genbio.docx

#### (GenBio) ♦ Microscopy and the Discovery of the Cell ♦ Historical Development of the Microscope  #### Figure 1.1. The Earliest Compound Microscope by Hans and Zacharias Janssen #### The Early Microscope ◾ It was in 1597 when Hans Janssen and his son. Zacharias Janssen,...

#### (GenBio) ♦ Microscopy and the Discovery of the Cell ♦ Historical Development of the Microscope  #### Figure 1.1. The Earliest Compound Microscope by Hans and Zacharias Janssen #### The Early Microscope ◾ It was in 1597 when Hans Janssen and his son. Zacharias Janssen, discovered that positioning a lens at each end of a tube allowed for the magnification of images when used to observe objects. This invention paved the way to more discoveries in the study of +-----------------------------------+-----------------------------------+ | Figure 1.4. Robert Hooke\'s | Leeuwenhoek\'s | | Microscope | | | | Microscope | +-----------------------------------+-----------------------------------+ microbiology. Some believe that the Janssen\'s based the idea for their Invention on the opposite mechanism of a telescope. #### Seventeenth-Century Microscopes and the Discovery of the Cell ◾ In the early part of the 17th century, Galileo Galilei arranged two glass lenses in a cylinder and examined the compound eye of an insect. Thus, a physicist, not a biologist, was the first to record a biological observation using a crude microscope. From here, the study of the cellular basis of life was not far from reality. Numerous optical workshops were set up throughout Europe by 1625. ◾The compound microscope by the Janssens was then modified by Robert Hooke, an English scientist who first discovered and named the cell. He is considered the \"English Father of Microscopy. One of his greatest discoveries was the cell, which he named after the small monastery rooms that looked similar to those he saw under the microscope. He called these small room like structures \"cells\". What he actually saw were dead plant cells. The first scientist to see the was Antonie van Leeuwenhoek in 1674.  ------------------------ ---------------------------------------------------- Figure 1.3. Cell Structure of Cork by Robert Hooke ◾ Antonie van Leeuwenhoek, a Dutch microscope maker, was the first to study protozoa. He created an instrument that provided a magnification of 270x, which was exceptionally greater than those of the early microscopes 20x to 30x magnifications. He mounted between brass plates a well-polished, double-convex lens. This paved the way for the development of the world\'s firg practical microscope. ◾ After about 50 years since the compound microscope was invented, Robert Hooke and Antonie van Leeuwenhoek discovered that the shorter the focal lengths of the lenses, the greater the magnifying power. This led to the use of double convex or spherical lenses to create compound microscopes with better resolution and higher magnification. Through the use of these microscopes, the bulk of the discoveries in biology were made. It was especially evident in the field of microbiology. Robert Koch\'s discovery of the bacteria that cause tuberculosis and cholera was among the greatest of these discoveries. ◾ Leeuwenhoek withheld how he made his lenses, which is why significant developments in the study of microbiology were made only in the 19th century, when the compound microscope was improved upon by other scientists. **The Parts of the Microscope and Their Functions** ◾ Most ordinary classroom laboratories use light compound microscopes to see living or preserved specimens and to give clear images of cells such as bacteria. This type of microscope can magnify specimens by up to about 1,000 times their original size, and specimens are often stained to make the images stand out. ◾ **One** objective is a lower-power lens. It magnifies ten times and is marked 10x. [◾ Ocular lens × Objective lens = Total magnification.] [Example: 10x × 10x = 100x (100 times larger)] ◾ The **second** objective lens is a high-power lens. High-power objectives can magnify 40x on the common compound microscope model you are using. [◾ Ocular lens × Objective lens = Total magnification.] [Example: 10x × 40x = 400x (400 times larger)] **RESOLUTION:** is the ability of a microscope to show the details of an object being examined. It refers to the shortest distance between two points on a specimen that can still be distinguished by the observer or camera system. **CONTRAST:** refers to the darkness of the background with reference to the specimen. Usually, lighter specimens could be seen clearly on darker backgrounds. In order to see colorless/transparent specimens, you need to use a phase contrast microscope, which is a type of microscope. **The Parts of Light Microscope** **I. Mechanical parts** --\> parts of the microscope that are involved in giving support or strength to the instrument. These are also the parts that are movable and can be adjusted. a. **Body Tube** -- a hollow tube through which light passes from the objective to the eyepiece b. **Revolving nosepiece** -- holds the objectives. It can be rotated to select the appropriate objective. The lenses must be "clicked" into place to successfully view a specimen. c. **Arm** -- connects the base and the body tube together. It serves as a handle for carrying the microscope. d. **Stage** -- the platform where the slide or specimen to be examined is placed. It has an opening at the center that allows light to pass from below to the specimen. e. **Stage clips** -- holds the slide in place f. **Base** -- the part where the microscope is firmly anchored. It gives support to the whole microscope and is the part where the illuminators are attached. g. **Inclination joint** -- a joint found in some microscopes at which the arm is attached to the pillar of the microscope. It is used for tilting the