NLN NEX Science Review Materials PDF

NLN Assessment Services Division NLN Nursing Entrance Exam (NEX) Review Materials Science Section Last Updated 6.3.2024 Copyright ©2023 by the National League for Nursing. All rights reserved. This online review guide is purchased for use by one person only. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the publisher. Although the author and publisher have made every effort to ensure that the information in this book was correct at press time, the author and publisher do not assume and hereby disclaim any liability to any party for any loss, damage, or disruption caused by errors and omissions, whether such errors or omissions result from negligence, accident, or any other cause. This product was written solely as a review guide for individuals planning to take the NLN NEX exam, and the content contained herein is not a substitute for seeking appropriate health care. National League for Nursing 2600 Virginia Ave. NW Washington D.C. 20037 2 Table of Contents GENERAL BIOLOGY................................................................................................................. 7 Cell Structure and Function..................................................................................................... 7 Levels of Organization......................................................................................................... 9 Diffusion and Osmosis........................................................................................................10 Evolution................................................................................................................................11 Evidence and Theories.......................................................................................................11 Classification of Organisms................................................................................................12 Microbiology..........................................................................................................................13 Ecology: Interrelationships and Problems..............................................................................14 Plants and Photosynthesis.....................................................................................................16 Genetics................................................................................................................................17 Dominance.........................................................................................................................18 Segregation........................................................................................................................18 Independent Assortment.....................................................................................................18 DNA....................................................................................................................................19 Lab and Research Procedures..............................................................................................20 HUMAN ANATOMY AND PHYSIOLOGY..................................................................................22 Gastrointestinal System.........................................................................................................22 Circulatory and Lymphatic Systems.......................................................................................26 Respiratory System...............................................................................................................31 Nervous System....................................................................................................................33 Endocrine System..................................................................................................................36 Musculoskeletal System........................................................................................................38 Connective Tissue..............................................................................................................40 Muscles..............................................................................................................................40 Urinary System......................................................................................................................41 Reproductive System.............................................................................................................43 Integumentary System...........................................................................................................45 Senses..................................................................................................................................46 Sight...................................................................................................................................47 Hearing...............................................................................................................................47 Taste and Smell..................................................................................................................48 Touch.................................................................................................................................48 BASIC CHEMISTRY.................................................................................................................49 Atomic Structure, Isotopes, Ions, and the Periodic Table.......................................................49 Bonding.................................................................................................................................53 States of Matter.....................................................................................................................54 3 Mixtures, Solutions, Tinctures, and Emulsions.......................................................................56 Chemical Reactions...............................................................................................................56 Synthesis or Combination Reactions..................................................................................57 Single Replacement Reactions...........................................................................................57 Double Displacement Reactions.........................................................................................58 HEALTH....................................................................................................................................60 Meaning of Health..................................................................................................................60 Levels of Health.....................................................................................................................61 Factors That Influence Health................................................................................................61 Rest and Sleep...................................................................................................................61 Diet and Nutrition................................................................................................................62 Exercise.............................................................................................................................67 Hygiene..............................................................................................................................67 Avoidance of Alcohol, Tobacco, and Drugs........................................................................67 Health Threats.......................................................................................................................67 Substance Abuse Disorder.................................................................................................67 Environment.......................................................................................................................68 Health Inequities.................................................................................................................68 Prevention and Safety............................................................................................................68 Health Screenings.................................................................................................................69 Vaccinations..........................................................................................................................70 4 List of Figures Figure 1: Structure of a Cell....................................................................................................... 9 Figure 2: Osmosis and Red Blood Cells....................................................................................11 Figure 3: Structure of a Flower..................................................................................................17 Figure 4: Punnett Square..........................................................................................................18 Figure 5: DNA Replication.........................................................................................................19 Figure 6: Effect of Pressure on the Volume of a Gas.................................................................21 Figure 7: Stages of Digestion....................................................................................................23 Figure 8: Gastrointestinal System.............................................................................................25 Figure 9: Human Heart..............................................................................................................28 Figure 10: Blood Composition...................................................................................................29 Figure 11: Lymphatic System....................................................................................................30 Figure 12: Respiratory System..................................................................................................31 Figure 13: Inhalation and Exhalation.........................................................................................32 Figure 14: Neuron.....................................................................................................................34 Figure 15: The Brain.................................................................................................................36 Figure 16: Endocrine System....................................................................................................37 Figure 17: Bone Structure.........................................................................................................39 Figure 18: Skelton.....................................................................................................................40 Figure 19: Urinary System.........................................................................................................42 Figure 20: Male Reproductive System......................................................................................44 Figure 21: Female Reproductive System..................................................................................45 Figure 22: Layers of the Skin....................................................................................................46 Figure 23: Structure of the Eye.................................................................................................47 Figure 24: Structure of the Ear..................................................................................................48 Figure 25: The Periodic Table...................................................................................................51 Figure 26: Locating an Atom's Mass Number and Atomic Number............................................52 Figure 27: Lewis Electron Dot Diagram.....................................................................................53 Figure 28: Covalent Bond: Cl2...................................................................................................54 Figure 29: Polar Covalent Bond: HCl........................................................................................54 Figure 30: Liquid to Gas Phase Change...................................................................................55 5 List of Tables Table 1: Chemical Digestion...................................................................................................................................26 Table 2: Endocrine Glands and Their Hormones................................................................................................37 Table 3: Recommended Daily Allowance, Function, and Source of Vitamins................................................63 Table 4: Recommended Daily Allowance, Function, and Source of Body Minerals......................................65 Table 5: Routine Health Screenings......................................................................................................................69 6 Science Content Review General science knowledge, skills, and abilities form the bedrock upon which nursing skills and expertise are built, making them essential components in academic assessments for nursing program entrance exams. This content review is intended to outline and provide a high-level overview of the five key subjects included in the science section of the National League for Nursing (NLN) Nursing Entrance Exam (NEX). These subjects include Biology, Anatomy, Physiology, Chemistry, and Health. These review materials are not intended to replace a high- school or college-level course in each of these subjects; instead, they should supplement the knowledge, skills, and abilities you have already gained from completing your high school science courses and help you refresh your memory of some of the content. Using this content review and the online practice exams, you will gain exposure to the types of questions and concepts you might encounter on the Science section of the NEX. You should prepare yourself to demonstrate your knowledge and comprehension of scientific concepts; ability to apply scientific principles, basic laboratory, research, and measurement concepts; and ability to interpret charts, graphs, and diagrams. GENERAL BIOLOGY General biology is a broad scientific discipline that encompasses the study of living organisms and their interactions with the environment. Included in the biology section of the NEX are topics such as cellular structure and function, evolution, ecology, microbiology, genetics, organizational levels and taxonomies, research and laboratory procedures, and general plant and photosynthesis concepts. Cell Structure and Function Terms to Be Defined cell mitochondria chromatin nucleus ribosome chromosomes DNA endoplasmic reticulum (ER) mitosis plasma (cell) membrane Golgi complex zygote interstitial fluid lysosome meiosis selectively permeable (semipermeable) cell wall semi-permeable membrane cytoplasm chloroplast ATP organelles vacuole chromatin The cell is the smallest, living functional and structural unit for all living things. Living cells are composed of approximately 60% water and vary in size and shape. For example, a red blood cell is disk-shaped, whereas nerve cells can be very long and have extensions on their main body. Different types of cells vary in terms of the roles they play in the body. Cells have a 7 number of common features and functions despite their differences. The following description is that of a general animal cell. The nucleus contains genetic information, or DNA (deoxyribonucleic acid), and controls the activities of the cell. The plasma (or cell) membrane is known as a semipermeable membrane that separates the contents of the cell from the surrounding fluid, the interstitial fluid. The interstitial fluid contains substances such as amino acids, sugars, fatty acids, hormones, neurotransmitters, and salts. The term, selectively permeable (semipermeable), refers to the selective nature of the plasma membrane. It contains pores and channels that allow only particles of the right size or the right chemical nature to pass through. Additionally, the plasma membrane contains receptors that bind with specific substances, thus allowing for special entry or signals the cell to perform a certain activity. The cytoplasm is the fluid matrix found between the plasma membrane and the nucleus that acts as scaffolding for the organelles. Organelles, or “little organs,” are specialized units in the cell that perform certain functions. The mitochondria are the locations for cellular respiration or the conversion of food to energy at the cellular level. Thus, the mitochondria are the sites of energy production and of most of its ATP (adenosine triphosphate), which is a chemical the cell uses to store and transfer energy within itself. Ribosomes are the sites of protein synthesis in the cell. Some ribosomes float freely, whereas others are attached to the endoplasmic reticulum (ER). The ER serves as a means for transport within the cell and is made up of many channels. Rough ER, named for the fact that it has ribosomes on its surface, serves to store and deliver the proteins made by the attached ribosomes. Smooth ER is free of ribosomes and is found in a variety of cells. It performs varying functions in different cells, including the storage of enzymes and minerals and the folding of proteins. It is thought to be involved in the detoxification of chemicals and the metabolism of fats. The Golgi complex modifies and packages proteins destined for use in the cell or for export from the cell. Lysosomes are sacs that contain strong digestive enzymes. These sacs are responsible for digesting waste and cell structures that are malfunctioning or dead. Plant cells can be distinguished from animal plants by the presence of a surrounding cell wall and chloroplasts. The cell wall is essential for protection of the cell, the maintenance of the shape, and water balance. Chloroplasts contain chlorophyll, which is necessary for photosynthesis. Plant cells also often have large vacuoles, which are compartments in the cytoplasm that act as places for secretion, excretion, and storage (See Figure 1). Cells divide for a number of reasons: growth, repair, and the production of gametes (sperm or egg cells). The most important result of cell division is that the genetic material, DNA, is transmitted to the offspring. DNA is found in the nucleus in the form of chromatin and chromosomes. When a cell is not dividing, DNA is found in the form of loosely structured chromatin, but when a cell is dividing, the DNA is seen in condensed rod-shaped bodies called chromosomes. When cells divide, the appropriate amount of genetic material must be passed on to the new daughter cells. In somatic (non-reproductive) cells, the new cells are identical copies of the parent cells. This is achieved by a doubling of the chromosomes prior to division. This type of cell division is referred to as mitosis, and it is useful in the growth and repair of our bodies. Mitosis occurs in both plant and animal cells, although the process is slightly different. Another type of division takes place in the production of gametes. These reproductive cells contain half of the normal number of chromosomes so that the zygote, the cell created by the union of a sperm and egg, contains a full set of chromosomes, half from each parent. This type 8 of division, or meiosis, consists first of a doubling of chromosomes and then two subsequent divisions. Thus, the products are four daughter cells, each with half the normal number of chromosomes. Figure 1: Structure of a Cell Levels of Organization Terms to Be Defined tissue nervous tissue organ system muscle tissue connective tissue organism epithelial tissue organ Cells with a common structure and function make up tissues. Tissues can be classified into four main categories: 1. muscle tissue (skeletal, cardiac, and smooth) 2. epithelial tissue (skin, the lining of organs) 3. nervous tissue (neurons) 4. connective tissue (cartilage, blood, fat, bone) 9 Various tissues are combined into an organ, which performs a specialized function in the body. For instance, the stomach is an organ involved in digestion and is made up of three types of tissue: muscle, epithelial, and connective. The next level of organization is the organ system, which is made up of a number of organs working together to carry out a major function. For example, the circulatory system includes many organs, such as the heart, blood vessels, spleen, tonsils, and lymph nodes. These organs work together to circulate and deliver necessary products throughout the body. The highest level of organization is the organism itself, such as the human body. Diffusion and Osmosis Terms to Be Defined active transport diffusion isotonic passive transport osmosis hypotonic hypertonic filtration facilitated transport The plasma membrane controls entry to and exit from the cell by means of either passive or active mechanisms. Active transport involves the use of energy in the form of ATP to move substances across the membrane. Passive transport does not require energy and makes use of diffusion and filtration. Facilitated transport is a form of passive transport that involves the use of membrane proteins. In diffusion, particles move in a random manner, spreading evenly throughout an available space and moving from regions of high concentration to those of low concentration. For instance, if you open a perfume bottle at the front of the room, it’ll take a little while for the people in the back of the room to smell the scent. A specific type of diffusion is that of water. This movement of water is also called osmosis. Water moves from an area of high-water concentration (or low particle concentration) to an area of low water concentration (high particle concentration). For example, assume that red blood cells are in water containing a certain concentration of a solute (See Figure 2). When the solute concentration of the water is the same as that inside the cell, the solution is said to be isotonic. Thus, the amount of water that leaves the cell and the amount that enters it are equal. When the solute is more concentrated outside the cell than inside it, the solution is hypertonic. Water leaves the cell due to osmosis; it moves from the high-water/low-particle concentration to low-water/high-particle concentration. As a result, the cell shrinks. If the solute concentration outside the cell is lower than that inside the cell, the solution is hypotonic. Water flows into the cell (again high-water/low-particle concentration to low- water/high-particle concentration). If the flow continues long enough, the cell bursts. Filtration is the movement of water and solutes through the membrane by fluid, or hydrostatic, pressure. 