Unit 1 Biology Study Guide: The Science of Life and the Chemistry of Living Systems

Introduction to Biology

Defining Biology

Biology is the scientific study of life and living organisms. It encompasses the structure, function, growth, origin, evolution, and distribution of living things.

• Biology: The study of living organisms and their interactions with one another and their environments.

• Living things share six common characteristics:

  • Order (organized structure)

  • Regulation (homeostasis)

  • Growth and development

  • Energy processing

  • Response to the environment

  • Reproduction

• Viruses are not considered living organisms because they cannot reproduce or carry out metabolic processes independently.

Levels of Biological Organization

Life is organized in a hierarchy from the largest to the smallest levels:

1. Biosphere

2. Ecosystem

3. Community

4. Population

5. Organism

6. Organ system

7. Organ

8. Tissue

9. Cell

10. Organelle

11. Molecule

12. Atom

Each level has unique properties and functions, building upon the previous level.

The Scientific Method

The scientific method is a systematic approach to understanding the natural world.

1. Observation

2. Question

3. Hypothesis

4. Prediction

5. Experiment

6. Analysis

7. Conclusion

• Hypothesis: A testable explanation for an observation.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

• Scientific fact: An observation that has been repeatedly confirmed.

Experimental Design

• Controlled study: Only one variable is changed at a time.

• Control group: Does not receive the experimental treatment.

• Experimental group: Receives the treatment.

• Independent variable: The variable that is changed or controlled.

• Dependent variable: The variable being tested and measured.

• Confounding variables: Other variables that may affect the outcome.

• Blind experiment: Participants do not know which group they are in, reducing bias.

Types of Scientific Studies

• Hypothesis-driven controlled experiments: Manipulate variables to test hypotheses.

• Observational studies: Observe subjects in natural settings without manipulation.

• Human clinical trials: Test medical interventions in human subjects.

Pseudoscience and Scientific Practice

• Pseudoscience: Claims presented as scientific but lacking supporting evidence or methodology.

• Good scientific practices include peer review, reproducibility, and transparency.

• Media may misrepresent scientific findings, leading to public misunderstanding.

The Chemistry of Life

Atoms, Molecules, and Chemical Reactions

• Atom: The smallest unit of matter, composed of protons, neutrons, and electrons.

• Molecule: Two or more atoms bonded together.

• Chemical reaction: The process by which atoms or molecules are rearranged to form new substances.

• Reactants: Substances present before the reaction.

• Products: Substances formed by the reaction.

Elements Essential to Life

• Four elements make up most living matter:

  • Oxygen (O)

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

Structure of Atoms

• Proton: Positive charge, found in the nucleus.

• Neutron: No charge, found in the nucleus.

• Electron: Negative charge, orbits the nucleus.

• Ion: An atom or molecule with a net electric charge due to loss or gain of electrons.

Chemical Bonds

• Covalent bond: Atoms share electrons.

• Ionic bond: Atoms transfer electrons, resulting in oppositely charged ions that attract.

• Hydrogen bond: Weak attraction between a hydrogen atom and another electronegative atom.

• Polar molecule: Molecule with uneven distribution of charge (e.g., water).

• Non-polar molecule: Molecule with even distribution of charge.

Example: Water (H2O) is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen.

Properties of Water

• Ice floats because solid water is less dense than liquid water.

• Water as a solvent: Water dissolves many substances due to its polarity.

• Temperature regulation: Water absorbs and releases heat slowly, stabilizing temperatures.

• Cohesion: Water molecules stick to each other.

• Adhesion: Water molecules stick to other substances.

• All these properties are due to hydrogen bonding between water molecules.

pH and Acidity

• pH: A measure of hydrogen ion (H+) concentration in a solution.

• Acidic: pH < 7, higher concentration of H+ ions.

• Basic: pH > 7, higher concentration of OH- ions.

• Neutral: pH = 7.

• Each pH unit represents a tenfold change in H+ concentration.

Example: A solution with pH 3 has 100 times more H+ ions than a solution with pH 5.

