Study Guide for Lab Exam (General Biology) PDF

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General Biology 101. Study guide for Lab Exam. Professor Pathapadu of Northern Virginia Community College....

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Study Guide for Lab Exam 1. Science comes from the Latin word, Scientia, which means knowledge. o The scientific method is a process for developing and testing predictions based on observed phenomena. It includes an observation, a question, a hypothesis, a prediction, and the experiment o A hypothesis must be a stated answer that is both testable and falsifiable o A prediction is a more detailed hypothesis. Specifically, a prediction includes not only the hypothesis, but also the game plan and predicted result o A variable is any factor or condition that can vary, in a controlled experiment the it varies between two groups. The independent variable is the one scientist changes between the groups and is being tested. The dependent variable changes in response to the independent variable. Controlled variables must be maintained to conduct an experiment. o Data generated can be quantitative such as temperature or qualitative such as color. o Data are typically placed into an easy to interpret visual form called a graph. o The pH scale has a range of values between 0 and 14, where 0 is more acidic, 14 is the most basic and 7 is neutral. 2. The microscope we use in the lab is a compound, brightfield light microscope. Objectives form a magnified image. Oculars are used to view the image of the specimen and to magnify the image. o Critical aspects of structure under microscope to analyze scientific data: Shape and form are the most critical elements of an image. Scale and relative proportions are indicated by a difference in relative sizes of the object and its parts. Completeness and roughness/smoothness of outlines are the finer features of form. o Low power objective is 10X, high power objective is 40X (working distance or the distance between slide and objective is very small) and scanning objective is 4X (shows most part of the slide) 3. Macromolecules are proteins, lipids and nucleic acids which contain the elements carbon, hydrogen and oxygen. They are tested by using a variety of chemicals and color change indicates the test as positive (presence) or negative (absence) o Benedicts reagent is used to test for the presence of small carbohydrates like glucose or sucrose and the color (blue) changes to a range of colors (Blue,green, yellow, orange or red) to indicate positive o Iodine is indicator of starch and it changes from pale yellow to blue black o Lipids are hydrophobic. Fats and oils are referred to as triglycerides. An emulsifying agent is required to help fats and oils disperse in water. Lipids can be detected by Sudan Black which causes them to appear red

o Proteins are polypeptides and become protein after assuming 3D shape. Biuret test is used to test their presence which changes from blue to violet 4. Chemical reactions occur when bonds are broken and bonds are formed with or without enzymes present. Enzymes act as catalysts and increase the rate of reaction. Reactants fit in the active site of enzyme precisely. Activation energy is needed to initially break bonds and enzymes lower the energy needed to begin a chemical reaction and favor breaking bonds. o Inhibitors block the active site and stop the enzyme activity. o A small increase in temperature can increase the speed of a reaction but too much increase in temperature denature the protein permanently. Adding too much acid or base can change the pH and affect reaction. Cofactors (elements from periodic tables) or coenzymes (from vitamins) can assist enzymes in doing their work. o Reduction reaction occurs when an electron (or H atom) is gained. Oxidation reaction occurs when an electron (or a H atom) is lost. Redox reaction involves both. o We used Catechol (reactant) which forms brown molecule benzoquinone in the presence of oxygen. The enzyme catecholase speeds up the reaction (catechol and catecholase are present in different pockets in the potato and other fruits which turn brown upon cutting and exposing to air) o In the above reaction, catechol is oxidized by the enzyme to form quinone which is converted to a group of polymers called melanins which give darker colors to the potato. o Serial dilution is a stepwise dilution of a substance, usually using the same dilution factor at each step. 5. Cell membranes are composed of a lipid bilayer, the interior is hydrophobic (nonpolar) because of which hydrophilic substances are limited in movement. The inner aqueous and outer aqueous environments are separated by cell membrane which acts as a barrier to the free movement of most polar solutes o Solutes tend to move by diffusion down their concentration gradient towards equilibrium o Water also moves down the concentration gradient by osmosis from regions of more water (less solutes) to less water (more solutes) o Hypotonic solution or low concentration solutes will tend to move into the cell whereas hypertonic solutions cause water to move out of the cell o Osmolarity is used to express a solution’s total concentration of osmotically active solute particles o Elodea plant cells appear plump or turgid in hypotonic solutions. Mostly the central vacuole is filled with fluid and confined by the tonoplast (vacuolar

