Biology

Cell Theory

Basic theory that explains the importance and role of cells in living organisms.

Cell

The basic structural and functional unit of life.

3 Main Statements of Cell Theory

All living organisms are composed of one or more cells; the cell is the basic structural and functional unit of life; all cells come from pre-existing cells.

Unicellular

An organism made of one cell.

Multicellular

An organism made of many cells.

Robert Hooke

Scientist who observed cork in 1665 and was the first to use the term "cell."

Antonie van Leeuwenhoek

Scientist who was the first to observe living cells and microorganisms.

Matthias Schleiden

German botanist who concluded that all plants are made of cells.

Theodor Schwann

German zoologist who concluded that all animals are made of cells.

Rudolf Virchow

Scientist who proposed that all cells come from pre-existing cells.

Prokaryotic Cell

A cell without a true nucleus or membrane-bound organelles.

Nucleoid Region

The region where DNA is located in a prokaryotic cell.

Eukaryotic Cell

A cell with a true nucleus and membrane-bound organelles.

Nucleus

The control center of the cell that contains DNA.

Nucleolus

The structure inside the nucleus that produces rRNA and helps make ribosomes.

Mitochondria

The organelle that produces ATP and is the site of cellular respiration.

Ribosomes

The site of protein synthesis.

Rough ER

The endoplasmic reticulum with ribosomes that produces and processes proteins.

Smooth ER

The endoplasmic reticulum without ribosomes that produces lipids and helps with detoxification.

Golgi Apparatus

Modifies, sorts, and packages proteins and lipids for transport.

Centrioles

Structures that help organize structures involved in cell division.

Lysosome

Contains digestive enzymes that break down waste and damaged organelles.

Cytoskeleton

A network of protein fibers that maintains cell shape and helps with movement and organization.

Peroxisomes

Break down fatty acids and harmful substances and help protect the cell from toxic by-products.

Chloroplast

The organelle where photosynthesis occurs and which contains chlorophyll.

Cytoplasm

Jelly-like material that holds organelles and is the site of many chemical reactions.

Vacuole

Stores water, nutrients, and waste.

Cell Membrane

A selectively permeable boundary that controls what enters and leaves the cell.

Cell Wall

Provides support, protection, and shape; in plants it is mainly made of cellulose.

Plant Cell

A eukaryotic cell found in plants that has a cell wall, chloroplasts, and usually a large central vacuole.

Animal Cell

A eukaryotic cell found in animals that does not have a cell wall or chloroplast.

Large Central Vacuole

A large structure in plant cells that stores water, nutrients, dissolved substances, and wastes and helps maintain turgor pressure.

Turgor Pressure

Pressure that helps keep plant cells firm and supports the plant.

Structures Found in Both Plant and Animal Cells

Nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, and cytoplasm.

Importance of Cell Wall

Provides plant cells with strength and rigidity and helps prevent excessive expansion when water enters.

Importance of Chloroplasts

Allows plants to capture light energy using chlorophyll for photosynthesis.

Phospholipid Bilayer

The two layers of phospholipids that form the main barrier of the cell membrane.

Hydrophilic Heads

The water-attracting heads of phospholipids that face watery environments.

Hydrophobic Tails

The water-repelling tails of phospholipids that face inward.

Membrane Proteins

Proteins that help transport substances and allow cell communication and recognition.

Cholesterol

A molecule in the membrane that helps regulate fluidity and stability.

Homeostasis

Maintenance of a stable internal environment.

Passive Transport

Movement of substances down their concentration gradient without requiring cellular energy.

Active Transport

Movement of substances against their concentration gradient using energy, usually ATP.

Diffusion

Movement of particles from an area of high concentration to low concentration.

Concentration Gradient

The difference in particle concentration between two areas.

Dynamic Equilibrium

A state where particles are evenly distributed and continue moving randomly.

Factors Affecting Diffusion

Temperature, concentration difference, surface area, distance, and particle size.

Osmosis

Movement of water molecules through a selectively permeable membrane from low solute concentration to high solute concentration.

