Biology Midterm Study Guide Essay Sample

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•The goal of science is to investigate and understand the natural world, to explain events in the natural world, and to use those explanations to make useful prediction •Scientific thinking usually begins with observation, the process of gathering information about events or processes in a careful -observation generally involves using the senses esp. hearing & sight -the information gathered from observations is called data.

•Quantitative date expressed as number
-Qualitative data are descriptive and involve characteristics •After observations, the researchers will propose one or more hypotheses. •A hypothesis- is a proposed scientific explanation for a set of observation -some hypotheses are tested by gathering more data

•Spontaneous generation- hypothesis stating that life could arise from nonliving matter •Whenever possible, a hypothesis should be tested by an experiment in which only one variable is changed at a time. All other variables should be kept unchanged, or controlled. •Controlled experiment-a test of the effect of a single variable by changing it while keeping all other variables the same. •Manipulated variable- factor in an experiment that a scientist purposely changes (INDEPENDENT VARIABLE) •Responding variable- factor in an experiment that a scientist wants to observe, which may change in response to the manipulated variable (DEPENDENT VARIABLE) •Theory- well-tested explanation that unifies a broad range of observation 1.3

•Living things share some characteristic
-living things are made up of units called cells
-living things reproduce
-living things are based on a universal genetic code
-living things grow and develop
-living things obtain and use materials and energy
-living things respond to their environment
-living things maintain a stable internal environment
-taken as a group, living things change over time
•Some of the levels at which life can be studied include molecules, cells, organisms, populations of a single kind of organism, communities of different organisms in an area, and the biosphere. At all these levels, smaller living systems are found within larger system •Levels of Organization

-Biosphere (largest & most complex)
-Groups of Cells
-Molecules (smallest, that make up living things)

•Most scientists use the metric system when collecting data and performing experiments •Metric system- a decimal system of measurement whose units are based on certain physical standards & are scaled on multiples of 10 •Microscopes are devices that produce magnified images of structures that are too small to see with the unaided eyes •Light microscopes produce magnified images by focusing visible light rays. Electron microscopes produce magnified images by focusing beams of electrons. -most commonly used microscope

•Compound light microscopes – allow light to pass through the specimen and use two lenses to form an image. •Electron microscope- use beams of electrons, rather than light, to produce images. •Transmission electron microscope (TEMs) shine a beam of electrons through a thin specimen. •Scanning electron microscopes (SEMs) scan a narrow beam of electrons back and forth across the surface of a specimen.

•Most elements are found combined with other elements in compound. •A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. •The main types of chemical bonds are ionic bonds and covalent bonds •An ionic is formed when one or more electrons are transferred from one atom to another -an atom that loses electrons has a positive charge.

-an atom that gains electrons has a negative charge
•These positively and negatively charged atoms are known as ions •A covalent bond- forms when electrons are shared between atoms. -when the atoms share two electrons, the bond is called a single covalent bond •When atoms are joined together by covalent bonds is called molecule •The molecule is the smallest unit of most compounds

•Water is neutral. It is polar. Water is not always pure it is often found as part of a mixture. •A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms •The attraction between the hydrogen atom on one water molecule & the oxygen atom on another water molecule is an ex: of a hydrogen bond •Cohesion- is an attraction between molecules of the same substance -water is extremely cohesive

•Adhesion- is an attraction between molecule of different substances •Mixture- is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined •All of the components of a solution are evenly distributed throughout the solution •Solute the substance that is dissolved ex: Table salt

•Solvent- the substance in which the solute dissolve. Ex: Water •Suspension- mixture of water and nondissolved material
•Chemists devised a measurement system called pH scale to indicate the concentration of H+ ions in solution
-0 to 6/6.5 is acidic
-7 is neutral
-7.5/8 to 14 is basic

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