Introduction to Biology

Domains of Life

The domain system classifies all living organisms into three major groups based on cellular organization and genetic differences.

• Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.

• Archaea: Prokaryotic, unicellular, often found in extreme environments; genetically distinct from bacteria.

• Eukarya: Eukaryotic organisms with cells containing a nucleus; includes animals, plants, fungi, and protists.

Hierarchy of Living Organisms

Biological organization follows a hierarchical structure from smallest to largest:

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organisms → Populations → Communities → Ecosystems → Biosphere

Scientific Method

The scientific method is a systematic approach to investigation:

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Analysis

7. Conclusion

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes. It is essential for survival and function.

• Example: Regulation of body temperature, blood glucose levels.

Shared Characteristics of Living and Nonliving Things

• Living things: Cellular organization, metabolism, growth, reproduction, response to stimuli, adaptation.

• Nonliving things: May have structure and interact with environment but lack metabolism and reproduction.

Chemistry of Life

Most Abundant Elements in Humanity

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Phosphorus (P)

• Sulfur (S)

Reductionism

Reductionism is the approach of understanding complex systems by studying their simpler components.

• Example: Studying cell function by analyzing individual organelles.

Importance of DNA

DNA (deoxyribonucleic acid) is the molecule that stores genetic information, guiding growth, development, and reproduction.

• DNA is essential for inheritance and protein synthesis.

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions.

• Covalent Bonds: Formed when atoms share electrons.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Polarity of Molecules

• Polar Molecules: Have uneven distribution of charge; one end is more positive, the other more negative (e.g., water).

• Nonpolar Molecules: Even distribution of charge; no distinct poles (e.g., methane).

Acids, Bases, and pH

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Radioisotope Technology

Radioisotopes are used in medical imaging, cancer treatment, and biological research due to their radioactive properties.

• Example: PET scans use radioisotopes to visualize metabolic activity.

Atoms and Charge

• Atoms change charge by gaining or losing electrons, forming ions.

• Negatively charged elements (anions) attract positively charged elements (cations).

Elements vs. Molecules

• Element: Pure substance consisting of one type of atom.

• Molecule: Two or more atoms bonded together.

Structure & Function of Cells

Cell Organelles: Names, Functions, and Shapes

Cell organelles are specialized structures within cells, each with distinct functions.

• Nucleus: Contains DNA; controls cell activities; spherical shape.

• Mitochondria: Site of ATP production; oval shape.

• Ribosomes: Protein synthesis; small, round particles.

• Endoplasmic Reticulum (ER): Rough ER (with ribosomes) synthesizes proteins; Smooth ER synthesizes lipids; tubular network.

• Golgi Apparatus: Modifies, sorts, and packages proteins; stack of flattened sacs.

• Lysosomes: Digestive enzymes; spherical vesicles.

• Plasma Membrane: Controls entry/exit; flexible, phospholipid bilayer.

• Chloroplasts: Photosynthesis (plants); oval shape.

Cell Size and Surface Area

Cell size is limited by surface area-to-volume ratio, affecting nutrient and waste exchange.

• Smaller cells have higher surface area relative to volume, allowing efficient exchange.

• Formula: for a cube

• Formula: for a cube

Microscopy Types

• Light Microscopy: Uses visible light; views live cells.

• Electron Microscopy: Uses electron beams; higher resolution; views cell ultrastructure.

• Fluorescence Microscopy: Uses fluorescent dyes; highlights specific cell components.

Diffusion

Diffusion is the passive movement of molecules from high to low concentration.

• Example: Oxygen diffusing into cells.

Plasma Membrane Structure

• Composed of phospholipid bilayer, proteins, cholesterol, and carbohydrates.

• Selective permeability: Allows some substances to pass, blocks others.

Transport Across the Plasma Membrane

• Passive Transport: No energy required; includes diffusion and facilitated diffusion.

• Active Transport: Requires energy (ATP); moves substances against concentration gradient.

• What can pass: Small, nonpolar molecules (e.g., O2, CO2).

• What cannot pass: Large, polar molecules and ions without transport proteins.

Isotonic Solutions

An isotonic solution has equal solute concentration as the cell, causing no net movement of water.

• Cells retain normal shape in isotonic solutions.

Glycolysis

Glycolysis is the first step in cellular respiration, breaking down glucose to produce ATP.

• Occurs in cytoplasm; produces pyruvate, ATP, and NADH.

Electron Transport Chain and ATP Production

• Most ATP is produced in the ATP synthase protein complex during the electron transport chain.

• Electron carriers (NADH, FADH2) donate electrons to the chain.

Tissues & Organ Systems

Types of Tissues and Their Functions

• Epithelial Tissue: Covers surfaces; protection, absorption, secretion.

• Connective Tissue: Supports and connects; includes bone, blood, cartilage, adipose.

• Muscle Tissue: Movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Communication; neurons and glial cells.

Types of Connective Tissues

• Loose Connective Tissue: Supports organs.

• Dense Connective Tissue: Tendons and ligaments.

• Adipose Tissue: Stores fat.

• Cartilage: Flexible support.

• Bone: Rigid support.

• Blood: Transport of substances.

Location of Tissue Types

• Epithelial: Skin, lining of organs.

• Connective: Throughout body; bones, blood, fat.

• Muscle: Skeletal muscles, heart (cardiac), stomach (smooth).

• Nervous: Brain, spinal cord, nerves.

Muscle Type in the Stomach

• Smooth Muscle: Involuntary, non-striated; found in stomach walls.

Types of Junctions

• Tight Junctions: Seal cells together; prevent leakage.

• Desmosomes: Anchor cells; provide mechanical strength.

• Gap Junctions: Allow communication; passage of ions and molecules.

Summary Table: Types of Tissues and Their Functions

Summary Table: Types of Cell Junctions

Additional info: Academic context was added to expand brief points into full explanations and to provide self-contained study notes.