Characteristics of Life and Human Uniqueness

Defining Features of Life

Living organisms share several key characteristics that distinguish them from non-living matter.

• Organization: Living things are composed of one or more cells, which are the basic units of life.

• Metabolism: The ability to obtain and use energy for growth, maintenance, and reproduction.

• Homeostasis: Regulation of internal environment to maintain a stable, constant condition.

• Growth and Development: Increase in size and complexity over time.

• Reproduction: Ability to produce new individuals.

• Response to Stimuli: Ability to sense and react to environmental changes.

• Evolutionary Adaptation: Populations change over generations through genetic variation and natural selection.

Example: Humans maintain a constant body temperature (homeostasis) despite changes in external temperature.

Unique Features of Humans

• Bipedalism: Walking upright on two legs.

• Opposable Thumbs: Thumbs that can touch the tips of other fingers, allowing for precise manipulation.

• Large Brain: High brain-to-body size ratio, enabling complex thought and problem-solving.

• Complex Language: Capacity for sophisticated verbal and written communication.

The Chemistry of Living Things

Atoms, Ions, and Isotopes

Understanding the basic units of matter is essential for studying biology.

• Atom: The smallest unit of an element, consisting of protons, neutrons, and electrons.

• Ion: An atom or molecule that has gained or lost electrons, resulting in a net charge.

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

Example: Carbon-12 and Carbon-14 are isotopes of carbon; Na+ is a sodium ion.

Hydrogen Bonds and Water

Hydrogen bonds are weak attractions between polar molecules, crucial for the properties of water, proteins, and DNA.

• Hydrogen Bond: Attraction between a hydrogen atom (attached to O, N, or F) and another electronegative atom.

• Importance: Responsible for water's high boiling point, cohesion, and the structure of proteins and DNA.

Example: The double helix structure of DNA is stabilized by hydrogen bonds between base pairs.

Elements Common in the Human Body

• Major Elements: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P).

• Minor Elements: Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg).

Example: Oxygen is the most abundant element in the human body by mass.

Biological Molecules

• Carbohydrates: Composed of carbon, hydrogen, and oxygen. Monosaccharides (e.g., glucose, fructose) are the simplest forms.

• Proteins: Polymers of amino acids. Examples include enzymes, hemoglobin, insulin, keratin.

• Nucleic Acids: DNA and RNA. DNA stores genetic information; RNA is involved in protein synthesis.

Example: Hemoglobin is a protein that transports oxygen in the blood.

Structure and Function of Cells

Cell Types and Organelles

Cells are the fundamental units of life. Eukaryotic cells contain membrane-bound organelles.

• Prokaryotes: Simple cells without a nucleus (e.g., bacteria). Note: Not a focus in this course.

• Eukaryotes: Complex cells with a nucleus and organelles (e.g., human cells).

• Organelles: Specialized structures within eukaryotic cells (e.g., nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes).

Example: The mitochondrion is the site of ATP production in eukaryotic cells.

Cell Membrane Transport

Cells regulate the movement of substances across their membranes through various mechanisms.

• Diffusion: Movement of solute particles from high to low concentration. No energy required.

• Osmosis: Diffusion of water across a selectively permeable membrane from high to low water concentration.

• Facilitated Diffusion: Movement of substances from high to low concentration via a protein channel. No energy required.

• Active Transport: Movement of substances from low to high concentration using energy (ATP).

• Exocytosis: Process by which substances are expelled from the cell using vesicles and ATP.

• Endocytosis: Process by which substances are taken into the cell via vesicles and ATP.

Example: Sodium-potassium pump is an active transport mechanism that uses ATP to move ions against their concentration gradients.

Effects of Solutions on Cells

From Cells to Organ Systems

Tissues: Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands.

• Types by Shape: Squamous (flat), Cuboidal (cube-shaped), Columnar (tall and column-like).

• Types by Layers: Simple (one layer), Stratified (multiple layers).

• Functions: Protection, absorption, secretion, filtration.

• Locations: Skin, lining of digestive tract, glands.

Example: Simple columnar epithelium lines the small intestine for absorption.

Metabolism and Energy

Metabolism Overview

Metabolism refers to all chemical reactions in the body, including energy conversion.

• Anabolism: Building larger molecules from smaller ones (requires energy).

• Catabolism: Breaking down molecules to release energy.

Example: The breakdown of glucose during cellular respiration is a catabolic process.

ATP Production Pathways

Cells generate ATP through a series of metabolic pathways.

• Glycolysis: Occurs in the cytoplasm; does not require oxygen (anaerobic); produces a small amount of ATP.

• Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondria; requires oxygen (aerobic).

• Electron Transport Chain: Occurs in the inner mitochondrial membrane; requires oxygen; produces the most ATP.

Example: During intense exercise, muscles rely on glycolysis for quick ATP when oxygen is limited.

Key Equation for Cellular Respiration:

The Digestive System and Nutrition

Nutrient Absorption

The small intestine is the primary site for nutrient absorption, aided by structures that increase surface area.

• Villi: Finger-like projections that increase the surface area for absorption.

• Microvilli: Even smaller projections on villi, forming the brush border.

Example: Glucose and amino acids are absorbed through the villi into the bloodstream.

Accessory Organs

• Pancreas: Produces digestive enzymes (e.g., amylase, lipase, proteases) that aid in the breakdown of carbohydrates, fats, and proteins.

Example: Pancreatic amylase breaks down starch into simple sugars.

Large Intestine

• Main Function: Absorbs water, salts, vitamins, and minerals; not primarily involved in nutrient absorption for energy.

Example: Water reabsorption in the colon prevents dehydration.

The Skeletal System

Functions of the Skeletal System

• Support: Provides structural framework for the body.

• Protection: Shields vital organs (e.g., skull protects the brain).

• Movement: Serves as attachment points for muscles.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Production: Occurs in bone marrow (hematopoiesis).

Joints, Tendons, and Ligaments

• Joints: Points where two or more bones meet, allowing movement.

• Tendons: Connect muscle to bone.

• Ligaments: Connect bone to bone.

Example: The patellar tendon connects the quadriceps muscle to the tibia; the anterior cruciate ligament (ACL) connects bones in the knee.