10 Figure 2: Osmosis and Red Blood Cells Evolution Evidence and Theories Terms to Be Defined natural selection vertebrates comparative embryology adaptation biogeography evolution fossil record comparative anatomy molecular biology In 1859, Charles Darwin published On the Origin of Species by Means of Natural Selection, which presented evidence for evolution, a theory regarding the processes that have produced the biological diversity we see today. Darwin’s two main arguments were that (1) the present species evolved from ancestral ones, and that (2) evolution occurs by means of natural selection, the process by which the traits that promote or enhance an organism’s ability to survive and reproduce are passed on to following generations. For natural selection to occur, organisms must have variations, some of which give the individuals having them an advantage in the struggle for survival. The struggle for survival occurs because each generation of a species produces more offspring than can survive. In this struggle, the individuals best suited to their environment survive (“survival of the fittest”) and pass on those traits to their offspring. This is called adaptation, the evolutionary process of an organism to survive in a given environment. There is evidence supporting the theory of evolution, such as the fossil record, which consists of remnants or traces of organisms from past geologic ages. Fossils that have been dated show a timeline for the appearance of different vertebrates (animals with backbones) in the following order: fish, then amphibians, then reptiles, and finally mammals and birds. This finding supports 11 Darwin’s first evolutionary argument and contradicts the theory that all species were created at the same time. Many other types of evidence have been found through the studies of: biogeography (the geographical distribution of plants and animals) comparative anatomy (the comparison of organisms’ structures), comparative embryology (the comparison of organisms’ embryos), and molecular biology (biology at the molecular level). We see examples of evolution occurring today (e.g., development of antibiotic resistant bacteria, insects developing resistance to insecticides, etc.). Classification of Organisms Terms to Be Defined taxonomy protist family kingdom fungi genus animal phylum species plant class monera order Due to the great biological diversity on our planet, a system was needed to organize the many species into groups. In taxonomy (the study of scientific classification), taxonomists group species according to their similarities and differences. They are classified in a hierarchical system in which each level is more specific than the one above it. The broadest units of classification are the kingdoms, of which there are five: animal, plant, monera (bacteria), protist (protozoa, algae, and some molds), and fungi (molds, mushrooms, yeasts, and the like). The next six classifications become increasingly specific: phylum, class, order, family, genus, and species. The scientific name of an organism is always the genus and the species of the organism, with the genus capitalized and the species not; for example, Escherichia coli (E. coli), the well-known bacterium found in the colons of warm-blooded animals, is of the genus Escherichia and the species coli. 12 Microbiology Terms to Be Defined microbiology microorganism bacteria virus fungi algae protozoa bacteriology virology pathogens Microbiology is defined as the study of microorganisms or organisms that are too small to be seen by the naked eye. Therefore, microscopes are used for visualization. Not all microorganisms cause disease, but those organisms that do cause disease are referred to as pathogens. Microorganisms are divided into groups: bacteria, viruses, fungi, algae, and protozoa. Bacteria are single-cell microorganisms with a cell wall, but no organelles or nucleus. Not all bacteria are bad and cause infection; many are beneficial and function to aid in digestion and manufacture of foods and antibiotics, destroy bad bacteria that cause disease, supply nutrients for energy, and clean up environmental contaminants and spills. They come in three basic shapes: spherical (cocci), rod-shaped (bacillus), or spiral (spirochetes). Bacteria may also be classified by a staining process. The most common is gram staining with organisms being either gram positive or gram negative. This information is especially helpful when selecting appropriate antibiotics for the treatment of bacterial infections. Over time, bacteria may become resistant to an antibiotic. A good example of this resistance is Methicillin-Resistant Staphylococcus aureus (MRSA). The study of bacteria is bacteriology. Viruses consist of DNA or RNA surrounded by protein. Viruses are often considered on the borderline of living organisms as they lack typical cellular structure, do not metabolize their own energy, and are unable to reproduce independently. Viruses are only able to replicate once they are inside a host cell at which point they begin directing cellular activity to reproduce. Viruses can infect all forms of life, including bacteria, plants, animals, and humans. Viruses are not responsive to antibiotics and are treated by antiviral drugs specific to the virus. The study of viruses is virology. Fungi constitute another group of microorganisms. Fungi may be single cell or multi-cellular. They are composed of a nucleus and organelles surrounded by a cell membrane. Surrounding the cellular membrane is the rigid fungal cell wall giving shape and providing protection. Nearly all fungi produce spores as their main reproductive unit. Common examples of fungi include yeast, mushrooms, and mold. Fungi play important roles in nutrient cycling and decomposition. Fungi can form mutualistic relationships with plants or cause diseases in plants and animals. Fungal infections are treated with antifungal drugs. The study of fungi is mycology. Algae vary greatly in size and may be microscopic or extremely large. They may be single or multi-cell and contain a nucleus. Most algae live in fresh or salt water using sunlight to produce food. If there is enough moisture, algae can grow on rocks, soil, or other vegetation. Although they use photosynthesis to produce food, they lack the typical structure of land plants. The study of algae is phycology. 13 Protozoa are single cell microorganisms, that, like animal cells, lack cell walls. Most protozoa ingest particles of food; however, some are plantlike and obtain energy from photosynthesis. Many protozoa are motile and use structures for propulsion or other types of movement. Most species are free living, in aquatic environments, and occasionally soil or sand. Protozoa may live within other organisms, producing asymptomatic to life threatening infections. Parasitic protozoa living within humans may produce diseases, such as malaria. The relationship between two species is termed symbiotic when both species benefit and parasitic when one species benefits, and another is harmed. Antibiotics are not effective in the treatment of protozoa infections. However, antiprotozoal drugs are often combined with antibiotics in creams and ointments. The study of protozoan is protozoology. Ecology: Interrelationships and Problems Terms to Be Defined autotroph food chain mutualism heterotroph food web biosphere primary consumer decomposer biome herbivore biotic deserts omnivore abiotic tropical rain forest secondary consumer predator deciduous forest carnivore prey coniferous forest tertiary consumer symbiosis tundra trophic level parasitism ecosystem commensalism Autotrophs are organisms that produce their own food from inorganic substances (i.e., plants). Heterotrophs, or consumers, on the other hand, obtain their food by consuming plants or other animals. Primary consumers may be herbivores (plant eaters) or omnivores (plant and meat eaters). Secondary consumers are carnivores (meat eaters) or omnivores that eat herbivores. Tertiary consumers are carnivores that eat other carnivores or omnivores. These divisions, which are made on the basis of how the organism meets its nutritional needs, make up the trophic levels of an ecosystem. The autotrophs are the most important trophic level in the ecosystem and are known as producers; the other levels are made up of the different types of consumers. The path along which food is transferred from level to level is called a food chain, and the interrelationship of many food chains is called a food web. An important role in an ecosystem is played by the decomposers, such as bacteria and fungi, which consume nonliving organic material and release inorganic material. Thus, material is recycled through the ecosystem, and inorganic material is made available to the plants. Factors that affect an ecosystem are classified as biotic or abiotic. Biotic factors include the living parts of the ecosystem, and abiotic factors are nonliving influences, such as temperature, humidity, or soil composition. Within an ecosystem are many interrelationships among species, such as 14 between predator and prey. Separate species living together (symbiosis) include parasitism (in which one species benefits and the other species are harmed, such as a tapeworm in a human host), commensalism (in which one species benefits and one is unaffected, such as a remora and shark), and mutualism (in which both species benefit, such as lichen, which is made up of a fungus and an alga and is found on a tree or rock). On