# Building Blocks for Understanding

## 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.