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Biology Definitions
| Question | Answer |
|---|---|
| Abiotic factors | These are non-living environmental factors that effect the number of organisms in an ecosystem. |
| Abscisic Acid | A plant hormone that inhibits growth and it is also responsible for leaf fall and dormancy in seeds. |
| Absorption | The process by which the products of digestion are transferred into the circulatory system, letting them reach the cells. |
| Acetylcholine | A chemical transmitter that relays messages across synapses between nerve cells. |
| Active Site | Temporary point of attachment for a substrate on the surface of an enzyme before it is converted into products. |
| Active Transport | the use of energy to transport molecules against a concentration gradient (from low concentrations to high concentrations). |
| Adaptation | Charles Darwin's theory that animals will adapt to their environment in order to survive. |
| Adenosine Diphosphate (ADP) | Lower energy form of ATP, having two (instead of the three in ATP) phosphate groups attached to the adenine base and ribose sugar. |
| Adenosine Triphosphate (ATP) | An energy-rich molecule. It supplies energy for cell reactions. It consists of a nucleotide (with ribose sugar) with three phosphate groups. |
| Alleles | Different forms of the same gene. |
| Allergens | Antigens that cause an allergic reaction. |
| Alveoli | Tiny, thin-walled, inflatable sacs in the lungs where gaseous exchange occurs. |
| Amensalism | A symbiotic relationship in which members of one population inhibit the growth of another population without being affected. |
| Amino Acids | The subunits from which proteins are made. Each amino acid consists of an amine group and a carboxyl acid group, and differs from other amino acids by the composition of an R group. |
| Amniocentesis | A method of prenatal testing in which amniotic fluid is withdrawn from the uterus through a needle. The fluid and the fetal cells it contains are analyzed to detect biochemical or chromosomal disorders. |
| Anabolic Reactions | These are reactions which convert small molecules into larger ones. |
| Anaerobic | Refers to organisms that are not dependent on oxygen for respiration. |
| Analogous Structures | Body parts that serve the same function in different organisms, but differ in structure and embryological development e.g. the wings of insects and birds. |
| Animalia | Animal Kingdom |
| Antagonistic Muscles | A pair of muscles that work to produce opposite effects. When one contracts the other relaxes e.g. the bicep and tricep muscles in your upper arm. |
| Anther | The top of a stamen's filament. It is divided into pollen sacs in which the pollen grains form. |
| Antibodies | Proteins produced by white blood cells (lymphocytes) that bind to antigens to inactivate them. |
| Anti Diuretic Hormone (ADH) | A hormone produced by the hypothalmus and released by the pituitary gland that increases the permeability of the renal tubule of the nephron and thereby increases water re-absorption, resulting in a high concentration of salt in the urine. |
| Antigen | A foreign molecule that stimulates the production of antibodies. |
| Aorta | The artery that carries blood from the left ventricle to the body (except lungs). |
| Apical Meristem | A meristem (plant cell capable of mitosis) at the tip of a shoot or root. |
| Appendicular Skeleton | Consists of the pelvic and pectoral girdles that join the limbs to the rest of the skeleton. |
| Artery | Thick-walled vessel that carries blood away from the heart. |
| Arterioles | The smallest arteries. They usually branch into capillaries |
| Asexual Reproduction | A method of reproduction in which offspring are produced from a single parent. |
| Atrioventricular (AV) Node | Tissue in the right ventricle of the heart that receives an impulse from the SA Node and transmits it along specialised fibres (Purkinje Fibres) through the ventricles causing them to contract. |
| Autotrophic | Means an organism that make it's own food. |
| Auxins | A growth regulator in plants. It causes stem and root growth, along with fruit formation. It is also involved with plant tropisms (as they cause growth or bending either towards or away from a stimulus. |
| Axial Skeleton | Consists of the skull, vertebrae, ribs and sternum. |
| Axons | Long fibers that carry signals away from the cell body of a neuron. |
| Bacteriophages | Viruses that infect bacteria |
| B Cells | A type of lymphocyte that is specific to a certain antigen. When a B-cell comes into contact with an antigen to which it is adapted, it divides to produce identical B-cells. |
| Binary Fission | The method by which bacteria reproduce. The DNA is replicated; then the cell splits into two identical cells. |
