Domains of Life

Classification of Living Organisms

The domain system is the highest level of biological classification, dividing all life into three major groups based on cellular structure and genetics.

• Bacteria: Prokaryotic cells, no nucleus, diverse metabolic pathways.

• Archaea: Prokaryotic cells, distinct membrane lipids, often found in extreme environments.

• Eukarya: Eukaryotic cells with a nucleus and membrane-bound organelles; includes animals, plants, fungi, and protists.

Cell Structure and Function

Cell Organelles: Names, Functions, and Shapes

Cells contain specialized structures called organelles, each with unique functions essential for cellular life.

• Nucleus: Stores genetic material (DNA); spherical shape.

• Mitochondria: Site of ATP production; oval with inner folded membranes (cristae).

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids; tubular network.

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

• Lysosomes: Digest cellular waste; spherical vesicles.

• Ribosomes: Protein synthesis; small, round particles.

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

• Cytoskeleton: Provides structural support; network of fibers.

Example: The mitochondria are often called the "powerhouse" of the cell because they generate most of the cell's energy.

Hierarchy of Living Organisms

Biological organization follows a hierarchy from smallest to largest:

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organism

Cell Size and Surface Area

Cell size is limited by the surface area-to-volume ratio, which affects the efficiency of material exchange.

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

• Larger cells may struggle to transport materials quickly enough.

Formula:

Types of Microscopy

Microscopes are essential tools for studying cells and tissues.

• Light Microscopy: Used for viewing live cells and tissues.

• Electron Microscopy: Provides high-resolution images of cell structures; includes Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM).

Chemistry of Living Things

Most Abundant Elements in Humans

The human body is primarily composed of a few key elements:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

Reductionism in Biology

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

• Helps explain biological processes at the molecular and cellular level.

Importance of DNA

DNA (Deoxyribonucleic Acid) is the molecule that stores genetic information and directs cellular activities.

• Contains instructions for protein synthesis.

• Inherited from parent to offspring.

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules.

• Ionic Bonds: Transfer of electrons between atoms; forms charged ions.

• Covalent Bonds: Sharing of electrons between atoms; strong and stable.

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

Polarity of Molecules

Polarity refers to the distribution of electrical charge in a molecule.

• Polar Molecules: Uneven charge distribution; dissolve in water (e.g., H2O).

• Nonpolar Molecules: Even charge distribution; do not dissolve in water (e.g., oils).

Interactions Between Charged Elements

Negatively charged elements (anions) attract positively charged elements (cations), forming ionic bonds.

pH Levels: Acids and Bases

pH measures the concentration of hydrogen ions in a solution.

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Formula:

Scientific Method

The scientific method is a systematic approach to investigation.

1. Observation

2. Hypothesis

3. Experiment

4. Data Collection

5. Analysis

6. Conclusion

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes.

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

Elements vs. Molecules

• Element: Pure substance consisting of one type of atom (e.g., O2).

• Molecule: Two or more atoms bonded together (e.g., H2O).

Characteristics of Living vs. Nonliving Things

• Living: Growth, reproduction, metabolism, response to stimuli, cellular organization.

• Nonliving: Lack these characteristics.

Radioisotope Technology

Radioisotopes are used in medical imaging, cancer treatment, and biological research.

• Example: PET scans use radioactive tracers to visualize metabolic activity.

Changing Atomic Charges

Atoms can gain or lose electrons to become ions:

• Cation: Positive charge (loss of electrons).

• Anion: Negative charge (gain of electrons).

Cellular Processes

Diffusion

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

• Occurs across cell membranes.

• Does not require energy.

ATP Production: Electron Transport Chain

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

Formula:

Plasma Membrane Permeability

• Can Pass: Small, nonpolar molecules (e.g., O2, CO2), water (via aquaporins).

• Cannot Pass: Large, polar molecules, ions (require transport proteins).

Active Transport

Active transport moves substances against their concentration gradient using energy (ATP).

• Example: Sodium-potassium pump.

Isotonic Solutions

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

• Cells retain their normal shape in isotonic solutions.

Glycolysis

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

• Occurs in the cytoplasm.

• Produces pyruvate, ATP, and NADH.

Electron Carriers in Citric Acid Cycle

Electron carriers such as NAD+ and FAD collect electrons during the citric acid cycle.

• NADH and FADH2 transport electrons to the electron transport chain.

Plasma Membrane Structure

The plasma membrane consists of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

Tissues and Organ Systems

Types of Connective Tissues

Connective tissues support and connect other tissues.

• Loose Connective Tissue: Cushions organs.

• Dense Connective Tissue: Forms tendons and ligaments.

• Adipose Tissue: Stores fat.

• Cartilage: Provides flexible support.

• Bone: Rigid support and protection.

• Blood: Transports substances.

Locations of Tissue Types

• Epithelial Tissue: Covers surfaces, lines cavities (e.g., skin, lining of gut).

• Connective Tissue: Found throughout the body (e.g., tendons, fat, bone).

• Muscle Tissue: Found in muscles, heart, digestive tract.

• Nervous Tissue: Brain, spinal cord, nerves.

Muscle Type in the Stomach

The stomach contains smooth muscle, which contracts involuntarily to mix and propel food.

Types of Tissues and Their Functions

• Epithelial: Protection, absorption, secretion.

• Connective: Support, transport, storage.

• Muscle: Movement.

• Nervous: Communication, control.

Types of Cell Junctions

Cell junctions connect cells and facilitate communication.

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap Junctions: Allow passage of ions and small molecules.

Additional info: Academic context and definitions were added to expand brief review points into comprehensive study notes.