Chapter 2: Cells 2024/2025 BIO091 PDF

CHAPTER 2: CELLS BIO091 Semester I 2024/2025 1 SUBTOPICS 2.1 : Cell Theory 2.2 : Differences between prokaryotes and eukaryotes 2.3 : Structure and function of organelles 2.4 : Specialised animal tissues 2.5 : Specialised plant tissues...

CHAPTER 2: CELLS BIO091 Semester I 2024/2025 1 SUBTOPICS 2.1 : Cell Theory 2.2 : Differences between prokaryotes and eukaryotes 2.3 : Structure and function of organelles 2.4 : Specialised animal tissues 2.5 : Specialised plant tissues 2  LEARNING OUTCOME LEARNING OUTCOMES 2.1 State the cell theory. 2.2 Compare and contrast the structures of prokaryotic and eukaryotic cells. 2.3 Describe the structure and function of organelles. 2.4 Describe the structure, functions and distributions of specialized animal tissues. 2.5 Describe the structure, functions and distributions of specialized plant tissues.  INTRODUCTION All organisms are made of cells. The basic structural and functional units of every organism. Basic features of all cells: i. Plasma membrane (selective barrier) ii. Cytosol (semifluid/ jellylike substance) iii. Chromosomes (carry genes/ DNA) iv. Ribosomes (protein factories)  2.1 CELL THEORY Two concepts of cell theory: i. Cells are the basic living units of organization and function in all organisms. i. All cells come from other cells.  CELLS / ORGANISMS Prokaryotes Eukaryotes Unicellular Multicellular Plant cells Animal cells  2. CELLS 2.2 PROKARYOTES AND EUKARYOTES Two types of organisms: A) PROKARYOTES Pro–before ; karyotes – nucleus Organisms of domains Bacteria and Archaea consist of prokaryotic cells (single cell microorganisms) Characteristics of prokaryotes cells: No nucleus DNA is located in the nucleoid region Lack of membrane-bound organelles Smaller than eukaryotic cells, 0.1- 0.5μm Types of bacteria based on shapes 8 B) EUKARYOTES Eu – true ; karyotes – nucleus Example or eukaryotic: plants, animals, fungi, amoeba, protozoa. Characteristics of eukaryotic cells: DNA in a nucleus, surrounded by a nuclear membrane. Organelles surrounded by membrane. Example: i. single membrane-bound organelle: vacuole ii. double membrane-bound organelle: chloroplast Cytoplasm in the region between the plasma membrane and nucleus. Larger than prokaryotic cells, 10-100μm. Examples of Eukaryotes  Comparisons Between Prokaryotic & Eukaryotic Cells Prokaryotes Eukaryotes - Ribosomes (site of protein synthesis) - Ribosome (site of protein synthesis) - Smaller - Larger - Free in the cytoplasm - Some are free in the cytoplasm - Some are bound to nuclear envelope or organelle like endoplasmic reticulum (ER). - Cell division generally by binary fission (a - Cell division involves mitosis (involves somatic type of asexual reproduction due to lacking cells) & or meiosis (involves gametes cells). nuclei). - Cell walls consist of peptidoglycan. - Plants & algae cell walls consist of cellulose; fungi contain chitin. - Have mesosomes (in bacteria) & plasma - No mesosomes. membrane (cyanobacteria) - Mitochondria - Site for cellular respiration - Site for cellular respiration - Produce ATP. - Produce ATP. - No chloroplast; - Have chloroplast - Only photosynthetic lamellae present in - Present in plant cells & algae. cyanobacteria. 12 2.2 PROKARYOTES AND EUKARYOTES B) EUKARYOTES Two categories : i) Unicellular eukaryote Microscopic Example: protist (protozoa), some algae and fungi Nucleus and other organelles surrounded by membrane ii) Multicellular eukaryote: Plant cell ii) Multicellular eukaryote: Animal cell  Differences Between Animal Cells & Plant Cells Animal Cell Plant Cell No cellulose cell wall. Have cellulose cell wall. only have plasma membrane (cell surface Have plasma membrane (cell surface membrane) membrane) No plasmodesmata & pits. Plasmodesmata & pits present in cell wall. No chloroplasts. Chloroplasts present in photosynthetic cells. Small, temporary vacuoles. Large permanent central vacuole filled with cell sap. No tonoplast. Tonoplast around vacuole.  