| Biosphere | The part of the Earth containing living things. |
| Biotechnology | The use of living things to manufacture useful products e.g. yeast to make beer. |
| Biotic Factors | these are living environmental factors that effect the number of organisms in an ecosystem. |
| Bladder | A hollow organ with muscular walls that stores urine and expels it through the urethra. |
| Blastocyst | The state in which a fertilized ovum is in 5 days after fertilisation. A blastocyst is formed when the morula divides by mitosis. It consists of an inner cell mass, an internal fluid cavity, and an outer layer of cells (known as the trophoblast). |
| Blood Group/Type | One of the classes into which blood can be separated on the basis of the presence or absence of certain antigens; notably, the ABO types and the Rh blood group. |
| B Memory Cells | B cells that are produced after an initial exposure to an antigen and they remain in the body so that if the same antigen is encountered again, they will facilitate a more rapid response to it. |
| Bolus | A mass of chewed food mixed with salivary secretions that is propelled into the oespohagus during the swallowing phase of digestion. |
| Bronchus | Tube that carries air from the trachea to the lungs |
| Bronchioles | Small tubes in the lungs that are formed by the branching of the bronchi. |
| Cancer | A disorder in which certain cells lose their ability to control the rate of mitosis. |
| Capillaries | Small, thin-walled blood vessels that allow oxygen to diffuse from the blood into the cells and carbon dioxide to diffuse from the cells into the blood. |
| Carbohydrates | composed of carbon, hydrogen, and oxygen. Used to produce energy. 3 types: monosaccharides, disaccharides and polysaccharides |
| Cardiac Muscle | The type of muscle that is found in the walls of the heart. |
| Carpals | The bones that make up the wrist joint. |
| Carpels | The female reproductive structures of a flower; consisting of the ovary, style, and stigma. |
| Catabolic Reactions | Reactions in which a complex molecule is broken down into simpler ones. |
| Cell Body | In a neuron, the part that contains the nucleus and most of the cytoplasm and the organelles. |
| Cellulose | A polysaccharide composed of chains of glucose. It is the major structural carbohydrate of plants and is insoluble in water. |
| Cell Wall | Structure produced by some cells outside their cell membrane for protection. |
| Central Nervous System (CNS) | The part of the nervous system that consists of the brain and spinal cord. |
| Centromere | The point at which two chromatids are connected to form a chromosome. |
| Cerebral Cortex | The outer layer of grey matter in the cerebrum. It consists mainly of neuron cell bodies and dendrites. |
| Cervix | The lower neck of the uterus that opens into the vagina. |
| Chemotrophs | Organisms (usually bacteria) that derive energy from inorganic reactions; also known as chemosynthetic. |
| Chitin | A polysaccharide contained in fungi. |
| Chlorophyll | The pigment in green plants that absorbs solar energy. |
| Chloroplasts | Double membraned organelles found in plant cells. They contain thylakoids and are the site of photosynthesis, a process in which ATP is generated by chemiosmosis. |
| Chorion | The two-layered structure formed from the trophoblast after implantation; secretes human chorionic gonadotropin. |
| Chromosomes | Structures in the nucleus of a eukaryotic cell that consist of DNA molecules that contain the genes. |
| Cilia | Mucous-secreting hairs that line the inner walls of the lungs. The sticky mucous traps particles such as dust, bacteria and viruses. The cilia beat and this forces the mucous up into the oesophagus and it then passes into the stomach. |
| Circulatory System | Transports oxygen, CO2, nutrients, and waste products between cells. It consists of the blood, heart, and blood vessels. |
| Circulatory System (closed) | A system that uses a continuous series of vessels of different sizes to deliver blood to body cells and return it to the heart. |
| Circulatory System (open) | A system in which the circulating fluid is not enclosed in vessels at all times. |
| Clavicle | The collar bone. |
| Cleavage Furrow | A constriction of the cell membrane at the equator of the cell that marks the beginning of cell division in animal cells. |
| Clitoris | A short shaft with a sensitive tip located where the labia minora meet. It consists of erectile tissue and is important in female sexual arousal. |
| Codon | A sequence of three nucleotides in mRNA that codes for a single amino acid. |
| Commensalism | A symbiotic relationship in which one species benefits and the other is not affected. |
| Compact bone | The outer layer of a long bone that is made up of 70% inorganic salts (such as calcium phosphate) and 30% organic material (a protein known as collagen). The calcium gives strength to the bone while the collagen gives flexibility. |
