뒤로Essential Chemistry for Biology: Chapter 2 Study Notes
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Essential Chemistry for Biology
Introduction to Chemistry in Biology
Chemistry is fundamental to understanding biological processes, as all living organisms are composed of chemical elements and compounds. The study of chemistry in biology helps explain how life functions at the molecular level.
Matter is anything that occupies space and has mass.
Mass is a measure of the amount of material in an object.
Element: A substance that cannot be broken down into other substances by chemical reactions.
All matter is composed of chemical elements.
Elements and Compounds
Elements are the building blocks of matter, and compounds are substances formed from two or more elements in a fixed ratio.
There are 92 naturally occurring elements; 25 are essential for humans.
Four elements—oxygen, carbon, hydrogen, and nitrogen—make up about 96% of the human body’s weight.
Trace elements are required in very small amounts but are essential for life (e.g., iron, iodine).
Compound: A substance containing two or more elements in a fixed ratio (e.g., water, H2O).
Chemical Composition of the Human Body
Element | Approximate % of Body Weight |
|---|---|
Oxygen (O) | 65% |
Carbon (C) | 18.5% |
Hydrogen (H) | 9.5% |
Nitrogen (N) | 3.3% |
Trace Elements | <0.01% |
Additional info: Other elements include calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium. |
Atoms and Subatomic Particles
An atom is the smallest unit of matter that retains the properties of an element. Atoms are composed of subatomic particles:
Proton: Positively charged
Neutron: Electrically neutral
Electron: Negatively charged
The atomic number is the number of protons in an atom. The mass number is the sum of protons and neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons.
Radioactive isotope: An isotope whose nucleus decays spontaneously, emitting radiation.
Radioactivity and Its Biological Significance
Radioactivity can damage cells by affecting DNA, but it also has medical uses, such as treating cancer through radiation therapy. Radioactive isotopes are used in radiometric dating to estimate the age of fossils.
Radiation therapy: Targets cancer cells with precise doses of radiation.
Radiometric dating: Uses the decay of radioactive isotopes to date fossils.
Chemical Bonding and Molecules
Chemical bonds form when atoms interact by transferring or sharing electrons. These bonds hold atoms together in molecules.
Ionic bonds: Formed when atoms transfer electrons, resulting in charged ions that attract each other.
Covalent bonds: Formed when atoms share pairs of electrons; these are the strongest bonds in molecules.
Hydrogen bonds: Weak attractions between polar molecules, such as water.
Types of Chemical Bonds
Bond Type | Description | Example |
|---|---|---|
Ionic | Transfer of electrons between atoms | NaCl (table salt) |
Covalent | Sharing of electron pairs between atoms | H2O (water) |
Hydrogen | Weak attraction between polar molecules | Between water molecules |
Water and Life
Water is essential for life due to its unique chemical properties, which arise from its polarity and hydrogen bonding.
Water molecules are polar, with an uneven distribution of charge.
Hydrogen bonds form between water molecules, leading to cohesion and high surface tension.
Water moderates temperature due to its high specific heat capacity.
Ice floats because it is less dense than liquid water, allowing aquatic life to survive beneath frozen surfaces.
Properties of Water
Property | Biological Significance |
|---|---|
Cohesion | Helps transport water in plants |
Surface tension | Allows small organisms to walk on water |
Temperature moderation | Stabilizes climate and body temperature |
Ice floating | Insulates aquatic environments |
Solutions, Acids, Bases, and pH
Water is known as the "solvent of life" because it dissolves many substances, forming solutions. The pH scale measures the concentration of hydrogen ions (H+) in a solution.
Acid: Releases H+ ions into a solution.
Base: Accepts H+ ions and removes them from a solution.
pH scale: Ranges from 0 (most acidic) to 14 (most basic); 7 is neutral.
Buffer: Minimizes changes in pH.
Each pH unit represents a tenfold difference in H+ concentration.
Example: A solution at pH 5 has 1,000 times more H+ ions than a solution at pH 8.
Major Biological Themes Illustrated
Pathways that transform energy and matter: Chemical reactions rearrange molecules, breaking and forming bonds.
Interactions within biological systems: Release of CO2 in one region can affect ecosystems elsewhere (e.g., coral reef acidification).
Relationship of structure to function: The structure of water molecules explains their life-supporting properties.
Evolution: Radioactive decay helps date fossils and understand evolutionary history.
Examples and Applications
Nuclear medicine: Uses radioactivity to treat cancer.
Coral reef death: Linked to acidification from atmospheric CO2.
Water transport in plants: Relies on cohesion and adhesion.
Evaporative cooling: Helps regulate body temperature.
Additional info: These notes expand on brief textbook points to provide a self-contained study guide for General Biology students.