Animal Cell Plant Cell Nucleus often central. Nucleus & cytoplasm usually peripheral. Cytoplasm throughout the cell. Contain glycogen granules for carbohydrate Contain starch granules for carbohydrate storage. storage. Smaller than plant cells. Often larger than animal cells. Some cells have cilia & flagella No cilia & flagella. example: Ciliated epithelium of trachea, oviducts, sperms. Lysosomes present. Lysosomes usually absent except insectivorous plants.  3. ORGANELLES 2.3 STRUCTURE AND FUNCTION OF ORGANELLES TYPES OF ORGANELLES /STRUCTURES BASED ON FUNCTION Manufacturing Oxidative Network of Extracellular Energy and/or Organelle fibers structures converting breakdown structures organelles organelles Peroxisome (cytoskeleton) Cell wall Ribosome Endomembrane Mitochondria Nucleus system Microtubules Extracellular Nuclear Endoplasmic matrix Chloroplast envelope reticulum Microfilaments Golgi Intermediate Intercellular Lysosome junctions Apparatus filaments Vesicles & Plasma Vacuoles membrane NUCLEUS Most of the cell’s DNA is located in the nucleus. ⮚ Some DNA in mitochondria and chloroplast. Usually spherical or oval. Typically located in the central region of the cell.  Nuclear envelope/membrane 3. ORGANELLES – Encloses the nucleus, separating it from the cytoplasm. – Double membrane; each consists of phospholipid bilayer. – Perforated by pores. Nuclear pore Nuclear lamina – Surrounded by a protein – Array of protein filaments / structure called pore complex. intermediate filaments. – Regulates the entry and exit – Lines the inner surface of the of macromolecules. nuclear envelope. – Helps maintain the shape of the nucleus.  Nuclear matrix – Network of protein fibers found throughout the nuclear interior. – Both nuclear lamina and matrix organize genetic material in the nucleus. Chromosomes Nucleolus (plu. Nucleoli) – Contain DNA molecule. – Each chromosome is a single DNA – Not enclosed by a membrane. molecule with many globular proteins called – Site for ribosomal RNA (rRNA) histones. synthesis, from instruction in – DNA coiled around the proteins forming the DNA. chromatin. – Chromatin condenses forming chromosomes as a cell prepares to divide. NUCLEUS RIBOSOMES Ribosome : structure made of ribosomal RNA (rRNA) and protein. – Site for protein synthesis. – Cells active in protein synthesis have a large number of ribosomes and prominent nucleoli (Example: pancreatic cells). Two types of ribosomes; i. free ribosomes ✔ suspended in the cytosol; ✔ produces proteins that function within the cytosol. i. bound ribosomes free ✔ attached to the outside of the endoplasmic ribosome bound ribosome reticulum or nuclear envelope; ✔ produce proteins to be inserted into the membrane or exported out of the cell (pancreatic enzymes). ENDOMEMBRANE SYSTEM The endomembrane system regulates protein traffic and performs metabolic functions in eukaryotic cells. Components of the endomembrane system: 1. Nuclear envelope 2. Endoplasmic reticulum 3. Golgi apparatus 4. Lysosomes 5. Vesicles & Vacuoles 6. Plasma membrane These components are either continuous or connected via transfer by vesicles. Properties of Endomembrane System Carries out a variety of tasks in the cell, including: ☑ Protein synthesis and transport of proteins into membranes and other organelles. ☑ Metabolism and movement of lipids. ☑ Detoxification of poisons. ☑ Membranes of this system are related either through direct physical continuity or by the transfer of vesicles (sacs made of membrane). ENDOMEMBRANE SYSTEM : ENDOPLASMIC RETICULUM ○ Extensive network of membranes. ○ Accounts for more than half of the total membranes in many eukaryotic cells. ○ Consists of a network of membranous tubules & flattened sacs called cisternae. Cisternal space ○ The internal lumen/space of the ER that is separated from the cytosol by the ER membrane. The ER membrane, ○ is a single-layer membrane, ○ is continuous with the outer nuclear membrane. ○ separates the ER lumen/cisternal space from the cytosol. There are two distinct regions of ER: 1. Smooth Endoplasmic Reticulum (smooth ER) ⮚ Lacks ribosomes at the outer surface. 