| Companion Cells | Specialized cells in the phloem that load sugars into the sieve elements and help maintain a functional plasma membrane in the sieve elements. |
| Competition | Two or more species competing for the same resources in a habitat. |
| Cones | Light receptors in the eyes that operate in bright light. They enable us to see in colour. |
| Contractile Vacuole | Organelle that uses active transport to get rid of excess water from the cell. |
| Coronary Arteries | Arteries that supply the heart's muscle fibres with nutrients and oxygen. |
| Corpus Callosum | Tightly bundled nerve fibres that connect the right and left hemispheres of the cerebrum. |
| Corpus Luteum | A structure formed from the ovulated follicle in the ovary which secretes progesterone. |
| Cotyledon | A leaf-like structure that is present in the seeds of flowering plants which is specialised for the storage of food. |
| Cranium | The brain-case composed of several bones fitted together at immovable joints. |
| Cristae | Structures formed by the folding of the inner membrane of a mitochondrion. |
| Cuticle | A waxy layer that is found on the external surface of plant stems and leaves which helps to prevent water loss. |
| Cytoplasm | The semi-liquid outside the nucleus of a cell where most of the reactions in the cell take place. |
| Dendrites | Short (often highly branched) fibres that carry signals toward the cell body of a neuron. |
| Deoxyribonucleic Acid (DNA) | Shape of a double helix. It contains the genetic information. The molecule is double-stranded and the two strands are linked by complementary base pairs. Nucleotides are the fundamental subunit of DNA and they consist of a molecule of deoxyribose sugar, a |
| Deoxyribose | Five-carbon sugar found in nucleotides of DNA. |
| Diaphragm | A dome-shaped muscle that helps with breathing. |
| Diffusion | The movement of particles under their own power from an area of high concentration to an area of low concentration. |
| Digestion | The chemical and physical break down of food. |
| Digestive System | Converts food into nutrient molecules that can be used and stored by the body and it also eliminates solid wastes. |
| Dihybrid Cross | In genetics, a cross that involves two sets of characteristics. |
| Disaccharides | Sugars made up of two monosaccharides held together by a covalent bond e.g. sucrose |
| Distal Tubule | The section of the renal tubule where tubular secretion occurs. |
| DNA Ligase | In genetic engineering, it is an enzyme that joins together two DNA fragments from different sources to form a recombinant DNA molecule. |
| Duodenum | The upper part of the small intestine. |
| Ecology | The study of how organisms interact with each other and with their physical environment. |
| Ecosystem | A self-sustaining community of organisms and their physical environment. |
| Ejaculatory Duct | In males, a short duct that connects the vas deferens from each testis to the urethra. |
| Embryo | Term applied to the zygote after the beginning of mitosis that produces a multicellular structure. |
| Endocrine System | It is a system of glands that work with the nervous system in controlling the activity of internal organs, especially the kidneys. |
| Endometrium | The inner lining of the uterus. |
| Endoplasmic Reticulum (ER) | A network of membranous tubules in the cytoplasm of a cell. They are involved in the production of phospholipids and proteins. Rough ER is studded with ribosomes. Smooth ER is not. |
| Enzymes | Protein molecules that speed up a reaction without being used up in the reaction. |
| Epidermis | The outermost layer of tissue in an organism. |
| Epididymis | A long, convoluted duct on the testis where sperm is stored. |
| Epiglottis | A flap of tissue that closes off the trachea during swallowing. |
| Eukaryote | A type of cell that is characterized by a membrane-bounded nucleus and other membraneous organelles. |
| Eutrophication | A process in which nutrients (such as agricultural fertiliser) run off into lakes and ponds. The addition of these nutrients to the water can use up the oxygen, therefore killing fish and other organisms. |
| Evolution | The adaptation of an organism to it's environment over long periods of time. It was referred to by Charles Darwin as natural selection. |
| Excretion | The removal of waste products of metabolism from the body. |
| Excretory system | It eliminates metabolic waste products from the internal environment of the body. |
| Fats | Lipid solid at room temperature. |
| Fauna | All animals in an area. |
| Femur | The thigh bone, thick bone in upper leg. |
| Fertilization | The fusion of two gametes (sperm and ovum) to produce a zygote that develops into a new organism. |