a larger scale, a biosphere is the entire portion of our planet that is inhabited by living things in a variety of ecosystems and communities. Within the biosphere are groups of ecosystems that are common to the various types of geographical areas. These geographical areas are called biomes. Many of the terrestrial biomes are classified according to differences in climate. Some of the most familiar terrestrial biomes are as follows: Deserts have little precipitation and are more arid than all of the other biomes. Tropical rain forests typically have a relatively constant temperature (68°F-90°F), constant daylight length throughout the year, high humidity, and abundant rain (200-400 cm/year). These forests are known for their biodiversity, having more species than any other area of the world. Trees grow very tall, and there is great competition for light. Little light reaches the forest floor. Deciduous forests are usually found in the temperate, mid-latitude regions of the world, where the air contains enough moisture to support the growth of large trees. Deciduous trees, such as oaks and maples, drop their leaves during the dry months. The temperatures in this biome can range widely from season to season. Coniferous forests (taigas) are found at high and cool elevations, where the seasons consist of short summers and long, chilly winters. These areas are characterized by conifers, such as pine and firs, which do not shed their leaves in the cold, dry months. Tundras are characterized by very cold temperatures and high altitude. The conditions allow shrubs and bushes to grow, but no trees. Aquatic biomes are abundant as well. Some familiar ones include swamps, wetlands, rivers and streams, coral reefs, and estuaries. Marine biomes occupy the oceans and are classified according to their water depth and proximity to the shoreline. 15 Plants and Photosynthesis Terms to Be Defined photosynthesis petal style chlorophyll stamen ovary cuticle filament ovule stomate anther seed sepal pistil fruit angiosperms stigma molecules All organisms obtain the organic substances they need by either autotrophic or heterotrophic means. To produce their own organic molecules from inorganic molecules in the environment, autotrophs use the process called photosynthesis. In this process, the pigment chlorophyll, which is located in the chloroplasts of plant cells, absorbs light energy. This energy, in turn, drives the synthesis of food molecules: 6CO2 + 6H2O + light energy--> C6H12O6 + 6O2 or carbon dioxide + water + light energy --> carbohydrates + oxygen Plants have acquired unique characteristics to help them survive in a terrestrial environment. The stems and leaves of most plants are covered by a cuticle, which is a waxy layer that helps prevent water loss through evaporation. Additionally, the leaves have stomates, which are pores on the lower surface of the leaves that allow carbon dioxide to enter and oxygen to be released during photosynthesis without losing too much water. The flower in flowering plants, or angiosperms, is responsible for reproduction (See Figure 3). The sepals encase the flower before it blooms, and the petals are useful in attracting pollinators. In the center of the petals are the stamen and pistils. The stamen consists of the filament, which supports the anther, where pollen is produced. The pistil consists of the stigma (which receives pollen), the style (which leads to the ovary), and the ovary (which contains the ovules and where fertilization occurs). After fertilization, the ovules within the ovary develop into seeds. The walls of the ovary thicken to protect the seed and this thick fleshy protective layer is what we know and love as fruit. 16 Figure 3: Structure of a Flower Genetics Terms to Be Defined gene linkage double helix allele heterozygote uracil dominance homozygote phosphate group phenotype sex-linked traits transcription genotype autosome messenger RNA (m-RNA) segregation replication transfer RNA (t-RNA) independent assortment nucleotide nitrogenous base codominance deoxyribose amino acid All living things possess a set of instructions (genes) that determines the characteristics of an organism. Genes are located on chromosomes. Chromosomes occur in homologous pairs, consisting of one chromosome from each of two parents, arranged in complementary patterns, and containing genes for the same traits at the same loci on the homologous pairs. Similarly, genes are found in pairs called alleles. An individual with two identical genes for a trait is called purebred, or homozygous. This phenomenon was first explained by Gregor Mendel with his laws of dominance, segregation, and independent assortment. 17 Dominance In observing pea plants, Mendel observed that, when individuals with contrasting traits are crossed, one trait, called the dominant trait, is expressed, and the other trait, called the recessive trait, is masked. This is the law of dominance. In the notation of genetics, the dominant gene is represented by a capital letter and the recessive trait by a lowercase letter. For example, if a tall plant (TT) is crossed with a short plant (tt), the result is 100% heterozygous (Tt) offspring, containing one allele for tall and one for short. The allele for tall (T, the dominant gene) is expressed, and the allele for short (t) is hidden. The phenotype, or appearance of the plants, is all tall, while the genotype is Tt. Segregation The law of segregation tells us that when two of these hybrids (heterozygotes) are crossed, the hidden trait becomes segregated and appears in 25% of the offspring. This happens because genes separate during meiosis and recombine during fertilization. This process can be pictured using a Punnett square (Figure 4), which looks like this: Figure 4: Punnett Square In the genes produced by these individuals, half of the gametes are T and half t. In arranging them on the Punnett Square (Figure 4), we see that 25% of the offspring have a genotype of TT, 50% Tt, and 25% tt. The phenotype is 75% tall and 25% short, because both the pure dominant (TT) and the heterozygote (Tt) exhibit the dominant trait. A recessive trait is expressed only if the individual has two recessive genes (tt). Independent Assortment According to the law of independent assortment genes on different chromosomes are inherited independently of each other. When genes for different traits are on the same chromosome, the traits are linked. Some traits do not show a pattern of dominance and the heterozygote for such a trait expresses a mixture of the two traits. This is called co-dominance. An example is roan cattle, in which cattle may be red (RR), white (WW), or roan (RW), which is a mixture of red and white fur. Humans have 46 chromosomes, or 23 homologous pairs, of which 22 pairs are autosomes (non-sex chromosomes) and one pair consists of the sex chromosomes (XX or XY). An individual with two X chromosomes is a female and an individual with an X chromosome and a 18 Y chromosome is a male. For some traits, the genes are found only on the X chromosome, but not on the Y, and these traits are called sex-linked traits. A male need inherit only one gene for such a trait from his mother for it to be expressed, but a female has to inherit two, one from each parent. Examples of sex-linked traits are color blindness and hemophilia. DNA Deoxyribonucleic acid (DNA) is what we have been calling the gene. The model explaining the structure of DNA was first proposed by James Watson and Francis Crick (See Figure 5). To understand the role of DNA in genetics, we must understand the structure of DNA, which is made up of thousands of units called nucleotides. Each nucleotide is composed of a phosphate group (PO4), a five-carbon sugar called deoxyribose, and a nitrogenous base (either adenine, cytosine, guanine, or thymine). Figure 5: DNA Replication The nucleotides form long chains, which are joined to form a double helix. Two strands of nucleotides are joined by nitrogenous bases connected to each other with hydrogen bonds. If you think of a DNA molecule as a ladder, the sugar and phosphate units form the uprights, and the pairs of nitrogenous bases are the rungs of the ladder. The bases can bond only in certain combinations: guanine (G) to cytosine (C) and adenine (A) to thymine (T), thus providing four possible pairings: G-C, C-G, A-T, T-A. Just as chromosomes replicate during cell division, DNA strands also replicate, or make exact copies of themselves. During replication, the DNA strand opens at the base pairs. Free (or unattached) nucleotides are incorporated into the unzipped portion of the DNA, so that complementary base pairs join to form two exact duplicates. For example, if an unzipped strand 19 has a sequence of ATCGA, it attracts nucleotides TAGCT. The result is two replicated DNA molecules that are identical to each other and to the original DNA. DNA also serves as a template for the production of messenger RNA (m-RNA). RNA differs from DNA in that it is single stranded, has sugar ribose in place of deoxyribose, and replaces thymine with uracil. The process of forming m-RNA according to the information contained in the DNA molecule is called transcription. The DNA strand opens, but in this case, acts as a template for the production of RNA. Similar to replication, the base sequence of the DNA strand determines the nucleotide order in the RNA strand. For example, if the DNA sequence is GCTTAA, the RNA strand is CGAAUU. A molecule of m-RNA, which is made in the nucleus, moves to the cytoplasm, and is attached to a ribosome. At the ribosome, transfer RNA (t-RNA) molecules, which are coded for specific amino acids, line up along the m-RNA molecule at the ribosome. In doing so, they align their amino acids according to the code in the m-RNA and form them into proteins. This mechanism produces proteins according to the information coded in the original DNA molecule (i.e., translation). Gene mutations are changes in the DNA nitrogenous base sequence, causing a change in the protein formed. There are also chromosomal mutations, in which either the structure or number of chromosomes changes, resulting in conditions such as polyploidy (a full set of chromosomes fails to separate, resulting in an individual that could be 3n) or nondisjunction, in which one chromosome pair fails to separate during meiosis, such as what happens in Down’s syndrome. Lab and Research Procedures Terms to Be Defined compound microscope variable constant electron microscope independent variable controlled experiment data dependent variable light microscope Microscopes, introduced in the seventeenth century, greatly affected the progress of science. Using a microscope, scientists were able to see individual cells. In a light microscope, light is first passed through a specimen and then through a glass lens, which bends light in such a manner that an image is magnified. However, many internal structures of the cell are too small to be seen, even with the light microscope. The invention of the electron microscope in the 1950s greatly enhanced the study of cell biology. The electron microscope, which sends a beam of electrons through a specimen, can be used to examine structures too small to be seen through a light microscope. The light microscope can magnify specimens up to 2,000 times, whereas the electron microscope can magnify them up to 2 million times. The compound microscopes you may have used in school usually magnify around 400 times, under high power. The quality of the lenses determines the resolution of the microscope. When we use a compound microscope, we often stain the specimen to make particular structures stand out. Common stains include Lugol’s solution, Methylene blue, and Wright’s stain. Gram staining uses crystal violet stain as the primary stain, followed by Gram’s Iodine and ethanol to differentiate between a positive and a negative stain. In science, we collect a good deal of data. During an experiment, we are often looking for data on variables, which are measurable factors or qualities that change during an experiment. 