Introduction to Biology

Levels of Biological Organization

Biology studies life at multiple levels, from atoms and molecules to organelles, cells, tissues, and organisms. Understanding these levels is essential for grasping how life functions.

• Atoms: Basic units of matter, composed of protons, neutrons, and electrons.

• Molecules: Groups of atoms bonded together, forming chemical compounds.

• Organelles: Specialized structures within cells, each with distinct functions.

• Cells: Fundamental units of life, capable of independent existence.

Chemistry

Atoms and Elements

Atoms are the smallest units of elements, which are pure substances consisting of only one type of atom. Elements are defined by their atomic number (number of protons).

• Subatomic Particles: Protons (+1 charge), neutrons (0 charge), electrons (-1 charge).

• Atomic Number: Number of protons in the nucleus; defines the element.

• Mass Number: Sum of protons and neutrons.

Elements Essential for Life

Living organisms are primarily composed of a few key elements.

• Major Elements: Oxygen, carbon, hydrogen, nitrogen.

• Minor Elements: Calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium.

Electron Shells and Stability

Electrons occupy energy levels called shells. The chemical reactivity of an atom is determined by the electrons in its outermost (valence) shell.

• Inner shell holds up to 2 electrons; second shell holds up to 8 electrons.

• Atoms are most stable when their valence shell is full (octet rule).

Biomolecules

Composition of Biomolecules

Biomolecules are organic compounds essential for life, including proteins, lipids, carbohydrates, and nucleic acids.

• Proteins: Made of amino acids; perform structural, enzymatic, and regulatory functions.

• Lipids: Composed of fatty acids; important for energy storage and membrane structure.

• Carbohydrates: Made of sugars; provide energy and structural support.

• Nucleic Acids: DNA and RNA; store and transmit genetic information.

Cell Components

Cellular Organelles and Their Functions

Cells contain various organelles, each with specialized roles.

• Nucleus: Contains DNA; controls cellular activities.

• Mitochondria: Site of cellular respiration; produces ATP.

• Endoplasmic Reticulum (ER): Synthesizes proteins and lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digest cellular waste.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

Chemical Bonds

Types of Chemical Bonds

Atoms interact to achieve stability by forming chemical bonds.

• Ionic Bonds: Formed by transfer of electrons between atoms, resulting in charged ions.

• Covalent Bonds: Formed by sharing electrons between atoms; can be polar or nonpolar.

Bond Polarity and Electronegativity

Bond polarity depends on the difference in electronegativity between atoms.

• Nonpolar Covalent Bonds: Electrons are shared equally; no charge difference.

• Polar Covalent Bonds: Electrons are shared unequally; partial charges develop.

• Ionic Bonds: Large difference in electronegativity; electrons are transferred.

Formulas and Molecules

Chemical Formulas

Chemical formulas represent the composition of molecules.

• Example: Glucose formula indicates 6 carbon, 12 hydrogen, and 6 oxygen atoms.

Bonding Patterns of Key Elements

Elements like hydrogen, oxygen, nitrogen, carbon, and phosphorus have characteristic bonding patterns based on their valence electrons.

• Hydrogen: 1 bond

• Oxygen: 2 bonds

• Nitrogen: 3 bonds

• Carbon: 4 bonds

• Phosphorus: 3 or 5 bonds (biologically relevant forms make 5 bonds)

Summary Table: Elements in the Human Body

Major and Trace Elements

Additional info:

• Biomolecules' polarity and chemical properties are crucial for their biological functions.

• Redox reactions involve electron transfer: oxidation (loss of electrons) and reduction (gain of electrons).