. Exocrine glands are classified according to their structure Unicellular or multicellular describes a single‐celled gland or a gland made of many cells, respectively. A multicellular gland consists of a group of secretory cells and a duct through which the secretions pass as they exit the gland. Branched refers to the branching arrangement of secretory cells in the gland. Simple or compound refers to whether the duct of the gland (not the secretory portion) does or does not branch, respectively. Tubular describes a gland whose secretory cells form a tube, while alveolar (or acinar) describes secretory cells that form a bulblike sac. In merocrine glands, secretions pass through the cell membranes of the secretory cells (exocytosis). For example, goblet cells of the trachea release mucus via exocytosis. In apocrine glands, a portion of the cell containing secretions is released as it separates from the rest of the cell. For example, the apical portion of lactiferous glands release milk in this manner. In holocrine glands, entire secretory cells disintegrate and are released along with their contents. For example, sebaceous glands release sebum to lubricate the skin in this manner. LEARNER’S MODULE | 20  Grade 12 BIOLOGY I Fig.2.3 Types of multicellular exocrine glands Connective Tissue The following information identifies a few select features of connective tissue. Nerve supply. Most connective tissues have a nerve supply (as does epithelial tissue). Blood supply. There is a wide range of vascularity among connective tissues, although most are well vascularized (unlike epithelial tissues, which are all avascular). Structure. Connective tissue consists of scattered cells immersed in an intercellular material called the matrix. The matrix consists of fibers and ground substance. The kinds and amounts of fiber and ground substance determine the character of the matrix, which in turn defines the kind of connective tissue. Cell types. Fundamental cell types, characteristic of each kind of connective tissue, are responsible for producing the matrix. Immature forms of these cells (whose names end in blast) secrete the fibers and ground substance of the matrix. Cells that have matured, or differentiated (whose names often end in cyte), function mostly to maintain the matrix: o Fibroblasts are common in both loose and dense connective tissues. o Adipocytes, cells that contain molecules of fat, occur in loose connective tissue, as does adipose tissue. o Reticular cells resemble fibroblasts, but have long, cellular processes (extensions). They occur in loose connective tissue. o Chondroblasts and chondrocytes occur in cartilage. o Osteoblasts and osteocytes occur in bone. o Hemocytoblasts occur in the bone marrow and produce erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (formerly called thrombocytes). LEARNER’S MODULE | 21 Grade 12 BIOLOGY I o In addition to the fundamental cell types, various leukocytes migrate from the bone marrow to connective tissues and provide various body defense activities: o Macrophages engulf foreign and dead cells. o Mast cells secrete histamine, which stimulates immune responses. o Plasma cells produce antibodies. Fibers. Matrix fibers are proteins that provide support for the connective tissue. There are three types: o Collagen fibers, made of the protein collagen, are both tough and flexible. o Elastic fibers, made of the protein elastin, are strong and stretchable. o Reticular fibers, made of thin collagen fibers with a glycoprotein coating, branch frequently to form a netlike (reticulate) pattern. Ground substance. Ground substance may be fluid, gel, or solid, and, except for blood, is secreted by the cells of the connective tissue: o Cell adhesion proteins hold the connective tissue together. o Proteoglycans provide the firmness of the ground substance. Hyaluronic sulfate and chondroitin sulfate are two examples. Classification. There are five general categories of mature connective tissue: o Loose connective tissue has abundant cells among few or loosely arranged fibers and a sparse to abundant gelatinous ground substance. o Dense connective tissue has few cells among a dense network of fibers with little ground substance. o Cartilage has cells distributed among fibers in a firm gellike ground substance. Cartilage is tough but flexible, avascular, and without nerves. o Bone has cells distributed among abundant fibers in a solid ground substance containing minerals, mostly calcium phosphate. Bone is organized in units, called osteons (formerly known as the Haversian system). Each osteon consists of a central canal, which contains blood vessels and nerves, surrounded by concentric rings (lamellae) of hard matrix and collagen fibers. Branching off the central canal at right angles are perforating canals. These canals consist of blood vessels that branch off the central vessels. Between the lamellae are cavities (lacunae) that contain bone cells (osteocytes). Canals (canaliculi) radiate from the central canal and allow nutrient and waste exchange with the osteocytes. o Blood is composed of various blood cells and cell fragments (platelets) distributed in a fluid matrix called blood plasma. Tissue origin. All mature connective tissues originate from embryonic connective tissue. There are two kinds of embryonic connective tissues: o Mesenchyme is the origin of all mature connective tissues. LEARNER’S MODULE | 22 Grade 12 BIOLOGY I o Mucous connective tissue is a temporary tissue formed during embryonic development. Fig.2.4 Classes of connective tissue Fig 2.5 Cells and fiber of connective tissue proper LEARNER’S MODULE | 23  Grade 12 BIOLOGY I Fig.2.6 Hyaline cartilage Fig.2.7 Elastic cartilage Fig. 2.8. Fibrocartilage Fig.2.9 Bone Muscle Tissue There are three kinds of muscle tissues Skeletal muscle consists of long cylindrical cells that, under a microscope, appear striated with bands perpendicular to the length of the cell. The many nuclei in each cell (multinucleated cells) are located near the outside along the plasma membrane, which is called the sarcolemma. Skeletal muscle is attached to bones and causes movements of the body. Because it is under conscious control, it is also called