2. Rough Endoplasmic Reticulum (Rough ER) ⮚ Has ribosomes on the outer surface of the membrane. ENDOMEMBRANE SYSTEM : SMOOTH ENDOPLASMIC RETICULUM Lacks ribosomes. System of interconnected tubules. Continuous from the Rough ER. Not involved in protein synthesis. The functions of smooth ER: 1. Metabolize lipids, synthesize cholesterol and phospholipids and synthesize lipid components of lipoproteins (liver cells). 2. Synthesize steroid-based hormone (testosterone). 3. Absorb, synthesize, and transport fats. 4. Detoxify drugs, certain pesticides, and cancer-causing chemicals (kidneys and liver). 5. Break down glycogen to form glucose (liver). 30  3. ORGANELLES ENDOMEMBRANE SYSTEM : ROUGH ENDOPLASMIC RETICULUM Have cisternae, studded with ribosome. Protein from bound ribosome enter the ER lumen and carbohydrates are attached to it to form glycoproteins. Glycoprotein is an example of a secretory protein (protein with carbohydrate that is covalently bonded to it). It then departs/buds off from the RER in a membranous vesicle called a transport vesicle. These transport vesicles, transit from one part of the cell to another. Act as membrane factory for the cell; ⮚ adding membrane protein and phospholipids to its own membrane in making secretory protein. ENDOMEMBRANE SYSTEM : 3. ORGANELLES GOLGI APPARATUS/ BODY Works as a receiving and shipping center. Consists of flattened membranous sacs called cisternae. Each Golgi stack has three areas; – The cis face: entry surface – The trans face: exit surface – The medial region: in between Functions of the Golgi apparatus: – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles CELLS Chapter 2 CELLS Chapter 2  SUMMARY OF SECRETORY PROTEIN TRANSPORT 1. Polypeptides synthesized on ribosomes bound to RER. 2. Protein assembled and carbohydrate component added in the lumen of ER. 3. Protein products (e.g.: glycoproteins) are packaged at the transitional region of RER. 4. Transport vesicles move proteins to the Golgi body (cis face). 5. Proteins further modified during transit from cis to trans region in Golgi. 6. Proteins (e.g.: glycoproteins or secretory proteins) are packaged in transport vesicles in the trans face. 7. Transport vesicle that departs from the trans face contains secreted products inside, may : i. fuse with the plasma membrane & release content from the cell. ii. give rise to specialized vesicles (e.g.: lysosome) or vacuoles. iii. fuse with less mature Golgi cisternae. iv. carry proteins back to ER (required in RER) *glycoprotein (shown as green-purple molecule) ENDOMEMBRANE SYSTEM : LYSOSOME A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules. Lysosomal enzymes; ☑ can hydrolyze proteins, fats, polysaccharides, and nucleic acids. ☑ Work best in an acidic environment (pH 5). If the lysosome breaks, the released enzymes are not effective, as cytosol has a neutral pH. However lysosomal membrane becomes fragile when the cell is injured, lacks oxygen, and when an excessive amount of vitamin A present causes the lysosome to rupture and leads to autolysis.  3. ORGANELLES Nucleus 1 µm Lysosome carry out intracellular digestion: ENDOMEMBRANE SYSTEM (a) Phagocytosis A process by engulfing food particles. Food vacuole formed and fused with lysosome. The enzyme digests the food. Lysosome Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis  Vesicle containing 1 µm (b) Autophagy two damaged organelles Recycle the cell’s own organic material. Mitochondrion Damaged organelle becomes fragment surrounded by membrane. Peroxisome fragment Lysosome fuses with this vesicle Lysosomal enzyme dismantles the Lysosome enclosed material and releases it into the cytosol for reuse. Peroxisome Mitochondrion Digestion Vesicle (b) Autophagy 38 ENDOMEMBRANE SYSTEM : 3. ORGANELLES VACUOLES Vacuoles are large, single membrane-enclosed sacs. A plant cell or fungal cell may have one or several vacuoles. Types of vacuoles: 1. Food vacuoles are formed by phagocytosis. 