Basic Concepts and Units of Measurement

1. Scientific Units and Measurements

• SI Units: The International System of Units (SI) is the standard system of measurement used in science.

  • Length: Meter (m)

  • Mass: Kilogram (kg)

  • Time: Second (s)

  • Temperature: Kelvin (K) or Celsius (°C)

  • Amount of Substance: Mole (mol)

  • Example: Measuring the length of a table in meters.

2. Prefixes and Conversions

• Common Prefixes:

  • Kilo- (k): 10³

  • Centi- (c): 10−² 

  • Milli- (m): 10−³ 

  • Micro- (μ): 10−⁶ 

  • Nano- (n): 10−⁹ 

  • Example: Converting 1 kilometer to meters (1 km = 1000 m).

3. Accuracy and Precision

• Accuracy: How close a measured value is to the true value.

  • Example: Measuring the boiling point of water to be 100.0°C.

• Precision: How close repeated measurements are to each other.

  • Example: Repeated measurements of a length giving values of 10.2 cm, 10.3 cm, and 10.1 cm.

The Structure of Atoms

1. Atomic Structure

• Subatomic Particles: Atoms are made up of protons, neutrons, and electrons.

  • Protons: Positively charged particles in the nucleus.

  • Neutrons: Neutral particles in the nucleus.

  • Electrons: Negatively charged particles orbiting the nucleus.

  • Example: The hydrogen atom has 1 proton and 1 electron.

2. Atomic Number and Mass Number

• Atomic Number (Z): The number of protons in an atom.

  • Example: Carbon has an atomic number of 6.

• Mass Number (A): The total number of protons and neutrons in an atom.

  • Example: Carbon-12 has 6 protons and 6 neutrons, so its mass number is 12.

3. Isotopes

• Definition: Atoms of the same element with different numbers of neutrons.

  • Example: Carbon-12, Carbon-13, and Carbon-14 are isotopes of carbon.

4. Electron Configuration

• Shells and Energy Levels: Electrons occupy energy levels or shells around the nucleus.

  • First Shell: Can hold up to 2 electrons.

  • Second Shell: Can hold up to 8 electrons.

  • Example: The electron configuration of oxygen is 2, 6.

Elements, Compounds, and Mixtures

1. Elements

• Definition: Pure substances consisting of only one type of atom.

  • Example: Oxygen (O), Hydrogen (H), and Carbon (C).

2. Compounds

• Definition: Substances formed from two or more elements chemically bonded together.

  • Types of Chemical Bonds:

    • Ionic Bonds: Transfer of electrons from one atom to another.

    • Covalent Bonds: Sharing of electrons between atoms.

  • Example: Water (H₂O), formed from hydrogen and oxygen atoms.

3. Mixtures

• Definition: A combination of two or more substances that are not chemically bonded.

  • Homogeneous Mixtures: Uniform composition throughout.

  • Heterogeneous Mixtures: Non-uniform composition.

  • Example: Saltwater is a homogeneous mixture, while a salad is a heterogeneous mixture.

Chemical Reactions

1. Types of Chemical Reactions

• Synthesis Reaction: Two or more simple substances combine to form a more complex substance.

  • Example: 2H₂ + O₂ → 2H₂O 

• Decomposition Reaction: A complex substance breaks down into simpler substances.

  • Example: 2H₂O → 2H₂ + O₂ 

• Single Replacement Reaction: One element replaces another in a compound.

  • Example: Zn + 2HCl → ZnCl₂ + H₂ 

• Double Replacement Reaction: Exchange of ions between two compounds.

  • Example: AgNO₃ + NaCl → AgCl + NaNO₃ ​

2. Balancing Chemical Equations

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.

  • Example: Balancing CH₄ + 2O₂ → CO₂ + 2H₂O 

3. Energy Changes in Reactions

• Exothermic Reactions: Release energy, usually in the form of heat.

  • Example: Combustion of methane.

• Endothermic Reactions: Absorb energy.

  • Example: Photosynthesis in plants.

Biological Macromolecules

1. Carbohydrates

• Definition: Organic compounds made up of carbon, hydrogen, and oxygen.

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

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

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

  • Example: Glucose (C₆H₁₂O₆) is a common monosaccharide used by cells for energy.

2. Proteins

• Structure: Composed of amino acids linked by peptide bonds.

  • Functions: Enzymes, structural components, transport molecules, antibodies.

  • Example: Hemoglobin, the protein in red blood cells that carries oxygen.

3. Lipids

• Structure: Made up of glycerol and fatty acids.

  • Functions: Energy storage, insulation, and making up cell membranes.

  • Example: Triglycerides, phospholipids in cell membranes.

4. Nucleic Acids

• Structure: Made up of nucleotides.

  • Types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

  • Functions: Store and transmit genetic information.

  • Example: DNA carries the genetic blueprint of an organism.

The Cell as the Basic Unit of Life

1. Cell Theory

• Principles:

  • All living organisms are composed of one or more cells.

  • The cell is the basic unit of life.

  • All cells arise from pre-existing cells.

  • Example: Unicellular organisms like bacteria consist of a single cell.

2. Prokaryotic and Eukaryotic Cells

• Prokaryotic Cells: Simple, lack a nucleus.

  • Example: Bacteria.

• Eukaryotic Cells: Complex, with a nucleus and membrane-bound organelles.

  • Example: Plant and animal cells.

3. Cell Organelles

• Nucleus: Contains genetic material (DNA).

  • Example: Control center of the cell.

• Mitochondria: Powerhouse of the cell, produces energy (ATP).

  • Example: Site of cellular respiration.

• Ribosomes: Synthesize proteins.

  • Example: Found in the cytoplasm or on the endoplasmic reticulum.

• Chloroplasts: Site of photosynthesis in plant cells.

  • Example: Contain chlorophyll, which captures light energy.

• Cell Membrane: Regulates what enters and exits the cell.

  • Example: Composed of a phospholipid bilayer.

4. Cellular Processes

• Photosynthesis: Conversion of light energy into chemical energy in plants.

  • Equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ 

  • Example: Plants use sunlight to produce glucose.

• Cellular Respiration: Process of breaking down glucose to produce ATP.

  • Equation: 

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy 

• Example: Cells use glucose and oxygen to produce energy.