Cellular and Tissue Level Biology Practice Flashcards
The Hierarchy of Biological Organization
The human body is organized into a specific hierarchy that increases in complexity at each successive stage. This structural framework begins at the most basic level and progresses toward the complete individual. The hierarchy is defined as follows: the chemical level leads to the organelle level, which forms the cellular level; cells group to form the tissue level; tissues combine to create the organ level; multiple organs work together at the system level; and finally, all systems integrate to form the organism.
The Chemical Level: Atoms, Molecules, and Bonds
All matter, whether it exists as a solid, liquid, or gas, is composed of various elements, which represent the purest form of matter. The fundamental unit of these elements is the atom. Atoms are composed of three subatomic particles: protons, neutrons, and electrons. Molecules are formed when atoms bond together. An isotope of an element is defined as an atom that possesses the same number of protons as other atoms of that element but contains a different number of neutrons.
Chemical bonding occurs in several forms. In a covalent bond, atoms share electrons. In an ionic bond, atoms give up or receive electrons from one another. When ionically bonded molecules are placed in water, they separate to become ions, which are referred to as electrolytes when in solution. A hydrogen bond is a relatively weak bond that forms between a positively charged hydrogen atom and a negatively charged oxygen or nitrogen atom.
Properties of Water and Aqueous Solutions
Water is essential for life and performs five vital functions within the human body. First, it allows for ions to exist in solution. Second, it acts as a lubricant for various bodily structures. Third, it facilitates and participates in chemical reactions. Fourth, it aids in the transportation of substances throughout the body. Fifth, it is critical for temperature regulation.
Solutions are comprised of a solute that is dissolved within a solvent. The term concentration refers to the amount of solute present relative to the amount of solvent. When comparing different solutions, three terms are used: a hypertonic solution is more concentrated than the reference, an isotonic solution has the same concentration, and a hypotonic solution is less concentrated.
Acids and bases are defined by their interaction with hydrogen ions. Acids are hydrogen () ion donors, while bases are hydrogen ion acceptors. The pH scale measures the level of acidity or alkalinity in a substance. This scale is logarithmic, meaning that every one-number difference represents a 10-fold change in the concentration of or ions.
Organic Molecules and Metabolic Reactions
Organic molecules are the building blocks of life and must contain both carbon and hydrogen. There are four major types of organic molecules: carbohydrates, lipids, proteins, and nucleic acids. These molecules are constructed from smaller building blocks.
Metabolism encompasses the sum of all chemical reactions occurring within the body. For molecules to react, they must come into physical contact. The rate of these reactions can be increased by increasing the concentration of the reactants, adding heat to increase the speed of the reactants, or utilizing a catalyst. One of the most critical chemical reactions is cellular respiration, which provides the cell with usable energy in the form of ATP (adenosine triphosphate). The formula for cellular respiration is represented as:
This translates to Glucose + Oxygen yielding Carbon dioxide + Water + Energy.
The Organelle Level
Organelles are specialized structures suspended within a fluid called cytoplasm. Each organelle performs a specific function necessary for cellular survival. The nucleus houses the cell's DNA. Mitochondria are responsible for performing cellular respiration and processing energy into . Ribosomes serve as the site where proteins are assembled. The endoplasmic reticulum (ER) is an extension of the nuclear membrane; the Rough ER is the site of protein synthesis, while the Smooth ER is the site of lipid synthesis. Golgi complexes consist of membrane-enclosed folds that receive and modify proteins and lipids. Secretory vesicles are membrane packages that transport materials from the Golgi complex to the cell membrane for export (exocytosis). Lysosomes are membrane-bound packages containing digestive enzymes.
The Cellular Level and Membrane Transport
The cell membrane is a phospholipid bilayer that provides structural integrity to the cell and acts as a selectively permeable barrier, regulating which materials may enter or leave. Materials move across this membrane via three primary methods: passive, active, or bulk transport.
Passive transport moves materials from areas of high concentration to areas of low concentration without requiring any energy. This categories includes filtration, simple diffusion, facilitated diffusion, and osmosis. Active transport moves materials against a concentration gradient, from areas of low concentration to high concentration, and requires energy to function.
Bulk transport is used to move large quantities of materials rather than individual molecules. Exocytosis is the process of moving materials out of the cell, while endocytosis is the process of moving materials into the cell.
Protein Synthesis and Cell Division
Protein synthesis is a two-step process involving transcription and translation. Transcription occurs in the nucleus, producing mRNA that carries DNA instructions to the ribosomes located on the rough endoplasmic reticulum. Translation occurs at the ribosome, where tRNA molecules transport specific amino acids for assembly based on the sequence coded in the mRNA. Once assembled, the amino acid sequence is sent to the Golgi complex for modification. While mistakes in protein synthesis can occur, they may or may not result in functional consequences.
Cell division in most human cells occurs via mitosis. Human DNA is normally spread out as chromatin but is packaged into 46 chromosomes before division. During mitosis, a parent cell replicates its 46 chromosomes and divides into two identical daughter cells. Each daughter cell receives a complete set of 46 chromosomes. Once division is finished, the original parent cell no longer exists. Mistakes during DNA replication may or may not have consequences for the cell.
Affecting the cellular level is the aging process. Telomeres are noncoding strings of nucleotides located at the ends of chromosomes, believed to protect the chromosome ends. A portion of the telomere is lost during every cell division. When telomeres are completely depleted, replication mistakes become more frequent, which potentially compromises cellular function as the organism ages.
The Tissue Level: Classifications and Growth
Tissues are groups of cells functioning together, categorized into four basic types. Epithelial tissue covers or lines all body surfaces; its types are named based on cell shape and the number of layers. Connective tissue consists of cells and fibers embedded in a matrix, which can range from fluid (blood) to dense and hard (bone). Muscle tissue contains a high concentration of proteins that allow for contraction. Nervous tissue is composed of neurons and support cells known as neuroglia, functioning to communicate via electrical and chemical signals.
Normal tissue growth occurs through hyperplasia (increasing the number of cells) or hypertrophy (increasing the size of existing cells). Metaplasia refers to the transformation of one tissue type into another. Conversely, atrophy is the shrinkage of tissue due to disuse or aging.
Tissue Death and Neoplasia
Tissue death can occur in several ways. Necrosis is premature tissue death; a sudden instance of this is called an infarction. Gangrene is tissue death resulting from insufficient blood supply, often linked to infection. Apoptosis is a regulated, programmed cell death.
Neoplasia is the uncontrolled proliferation of abnormal or nonfunctional tissue, resulting in neoplasms (tumors). These may be benign (encapsulated and localized) or malignant (cancerous and capable of metastasis). Tumors are harmful because they compete with healthy tissues for nutrients and space. Most cancers result from genetic mutations caused by replication errors or environmental carcinogens. Cancers are named after their tissue of origin: carcinomas (epithelial), sarcomas (connective or muscle), lymphomas (lymphoid), and leukemias (blood-forming tissues in red bone marrow).
Organ and System Levels
At the organ level, different types of tissues function collectively to perform specific tasks. At the system level, multiple organs work together. There are 11 systems in the human body: integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, excretory/urinary, male reproductive, and female reproductive.