Page 1 - Chemical and Physical Foundations of Biological Systems Study Guide for the MCAT
The principles of chemistry and physics apply also to the functions of living organisms and these are the concepts featured on this section of the MCAT. It contains questions that refer to given passages, as well as some stand-alone type of questions. There are 59 questions that you will have to complete in a total of 95 minutes.
Physics studies the motion of matter in space and time. In biological systems, the use of physics enhances our understanding of and our ability to describe important biological processes, including how blood is pumped through the body, how neurons transmit electrical signals, and how molecules move through the cytoplasm. The scope of your review should encompass concepts taught in two semesters of basic college physics.
Force and Related Laws
Force is any interaction that changes the motion of an object, if unopposed. Newton’s first law describes inertia. Newton’s second law states that force is equal to mass/acceleration. Newton’s third law states that for every action there is an equal and opposite reaction and is important for studying the interaction of two or more objects.
Translational motion is movement of an object relative to a fixed point. Examples of motion include velocity and speed, which both describe the distance an object travels over time. For velocity, the direction of the motion is indicated (vector); in contrast, speed does not describe the direction of the motion (scalar). The movement of an object can be determined by adding all of the vectors that describe an object’s motion together.
Rotational motion is movement of an object around an axis or fulcrum. Torque is defined as the rate of change in angular momentum of an object and is used to describe the force needed to rotate an object around the fulcrum. An object’s motion is normally a combination of translational and rotational motion.
The term equilibrium refers to a balanced, unchanging state. In physics terms, an object that is at rest or unaccelerated is at equilibrium.
Work is done when a force is applied to an object to displace the object. Work is equal to the force x displacement of the object x cos \(\theta\). The symbol \(\theta\) stands for the angle between the force and the displacement. A Joule (newton x meter) is the unit of work.
Point Object Systems and Their Energy
Kinetic energy is the energy possessed by an object due to movement. Kinetic energy is relative to another object and this energy can be transferred to another object (e.g. collision of two cars). In contrast, potential energy, the energy due to the position or state of an object, cannot be transferred and is not dependent on other objects. An example of potential energy is a cup sitting on a desk before it falls (gravitational potential energy). The conservation of energy law states that energy cannot be made or destroyed, but it can be converted. For example, a descending pendulum converts its potential energy (gravitational) into kinetic energy (movement) and an ascending pendulum converts the kinetic energy to potential energy.
Periodic Motion Concepts
Periodic motion is a motion that is repetitive and occurs regularly. Examples include vibrations, waves, swinging pendulums, and bouncing balls. The period is the time it takes the object to complete one full cycle. Frequency describes the number of cycles completed per unit of time. Period and frequency are inversely related. Amplitude is the maximum distance that an object travels from a resting position.
Behavior of Fluids
Fluids are substances that flow and deform. Liquids and gases are fluids, but liquids are more viscous than gases. Surface tension is the tendency for a liquid to stick together and take up the least surface area (of a surface); whereas gases will completely fill the container or area. One important term to understand is density (mass/volume). Less dense objects float in liquids (buoyancy) and denser objects sink.
Physics and the Circulatory System
The heart is a pump needed for the flow of blood throughout the body. Arteries and veins can be thought of as tubes or pipes that the fluid, blood, moves through. Flow and pressure contribute to blood circulation.
The Behavior of Gases
Gas is one of the four states of matter and the molecules in a gaseous state are separated by vast amounts of space. Because they are difficult to see, gases are described using four properties: temperature, volume, pressure, and the number of molecules present. Important equations that are used to describe the relationship of these four characteristics are the ideal gas law, Charles’s law, Boyle’s law, Dalton’s law, and Avogadro’s law. Real gases may act a bit differently than ideal gases.
Electrostatics is the study of the interactions that electrical charges exert on each other and these interactions are described using Coulomb’s law. Electrical field lines are depictions of the electrical field and can tell you the magnitude and the direction of the charge. Different materials convey electricity differently. Conductors and insulators are materials that do and do not conduct electrical charge, respectively.