| Fibrous root | A root system found in monocots in which branches develop from the adventitious roots, forming a system in which all roots are about the same size and length. |
| Filtration | The removal of water and other minerals from the blood. It occurs in the glomerulus of the nephron. |
| Flagella | long, whip-like organelles that allow a cell to move. |
| Flora | All of the plants in an area. |
| Follicles (ovary) | Structures in the ovary consisting of a developing egg surrounded by a layer of follicle cells. |
| Follicle-stimulating hormone (FSH) | A hormone secreted by the anterior pituitary that promotes gamete formation in both males and females. |
| Food | food is any substance used by living organisms to provide energy, materials for repair and maintenance or to control metabolism. |
| Food chain | The simplest representation of energy flow in a community. At the base is energy stored in plants, which are eaten by small organisms, which in turn are eaten by progressively larger organisms. |
| Food pyramid | A way of depicting energy flow in an ecosystem; shows producers (mostly plants or other phototrophs) on the first level and consumers on the higher levels. |
| Food web | A complex network of feeding interrelations among species in a natural ecosystem. |
| Fovea | The area of the eye in which the cones are concentrated. |
| Fungi | Non-mobile, heterotrophic, mostly multi-cellular eukaryotes e.g. yeasts and mushrooms. |
| Gametes | Haploid reproductive cells (ovum and sperm). |
| Gastroesophageal sphincter | A ring of muscle at the junction of the oesophagus and the stomach that remains closed except during swallowing to prevent the stomach contents from entering the esophagus. |
| Genes | Specific segments of DNA that control cell structure and function; the functional units of inheritance. Sequence of DNA bases usually code for a polypeptide sequence of amino acids. |
| Genetic code | The series of nucleotides (read as triplets) that specifies the sequence of amino acids in proteins. |
| Genetics | The study of the structure and function of genes as well as the transmission of genes from parents to offspring. |
| Genotype | The genetic makeup of an organism. |
| Geotropism | Plant's response to gravity. |
| Glomerulus | A branch of capillaries that filters blood into Bowmann's capsule in a nephron. |
| Glucocorticoids | A group of steroid hormones produced by the adrenal cortex that are important in regulating the metabolism of carbohydrates, fats, and proteins. |
| Glucose | A six-carbon single sugar. It is the most common energy source. |
| Glycolysis | The metabolic process in the cell's cytoplasm where 6-carbon glucose is split into two 3-carbon pyruvic acid molecules, and some ATP is produced. |
| Golgi complex | Organelles in animal cells that sort, chemically modify, and package proteins produced on the rough ER. |
| Gonadotropin-releasing hormone (GnRH) | A hormone produced by the hypothalmus that controls the secretion of luteinising hormone. |
| Grana | A series of stacked thylakoid disks containing chlorophyll. They are found in the inner membrane of chloroplasts. |
| Ground system | Plant tissue system that occupies the space between the epidermis and the vascular system. It is involved in photosynthesis, water and food storage, and support. |
| Growth hormone (GH) | A peptide hormone produced by the anterior pituitary that is essential for growth. |
| Guard cells | Specialized epidermal cells whose opening and closing regulates gas exchange and water loss. |
| Haemoglobin | A red pigment in red blood cells that carries oxygen. |
| Haemophilia | A human genetic disorder that results in the absence of certain blood-clotting factors. It causes the inability to clot blood. |
| Hair root | The portion of a hair that is above the skin's surface. |
| Heart | The multicellular, chambered, muscular structure that pumps blood through the circulatory system by alternately contracting and relaxing. |
| Helper T cells | A type of lymphocyte that stimulates the production of antibodies by activating B cells when an antigen is present. |
| Heterotrophic | Refers to organisms, such as animals, that depend on preformed organic molecules from the environment (or another organism) as a source of nutrients/energy. |
| Heterozygous | Having two different alleles (one dominant, one recessive) of a gene pair. |
| Histamine | A chemical released during the inflammatory response that increases capillary blood flow in the affected area, causing heat and redness. |
| Homeostasis | The ability to maintain a relatively constant internal environment. |
| Homozygous | Having identical alleles for a given gene. |
| Hormones | Chemical substances that are produced in the endocrine glands and travel in the blood to target organs where they elicit a response. |