2. Contractile vacuoles 1. found in many freshwater protists, to pump excess water out of cells (osmoregulatory function). 3. Central vacuoles found in many mature plant cells, hold organic compounds and water. Enclosed by a membrane called tonoplast.  food vacuole Central vacuole Cytosol Tonoplast cilia nucleus Nucleus Central Contractile vacuole vacuole Cell wall (a) Food vacuole and contractile vacuole in Paramecium Chloroplast 5 µm  Relationship among organelles of the 1. Nuclear envelope is connected to endomembrane system rough ER. Rough ER is continuous with smooth ER. 2. Membranes & proteins produced by the ER, flow in the form of transport vesicles to the Golgi. 3. Golgi pinches off transport vesicles & other vesicles that give rise to lysosomes, other types of specialized vesicles & vacuoles. 4. Lysosome fuses with other 5. Transport protein carries 6. Plasma membrane expands by vesicle for digestion proteins to plasma fusion of vesicles & proteins are membrane for secretion. secreted form the cell. ENERGY CONVERTING ORGANELLES MITOCHONDRIA AND CHLOROPLASTS – Not part of the endomembrane system. – Double membrane organelles. – Contain proteins made by free ribosomes. – Contain circular DNA. – Grow and reproduce somewhat independently in cells (semi-autonomous). Mitochondria - site for cellular respiration to produce ATP. Chloroplasts - site of photosynthesis and found in plants and algae.  3. ORGANELLES MITOCHONDRIA Mitochondria are found in nearly all eukaryotic cells. Motile or contractile cells have more mitochondria per volume than less active cells. A double membrane forms two compartments: intermembrane space and matrix; – The outer mitochondrial membrane is smooth, Intermembrane space allowing small molecules to pass through it. – The inner mitochondrial membrane strictly regulates molecules that move across it and fold into cristae.  Mitochondrial matrix has many different enzymes, mitochondrial DNA, and ribosomes. Intermembrane space Some steps of cellular Outer membrane respiration occurred in the mitochondrial matrix. Free CELLS ribosomes Cristae present a in the mitochondrial Inner matrix membrane large surface area Cristae for enzymes that Matrix Chapter 2 synthesize ATP. 0.1 µm  3. ORGANELLES CHLOROPLAST A member of plastids. Plastids ✔ a group of organelles that produce and store food materials in plants and algae. ✔ examples of plastids – chloroplasts, chromoplasts & leucoplasts (amyloplast). Chloroplasts contain chlorophyll, carotenoids, enzymes, and other molecules that function in photosynthesis. Found in leaves of plants and algae.  Chloroplast ✔ Larger than mitochondria. ✔ disc-shaped structures. ✔ bounded by a double membrane. Chloroplast structure includes: Three regions (separated by 1. Thylakoids membrane): 1. Intermembrane space ⮚ membranous sacs, stacked 2. Stroma to form a granum. 3. Thylakoid lumen 2. Stroma ⮚ fluid-filled internal space - contains enzymes.  CHLOROPLAST Ribosomes Stroma Inner and outer membranes Granum 1 µm Thylakoid OXIDATIVE ORGANELLES 3. ORGANELLES PEROXISOME PEROXISOMES Specialized metabolic compartments bounded by a single membrane. Peroxisomes are numerous in the kidneys and liver, which are active in detoxification. Peroxisomes contain oxidase that transfers hydrogen from various substrates to oxygen and produces hydrogen peroxide (H2O2), but if H2O2 escape from the peroxisomes, they might damage other membranes in cells. Catalase breaks down H2O2 into water and oxygen (.: harmless). Oxygen is also used by peroxisomes to break down fatty acids into smaller molecules that are transported to mitochondria and used as fuel for cellular respiration. Chloroplast Peroxisome Mitochondrion 1 µm  CYTOSKELETON A dense network of protein fibers extending throughout the cytoplasm. Three types of fibers make up the cytoskeleton: 1. Microtubules the thickest of the three components of the cytoskeleton. 2. Microfilaments also called actin filaments, the thinnest components. 3. Intermediate filaments ⮚ have diameters in the middle range ⮚ are made from fibrous protein subunits ⮚ are more stable than microtubules & microfilaments. Microtubules & microfilaments: o formed from globular protein (beadlike) subunits o Can be rapidly assembled & disassembled.  Function of Cytoskeleton Gives cells mechanical strength, supports the cell, and maintains its shape. Organizes the cell’s structures and activities, anchoring many organelles. Certain cytoskeleton /microtubules interact with motor proteins to produce motility. Inside the cell, vesicles travel along tracks made up of microtubules of the cytoskeleton. Function in cell division.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vesicle Molecular motors : vesicles transported along microtubules using motor proteins that use ATP to generate force. The vesicles are attached to motor Dynactin complex proteins, example; dynein by = connector molecule connector molecules, example; Dynein = motor protein dynactin. Dynein moves the vesicle along microtubules. Microtubule 54  3. ORGANELLES CYTOSKELETON: MICROTUBULESMICROTUBULES  3. ORGANELLES MICROTUBULES EXAMPLE 1: Centrosomes and Centrioles ⮚ function in cell division. In many cells, microtubules grow out from a centrosome near the nucleus. The centrosome is a “microtubule-organizing center (MTOC)”. In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring, (known as 9 X 3 structure)  CYTOSKELETON: MICROTUBULES nine triplets of microtubules arranged in a ring (9 X 3 structure)  3. ORGANELLES MICROTUBULES The centrioles are duplicated before cell division & may play a role in some types of microtubule assembly. The ability of microtubules to assembles & disassemble is rapidly seen during cell division. At that time, tubulin subunits organizes into a structure called mitotic spindle – which serves as a framework for the orderly distribution of chromosomes during cell division. MICROTUBULES 3. ORGANELLES MICROTUBULES EXAMPLE 2: Cilia and Flagella Direction of swimming Microtubules control the beating of cilia and flagella. Cilia and flagella differ in their beating patterns. (a) Motion of flagella 5 µm Cilia and flagella share a common ultrastructure: Direction of organism’s movement – A core of microtubules covered by the plasma membrane. Power Recovery stroke stroke – A basal body that anchors the cilium or flagellum. – A motor protein called dynein, which (b) Motion of cilia drives the bending movements of a cilium or flagellum.  Outer microtubule 0.1 µm Plasma doublet membrane Dynein proteins Central microtubule Radial spoke Nine doublets or pairs of Protein cross- microtubules encircling one Microtubules CELLS linking outer doublets central pair (b) Cross section of Plasma cilium ✔ Cilium has a 9 X 2 + 2 membrane ring structure Basal body 0.5 µm Chapter 2 (a) Longitudinal 0.1 µm section of cilium Triplet Centrioles form the base of cilia and flagella are known as basal body. ✔ Basal body has a 9 x 3 structure. (c) Cross section of basal body 61 62 MICROFILAMENTS MICROFILAMENTS MICROFILAMENTS Muscle cell Actin filament arranged parallel to one another in CELLS muscle tissue Chapter 2 Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction MICROFILAMENTS Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Localized contraction helped by actin and myosin drives amoeboid movement. MICROFILAMENTS c) Cytoplasmic streaming A circular flow of cytoplasm within cells. Occurs due to the motion of organelles attached to actin filaments via myosin-motor proteins.  