microscope. **II. Illuminating Parts** -- parts of the microscope that provide and capture light for illumination a. **Mirror** -- reflects light from the surroundings to the specimen on the stage. It is planar on one side and concave on the other. The concave side of the mirror is used for natural light, while the flat side is used for artificial light. It is supported by the mirror rack. In more modern microscopes, this is already replaced with a light source or a bulb that provides light. b. **Condenser** -- concentrates the light from the light source or mirror onto the object of specimen being studied. It is located below the stage, and it is held in place by a rack. c. **Iris diaphragm** -- regulates the amount of light that reaches the specimen. It is attached beneath the condenser. **III. Magnifying Parts** -- parts of the microscope that are involved in magnifying the image of the specimens, including the resolution a. **Eyepiece or ocular** -- The part through which an observer look s to view a specimen. It usually has a magnification of 10x, through eyepiece with 5x to 30x magnification are also available b. **Objectives** -- the main lenses that magnify the specimen being observed. Usually, microscopes have three objectives, but more modern ones house four or even five objectives. Typical objectives have magnifying power of 4x, 10x, 40x, and 100x **Cell Theory: The Unifying Foundation of Cell Biology** ◾ In the **1820s**, improvements in lens design provided more details in cell structures. It was **Robert Brown**, a botanist, who first observed the spherical structure in plant cells. He called this structure the "nucleus" of the cell. By **1839**, **Theodore Schwann**, a zoologist, discovered the presence of cells in animal tissues, followed by the discovery of **Matthias Schleiden**, the botanist who conclude that all plant tissues are composed of cells. ◾ More than a decade after the discoveries of Schwann and Schleiden, another German scientist, **Rudolf Virchow,** a physician by profession, studied the growth and development of cells and discovered that all cells arise from preexisting cells. ◾ The cell theory is one of the foundations or doctrines in the study of life. The observations made by these three scientists comprised the cell theory which includes the following tenets: a. Cells are the smallest unit of life. All living things are composed of one or more cells. b. Cells are the basic unit of organization of all organisms. c. Cells come only from preexisting cells. ◾ Modern cell theory adds two additional key points: **a.** Cells carry and pass on to the offspring hereditary units during cell division. **b.** All cells are relatively the same in terms of chemical composition and metabolic activity. #### Cell Size ◾ Most cells are microscopic; however, unfertilized bird eggs are typically large enough to be seen with the naked eye. Bacterial cells range about 1-10μm (microns or micrometers) in diameter. Most plant and animal cells are visible only under the microscope, ranging from a size of 10-50μm in diameter. These include the cells that comprise your body. #### Cell Shape ◾ Cells vary not only in **size** but also in **shape**. A cell's shape depends on its function. For example, most nerve cells are long, which are related to their functions of transmitting impulses from the central nervous system to the different parts of the body. A **neuron** or nerve cell has cytoplasmic extensions, such as axons and dendrites, that are important in the performance of its functions. **Skin cells** are flat cells that help cover the body from the external environment, while blood cells can change shape, helping them digest and kill diseasecausing germs that invade the body. #### Internal Organization ◾ Cells also vary in terms of **internal organization**. The structural characteristics of a particular cell are closely related to its function. The diversity in cells could be seen between different species. Take, for example, a plant cell and animal cell. These two cells show great variations in parts because they function differently to perform specific tasks. Even a single human body carries several different kinds of cells. Each cell in the human body is specialized and adapted for a particular job. For example, glandular cells are different from muscle cells. Glandular cells produce secretory materials such as #### Cell Basic and fundamental unit of life, it possesses a highly organized structure that enables it to carry out its vital functions. **TYPES OF CELL:** #### Structure and basic functions ◾ These components work together to maintain cellular homeostasis and perform essential life activities. ##### Cell membrane ◾ The cell membrane surrounds the cell and is a selective barrier between the interior and the exterior. ◾ Its primary role lies in regulating the passage of substances, including nutrients and waste materials. ◾ Within it, specialized proteins play a crucial role in facilitating molecular transport and cellular communication. ##### Cell nucleus ◾ An organelle that houses DNA, located in the center of eukaryotic cells. ◾ Its primary function is to store and safeguard genetic information, controlling gene expression and DNA replication. ◾ It also contains the nucleolus, which is involved in ribosome synthesis. ##### Cytoplasm ◾ The cytoplasm is a gel-like matrix containing water, salts, proteins, and other molecules. It occupies the intracellular space between the cell membrane and the nucleus. ◾ It plays a crucial role in biochemical reactions, energy production, and substance transport. Essential for cellular metabolism, it provides structural support to the cell. ##### Protein Synthesis ◾ Building and repairing cellular structures, regulating biological processes, and expressing specific characteristics of each organism. ##### Ribosome ◾ Ribosomes are essential organelles for cellular functioning and survival. ◾ They synthesize proteins using the genetic information from messenger RNA (mRNA), which is crucial for cellular structure, function, and regulation. ◾ Ribosomes are located in the cytoplasm and the rough endoplasmic reticulum. ##### Endoplasmic reticulum ◾ A network of interconnected membranes that extends from the nuclear membrane to the cell membrane. It plays a fundamental role in the transport, processing, and distribution of proteins and lipids within the cell. **There are two main types of ER:** **The Rough Endoplasmic Reticulum (RER)** is studded with ribosomes and is involved in the synthesis and modification of proteins. **The Smooth Endoplasmic Reticulum (SER)** specializes in lipid synthesis, carbohydrate metabolism, and detoxification. ##### Golgi apparatus ◾ Key in the processing and packaging of proteins and lipids produced in the endoplasmic reticulum. ◾ It synthesizes carbohydrates and lipoproteins and is essential for maintaining the cell\'s internal balance and facilitating communication with the outside. ◾ Composed of a series of flattened sacs called cisternae, it acts as the \'shipping center\' of the cell, sorting and packaging proteins into vesicles for transport and distribution. ##### Energy Supply ◾ To carry out vital functions and necessary metabolic processes essential for the proper functioning of the cell and/or organism. ##### Mitochondria ◾ Present in eukaryotic animal and plant cells. Their primary function is energy generation through cellular respiration (ATP production). ◾ The double membrane of mitochondria allows for the organization of various stages of the respiratory chain, making it crucial for cellular function and survival. ##### Chloroplasts ◾ Exclusive to plant cells and photosynthetic organisms, chloroplasts carry out photosynthesis, converting solar ◾ energy into chemical energy. ◾ During photosynthesis, they synthesize glucose and other organic compounds using carbon dioxide and water, releasing oxygen as a byproduct. ◾ They are responsible for the crucial production of oxygen that sustains the planet. ##### Cellular Digestion ◾ It involves breaking down molecules and unwanted materials, enabling the recycling of nutrients and cellular maintenance. ##### Lysosomes ◾ They contain digestive enzymes that break down molecules and unwanted cellular materials. ◾ They facilitate cellular digestion, by disposing of waste, recycling nutrients, and defending against pathogenic invasions. ##### Peroxisomes ◾ They contain enzymes that degrade hydrogen peroxide and toxic compounds, thereby protecting the cell from oxidative damage. ◾ Additionally, they play a role in the synthesis and degradation of lipids and bile acids, regulating lipid metabolism and overall homeostasis. ##### Support and Movement ◾ Maintaining cellular shape, enabling cellular movement and division, are essential for its functioning and survival. ##### Cytoskeleton ◾ It is composed of protein filaments (microtubules, microfilaments, and intermediate filaments) and provides support and enables movement in eukaryotic cells. ◾ Its specific functions encompass stability, intracellular transport, and contraction. Furthermore, it regulates cellular shape and plays a role in division, migration, and communication. ##### Flagella and cilia ◾ Specialized structures for movement. They are elongated and enable locomotion in liquid environments, whereas cilia are shorter and create coordinated flow on the cell surface. ◾ Composed of microtubules in a \'9+2\' pattern, they are essential for sperm motility. ##### Storage and Transportation ◾ They manage nutrients, eliminate waste, and regulate metabolic processes. ##### Vacuoles ◾ **Membrane**-bound organelles found in plant cells and some animal cells. They store nutrients, water, ions, and waste materials, regulating turgor pressure and osmotic balance. ◾ Vacuoles can also be involved in the digestion of substances and serve as a defense mechanism against predators by containing toxins. **Vesicles and endosomes** ◾ Membranous vesicles that transport specific materials between organelles and the cell membrane. **Vesicles:** They transport materials from the endoplasmic reticulum and the Golgi apparatus to other destinations. **Endosomes:** They capture and distribute materials for degradation, recycling, or their incorporation into metabolic pathways. **(GenBio) CELL STRUCTURES AND THEIR FUNCTIONS** Similar to a computer with parts performing specific functions, the cells of your body have parts that also perform specific tasks. These parts work together to make it possible for you to do different activities such as jogging, sleeping, and studying. ##### Types of Cells - Improvements in microscopy and the study of cells led to the classification of organisms according to cellular organization and architecture. When scientists started using microscopes, two basic cellular architectures were discovered: **prokaryotic and eukaryotic**. **Prokaryotic cells**- have a relatively simple organization. They are mostly microscopic, measuring from 1 to 10 μm in diameters, and exist in unicellular form. The term prokaryote is derived from the word's **pro and karyon**, which mean **"before" and "kernel**," respectively. This term describes cells that already exist before the evolution of the cell nucleus. - Prokaryotic cells do not have a membrane-bound nucleus. Their organelles a real so not membranebound. There are two groups of bacteria in terms of evolution---the **archaebacteria and the eubacteria**. Both of these groups are prokaryotic. **PARTS OF PROKARYOTIC CELL:**  1. **Glycocalyx** -- an outer layer that provides protection. It is an important virulence factor since it protects disease-causing bacteria. It helps bacteria hold on to surfaces and protects them from being engulfed by macrophages. It may exist as a rigid capsule or a more unstructured slime layer. 