Nat Sci 12: Human Anatomy and Physiology (2nd Sem. AY-2024-25)

**Nat Sci 12: Human Anatomy and Physiology** **7:30-1:00, 11:00-4:30pm, TTH (2^nd^ Sem. AY-2024-25)** **Introduction: History of Biology (Human Anatomy and Physiology)** I. **HISTORY OF ANATOMY AND PHYSIOLOGY** Human history has a very rich and prestigious history. The history of human anatomy...

**Nat Sci 12: Human Anatomy and Physiology** **7:30-1:00, 11:00-4:30pm, TTH (2^nd^ Sem. AY-2024-25)** **Introduction: History of Biology (Human Anatomy and Physiology)** I. **HISTORY OF ANATOMY AND PHYSIOLOGY** Human history has a very rich and prestigious history. The history of human anatomy has an important role in some intelligent anatomists. To study and understand the history of human anatomy we can classify into various time period are the following: - Ancient anatomy - Medical to early modern anatomy - Modern anatomy A. **Ancient Anatomy** The history of human anatomy starts from the beginning of human civilization and that time the early idea of Arabian human beings is that when we healed certain vital parts then the animal died soon. They applied this knowledge in the intertribal war that it is "Art of killing not the science of healing" that we see now. - In 2700- 2600 BC -- The earliest book on Human Anatomy which is "Neiching" in China. - ***Egyptians- ***They are perfected in the science of mummification. They opened up the whole dead body and removed major organs and placed them in the jars. After that, they filled the dead body with "sawdust" material and wrapped it into linen cloth shrouds. They are known as the earliest record of a human structure by dissection. - ***India -- ***In 1000 BC, Sushruta was considered as the father of Indian surgery. He practiced for purposeful surgery. His first surgery was on intestinal obstruction. He also gave the aseptic precaution just before surgery. - ***Hippocrates- (460-377 BC) **He was the father of medicine. He was known as the founder of anatomy as he gave the guideline for dissection use of a scalpel and dissected dead bodies from the battlefield.* - ***Aristotle -- (384-332 BC) **He gave the term "Anatomy" and he wrote the first-ever account on the embryology and analyzed various veins and arteries and named them He believed that heart as the center of intelligence and emotions.* - ***Herophilus- (300-325 BC) **He is known as the father of human anatomy. He dissected the criminals which are actually known as vivisection as Aristotle and Herophilus had special permission from the tolomic dynasty They dissected the living criminals and defined the parts of the brain and spinal cord. He said the brain is the seat of intelligence.* B. **Medieval to early modern anatomy --** - ***Galen of Pergamum- **He was the most prominent* anatomist of this period. He is known as the "Prince of Physicians" because he was the first experimental physiologist. He dissected the monkeys and other animals and correlated their anatomy with human anatomy. He also stated the importance of the spinal cord and nervous system. That time was known as Galenic age. - ***15^th^centaury- **In 13^th^ to 14^th^ century all dissection was prohibited by Pope Boniface. And then Leonardo da Vinci was the greatest geniuses at all times He was known as the originator of cross-sectional anatomy. He gave anatomy drawings that were found after 160 years of his death.* These drawings were made with extreme perfection. He made a total of 500 diagrams in his 60 notebooks. - ***16^th^century - **The greatest anatomist at all times was Andrews Vesalius. He was considered as the "Founder of modern anatomy "he mathematized or dissect all the previous theory and believed that anatomy can be taught only through dissection. He wrote a book which name was "De humani corporis fabrica" in this book he gave a detailed view of human anatomy.* - ***17^th^century- **There was William Harvey, the famous English anatomist who described the circulation of blood through the human body. But at that time he was not able to describe the need for blood in the human body as oxygen not discovered that time.* - ***Eighteenth and Nineteenth century: **In these two centuries, major steps were taken in learning procedure for anatomy. Dissection was made compulsory for medical students. Warburton Anatomy Act was passed in England under which the unclaimed bodies were made available for dissection. The use of formalin as a fixative started in this period and techniques of endoscopy were also discovered. Prominent anatomists of this century included George Cuvier, Johann Friedrich Meckel and Henry Gray.* C. **Modern anatomy-** - T*he Advancement in radiological techniques in the twentieth century which help researchers to make remarkable connections between anatomy and physiology.  * - *The success in easy access to advanced technology such as PET and CAT scanners, and magnetic resonance imaging (MRI) helps physicians and scientists to have a glimpse of what is inside the body without performing surgery or even dissection (Anatomy Notes, 2022)* The term biology is derived from the Greek word βίος, bios, \"life\" and the suffix -λογία, -logia, \"study of.\" The Latin-language form of the term first appeared in 1736 when Swedish scientist Carl Linnaeus (Carl von Linné) used biologi in his Bibliotheca botanica. **Biology** is the science that studies **living** organisms. Biologists study the structure, function, growth, origin, evolution and distribution of living organisms. **D. Two main parts of Biology** - **Zoology** is the discipline responsible for **study animal life**. As in the rest of the main branches of biology, here there are some sub disciplines as can be aquariology or arachnology, to name a few. - B**otany** deals directly with the **study of plants.** It is a very large branch as it studies everything that has to do with the plant world. It can classify, describe, identify and learn about reproduction, morphology or physiology of the natural beings of the plant world. E. - **Anatomy** is the branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts. - **Physiology** is the study of the **functions of living beings**. A branch that deals with studying the respiratory, reproductive, nervous system etc., within physiology, and depending on the type of living organism, we can distinguish between three groups of plant physiology, animal physiology and lastly human physiology. - **Morphology** it deals with the study of size, shape, and structure of an organism or one of its parts. - **Genetics** is a branch of biology that attempts to study biological heritage which is transmitted from generation to generation. It is a fairly complex branch whose main object is the study of genes formed by segments of DNA and RNA. - **Biogeography** deals with the study of the geographic distribution of plants and animals. It is concerned not only with habitation patterns but also with the factors responsible for variations in distribution. - **Taxonomy** is the science of naming, describing, and classifying organisms and includes all plants, animals and microorganisms of the world. - **Ecology** is the branch of biology that is responsible for studying the relationship of living being with their natural habitat. It is the study of everything that affects the adaptation of living organisms to their different habitats as of climate or geology. - **Pathology** deals with the study of diseases of living organisms primarily concerning the cause, origin and nature of disease and their control. - **Cellular biology or cytology** (from Greek κύτος, kytos, \"a hollow\"; and -λογία, -logia) is the branch of biology which studies the structure and function of cells. This discipline is responsible for understanding amongst other matters the properties, structures and functions of these as well as their interaction with the environment. Undoubtedly, it is a fairly wide field which started being studied following the invention of the optical microscope. - **Histology** is the study of the microscopic structures of cells and tissues of plants