20 Variables are classified as independent and dependent. An independent variable is one that is changed by the experimenter. The variable that changes in response to the independent variable is called the dependent variable. Unchanging factors are called constants. For example, suppose we performed an experiment to determine the effect of pressure on the volume of a gas. We would vary the pressure (the independent variable), record the change in volume caused by the pressure change (the dependent variable), and keep the temperature constant. We call such an experiment a controlled experiment because we are seeking data on only one independent variable while other factors remain constant. If we allowed temperature and pressure to vary together, we would not know whether the volume changed because of pressure or temperature. Having collected data, it is important to represent it in ways that help us to analyze it and draw conclusions. One way of representing data is in the form of a graph, which often helps us to see correlations. When we represent data in the form of a graph, the independent variable is always plotted on the x-axis and the dependent variable on the y-axis. For example, Figure 6 shows the effect of pressure on the volume of a gas. Figure 6: Effect of Pressure on the Volume of a Gas 21 HUMAN ANATOMY AND PHYSIOLOGY Human anatomy and physiology are scientific disciplines focused on the structure and function of a complex machine, the human body. Anatomy focuses on physical elements and their spatial relationships within the body, while physiology explores the mechanisms and processes that sustain life. Included in the anatomy and physiology sections of the NEX are items related to each of the various systems and senses presented in this section. Gastrointestinal System Terms to Be Defined mechanical digestion pharynx liver chemical digestion esophagus bile hydrolysis epiglottis gallbladder enzymes stomach pancreas anus peristalsis villi alimentary canal gastric juice large intestine (colon) accessory organs protease rectum surface area chyme defecation salivary glands small intestine amylase pyloric sphincter Digestion is the breaking down of nutrients into small, soluble molecules that can be absorbed into the blood. This process is accomplished by mechanical digestion (breaking food into smaller pieces) and chemical digestion (breaking nutrients into small molecules). The process by which chemical digestion occurs is called hydrolysis (splitting molecules by adding water). Chemical digestion is sped up by the action of digestive enzymes (hydrolases). The stages of digestion with explanations of each stage are shown in Figure 7. 22 Figure 7: Stages of Digestion Esophagus Humans, as opposed to simpler animals, such as jellyfish, have a digestive system that is composed of a tube that extends between two openings: the mouth and the anus (See Figure 8). This tube, called the alimentary canal, is organized into specialized regions that carry out specific phases of the digestive process (e.g., mechanical digestion, chemical digestion, and absorption). In addition to the alimentary canal, the digestive system has accessory organs (liver, gallbladder, and pancreas). Food enters through the mouth, where it is chewed (mechanical digestion), increasing the surface area, which makes it easier to both swallow and digest. The presence of food also stimulates the salivary glands to release saliva, which contains an enzyme called amylase. Amylase breaks down starches into smaller carbohydrate molecules (monosaccharides and 23 disaccharides). As food is swallowed, it is pushed by the tongue into the pharynx (throat), which leads to both the windpipe and the esophagus. When swallowing, the top of the windpipe is covered by the epiglottis which prevents food from entering the respiratory system. From the esophagus, the food is passed to the stomach by muscular contractions called peristalsis. The lining of the stomach releases gastric juice, which is made up of hydrochloric acid and proteases (protein digesting enzymes). The environment of the stomach is acidic, with a pH of approximately 2, because gastric enzymes work best in this environment. Fortunately, cells in the stomach lining secrete mucus, which protects the stomach wall from the very acidic gastric juice. The smooth muscles of the stomach mix the partially digested food, and the result is a liquid called chyme. Chyme is released to the small intestine in a series of small portions through the pyloric sphincter. Most of the digestion of food takes place in the small intestine, which can be up to 6 meters long in humans. The small intestine is the major site not only for digestion but also for the absorption of nutrients into the bloodstream. Digestive enzymes are secreted by intestinal glands. Also contributing to digestion are the liver, the pancreas, and the gallbladder. The liver produces bile, a substance stored and concentrated in the gallbladder, which helps in the breakdown of fats. The pancreas supplies a number of enzymes needed for digestion. To facilitate absorption, the small intestine is lined with villi, which greatly increase the intestinal surface area for the absorption of the end products of digestion into the blood and lymph. Undigested food is moved to the large intestine, or colon, which is responsible for reabsorbing water that has entered the alimentary canal. Waste, or feces, moves along the colon by peristalsis, becoming increasingly solidified and is ultimately stored in the rectum until defecation (elimination from the body). Diarrhea is a result of peristalsis moving feces through the colon too quickly so that water is not reabsorbed, whereas constipation results from too little peristalsis and thus too much reabsorption of water. 24 Figure 8: Gastrointestinal System Esophagus Chemical digestion, as presented in Figure 8, occurs as enzymes break down three macronutrients: carbohydrates, proteins, and lipids, into more absorbable components. Bonds for each macronutrient are broken down by specific enzymes, in various stages and locations, to produce a single molecule end product as shown in Table 1. 25 Table 1: Chemical Digestion Nutrient Enzymes End product1 Location Carbohydrate Salivary Amylase Maltose Start: Mouth Pancreatic Amylase Maltose Continue: Small intestine Sucrase, Maltase, Monosaccharides End: Small intestine and Lactase (e.g., glucose, (microvilli) fructose, and galactose) Proteases Pepsin Peptides Start: Stomach Trypsin and Chymotrypsin Smaller peptides Continue: Small Protein intestine Peptidaeses Aminopeptidase and Dipeptidase Amino acids End: Small intestine Lipases Lingual and Start: Mouth Lipids Gastric Lipases Pancreatic Lipase Fatty acids and and Bile Salts glycerol End: Small intestine 1 End product is in bold; other products represent stages of macronutrient breakdown. Circulatory and Lymphatic Systems Terms to Be Defined atrium diastole platelets ventricle pulmonary circulation lymph capillaries atrioventricular valve systemic circulation lymph nodes pulmonary artery coronary circulation arteries deoxygenated blood blood veins oxygenated blood plasma capillaries pulmonary vein hemoglobin circulatory system systole white blood cells Circulation is the internal transport of blood and lymph throughout the body, which allows for the exchange of gases, the absorption of nutrients, and the disposal of waste. The circulatory system is made up of the cardiovascular and lymphatic systems, which function together to achieve these goals. 26 The cardiovascular system in humans is made up of the heart, blood vessels, and blood. The heart consists of four chambers: two atria (singular: atrium), which receive blood, and two ventricles, which pump blood to the body (See Figure 9). The pathway of blood through the heart and lungs, beginning at the vena cava, is as follows: Blood enters the right atrium from the upper and lower body through veins called the superior vena cava and the inferior vena cava. From there, it passes through an atrioventricular valve (tricuspid) into the right ventricle (valves prevent backflow when ventricles contract). The right ventricle pumps blood through the semilunar valve into the pulmonary arteries, which carry the blood to the lungs. This blood is deoxygenated and becomes oxygenated in the lungs where gas exchange occurs. Newly oxygenated blood leaves the lungs via the pulmonary veins, which return blood to the left atrium. From there, it passes through another atrioventricular (mitral) valve to the left ventricle. Muscular contractions of the left ventricle pump blood through the aorta to all parts of the body. 27 Figure 9: Human Heart Blood pressure from the pumping action of the heart forces blood to circulate. When the heart contracts, the pressure increases (systole), and when the heart relaxes, the pressure is lowered (diastole). There are three ways blood circulates: coronary circulation, (circulation of blood to the heart ), pulmonary circulation (circulation of blood through the lungs), and systemic circulation (circulation throughout the body). Interestingly, blood is considered a type of connective tissue that is made up of various cells suspended in a liquid called plasma (See Figure 10). Red blood cells, white blood cells, and platelets make up 45% of whole blood, whereas plasma, which contains proteins, ions, hormones, and gases, makes up the other 55%. Red blood cells, or erythrocytes, are responsible for transporting oxygen, and they do not have nuclei or mitochondria. To suit their main function of transporting oxygen, red blood cells are small and thin (to allow for diffusion), and each cell contains approximately 250 million molecules of hemoglobin, an oxygen carrier. Hemoglobin is an iron-rich globular protein, which explains the need for iron in our diets. White blood cells, or leukocytes, are less abundant than red blood cells and are involved in host defense. Not surprisingly, an infection is indicated when the number of white blood cells exceeds the normal concentration. Platelets, also found in plasma, are pieces of cells that are important in blood clotting. 