voluntary muscle. LEARNER’S MODULE | 24 Grade 12 BIOLOGY I Cardiac muscle, like skeletal muscle, is striated. However, cardiac muscle cells have a single, centrally located nucleus, and the muscle fibers branch often. Where two cardiac muscle cells meet, they form an intercalated disc containing gap junctions, which bridge the two cells. Cardiac cells are the only cells that pulsate in rhythm. Smooth muscle consists of cells with a single, centrally located nucleus. The cells are elongated with tapered ends and do not appear striated. Smooth muscle lines the walls of blood vessels and certain organs such as the digestive and urogenital tracts, where it serves to advance the movement of substances. Smooth muscle is called involuntary muscle because it is not under direct conscious control. Fig.2.10 Skeletal muscle Fig.2.11 Cardiac muscle Fig.2.12 Smooth muscle LEARNER’S MODULE | 25  Grade 12 BIOLOGY I Nervous Tissue Nervous tissue consists of two kinds of nerve cells: Neurons are the basic structural unit of the nervous system. Each cell consists of the following parts: ▪ The cell body contains the nucleus and other cellular organelles. ▪ The dendrites are typically short, slender extensions of the cell body that receive stimuli. ▪ The axon is typically a long, slender extension of the cell body that sends stimuli. ▪ The axon branches are, typically, smaller extensions of the axon. Neuroglia, or glial cells, provide support functions for the neurons, such as insulation or anchoring neurons to blood vessels. Fig.2.13. Neural Tissue *Note: Quiz will be posted in the group chat via google forms. LEARNER’S MODULE | 26  Grade 12 BIOLOGY I LESSON 4 CELL CYCLE AND CELL DIVISION Learning Outcomes 1) characterize the phases of the cell cycle and their control points 2) describe the stages of mitosis and meiosis 3) discuss crossing over and recombination in meiosis 4) explain the significance or applications of mitosis/meiosis 5) identify disorders and diseases that result from the malfunction of the cell during the cell cycle CELL DIVISION AND GROWTH o The cells in your body constantly change. They change when substances get in and out of them. As they grow old, they are replaced by new cells; and when they are worn out, new cells are formed. An adult produces 25 million new cells every second. o New cells are formed during the process of cell division. In unicellular organisms such as bacteria, cellular division is a means to produce offspring. Bacterial cells divide, through a type of cell division called binary fission. o Binary fission is an asexual type of reproduction, where the genetic material (DNA) is copied and the cell splits. The resulting two new daughter cells, are identical in genetic content. Fig. 4.1 Binary fission o In multicellular organisms, cellular division is a means for the production of new tissues or body parts during growth and development. Even after birth, cells continue to divide for continuous growth and development of tissues. o Cellular division is likewise a means to replaceworn-out and damaged cells. The ability of a wound to heal involves cellular division. The epithelial cells that are sloughed-off when you rub your skin with a towel after taking a bath are replaced with new epithelial cells by cellular division. Cells in the digestive and respiratory tracts are also replaced by cell division every time they are damaged. Cellular division is a means to produce new individuals in asexually-reproducing organisms. The growth and development of stem- cuttings, such as santan stem and the formation of a bud are examples of asexual reproduction through cell division. o Cell division is a complex process that is divided into two distinct stages- cellular growth and maturation and cell reproduction. LEARNER’S MODULE | 27 Grade 12 BIOLOGY I CELL CYCLE o Cell cycle is a series of events that takes place in a cell as it grows and divides. It starts from the moment the cell begins to divide and ends at the beginning of the next cell division. However, growth is necessary before another cell division. o The entire cycle is divided into two main stages, interphase and M phase, where M stands for either mitosis or meiosis. The interphase is further divided into three stages: G1, S and G2 phase Fig. 4.2 Cell cycle Interphase o Portion of the cell cycle preceding mitosis in which the cell grows and carries out life functions. o The longest phase of the cell cycle ❖ G1 (Growth or Gap1) Phase o Cell at this stage is still young and it undergoes rapid growth o Organelles are formed o RNA and Proteins including enzymes needed for making DNA are synthesized ❖ S (Synthesis) Phase o DNA doubles through a process called replication o At the end of this stage, each chromosome is made up of two sister chromatids attached at the centromere. ❖ G2 (Growth or Gap 2) Phase o Final preparation of the cell for division o Assembly of proteins such as microtubules M (Mitosis or Meiosis) Phase o The cell undergoes division o The nucleus and the cytoplasm were divided o The Cell Cycle control system is driven by a built-in clock that can be adjusted by external stimuli (i.e., chemical messages). o Checkpoint—a critical control point in the Cell Cycle where ‘stop’ and ‘go- ahead’ signals can regulate the cell cycle. Animal cells have built-in ‘stop’ signals that halt the cell cycles and checkpoints until overridden by ‘go-ahead’ signals. Three major checkpoints are found in the G1, G2, and M phases of the Cell Cycle. The G1 Checkpoint—the Restriction Point LEARNER’S MODULE | 28 Grade 12 BIOLOGY I o The G1 checkpoint ensures that the cell is large enough to divide and that enough nutrients are available to support the resulting daughter cells. o If a cell receives a ‘go-ahead’ signal at the G1 checkpoint, it will usually continue with the Cell Cycle. If the cell does not receive the ‘go-ahead’ signal, it will exit the Cell Cycle and switch to a non-dividing state called G0. o Most cells in the human body are in the G0 phase. The G2 Checkpoint—ensures that DNA replication in S phase has been successfully completed. The Metaphase Checkpoint—ensures that all of the chromosomes are attached to the mitotic spindle by a kinetochore. Kinase—a