Module+3_Cell+Specialization+and+Modification.pdf

UNIT I: CELL General Biology 1...

UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 CELL SPECIALIZATIONS AND MODIFICATIONS Topics: 1. Plant Tissues 2. Animal Tissues 3. Cell Modifications A. Plant Cell Modifications B. Animal Cell Modifications 3.1 INTRODUCTION Multi-celled living things such a plants and animals are very complex and highly organized. They start a life as a single cell, the fertilized egg or zygote produced from the union of egg and sperm cells. The zygote undergoes a series of cell divisions, producing many cells that will eventually form the variety of tissues that make up the organs and organs system. Although all of these cells carry out a number of common functions – such as obtaining nutrients, metabolizing them to produce energy and synthesize basic cellular constituents, and then later on reproducing themselves – the cells of multicellular organisms further differentiate so that they can become specialized for additional and unique functions. A tissue is composed of specialized cells of the same or similar type that perform a common function in the body. 3.2 PLANT TISSUES A flowering plant can grow throughout its entire life because it possesses meristematic (embryonic) tissue. 1. Meristematic tissue o Embryonic tissues are undifferentiated capable of continuous cell divisions. o Located at the or near the tips of stems and roots (apical meristems). o Another type of meristem is the intercalary meristems which occur in between mature tissues. o Intercalary meristems – Accounts for why grass can so readily regrow after being grazed by a cow or cut by a lawnmower. Three types of Apical Meristem: Protoderm – Gives rise to epidermis Ground meristem – Produces ground tissues Procambrian – Produces vascular tissue The specific functions of these specialized tissues are: 1. Epidermal tissue forms the outer protective covering of a plant. 2. Ground tissue fills the interior of a plant. 3. Vascular tissue transports water and nutrients within the plants as well as providing support. 2. Epidermal Tissue o The entire body of both nonwoody (herbaceous) and young woody plants are made up of closely packed cells called epidermis. o The walls of epidermal cells exposed to air are covered with a waxy cuticle to minimize water loss, and to protect against bacteria and other organisms that might cause disease in plants. o In roots, certain epidermal cells develop long, slender projections called root hairs. The root hairs increase the surface area of the root for absorption of water and minerals from the soil, as well as anchor the plant to various substrates. o On the surfaces of stems, leaves, and reproductive organs, epidermal cells produce hairs called trichomes. These hair-like projections have two important functions: a. To protect the plant from too much sun b. To conserve moisture o In leaves, specialized cells called guard cells are present in the lower epidermis of eudicots and both surfaces of monocots. o Guard cells are epidermal cells containing chloroplasts. A pair of guard cells surrounds microscopic pores called stomata which regulate gas exchange and water loss in leaves. 1 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Figure 1. Internal Structure of a Leaf As woody plants get older, the epidermis of young stems is replaced by periderm. The major component of periderm is composed of boxlike cork cells. At maturity cork cells can be sloughed off and replaced by new cork cells produced by a meristem called cork cambium. As the new cork cells mature their walls become encrusted with suberin, a lipid material that serves to waterproof and make the cork cells chemically inert. These nonliving cells protect the plant by resisting the fungal, bacterial, and animal attacks. Over productions of cork cells by the cork cambium in certain areas of the stem surface cause ridges and cracks to spear. These features on the surface are the lenticels where gas exchange between the interior of a stem and the air takes place. 3. Ground Tissue o Ground tissue forms the bulk of a flowering plant and contains parenchyma, collenchyma and sclerenchyma cells. Figure 2. Plant Ground Tissues Parenchyma cells o Most abundant type of plant tissue found in all organs but the least specialized. o Their functions depend on the type of pigment they contain. When chloroplasts are present, the store products of photosynthesis. A juicy bite from an apple is due mostly to storage parenchyma cells. o Some parenchyma cells line the connected air spaces of a water lily and other aquatic plants; while others can divide and give rise to more specialized cells, such as when roots develop from stem cuttings placed in water. Collenchyma cells Like parenchyma cells except that they have thicker primary walls The thickness is uneven and usually found in the corners of the cell. Collenchyma cells provide support and flexibility to immature regions of a plant body by forming bundles just beneath the epidermis. An example of this are the visible strands in celery stalks composed mostly of collenchyma cells. 