and animals. It is often carried out by examining a thin slice (called a \"section\") of tissue under a light microscope or an electron microscope. - **Embryology** (from Greek ἔμβρυον, embryon, \"the unborn, embryo\"; and -λογία, -logia) is the branch of biology that studies the development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology is the study of congenital disorders that occur before birth. - **Entomology** (from Greek ἔντομον, entomon \"insect\"; and -λογία, -logia) is the scientific study of insects. - **Microbiology** is a science or branch of biology that focuses on the study of microorganisms, which the smallest living things. These organisms are completely invisible to the human eyes they are only visible through the use of a microscope. - **Mycology** a branch of biology deals with the study of fungi. - **Bacteriology** a branch of microbiology dealing with the identification, study, and cultivation of bacteria and with their applications in medicine, agriculture, industry, and biotechnology. - **Forestry** is the science, art and practice of understanding, managing and using wisely the natural resources associated with, and derived from forest lands, and it deals with the study of trees. - **Pomology** (from Latin pomum (fruit) + -logy) is a branch of botany that studies and cultivates fruit. - [**Molecular biology**](http://education.onehowto.com/article/how-does-molecular-biology-support-the-theory-of-evolution-11185.html) is the discipline which studies the **biological processes on a molecular level**. The truth is that this branch shares elements of biology with chemistry, particularly genetics and biochemistry. It focuses mainly on studying the interactions of different cell systems. - **Developmental biology** is the branch of biology that studies the **development of living organisms from birth until death**. A less superficial description would state that this discipline studies the processes by which organisms grow. So it focuses on the genetic control of cell growth and cell differentiation and morphogenesis. - **Marine biology** is the branch of biology that is responsible for **studying all the creatures that live within the marine environment**. This discipline engulfs a series of specializations that are centered in more specific areas. And so, amongst these, we can highlight ichthyology, which directly studies fish; malacology, which studies mollusks; phycology, which centers on the study of seaweed; cetology, which studies marine mammals. F. **The characteristics of living organisms** - **Living Things are Composed of Cells** Single-cell organisms have everything they need to be self-sufficient. In multicellular organisms, specialization increases until some cells do only certain things. - **Living Things Have Different Levels of Organization:** Both molecular and cellular organization. \- Living things must be able to organize simple substances into complex ones. \- Living things organize cells at several levels: \- Organism - any complete living thing.   - **Living Things Use Energy:** Living things take in energy and use it for maintenance and growth. - **Living Things Respond To Their Environment:** Living things will make changes in response to a stimulus in their environment. A behavior is a complex set of responses. - **Living Things Grow:** Cell division - the orderly formation of new cells. Cell enlargement - the increase in size of a cell. Cells grow to a certain size and then divide. An organism gets larger as the number of its cells increases. - **Living things Reproduce:** Reproduction is not essential for the survival of individual organisms but must occur for a species to survive. All living things reproduce in one of the following ways: Asexual reproduction - Producing offspring without the use of gametes. Sexual reproduction - Producing offspring by the joining of sex cells. - **Living things adapt to their environment:** Adaptations are traits giving an organism an advantage in a certain environment. Variation of individuals is important for a healthy species. G.   - **ANATOMY** is the study of the structure of the body and the relationship between its various parts. Anatomy has a certain appeal because it is concrete and the body structures can be seen, felt and examined closely - it is purely a descriptive approach. - **PHYSIOLOGY** is the study of the function of the body and how the parts of the body work. Physiology is concerned with the functioning of normal vital processes in animal and plant organisms, including their biochemical composition and how drugs and disease affect them. Physiology reveals the dynamic nature of the workings of the living body and Anatomy provides the static image. H. **Complementarity of Structure and Function**  Although it is possible to study Anatomy and Physiology in isolation from one another, they are truly inseparable sciences because the function always reflects the structure. This is called the principle of complementarity. In studying Anatomy and Physiology, a description of the anatomy of a structure is often accompanied by an explanation of its function - what a structure can do depends on its specific form. *The intimate relationship between anatomy and physiology is stressed throughout any textbook to make learning more meaningful. In all cases, a description of the anatomy of a structure is accompanied by an explanation of its function, emphasizing the structural characteristics contributing to that function.* For example: Bones: A function (i.e. Physiology) of bones is that they are able to provide support and protection to body organs because their structure (i.e. Anatomy) contains hard mineral deposits. Heart: A heart** **functions (i.e. Physiology) by pumping blood flow in one direction because of its structure (i.e. Anatomy) contains valves that prevent the backflow of blood. Lungs: The lungs** **function (i.e. Physiology) as a site for gas exchange because the structure (i.e. Anatomy) of the walls of their air sacs is extremely thin. I. **Fields of Study of Anatomy and Physiology Anatomy: ** - **Gross Anatomy** Often regarded as general anatomy, so far as it can be studied without the use of the microscope (i.e. body structures are visible to the naked eye); commonly used to denote the study of anatomy by dissection of a cadaver. - **Systemic Anatomy**  An approach to anatomical study organized by systems of the body, e.g. the cardiovascular system, emphasizing an overview of the system throughout the body. - **Regional Anatomy** The study of one particular region, part or division of the body (e.g. the foot or the groin region), emphasizing the relationships of various systemic structures (e.g. muscles, nerves and arteries) within that area. Also referred to as topographic anatomy. - **Surface Anatomy**  The study of the configuration of the surface of the body, especially in its relation to deeper parts. - **Microscopic Anatomy** The study of structures too small to be seen with the naked eye. The structure of cells, tissues and organs is studied with a light microscope. Two categories of Microscopic Anatomy are:    - **Histology**  The science concerned with the minute structure of cells, tissues and organs in relation to their function. - **Cytology**  The study of the anatomy, physiology, pathology and chemistry of the cell. Synonymous with Cellular Biology. - **Developmental Anatomy**  The study of the structural changes in an individual from conception through to old age; includes embryology, fetology, and postnatal development. ** ** - **Pathological Anatomy** The study of the structural changes in the body caused by disease including both the gross and microscopic analysis and interpretation of diseased organs and tissues removed by biopsy or during post-mortem examination and also the interpretation of the results of such study. - **Radiographic Anatomy** The study of internal structures using x-ray images.  - **Physiology** Physiology is also subdivided into several specialized areas. Common subdivisions of Physiology consider the operation of specific organ systems. For example:  - Renal Physiology investigates urine production and kidney function - Neurophysiology explains the workings of the nervous system - Cardiac Physiology examines the operation of the heart. J. **Characteristics of Life**  What constitutes life? No single criterion defines it. Instead, characteristics of life consist of the following: - **Maintenance of boundaries** Keeping the internal environment distinct from the external environment. - **Movement** The ability to transport the entire being, as well as internal components, throughout the body. - **Responsiveness** The ability to sense, monitor and respond to changes in the external environment. - **Conductivity** The movement of energy from one point to another. - **Growth** A normal increase in size and/or number of cells. - **Respiration** The absorption, transport and use or exchange of respiratory gases (oxygen and carbon dioxide). - **Digestion** The process by which food products are broken down into simple substances to be used by individual cells. - **Absorption** The transport and use of nutrients. - **Secretion** The production and delivery of specialized substances for diverse functions. - **Excretion** The removal of waste products. - **Circulation** The movement of fluids, nutrients, secretions and waste products from one area of the body to another. - **Reproduction** The formation of a new being, including the formation of new body cells to permit growth, repair and replacement. - **Metabolism** A chemical reaction that occurs in cells to effect transformation, production, or consumption of energy. Each characteristic of life is related to the sum of all the physical and chemical reactions that occur in the body. Physiology, or function, characterizes life. We can study form (structure) without life, for example through cadaver dissection; however, we can study physiology only in terms of living dynamics. This subject represents the study of life and the dynamic process of living. K. **Framework of understanding** All the branches of biology can be unified within a framework of five basic understandings about living things. Studying the details of these five ideas provides the endless fascination of biological research: - **Cell Theory**: There are three parts to cell theory --- the cell is the basic unit of life, all living things are composed of cells, and all cells arise from pre-existing cells. - **Energy**: All living things require energy, and energy flows between organisms and between organisms and the environment. - **Heredity**: All living things have DNA and genetic information codes the structure and function of all cells. - **Equilibrium**: All living things must maintain homeostasis, a state of balanced equilibrium between the organism and its environment. - **Evolution**: This is the overall unifying concept of biology. Evolution is the change over time that is the engine of biological diversity. L. **The Organ System of the Body** This illustration shows eight silhouettes of a human female, each showing the components of a different organ system. The integumentary system encloses internal body structures and is the site of many sensory receptors. The integumentary system includes the hair, skin, and nails. The skeletal system supports the body and, along with the muscular system, enables movement. The skeletal system includes cartilage, such as that at the tip of the nose, as well as the bones and joints. The muscular system enables movement, along with the skeletal system, but also helps to maintain body temperature. The muscular system includes skeletal muscles, as well as tendons that connect skeletal muscles to bones. The nervous system detects and processes sensory information and activates bodily responses. The nervous system includes the brain, spinal cord, and peripheral nerves, such as those located in the limbs. The endocrine system secretes hormones and regulates bodily processes. The endocrine system includes the pituitary gland in the brain, the thyroid gland in the throat, the pancreas in the abdomen, the adrenal glands on top of the kidneys, and the testes in the scrotum of males as well as the ovaries in the pelvic region of females. The cardiovascular system delivers oxygen and nutrients to the tissues as well as equalizes temperature in the body. The cardiovascular system includes the heart and blood vessels. Figure 1.4 Organ Systems of the Human Body Organs that work together are grouped into organ systems.  Figure 1.5 Organ Systems of the Human Body (continued) Organs that work together are grouped into organ systems. M. **Theory of Life** a. Divine Law - God Created the heavens and the Earth and all human beings... Ge. 1:27, 28 b. Abiogenesis -- a non-living can produce a non-living and living organism. c. Biogenesis - the idea of reproduction "life begets life." d. The theory of evolution -- gradually change from characteristics of an organism. **II. THE CHEMICAL LEVEL OF ORGANIZATION** - **Chemical Level** What is your body made of? Your first thought might be that it is made up of different organs---such as your heart, lungs, and stomach---that work together to keep your body going. Or you might zoom in a level and say that your body is made up of many different types of cells. However, at the most basic level, your body---and, in fact, all of life, as well as the nonliving world---is made up of atoms, often organized into larger structures called molecules. Atoms and molecules follow the rules of chemistry and physics, even when they\'re part of a complex, living, breathing being. If you learned in chemistry that some atoms tend to gain or lose electrons or form bonds with each other, those facts remain true even when the atoms or molecules are part of a living thing. In fact, simple interactions between atoms---played out many times and in many different combinations, in a single cell or a larger organism---are what make life possible. One could argue that everything you are, including your consciousness, is the byproduct of chemical and electrical interactions between a very, very large number of nonliving atoms! So as an incredibly complex being made up of roughly 7,000,000,000,000,000,000,000,000,000 atoms, you\'ll probably want to know some basic chemistry as you begin to explore the world of biology, and the world in general (Khan Academy, 2023). - The human body is made up of many elements, including oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium. - **Major elements** - Oxygen: The most abundant element in the body, making up about 65% of its mass - Carbon: The second most abundant element, making up about 18.5% of body mass - Hydrogen: The third most abundant element, making up about 9.5% of body mass - Nitrogen: The fourth most abundant element, making up about 3.3% of body mass - Calcium: A key component of bones, which are the main storage site of calcium in the body - Phosphorus: A key component of bones and teeth, and it also helps the body use carbohydrates and fats - **Other elements** - Potassium: Helps muscles contract and nerves respond to stimulation - Sulfur: Helps make skin, hair, and nails strong and flexible The body also contains trace elements, which are necessary for life. - **Levels of Organization** As can be seen, anatomy can be studies in multiple ways, and at various levels. Understanding the hierarchy of these levels, provides context to the complexity of the human organism. The simplest level of organization is the **chemical level** of organization. At this level, simple atoms combine to form relatively simple *molecules*. For example, carbon dioxide (CO~2~) is made up of one carbon atom, and two oxygen atoms, and water (H~2~O) is made up of two hydrogen atoms and one oxygen atom. *Macromolecules* (*macro*: big) are larger and more complex and include four key types in the human body; carbohydrates (sugars), lipids (fats), proteins and nucleic acids (DNA). These four macromolecules form the building blocks of the next level of organization: the **cellular level**. Cells are the smallest units of life and are responsible for regulating their own environment. The four macromolecules, interact to complete complex tasks for the cell, like generating energy (ATP) or producing muscle contractions (through the interactions of two protein complexes: actin and myosin). a\. The **tissue level** of organization consists of a group of cells that work together to accomplish one or more specific functions. There are only four distinct types of tissue in an adult human. *Muscle* tissue is specialized for contraction to generate movement; *neural* tissue is specialized for generating action potentials for rapid communication within the body; *epithelial* tissue provides a physical barrier for entry into the body and produces specialized secretions via glands; and *connective* tissue shows the greatest variability of all of the tissues, and forms much of the structure of the body (among many other things).  