protein which activates or deactivates another protein by phosphorylating them. Kinases give the ‘go-ahead’ signals at the G1 and G2 checkpoints. The kinases that drive these checkpoints must themselves be activated. o The activating molecule is a cyclin, a protein that derives its name from its cyclically fluctuating concentration in the cell. Because of this requirement, these kinases are called cyclin-dependent kinases or CDKs. o Cyclins accumulate during the G1, S, and G2 phases of the Cell Cycle. o By the G2 checkpoint, enough cyclin is available to form MPF complexes (aggregations of CDK and cyclin) which initiate mitosis. o MPF functions by phosphorylating key proteins in the mitotic sequence. o Later in mitosis, MPF switches itself off by initiating a process which leads to the destruction of cyclin. o CDK, the non-cyclin part of MPF, persists in the cell as an inactive form until it associates with new cyclin molecules synthesized during the interphase of the next round of the Cell Cycle. In instances when the cell cycle checkpoints detect abnormalities, the cell is instructed not to proceed to the next stage but instead repair the abnormality. When the abnormality or damage is beyond repair, the cell undergoes programmed cell death, called apoptosis. These mechanisms are important to ensure that all daughter cells produced are of normal structure and function. However, there are cases when the cell cycle checkpoints are not fully functioning and thus the quality of the cells produced are not properly controlled. Such malfunctions may result in unregulated cell division, which might leaad to cancer. Cancer is an abnormal growth of cells that has malignant characteristics. Cancer cells fail to respond to the signals that regulate the growth of cells. They can spread throughout the body, thus the normal functions are disrupted causing serious medical problems and eventually death. LEARNER’S MODULE | 29 Grade 12 BIOLOGY I MITOSIS Mitosis is a type of cell division in which the nucleus of the cell divides into two nuclei with identical genetic material. The resulting two daughter cells have the same number of chromosomes similar to the parent cell; thus a diploid parent cell containing two sets of chromosomes (paternal and maternal chromosome) will result in two diploid daughter cells after mitosis. Fig. 4.3 Mitosis Prophase o DNA condenses into chromosomes as they become shorter and thicker. Each chromosome consists of two identical chromatids called sister chromatids. The chromatids are attached through the centromere. o Nucler membrane disappears o In animal cells,centrioles separate and move to opposite poles and serve as basis for the formation of spindle fibers. Metaphase o Chromosomes are completely attached to the spindle fibers (kinetochore fibers) and are aligned at the center or equator. o The spindle fibers attach at opposite sides Anaphase o The sister chromatids migrate to the opposite poles of the spindle fibers due to the splitting of the centromere Telophase o The chromosomes at the pole spread out o Nuclear membrane begins to form around the chromosomes, forming two nuclei o Each nucleus goes to each cell formed o Spindle fibers break apart o Cytokinesis occurs or the division of the cytoplasm Fig. 4.4 Cytokinesis LEARNER’S MODULE | 30 Grade 12 BIOLOGY I MEIOSIS Meiosis is a type of cell division used by multicellular organisms in the formation of reproductive cells (gametes), such as sperm cells, egg cells or spores. Meiosis is similar to Mitosis in several ways. One meiotic process is also divided into the same four basic steps: prophase, metaphase, anaphase, and telophase. Like mitosis, karyokinesis is followed by cytokinesis. However, meiosis is different from mitosis in some very important ways. o Meiosis results in the production of daughter cells containing half the number of chromosomes of the parent cell. The resulting daughter cell with half the number of chromosomes is called a haploid cell. o The daughter cells that are produced after meiosis are not identical because of the manner in which the chromosomes divide o There are four daughter cells produced after one meiotic process because the parent cell divides twice in meiosis. Meiosis involves two successive cell divisions. The first part, called Meiosis I, halves the number of chromosomes from diplod to haploid number. This stage of Meiosis is called reduction division. The second part, Meiosis II, is similar to mitosis, thus it is called equational division. Both meiosis I and meiosis II are subdivided into four stages. Fig. 4.5 Meiosis I LEARNER’S MODULE | 31 Grade 12 BIOLOGY I Fig. 4.6 Meiosis II Prophase I o Chromosomes start to coil and shorten o The nuclear envelop disintegrates o Homologous chromosomes pair to form a tetrad by a process called synapsis Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids). o Crossing over occurs (segments of non-sister chromatids break and reattach to the other chromatid) The Chiasmata (chiasma) are the sites of Fig 4.7 Synapsis crossing over. Metaphase I o The paired homologous chromosomes align at the center or equator o Chromosomes in pairs are attached to spindle fibers Anaphase I o Homologous chromosomes separate o The chromosomes are pulled toward opposite poles of the cell by the Fig 4.8 Crossing over shortening spindle fibers. Telophase I o Chromosomes reach opposites poles. o In most organisms, the nuclear membrane forms. This is followed by cytokinesis. LEARNER’S MODULE | 32 Grade 12 BIOLOGY I MEIOSIS II Prophase II o The nuclear membrane disintegrates. o New spindle fibers are formed around the chromosomes. Metaphase II o The chromosomes align at the metaphase plate and the spindle fibers attach to their centromeres. Anaphase II o Each chromosome is divided into two sister chromatids. o The chromatids move to opposite poles Telophase II o Nuclear membrane is formed around each set of chromosomes. o Spindle fibers disintegrate o The cell undergoes cytokinesis. SPERMATOGENESIS o Meiosis is the main event in the process of gamete formation called gametogenesis. o Gamete formation in males, called spermatogenesis, produces sperm cells. While gamete formation in females, called oogenesis