28 Figure 10: Blood Composition As blood passes through the capillary vessels of the circulatory system, fluid and proteins can leak out into the interstitial space. This lost fluid diffuses into lymph capillaries, which are found throughout the cardiovascular system, and thus enters the lymphatic system (See Figure 11). Inside the lymphatic system, the fluid, or lymph, returns to the circulatory system. Lymph nodes are special pockets in the lymphatic system where the lymph is filtered. White blood cells are present in these nodes to attack bacteria and viruses that may be present in the fluid. Thus, swollen and tender lymph nodes are usually a sign of an infection. There are three kinds of blood vessels: arteries, veins, and capillaries. Arteries transport blood away from the heart. Because they carry blood at relatively high pressure, they are muscular. We feel a pulse in the arteries. Veins transport blood to the heart, and they contain valves to prevent the backflow of blood as it returns to the heart. Capillaries are tiny blood vessels that connect arteries and veins. It is through the capillary walls (only one cell thick) that nutrients and oxygen leave the blood to enter the interstitial space and tissue cells and waste products and carbon dioxide leave the tissue to enter the blood. 29 Figure 11: Lymphatic System 30 Respiratory System Terms to Be Defined pharynx larynx bronchi bronchioles alveoli diaphragm aerobic respiration anaerobic respiration lactic acid Air enters the respiratory system through the nasal cavities, which lead to the pharynx (See Figure 12). Here, the glottis remains open and the air travels to the larynx (the voice box). From the larynx, the air travels to the trachea, or windpipe, which branches into two main bronchi, which lead to the lungs. Inside each lung, the branching continues, creating thinner and thinner tubes called bronchioles. Finally, at the end of each bronchiole is an air sac, called an alveolus (pl. alveoli). These thin and permeable air sacs are the functional units of the lung. The deoxygenated blood arrives at the lung via the pulmonary arteries from the right ventricle. The arteries branch into smaller and smaller vessels and finally become capillaries, which surround the alveoli. At the point where the capillaries and alveoli are in contact, a gas exchange occurs across the alveolar membrane via diffusion: blood picks up oxygen, which is carried back to the heart and releases carbon dioxide, which is exhaled. Figure 12: Respiratory System 31 Breathing is the process by which air is moved into and out of the lungs (See Figure 13). It involves the muscular movement of the diaphragm (a sheet of muscle lining the bottom of the thoracic cavity) and of the rib cage, which raises and lowers the pressure in the chest cavity. Lowering pressure in the chest forces outside air into the lungs, and increasing pressure forces exhaled air out of the lungs. Exhaled air has a higher concentration of carbon dioxide (CO2) and water than inhaled air. The rate of breathing is controlled by the nervous system, in response to CO2 levels in the blood. We can show the high CO2 concentration in exhaled air by blowing into an indicator such as lime water (which turns cloudy) or bromthymol blue (which turns yellow). Figure 13: Inhalation and Exhalation Cellular respiration is the process by which we get energy from the food that we eat. Cellular respiration can be anaerobic or aerobic. Aerobic respiration occurs when oxygen is present, and it is the opposite process to that of photosynthesis. During photosynthesis, a plant uses light energy to convert water and carbon dioxide to glucose. In aerobic respiration, we use glucose, at a cellular level, to obtain energy (i.e., ATP). Its formula is: 32 C6H12O6 + 6O2 --> 6CO2 + 6H2O + ATP or (glucose + oxygen -> carbon dioxide + water + ATP) Aerobic respiration, a very efficient process, begins in the cytoplasm of the cell and ends in the mitochondria, where the energy from glucose is stored in the form of ATP. If oxygen is not present, anaerobic respiration occurs, which is less efficient, producing a lower amount of ATP. Lactic acid, which is produced during anaerobic respiration, is a cause of sore muscles after strenuous exercise. Anaerobic respiration in yeast is called fermentation, producing ethanol rather than lactic acid. Nervous System Terms to Be Defined neuron dendrite neurotransmitter sodium cell body synapse potassium axon sensory neuron impulse axon terminal interneuron motor neuron brain nerve somatic cerebrum central nervous system (CNS) autonomic cerebellum reflex arc brain stem peripheral nervous system (PNS) spinal cord medulla The nervous system directly regulates body functions and responds to environmental stimuli. The functional unit of the nervous system is the neuron (See Figure 14). At rest, neurons have an electrical potential due to differences in sodium and potassium ion concentrations across the cell membrane. Generally, an impulse is generated when the dendrites of a neuron are stimulated by the environment or by another neuron. The stimulus results in a moving electrical charge. The impulse travels from the cell body along the axon until it reaches the ends (axon terminals). This triggers the release of neurotransmitters, which travel across synapses and may trigger other neurons or muscles. Axons may have myelin sheaths, which help transmit impulses faster. 33 There are three main types of neurons: 1. Sensory neurons transmit impulses from sense organs and receptors. 2. Interneurons make up the brain and spinal cord. 3. Motor neurons carry impulses from interneurons to skeletal and visceral muscles and glands. Figure 14: Neuron Nerves are groups, or bundles, of the axons of sensory and/or motor neurons. The nervous system includes other types of cells that nourish and support the neurons. The nervous system is usually divided into the two subsystems: 1. The central nervous system (CNS) includes the brain and spinal cord. 2. The peripheral nervous system (PNS) includes the nerves and sense receptors. The PNS is responsible for transmitting information to and from the CNS, which is responsible for processing information. The PNS is further divided into two branches: the somatic branch is concerned with the external environment and the autonomic branch is concerned with the internal environment, such as the digestive system. 34 A reflex arc carries out simple, quick, and automatic responses to certain stimuli. Reflex actions are commonly defensive and do not necessarily involve the brain. Examples of reflex actions include the reaction to stepping on a sharp object or touching a hot stove. The spinal cord extends from the brain downward and is enclosed by the bones of the vertebral column, or spine. Openings between the vertebrae allow peripheral nerves to join with the spinal cord. The spinal cord passes messages to and from the brain and acts as the center for reflex actions. Damage to the spinal cord may result in paralysis and may be permanent. The brain is protected and enclosed within the cranium and is divided into three areas: the cerebrum, cerebellum, and brain stem or medulla (See Figure 15). The cerebrum makes up the largest portion of the human brain and is the site of complex and high-level thinking. It is comprised of the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. Conscious and voluntary actions are controlled here, as are other functions such as speech, vision, hearing, and memory. The cerebellum is located below and behind the cerebrum. It is responsible for muscular coordination and balance. The brain stem, or medulla, controls basic homeostatic functions such as body temperature, blood pressure, and breathing. (Homeostasis is explained in the next section.) 35 Figure 15: The Brain Endocrine System Terms to Be Defined homeostasis hormone negative-feedback mechanism An important function of the endocrine system is to maintain homeostasis, which is the body’s way of keeping its internal environment stable by means of secretions from the endocrine glands (See Figure 16). These glands are also called ductless glands because they secrete hormones directly into the bloodstream. Hormones are chemicals that act as messengers and that help control the important processes of growth, metabolism, reproduction, osmotic balance, and development. Most hormones work by binding to their target cells by means of a receptor and influencing the activity of the cell. Hormones are usually activated by some type of stimulus. One example is the hormone insulin. When we ingest a meal, the food is broken down by our digestive system, and glucose is released from starches into our bloodstream. This increase in the concentration of glucose triggers the release of insulin from the pancreas, and insulin binds to cells in the body, causing them to uptake the glucose in the bloodstream. Thus, cells are able to use this glucose for energy. When the glucose levels in the bloodstream start to decline, the stimulus for the release of insulin also declines. This sort of hormone release is called a negative-feedback mechanism and prevents over-secretion of hormones. 36 Figure 16: Endocrine System Endocrine glands and their hormones are presented in Table 2. Table 2: Endocrine Glands and Their Hormones Gland Location Hormone(s) Function pituitary gland under the brain growth hormone, master gland, controls follicle-stimulating other endocrine hormone (FSH), glands thyroid-stimulating hormone (TSH) thyroid gland on the trachea, in the thyroxin (iodine- regulates metabolism neck region containing compound) parathyroid gland behind the thyroid parathormone regulates calcium gland metabolism thymus gland on chest thymosin supports immune system in young children adrenal gland on the kidneys adrenaline (i.e., so-called fight-or- (epinephrine) flight hormone regulates water balance blood pressure 37 Gland Location Hormone(s) Function Isles of Langerhans pancreas insulin, glucagon controls storage of sugar in liver and blood level of sugar testes (male gonad) in scrotum testosterone male secondary sex characteristics ovaries (female pelvic region estrogen female secondary sex gonad) progesterone characteristics Menstrual cycle Musculoskeletal System Terms to Be Defined red marrow ligament cardiac muscle osteocytes tendon smooth muscle skeleton cartilage skeletal (striated) muscle axial osteoarthritis flexor appendicular rheumatoid arthritis extensor joints osteoporosis bones The musculoskeletal system is composed of bones, connective tissue, and muscle. The system’s functions are the support and protection of the internal organs and movement. In addition, blood cells are made in the red marrow of the long bones (See Figure 17). 