| Human chorionic gonadotropin (HCG) | A peptide hormone secreted by the chorion that prolongs the life of the corpus luteum and prevents the breakdown of the uterine lining. |
| Hypertension | High blood pressure i.e when blood pressure is consistently above 140/90. |
| Hyphae | The multicellular filaments that make up the mycelium (body) of a fungus. |
| Hypothalmus | A region in the brain beneath the thalmus. It controls a variety of autonomic functions aimed at maintaining homeostasis. |
| Ileum | The third and last section of the small intestine. |
| Immune system | It protects the body against invading microorganisms and viruses. |
| Implantation | The process in which the blastocyst embeds itself in the endometrium. |
| Insulin | A hormone secreted by the pancreas that stimulates the uptake of glucose by body cells. Insulin works antagonistically with glucagon to control blood sugar levels. |
| Interferons | Proteins released by cells in response to viral infection. They activate the synthesis and secretion of antiviral proteins. |
| Interneurons | Neurons that process signals from one or more sensory neurons and relay signals to motor neurons. |
| Islets of Langerhans | A group of cells in the pancreas that produce insulin. |
| Jejunum | The second portion of the small intestine. |
| Keratin | A fibrous protein that fills mature keratinocytes near the skin's surface. |
| Kidney stones | Crystallized deposits of excess wastes such as uric acid, calcium, and magnesium that may form in the kidney. |
| Lactose intolerance | A genetic trait characterized by the absence of the enzyme lactase, which breaks down lactose, the main sugar in milk and other dairy products. |
| large intestine | It absorbs some nutrients, but mainly prepares faeces for elimination. It consists of the caecum, appendix, colon, and rectum. |
| Larynx | A hollow structure at the beginning of the trachea. The vocal cords extend across the opening of the larynx. |
| L-dopa | A chemical related to dopamine that is used in the treatment of Parkinson's disease. |
| Leukocytes | A type of white blood cell that is primarily engaged in fighting infection. |
| Life | life is defined as possessing the 7 characteristics of life: 1.Respiration 2.Nutrition 3.Metabolism 4.Movement 5.Growth 6.Reproduction 7.Excretion |
| Respiration | the chemical release of energy from food. |
| Nutrition | the means by which an organism obtains its energy to live |
| Metabolism | the chemical reactions that take place inside the organism in order to survive. |
| Growth | an increase in size due to an increase in solid matter in the body |
| Reproduction | the ability to produce new individuals of the same species. |
| Excretion | the removal of wastes produced in metabolism from the body. |
| Ligaments | Strong, slightly elastic fibres the connect bone to bone. |
| Lignin | A polymer in that helps to strengthen the cell wall of woody plant cells. |
| Lipids | They contain the elements carbon, hydrogen and oxygen. Their function is the long-term storage of energy, insulation, structure and control. E.g fats, waxes, oils. |
| Lipases | Enzymes secreted by the pancreas that are active in the digestion of fats. |
| Loop of Henle | A U-shaped loop between the proximal and distal tubules in the kidney. |
| Lungs | Sac-like structures where gaseous exchange occurs. |
| Luteal phase | The second half of the ovarian cycle when the corpus luteum is formed. It occurs after ovulation. |
| Luteinising hormone (LH) | A hormone secreted by the anterior pituitary gland that stimulates the secretion of testosterone in men and oestrogen in women. |
| Lymph | Tissue fluid in the lymphatic system. |
| Lymphatic system | A network of glands and vessels that drain tissue fluid from body tissues and return it to the circulatory system. |
| Lymphocytes | White blood cells that arise in the bone marrow and mediate the immune response. They include T cells and B cells. |
| Lysosomes | Membrane-enclosed organelles containing digestive enzymes. They fuse with food vacuoles and enzymes contained within the lysosome chemically breakdown and/or digest the food vacuole's contents. |
| Macrophages | A type of white blood cell derived from monocytes that engulf invading antigens, micro-organisms, and viruses and then display fragments of the antigen to activate helper T cells. |
| Medulla oblongata | The region of the brain that controls heart rate, constriction and dilation of blood vessels, respiration and digestion. |
| Megakarocytes | Cells found in the bone marrow that produce platelets. |
| Meiosis | Method of cell division where the chromosome number is halved. Used to form gametes. |