produces egg cells. o Both spermatogenesis and oogenesis involve the same steps of meiosis; thus, the resulting daughter cells are haploid cells. o The two processes differ, however, in the number of gametes produced because four functional sperm cells are produced in spermatogenesis, while only one functional ovum and three polar bodies are produced in oogenesis. Fig. 4.9 Spermatogenesis LEARNER’S MODULE | 33 Grade 12 BIOLOGY I o The gametes produced after gametogenesis are haploid cells. This number of chromosomes, however, becomes a diploid during the process of OOGENESIS fertilization, when a sperm cell fuses with an egg cell (haploid + haploid = diploid). o Thus, in organisms that undergo sexual reproduction, the diploid number of chromosomes (46 in humans) is restored during fertilization. o The process of meiosis is an important event because it produces genetic variations among sexually reproducing organisms. o Genetic variations are the reasons no two individuals are identical. Because of this genetic variation, every individual is unique when compared to others. Fig. 4.10 Oogenesis o Three mechanisms contribute to this genetic variation: independent assortment, crossing over and random fertilization. Independent assortment takes place during the alignment of homologous chromosomes during metaphase I. o This alignment is a random process such that the number of paternal and maternal chromosomes that moves toward the opposite poles during anaphase I is dependent on how the homologous chromosomes aligned themselves at the metaphase plate. Fig. 4.11 Fertilization o In humans with 23 pairs of homologous chromosomes, independent assortment and crossing over result in a great number of variations. Added to this great number of variations, the process of crossing-over, or the exchange of genetic material between homologous chromosomes add even more variations. Making the situation more complicated is the process of random fertilization. During the process of fertilization, the fusion of sperm and egg cell involves a random process. LEARNER’S MODULE | 34  Grade 12 BIOLOGY I Activity Directions: A. Complete the table below by comparing Mitosis and Meiosis. B. Identify three disorders and diseases that result from the malfunction of the cell during the cell cycle. Give a short description of each disorder. *Note: Quiz will be posted in the group chat via google forms. LEARNER’S MODULE | 35  Grade 12 BIOLOGY I LESSON 5 CELL MEMBRANE STRUCTURE Learning Outcomes 1) Describe the structural components of the cell membrane 2) Explain how cell membranes are arranged in the presence of water. 3) Relate the structure and composition of the cell membrane to its function. 4) Outline the properties of the lipid bilayers and associated proteins that compose cell membranes. CELL MEMBRANE o Separates the internal environment of the cell from the external environment. o Regulates the entrance and exit of molecules into the cell, in this way, it helps the cell and the organism maintain a steady internal environment o It is made up of a phospholipid bilayer with embedded proteins. Some of the proteins span the membrane and others do not. Some are on the inside surface of the membrane. All together, the proteins form a mosaic pattern. Fluid Mosaic Model o S. Singer and G. Nicolson introduced the fluid mosaic model of membrane structure, which proposes that the membrane is a fluid phospholipid bilayer in which protein molecules are either partially or wholly embedded. Fig 5.1- Fluid mosaic model of cell membrane LEARNER’S MODULE | 36  Grade 12 BIOLOGY I Cell Membrane Structure and Function o A phospholipid is a molecule that has both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region. o The hydrophilic polar heads of the phospholipid molecules face the outside and inside of the cell, where water is found. o The hydrophobic nonpolar tails face each other. o Cholesterol is another lipid found in animal plasma membrane; related steroids are found in the plasma membrane of plants. Cholesterol stiffens and strengthens the membrane, thereby helping to regulate its fluidity. o The proteins in a membrane may be peripheral proteins or integral proteins o The peripheral proteins on the inside surface of the membrane are often held in place by cytoskelatal filaments. o Integral proteins are embedded in the membrane, but they can move laterally back and forth. Some integral proteins protrude from only one surface of the bilayer. These proteins are known as transmembrane proteins. o Both phospholipids and proteins can have attached carbohydrate (sugar) chains. Fig. 5.2-Phospholipid and Cholesterol Fig.5.3- Transmembrane Proteins Molecules Functions of the Proteins o The plasma membranes of various cells and the membranes of various organelles each have their own unique collection of proteins. o The proteins form different patterns according to the to the particular membrane and also within the same membrane at different times. o The integral proteins largely determine a membrane’s specific functions. The integral proteins can be: ▪ Channel proteins -Channel proteins are involved in the passage of molecules through the membrane. They have a channel that allows a substance to simply move across the membrane. (Fig. 5.4a). ▪ Carrier proteins -Carrier proteins are also involved in the passage of molecules through the membrane. They combine with a substance and help it move across the membrane (Fig. 5.4b). A carrier protein transports sodium and potassium ions across a nerve cell membrane. Without this carrier protein, nerve conduction would be impossible. ▪ Cell recognition proteins LEARNER’S MODULE | 37 Grade 12 BIOLOGY I -Cell recognition proteins are glycoproteins (Fig. 5.4c). Among other functions, these proteins help the body recognize when it is being invaded by pathogens so that an immune reaction can occur. Without this recognition, pathogens would be able to freely invade the body. ▪ Receptor proteins -Receptor proteins have a shape that allows a specific molecule to bind to it (Fig. 5.4d). The binding of this molecule causes the protein to change its shape and thereby bring about a cellular response. The coordination of the body's organs is