2 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Sclerenchyma cells Have thick secondary walls filled with a highly resistant organic substance called lignin that makes the walls tough and hard. Most sclerenchyma cells are nonliving and function primarily to support the mature regions of a plant. There are two types of sclerenchyma cells: 1. Fibers – Long and slender structures and may be grouped in bundles. They are mostly found in vascular tissue, although they may be occasionally found in ground tissue. Example: Hemp fibers (rope), flax fibers 2. Sclereids – (Stone cells) shorter than fibers and more varied in shape, are found in seed coats and nutshells. Responsible for the gritty structure of pears, as well as the hardness of nuts and peach pits. 4. Vascular Tissue There are two types of vascular tissues: 1. Xylem – Transports water and minerals from the roots to the leaves. 2. Phloem – Transports sucrose and other organic compounds, usually from the leaves to the roots. Figure 3. Plant Vascular Tissues Both are considered complex tissues because they are composed of two or more kinds of cells. Two types of xylem: a. Tracheids – Form a less obvious means of transport (elongated with tapered ends). Water can move across the end walls and side walls because there are pits, or depressions, where the secondary walls do not form. b. Vessel elements – Larger, may have perforation plates in their end walls, and are arranged to form a continuous vessel for water and mineral transport. Both types of conducting cells hollow and nonliving. Phloem is composed of several tissues: a. Sieve tube members – Specialized elongated parenchyma cells which are arranged end to end forming a continuous column. b. Companion cells – Has a nucleus and help the sieve tube members carry out their function. c. Fibers – Lend supports to the phloem. d. Parenchyma 3.3 ANIMAL TISSUES The four major types of tissues their function are as follows: 1. Epithelial tissue covers body surfaces, line body cavities, and forms glands. 2. Connective tissue binds and supports body parts. 3. Muscular tissue moves the body and its parts. 4. Nervous tissue receives stimuli and transmits nerve impulses. 3 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 1. Epithelial Cells o Consists of tightly packed cells that form a continuous layer. o Covers surfaces and lines body cavities and therefore provides protective function. o Can be modified to carry out secretion, absorption, excretion, and filtration. o Can be connected to one another by three types of junctions composed of proteins: a. Tight junction - Form impermeable barrier between cells. b. Adhesion junctions - Add strength and allow epithelial cells to stretch and bend. c. Gap junctions - Permit the passage of molecules between two adjacent cells. o Often exposed to the environment on one side but attached to a basement membrane on the other side. o Basement membrane – Thin layer of various types of proteins that anchor the epithelium to the extracellular matrix which is often a type of connective tissue. Figure 4. Epithelial Tissues Types of Epithelial Tissue 1. Simple epithelium – Single layer of cells and is classified according to the shape of cells a. Squamous epithelium – composed of flattened cells and found in lining blood vessels and the air sacs of lungs b. Cuboidal epithelium – Contains cube-shaped cells and found lining the kidney tubules and various glands c. Columnar epithelium – Resembles rectangular pillars found in lining the digestive tract. Ciliated columnar epithelium is found lining the oviducts where it propels the egg towards the uterus. d. Pseudo stratified epithelium – Appears to be layered, but true layers do not appear because each cell is attached to the basement membrane. Also, the presence of nuclei seen at different levels makes it appear layered. Hence, it is still classified as a simple epithelium. This is found in the lining of the windpipe, or trachea. 2. Stratified epithelium – Made up of more than one layer of cells. Only the bottom layer touches the basement membrane. This type of epithelium is found lining the nose, mouth, esophagus, anal canal, and vagina. The skin is also lined with stratified squamous epithelium reinforced by keratin to give it strength. 