IDENTICAL TWINS TWO INDIVIDUALS PRODUCED WHEN ONE EGG IS FERTILIZED BY ONE SPERM. THE EMBRYO LATER SPLITS IN TWO. IMMUNITY THE ABILITY OF THE BODY, EITHER NATURAL OR ACQUIRED, TO RESIST A GIVEN DISEASE. IMPLANTATION THE PROCESS BY WHICH THE EMBRYO (IN THE GASTRULA STAGE) ATTACHES TO THE WALL OF THE UTERUS. INPULSE A REGION OF ELECTROCHEMICAL ACTIVITYTHAT TRAVELS ALONG A NERVE CELL. INCOMPLETE DOMINANCE OCCURS WHEN THERE ARE TWO DOMINANT GENES FOR A TRAIT AND BOTH ARE EX- PRESSED. PHENOTYPE IS INTERMEDIATE. INCOMPLETE PROTEIN A PROTEIN THAT DOES NOT CONTAIN ALL THE ESSENTIAL AMINO ACIDS NEEDED BY HUMANS. TYPICAL OF PLANT PROTEINS. INDEPENDENT ASSORTMENT THE PRINCIPLE THAT DIFFERENT ALLELESARE SEPARATED INTO DIFFERENT GAMETESBY MEIOSIS (UNLESS LINKED). INGESTION TO TAKE IN (AS FOOD). TO EAT. INHALATION TAKING AIR INTO THE LUNGS. INORGANIC REFERRING TO THINGS WHICH ARE NOT AND NEVER WERE ALIVE. COMPOUNDS NOT CONTAINING CARBON ATOMS. INORGANIC COMPOUND A COMPOUND (CHEMICAL) WHICH DOES NOTCONTAIN CARBON; WATER, FOR EXAMPLE. INSTINCT AN INBORN PATTERN OF BEHAVIOR. INSULIN A HORMONE PRODUCED BY ISLET CELLS INTHE PANCREAS. PROMOTES CONVERSION OFGLUCOSE TO GLYCOGEN IN THE LIVER. INTERCELLULAR FLUID THE FLUID FOUND IN BETWEEN CELLS. MOSTLY PLASMA THAT HAS LEAKED FROM CAPILLARIES. RETURNED AS LYMPH. INTERNAL FERTILIZATION FERTILIZATION (UNION OF SPERM AND EGG) WHICH TAKES PLACE INSIDE THE BODY OF THE FEMALE. INTERNEURON A NEURON (NERVE CELL) WHICH RELAYS AN IMPULSE FROM A SENSORY NERVE TO AMOTOR NERVE IN A REFLEX PATHWAY. INTERPHASE THE PHASE IN THE CELL CYCLE WHEN THECELL IS NOT IN THE PROCESS OF DIVID-ING. IN BETWEEN CELL DIVISIONS. INVOLUNTARY NOT UNDER CONSCIOUS CONTROL. SEE INVOLUNTARY MUSCLE. INVOLUNTARY MUSCLE ALSO CALLED SMOOTH MUSCLE. NOT UNDERCONSCIOUS CONTROL. FOUND IN THE DI- GESTIVE SYSTEM AND ARTERIAL WALLS. ISLET SEE ISLETS OF LANGERHANS ISLET CELLS SEE ISLETS OF LANGERHANS ISLETS OF LANGERHANS CLUSTERS OF CELLS IN THE PANCREAS WHICH SECRETE THE HORMONES INSULIN AND GLUCAGON. ISLANDS OF LANGERHANS CLUSTERS OF CELLS IN THE PANCREAS WHICH SECRETE THE HORMONES INSULIN AND GLUCAGON. ISOLATION GEOGRAPHIC SEPARATION OF MEMBERS OF A SPECIES ALLOWING EACH GROUP TO EVOLVE SEPARATELY INTO NEW SPECIES. ISOTOPE A TYPE OF ATOM (OFTEN RADIOACTIVE) WHICH CAN BE USED TO TRACE THE PATH OF SUBSTANCES IN LIVING SYSTEMS. ISOTONIC A TERM DESCRIBING TWO SOLUTIONS WHICH HAVE THE SAME CONCENTRATION OF SOLUTES. EQUAL CONCENTRATIONS. JOINT THE JUNCTION OF TWO BONES. A MOVABLEPIVOT POINT IN THE SKELETON. JUVENILE HORMONE A HORMONE PRODUCED BY THE LARVAL STAGE OF MANY INSECTS WHICH PREVENTSMETAMORPHOSIS INTO THE ADULT FORM. KARYOTYPE A PHOTOGRAPH OF AN INDIVIDUALS CHRO-MOSOMES WHICH PERMITS DETECTIONS OF CHROMOSOMAL ABNORMALITIES. KARYOTYPING THE PROCESS OF PHOTOGRAPHING AND STUDYING THE CHROMOSOMES OF AN INDI-VIDUAL TO DETECT ANY ABNORMALITIES. KIDNEY (USUALLY PAIRED) ORGAN WHICH REMOVESWASTES AND EXCESS WATER FROM THE BLOOD. KINGDOM THE LARGEST CATEGORY IN THE MODERN SYSTEM OF CLASSIFICATION. THERE ARE FIVE MAJOR KINGDOMS.