totally dependent on such signal molecules. For example, the liver stores glucose after it is signaled to do so by insulin. ▪ Enzymatic proteins - Some plasma membrane proteins are enzymatic proteins that carry out metabolic reactions directly (Fig. 5.4e). Without the presence of enzymes, some of which are attached to the various membranes of the cell, a cell would never be able to perform the metabolic reactions necessary to its proper function. o The peripheral proteins often have a structural role in that they help stabilize and shape the plasma membrane. Fig 5.4- Membrane Protein Diversity LEARNER’S MODULE | 38  Grade 12 BIOLOGY I Membrane Permeability o Small, hydrophobic or fat-soluble molecules, such as oxygen, cross the cell membrane quite readily because of "fat dissolving fat" interaction. o Small, uncharged, hydrophilic or water-soluble molecules, such as water and carbon dioxide, would also be able to cross the cell membrane although there is no "fat dissolving fat" the cell membrane although there is no "fat dissolving fat" interaction. o Large, hydrophilic molecules are usually impermeable to cell membrane. o Any molecules carrying strong electrical charges (i.e. ions) are always impermeable to cell membrane, unless transported by special mechanisms. *Note: Quiz will be posted in the group chat via google forms. LEARNER’S MODULE | 39  Grade 12 BIOLOGY I LESSON 6 CELL TRANSPORT Learning Outcomes 1) explain transport mechanisms in cells (diffusion, osmosis, facilitated transport, active transport) 2) explain factors that affect the rate of diffusion across a cell membrane 3) predict the effects of hypertonic, isotonic and hypotonic environments on osmosis in animal cells 4) differentiate exocytosis and endocytosis Transport Across Membranes o The molecular make-up of the phospholipid bilayer limits the types of molecules that can pass through it. For example, hydrophobic (water-hating) molecules, such as carbon dioxide (CO2) and oxygen (O2) can easily pass through the lipid bilayer, but ions such as calcium (Ca2+) and polar molecules such as water (H2O) cannot. o The hydrophobic interior of the phospholipid bilayer does not allow ions or polar molecules through because these molecules are hydrophilic, or water loving. In addition, large molecules such as sugars and proteins are too big to pass through the bilayer. o Transport proteins within the membrane allow these molecules to pass through the membrane, and into or out of the cell. This way, polar molecules avoid contact with the nonpolar interior of the membrane, and large molecules are moved through large pores. o Every cell is contained within a membrane punctuated with transport proteins that act as channels or pumps to let in or force out certain molecules. The purpose of the transport proteins is to protect the cell's internal environment and to keep its balance of salts, nutrients, and proteins within a range that keeps the cell and the organism alive. o There are three main ways that molecules can pass through a phospholipid membrane. The first way requires no energy input by the cell and is called passive transport. The second way requires that the cell uses energy to pull in or pump out certain molecules and ions and is called active transport. The third way is through vesicle transport, in which large molecules are moved across the membrane in bubble-like sacks that are made from pieces of the membrane. Passive Transport o Passive transport occurs when substances cross the plasma membrane without any input of energy from the cell. o No energy is needed because the substances are moving from an area where they have a higher concentration to an area where they have a lower concentration. LEARNER’S MODULE | 40  Grade 12 BIOLOGY I o Concentration refers to the number of particles of a substance per unit of volume. The more particles of a substance in a given volume, the higher the concentration. o During passive transport a substance always moves from an area where it is more concentrated to an area where it is less concentrated. It’s a little like a ball rolling down a hill. It goes by itself without any input of extra energy. o There are several different types of passive transport, including simple diffusion, osmosis, and facilitated diffusion. o The permeability of a membrane is dependent on the organization and characteristics of the membrane lipids and proteins. o In this way, cell membranes help maintain a state of homeostasis within cells (and tissues, organs, and organ systems) so that an organism can stay alive and healthy. 3 Types of Passive Transport 1. Diffusion o Diffusion is the movement of a substance across a membrane, due to a difference in concentration, without any help from other molecules. o The difference in the concentrations of the molecules in the two areas is called the concentration gradient. o The substance simply moves from the side of the membrane where it is more concentrated to the side where it is less concentrated. o Diffusion will continue until this gradient has been eliminated. o Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient." o The end result of diffusion is an equal concentration, or equilibrium, of molecules on both sides of the membrane. o Substances that can squeeze between the lipid molecules in the plasma membrane by simple diffusion are generally very small, hydrophobic molecules, such as molecules of oxygen and carbon dioxide. Fig.6.1 Molecular movement during diffusion Fig.6.2 Concentration gradient 2. Osmosis o Osmosis is a special type of diffusion — the diffusion of water molecules across a membrane. o Like other molecules, water moves from an area of higher concentration to an area of lower concentration. o Water moves in or out of a cell until its concentration is the same on both sides of the plasma membrane. LEARNER’S MODULE | 41 Grade 12 BIOLOGY I o Imagine you have a cup that has 100ml water, and you add 15g of table sugar to the water. The sugar dissolves and the mixture that is now in the cup is made up of a solute (the sugar) that is dissolved in the solvent (the water). The mixture of a solute in a solvent is called a solution. o Imagine now that you have a second cup with 100ml