3. Glandular epithelium – Kind of epithelium that secretes a product. A gland can be a single – cell gland is the mucus – secreting goblet cells found within the columnar epithelium lining the digestive tract. a. Exocrine glands – Secretes their products into ducts. Example: Sweat and salivary glands b. Endocrine glands – Have no ducts and secrete their products directly into the blood stream. Example: Pituitary and thyroid glands 2. Connective Tissue o Most abundant and widely distributed tissue in complex animals o Quite diverse in nature, but all types have three components: 4 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 a. Specialized cells b. Ground substance – Found in between the cells, is a noncellular material that varies in consistency from solid to semifluid to fluid c. Protein fibers 1. White collagen fibers – Contain collagen – protein that gives them flexibility and strength 2. Reticular fibers – Contain very thin collagen fibers which are highly branched and form delicate supporting networks 3. Yellow elastic fibers – Contains elastin, protein that is not long as strong as collagen but is more elastic The ground substance, together with the fibers, is referred to as the connective tissue matrix. Figure 5. Connective Tissues The Three Categories of Connective Tissues 1. Fibrous 2. Supportive 3. Fluid Fibrous Connective Tissue 1. Loose Fibrous Connective Tissue 2. Dense Fibrous Connective Tissue Both cells have called fibroblast which are located some distance from one another and are separated by a jellylike matrix containing white collagen fibers and yellow elastic fibers. Loose Fibrous Connective Tissue o Has fibroblasts and collagen fibers widely scattered in its matrix o Found in many internal organs like the lungs, arteries, and urinary bladder, supporting them and allowing them to expand. It also forms protective covering around internal organs such as muscles, blood vessels, and nerves o Adipose tissue – loose connective tissue composed mostly of enlarged fat-storing fibroblast called adipocytes. It also serves as the body’s primary energy reservoir. It also insulates the body, contributes in body contours, and provides cushioning. In mammals, adipose tissue is found well distributed beneath the skin, around the kidneys, and on the surface of the heart. The number of adipocytes in an individual is fixed. As a person gains weight, the cells become larger, and as he loses weight, the cells shrink. In obese people, the individual cells may be up to 5x larger than normal. 5 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Dense Fibrous Connective Tissue o Contains many collagen fibers that are tightly packed together o Found in tendons which connect muscles to bones and in ligaments which connect bones to other bones at joints. Supportive Connective Tissue o This type of tissue includes cartilage and bones which are the two main supportive connective tissue that provide structure, shape and protection, and leverage for movement. o Cartilage is generally more flexible than bone because its matrix lacks calcium deposits. 1. Cartilage contains cells that lie in small chambers called lacunae which are separated by a solid but flexible matrix. It heals very slowly because it lacks a direct blood supply. Three types of cartilage: a. Hyaline cartilage – most common cartilage containing only very fine collagen fibers. This type of cartilage with a white translucent matrix is found in the nose, at the ends of the long bones and the ribs, and walls of the respiratory passages. The fetal skeleton is mostly made up of cartilage which is later replaced by bone. b. Elastic cartilage – has more fibers making it more flexible than hyaline cartilage. It is found in the framework of the outer ear c. Fibro cartilage – has a matrix containing strong collagen fibers. This is found in structures that withstand tension and pressure like the pads between the vertebrae in the backbone, and the wedges in the knee joint Figure 6. Cartilages in an Adult Human Body 2. Bone has extremely hard matrix made up mostly of calcium salts deposited among protein fibers especially collagen fibers. The inorganic salts give bones rigidity, and the protein fibers provide elasticity and strength, much as steel rods do in reinforced concrete. This is the most rigid type of connective tissue. Two types of bones: a. Compact bone – consists of cylindrical structural units called osteons (Harvesian system). Bone cells (osteocytes) are in spaces called lacunae found between the rings of matrix. b. Spongy bone – found at the ends of a long bone, contains numerous bony bars and plates separated by irregular spaces. 