2. **Cell wall** -- a structure that confers rigidity and shape to the cell. It is found outside of the plasma membrane and is composed of peptidoglycan. 3. **Plasma membrane** -- a structure that prevents the loss of water and electrolytes inside the cell. It also prevents the entry of unwanted substances into the cell. It is composed of phospholipid bilayer. 4. **Plasmid** -- a small, circular, extra chromosomal DNA molecule found in the cytoplasm. It is separate from chromosomal DNA. 5. **Nucleoid** -- the region where DNA is concentrated **6. Cytoplasm** -- the whole inside region of the cell where chromosomes, ribosomes, and other cellular inclusions are suspended 7. **Ribosome** -- the site where proteins are synthesized or created 8. **Pilus (plural, pili)** -- a short, hair like appendage on the surface of some bacteria. It helps bacteria adhere to the surfaces of host cells. It can also be used to transfer genetic material from one bacterium to another, in which case it is called sex pilus. 9. **Flagellum (plural, Flagella**) -- a long, threadlike structure that facilitates movement in bacteria **10. Fimbriae** -- bristle-like Fibers that are shorter than pili. It is primarily used for bacterial attachment to tissue surfaces. **Eukaryotic cells**- are more complex than prokaryotic cells. A typical eukaryotic cell measures 10 to 100 µm in diameter. They are bigger than prokaryotic cells. These cells have components that are surrounded by membranes which are called **organelles**. - The **nucleus**, the largest cell organelle, encloses the genetic material and is suspended in the cytoplasm. - The most distinguishing feature of this type of cell is **compartmentalization**, which is achieved by the endomembrane system that occupies the interior of the cell, including the membrane-bound organelles. Most of these organelles independently perform their multiple biochemical jobs, which can proceed independently or simultaneously. **Examples:** of eukaryotic cells are those that come from animals, plants, protists, and fungi. - The **eukaryotic cells** in your body and in other multicellular organisms vary in many aspects. It may vary in terms of size, shape, internal organization, and function. ##### Cell Structures and Their Functions \- Cells vary in many aspects. They vary in size, shape, and complexity. However, they are alike in a few basic characteristics. Every cell, except for bacteria, has three main parts: the nucleus, the cytoplasm, and the cell membrane. In this topic, you will learn about the various organelles and cellular components that allow the cells in the body to perform activities necessary for survival. #### A. Cell Membrane \- The cell membrane, sometimes called the **plasma** membrane, is a thin layer that separates the cell from its external environment. It is the outermost covering of animal cells and functions as a selective barrier that regulates the entrance and exit of substances into and out of cells. It is said to be a selectively permeable membrane. It provides shape and Flexibility for the cell. However, in plant cells, the cell wall is the outermost covering. The cell membrane can be described in two models: the classical model and the Fluid mosaic model. ##### - In 1930, British biologists Hugh Davson and James **Danielli** hypothesized that the cell is covered by a thin, Flexible envelope made up of phospholipid bilayer and proteins. This was the classical plasma membrane model. Through the help of the early electron macroscopics, it was confirmed that the phospholipid membrane has hydrophobic and hydrophilic ends. -- In **1972**, **Jonathan Singer and Garth Nicholson** proposed the fluid mosaic model of the plasma membrane which revolutionized our understanding of the nature of the membrane. This became more popular than the model of Davson and Danielli. - This was made possible using a modern electron microscope, which is more precise in nature. It states that at normal temperature, the plasma membrane behaves like a thin layer of fluid covering the surface of the cell and that individual phospholipids diffuse rapidly throughout the surface of the membrane. - It is termed mosaic because it includes integral proteins that protrude above or below the lipid bilayer, peripheral proteins, glycolipid, cholesterol, and other molecules.  The **glyocalyx** is the external coating of the cell membrane and is made up of glycoproteins and polysaccharides. It serves different functions as summarized below. It provides protection. - It enables cell-to-cell recognition. - It contains receptor or contact sites for enzymes and hormones. - It allows the cell to respond to changes in electrical potentials. - It acts as a filtration barrier. #### B. Cytoplasm \- The region of the cell that surrounds the nucleus is the cytoplasm. It is a semifluid matrix, and it is the largest interior part of the cell where organelles and cellular inclusions are suspended. The following are the organelles and other cellular inclusions found in the cytoplasm: Cytoplasmic Organelles **1. The endoplasmic reticulum (ER)** - is a network of intercommunicating channels composed of membrane-enclosed sacs and tubules. It serves as an intracellular highway through which molecules can be transported from one part of the cell to another. The amount of ER varies in each cell depending on its activity. There are two forms: the rough endoplasmic reticulum (RER)and the smooth endoplasmic reticulum (SER). RER looks rough due to the presence of ribosomes on its membrane surface. A cell with more RER produces a large amount of proteins to be inserted into the membranes or exported to the outside. On the other hand, the SER is more tubular and nongranular due to the absence of ribosomes. SER