b\. The **organ level** of organization is when two or more tissues work together for a specific function. For example, the bladder consists of an inner lining of epithelial tissue, bound by various connective tissues to (smooth) muscle. Throughout the bladder, there are also neurons that control the muscle tissue directing it to contract or relax during the urination reflex. c\. The **organ system** level of organization is when two or more organs work together for a specific function. The bladder mentioned, when combined with the kidneys (another organ), and the ureters ("tubes" connecting the kidneys to the bladder, form the urinary system (or urinary tract). The kidneys filter the blood, and the waist products drain through the ureters to be stored in the bladder. The waist is eliminated from the body when we urinate. The urinary system is one of the eleven body systems that can be examined using systemic anatomy.  The most complex level of organization is the **organismal level**, where all eleven organ systems function in the human organism, the whole living person. - **How Matter is Organized** Matter is a substance which gives rise to physical objects. Or we can say that physical objects are composed of matter. Matter consists of chemical substances. All the chemical substances are made from atoms. The organization of matter is based on the structure of Atoms. Atoms have three particles which are protons, neutrons and electrons. Various atoms combine to form matter. Matter also consists of various baryons and mesons (Blurtit, 2023). - **Matter and elements** ----------------------- The term **matter** refers to anything that occupies space and has mass---in other words, the "stuff" that the universe is made of. All matter is made up of substances called elements, which have specific chemical and physical properties and cannot be broken down into other substances through ordinary chemical reactions. Gold, for instance, is an element, and so is carbon. There are 118 elements, but only 92 occur naturally. The remaining elements have only been made in laboratories and are unstable. Each element is designated by its chemical symbol, which is a single capital letter or, when the first letter is already "taken" by another element, a combination of two letters. Some elements follow the English term for the element, such as C for carbon and Ca for calcium. Other elements' chemical symbols come from their Latin names; for example, the symbol for sodium is Na, which is a short form of *natrium*, the Latin word for sodium. The four elements common to all living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), which together make up about 96% of the human body. In the nonliving world, elements are found in different proportions, and some elements common to living organisms are relatively rare on the earth as a whole. All elements and the chemical reactions between them obey the same chemical and physical laws, regardless of whether they are a part of the living or nonliving world. **a. Chemical Bonds** - A chemical bond is an attraction between atoms. This attraction may be seen as the result of different behaviors of the outermost or valence electrons of atoms. These behaviors merge into each other seamlessly in various circumstances, so that there is no clear line to be drawn between them. It remains useful and customary to differentiate between different types of bond, which result in different properties of condensed matter (Housecroft, 2015). - Chemical Bonding refers to the formation of a chemical bond between two or more atoms, molecules, or ions to give rise to a chemical compound. These chemical bonds are what keep the atoms together in the resulting compound. **b. Chemical Reactions** - A chemical reaction is a process in which one or more substances, also called reactants, are converted to one or more different substances, known as products. Substances are either chemical elements or compounds. - A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. The properties of the products are different from those of the reactants. - Chemical reactions differ from physical changes, which include changes of state, such as ice melting to water and water evaporating to vapor. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same (Kotz & Treichel, 2023). **c. Inorganic Compounds** - The major inorganic compounds are water (H2O), bimolecular oxygen (O2), carbon dioxide (CO2), and some acids, bases, and salts. The body is composed of 60--75% water. Oxygen is required by all cells for cellular metabolism and circulating blood must be well oxygenated for maintenance of life. - Water is the most abundant inorganic compound, making up over 60% of the volume of cells and over 90% of body fluids like blood. Many substances dissolve in water and all the chemical reactions that take place in the body do so when dissolved in water. **d. Organic Compound** - An organic compound is one of a broad class of chemical compounds in which one or more atoms of carbon, most commonly hydrogen, oxygen, or nitrogen, are covalently bound to atoms of other elements. Carbides, carbonates, and cyanides form the only carbon-containing compounds not known as organic. Why are organic compounds important? - Chemical compounds are essential since carbon is found in all living organisms. For example, in photosynthesis and cellular respiration, the carbon cycle requires the exchange of carbon between plants and animals. Chemical compounds interact to form organometallic compounds with metals. How many inorganic compounds are there? - Although about 19 million known carbon compounds have been found in organic chemistry, inorganic chemistry contains only about 500,000 known compounds. However, major economic benefits are provided by inorganic compounds. Is salt an inorganic compound? - As they do not form the complex molecular bonds that carbon makes possible, inorganic compounds are also very simple. Sodium chloride, known more generally as household salt, is a typical example of a basic inorganic compound. Just two atoms, sodium (Na) and chlorine ( Cl), are in this formula. **e. Difference Between Organic and Inorganic Compounds** - Organic and inorganic compounds are said to be one of the large class of members. The primary difference that lies between these organic compounds and inorganic compounds is that organic compounds always have a carbon atom, while most of the inorganic compounds do not contain a carbon atom in them. Almost all organic compounds contain carbon-hydrogen or a simple C-H bond in them. - The most common fact that differentiates [organic compounds](https://byjus.com/chemistry/classification-organic-compounds/) from inorganic compounds is that organic compounds mainly result from the activities of a living being. In contrast, inorganic compounds are obtained from natural processes which are not related to any of the life forms on earth or any result of human experiments which are conducted in laboratories. - The difference between organic and inorganic compounds does not end with the presence or the absence of carbon atoms in them. These have characteristics