Properties of Water

Hydrogen Bonding

Hydrogen bonding is a type of weak chemical bond that forms when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule. In water, hydrogen bonds are responsible for many of its unique properties.

• Definition: An attraction between a hydrogen atom carrying a partial positive charge and an electronegative atom (often oxygen or nitrogen).

• Example: The bonds between water molecules.

Cohesion

Cohesion refers to the attraction between molecules of the same substance. In water, cohesion is due to hydrogen bonding and is responsible for phenomena such as surface tension.

• Key Point: Cohesion allows water molecules to stick together, contributing to the transport of water in plants.

Adhesion and Surface Tension

Adhesion is the attraction between different types of molecules, such as water and glass. Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.

• Adhesion: Helps water climb up plant vessels (capillary action).

• Surface Tension: Allows small insects to walk on water.

High Specific Heat

Water has a high specific heat, meaning it can absorb or release a large amount of heat with only a slight change in its own temperature.

• Equation:

• Importance: Helps stabilize temperatures in organisms and environments.

Evaporative Cooling

Evaporative cooling occurs when the surface of an object becomes cooler during evaporation, as a result of the loss of highly kinetic molecules to the gaseous state.

• Example: Sweating in humans helps regulate body temperature.

Density of Ice

Unlike most substances, solid water (ice) is less dense than liquid water due to the hydrogen-bonded lattice structure that forms at low temperatures.

• Key Point: Ice floats on water, insulating aquatic life in winter.

Solvent of Life

Water is known as the "universal solvent" because it can dissolve a wide variety of substances, especially ionic and polar compounds.

• Key Point: Facilitates chemical reactions in cells by dissolving reactants.

pH and Buffers

The pH scale measures the concentration of hydrogen ions in a solution. Buffers are substances that minimize changes in pH by accepting or donating H+ ions.

• Equation:

• Example: Blood contains buffers to maintain a stable pH.

Carbon Chemistry

Carbon’s Versatility

Carbon atoms can form four covalent bonds, allowing for a diversity of stable organic molecules with various shapes and functions.

• Key Point: Forms the backbone of biological macromolecules.

Hydrocarbons

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. They are nonpolar and hydrophobic.

• Example: Methane (CH4), ethane (C2H6).

Isomers

Isomers are compounds with the same molecular formula but different structures and properties.

• Types: Structural isomers, cis-trans isomers, enantiomers.

• Example: Glucose and fructose (C6H12O6).

Key Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity.

• Examples: Hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2), sulfhydryl (-SH), phosphate (-PO42-), methyl (-CH3).

Macromolecules

Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

• Key Point: Built from smaller subunits called monomers.

Dehydration and Hydrolysis

Dehydration synthesis (condensation) joins monomers by removing water, while hydrolysis breaks polymers into monomers by adding water.

• Equation (Dehydration):

• Equation (Hydrolysis):

Carbohydrates

Carbohydrates are sugars and their polymers, serving as energy sources and structural materials.

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

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

Lipids

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids. They function in energy storage, membrane structure, and signaling.

• Key Point: Not true polymers; composed of fatty acids and glycerol.

Function Depends on Shape – Denaturation

The function of biological macromolecules, especially proteins, depends on their three-dimensional shape. Denaturation is the loss of this shape due to environmental changes, leading to loss of function.

• Example: Cooking an egg denatures its proteins.

Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

• DNA: Deoxyribonucleic acid; double-stranded; stores genetic information.

• RNA: Ribonucleic acid; single-stranded; involved in protein synthesis.

Cell Structure and Function

Vacuoles: Structure and Function

Vacuoles are membrane-bound organelles found in plant and some animal cells. They store substances and help maintain cell structure.

• Plant Cells: Large central vacuole stores water, nutrients, and waste; maintains turgor pressure.

• Animal Cells: Smaller vacuoles, mainly for storage and transport.

Cell Organelles: Structure and Function (Animal and Plant Cells)

Cells contain specialized structures called organelles, each with specific functions necessary for cell survival.

Animal Cells vs Plant Cells (Similarities and Differences)

Animal and plant cells share many organelles but also have key differences.

Find and Label Structures/Organelles in Both Animal and Plant Cells

Students should be able to identify and label the following structures in diagrams of animal and plant cells:

• Nucleus

• Mitochondria

• Endoplasmic Reticulum (Rough and Smooth)

• Golgi Apparatus

• Lysosomes (mainly animal cells)

• Vacuole (large in plants, small in animals)

• Chloroplasts (plants only)

• Cell Membrane

• Cell Wall (plants only)