is usually involved in the synthesis of steroids in gland cells, breakdown of toxic substances by liver cells, and regulation of calcium levels in muscle cells. ##### 2. The Golgi apparatus \- which is similar to the endoplasmic reticulum, is also a system of membranes. It appears as a series of flattened sacs with a characteristic convex shape. It is surrounded with numerous vesicles filled with fluid and suspended substances. It works in close association with the endoplasmic reticulum. It is responsible for the processing, packaging, and sorting of secretory materials for use within the cell or for exocytosis (cell secretion). For example, after protein is synthesized by the ribosome, it passes into the interior of the rough endoplasmic reticulum. Then, it moves into the interior of the smooth ER, in which, the protein is enclosed by a membranous pouch that buds off from the smooth ER. Then, it migrates and fuses with the Golgi apparatus where a new vesicle is formed and passed on to the cell membrane and expelled to the outside (exocytosis). ##### 3. The mitochondrion (plural, mitochondria) \- is the power plant of the cell. It varies in size, shape, and number depending on the degree of cellular activity. It contains enzymes that help in the chemical oxidation of food molecules and produces energy in the form of ATP. Studies have shown that active cells such as your liver cells have more mitochondria compared to less active cells such as your skin cells. A single liver cell may contain as many as 2,500 mitochondria, while a skin cell will have only a few hundred. Take note that mitochondria have their own ribosomes and DNA, which means that new mitochondria arise only when existing ones divide. ##### 4. Lysosomes \- are small, spherical, membrane-bound organelles which contain various kinds of enzymes. Enzymes are molecules that digest proteins, nucleic acids, polysaccharides, and lipids. They protect a cell from invading bacteria and other pathogens. They also break down damaged or worn out cell parts. They can engulf and digest targeted molecules. When a molecule is broken down, the products pass through the lysosome membrane and are returned back into the cytoplasm to be recycled. ##### 5. Secretory granules \- are large, dense granules with membranes. These fuse with the cell membrane to secrete substances such as enzymes, proteins, and signaling molecules out of the cell. **6. Lipid droplets**- store fatty acids and sterols. They take up much space and volume in adipocytes or fat cells. They appear as black spherical bodies of varying sizes when stained. #### Cellular Macromolecules \- are substances suspended in the cytoplasm with varying functions and are not membrane-bound structures. Their quantity is dependent on the cell type. **1. Ribosomes**- are not considered organelles because they are not surrounded by membranes. Each ribosome is an assemblage of two organic compounds, namely, proteins and RNA. In the cytoplasm, some ribosomes remain free, while others are attached to the endoplasmic reticulum. They are the molecules that synthesize proteins. The distribution of ribosomes inside the cell varies. This depends on how the proteins will be used. Proteins that are needed by the cell itself are produced by the free ribosomes, while proteins that will be inserted into the cell membrane or exported outside of the cell are produced by those attached to the endoplasmic recticulum. ##### 2. The centrosome \- is the part of the cytoplasm that produces microtubules. In animal cells, it forms two small parts called the centrioles. The centrioles are small cylindrical structures made of short microtubules arranged in a circle. Though their main function is to assist in cell division, studies have shown that certain cells continue to divide even without them. ##### 3. The cytoskeleton \- provides motility and strength for the cell. It is the collective term for the network of filaments and tubules that extends throughout the cell. The types of fibers comprising the cytoskeleton are as follows: a. Microtubules are long, slender, protein tubes. Together with microfilaments, they form the cytoskeleton or the framework of the cell. It is composed of linear polymers of tubulin. A network of microtubules forms the spindle apparatus that appears during cell division. These also form the cores of the cilia and flagella of sperm cells and play a role in maintaining cell shape. b\. Microfilaments support the cell to maintain its structure and shape, as it provides resiliency against forces that can alter its shape. Spindle fibers are examples of microfilaments that aid in the movement of chromosomes during cell division. They are also important in cytoplasmic streaming or cyclosis. **4. Glycogen granules**, which are abundant in liver cells, play an important role in glucose metabolism. ##### 5. Biological pigments \- are especially abundant in plant cells, particularly in photosynthetic cells. These are usually found in the plastids, such as the chloroplastids, where the chlorophyll pigments abound. In animals, pigments are mostly found in the cells of the skin, eyes, hair, and feathers ##### C. Nucleus - The most visible part of a eukaryotic cell is the nucleus. In an animal cell, it is roughly spherical in shape and is generally located at the center of the cell. It is the site where nucleic acids are synthesized. The nucleus also serves as the site for the storage of hereditary factors. It is the source of ribonucleic acid (RNA), a molecule responsible for converting genetic instructions in DNA into functional substances such as proteins. Some cells, however, such as red blood cells and platelets, lose their nucleus as they mature. **The nuclear membrane-** is composed of two layers which separate the nucleus from the cytoplasm. It contains ribosomes on its outer