Biological Molecules

• Four major classes:

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic acids (not covered in detail in this unit)

Carbohydrates

• Monomers: Monosaccharides (simple sugars, e.g., glucose)

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

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose)

• Function: Energy storage and structural support

Lipids

• Categories: Fats, oils, phospholipids, steroids

• Structure: Mostly hydrophobic molecules

• Triglyceride: Glycerol + 3 fatty acids

• Saturated fats: No double bonds, straight chains, solid at room temperature

• Unsaturated fats: Double bonds, bent chains, liquid at room temperature

• Trans fats: Man-made, unhealthy, hydrogenated unsaturated fats

• Omega-3 fatty acids: Healthy fats found in fish and some plants

Proteins

• Monomers: Amino acids (20 different types)

• Structure: Long chains of amino acids fold into specific shapes

• Function: Enzymes, structural support, transport, signaling

Enzymes

• Enzyme: Protein that catalyzes chemical reactions

• Substrate: The molecule upon which an enzyme acts

• Active site: Region on the enzyme where the substrate binds

• Enzymes are specific to their substrates

• Enzymes lower the activation energy required for reactions

$\text{Enzyme} + \text{Substrate} \rightarrow \text{Enzyme-Substrate Complex} \rightarrow \text{Enzyme} + \text{Product}$

The Cell: The Fundamental Unit of Life

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells: Lack a nucleus, simpler structure (e.g., bacteria)

• Eukaryotic cells: Have a nucleus and membrane-bound organelles (e.g., plants, animals)

Cell Organelles

• Organelles common to plant and animal cells:

  • Nucleus

  • Endoplasmic reticulum (rough and smooth)

  • Ribosomes

  • Golgi apparatus

  • Mitochondria

  • Plasma membrane

  • Vesicles

• Unique to plant cells: Chloroplasts, cell wall, large central vacuole

• Unique to animal cells: Lysosomes, centrioles (not covered in detail here)

Plasma Membrane

• Composed of a phospholipid bilayer with embedded proteins

• Functions: Selective barrier, communication, transport

• Phospholipids have hydrophilic heads and hydrophobic tails, forming a semi-permeable membrane

• Membrane proteins assist in transport, signaling, and structural support

Diffusion and Osmosis

• Diffusion: Movement of molecules from high to low concentration

• Osmosis: Diffusion of water across a selectively permeable membrane

• Goal: Achieve equilibrium in concentration

• "Salt sucks": Solutes draw water toward them during osmosis

Functions of Key Organelles

• Nucleus: Contains genetic material (DNA), controls cell activities

• Rough endoplasmic reticulum (RER): Studded with ribosomes, synthesizes proteins

• Smooth endoplasmic reticulum (SER): Synthesizes lipids, detoxifies substances

• Ribosomes: Sites of protein synthesis

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids

• Vesicles: Transport materials within the cell

• Chloroplasts: Site of photosynthesis in plant cells

• Mitochondria: Site of cellular respiration, produces ATP

• Vacuoles (plant cells): Storage and structural support

• Cell wall (plant cells): Provides rigidity and protection

Chloroplasts and Mitochondria

• Chloroplasts: Found in plant cells, convert solar energy to chemical energy via photosynthesis

• Mitochondria: Found in both plant and animal cells, convert chemical energy in food to ATP via cellular respiration

• Mitochondria contain their own DNA, suggesting an evolutionary origin via endosymbiosis

• Significance of mitochondrial DNA: Maternal inheritance, used in evolutionary studies

$\text{Photosynthesis:} \quad 6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

$\text{Cellular Respiration:} \quad C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

Core Issue: Nutrition and Biological Molecules

Biological Molecules in Nutrition

• Carbohydrates: Found in grains, fruits, vegetables; provide quick energy

• Lipids: Found in oils, butter, nuts; provide long-term energy storage and insulation

• Proteins: Found in meat, beans, dairy; used for structure, enzymes, and transport

Digestion and Absorption

• Biological molecules are ingested as polymers and broken down into monomers during digestion

• Monomers (e.g., amino acids, monosaccharides, fatty acids) are absorbed into the bloodstream and transported to cells

• Cells use these monomers for energy production and building cellular structures

Energy Extraction from Food

• Cells extract energy from carbohydrates, lipids, and proteins via cellular respiration

• ATP is produced as the main energy currency of the cell

Graph Interpretation

• Be able to interpret scientific graphs, such as those showing the relationship between sweetened beverage consumption and hypertension risk

• Identify variables, trends, and draw conclusions from data

Biological Molecule	Monomer	Main Function	Example Foods
Carbohydrates	Monosaccharides	Energy source	Bread, rice, fruit
Lipids	Fatty acids, glycerol	Energy storage, insulation	Butter, oil, nuts
Proteins	Amino acids	Structure, enzymes	Meat, beans, eggs

Additional info: Some explanations and context have been expanded for clarity and completeness, as per academic standards.