Domain of Life

Classification of Living Organisms

The domain of life categorizes all living organisms into three major groups based on cellular structure and genetic differences.

• Bacteria: Prokaryotic cells, lack a nucleus, found in diverse environments.

• Archaea: Prokaryotic cells, distinct from bacteria, often found in extreme environments.

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

Example: Humans belong to the domain Eukarya.

Cell Organelles

Names, Functions, and Shapes

Cell organelles are specialized structures within cells that perform distinct functions.

• Nucleus: Contains genetic material (DNA); controls cell activities; generally spherical.

• Mitochondria: Site of ATP production; oval-shaped; "powerhouse" of the cell.

• Endoplasmic Reticulum (ER): Network of membranes; rough ER (with ribosomes) synthesizes proteins; smooth ER synthesizes lipids.

• Golgi Apparatus: Stack of flattened sacs; modifies, sorts, and packages proteins.

• Lysosomes: Spherical vesicles; contain digestive enzymes; break down waste.

• Ribosomes: Small, round structures; synthesize proteins; found on ER or in cytoplasm.

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

• Cytoskeleton: Network of fibers; maintains cell shape and enables movement.

Example: The mitochondria generate most of the cell's energy through cellular respiration.

Hierarchy of Living Organisms

Levels of Biological Organization

Living organisms are organized in a hierarchical structure from simplest to most complex.

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

Example: Muscle tissue is made of muscle cells, which contain mitochondria and other organelles.

Cell Size and Surface Area

Relationship and Importance

The surface area-to-volume ratio affects cell efficiency in exchanging materials.

• Smaller cells have a higher surface area-to-volume ratio, allowing efficient nutrient and waste exchange.

• Larger cells may struggle with transport across the membrane.

Formula:

(for a cube, where a is the length of a side)

Example: Red blood cells are small to maximize surface area for gas exchange.

Microscopy

Types and Uses

Microscopes are essential tools for studying cells and tissues.

• Light Microscope: Uses light to view specimens; suitable for living cells.

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

• Scanning Electron Microscope (SEM): Views surface details.

• Transmission Electron Microscope (TEM): Views internal structures.

Example: TEM is used to study mitochondria structure.

Most Abundant Elements in Humans

Key Elements

Human bodies are composed primarily of a few elements.

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

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

Reductionism

Importance in Biology

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

• Helps understand biological processes at molecular and cellular levels.

• Allows for targeted research and medical interventions.

Example: Studying DNA to understand genetic diseases.

DNA

Importance and Function

DNA (deoxyribonucleic acid) is the molecule that stores genetic information.

• Directs cell activities and protein synthesis.

• Inherited from parents; determines traits.

Example: Mutations in DNA can lead to genetic disorders.

Types of Chemical Bonds

Ionic, Covalent, and Hydrogen Bonds

Chemical bonds hold atoms together in molecules.

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

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

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

Example: Water molecules are held together by hydrogen bonds.

Polarity

Polar vs. Nonpolar 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., O2).

Example: Lipids are nonpolar and form cell membranes.

Charged Elements

Interactions Between Ions

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

• Electrostatic attraction stabilizes compounds.

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

pH Levels

Acidic and Basic Substances

pH measures the concentration of hydrogen ions in a solution.

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Example: Human blood has a pH of about 7.4 (slightly basic).

Scientific Method

Steps in Scientific Inquiry

The scientific method is a systematic approach to research.

1. Observation

2. Hypothesis

3. Experiment

4. Data Collection

5. Analysis

6. Conclusion

Example: Testing the effect of a drug on cell growth.

Homeostasis

Maintaining Internal Balance

Homeostasis is the process by which organisms maintain stable internal conditions.

• Regulates temperature, pH, and other variables.

• Essential for survival and function.

Example: Sweating cools the body during exercise.

Elements vs. Molecules

Definitions and Differences

• Element: Pure substance made of one type of atom (e.g., O, C).

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

Example: Oxygen gas (O2) is a molecule of the element oxygen.

Characteristics of Living vs. Nonliving Things

Shared and Distinct Features

• Living: Growth, reproduction, metabolism, response to stimuli, homeostasis.

• Nonliving: May have structure, but lack biological processes.

Example: Rocks are nonliving; plants are living.

Radioisotope Technology

Importance in Biology

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

• Trace biochemical pathways.

• Diagnose diseases (e.g., PET scans).

Example: Radioactive iodine is used to study thyroid function.

Atomic Charge Changes

How Atoms Become Ions

Atoms change charge by gaining or losing electrons.

• Cation: Loses electrons; becomes positively charged.

• Anion: Gains electrons; becomes negatively charged.

Example: Sodium loses an electron to become Na+.

Diffusion

Process and Importance

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

• Passive process; no energy required.

• Essential for gas exchange and nutrient transport.

Example: Oxygen diffuses into blood in the lungs.

ATP Production and Electron Transport Chain

Protein Complexes Involved

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

• Electron carriers (NADH, FADH2) donate electrons.

• Proton gradient drives ATP synthesis.

Formula:

Example: ATP synthase uses energy from protons to make ATP.

Plasma Membrane Permeability

What Can and Cannot Pass

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

• Cannot Pass: Large, polar molecules; ions (without channels or transporters).

Example: Glucose requires a transporter to enter cells.

Active Transport

Mechanism and Function

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

• Requires protein pumps (e.g., sodium-potassium pump).

Formula:

(via Na/K pump)

Example: Nerve cells use active transport to maintain ion gradients.

Isotonic Solutions

Effects on Cells

An isotonic solution has equal solute concentration as the cell; cells retain their shape.

• No net movement of water.

Example: Saline solution is isotonic to human cells.

Glycolysis

Purpose and Process

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

• Occurs in cytoplasm.

• Produces pyruvate, ATP, and NADH.

Formula:

Example: Glycolysis provides energy for cells when oxygen is limited.

Electron Carriers in Citric Acid Cycle

Function and Source of Electrons

• NADH and FADH2 are electron carriers.

• Electrons are obtained from oxidation of substrates in the cycle.

Example: NAD+ accepts electrons to become NADH.

Plasma Membrane Structure

Components

• Phospholipid bilayer

• Proteins (channels, carriers, receptors)

• Cholesterol (stability)

• Carbohydrates (cell recognition)

Example: Membrane proteins facilitate transport.

Connective Tissues

Types and Functions

• Loose connective tissue: Supports and binds other tissues.

• Dense connective tissue: Provides strength (e.g., tendons).

• Adipose tissue: Stores fat.

• Cartilage: Flexible support.

• Bone: Rigid support.

• Blood: Transports substances.

Example: Bone tissue supports the body.

Locations of Tissue Types

Where Each Tissue Is Found

• Epithelial: Skin, lining of organs.

• Connective: Tendons, ligaments, fat, bone, blood.

• Muscle: Skeletal (attached to bones), cardiac (heart), smooth (walls of organs).

• Nervous: Brain, spinal cord, nerves.

Example: Smooth muscle is found in the stomach.

Muscle Type in the Stomach

Function and Characteristics

• Smooth muscle: Involuntary, non-striated; contracts to move food.

Example: Peristalsis in the stomach is driven by smooth muscle.

Tissue Types and Functions

Overview

• Epithelial: Protection, absorption, secretion.

• Connective: Support, transport, storage.

• Muscle: Movement.

• Nervous: Communication, control.

Example: Nervous tissue transmits signals.

Cell Junctions

Types and Functions

• Tight junctions: Seal cells together; prevent leakage.

• Desmosomes: Anchor cells; provide strength.

• Gap junctions: Allow communication between cells.

Example: Gap junctions in heart muscle allow coordinated contraction.