3. ORGANELLES INTERMEDIATE FILAMENTS  3. ORGANELLES EXTRACELLULAR STRUCTURE Extracellular components and connections between cells help coordinate cellular activities. Most cells synthesize and secrete materials that are external to the plasma membrane. These extracellular structures include: 1. Cell walls of plants 2. The extracellular matrix (ECM) of animal cells 3. Cell junctions CELL WALL OF PLANTS The cell wall is an extracellular structure that distinguishes plant cells from animal cells. Prokaryotes, fungi, and some protists also have cell walls. The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water. Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein.  3. ORGANELLES Plants cell wall may have multiple layers: 1. Primary cell wall: thin and flexible. Secondary cell wall Primary cell wall 2. Middle lamella: thin layer rich in Middle pectins, glues adjacent cells. lamella 3. Secondary cell wall (in some cells): 1 µm Central vacuole deposited in several laminated Cytosol Plasma membrane layers, strong and durable for cell Plant cell walls protection and support. Plasmodesmata: channels between Plasmodesmata adjacent plant cells EXTRACELLULAR MATRIX MATRIX EXTRACELLULAR Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM). The ECM is made up of the followings: Collagen Fibres embedded in web of proteoglycan complexes. Proteoglycan Hundreds of proteoglycan (small core complexes protein with many carbohydrate chain covalently attached) attach to single long polysaccharide molecule. Fibronectin Attach the ECM to integrins that embedded in plasma membrane.  CELLS Integrins: two subunits of membrane proteins, (a) bind with ECM on the outside (b) attach to the microfilaments on the inside. In a position to transmit signals between ECM and the cytoskeleton inside.  3. ORGANELLES CELL JUNCTIONS CELL JUNCTIONS Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact. There are several types of cell junctions: i. Plasmodesmata ii. Tight junctions iii. Desmosomes iv. Gap junctions PLANT CELL JUNCTION: PLASMODESMATA Channels that perforate plant cell walls. Through it, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell. Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes Plasmodesmata : plant cells can communicate through specialized openings in their cell walls, called plasmodesmata, where the cytoplasm of adjoining cells are connected. ANIMAL CELL JUNCTIONS CELL JUNCTIONS Consist of: i. Tight junctions: i. Desmosomes (anchoring junctions) iii. Gap junctions (communicating junctions) ANIMAL CELL JUNCTIONS CELL JUNCTIONS i. Tight junctions: ✔ Areas of tight connections between membranes of adjacent cells. ✔ No space remains between the cells, preventing leakage of extracellular fluid & substances between cells. ANIMAL CELL JUNCTIONS CELL JUNCTIONS ii. Desmosomes (anchoring junctions) ✔ are points of attachment between cells. ✔ fasten cells together into strong sheets. ✔ Substances can still pass freely through the spaces between the plasma membranes. ANIMAL CELL JUNCTIONS CELL JUNCTIONS iii. Gap junctions (communicating junctions) ✔ Provide cytoplasmic channels between adjacent cells. ✔ Allows the transfer of small molecules & ions between adjacent cells. 2.4 SPECIALISED TISSUES IN ANIMAL Cells undergo cell differentiation and become specialized in structure and function Tissues: groups of cells with similar appearance and a common function Different tissues have different structures to suit their functions Four categories of animal tissues: i. epithelial ii. connective iii. muscle iv. nervous 80 a) EPITHELIAL TISSUE Covers the outside of the body and lines the organs and cavities within the body. It contains cells that are closely joined. The shape of epithelial cells may be: i. squamous ii. cuboidal iii. Columnar The arrangement of epithelial cells may be: i. simple (single-cell layer) ii. stratified (multiple layers of cells) iii. pseudostratified (a single layer of cells of varying length) 81  Epithelial Tissue Stratified squamous epithelium Basement membrane Pseudostratified Cuboidal Simple columnar Simple squamous columnar epithelium epithelium epithelium epithelium 82 i) Simple Squamous Epithelium Cells are flat and arranged in a single layer. Lines blood vessels Allow diffusion and passage of materials. and air sacs in lungs Permits exchange of Example: ✔ Air sacs of lungs and lining of blood materials by diffusion vessels. 