38 Figure 17: Bone Structure Bone contains osteocytes, which produce a hard, calcium-rich extracellular matrix. Blood vessels extend through bone, providing nutrients and oxygen and taking away waste. More than 200 bones make up the human skeleton (See Figure 18). The axial portion of the skeleton consists of the skull, vertebrae, ribs, and sternum. The appendicular skeleton is made up of the bones of the shoulders, arms, pelvis, and legs. Joints connect the bones of the skeleton. Sutures are immovable joints that join the bones of the skull, permitting growth but no movement. Other types of joints are movable, allowing muscles to move bones at a point of articulation (where the bones meet).The shoulders and hips have ball-and-socket joints, the elbows and knees have hinge joints, and sliding or gliding joints are found at the wrists. 39 Figure 18: Skelton Diseases affecting the skeletal system are: Osteoarthritis (a degenerative bone and joint disease) Rheumatoid arthritis (a degenerative joint disease caused by an autoimmune response) Osteoporosis (a disease caused by calcium loss; often found in older people, especially postmenopausal women Connective Tissue There are three types of connective tissue: ligaments, tendons, and cartilage. Ligaments connect bones to other bones. Tendons connect muscles to bones. Cartilage cushions bones at the joints. Muscles Muscle cells are among the most active in the body, using an enormous amount of energy in the form of ATP. The human body has three types of muscle: 1. Cardiac muscle is found only in the heart and is involuntary. 2. Smooth muscle, also involuntary, is found in the internal organs of the digestive tract and in blood vessels. 3. Skeletal muscle is also called striated muscle due to the microscopic appearance of the individual muscle cells or fibers. Skeletal muscles move bones and are responsible for voluntary movements. Skeletal muscles, attached to bones by tendons, move the bones when they contract and thereby shorten. 40 Many skeletal muscles are found in opposing pairs. In such a pair, one muscle, the flexor, bends or moves a limb away from anatomical position. The other muscle, the extensor, returns the limb to the anatomical position. The biceps muscle (a flexor) and the triceps muscle (an extensor) of the upper arm are good examples of this movement. Thus, the musculoskeletal system can be thought of as a system of levers (bones), moving around fulcrums (joints), with the forces provided by the muscles. Urinary System Terms to Be Defined kidney loop of Henle urethra nephron distal convoluted tubule sweat glands glomerulus ureter liver Bowman’s capsule urine proximal convoluted tubule urinary bladder The kidneys are the principal excretory organs of the body (See Figure 19). The outer portion of the kidneys is the renal cortex, and the inner portion is called the renal medulla. The functional unit of the kidney is the nephron, which consists of the glomerulus, Bowman’s capsule, the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule. Blood, under pressure, enters the capillaries of the glomerulus, which is located inside the cup-shaped Bowman’s capsule. Materials in the blood, such as water, soluble salts, urea, and soluble nutrients, are filtered out of blood into Bowman’s capsule. The kidneys also filter any small soluble particles that are in high concentration from the blood, thus helping to maintain homeostasis. As this filtrate passes through the tubules of the nephron, the water, nutrients, and ions are reabsorbed into the blood by diffusion, osmosis, or active transport into the capillaries surrounding the tubules. The concentrated mixture of wastes that is left in the tubules forms urine, which enters the collecting tubules to the ureters. The ureters transport urine to the urinary bladder for storage. Urine is excreted through the urethra, which is near the vagina in females and through the penis in males. In addition to the kidneys, the sweat glands, lungs, and liver function in excretion. 41 Figure 19: Urinary System 42 Reproductive System Terms to Be Defined gamete zygote penis sperm monoploid scrotum egg diploid testes testosterone ovulation placenta vas deferens fallopian tubes fetus ovaries uterus umbilical cord oocyte endometrium seminiferous tubules ovum menstruation interstitial cells epididymis ejaculatory duct progesterone estrogen Sexual reproduction starts with the fusion of two gametes (sperm and egg) to form a zygote (united sperm and egg). Each gamete is monoploid (or haploid), containing half of the normal complement of chromosomes. When the zygote is created from the union of a sperm and an egg, it contains the full complement of chromosomes and is diploid. In the male, the genitalia, or the external reproductive organs, are the penis and the scrotum (See Figure 20). The internal reproductive organs consist of the testes, the primary male reproductive organs. The testes contain seminiferous tubules, where sperm form, and interstitial cells, which produce male sex hormones such as testosterone. When sperm is produced in the seminiferous tubules, it then travels into the epididymis, which is made of coiled tubes that store sperm while they mature. The sperm are sent through the epididymis during ejaculation into the vas deferens to the ejaculatory duct to the urethra. The urethra, which runs the length of the penis and opens to the external environment, is common to both the reproductive and urinary systems. 43 Figure 20: Male Reproductive System In the female, the primary reproductive organs are the ovaries, which produce both eggs and the hormones progesterone and estrogen (See Figure 21). Inside the ovaries are ovarian follicles, each of which contains an immature egg called an oocyte. As the egg develops, the follicle also matures and enlarges. When fully mature, the follicle releases the egg in the stage called ovulation, which occurs approximately every 28 days. The egg then travels through the fallopian tubes, where it can be fertilized. If fertilized, the egg travels to the uterus, where it becomes implanted in the uterine lining, the endometrium, and remains there for the rest of its development. If the egg is not fertilized (i.e., the woman is not pregnant), the endometrial lining is shed, and it thickens again in preparation for the possibility of implantation in the next cycle. The shedding is a process known as menstruation. If fertilization occurs, the developing embryo implants itself in the uterus, where it develops during its gestation period of nine months. Tissues of the embryo and the mother grow together to form the placenta. The blood of the embryo and mother are never directly connected, but nutrients and oxygen from the mother and waste from the embryo are exchanged through the placenta. The fetus is connected to the placenta by the umbilical cord. 44 Figure 21: Female Reproductive System Integumentary System Terms to Be Defined skin epidermis dermis hypodermis The integumentary system consists of the skin, nails, hair, nerves, and glands. It serves as the body’s first line of defense, protecting against injury and infection. Additionally, it helps in the regulation of body temperature and eliminates waste. The skin is the largest organ and consists of three layers: epidermis, dermis, and hypodermis (see Figure 22). The epidermis is the outer layer that serves as a barrier and adds skin tone. The second layer of skin is the dermis. It consists of connective tissue, hair follicles, blood vessels, and sweat glands. Both oil and sweat glands are located in the dermis. The innermost layer is the subcutaneous layer, also called the hypodermis. It consists of connective tissue and fat. Nerve endings in the skin are responsible for the sense of touch and pain while fat functions not only in maintaining body temperature, but also in protecting bones and muscles. 45 Figure 22: Layers of the Skin Senses Terms to Be Defined cornea optic nerve stapes iris outer ear Eustachian tube pupil tympanic membrane inner ear retina middle ear cochlea rod cells malleus olfaction cone cells incus light pressure discriminative touch touch pressure lens 46 There are five commonly accepted senses: sight, hearing, touch, taste, and smell. Sight At the front of the eyeball, the transparent cornea allows light to enter the eye (See Figure 23). Behind the cornea is the iris, which not only gives our eyes color, but also changes in size, regulating how much light is allowed to enter the pupil, which is in the middle of the iris. The lens focuses light onto the retina; its shape is changed by attached muscles. The retina is the innermost layer of the eyeball and contains two types of photoreceptor cells: rod cells and cone cells. Rod cells are sensitive to light, distinguish between black and white, and allow us to see at night. Cone cells allow us to distinguish colors in the day. When they are stimulated by light, the photoreceptor cells transmit information along the optic nerve to the brain. Figure 23: Structure of the Eye Hearing The ear is responsible not only for hearing, but for balance as well (See Figure 24). Its anatomy can be divided into three regions: the outer ear, the middle ear, and the inner ear. 1. The outer ear collects sounds and transmits them to the tympanic membrane, which separates the outer ear from the middle ear. 2. In the middle ear, the vibrations produced by sound are transmitted through three small bones (ossicles): the malleus, incus, and stapes. As the vibrations pass through the oval window, they enter the inner ear. The middle ear is also connected to the Eustachian tube, which opens into the pharynx. This tube equalizes the pressure between the middle ear and the atmosphere, sometimes making your ears “pop.” 3. The inner ear has many channels containing fluid that moves in response to your movement or to sound. Sound coming into the inner ear moves the fluid, causing the cochlea, a part of the inner ear, to transduce (or convert) the movement into signals or action potentials. Movement of the small hair cells in a portion of the cochlea influences the signals sent from sensory neurons to the brain. The semi-circular canals are involved in balance. 