of both types of compounds which are said to be different (Byju, 2023). **Organic Compounds** **Inorganic Compounds** ---- ------------------------------------------------------------------------------------------------------------ -------------------------------------------------------------------------------------------------------------------------------------- 1 Organic compounds are characterized by the presence of carbon atoms in them Most inorganic compounds do not have carbon atoms in them (some exceptions do exist) 2 Organic compounds consisting of hydrogen, oxygen, carbon, and their other derivatives They do not possess hydrogen or oxygen, and their derivatives 3 Organic compounds are said to be more volatile and also highly inflammable These compounds are not inflammable and are non-volatile in nature 4 These compounds exist in the form of solids, gases, and liquids. These exist as solids 5 These are insoluble in water These are soluble in water and also non-soluble in some of the organic solutions 6 These compounds have the carbon-hydrogen bonds These do not have the carbon-hydrogen bonds 7 Organic compounds are mainly found in most of the living things These compounds are found in non-living things 8 Organic compounds form covalent bonds Inorganic compounds form ionic bonds between the atoms of molecules 9 In most of the aqueous solutions, these are poor conductors of heat and electricity In aqueous solutions, these are known to be good conductors of heat and electricity 10 Examples of organic compounds include fats, nucleic acids, sugars, enzymes, proteins and hydrocarbon fuels Example for inorganic compounds includes non-metals, salts, metals, acids, bases, and substances which are made from single elements 11 These are biological and more complex in nature These are of mineral and not much complexity in nature 12 Organic compounds cannot make salts Inorganic compounds can make salts 13 The rate of reaction is slow in organic compounds Inorganic compounds have a high rate of reaction **III. CELLULAR LEVEL OF ORGANIZATION** **1. Parts of a Cell** All cells contain specialized, subcellular structures that are adapted to keep the cell alive. Some of these structures release energy, while others produce proteins, transport substances, and control cellular activities. Collectively, these structures are called organelles. Plant and animal cells both contain organelles, many of which are found in both types of cells. However, there are some organelles (such as chloroplasts, the cell wall, and large vacuoles) that are only found in plant cells (Latham, K. 2021). Cells are the basic, fundamental unit of life. So, if we were to break apart an organism to the cellular level, the smallest independent component that we would find would be the cell.  Cells are the fundamental unit of life. They range in size from 0.0001 mm to nearly 150 mm across. A. **Cell Definition** ***"A cell is defined as the smallest, basic unit of life that is responsible for all of life's processes."*** Cells are the structural, functional, and biological units of all living beings. A cell can replicate itself independently. Hence, they are known as the building blocks of life***. *** Each cell contains a fluid called the cytoplasm, which is enclosed by a membrane. Also present in the cytoplasm are several biomolecules like proteins, nucleic acids and lipids. Moreover, cellular structures called cell organelles are suspended in the cytoplasm. **What is a Cell?** - A cell is the structural and fundamental unit of life. The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology. Robert Hooke was the first Biologist who discovered cells. - All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular).  Mycoplasmas are the smallest known cells. Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy. - Cells are complex and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like bricks of the buildings. Our body is made up of cells of different shapes and sizes. - Cells are the lowest level of organization in every life form. From organism to organism, the count of cells may vary. Humans have more number of cells compared to that of [bacteria](https://byjus.com/biology/bacteria/). - Cells comprise several cell organelles that perform specialized functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells. B. **Discovery of Cells** Discovery of cells is one of the remarkable advancements in the field of science. It helps us know that all the organisms are made up of cells, and these cells help in carrying out various life processes. The structure and functions of cells helped us to understand life in a better way. - Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of bottle cork under a compound microscope and noticed minuscule structures that reminded him of small rooms. Consequently, he named these "rooms" as cells. However, his compound microscope had limited magnification, and hence, he could not see any details in the structure. Owing to this limitation, Hooke concluded that these were non-living entities. - Later Anton Van Leeuwenhoek observed cells under another compound microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were "alive." Eventually, after a host of other observations, these entities were named as animalcules. - In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He was able to describe the nucleus present in the cells of orchids. C. **Characteristics of Cells** Following are the various essential characteristics of cells: - Cells provide structure and support to the body of an organism. - The cell interior is organized into different individual organelles surrounded by a separate membrane. - The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth. - Every cell has one nucleus and membrane-bound organelles in the cytoplasm. - Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell. - Lysosomes digest unwanted materials in the cell. - Endoplasmic reticulum plays a significant role in the internal organization of the cell by synthesizing selective molecules and processing, directing and sorting them to their appropriate locations. D. **Types of Cells** Cells are like factories with different laborer and departments that work towards a common objective. Various types of cells perform different functions. Based on cellular structure, there are two types of cells: - Prokaryotes - Eukaryotes **a. Prokaryotic Cells** 1. Prokaryotic cells have no nucleus. Instead, some prokaryotes such as bacteria have a region within the cell where the genetic material is freely suspended. This region is called the nucleoid. 2. They all are single-celled microorganisms. Examples include archaea, bacteria, and cyanobacteria. 3. The cell size ranges from 0.1 to 0.5 µm in diameter. 4. The hereditary material can either be DNA or RNA. 5. Prokaryotes generally reproduce by binary fission, a form of asexual reproduction. They are also known to use conjugation -- which is often seen as the prokaryotic equivalent to sexual reproduction (however, it is NOT sexual reproduction). **b. Eukaryotic Cells** 1. Eukaryotic cells are characterized by a true nucleus. 2. The size of the cells ranges between 10--100 µm in diameter. 3. This broad category involves plants, fungi, protozoans, and animals. 4. The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells. It is also responsible for cell-to-cell communication. 5. They reproduce sexually as well as asexually. 6. There are some contrasting features between plant and animal cells. For eg., the [plant cell](https://byjus.com/biology/plant-cell/) contains chloroplast, central vacuoles, and other plastids, whereas the animal cells do not. E. **Cell Structure** The cell structure comprises individual components with specific functions essential to carry out life's processes. These components include- cell wall, cell membrane, cytoplasm, nucleus, and cell organelles. Read on to explore more insights on cell structure and function. F. **Cell Membrane** - The cell membrane supports and protects the cell. It controls the movement of substances in and out of the cells. It separates the cell from the external environment. The cell membrane is present in all the cells. - The cell membrane is the outer covering of a cell within which all other organelles, such as the cytoplasm and nucleus, are enclosed. It is also referred to as the plasma membrane. - By structure, it is a porous membrane (with pores) which permits the movement of selective substances in and out of the cell.  