83 ii) Simple Columnar Epithelium The large, brick-shaped cells Found where secretion or active absorption is important. Lining of the intestines, secreting digestive juices and absorbing nutrients. 84 iii) Simple Cuboidal Epithelium Dice-shaped cells. Lines blood vessels Specialized for secretion. and air sacs in lungs Found in kidney tubules and many Permits exchange of glands, including the thyroid gland and materials by diffusion salivary glands. 85 iv) Stratified Squamous Epithelium Multilayered and regenerates rapidly. Found on surfaces subject to abrasion. Eg: the outer skin and linings of mouth, anus, and vagina. 86 v) Pseudostratified Columnar Epithelium Consists of a single layer of cells varying in height. A pseudostratified epithelium of ciliated cells forms a mucous membrane that lines the respiratory tract. Example: Beating cilia sweep mucus along the surface. 87 Glands: Specialized Epithelial Tissue a) Goblet cells - unicellular exocrine glands that secrete mucus. b) Exocrine glands - secrete product through a duct onto the exposed epithelial surface. - example: sweat and salivary gland c) Endocrine glands - release hormones into interstitial fluid or blood. - example: Pituitary glands 88  Unicellular glands Cilia (goblet cells) Basement membrane (a) Goblet cells. Skin (d) Endocrine gland (b) Sweat gland. (c) Parotid salivary gland. 89 b) CONNECTIVE TISSUE Mainly binds and supports other tissues. Made of three main elements: i. Ground substance (example: fluid) ii. Fibers (example: collagen) iii. Cells (example: blood cells) 90  Connective Tissue Loose connective tissue Collagenous fiber Blood Plasma White blood cells 120 μm 55 μm Elastic Red blood cells fiber Cartilage Fibrous connective tissue Chondrocytes 100 μm 30 μm Chondroitin sulfate Nuclei Bone Adipose tissue Central canal Fat droplets 700 μm 150 μm Osteon 91  Types of Connective tissue Descriptions 1) LOOSE CONNECTIVE TISSUE The most widespread. Found in the skin and throughout the body. 2) FIBROUS CONNECTIVE TISSUE Dense with collagenous fibers. Found in: - tendons which attach muscles to bones - ligaments which connect bones at joints. Types of Connective tissue Descriptions 3) BONE Mineralized connective tissue. Osteoblasts, bone-forming cells deposit a matrix of collagen. Combine with calcium, magnesium, and phosphate ions into a hard mineral within the matrix. 4) BLOOD Has a liquid extracellular matrix called plasma. Suspended in plasma are erythrocytes, leukocytes platelets. Types of Connective tissue Descriptions 5) CARTILAGE Strong yet flexible support material. Skeletons of embryos contain cartilage; replaced by bone as the embryo matures. 6) ADIPOSE TISSUE Specialized loose connective tissue that stores fat in adipose cells. Insulates the body and stores fuel as fat molecules. C) NERVOUS TISSUE Nervous tissue senses stimuli and transmits signals throughout the animal. Nervous tissue contains (a) Neurons, or nerve cells, that transmit nerve impulses. (b) Glial cells, or glia, that help nourish, insulate, and replenish neurons. D) MUSCLE TISSUE Responsible for many types of body movement The cells contain actin and myosin, which together enable the muscle to contract Three types: i. Cardiac muscle ii. Smooth muscle iii. Skeletal muscle/striated muscle i. Cardiac Muscle Forms wall of heart. Striated. Has similar contractile properties. Have intercalated discs (composed of gap junctions) that interconnect cell to cell which relay signals between them. to synchronize heart contraction.  