of water, and you add 45 grams of table sugar to the water. Just like the first cup, the sugar is the solute, and the water is the solvent. But now you have two mixtures of different solute concentrations. o In comparing two solutions of unequal solute concentration, the solution with the higher solute concentration is hypertonic, and the solution with the lower solute concentration is hypotonic. Solutions of equal solute concentration are isotonic. The first sugar solution is hypotonic to the second solution. The second sugar solution is hypertonic to the first. o You now add the two solutions to a beaker that has been divided by a selectively permeable membrane, with pores that are too small for the sugar molecules to pass through, but are big enough for the water molecules to pass through. o The hypertonic solution is on one side of the membrane and the hypotonic solution on the other. The hypertonic solution has a lower water concentration than the hypotonic solution, so a concentration gradient of water now exists across the membrane. Water molecules will move from the side of higher water concentration to the side of lower concentration until both solutions are isotonic. At this point, equilibrium is reached. o If a cell is in a hypertonic solution, the solution has a lower water concentration than the cell cytosol, and water moves out of the cell until both solutions are isotonic. Cells placed in a hypotonic solution will take in water across their membrane until both the external solution and the cytosol are isotonic. o A cell that does not have a rigid cell wall, such as a red blood cell, will swell and lyse (burst) when placed in a hypotonic solution, a process called cytolysis. Cells with a cell wall will swell when placed in a hypotonic solution, but once the cell is turgid (firm), the tough cell wall prevents any more water from entering the cell. When placed in a hypertonic solution, a cell without a cell wall will lose water to the environment, shrivel, and probably die. In a hypertonic solution, a cell with a cell wall will lose water too. The plasma membrane pulls away from the cell wall as it shrivels, a process called plasmolysis. Animal cells tend to do best in an isotonic environment, plant cells tend to do best in a hypotonic environment. Fig 6.3 Hypotonic solution. Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis). LEARNER’S MODULE | 42  Grade 12 BIOLOGY I Fig 6.4 Hypertonic solution. Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis). Fig 6.5 Isotonic solution. Water moves equally in both directions and the cell remains same size. Dynamic Equilibrium). 3. Facilitated Diffusion o Facilitated diffusion is the diffusion of solutes through transport proteins in the plasma membrane. Facilitated diffusion is a type of passive transport. Even though facilitated diffusion involves transport proteins, it is still passive transport because the solute is moving down the concentration gradient. o Small nonpolar molecules can easily diffuse across the cell membrane. However, due to the hydrophobic nature of the lipids that make up cell membranes, polar molecules (such as water) and ions cannot do so. Instead, they diffuse across the membrane through transport proteins. o A transport protein completely spans the membrane, and allows certain molecules or ions to diffuse across the membrane. Channel proteins, gated channel proteins, and carrier proteins are three types of transport proteins that are involved in facilitated diffusion. 3 Types of Transport proteins ▪ Channel protein, a type of transport protein, acts like a pore in the membrane that lets water molecules or small ions through quickly. Water channel proteins allow water to diffuse across the membrane at a very fast rate. Ion channel proteins allow ions to diffuse across the membrane. An ion channel is a transport protein that moves electrically charged atoms LEARNER’S MODULE | 43  Grade 12 BIOLOGY I called ions. Ions such as sodium (Na+ ), potassium (K+ ), calcium (Ca2+), and chloride (Cl- ), are important for many cell functions. Because they are polar, these ions do not diffuse through the membrane. Instead, they move through ion channel proteins where they are protected from the hydrophobic interior of the membrane. Ion channels allow the formation of a concentration gradient between the extracellular fluid and the cytosol. Ion channels are very specific, as they allow only certain ions through the cell membrane. Some ion channels are always open; others are "gated" and can be opened or closed. Gated ion channels can open or close in response to different types of stimuli, such as electrical or chemical signals. ▪ Gated channel protein - is a transport protein that opens a "gate," allowing a molecule to pass through the membrane. Gated channels have a binding site that is specific for a given molecule or ion. A stimulus causes the "gate" to open or shut. The stimulus may be chemical or electrical signals, temperature, or mechanical force, depending on the type of gated channel. For example, the sodium gated channels of a nerve cell are stimulated by a chemical signal which causes them to open and allow sodium ions into the cell. Glucose molecules are too big to diffuse through the plasma membrane easily, so they are moved across the membrane through gated channels. In this way glucose diffuses very quickly across a cell membrane, which is important because many cells depend on glucose for energy. ▪ Carrier protein -is a transport protein that is specific for an ion, molecule, or group of substances. Carrier proteins "carry" the ion or molecule across the membrane by changing shape after the binding of the ion or molecule. Carrier proteins are involved in passive and active transport. Fig.6.6 Channel protein and carrier proteins Fig.6.7 Facilitated diffusion LEARNER’S MODULE | 44  Grade 12 BIOLOGY I ACTIVE TRANSPORT Active transport occurs when energy is needed for a substance to move across a plasma membrane. Energy is needed because the substance is moving from an area of lower concentration to an area of higher concentration, or up the concentration gradient. This is a little like moving a ball uphill; it can’t be done without adding energy. The energy for active transport comes from the energy-carrying molecule called ATP. Like passive transport, active transport may also involve transport proteins. The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins that are found in the membrane. Larger molecules such as starch can also be actively transported across the cell membrane by processes called endocytosis and exocytosis. 