membrane), in hypertonic solution the cell will shrink and the process is plasmolysis o Blood cells hemolyze or break under hypotonic condition when water enters the cell. In hypertonic solution the blood cells undergo crenation. 6. Many metabolic reactions require ATP (adenosine triphosphate) a source of energy. The major source of ATP is oxidation of glucose by a series of enzymatic reactions which include glycolysis and anaerobic process (absence of oxygen) or aerobic process (presence of oxygen). The end product of glycolysis is pyruvic acid. o In organisms such as yeasts, it is metabolized by fermentation which results in the production of alcohol and carbon dioxide. o Lactic acid can also be formed by anaerobic fermentation for example in muscle cells which are oxygen depleted during strenuous exercise. o When oxygen is available, Krebs cycle or citric acid cycle and electron transport occurs in the mitochondria and increase the energy harvest from the oxidation of glucose. o Yeasts are heterotrophs (cannot carryout photosynthesis) and facultative anaerobes (can live in aerobic or anaerobic environments). Under anaerobic condition they undergo fermentation, and grow on grapes and grains such as barley and produce alcohol in wine, beer and other beverages  Only 2 ATP is produced from every glucose molecule metabolized but this is sufficient to sustain yeast cells o Live yeast and food source (glucose or sucrose) is required for fermentation. But all the sugars are not used at same rate. Monosaccharides maximize the rate of fermentation o One of the tests used to check viability of seeds before planting is use of the dye tetrazolium which is colorless when oxidized but becomes reddish when reduced. If the seeds ETP is working it interacts with tetrazolium and turns reddish, if the seed is dead it remains colorless 7. Just like manmade solar cells, chlorophyll collects solar energy and releases a controlled energy for the plants to use. o Chloroplasts are green because of thylakoids which house chlorophyll molecules that absorb sunlight and form oxygen, ATP within chloroplasts (light reactions). ATP is used to build sugar out of carbon dioxide molecules in Calvin cycle which occurs in the stroma of chloroplast (dark reaction) o Chlorophyll cannot collect all wavelengths (colors) of sunlight, accessory pigments absorb light colors that chlorophyll cannot collect. Mostly all these accessory pigments together add up only to a fraction amount of chlorophyll and remain hidden under the bright green color. During fall when chlorophyll levels are reduced these other pigments become visible. o Chromatography solvent is used to separate the pigments from spinach leaf

o Spectrophotometer is used to read the absorption spectrum of chlorophyll and we observe that the least absorbed color by chlorophyll is green, which is reflected 8. Gregor Mendel proposed laws of inheritance. Selective breeding was in use for crops long before his observations. We used corn cobs to study genetics in lab o Each gene has two copies or alleles (PP,Pp,pp). A diploid has two copies or alleles where as a haploid has only one copy of every gene. In corn purple is dominant and is expressed under homozygous dominant (PP) or heterozygous (Pp) condition where as white is recessive (pp) trait for the character color of the corn o Phenotype is physical appearance and genotype (pair of alleles) is responsible for it. Monohybrid cross is following only one character and one gene Ex. seed color. It illustrates Mendel’s law of segregation o Parental generation is P generation, F1 generation is first filial generation is produced from the parental cross. A Punnett square predicts the possible genotypes and phenotypes expected in the offspring from this cross (PPXpp). F2 generation is crossing F1 XF1 o Test cross is used to determine unknown genotype (PPXPp) of a dominant phenotype, ex. purple. It is crossed by homozygous recessive pp o Dihybrid cross examines two genes at a time like seed color and seed texture in corn. Phenotype ratio of F2 is 9:3:3:1 9. Natural selection is differential survival and reproductive success based on favorable traits o Over the generations, individuals with unfavorable traits will be weeded out and decrease in proportion. The change in allele frequency over the generation is evolution by natural selection. Adaptation is specific heritable trait that increased the survival and reproduction of an individual o Predator success is the percentage of all the prey caught. Prey success is percentage of prey that survive/avoid capture and survives to reproduce 10. Historical footprint of evolution can be depicted by evolutionary tree or phylogeny o Phylogenetics reconstructs evolutionary trees by evaluating alternative hypotheses of evolutionary relationships of organisms. These hypotheses are summarized in the form of cladograms (branching diagrams inferred from a comparative analysis of character data o Homology is a historical identity of parts related through descent. Homoplasy is similarity in character states between taxa that do not share common ancestry. It results from convergent evolution o A plesiomorphy is a character observed in the outgroup, group of taxa related to remaining taxa is called ingroup.

o An apomorphy is character derived from plesiomorphy, representing modification of ancestral condition. Derived character may be autapomorphic (unique), synapomorphic (shared) or homoplastic (derived independently)...