| Melanin | A pigment that gives the skin colour and protects the underlying layers against damage by ultraviolet light. It is produced by melanocytes in the inner layer of the epidermis. |
| Melanocytes | The cells in the inner layer of the epidermis that produce melanin. |
| Menstrual cycle | The recurring secretion of hormones and associated uterine tissue changes in females. Usually 28 days in length. |
| Menstruation | The process in which the uterine endometrium breaks down and sheds cells, resulting in bleeding. It occurs approximately once a month. The first day marks the beginning of the menstrual and ovarian cycles. |
| Meristematic tissue | A type of tissue in plants that is capable of mitosis. |
| Mesoderm | The middle layer of cells in embryonic development; gives rise to muscles, bones, and structures associated with reproduction. The middle embryonic tissue layer. Cells and structures arising from the mesoderm include the bone, blood, muscle, skin, and rep |
| Mesophyll | Layer of leaf tissue between the epidermis layers. |
| Metabolism | All chemical reactions in cells. |
| Metastasis | The process in which cancer cells break away from the original tumour mass and establish new tumour sites elsewhere in the body. |
| Microvilli | Hair-like projections on the surface of the epithelial cells of the villi in the small intestine. They increase the surface area of the intestine to improve absorption of digested nutrients. |
| Minerals | Trace elements required for normal metabolism, as components of cells and tissues, and in nerve conduction and muscle contraction. |
| Mitochondria | Self-replicating organelles in most eukaryotic cells that complete the breakdown of glucose, producing energy (NADH and ATP). |
| Mitosis | A form of cell division in which one nucleus divides to form two nuclei, each containing identical sets of chromosomes. |
| Monera | Prokaryotic kingdom that includes all types of bacteria. |
| Monocots | They are characterized by having a single cotyledon, floral organs arranged in threes or multiples of three, and parallel-veined leaves e.g. grasses, lilies, and palm trees. |
| Monocytes | White blood cells that clean up dead viruses, bacteria, and fungi and dispose of dead cells and debris at the end of the inflammatory response. |
| Monohybrid cross | In genetics, a cross that involves only one characteristic. |
| Monomer | An organic chemical unit linked to other units (usually by a covalent bond) to produce a larger molecule known as a polymer. |
| Monosaccharides | A carbohydrate composed of a single sugar unit e.g. glucose |
| Morula | The solid-ball stage of the pre-implantation embryo. |
| Motor neurons | Nerve cells connected to a muscle or gland.They receive signals from interneurons and transfer the signals to effector cells that produce a muscular response. |
| Mucous | A thick, lubricating fluid produced by the mucous membranes serves as a barrier against infection and, in the digestive tract, moistens food, making it easier to swallow. |
| Muscle fibers | Long, multi-nucleated cells found in skeletal muscles. They are made up of myofibrils. Muscle cells contract/relax, allowing movement of an animal. |
| Muscular system | A system that allows movement and locomotion, powers the circulatory, digestive, and respiratory systems, and plays a role in regulating temperature. |
| Mutation | Any change in the nucleotide sequence of DNA. |
| Mutualism | A form of symbiosis in which both species benefit. E.g. lichens, which is a symbiosis between an alga and a fungus. The alga provides food and the fungus provides water and nutrients. |
| Mycelium | The mass of interwoven filaments of hyphae in a fungus. |
| Myelin sheath | Layers of specialized cells, called Schwann cells, that coat the axons of many neurons. |
| Natural selection | Survival of the fittest. This means that organisms that are better adapted to their environment are more likely to survive. |
| Nephron | A tubular structure that is the filtering unit of the kidney. It consists of a glomerulus and renal tubule. |
| Nervous system | A system in animals that co-ordinates and controls actions of internal organs and body systems, receives and processes sensory information from the external environment, and coordinates short-term reactions to these stimuli. |
| Neuromuscular junction | The point where a motor neuron attaches to a muscle cell. |
| Neurons | Highly specialized cells that generate and transmit electrical impulses from one part of the body to another. |
| Neurotoxin | Chemical that paralyzes nerves. |
| Neurotransmitters | The chemical released by the tip of an axon that crosses the synaptic cleft and causes the transmission of the nerve message in an adjacent neuron or the stimulation of a muscle or gland. |
| Niche | The biological role played by a species. |
| Node of Ranvier | A gap between two Schwann cells that make up an axon's myelin sheath. |