6 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Figure 7. Compact Bone and Spongy Bone Fluid Connective Tissue o Blood, consisting of formed elements and plasma, is a fluid connective tissue located in blood vessels. Formed elements of blood consists of many kinds of blood cells and the plates. Functions of blood: 1. Transports nutrients and oxygen to tissue fluid and removes carbon dioxide and other wastes. 2. Helps distribute heat. 3. Plays a role in fluid, ion and pH balance. Figure 8. Blood Cells The formed elements of blood have each a special function: 1. Red blood cells – Small biconcave disk-shaped cells without nuclei. They contain red pigment called hemoglobin which is made up of protein globin and a complex iron – containing heme. 2. White blood cells – Much larger than red blood cells and contain nuclei which when stained typically looks blue or purple. White blood cells can fight infection primarily in two ways: a. Engulfing infectious pathogens. b. Producing antibodies that combine with substances, either to inactivate them, or kill them outright. 3. Platelets – Not complete cells but fragments of large cells present only in bone marrow. They stop bleeding by forming a plug that seals the blood vessels. 4. Lymphocytes – Specialized white blood cells, which together with other cells, remove any foreign materials from the body by phagocytosis. 3. Muscular Tissue o It is composed of cells muscle fibers that contain actin and myosin filaments. The interaction between these two protein filaments account for the movement of body parts. As muscles contact, body heat is generated. 7 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Figure 9. Muscle Tissues Three types of muscle tissue: 1. Skeletal muscle – Made up of long and cylindrical muscle fibers that sometimes run the entire length of the muscle. It is a voluntary muscle because it is under the control of the will. 2. Smooth muscle – Made up of spindle – shaped mononucleated cells which are not under voluntary control. Contractions of the smooth muscle in certain parts of the body: a. Movement of food along the lumen of the small intestine b. Rise in blood pressure inside the blood vessels 3. Cardiac muscle – Found only in the heart, has both features of skeletal and smooth muscles. It has striations, but its contractions are involuntary like the smooth muscles. It has a single and centrally – located nucleus. 4. Nervous Tissue o It is made up of specialized signaling cells called neurons and supporting cells called neuroglia. About trillion neurons are present in an average human body. The nervous system conducts signal termed nerve impulses throughout the body. Figure 10. Parts of a Nerve Cell Neurons contains three parts: 1. Cell body – processes such as the dendrites and the axons 2. Dendrites – conducts signals toward the cells body, while axons are covered by a fatty substance called myelin 3. Axon – conducts signals away from the cell body Neuroglia o More than half of the brain volume is made up of cells called neuroglia which functions to support, nourish and protect neurons. 8 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Types of neuroglia: a. Microglia – Give support, as well as protection to the neurons by engulfing bacterial and cellular debris. b. Astrocytes – Provide nutrients to neurons and produce a hormone known as glial cell – derived growth factor which is being studied as a possible treatment for Parkinson’s diseases caused by neuron degeneration. c. Oligodentrocytes – Form myelin in the brain. The nervous system carries out three major functions: 1. Sensory input 2. Integration of data 3. Motor output 3.4 CELL MODIFICATIONS Features or structures of the cell that make them different from another type of cell and at the same time enable them to carry out unusual functions are called cell modifications. This commonly occurs in multicellular eukaryotes, where the opportunity for cell specialization arises. Plant Cell Modifications 1. Succulent leaves of century plant (Agave), aloes, sedums, and desert plants, which are thick and fleshy, store water to enable them to survive long periods of drought and semidesert conditions. 2. Tendrils (modified leaf petioles, veins, or stipules), growing in climbing plants like garden peas, bitter gourd and cucumber, can coil around support for anchorage. 3. Younger leaves of poinsettia are brightly colored to help in attracting pollinators. 4. Tubular or vase- shaped leaves of Pitcher plants secrete a fluid for digesting insects falling into their cavities. 5. Lateral roots of mangrove trees growing in swamps produce pneumatophores (upright conical growths) that aerate the submerge roots. 6. Adventitious roots (called brace or prop roots) that develop from the stem or even from the leaves, such as in pandan or corn, grow into the ground to help underground roots support the stem. Figure 11. Plant Cell Specialization Animal Cell Modifications 1. Microvilli – Finger-like projections extending from the free surface of epithelial cells that increase the surface area across which substance are absorbed. 