Besides this, the cell membrane also protects the cellular component from damage and leakage. - It forms the wall-like structure between two cells as well as between the cell and its surroundings. - Plants are immobile, so their cell structures are well-adapted to protect them from external factors. The cell wall helps to reinforce this function. G. **Cell Wall** - The cell wall is the most prominent part of the plant's cell structure. It is made up of cellulose, hemicellulose and pectin. - The cell wall is present exclusively in plant cells. It protects the plasma membrane and other cellular components. The cell wall is also the outermost layer of plant cells. - It is a rigid and stiff structure surrounding the cell membrane. - It provides shape and support to the cells and protects them from mechanical shocks and injuries. H. **Cytoplasm** - The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane. - Most of the chemical reactions within a cell take place in this cytoplasm. - The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes, are suspended in this cytoplasm. I. **Nucleus** - The nucleus contains the hereditary material of the cell, the DNA. - It sends signals to the cells to grow, mature, divide and die. - The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell. - The nucleus protects the DNA and is an integral component of a plant's cell structure. J. **Cell Organelles** Cells are composed of various cell organelles that perform certain specific functions to carry out life's processes. The different cell organelles, along with its principal functions, are as follows: **Cell Organelles and their Functions** -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Nucleolus** The nucleolus is the site of ribosome synthesis. Also, it is involved in controlling cellular activities and cellular reproduction. **Nuclear membrane** The nuclear membrane protects the nucleus by forming a boundary between the nucleus and other cell organelles. **Chromosomes** Chromosomes play a crucial role in determining the sex of an individual. Each human cells contain 23 pairs of chromosomes. **Endoplasmic reticulum** The endoplasmic reticulum is involved in the transportation of substances throughout the cell. It plays a primary role in the metabolism of carbohydrates, synthesis of lipids, steroids and proteins. **Golgi Bodies** Golgi bodies are called the cell's post office as it is involved in the transportation of materials within the cell. **Ribosome** Ribosomes are the protein synthesizers of the cell. **Mitochondria** The mitochondrion is called "the powerhouse of the cell." It is called so because it produces ATP -- the cell's energy currency. **Lysosomes** Lysosomes protect the cell by engulfing the foreign bodies entering the cell and help in cell renewal. Therefore, they are known as the cell's suicide bags. **Chloroplast** Chloroplasts are the primary organelles for photosynthesis. It contains the pigment called chlorophyll. **Vacuoles** Vacuoles store food, water, and other waste materials in the cell. K. **Cell Theory** Cell Theory was proposed by the German scientists, Theodor Schwann, Matthias Schleiden, and Rudolf Virchow. The cell theory states that: - All living species on Earth are composed of cells. - A cell is the basic unit of life. - All cells arise from pre-existing cells. A **modern version of the cell theory** was eventually formulated, and it contains the following postulates: - Energy flows within the cells. - Genetic information is passed on from one cell to the other. - The chemical composition of all the cells is the same. L. **Functions of Cell** A cell performs major functions essential for the growth and development of an organism. Important functions of cell are as follows: - **Provides Support and Structure** All the organisms are made up of cells. They form the structural basis of all the organisms. The cell wall and the cell membrane are the main components that function to provide support and structure to the organism. For eg., the skin is made up of a large number of cells. Xylem present in the vascular plants is made of cells that provide structural support to the plants. - **Facilitate Growth Mitosis** In the process of mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply and facilitate the growth in an organism. - **Allows Transport of Substances** - Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical processes is eliminated from the cells by active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol diffuse across the cell membrane along the concentration gradient. This is known as passive transport. The larger molecules diffuse across the cell membrane through active transport where the cells require a lot of energy to transport the substances. - **Energy Production** - Cells require energy to carry out various chemical processes. This energy is produced by the cells through a process called [photosynthesis](https://byjus.com/biology/photosynthesis/) in plants and respiration in animals. - **Aids in Reproduction** - A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed as the asexual reproduction where the parent cell divides to form daughter cells. Meiosis causes the daughter cells to be genetically different from the parent cells. - Thus, we can understand why cells are known as the structural and functional unit of life. This is because they are responsible for providing structure to the organisms and perform several functions necessary for carrying out life's processes (Byjus, 2022). **2. The Plasma Membrane** **a. Plasma Membrane Definition** --------------------------------- The plasma membrane of a cell is a network of lipids and proteins that forms the boundary between a cell's contents and the outside of the cell. It is also simply called the cell membrane. The main function of the plasma membrane is to protect the cell from its surrounding environment. It is semi-permeable and regulates the materials that enter and exit the cell. The cells of all living things have plasma membranes. **b. Functions of the Plasma Membrane** --------------------------------------- - ### A Physical Barrier The plasma membrane surrounds all cells and physically separates the cytoplasm, which is the material that makes up the cell, from the extracellular fluid outside the cell. This protects all the components of the cell from the outside environment and allows separate activities to occur inside and outside the cell. The plasma membrane provides structural support to the cell. It tethers the cytoskeleton, which is a network of protein filaments inside the cell that hold all the parts of the cell in place. This gives the cell its shape. Certain organisms such as plants and fungi have a cell wall in addition to the membrane. The cell wall is composed of molecules such as cellulose. It provides additional support to the cell, and it is why plant cells do not burst like animal cells do if too much water diffuses into them. - ### Selective Permeability Plasma membranes are selectively permeable (or semi-permeable), meaning that only certain molecules can pass through them. Water, oxygen, and carbon dioxide can easily travel through the membrane. Generally, ions (e.g. sodium, potassium) and polar molecules cannot pass through the membrane; they must go through specific channels or pores in the membrane instead of freely diffusing through. This way, the membrane can control the rate at which certain molecules can enter and exit the cell. - ### Endocytosis and Exocytosis Endocytosis is when a cell ingests relatively larger contents than the single ions or molecules that pass through channels. Through endocytosis, a