Comprehensive Biology: Cell Biology, Physiology, and Homeostasis

A comprehensive vocabulary review of core biological concepts spanning cellular structures and organelles, life processes, stem cell differentiation, organ systems, neuroendocrine regulation, homeostasis, thermoregulation, and related chemical properties.

Cell

The smallest unit of life; the basic structural and functional unit of living organisms that carries out life processes.

Cell theory

All living things are made of cells; cells are the basic unit of life; all cells come from pre-existing cells.

Microscope

An instrument used to view objects too small to see clearly with the unaided eye.

Magnification

How many times larger an image appears than the actual object.

Scale bar

A line on an image that represents a known real-world distance.

Resolution

The ability to distinguish two close points as separate; higher resolution shows more detail.

Electron microscope

A microscope that uses a beam of electrons to produce highly detailed images.

DNA

Deoxyribonucleic acid; the molecule that stores genetic information.

Cytoplasm

The cell contents between the plasma membrane and nucleus, including cytosol and organelles.

Plasma membrane

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

Nucleoid region

The area in a prokaryotic cell where its DNA is located; it is not enclosed by a membrane.

Prokaryote

An organism whose cells lack a nucleus and other membrane-bound organelles.

Eukaryote

An organism whose cells contain a nucleus and membrane-bound organelles.

Metabolism

All chemical reactions occurring in a cell or organism.

Ribosome

A structure that makes proteins by translating messenger RNA.

Nucleus

A membrane-bound organelle that contains most of a eukaryotic cell's DNA.

Chromosome

A DNA molecule packaged with proteins that carries genes.

Sister chromatids

Two identical copies of a replicated chromosome joined at the centromere.

Histone protein

A protein around which DNA wraps to help package and organize it.

Organelle

A specialized structure inside a cell that performs a particular function.

Mitochondrion

An organelle where aerobic cellular respiration produces most of a cell's ATP.

Rough endoplasmic reticulum

Membrane network covered with ribosomes; makes and processes proteins for secretion or membranes.

Smooth endoplasmic reticulum

Membrane network that makes lipids, detoxifies substances, and stores calcium in some cells.

Golgi apparatus

Organelle that modifies, sorts, and packages proteins and lipids into vesicles.

Vacuole

A membrane-bound sac used for storage and, in plants, maintaining turgor pressure.

Lysosome

An enzyme-filled organelle that digests waste, macromolecules, and worn-out cell parts.

Cytoskeleton

A network of protein fibers that supports cell shape, movement, and internal transport.

Unicellular

Made of a single cell that carries out all life functions.

Multicellular

Made of many cells, often specialized to perform different functions.

Homeostasis

Maintaining relatively stable internal conditions despite external changes.

Nutrition

Taking in or making nutrients needed for energy, growth, and repair.

Movement

A change in position of an organism or a part of it.

Growth

A lasting increase in size or cell number.

Response to stimuli

Detecting and reacting to changes in the internal or external environment.

Reproduction

The process by which organisms produce offspring.

Plastids

Plant and algal organelles involved in storage or pigment-related functions; chloroplasts are one type.

Chloroplasts

Organelles in plants and algae where photosynthesis converts light energy into chemical energy.

Centrioles

Cylindrical structures that help organize microtubules and the spindle in many animal cells.

Fungal hyphae

Long, branching filaments that make up the body of many fungi.

Aseptate

Describes fungal hyphae without cross-walls (septa), often containing many nuclei in a shared cytoplasm.

Cell wall

A rigid outer layer that supports and protects cells; composition varies by organism.

Microvilli

Tiny membrane projections that increase a cell's surface area for absorption.

Sap vacuole

A large plant-cell vacuole containing cell sap; stores substances and helps maintain turgor.

Flagellum

A long, whip-like structure that propels a cell or moves fluid.

Cilia

Short, hair-like projections that move cells or sweep substances across cell surfaces.

Cellulose

A strong polysaccharide that forms the main structural component of plant cell walls.

Peptidoglycan

A mesh-like polymer of sugars and peptides that strengthens bacterial cell walls.

Pilus

A short, hair-like bacterial structure used for attachment or, in some cases, DNA transfer.

Gametes

Haploid reproductive cells that fuse during fertilization.

Sperm

The male gamete; typically small and motile.

Egg (Ovum)

The female gamete; typically large and contains nutrients and cytoplasm.

Fertilization

Fusion of the nuclei of two haploid gametes to form a diploid cell.

Zygote

The diploid cell formed when two gametes fuse.

Stem cell

An undifferentiated cell that can self-renew and develop into specialized cell types.

Totipotent

Able to form all cell types, including extraembryonic tissues needed for a whole organism.

Pluripotent

Able to form nearly all body cell types, but not a whole organism on its own.

Multipotent

Able to form a limited range of related cell types.

Embryonic stem cells

Pluripotent stem cells from an early embryo.

Adult stem cells

Stem cells found in developed tissues that maintain and repair those tissues.

Specialized cells

Cells with structures and features adapted to perform particular functions.

Cell differentiation

The process by which a cell develops specific structures and functions.

Morphogens

Signaling substances whose concentration differences help guide cell fate and tissue patterning.

Stem cell niche

The local environment that regulates stem-cell survival, self-renewal, and differentiation.

Neurons

Nerve cells that receive and transmit information using electrical and chemical signals.

Striated muscle cells

Muscle cells with a striped appearance from organized contractile proteins; skeletal and cardiac muscle are striated.

Scientific model

A simplified representation used to explain, test, or predict aspects of a real system.

Erythrocytes

Red blood cells that transport oxygen using hemoglobin.

Proximal convoluted tubule

A nephron segment that reabsorbs most filtered water, ions, glucose, and amino acids.

Nephron

The kidney's functional unit that filters blood and forms urine.

Tissues

Groups of similar cells working together to perform a function.

Organs

Structures made of multiple tissue types working together for specific functions.

Organ systems

Groups of organs that work together to carry out major body functions.

Emergent properties

New characteristics that arise from interactions among parts of a system.

Nervous system

System of neurons and supporting cells that rapidly coordinates responses using electrical and chemical signals.

Endocrine system

Glands and tissues that release hormones into the blood to regulate body processes.

Blood plasma

The liquid part of blood that carries cells, nutrients, hormones, proteins, and wastes.

Effector

A muscle or gland that carries out a response to a signal.

Circadian rhythms

Internal cycles of about 24 hours that regulate processes such as sleep and body temperature.

Melatonin

A hormone from the pineal gland that helps signal biological night and regulate sleep timing.

Pineal gland

A small endocrine gland in the brain that secretes melatonin.

Epinephrine / Adrenaline

A hormone that prepares the body for rapid action, increasing heart rate and mobilizing energy.

Adrenal glands

Endocrine glands above the kidneys that release hormones including adrenaline and cortisol.

Baroreceptors

Receptors that detect changes in blood pressure by sensing stretch in blood vessel walls.

Chemoreceptors

Receptors that detect chemical changes, such as blood carbon dioxide, oxygen, or pH.

pH

A measure of how acidic or basic a solution is, related to hydrogen-ion concentration.

Ventilation

Movement of air into and out of the lungs; breathing.

Digestive system

Organs that ingest food, break it down, absorb nutrients, and eliminate undigested material.

Peristalsis

Wave-like smooth-muscle contractions that move food through the digestive tract.

Autonomic nervous system

The part of the nervous system that controls involuntary functions such as heart rate and digestion.

Enteric nervous system

A network of neurons in the digestive tract that helps control gut movement and secretion.

Swallowing

The process of moving food or liquid from the mouth through the pharynx into the esophagus.

Egestion

Removal of undigested material from the digestive tract as feces.

Voluntary control

Control of an action through conscious choice, such as intentionally moving a skeletal muscle.

Involuntary control

Control of a process without conscious direction, such as heart rate or peristalsis.

Negative feedback

A control mechanism in which a change triggers responses that counteract that change.

Positive feedback

A control mechanism in which a change triggers responses that amplify the change until an endpoint.

Hormones

Chemical messengers released by cells or glands that affect target cells with matching receptors.

Alpha cells of the Islets of Langerhans

Pancreatic cells that release glucagon when blood glucose is low.

Beta cells of the Islets of Langerhans

Pancreatic cells that release insulin when blood glucose is high.

Insulin

A hormone that lowers blood glucose by promoting uptake and storage of glucose.