membrane. It is also continuous with the endoplasmic reticulum. The dense, protein-rich substance inside the nucleus is the nucleoplasm in which the spherical, unbound nucleolus (structures responsible for ribosome formation) is suspended. It is rich in proteins and nucleic acids, and it is where RNA is transcribed and assembled. **Nuclear pores**- are openings in the nuclear membrane. These act as selective channels between the cytoplasm and the inside of the nucleus, selectively allowing molecules that come in and out of the nucleus. The proteins that make up the nuclear pore complex are arranged radially with a large central hole. - Found inside the nucleus is the chromatin, which is made up of DNA and proteins and forms chromosomes during cell division. Chromosomes contain the genes inherited by the offspring from their parents - Humans have 46 chromosomes. Each organism has its own specific number of chromosomes. Abnormalities in the chromosome structure or aberration in the chromosome number can lead to a genetic disorder or even death. **Cell Modifications and Adaptations** - refers to a process in which an ordinary or generic cell is transformed into a specialized cell in order to do a specific task for the body. The function that they perform after modification becomes different from their previous tasks. This process has contributed much to the adaptation and survival of organisms. For instance, not all cells in the small intestine are the same in structure and function. Some have microvilli, while others do not. **Microvilli** are cytoplasmic extensions that increase the surface area of a cell, hence, increasing the absorption of nutrients. **Nerve cells**, which are mostly elongated, facilitate the transmission of impulses from the brain to the spinal cord and different parts of the body. ##### Red blood cells (RBCs) - have a biconcave-disc shape and are highly deformable. Their size of 2-3 µm in diameter allows for easy movement through the blood vessels. Red blood cells and platelets lose their nucleus as they mature. Losing the nucleus increases the surface area for gas exchange, enabling the optimal oxygenation of tissues in the body. **The sperm cell** - is another specialized cell with parts that help it carry out its function. Sperm cells have a tail, the flagellum, which propels them toward the egg for fertilization. Sperm cells have plenty of mitochondria along their middle piece, which power the flagellum to move them toward the egg cell. **The skin**- of some animals such as amphibians, squids, and octopuses contain **chromatophores**. These are star-shaped cells containing bioluminescent pigments that facilitate the changing of the color of the body. Jellyfish and Hydra have nematocysts or stinging cells that contain a needle-like structure used to inject a toxic substance into the prey of interest. **In plant cells**, there are also specialized cells such as *root hairs*, which are elongated outgrowths from the outer layer of root cells that help absorb water and minerals. They increase the absorption area and capacity of the roots. Cells on the surface of the leaf are elongated in shape and are loaded with chloroplasts. Plant cells also have **plasmodesmata** or small pits that link one plant cell to another. They facilitate the movement of molecules between adjoining cells. **Guard cells** are specialized to regulate the opening and closing of the stomata. - Another specialized modification in eukaryotic cells is the presence of **cell-cell junctions**, the point where two cells come together. Through the cell junctions, the cells are joined in long term associations, thus, forming tissues and organs Cellular diversity is reflected in the different shapes and sizes of cells found in tissues. Cells are small to maximize cellular processes. - Prokaryotic cells and eukaryotic cells differ greatly in terms of internal organization and parts. - Prokaryotic cells lack a nuclear envelope and membrane-bound organelles. - Eukaryotic cells are generally larger and have a very distinct nucleus that is clearly surrounded by a nuclear envelope. - The cell membrane, sometimes called the plasma membrane, is the outermost covering of animal cells. The materials in the cell that surround the nucleus make up the cytoplasm. - Organelles are tiny structures in the cytoplasm that are surrounded by a membrane. - Some organelles found in the cytoplasm include the endoplasmic reticulum, the Golgi apparatus, the mitochondrion, lysosomes, secretory granules, and lipid droplets. - Cytoplasmic inclusions are non-membranous substances and structures suspended in the cytoplasm. Some cytoplasmic inclusions in the cell include the ribosomes, centrioles, microtubules, microfilaments, glycogen granules, and pigments. - Most eukaryotic cells have a nucleus. It houses an organism's genetic material. - Plant cells have cell walls and plastids. They also have larger water vacuoles than animal cells. - Cell specialization or modification refers to the process by which an ordinary or typical cell is converted into a specialized cell to do a different task for the body. GENBIO #### Cellular Transport -Living cells exist in a liquid environment. This condition makes the plasma membrane an extremely important cellular structure because it is selectively permeable. It regulates the movement of molecules into and out of the cell. For cells to function, some substances, such as nutrients and oxygen must be allowed to enter the cell, while other substances, such as waste products of metabolism, must be moved out. ##### Different Transport Processes - Passive Transport - Active Transport - Bulk Transport #### Passive Transport -**Passive transport** is the movement of substances across membranes without the use of energy. One means of passive transport is **diffusion**, which is the net movement