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General Biology I: Unit 1 Study Guide – Foundations of Life, Chemistry, and Cell Structure

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Chapter 1: Biology – The Study of Life

Characteristics of Living Things

Biology is the scientific study of life and living organisms. All living things share certain fundamental characteristics that distinguish them from non-living matter.

  • Composed of Cells: All living organisms are made up of one or more cells, which are the basic units of life. Each cell contains a plasma membrane, cytoplasm, DNA, and ribosomes.

  • Replication: Living things reproduce to pass on their genetic information. Single-celled organisms divide by cell division, while multicellular organisms may reproduce sexually or asexually.

  • Information: Organisms inherit hereditary information in the form of DNA. Homeostasis is the maintenance of a stable internal environment.

  • Energy: Living things acquire and use energy. Autotrophs produce their own food, while heterotrophs consume other organisms.

  • Evolution: Populations of organisms change over time through mutations, genetic variation, and natural selection.

Example: Humans are multicellular, reproduce sexually, maintain homeostasis, and evolve over generations.

Major Themes in Biology

  • Evolution: The process by which populations change over time through natural selection and genetic drift.

  • Natural Selection: The mechanism by which advantageous traits become more common in a population.

  • Fitness: The ability of an organism to survive and reproduce in its environment.

  • Speciation: The formation of new and distinct species in the course of evolution.

Domains of Life

The tree of life classifies all living organisms into three domains based on evolutionary history:

  • Bacteria: Prokaryotic, unicellular organisms without a nucleus.

  • Archaea: Prokaryotic, unicellular organisms with unique membrane lipids and genetic features.

  • Eukarya: Eukaryotic organisms with cells containing a nucleus and organelles; includes plants, animals, fungi, and protists.

The Scientific Method and Hypothesis Testing

Scientific research follows a systematic approach to answer questions about the natural world.

  • Observation: Gathering information based on what is seen or measured.

  • Question: Formulating a question based on the observation.

  • Hypothesis: A testable statement that predicts an outcome.

  • Experimental Variable: The factor that is changed or tested in an experiment.

  • Results: The data collected from the experiment.

  • Conclusion: Interpretation of the results to support or refute the hypothesis.

Example: Testing whether plants grow faster with more sunlight by comparing growth rates under different light conditions.

Chapter 2: Water and Carbon – The Chemical Basis of Life

Atoms and Elements

All matter is composed of atoms, which are the smallest units of elements. Understanding atomic structure is fundamental to biology.

  • Subatomic Particles: Atoms consist of protons (positive charge), neutrons (neutral), and electrons (negative charge).

  • Atomic Number: The number of protons in an atom, which determines the element.

  • Mass Number: The sum of protons and neutrons in the nucleus.

Chemical Bonds and Molecules

  • Covalent Bonds: Atoms share electrons to form molecules. Can be polar (unequal sharing) or nonpolar (equal sharing).

  • Ionic Bonds: Atoms transfer electrons, resulting in charged ions that attract each other.

  • Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Properties of Water

Water is essential for life due to its unique chemical and physical properties.

  • Polarity: Water molecules are polar, allowing them to form hydrogen bonds.

  • Cohesion and Adhesion: Cohesion is the attraction between water molecules; adhesion is the attraction between water and other substances.

  • Surface Tension: The result of cohesive forces at the surface of water.

  • High Specific Heat and Heat of Vaporization: Water can absorb or release large amounts of heat with little temperature change.

  • Hydrophilic vs. Hydrophobic: Hydrophilic substances interact with water; hydrophobic substances do not.

Acids, Bases, and pH

  • Acid: A substance that increases the hydrogen ion (H+) concentration in a solution.

  • Base: A substance that decreases the H+ concentration.

  • pH Scale: Measures the acidity or basicity of a solution. Lower pH = more acidic; higher pH = more basic.

Chemical Reactions

  • Condensation (Dehydration) Reaction: Two molecules combine, releasing water.

  • Hydrolysis Reaction: A molecule is split into two by the addition of water.

Example: Formation of a peptide bond between amino acids (condensation); breakdown of starch into glucose (hydrolysis).

Chapter 3: Protein Structure and Function

Amino Acids and Protein Structure

Proteins are polymers made of amino acid monomers. Their structure determines their function.

  • Amino Acid Structure: Each amino acid has a central carbon, an amino group, a carboxyl group, a hydrogen atom, and an R group (side chain).