| Nuclear pores | Openings in the membrane of a cell's nuclear envelope that allow the exchange of materials between the nucleus and the cytoplasm. |
| Nucleic acids | Polymers composed of nucleotides; e.g., DNA and RNA. |
| Nucleolus | A round body in the nucleus of a eukaryotic cell; consists of DNA and RNA and produces ribosomal RNA. |
| Nucleotides | The subunits of DNA and RNA. They are composed of a base, a phosphate group and a sugar. They are involved in protein synthesis. |
| Occipital lobe | The lobe of the cerebral cortex that is responsible for receiving and processing visual information. |
| Oesophagus | The muscular tube that connects the pharynx to the stomach. |
| Oestrogen | A female sex hormone that performs many important functions in reproduction. |
| Oils | Lipid liquid at room temperature. |
| Oncogenes | Genes that are cancer-causing. |
| Oocyte | A cell that is undergoing (will undergo) development into a female gamete. |
| Oogenesis | The production of ova. The development of a diploid cell into a haploid ovum or egg cell. |
| Organelles | Sub-cellular structures (usually membrane-bound and unique to eukaryotes) that perform some function, e.g. chloroplast, mitochondrion, nucleus. |
| Organs | A group of tissues that perform a similar function in an organism e.g. the heart, kidneys, liver, stomach. |
| Osmoregulation | The regulation of the movement of water by osmosis in and out of cells. |
| Osmosis | The movement of water molecules from a high concentration to a low concentration across a semi-permeable membrane. |
| Osteoporosis | A disorder in which the mineral portion of bone is lost, making the bone weak and brittle. It occurs most commonly in post-menopausal women. |
| Ovaries | The female gonads in animals which produce eggs (ova) and female sex hormones. In flowers, part of the female reproductive structure in the carpel, it contains the ovules and it is where egg development occurs. |
| Oviducts | A collective term for the uterus and the fallopian tubes. |
| Ovulation | The release of the oocyte onto the surface of the ovary. It occurs at the midpoint of the ovarian cycle |
| Ovule | In seed plants, a protective structure in which the female gametophyte develops, fertilization occurs, and seeds develop. It is contained within the ovary. |
| Ovum | The female gamete, egg. |
| Oxytocin | A peptide hormone secreted by the posterior pituitary that stimulates the contraction of the uterus during childbirth. |
| Palisade | Layer of mesophyll cells in leaves that are closely placed together under the epidermal layer of the leaf. |
| Palisade Layer | A column of cells located just below the upper epidermis in leaves the cells where most of the light absorption in photosynthesis occurs. |
| Pancreas | A gland that secretes digestive enzymes into the small intestine e.g. trypsin and chymotrypsin. It also secretes the hormones insulin and glucagon into the blood, where they regulate blood sugar levels. |
| Parasitism | A type of symbiosis in which one organism benefits at the expense of the other, for example the influenza virus is a parasite on its human host. Therefore, viruses are obligate intracellular parasites. |
| Parietal lobe | The lobe of the cerebral cortex that processes information about touch, taste, pressure, pain, and heat and cold. |
| Pectoral girdle | In humans, the bony arch by which the arms are attached to the rest of the skeleton. It is composed of the clavicle and scapulae. |
| Pelvic girdle | In humans, the bony arch by which the legs are attached to the rest of the skeleton. It is composed of the two hipbones. |
| Pelvis | The hollow cavity formed by the two hipbones. |
| Pepsin | An enzyme, produced by the stomach, that digests protein by breaking it down into large peptide fragments |
| Pepsinogen | An inactive form of pepsin; synthesized and stored in cells lining the gastric pits of the stomach. |
| Peptic ulcer | Damage to the epithelial layer of the stomach lining. It is generally caused by a bacterial infection. |
| Peptide bond | A covalent bond that links two amino acids together to form a polypeptide chain. |
| Peptides | Short chains of amino acids. |
| Peripheral nervous system | The division of the nervous system that transmits messages to the central nervous system. |
| Peristalsis | Involuntary contractions of the smooth muscles in the walls of the oesophagus, stomach, and intestines that propel food along the digestive tract. |
| Petiole | The stalk connecting the leaf blade to the stem. |
| Phagocytes | White blood cells that can engulf (by phagocytosis) and destroy micro-organisms including viruses and bacteria. |
| Pharynx | The passageway between the mouth and the oesophagus and trachea. Food passes from the pharynx to the oesophagus, and air passes from the pharynx to the trachea. |