2. Fimbriae – Finger-like extensions from the oviduct near the ovary that help to propel the released ova towards the fallopian tube. 3. Alveoli – Microscopic, grapelike air sacs found at the tip of the bronchioles in the lungs that provide tremendous surface area for gas exchange during respiration. 4. Goblet cell – A glandular, modified simple columnar epithelial cell that secretes gel-forming mucins, the major components of mucus. 5. Red blood cells – A biconcave disk-shaped cell that provides more surface area for gas exchange; absence of its nucleus in mature red blood cells give more space for the hemoglobin. 9 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 6. White blood cell – Also called leukocyte, contain enzymes and other proteins needed to protect the body against both infectious diseases and foreign invaders. 7. Neuron – A specialized cell with three parts: a. Dendrites b. Cell body c. Axon 8. Sperm cell – Has lots of mitochondria that will produce the energy needed to propel its flagellum towards the egg cell during fertilization; and contains the enzyme needed to penetrate the thick membrane surrounding the egg and deliver its genetic material. 9. Ciliated epithelium – Located in the upper airways sweeps mucus with inhaled particles away from the lungs. Cilia in the oviduct move an egg towards the uterus Figure 12. Animal Cell Specialization and Differentiation 10. Stem Cells – Unique cells of the body in that they are unspecialized and have the ability to develop into specialized cells for specific organs or to develop into tissues. Stem cells are able to divide and replicate many times in order to replenish and repair tissue. In the field of stem cell research, scientists are attempting to take advantage of the renewal properties of stem cells by utilizing them to generate cells for tissue repair, organ transplantation, and for the treatment of disease. 11. Cancer Cells - Results from the development of abnormal properties in normal cells that enable them to divide uncontrollably and spread to other locations. Cancer cell development can be caused by mutations that occur from factors such as chemicals, radiation, ultraviolet light, chromosome replication errors, or viral infection. Cancer cells lose sensitivity to anti-growth signals, proliferate rapidly, and lose the ability to undergo apoptosis or programmed cell death. 12. Endothelial Cells - Form the inner lining of cardiovascular system and lymphatic system structures. These cells make up the inner layer of blood vessels, lymphatic vessels, and organs including the brain, lungs, skin, and heart. Endothelial cells are responsible for angiogenesis or the creation of new blood vessels. They also regulate the movement of macromolecules, gases, and fluid between the blood and surrounding tissues, and help to regulate blood pressure. 13. Cilia - An organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body. Types of Cilia: Motile Cilia: o Motile cilia are usually present on a cell's surface in large numbers and beat in coordinated waves. For example, motile cilia are found in the lining of the trachea (windpipe), where they sweep mucus and dirt out of the lungs. In female mammals, the beating of cilia in the Fallopian tubes moves the ovum from the ovary to the uterus. o Motile cilia for the transport of fluids (e.g. transport of mucus by stationary ciliated cells in the trachea). o However, cilia are also used for locomotion (through liquids) in organisms such as Paramecium. 10 | STEM – General Biology 1 Module Unit I: Cell  UNIT I: CELL General Biology 1 1st Semester A.Y 2024-2025 Non-motile (Primary cilia): o Usually occur one per cell; all mammalian cells have a single non-motile primary cilium. For example, sensory organs like eye and nose o Mechanoreceptors - A primary cilium extends from the apical surface of the epithelial cells lining the kidney tubules and monitors the flow of fluid through the tubules. o Chemoreceptors - Detect odors by receptors on the primary cilium of olfactory neurons. o Photoreceptors - The outer segment of the rods in the vertebrate retina is also derived from a primary cilium. 14. Flagella - A tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and functions in locomotion. o Flagella serve for the propulsion of single cells (e.g. swimming of protozoa and spermatozoa), and motile cilia for the transport of fluids (e.g. transport of mucus by stationary ciliated cells in the trachea). However, cilia are also used for locomotion (through liquids) in organisms such as Paramecium.