cell can take in large quantities of molecules or even whole bacteria from the extracellular fluid. Exocytosis is when the cell releases these materials. The cell membrane plays an important role in both of these processes. The shape of the membrane itself changes to allow molecules to enter or exit the cell. It also forms vacuoles, small bubbles of membrane that can transport many molecules at once, in order to transport materials to different places in the cell. - ### Cell Signaling Another important function of the membrane is to facilitate communication and signaling between cells. It does so through the use of various proteins and carbohydrates in the membrane. Proteins on the cell "mark" that cell so that other cells can identify it. The membrane also has receptors that allow it to carry out certain tasks when molecules such as hormones bind to those receptors. **c. Plasma Membrane Structure** -------------------------------- Cell membrane detailed diagramCell membrane detailed diagram - ### Phospholipids The membrane is partially made up of molecules called phospholipids, which spontaneously arrange themselves into a double layer with hydrophilic ("water loving") heads on the outside and hydrophobic ("water hating") tails on the inside. These interactions with water are what allow plasma membranes to form. - ### Proteins Proteins are wedged between the lipids that make up the membrane, and these transmembrane proteins allow molecules that couldn't enter the cell otherwise to pass through by forming channels, pores or gates. In this way, the cell controls the flow of these molecules as they enter and exit. Proteins in the cell membrane play a role in many other functions, such as cell signaling, cell recognition, and enzyme activity. - ### Carbohydrates Carbohydrates are also found in the plasma membrane; specifically, most carbohydrates in the membrane are part of glycoproteins, which are formed when a carbohydrate attaches to a protein. Glycoproteins play a role in the interactions between cells, including cell adhesion, the process by which cells attach to each other. - ### Fluid Mosaic Model Technically, the cell membrane is a liquid. At room temperature, it has about the same consistency as vegetable oil. Lipids, proteins, and carbohydrates in the plasma membrane can diffuse freely throughout the cell membrane; they are essentially floating across its surface. This is known as the fluid mosaic model, which was coined by S.J. Singer and G.L. Nicolson in 1972 (Biology Dictionary, 2023). **3. Transport Across the Plasma Membrane** **a. Transport Across a Cell Membrane** The cell membrane is one of the great multi-taskers of biology. It provides structure for the cell, protects cytosolic contents from the environment, and allows cells to act as specialized units. A membrane is the cell's interface with the rest of the world - it's gatekeeper, if you will. This phospholipid bilayer determines what molecules can move into or out of the cell, and so is in large part responsible for maintaining the delicate homeostasis of each cell. **b. Semi-Permeability** Some cells function best at a pH of 5, while others are better at pH 7. The steroid hormone aldosterone is made in the adrenal gland, but affects mostly the kidney. Sodium is more than ten times more concentrated outside of cells rather than inside. If our cells couldn't control what crossed their membranes, either no molecules would make it across, or they'd be traveling willy-nilly and the internal environment would always be in flux. It'd be like taking every item on a menu and blending it together before serving (not the tastiest idea). So how do cells maintain different concentrations of proteins and molecules despite the pressures on them to be homogenous? Cell membranes are semipermeable, meaning they have control over what molecules can or cannot pass through. Some molecules can just drift in and out, others require special structures to get in and out of a cell, while some molecules even need an energy boost to get across a cell membrane. Each cell's membrane contains the right mix of these structures to help that cell keep its internal environment just right. Cartoon representing the cell membrane as a shield preventing things from entering the cell which is represented as a castle. **c. Movement Across a Membrane and Energy** There are two major ways that molecules can be moved across a membrane, and the distinction has to do with whether or not cell energy is used. Passive mechanisms like diffusion use no energy, while active transport requires energy to get done. Cartoon representing passive transport as rolling a boulder down a hill and active transport as rolling a boulder up a hill. **d. Diffusion: the Simple and the Facilitated** Diffusion is the movement of particles down their gradient. A gradient is any imbalance in concentration, and moving down a gradient just means that the particle is trying to be evenly distributed everywhere, like dropping food coloring in water. This is what happened when we made our granola - a bunch of separate ingredients came together and spread out across the whole mixture. We call this evening-out moving "downhill", and it doesn't require energy. The molecule most likely to be involved in simple diffusion is water - it can easily pass through cell membranes. When water undergoes simple diffusion, it is known as **osmosis**.  Image showing purple ink diffuse from a tiny drop into a beaker of water. \"Simple diffusion.\" - **Simple diffusion** is pretty much exactly what it sounds like -- molecules move down their gradients through the membrane. Molecules that practice simple diffusion must be small and nonpolar\*, in order to pass through the membrane. Simple diffusion can be disrupted if the diffusion distance is increased. If the alveoli in our lungs fill with fluid (pulmonary edema), the distance the gases must travel increases, and their transport decreases. - **Facilitated diffusion** is diffusion that is helped along (facilitated by) a membrane transport channel. These channels are glycoproteins (proteins with carbohydrates attached) that allow molecules to pass through the membrane. These channels are almost always specific for either a certain molecule or a certain type of molecule (i.e. an ion channel), and so they are tightly linked to certain physiologic functions. For example, one such transporter channel, GLUT4, is incredibly important in diabetes. GLUT4 is a glucose transporter found in fat and skeletal muscle. Insulin triggers GLUT4 to insert into the membranes of these cells so that glucose can be taken in from the blood. Since this is a passive mechanism, the amount of sugar entering our cells is proportional to how much sugar we consume, up to the point that all our channels are being used (saturation). In type II diabetes mellitus, cells do not respond as well to the presence of insulin, and so do not insert GLUT4 into their membranes. This can lead to soaring blood glucose levels which can cause heart disease, stroke, and kidney failure. e\. **Active Transport** Sometimes the body needs to move molecules against their gradient. This is known as moving "uphill" and requires energy from the cell - imagine how much easier it is to shake the trail mix together than it would be to then separate all the pieces again. This is most obvious in the sodium-potassium pump (Na+/K+ ATPase) that helps maintain resting potential in the cell. This protein uses the energy released from hydrolysis of ATP (adenosine triphosphate) to pump three sodium ions out of and two potassium ions into the cell. ATP is an energy molecule, and when hydrolysis happens, it gets broken down to release the energy that was stored in its chemical bonds. Transport that directly uses ATP for energy is considered **primary active transport**. In this case, that's moving sodium from a concentration of 10mM to one of 145 mM. A similar gradient is being surpassed with potassium, whose intracellular and extracellular concentrations are 140mM and 5mM, respectively. Since these types