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Biology is the scientific study of living things (organisms).
Characteristics of organisms:
-Made of a common set of chemical components: carbohydrates, fatty acids, nucleic acids, amino acids
-Most are made of cells enclosed by plasma membranes
-Convert molecules from their environment into new biological molecules
-Extract energy from the environment and use it to do biological work
-Contain genetic information that uses a universal code to specify proteins
-Share similarities among a fundamental set of genes, and replicate this genetic information when reproducing
-Self-regulate their internal environment, maintaining conditions that allow them to survive
-Exist in populations that evolve through changes in frequencies of genetic variants over time
Biology Is Studied at Many Levels of Organization (1)
Eventually, some cells did not separate after division and started living as colonies. This allowed some cells to specialize for
certain functions, which led to multicellular organisms (plants, animals, and fungi).
Cells became specialized, and a hierarchy emerged: differentiated cells are organized into tissues (e.g., muscle). Different tissue
types form organs (e.g., a heart); organs are grouped into organ systems (e.g., the circulatory system).
A group of individuals of the same species is a population.
Populations of all the species that live and interact in a defined area are called a community.
Communities together with their abiotic (nonliving) environment constitute an ecosystem.
The Fundamental Properties of Matter
All matter is composed of atoms.
Atoms are composed of a dense positively charged nucleus, and one or more
negatively charged electrons.
Electrons move around the nucleus.
The nucleus always contains a positively charged proton and, sometimes,
neutral neutrons.
The number of protons determines the identity of an atom.
Variations in the number of neutrons give rise to isotopes.
Unstable isotopes are radioisotopes
Electrons and the Properties of Elements
Electrons orbit around the nucleus in defined shells.
The 1st shell has the capacity to accommodate 2 electrons.
The 2nd and 3rd shell can accommodate 8 electrons each.
The number of electrons in the outermost shell determines the reactivity of an atom.
Atoms with unfilled orbitals are unstable and will undergo reactions to fill the orbitals.
Elements with the same number of electrons in the outermost shell (the valence shell) share similar reactive properties.
Chemical Bonds and Interactions
Atoms react with each other (via electrons) to form chemical bonds.
Energy is stored in chemical bonds.
Energy is liberated in the breaking of chemical bonds.
Covalent Bonds are Formed by Sharing
Each hydrogen atom lacks one electron in its outer shell. It can
participate in the formation of one covalent bond.
In sharing the 2 electrons, the 2 nuclei in the hydrogen molecule —
H2 — both have 2 electrons in their outer (“valence”) shells.
The 2 electrons orbit both nuclei, holding them together by a
covalent bond.
Each carbon atom lacks 4 electrons in its outer shell. It can
participate in the formation of 4 covalent bonds.
In the formation of the 4 covalent bonds, the carbon atom forms
the center of a tetrahedron
Outer Shell Electrons and Valency
In general, the electron deficit in the outer shell of an atom is
correlated with the valency — the number of covalent bonds that
can be formed
Hydrogen Bonds
Sharing of electrons may be unequal among atoms within a
molecule.
Since electrons are charged, distribution of charges becomes polarized within the molecule.
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