1. Sodium-Potassium Pump o energy-requiring process of pumping molecules and ions across membranes "uphill" - against a concentration gradient. o To move these molecules against their concentration gradient, a carrier protein is needed. Carrier proteins can work with a concentration gradient (during passive transport), but some carrier proteins can move solutes against the concentration gradient (from low concentration to high concentration), with an input of energy. As in other types of cellular activities, ATP supplies the energy for most active transport. o One-way ATP powers active transport is by transferring a phosphate group directly to a carrier protein. This may cause the carrier protein to change its shape, which moves the molecule or ion to the other side of the membrane. Fig 6.7 The sodium-potassium pump system moves sodium and potassium ions against large concentration gradients. It moves two potassium ions into the cell where potassium levels are high, and pumps three sodium ions out of the cell and into the extracellular fluid. 2. Vesicle Transport o Some molecules, such as proteins, are too large to pass through the plasma membrane or to move through a transport protein, regardless of their concentration inside and outside the cell. LEARNER’S MODULE | 45 Grade 12 BIOLOGY I o Very large molecules cross the plasma membrane with a different sort of help, called vesicle transport. Vesicle transport requires energy, so it is also a form of active transport. o There are two types of vesicle transport: endocytosis and exocytosis. Endocytosis o is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. o The membrane folds over the substance and it becomes completely enclosed by the membrane. o At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytosol. o There are two main kinds of endocytosis: Phagocytosis, or cellular eating, occurs when the dissolved materials enter the cell. The plasma membrane engulfs the solid material, forming a phagocytic vesicle. Pinocytosis, or cellular drinking, occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell. When the channel is closed, the liquid is encircled within a pinocytic vesicle. Exocytosis o describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. o Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. o Newly made membrane proteins and membrane lipids are moved on top the plasma membrane by exocytosis. Fig. 6.8 Illustration of the two types of vesicle transport, exocytosis and endocytosis LEARNER’S MODULE | 46  Grade 12 BIOLOGY I Activity Direction: Read the instructions carefully before answering the given set of questions. Prepare one whole sheet of paper to be used as your answer sheet. 1. Foods treated with salt or sugar have longer shelf life. Explain the reason for using salt and sugar for food preservation. 2. The beaker in the diagram has a selectively permeable membrane separating two solutions. Suppose that the salt molecules are small enough to pass through the membrane but the starch molecules are too large to pass through. Will the water level on either side of the membrane change? Explain your answer. 3. Choose one (1) Transport Mechanism in a cell and make a relatable analogy based on your experience recently. Illustrate and explain your work. *Note: Quiz will be posted in the group chat via google forms. LEARNER’S MODULE | 47  Grade 12 BIOLOGY I Lesson 7 Structures and Functions of Biological Molecules: Carbohydrates and Lipids Learning Outcomes 1) distinguish between carbohydrates, proteins, lipids, and nucleic acids according to their structure and function; 2) summarize the general characteristics of each biomolecule; and 3) relate the structures of the biomolecules with their properties. What do humans get from food? Heterotrophs, such as human beings, obtain energy and raw materials from food. These are important for cell growth, cell division, metabolism, repair, and maintenance of the body. Nutrients can be classified as either organic nutrients (i.e., those that contain carbon such as carbohydrates, fats, proteins, vitamins, and nucleic acids) or inorganic nutrients (i.e., those that do not contain carbon such as water and mineral salts). What are Carbohydrates? Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. These compounds have a general formula of CnH2mOm. This means that the hydrogen and oxygen atoms are present in a ratio of 2:1. For example, glucose has a formula of C6H12O6 and sucrose has a formula of C12H22O11. Carbohydrates are usually good sources of raw materials for other organic molecules and energy. One gram of carbohydrates provides four food calories or 16 kJ of energy. In the human diet, carbohydrates mainly come from plants although they are found in all organisms. How are carbohydrates formed? Carbohydrates are examples of macromolecules. These are chainlike molecules called polymers (mere means part) made from repeating units like monomers. Polymers can be formed from covalently-bonded monomers much like a single structure can be made out of repeated building blocks linked to each other. These monomers, called monosaccharides, form covalent bonds when one monomer loses a hydroxyl group and the other loses a hydrogen atom in dehydration or condensation reactions, forming disaccharides. This reaction requires energy to occur. The bond formed is called a glycosidic linkage. Longer polysaccharide chains are formed by monomer addition through succeeding dehydration reactions. These reactions can occur in the human liver as carbohydrates LEARNER’S MODULE | 48  Grade 12 BIOLOGY I are stored as polysaccharides called glycogen or in ground tissues of plants where these are stored as starch. Polysaccharides are broken down into simpler components through the use of water to break covalent bonds and release energy. The process, known as hydrolysis (hydro means water and lysis means split), is the opposite of dehydration reactions and often occurs in the digestive tract during chemical and mechanical digestion. Here, enzymes break bonds within polysaccharides. With the aid of water, one –H group attaches to a monosaccharide while another –OH group attaches to the other. Dehydration synthesis of disaccharides from monosaccharide components (Source: https:// bealbio.wikispaces.com/file/view/disaccharides.JPG/364413582/disaccharides.JPG) How are carbohydrates classified? Carbohydrates can be classified into three main categories, according to increasing complexity: monosaccharides (monos means single and sacchar means sugar) disaccharides (di means two) polysaccharides (poly means many) 1. Monosaccharide Functions major cellular nutrient often incorporated into more complex carbohydrates LEARNER’S MODULE | 49  Grade 12 BIOLOGY I Structure contains a carbonyl group (C=O) and may be classified as an aldose or ketose depending on the position may have three to seven carbons in the skeleton may be arranged in a linear form when solid and is converted into a ring form in aqueous solution (α form when H is on top of plane of ring and β form when -OH is on top of plane of ring) Examples Ribose—a 5C aldose that forms part of the backbone of nucleic acids Glucose—a 6C aldose that is the product of photosynthesis and the substrate for respiration that provides energy for cellular activities Fructose—a 6C ketose that is found in many plants and is often bonded to glucose 2. Disaccharide Functions energy source sweetener and dietary component Structure forms when a glycosidic linkage forms between two monosaccharides Examples Maltose (glucose + glucose)—malt sugar often found in sprouting grains, malt-based energy drinks, or beer LEARNER’S MODULE | 50  Grade 12 BIOLOGY I Lactose (glucose + galactose)—milk sugar that is a source of energy for infants; an enzyme called lactase is required to digest this. Many adult Filipinos have low levels of this enzyme leading to a condition called lactose intolerance. Sucrose (glucose + fructose)—found in table sugar processed from sugar cane, sweet fruits, and storage roots like carrots 3. Polysaccharide Functions storage material for important monosaccharides structural material for the cell or the entire organism Structure forms when hundreds to thousands of monosaccharides are joined by glycosidic linkages Examples Storage polysaccharides are large molecules retained in the cell and are insoluble in water (formed from α 1,4 linkage monomers; with a helical structure) Starch —amylase is unbranched starch forming a helical structure while amylopectin is branched starch, these are present in plant parts like potato tubers, corn, and rice and serve as major sources of energy. Glycogen —found in animals and fungi; often found in liver cells and muscle cells Structural polysaccharides (formed from β 1,4 linkage of monomers; strands associate to form a sheet-like structure) Cellulose—tough sheet-like structures that make up plant and algal cell walls that may be processed to form paper and paper-based products; humans lack the enzymes to digest β 1,4 linkages so is passed out of the digestive tract and aids in regular bowel movement. LEARNER’S MODULE | 51  Grade 12 BIOLOGY I Chitin —used for structural support in the walls of fungi and in external skeletons of arthropods Peptidoglycan —used for structural support in bacterial cell walls What are lipids? Lipids are a class of large biomolecules that are not formed through polymerization. They have diverse structures but are all non-polar and mix poorly, if at all, with water. They may have some oxygen atoms in their structure but the bulk is composed of abundant nonpolar C-H bonds. They function for energy storage, providing nine food calories or 37 kJ of energy per gram. They also function for the cushioning of vital organs and for insulation. Furthermore, they play important roles in plasma membrane structure and serve as precursors for important reproductive hormones. How are lipids classified? Lipids can be divided into three main classes according to differences in structure and function. 1. Fats (triacylglycerols or triglycerides) Functions energy storage cushioning of vital organs (adipose tissue) insulation Structure formed from dehydration reactions between glycerol (an alcohol with three Cs, each with an –OH group) forming three ester linkages with three fatty acids (16-18 Cs, with the last C as part of a –COOH group) and producing three molecules of water. component fatty acids (FA) may be either saturated or unsaturated Saturated FA (e.g., palmitic acid) have the maximum number of hydrogen atoms bonded to each carbon (saturated with hydrogen); there are no double bonds between carbon atoms LEARNER’S MODULE | 52  Grade 12 BIOLOGY I Unsaturated FA (e.g., oleic acid) have at least one double bond, H atoms are arranged around the double bond in a cis configuration (same side) resulting in a bend in the structure Examples Saturated fat—animal products such as butter and lard have a lot of saturated fatty acids. The linear structure allows for the close packing of the fat molecules forming solids at room temperature, diets high in these fats may increase the risk of developing atherosclerosis, a condition in which fatty deposits develop within the walls of blood vessels, increasing the incidence of cardiovascular disease. Unsaturated fat—plant and fish oils have unsaturated fatty acids. The bent structure prevents close packing and results in oils or fats that are liquid at room temperature. Homemade peanut butter has oils that separate out of solution for this reason. Industries have developed a process called hydrogenation that converts unsaturated fats into saturated fats to improve texture spreadability. Trans fat—may be produced artificially through the process of hydrogenation described above. The cis double bonds are converted to trans double bonds (H atoms on opposite sides) resulting in fats that behave like saturated fats. Studies show that trans fat are even more dangerous to health than saturated fats to the extent that they have been banned from restaurant