of solute substances from an area of higher concentration to an area of lower concentration or what is sometimes described as down the concentration gradient. Diffusion is spontaneous and proceeds even without energy input. -**Osmosis**, another means of passive transport, is the diffusion of water molecules across a selectively permeable membrane. It is the process where solvent molecules such as water move from a region of less concentrated solution **(hypotonic solution)** to a region of more concentrated solution **(hypertonic solution)** through a selectively permeable membrane. -Consider a cell that is placed in a hypotonic environment wherein the solute concentration is lower than that inside the cell. Water from the environment enters the cell, causing it to bulge or even burst. In other words, a hypotonic environment is harmful to a living cell. Conversely, if a cell is placed in a hypertonic environment wherein the solute concentration is higher than that inside the cell, water leaves the cell, causing it to shrivel and die. As in a hypotonic environment, a cell's exposure to a hypertonic environments is harmful to it. -Plants, fungi, some protists, and prokaryotes have cells that are surrounded by rigid cell walls. When these cells are placed in a hypotonic solution, the inward movement of water builds up the turgor pressure of the cell, and the cell then becomes very firm. In the case of plants, without this firmness or turgidity, the plant wilts. On the other hand, when cells with rigid cell walls are placed in a hypertonic solution, water moves out, causing the plasma membrane to pull away from the cell wall and the cell to wilt or plasmolyze. This process is called **plasmolysis**. -**Facilitated diffusion** is another form of passive transport. It is the movement of solutes through protein channels down the concentration gradient without energy expenditure. Through facilitated diffusion, water and certain hydrophilic (water-loving) solutes cross the membrane. The **two types of transport proteins** are channel proteins and carrier proteins. -**Channel proteins** [open or close] as they respond to stimuli. Some channel proteins open or close when a specific substance, other than substance to be transported, binds to the channel. **Carrier proteins** [change in shape], which is triggered by the binding and release of a substance it transports. #### Active Transport **-Active transport** uses energy in moving solutes across a membrane by moving up the concentration gradient. This process requires the expenditure of energy through transport proteins called carrier proteins. Because active transport requires energy, it utilizes adenosine triphosphate (ATP), a molecule that carries the energy that the cell uses. The last phosphate group of ATP attaches to the transport protein which enables the solute to be transported. -Active transport is **essential** to the cell mainly **for three reasons**: 1. it enables the transport nutrients to the cell even when the concentration on the inside is already higher; 2. It makes the removal of waste materials from the cell possible despite the higher concentration outside the cell; and 3. It enables the cell to maintain the concentration of essential ions such as #### Bulk Transport -Water and small solutes enter and leave the cell through passive and active diffusion. However, large molecules, such as proteins and polysaccharides cross membranes in bulk through the process of exocytosis and endocytosis. **Exocytosis** is the process of removing materials from the cell through the vesicles that fuse with the plasma membrane, thus, subsequently releasing their contents outside the cell. -**Endocytosis** is the reverse process of exocytosis wherein cells engulf materials. A substance outside the cell is captured when the plasma membrane merges with that substance and engulfs it. The engulfed substance then enters the cytoplasm while it is enclosed in a vesicle. Endocytosis happens either through phagocytosis or pinocytosis. 1. **Phagocytosis** ("cellular eating") is the most common form of endocytosis. It occurs when an undissolved material enters the cell. The plasma membrane wraps around the solid material and engulfs it. This describes how some single-celled protists (e.g., Amoeba) capture food. Another example is how white blood cells engulf bacteria. 2. **Pinocytosis** ("cellular drinking") occurs when dissolved substances enter the cell. Like phagocytosis, the plasma membrane wraps around the material and forms a vesicle that contains the engulf material. The human egg cell's uptake of nutrients from its surroundings is an example of pinocytosis. #### Animal and Plant Tissues -The individual cells in a multicellular organism are arranged into groups that function collectively as tissues. Each tissue type is composed of simple cells performing similar or closely related functions. A group of tissues composes an organ; organs that work together to perform a specific function compose an organ system; organ systems compose the body of an organism. #### [Animal Tissue] -There are trillions of cells that comprise your body. These cells form aggregates and group together to support and cover your body and cause it to contract, react, and secrete fluids and other substances. Animal tissues are generally classified into four types: epithelial, connective, vascular, and nervous tissues. #### [Epithelial Tissues] -Epithelial tissues consist of sheets of cells that cover organs and line cavities. Different types of epithelial tissues cover the surfaces of mouth, stomach, lungs, heart, and blood vessels. They also form glands that secrete substances, such as the sebaceous and salivary glands. Epithelial tissues **can be classified** according to the following: 3. Number of cell layers: simple or stratified 4. Shape of cells on free