Hypotonic

Condition where more water enters the cell, causing it to swell.

Hypertonic

Condition where water leaves the cell, causing it to shrink.

Isotonic

Condition where water moves in and out at equal rates and the cell stays about the same size.

Facilitated Diffusion

Passive transport that moves substances down their concentration gradient with the help of transport proteins.

Sodium-Potassium Pump

A transport protein that uses ATP to move substances against their concentration gradient.

Cellular Respiration

The process where cells break down glucose to release energy and produce ATP.

Overall Cellular Respiration

Glucose + Oxygen → Carbon dioxide + Water + ATP.

Glycolysis

The stage of cellular respiration that occurs in the cytoplasm and breaks glucose into pyruvate.

Krebs Cycle

The stage that occurs in the mitochondrial matrix and releases CO₂ and produces electron carriers.

Electron Transport Chain (ETC)

The stage that occurs in the inner mitochondrial membrane and produces most ATP.

Aerobic Respiration

Respiration that requires oxygen and produces much more ATP.

Anaerobic Respiration/Fermentation

Energy production that occurs without oxygen and produces much less ATP.

Photosynthesis

The process where plants, algae, and some bacteria use light energy to make food.

Photosynthesis Equation

Carbon dioxide + water → glucose + oxygen.

Main Requirements of Photosynthesis

Sunlight, water, carbon dioxide, and chlorophyll.

Main Products of Photosynthesis

Glucose and oxygen.

Light-Dependent Reactions

Photosynthesis reactions in the thylakoid membranes that capture light energy and produce ATP and NADPH.

Calvin Cycle

The light-independent stage that occurs in the stroma and uses CO₂, ATP, and NADPH to build sugars.

DNA

Genetic material that stores instructions for growth, development, and cell functions.

DNA Structure

A double-stranded structure called a double helix.

DNA Sugar

Deoxyribose.

DNA Bases

Adenine, Thymine, Cytosine, and Guanine.

DNA Base Pairing

A pairs with T; C pairs with G.

RNA

A molecule that helps use genetic information to make proteins.

RNA Structure

Usually single-stranded.

RNA Sugar

Ribose.

RNA Bases

Adenine, Uracil, Cytosine, and Guanine.

RNA Base Pairing

A pairs with U; C pairs with G.

mRNA

Messenger RNA that carries genetic instructions from DNA to the ribosome.

tRNA

Transfer RNA that carries amino acids to the ribosome during protein synthesis.

rRNA

Ribosomal RNA that forms part of the ribosome and helps in protein synthesis.

Gene

A segment of DNA containing instructions for making a functional product, usually a protein.

Chromosome

A structure made of DNA tightly coiled around proteins that contains many genes.

Relationship Between DNA, Genes, and Chromosomes

DNA contains genetic information; a gene is a specific segment of DNA; many genes are found on a chromosome.

Human Chromosomes

Humans normally have 46 chromosomes arranged in 23 pairs.

Homologous Chromosomes

A pair of chromosomes similar in size and structure that carry the same types of genes at the same locations.

Mendelian Genetics

The study of how traits are passed from parents to offspring based on the work of Gregor Mendel.

Gregor Mendel

Scientist known as the Father of Genetics who studied inheritance using pea plants.

Allele

A different form of a gene.

Dominant Allele

An allele expressed when at least one copy is present.

Recessive Allele

An allele expressed only when two copies are present.

Genotype

The genetic combination or makeup of alleles.

Phenotype

The observable trait or characteristic of an organism.

Homozygous

Has two identical alleles.

Heterozygous

Has two different alleles.

Law of Dominance

A dominant allele can mask the effect of a recessive allele.

Law of Segregation

Alleles separate during the formation of gametes, and each gamete receives one allele.

Law of Independent Assortment

Genes for different traits can be inherited independently of each other.

Monohybrid Cross

A genetic cross involving one trait.

Genotypic Ratio

For Tt × Tt, the ratio is 1 TT : 2 Tt : 1 tt.

Phenotypic Ratio

For Tt × Tt, the ratio is 3 Dominant : 1 Recessive.