Cells and Biological Organization

Structure and Function of Cells

The cell is the fundamental unit of structure and function in all living organisms. Cells can be classified as prokaryotic or eukaryotic, each with distinct features.

• Cell: The basic unit of life, capable of performing all necessary functions for survival.

• Tissue: A group of cells working together to perform a specialized function.

• Eukaryotic cells: Larger and more complex than prokaryotic cells; contain membrane-bound organelles.

• Prokaryotic cells: Smaller, lack membrane-bound organelles.

Example: Muscle tissue is composed of muscle cells working together to produce movement.

Ecosystems and Communities

Living organisms interact within ecosystems, which are defined areas containing various communities of organisms.

• Ecosystem: All living things in a particular area, interacting with each other and their environment.

• Community: Organisms inhabiting a particular ecosystem (e.g., a college campus).

Evolution and Natural Selection

Evolution is the process by which populations of organisms change over time in response to environmental pressures. Natural selection is a key mechanism driving evolution.

• Evolution: Change in heritable traits of populations over generations.

• Natural selection: The environment selects for traits that enhance survival and reproduction.

• Hypothesis: A testable and falsifiable statement used in scientific inquiry.

Example: Peppered moths changed coloration in response to industrial pollution, demonstrating natural selection.

Chemistry of Life

Atoms, Elements, and Compounds

All matter is composed of atoms, which combine to form elements and compounds.

• Element: A substance that cannot be broken down by chemical reactions.

• Compound: A substance consisting of two or more elements in a fixed ratio.

• Atom: The smallest unit of matter retaining properties of an element.

• Proton: Positively charged subatomic particle.

• Neutron: Subatomic particle with no charge.

• Electron: Negatively charged subatomic particle.

Atomic Structure and Isotopes

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells.

• Atomic number: Number of protons in the nucleus.

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

• Valence shell: The outermost electron shell, determines chemical reactivity.

Equation:

Chemical Bonds

Atoms interact to form chemical bonds, which hold molecules together.

• Ionic bond: Formed by transfer of electrons between atoms, resulting in charged ions.

• Covalent bond: Formed by sharing of electrons between atoms.

• Polar covalent bond: Unequal sharing of electrons, leading to partial charges.

• Cation: Positively charged ion.

• Anion: Negatively charged ion.

Water and Its Properties

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

• Hydrogen bonds: Weak attractions between water molecules, responsible for cohesion, adhesion, and surface tension.

• Cohesion: Water molecules stick to each other.

• Adhesion: Water molecules stick to other surfaces.

• Surface tension: Water resists external force due to hydrogen bonding.

Example: Water droplets forming on a leaf due to cohesion and adhesion.

Acids, Bases, and pH

Acids and bases are substances that alter the concentration of hydrogen ions in a solution.

• Acid: Substance that increases hydrogen ion concentration (pH < 7).

• Base: Substance that decreases hydrogen ion concentration (pH > 7).

• pH scale: Measures acidity or alkalinity, ranging from 0 (most acidic) to 14 (most basic).

Carbon Chemistry and Macromolecules

Carbon Compounds

Carbon forms the backbone of organic molecules, allowing for complex and diverse structures.

• Organic compounds: Carbon-based molecules found in living organisms.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen.

• Carbon skeleton: The chain or ring structure of carbon atoms in organic molecules.

Carbohydrates

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

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

• Disaccharides: Two monosaccharides joined by glycosidic linkage (e.g., lactose).

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

Additional info: Polysaccharides are broken down by hydrolysis, releasing energy for cellular processes.

Lipids

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids, important for energy storage and cell membranes.

• Fats: Composed of glycerol and fatty acids; formed by dehydration reactions.

• Saturated fatty acids: No double bonds; solid at room temperature (e.g., butter, lard).

• Unsaturated fatty acids: One or more double bonds; liquid at room temperature (e.g., plant oils).

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with four fused carbon rings (e.g., cholesterol, hormones).

Example: Cholesterol is a steroid found in animal cell membranes and is a precursor for hormone synthesis.

Additional Key Concepts

Macromolecules and Polymers

Macromolecules are large molecules formed by joining smaller units called monomers.

• Polymer: Long chain of repeating monomers (e.g., polysaccharides, proteins, nucleic acids).

• Dehydration reaction: Chemical reaction that joins monomers by removing water.

• Hydrolysis: Chemical reaction that breaks polymers into monomers by adding water.

Equation:

Impact of Environment on Chemical Bonds and Evolution

Environmental factors such as temperature and pH can affect chemical reactions and evolutionary processes.

• Heat can increase reaction rates; cold can slow them down.

• Environmental changes can drive evolution by selecting for traits that enhance survival.

Example: Climate change can impact animal habitats, farming practices, migration patterns, and ocean temperature.