of transporters are so costly in terms of energy, they are relatively rare. One other location for such an ATP pump is the proton/potassium exchanger (H+/K+ ATPase) found in the stomach. These proton pumps are responsible for creating the acidic environment of the stomach, and can cause acid reflux. Proton pump inhibitors like omeprazole are prescribed to patients with ulcers or acid reflux to help reduce the acidity of their gut. Illustration showing active transport of sodium and potassium across the cell membrane via the sodium-potassium ATPase pump. Illustration showing active transport of sodium and potassium across the cell membrane via the sodium-potassium ATPase pump. Sodium potassium pump. As you can see, transmembrane channels on either side of the pump allow the ions to flow down their gradient. **Secondary active transport** moves multiple molecules across the membrane, powering the uphill movement of one molecule(s) (A) with the downhill movement of the other(s) (B). For example, SGLT2 is a glucose transporter that allows glucose (Molecule A) into our cells (against its gradient) by bringing in a sodium molecule (Molecule B) as well. Remember, sodium wants to get inside the cell, and the energy released by it traveling down its gradient is enough to power glucose into the cell. Since both molecules moved in the same direction, this molecule is known as a **symporter.** Proteins that allow molecules to go in opposite directions are **antiporters** -- one great example of this is the sodium/calcium exchanger used to restore cardiomyocyte (heart cell) calcium concentrations after an action potential. An influx of calcium causes the heart to contract, and the antiporter pushes calcium (Molecula A) out against its gradient, while bringing in a sodium ion (Molecule B) to let the heart relax. Illustration showing a symporter and an antiporter. You may notice that many of these secondary active transporters use sodium to propel other molecules against their gradients. This is one major explanation for why the sodium/potassium pump is so important -- that one molecule helps set up the needed gradient to allow for the movement of many chemicals into and out of the cell. In fact, this relationship is taken advantage of in certain heart disease medications. Digoxin is given to patient with atrial fibrillation (abnormal, fast heart rate) and it inhibits the sodium/potassium pump. This leads to the accumulation of intracellular sodium, which causes the sodium/calcium pump to change directions! Now sodium is being pumped out and calcium being brought in -- making heart contractions stronger (Khan Academy, 2023). M. **The Cytoplasm** Cytoplasm is a gel-like fluid that fills the inside of a cell. It\'s made up of water, salts, and organic molecules.  - **What does cytoplasm do?** - Organelles: Cytoplasm provides a platform for organelles to function within the cell. - Chemical reactions: Cytoplasm is the medium for chemical reactions that take place within the cell. - Cell growth: Cytoplasm is where cell growth, replication, and expansion take place. - Structure: Cytoplasm is highly organized and has a framework of protein scaffolds called the cytoskeleton. - **What are the parts of cytoplasm?** - Cytosol The soluble portion of cytoplasm that\'s outside of organelles. It\'s mostly made up of water and low molecular weight compounds. - Organelles These include the nucleus, mitochondria, endoplasmic reticulum, and ribosomes. - **What cells have cytoplasm?** - All cells have cytoplasm. - Eukaryotic cells, like plant and animal cells, have cytoplasm and membrane-bound organelles. N. **Nucleus** The nucleus is a cell organelle that contains DNA and other instructions for cellular processes. It\'s surrounded by a double membrane called the nuclear envelope, which protects the DNA from chemical reactions outside the nucleus. A diagram of a cell Description automatically generated - **Parts of the nucleus** - **Nuclear envelope**  - **Nucleolus** A spherical structure that produces and assembles ribosomes. The nucleolus is made up of granules and fibers attached to chromatin.  - **Chromatin** A complex of DNA and proteins that forms chromosomes within the nucleus. DNA is highly condensed and wrapped around nuclear proteins to fit inside the nucleus.  - **Function of the nucleus ** - Contains the genetic material for the cell - Provides instructions for cellular processes - Protects the cell\'s DNA from chemical reactions outside the nucleus O. **Protein Synthesis** Protein synthesis is the process of making proteins from amino acids in a cell\'s ribosomes. It\'s a vital metabolic process that determines the structure and function of a cell.  - **Steps of protein synthesis** - Transcription: DNA is copied into messenger RNA (mRNA). - Translation: The ribosome reads the mRNA and assembles amino acids into a polypeptide chain. - Post-translational modification: The protein may need to be modified before it\'s functional. - **Factors that affect protein synthesis** - DNA structure: The DNA template determines which protein is synthesized. - Ribosomes: The number and state of ribosomes affects the rate of protein synthesis. - Transcription rate: The rate at which specific genes are transcribed affects the rate of protein synthesis. - Stimuli: Endogenous and exogenous stimuli can stimulate or inhibit protein synthesis. - **Importance of protein synthesis** - Protein synthesis is a key part of cellular regulation. - Proteins are responsible for cell growth, repair, and function. - Diseases like cancer can occur if protein synthesis goes wrong. **P. Cell Division** Cell division is the process by which a cell splits into two daughter cells. It\'s a fundamental process for life that\'s essential for growth, repair, and reproduction. A diagram of cell division Description automatically generated - **Types of cell division** - Mitosis The process of making new body cells. Mitosis is a complex process that involves duplicating the cell\'s contents, including its chromosomes, and splitting into two identical daughter cells. - Meiosis The process of creating egg and sperm cells. Meiosis is a two-step process that reduces the number of chromosomes by half. - **When cell division occurs** - Growth: Cell division is required for the growth of multicellular organisms. - Repair: Cell division replaces cells that are lost due to damage or disease. - Reproduction: Cell division is required for the reproduction of unicellular organisms and the creation of egg and sperm cells in multicellular organisms. - **When cell division goes wrong** - Cancer: When cell division is not regulated correctly, it can lead to cancer. - Developmental defects: When cell division is not regulated correctly, it can lead to developmental defects. - Aging-related diseases: When cell division is not regulated correctly, it can lead to aging-related diseases, such as Alzheimer\'s disease. **Q. Cellular Diversity** Cellular diversity is the variety of cell types, shapes, and functions that exist in an organism. It\'s a fundamental characteristic of life. - **Cell diversity in the human body** - The human body has around 200 different types of cells. - Cells can vary in shape, size, and function. For example, nerve cells can be star-shaped and live for the entire life of the organism. - Cells in the same location, like the brain or heart, can be slightly different from each other. This is due to the arrangement of membrane proteins on the cell surface. - **Factors that contribute to cellular diversity** - Cell fate determination - Notch signaling - Epigenetic regulators - **Examples of cellular diversity** - Taste buds: Taste buds are made up of specialized columnar epithelial cells that are organized into a garlic bulb-like assembly. - Neurons: Different types of neurons perform different roles in the nervous system. IV\. THE TISSUE LEVEL OF ORGANIZATION A. Types of Tissues and their Origins B. Cell Junctions C. Epithelial Tissues D. Connective Tissues E. Membranes F. Muscular Tissue G. Nervous Tissue H. Tissue Repair REFS: