Human Perspectives: ATAR Units 1 & 2 - Human Biology Vocabulary

Essential vocabulary terms and definitions covering scientific method, cellular biology, human physiology, organ systems, genetics, and reproduction from ATAR Human Biology.

Independent variable

The factor that is being investigated and is deliberately changed in an experiment to determine how it affects the results; also known as the experimental or manipulated variable.

Controlled variables

The factors that are kept constant and identical for both the experimental and control groups during an investigation to ensure a fair test.

Fluid mosaic model

The accepted model of cell membrane structure, describing a bilayer of phospholipid molecules with hydrophilic heads on the outside and hydrophobic tails on the inside, with shifting proteins and cholesterol embedded throughout.

Facilitated diffusion

A passive transport process in which substances move along their concentration gradient across a cell membrane through channel proteins or carrier proteins without the expenditure of cellular energy ($\text{ATP}$).

Active transport

The energy-requiring process wherein carrier proteins transport substances across a cell membrane against the concentration gradient, utilising energy in the form of $\text{ATP}$.

Osmosis

A special form of diffusion defined as the net movement of solvent (water) molecules through a differentially permeable membrane from a region of higher water concentration to a region of lower water concentration.

Catabolism

Metabolic reactions in which large, complex organic molecules are broken down into smaller, simpler molecules, resulting in the release of energy.

Anabolism

Metabolic reactions in which small, simple molecules are combined to form larger, more complex molecules; these reactions require an input of energy.

Activation energy

The minimum amount of energy required to break existing chemical bonds in reactant molecules to initiate a chemical reaction.

Glycolysis

The initial anaerobic stage of cellular respiration occurring in the cytosol, in which a single molecule of glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) is broken down through ten steps into two molecules of pyruvate, yielding a net gain of $2\,\text{ATP}$.

Aerobic respiration

The complete breakdown of pyruvate in the presence of oxygen within the mitochondria, passing through the citric acid cycle (Krebs cycle) and electron transport system to produce $\text{CO}_2$, $\text{H}_2\text{O}$, and up to $36\,\text{ATP}$ (yielding up to $38\,\text{ATP}$ total per glucose).

Alveoli

Microscopic, thin-walled air sacs in the lungs surrounded by capillary networks that serve as the primary functional units for gas exchange between alveolar air and circulating blood.

Inspiration

The active process of drawing air into the lungs, brought about by the contraction of the diaphragm (which flattens) and external intercostal muscles (which lift the ribs upwards and outwards), increasing thoracic volume and decreasing pulmonary air pressure below atmospheric pressure.

Erythrocytes

Biconcave, anucleated formed elements of blood containing haemoglobin that function to transport oxygen from the lungs to body tissues and account for approximately $40\text{--}45\%$ of blood volume (haematocrit).

Systole

The contraction phase of the cardiac cycle during which heart muscle contracts to pump blood out of the chambers (atrial systole forces blood into ventricles; ventricular systole forces blood into arteries).

Diastole

The relaxation phase of the cardiac cycle during which heart muscle relaxes and the heart chambers fill with blood.

Peristalsis

Coordinated, successive waves of involuntary contraction of circular smooth muscle behind a food bolus or chyme, paired with relaxation ahead of it, that propel contents along the alimentary canal.

Villi

Small, finger-like projections of the mucous membrane lining the small intestine that increase surface area for nutrient absorption, each containing blood capillaries and a central lacteal.

Deamination

The biochemical removal of an amino group ($\text{NH}_2$) from an excess amino acid in the liver, leading to the conversion of the amino group into highly toxic ammonia ($\text{NH}_3$) and subsequently into non-toxic urea.

Nephron

The microscopic structural and functional unit of the kidney, consisting of a renal corpuscle (glomerulus and glomerular capsule) and a renal tubule, responsible for urine production.

Glomerular filtration

The passive process occurring in the renal corpuscle where high blood pressure forces water, dissolved ions, and small molecules across capillary membranes from the glomerulus into the glomerular capsule to create filtrate.

Tubular secretion

The active or passive transport of substances, such as potassium ions, hydrogen ions, creatinine, and drugs, directly from peritubular capillaries into the renal tubule filtrate to regulate blood and urine pH.

Sarcomere

The functional contractile unit of a myofibril in striated muscle tissue, defined as the region between two adjacent Z lines, comprising overlapping thin actin and thick myosin protein filaments.

Antagonist

A muscle that yields and relaxes to produce an action opposite to that of the prime mover (agonist), working in an antagonistic pair to allow reversible movements around a joint.

Osteon

The fundamental microscopic unit of compact bone (also known as a Haversian system), consisting of a central canal containing blood vessels surrounded by concentric rings of matrix called lamellae and lacunae containing osteocytes.

Synovial joint

A freely movable joint characterised by a fluid-filled synovial cavity surrounded by an articular capsule and articular cartilage covering the articulating bone ends.

Transcription

The process occurring in the cell nucleus where the genetic instructions on the DNA template strand of a gene are copied into a complementary single strand of messenger RNA (mRNA) by the enzyme RNA polymerase.

Translation

The synthesis of a polypeptide chain at a ribosome in the cytosol, where the codon sequence of an mRNA molecule is decoded using complementary anticodons on tRNA molecules to assemble amino acids in the specified order.

Epigenetics

The study of heritable changes in gene expression and cellular phenotype caused by factors other than alterations in the underlying DNA nucleotide sequence, such as histone acetylation and DNA methylation.

Mitosis

The division of a single cell nucleus into two genetically identical daughter nuclei, each retaining the original diploid chromosome number ($2n = 46$ in humans), essential for growth, tissue repair, and replacement.

Totipotent stem cells

Stem cells produced during the first few divisions of a zygote that retain the potential to differentiate into any cell type required for complete embryonic development, including the embryo and its extraembryonic membranes.

Meiosis

A specialised form of two-stage cell division occurring in gonads that produces four genetically unique haploid ($n = 23$) gametes from a single diploid ($2n = 46$) germ cell.

Crossing over

The physical exchange of non-sister chromatid segments between homologous chromosomes at chiasmata during prophase I of meiosis, resulting in genetic recombination of alleles.

Non-disjunction

The failure of homologous chromosomes to separate during meiosis I, or sister chromatids during meiosis II, causing daughter gametes to carry an abnormal number of chromosomes ($24$ or $22$).

Spermatogenesis

The continuous process within the seminiferous tubules of the testes where diploid spermatogonia undergo mitosis, meiosis, and maturation to produce four viable, mobile haploid spermatozoa.

Oogenesis

The formation and maturation of female gametes within the ovaries, where a diploid primary oocyte undergoes meiosis with unequal cytokinesis to yield one functional haploid ovum and up to three non-functional polar bodies.

Corpus luteum

The temporary endocrine structure formed from the ruptured ovarian follicle following ovulation; it secretes high amounts of progesterone and oestrogen to maintain the endometrium.

Blastocyst

A stage of early embryonic development reached approximately six days post-fertilisation, consisting of a hollow sphere of outer cells, a fluid-filled cavity, and an inner cell mass destined to form the embryo.

Primary germ layers

The three fundamental embryonic tissue layers—ectoderm, mesoderm, and endoderm—formed by the inner cell mass of the blastocyst, from which all tissues and organ systems differentiate.

Ductus arteriosus

A foetal blood vessel linking the pulmonary artery directly to the aorta, bypassing the high vascular resistance of the collapsed, non-functional foetal lungs.

Foramen ovale

An anatomical opening in the interatrial septum of the foetal heart that allows highly oxygenated blood from the placenta to flow directly from the right atrium into the left atrium.

Teratogen

Any environmental, chemical, or biological agent—such as alcohol, thalidomide, or rubella—that causes physical abnormalities and congenital defects in a developing embryo or foetus.

Intrauterine device (IUD)

A small T-shaped plastic or copper device inserted into the uterine cavity by a doctor to prevent pregnancy by impeding sperm movement, altering the endometrial lining, or releasing levonorgestrel.

In vitro fertilisation (IVF)

An assisted reproductive technology where mature eggs are surgically retrieved from the ovaries, mixed and fertilised with sperm outside the body in a laboratory dish, and subsequently transferred into the uterus as embryos.

Allele

An alternative or variant form of a specific gene situated at a corresponding locus on a homologous chromosome.

Co-dominance

A genetic inheritance pattern in which two alternative alleles are equally dominant, such that both alleles are completely expressed in the phenotype of a heterozygous individual (e.g. blood group AB, MN blood group).

Gel electrophoresis

A laboratory technique in which negatively charged DNA fragments are separated through a gel matrix using an electric field based on their molecular size, producing a characteristic banding pattern known as a DNA profile.