surface: squamous, cuboidal, or columnar 5. Surface specialization: cilia, keratin, or glands #### [Connective Tissues] -Are you familiar with ligaments and tendons? These are examples of connective tissues. They connect and bind parts together just like the Archilles tendon found in your calf. Tendons usually bind a muscle to a bond, while ligaments connect a bone to another bone. The most common types of connective tissues are the areolar connective tissue, fibrous connective tissue, bone, adipose, cartilage, and blood. #### [Muscle Tissues] -Body form is mostly shaped by muscles. They also help the bones move the body by contracting or relaxing. The different kinds of muscle tissues in the body are the skeletal, visceral, and cardiac muscles. Muscles can also be classified into voluntary and involuntary muscles. Voluntary muscles are those that can be controlled at will by organism. These are controlled by the somatic nervous system. -An example of voluntary muscles are the skeletal muscles attached to the bones. They only move at organism's will. Involuntary muscles, however, move without the organism's conscious control. This is controlled by the autonomic nervous system. Whether you like it or not, they will move and perform their functions. The muscles of the digestive tube and heart are examples of this kind of muscles. There are **three types of muscle tissues** according to **structures**. 1. **Skeletal muscles** are made up of very long, cylindrical, multinucleated cells capable of quick and forceful contractions that are usually controlled voluntarily. 2. **Visceral muscles** are collections of cells that do not show cross-striations. They are the largest at their midpoints and taper toward their ends (fusiformshaped cells). Their contraction process is slow and involuntary. Examples of these are the smooth muscles of the digestive system. 3. **Cardiac muscles or muscles** of the heart are composed of elongated, branched individual cells that are configured parallel to each other. They are capable of involuntary, vigorous, and rhythmic contractions. Intercalated discs connect adjacent cells and ensure the synchronicity of cardiac contractions. #### [Nervous Tissues] -Cells comprising nervous tissues are specialized for the reception and conduction of impulses. The tissues are mostly found in the brain and in the spinal cord. The individual cells of the brain and spinal cord consist of neurons or nerve cells. There are **two types of nerve cells** according to its **function**. 1. **Sensory neurons** carry information obtained from the interior of the body and the outside environment to the central nervous system. 2. **Motor neurons** carry impulses from the central nervous system to effector organs commanded by these centers. #### [Plant Tissues] -Like animals, plants are also made up of different type of tissues. A plant is composed of a number of different tissues classified according to origin and function. Based on **origin**, plant tissues may be **classified into two types**. 1\. Meristematic or Embryonic Tissues -These tissues are mostly located at the tips of the roots and shoots of the plant where cells actively divide. They are responsible for the production of more cells. Newly formed cells typically small, each with a proportionately large nucleus at the center with very few tiny vacuoles. The following are the kinds of meristematic tissues based on location: a. **Apical meristems** -- found at the tips of the shoots and roots. These are responsible for the increase in length of roots and stem. b. **Intercalary meristems** -- found at the vicinity of nodes which occur at intervals along stems. Just like the apical meristems, they also increase the length of stems. c. **Lateral meristem**s -- meristems that increase the girth or diameter of plants. They are found along the sides of some roots and stems. 2\. Non-meristematic or Permanent Tissues -These are tissues formerly derived from meristems but have already developed, matured, and assumed various shapes and sizes related to their specific functions. Most of these no longer undergo cell division. Plant tissues can also be classified according to structure and function: 1\. **[Surface tissues]** serve as the outermost covering of plants. There are two types: a. **Epidermis** -- the outermost layer of cells of all young plant organs b. **Periderm** -- the layer of cells that replaces the epidermis. It gives added protection and is usually found in mature plants. This consists of several layers of dead cells impregnated with suberin, a waxy substance. The periderm is found in barks of trees. 2\. **[Fundamental tissues]** are designed to give strength to the plant. Examples are the following: c. **Parenchyma** -- the most abundant of all cell types. It is found in almost all major soft parts of higher d. plants. The cells are more or less spherical in shape when newly produced, but when they mature, they pushed against each other and their thin pliable cells are flattened at the points of contact. These are the groups of cells mostly active in photosynthesis, secretion, food storage, and other plant activities. e. **Collenchyma** -- composed of thick-walled cells with uneven thickness. They often occur just beneath the epidermis. These cells are "stretchy" in nature to allow some parts of the plant to bend and not to break. f. **Sclerenchyma** -- characterized by cells with thick and tough cell walls. These are normally impregnated with lignin. Most of them are dead at maturity and function for support. They are commonly found in pears and chicos. These are also known as stone cells. 3.**[Vascular tissues]** are involved in the transport of substances inside the body of plants. a. **Xylem** -- conducts water and minerals upward b. **Phloem** -- translocate food materials to the different parts of a plant.