  • Peptide Bonds: Amino acids are linked by peptide bonds formed through condensation reactions.

  • Levels of Protein Structure:

    • Primary: Sequence of amino acids.

    • Secondary: Local folding (α-helix, β-sheet) due to hydrogen bonding.

    • Tertiary: 3D shape formed by interactions among R groups.

    • Quaternary: Association of multiple polypeptide chains.

  • Denaturation: Loss of protein structure (and function) due to heat, pH, or chemicals.

Protein Function

  • Enzymes: Proteins that catalyze biochemical reactions.

  • Other Functions: Structural support, transport, defense (antibodies), signaling, and movement.

  • Active Site: The region of an enzyme where substrate binds and reaction occurs.

Chapter 4: Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) store and transmit genetic information.

  • Nucleotides: Monomers consisting of a phosphate group, a five-carbon sugar (deoxyribose or ribose), and a nitrogenous base.

  • DNA vs. RNA: DNA contains deoxyribose and is double-stranded; RNA contains ribose and is usually single-stranded.

  • Bases: DNA: Adenine (A), Thymine (T), Cytosine (C), Guanine (G); RNA: A, Uracil (U), C, G.

  • Base Pairing: A pairs with T (or U in RNA), C pairs with G.

  • Directionality: Nucleic acids have a 5' to 3' direction.

  • ATP (Adenosine Triphosphate): The primary energy carrier in cells.

Base Composition Table

The following table shows the percentage of each base in nucleic acids from different sources. Use the ratios to determine if the sample is DNA or RNA, and if it is double- or single-stranded.

A

C

T

G

U

1

43

26

0

20

11

2

30

14

0

46

10

3

28

22

20

30

0

4

25

25

25

25

0

5

20

25

30

25

0

Additional info: In double-stranded DNA, %A ≈ %T and %C ≈ %G. In RNA, T is replaced by U.

Chapter 5: Carbohydrates

Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They serve as energy sources and structural components.

  • Monosaccharides: Simple sugars (e.g., glucose, fructose).

  • Disaccharides: Two monosaccharides joined (e.g., sucrose).

  • Polysaccharides: Large carbohydrates made of many monosaccharides (e.g., starch, glycogen, cellulose).

  • Glycosidic Linkage: The covalent bond joining monosaccharides in a carbohydrate polymer (e.g., 1-4 glycosidic linkage).

Functions of Carbohydrates

  • Energy Storage: Starch (plants), glycogen (animals).

  • Structural Support: Cellulose (plants), chitin (fungi, arthropods).

  • Cell Recognition and Signaling: Glycoproteins and glycolipids on cell surfaces.

Chapter 6: Lipids and Membranes (Movement Across the Lipid Membrane)

Lipid Structure and Types

Lipids are hydrophobic molecules that include fats, phospholipids, and steroids. They are not polymers.

  • Fats (Triglycerides): Composed of glycerol and three fatty acids. Used for energy storage.

  • Phospholipids: Contain a hydrophilic head and two hydrophobic tails. Form the bilayer of cell membranes.

  • Steroids: Lipids with a four-ring structure (e.g., cholesterol).

  • Saturated vs. Unsaturated Fats: Saturated fats have no double bonds (solid at room temp); unsaturated fats have one or more double bonds (liquid at room temp).

Cell Membranes and Transport

  • Phospholipid Bilayer: Phospholipids arrange themselves with hydrophilic heads facing outward and hydrophobic tails inward, forming a bilayer.

  • Micelle: A spherical structure formed by phospholipids in water.

  • Diffusion: Movement of molecules from high to low concentration without energy input.

  • Facilitated Diffusion: Movement of molecules across membranes via transport proteins, no energy required.

  • Active Transport: Movement of molecules against a concentration gradient, requiring energy (usually ATP).

Osmosis and Tonicity

  • Osmosis: Diffusion of water across a selectively permeable membrane.

  • Hypotonic Solution: Lower solute concentration outside the cell; water enters the cell, which may swell or burst.

  • Hypertonic Solution: Higher solute concentration outside the cell; water leaves the cell, which may shrink.

  • Isotonic Solution: Equal solute concentration; no net water movement.

Example: Red blood cells placed in pure water (hypotonic) will swell; in salty water (hypertonic), they will shrink.

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