Domain of Life

Classification of Living Organisms

The domain of life is the highest taxonomic rank in the classification of organisms. There are three domains:

• Bacteria: Single-celled prokaryotes without a nucleus.

• Archaea: Single-celled prokaryotes, distinct from bacteria, often found in extreme environments.

• Eukarya: Organisms with eukaryotic cells, including protists, fungi, plants, and animals.

Example: Humans belong to the domain Eukarya.

Cell Organelles: Names, Functions, and Shapes

Major Cell Organelles

• Nucleus: Contains genetic material (DNA); usually spherical.

• Mitochondria: Site of ATP production; oval-shaped with inner folds (cristae).

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

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

• Lysosomes: Contain digestive enzymes; spherical vesicles.

• Ribosomes: Sites of protein synthesis; small, round structures.

• Plasma Membrane: Phospholipid bilayer; controls entry and exit of substances.

• Cytoskeleton: Network of protein fibers; provides structural support.

Example: The mitochondrion is often called the "powerhouse of the cell."

Hierarchy of Living Organisms

Levels of Biological Organization

• Atom

• Molecule

• Organelle

• Cell

• Tissue

• Organ

• Organ System

• Organism

• Population

• Community

• Ecosystem

• Biosphere

Example: Muscle tissue is made of muscle cells working together.

Cell Size and Surface Area

Relationship Between Cell Size and Surface Area

• As a cell increases in size, its volume grows faster than its surface area.

• This limits the efficiency of material exchange with the environment.

Formula:

Key Point: Smaller cells have a higher surface area-to-volume ratio, which is more efficient for exchange.

Microscopy Types and Uses

Types of Microscopy

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

• Transmission Electron Microscopy (TEM): Used for viewing internal cell structures at high resolution.

• Scanning Electron Microscopy (SEM): Used for viewing cell surfaces in 3D.

Example: TEM can reveal the internal structure of mitochondria.

Most Abundant Elements in Humans

Key Elements

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

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

Reductionism

Importance in Biology

• Reductionism is the approach of studying complex systems by breaking them down into simpler components.

• Helps in understanding the function of individual parts of biological systems.

Example: Studying the function of a single enzyme to understand metabolism.

Importance of DNA

Role of DNA

• DNA stores genetic information necessary for the development, functioning, and reproduction of organisms.

• It is the blueprint for protein synthesis.

Example: Mutations in DNA can lead to genetic disorders.

Chemical Bonds

Types of Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another.

• Covalent Bonds: Formed when atoms share electrons.

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

Example: Water molecules are held together by hydrogen bonds.

Polarity of Molecules

Polar vs. Nonpolar Molecules

• Polar Molecules: Have unequal sharing of electrons, resulting in partial charges (e.g., water).

• Nonpolar Molecules: Have equal sharing of electrons, no partial charges (e.g., oxygen gas).

Key Point: Polarity affects solubility and interactions with other molecules.

Interactions of Charged Elements

Electrostatic Attraction

• Negatively charged elements (anions) attract positively charged elements (cations) to form ionic bonds.

Example: Sodium (Na+) and chloride (Cl-) form sodium chloride (NaCl).

pH Levels: Acids and Bases

Understanding pH

• pH is a measure of hydrogen ion concentration.

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula:

The Scientific Method

Steps in Order

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Peer Review/Publication

Homeostasis

Definition and Importance

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

• Essential for normal cell function and survival.

Example: Regulation of body temperature in humans.

Elements vs. Molecules

Key Differences

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

• Molecule: Two or more atoms bonded together (can be the same or different elements, e.g., H2O).

Characteristics of Living vs. Nonliving Things

Shared and Distinct Features

• Living things: Composed of cells, grow, reproduce, respond to stimuli, maintain homeostasis, and evolve.

• Nonliving things: Do not exhibit all characteristics of life.

Radioisotope Technology

Importance in Biology

• Radioisotopes are used in medical imaging, cancer treatment, and as tracers in biochemical research.

Example: PET scans use radioisotopes to detect metabolic activity.

Changing Atomic Charges

Ion Formation

• Atoms can gain or lose electrons to become ions (charged particles).

• Losing electrons: Forms cations (positive charge).

• Gaining electrons: Forms anions (negative charge).

Diffusion

Process and Importance

• Diffusion is the movement of molecules from an area of higher concentration to lower concentration.

• It is a passive process (does not require energy).

Example: Oxygen diffuses into cells from the bloodstream.

ATP Production and the Electron Transport Chain

Protein Complex Involved

• Most ATP is produced by ATP synthase during the electron transport chain in mitochondria.

Formula:

Plasma Membrane Permeability

What Can and Cannot Pass

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

• Large or charged molecules (e.g., ions, glucose) require transport proteins.

Active Transport

Definition and Function

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

• Example: Sodium-potassium pump in nerve cells.

Isotonic Solutions

Effect on Cells

• An isotonic solution has the same solute concentration as the cell.

• No net movement of water; cell shape remains unchanged.

Glycolysis

Purpose and Process

• Glycolysis breaks down glucose into pyruvate, producing ATP and NADH.

• Occurs in the cytoplasm; does not require oxygen.

Formula:

Electron Carriers in the Citric Acid Cycle

Types and Sources

• NADH and FADH2 are the main electron carriers.

• They gain electrons during oxidation of substrates in the citric acid cycle.

Plasma Membrane Structure

Components

• Phospholipid bilayer

• Proteins (integral and peripheral)

• Cholesterol

• Carbohydrate chains (glycoproteins and glycolipids)

Connective Tissues

Types and Locations

Muscle Type in the Stomach

Type and Function

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

Tissue Types and Functions

Major Tissue Types

Cell Junctions

Types and Functions

• Tight Junctions: Seal cells together to prevent leakage (e.g., in the gut lining).

• Desmosomes: Anchor cells together, providing mechanical strength (e.g., skin).

• Gap Junctions: Allow communication between cells via small molecules and ions (e.g., heart muscle).

Additional info: Some explanations and tables were expanded for academic completeness and clarity.