A circuit is a closed loop through which a current, or an electrical charge, flows. Important terms used to characterize a circuit are voltage, resistance, capacitance, and conductivity. Resistors and capacitors can be in series or in parallel.
A magnetic field is the physical phenomena that results from electrical currents and magnetic materials. A magnetic field (B) is described commonly using Lorentz force. Lorentz force is the electrical and magnetic force of an electromagnetic field acting on a point charge.
Electrochemistry involves the study of the chemical reactions that occur between an electrode (either an anode or cathode) and an electrolyte. Electrolysis drives a nonspontaneous chemical reaction; in contrast, batteries are driven by spontaneous chemical reactions that generate current. Important concepts for this topic include oxidation, reduction, and flow of electrons.
Nerve Cells and Physics
Nerve cells use electrical signals to transmit information. The axon of a neuron is wrapped in Schwann cells and/or myelin that insulate the axon. Gaps in the myelin sheath are called Nodes of Ranvier. The ionic charge flows across the plasma membrane (action potential) at the Node of Ranvier, which is essential for transmitting the action potential signal.
Concepts Concerning Sound
Sound is oscillating pressure waves that travel through gases, liquids, or solids. Decibels are used to measure sound. Important uses of sound include the Doppler effect (weather), resonance (music), and ultrasound (imaging).
Light and Electromagnetic Radiation
Light is electromagnetic radiation and has the properties of both particles and waves. Properties of light include wavelength or frequency, intensity, polarization, and direction. Frequency and wavelength are inversely related. Light provides information to some organisms (vision) and can be used for diagnostic purposes (X-rays).
Molecular Structure and Absorption Spectra
Light can be subdivided based on wavelength or frequency. Visible light, which is necessary for vision, is from 400 nm to 700 nm. Infrared, or radiant energy, is from 700 nm to 1 mm. Thermal energy is an example of infrared. Ultraviolet is from 100 nm to 400 nm and an example would be sunlight. X-rays are from 0.1 nm to 10 nm.
Geometrical optics uses rays to describe light. Light can be reflected (e.g. mirror) or refracted. Refraction is a phenomena that occurs when light travels through a medium. Lens and mirrors (flat and curved) are important tools to study geometric optics.
Structure of an Atom
The atomic nucleus is positively charged and surrounded by a negatively charged electron shell or cloud. The atomic nucleus contains protons (positively charged) and neutrons (neutrally charged). The atomic number is equal to the number of protons. The atomic weight or mass is approximately equivalent to the number of protons and neutrons in an atom because electrons are so small and contribute very little mass. Isotypes have different atomic masses from elements listed on the periodic table because they contain a different number of neutrons. Unstable atoms emit alpha, beta, or gamma radiation.
Structure of Electronics
Atomic orbitals or electron clouds (s, p, d, and f) are used to predict the probability of finding an electron in a given area. Quantum numbers are used to describe the size, shape, and orientation of the orbitals. When an electron shifts from one orbital to another, energy is released (electron moves from an outer orbital to an inner orbital) or absorbed (electron moves from an inner orbital to an outer orbital).
The Periodic Table
The periodic table organizes all the elements by atomic number. Rows on the table are called periods and columns are called groups. Elements in the same period or column share characteristics. For example, group 18 contains all the noble gases. Further, metals are generally on the left and nonmetals are on the right. An element’s electron configuration can be determined based on its placement in the table.
Note: A copy of the periodic table will be available to test-takers during the testing session.
Stoichiometry is determining the relative amounts of reactants and products in a chemical reaction. Mass and charge are conserved during chemical reactions; thus, the amount of reactants converted and the quantity of the resulting products for chemical reactions can be determined by balancing the equation. This is an important concept for understanding oxidation and reduction reactions.
Important Terms for this Section
static friction, kinetic friction, instantaneous speed, average speed, instantaneous velocity, average velocity, conservative force, mechanical advantage, lever, specific gravity, hydrostatic pressure, turbulence, absolute temperature, ground state, excited state, paramagnetism, diamagnetism, halogens, alkali metals, alkaline metals, transition metals, molecular formula, mole, Avogadro’s number, limiting reactants, attenuation or dampening of sound, pitch, diffraction, color, NMR spectroscopy