ii. Smooth Muscle Lacks striations. Found in the walls of the digestive tract, urinary bladder, arteries, and other internal organs. Responsible for involuntary body activities, for example: peristalsis of small intestines, churning of the stomach and constriction of arteries. iii. Skeletal Muscle Attached to bones by tendons, Responsible for voluntary movements. Skeletal muscle fibers form by the fusion of many cells, resulting in multiple nuclei in each muscle fiber. Arrangement of contractile units (sarcomere) and fibers gives the cells a striped (striated) appearance. 2.5 SPECIALISED TISSUES IN PLANTS 3 basic plant organs; roots, stems, leaves Each organ is composed of 3 basic tissues; a) dermal, b) vascular c) ground Each tissue forms continuous tissue system throughout the plant. 3 tissue systems in plant 101 a) Dermal Tissue System Plant’s outer protective covering. First line of defense against physical damage and pathogens. Non-woody plants; single tissue called the epidermis, a layer of tightly packed cells. Woody plants, the periderm replace the epidermis in older regions. a) Dermal Tissue System Waxy epidermal coating (cuticle) prevents water loss. In roots, water and minerals absorbed enter through the epidermis of root hairs. In shoots, guard cells are involved in gaseous exchange. Trichomes, specialized epidermal cells in shoots reduce water loss and reflect excess light. b) Vascular Tissue System The vascular tissue system are embedded in the ground tissue. Facilitate the transport of materials through the plant via xylem and phloem. Provide mechanical support. Both xylem and phloem are continuous throughout the plant body..  Two types of vascular tissues are: 1) Xylem Conducts water and dissolved minerals upward from roots into the shoots. Two types of conducting cells: i. Tracheids: ▪ main conducting cells of gymnosperms and ferns. ▪ Occurs in clumps in xylem throughout the plant body. ▪ Function: i) Conduction of water & nutrient minerals; ii) Support. ii. Vessel elements: ▪ main conducting cells of angiosperms. ▪ Function: i) Conduction of water & nutrient minerals; ii) Support. ▪ More efficient than tracheids in conduction. 2. Phloem transports sugars the products of photosynthesis and transports other nutrients, from where they are made (usually the leaves) to other parts of the plant. Made up of two specialized cells: a) Sieve tube elements ▪ Living but lacks nucleus & other organelles at maturity. ▪ End walls are sieve plates - have perforated ends. ▪ Function: Conduction of sugar in solution. b) Companion cells ▪ Living ▪ Has cytoplasmic connections with sieve tube element. ▪ Function: i) Provide ATP and materials to maintain sieve tube elements; ii) Assists in moving sugars into and out of sieve tube element. c) Ground Tissue System Forms the bulk of the plant. Composed of three tissues: i. parenchyma ii. collenchyma iii. sclerenchyma These tissues can be differentiated from each other by their cell wall structures.  Feature Parenchyma Collenchyma Sclerenchyma 1. Cell Shape Isodiametric cells which are oval, Circular, oval or polyhedral. Variable in shape. spherical or polygonal in shape. Two types: Fibres and sclereids. 2. Cell wall Thin cellulosic wall Uneven thickening on primary cell wall. Have both primary and lignified thick secondary cell wall 3. Cytoplasm Abundant Present Absent 4. Nucleus Present – Living Tissue Present – Living Tissue Absent – Dead tissue 5. Vacuoles Large vacuole Vacuolated Absent 6. Intercellular Present Absent Absent Spaces 7. Occurrence Basically packing tissue. All soft part Dicot stems (e,g: elderberry), petiole and Dicot hypodermis, bundle sheath, of plant, leaf cells, root, pith, cortex, beneath the epidermis. Absent in monocot pericycle, seed, pulp of fruits, shells of medullary rays. and roots. walnuts & coconuts, pits of cherries & peaches. 8. Function Food storage (oil droplets, water & Provide tensile strength (elastic support), Protection from stress and strain, salts), Photosynthesis (green Mechanical support, Flexible structure. Mechanical strength & support. chloroplasts) & secretions (resins, Photosynthesis. tannin, sugary nectar and hormones) THE END