47 Figure 24: Structure of the Ear Taste and Smell Chemical receptors in the tongue and nasal passage receive stimuli from the environment and are associated with your sense of taste and smell. Receptor cells for taste are located in the taste buds, found primarily on the tongue. The basic tastes include salty (presence or absence of salt), sweet (presence of carbohydrates or sugar), sour (presence of acid), bitter (bitter ingredients such as coffee, unsweet cocoa, or alcohol), and savory referring to a pleasant or delicious sense of taste (presence of protein). The sense of smell is called olfaction. Sensory cells for smell are located in the nasal passages. Smell is less developed in humans than in other animals. It may work alone or in combination with the sense of taste. Touch The sense of touch is detected when something comes into contact with the skin. It may be light, discriminative, or pressure. Light pressure is protective. It allows us to pull away from something that is dangerous, hot, or cold. An example of light touch is tickling. Discriminative touch allows us to differentiate among various touches. It is most important in the development of fine motor skills. Touch pressure provides information on how hard a squeeze is. 48 BASIC CHEMISTRY Chemistry is a scientific discipline that focuses on the study of matter and the interactions among the various forms of matter. It includes topics such as atomic structure, isotopes, ions, and the periodic table; bonding of matter; elements, compounds, and states of matter; the various forms of matter, including mixtures, solutions, tinctures, and emulsions; the physical and chemical changes that occur in matter. Atomic Structure, Isotopes, Ions, and the Periodic Table Terms to Be Defined matter atom neutron pure substance compound proton electron element cation metal atomic number anion mass number valence electron metalloid nonmetal isotope periodic table noble gas atomic mass period ion group nucleons mixture Chemistry is the study of the properties of matter. Matter is defined as anything that has mass and occupies space. Matter can be subdivided into two categories known as pure substances and mixtures. Pure substances are a form of matter with a fixed composition and characteristic chemical properties. There are two types of pure substances. The first type of pure substance is known as elements. Pure substances that are elements are pure substances composed of a single type of element as listed in the 118 chemical elements in the periodic table (Figure 25). The second type of pure substance is known as a compound. Pure substances known as compounds are made up of a fixed ratio of two or more elements taken from the 118 chemical elements in the periodic table (Figure 25). A mixture is a form of matter that is made up of two or more substances that are not chemically combined. An atom is the smallest unit of an element that still retains the properties of that element. Atoms contain three types of subatomic particles: 49 1. Protons carry a positive charge and are found in the nucleus of an atom. 2. Neutrons are neutral and are also found in the nucleus. 3. Electrons carry a negative charge and are found outside the nucleus and arranged according to their energy level. An atom of an element is identified by its symbol and its atomic number as shown in the periodic table (Figure 25). The atomic number for an element is the number in the upper left- hand corner for that element’s entry in the periodic table. For example, the element Lithium has an entry in the periodic table consisting of its symbol “Li” with the number 3 in the upper left- hand corner of its entry. This means that every atom of the element Lithium has 3 protons in its nucleus. The periodic table (Figure 25) contains all the known elements, arranged in horizontal rows called periods, in order of increasing atomic number. The columns, or groups, on the table contain elements with similar properties because of their similar electron configurations. From left to right across a period, the elements move from metals on the left-hand side of the chart to metalloids and finally to nonmetals on the right-hand side. The last group (18) on the right is the noble gases, which have full valence shells; some of them can form compounds with other elements. There are many more metals than nonmetals. 50 Figure 25: The Periodic Table Atoms of the same element that have the same number of protons but contain a different number of neutrons are called isotopes. Different isotopes that exist for atoms of the same element can be represented using isotopic notation as shown below for the carbon isotope known as Carbon-14 and the iodine isotope known as Iodine-127: 51 Figure 26: Locating an Atom's Mass Number and Atomic Number 𝟏𝟒 𝟏𝟐𝟕 𝟔𝑪 𝟓𝟑𝑰 Mass Number Mass Number The mass number of an atom, which is the number at the top left of the isotopic notation symbol (14C), is equal to the number of nucleons (protons + neutrons) in its nucleus. To find the number of protons in an atom, just look at its atomic number which is found in the lower left corner of the isotopic notation symbol or on the periodic table. All atoms of individual elements have a neutral charge when the number of electrons in an atom equals the number of protons in the atom. To find the number of neutrons in an atom, subtract the atomic number from the mass number of the element. For example, in Figure 26., the carbon-14 isotope (C) has an atomic number of 6, indicating 6 protons. We can infer that the number of electrons is also 6, and because carbon carries no charge, it is neutral. Therefore, the mass number of carbon, or the sum of the number of protons and neutrons, is 14, and the number of neutrons in carbon-14 is 8 (14-6 = 8). If we consider the element iodine (I), the atomic number is 53; the mass number is 127 for the isotope iodine-127; therefore, the number of neutrons is 74 in the iodine-127 isotope (127- 53). The number of electrons in an atom can change as well because an atom can gain or lose electrons. When the number of electrons does not equal the number of protons, the atom carries a charge. Charged atoms are called ions. For instance, a neutral sodium atom has 11 protons and 11 electrons. However, a sodium ion (Na+), which forms by losing an electron, has 11 (positively charged) protons and 10 (negatively charged) electrons. Losing an electron is the same as losing one unit of negative charge. The sodium ion, therefore, has a plus sign after it: Na+. An ion with a positive charge, like this one, is called a cation. An ion with a negative charge is called an anion; it has more electrons than protons. The net charge on an ion can be calculated by subtracting the number of electrons from the number of protons in the atom. Electrons are found at different energy levels of an atom. Electrons found in the outermost energy level are called valence electrons. Elements located in the first period (row 1) of the periodic table have atoms that can contain a maximum of two valence electrons; Elements that exist in the second period (row 2) of the periodic table have a maximum of eight valence electrons. Elements that exist in periods 3 (row 3) and above (rows 4, 5, etc.) are able to have more than eight valence electrons however, this is not the general rule in most cases. 52 Bonding Terms to Be Defined octet rule covalent bond dipole ionic bond nonpolar covalent bond Lewis electron dot diagram polar covalent bond An atom becomes more stable as its electron configuration becomes like that of a noble gas. This means 2 valence electrons for atoms located in period 1 of the periodic table and 8 valence electrons for most atoms in period 3 and higher of the periodic table. The octet rule states that atoms tend to combine in such a way that they each atom in a molecule will have 8 electrons in their valence shells (except for hydrogen which only needs two electrons in its valence shell), giving them the same electronic configuration as a noble gas. Atoms can achieve this stable configuration by gaining, losing, or sharing electrons. When an atom loses electrons, it becomes a positive ion. When an atom gains electrons, it becomes a negative ion. Positive and negative ions attract each other forming an ionic bond. We can represent the valence shell of atoms using Lewis electron dot diagrams (See Figure 27). In the figure, sodium (Na) loses an electron to form a sodium ion (Na+), and chlorine (Cl) gains an electron from sodium to form a chloride ion (Cl-). Figure 27: Lewis Electron Dot Diagram Sodium and chloride ions attract each other, forming a sodium chloride crystal. Ionic compounds have high melting and boiling points, but dissolve in polar solvents such as water. Some atoms form molecules by sharing pairs of electrons, forming what is known as a covalent bond. In Figure 28, two chlorine atoms share electrons. When two atoms share electrons equally, as in Cl2, we say the bond is a nonpolar covalent bond. 53 Figure 28: Covalent Bond: Cl2 If, however, two different atoms form a polar covalent bond (Figure 29), they share electrons unequally, the electrons being held closer to one atom than to the other. Figure 29: Polar Covalent Bond: HCl HCl is an example; the shared electrons are held closer to chlorine than to hydrogen. This makes the chlorine end of the molecule slightly negative and the hydrogen end of the molecule slightly positive, hence a dipole. Molecules can have single, double, or triple covalent bonds. If a molecule has polar covalent bonds and the distribution of charge in the molecule is unequal, so that the molecule has a positive and a negative end, the molecule is called a polar molecule because it has a molecular dipole (two poles). Molecules with molecular dipoles attract other molecules with molecular dipoles as well as molecules or atoms that have a non-zero net charge (ions), and polar molecules have higher melting and boiling points than nonpolar molecules. A special type of dipole attraction is the hydrogen bond. Polar solvents are solvents that are dipoles. For example, water is a polar molecule with a molecular dipole and because of this it has many special properties, such as surface tension and capillary action which are caused by the attractive forces that exist between polar molecules. States of Matter Terms to Be Defined gas evaporation sublimation liquid vapor pressure solid condensation melting freezing As presented above, an element is a simple substance, made up of one type of atom. A compound is a substance made up of two or more different atoms bonded together. An element cannot be broken down into anything simpler; a compound can be broken down into elements. Both forms of matter are pure substances because their composition and properties do not vary. Matter can be found in different phases:

NLN NEX Science Review Materials PDF

Document Details

Tags

Related

Summary

Full Transcript