| Phenotype | The physical make-up of an organism. |
| Phloem | Cells of the vascular system in plants that transport food from leaves to other areas of the plant. Phloem tissue consists of cells called sieve tubes and companion cells. |
| Phospholipids | One glycerol molecule joined to two fatty acids and a phosphate group. Phospholipids are important in the structure of cell membranes. |
| Photosynthesis | The process by which plant cells use solar energy to produce ATP. The conversion of unusable sunlight energy into usable chemical energy. |
| Phototropism | The reaction of plants to light in which the plants bend toward the light due to a higher concentration of IAA(Indole Acetic Acid) on one side (dark side) of the plant than the other. |
| Pineal gland | A small gland located between the cerebral hemispheres of the brain that secretes melatonin. |
| Pistil | Female reproductive structures in flowers, consisting of the stigma, style, and ovary. Also known as a carpel. |
| Pituitary gland | A small gland located at the base of the brain that releases hormones that have specific targets as well as those that stimulate other glands to secrete hormones. Part of the pituitary is nerve tissue, the rest is glandular epithelium. |
| Placenta | An organ produced from interlocking maternal and embryonic tissue in placental mammals. It supplies nutrients to the embryo and foetus and removes wastes. |
| Placental mammals | This is a term applied to mammals that carry their young in the mother's body for long periods during which the foetus is nourished by the placenta. |
| Plasma | The liquid part of the blood. |
| Plasmids | Self-replicating, circular DNA molecules found in bacterial cells |
| Plastids | Membrane-bound organelles in plant cells that function in storage (of food or pigments) or food production. Term for any double membrane-bound organelle. Chloroplasts contain the chemicals for photosynthesis, leukoplasts store starch, chromoplasts contain |
| Platelets | A component of the blood that carries chemicals needed for blood clotting. |
| Pollination | The transfer of pollen from the anthers to the stigma by a pollinating agent such as wind, insects or birds. |
| Polysaccharides | Long chains of monosaccharide units bonded together; e.g., glycogen, starch, and cellulose. |
| Portal system | A system that starts and ends in capillaries. |
| Prenatal testing | Testing to detect the presence of a genetic disorder in an embryo or foetus. It is commonly done by amniocentesis or chorionic villi sampling. |
| Principle of independent assortment | Mendel's second law. It states that at gamete formation, either member of a pair of factors is equally likely to recombine with either of another pair of factors. |
| Principle of segregation | Mendel's first law. It states that inherited characteristics are controlled by pairs of factors and these factors segregate (split) at gamete formation so that only one factor is carried in each gamete. |
| Producers | The first level in a food pyramid. They consist of organisms that generate their own food that is then used by all other organisms in the ecosystem. |
| Progesterone | One of the two female reproductive hormones secreted by the ovaries. |
| Prokaryote | Type of cell that lacks a membrane-bound nucleus and has no membrane organelles. Prokaryotes are more primitive than eukaryotes. Prolactin |
| Prostate gland | A gland that produces a secretion that enhances sperm viability. Gland involved in the reproductive system in males, the prostate secretes a sperm activating chemical into the semen during the arousal/ejaculation response. |
| Proteins | Proteins are polymers of amino acids linked together by peptide bonds. |
| Proximal tubule | The winding section of the renal tubule where most re-absorption of water, sodium, amino acids, and sugar takes place. |
| Pseudopodia | "False feet" that allow amoeba to move |
| Pulmonary artery | The artery that carries de-oxygenated blood from the right ventricle of the heart to the lungs. |
| Pulmonary circuit | The loop of the circulatory system that carries blood to and from the lungs. |
| Pulmonary vein | The vein that carries oxygenated blood from the lungs to the left atrium of the heart. |
| Pyloric sphincter | The ring of muscle at the junction of the stomach and small intestine that regulates the movement of food into the small intestine. |
| Re-absorption | The return to the blood of most of the water, sodium, amino acids, and sugar that were removed during filtration in the nephron. |
| Recessive | Refers to an allele of a gene that is expressed when the dominant allele is not present. |
| Red blood cell | Component of the blood that transports oxygen. |
| Reflex | A response to a stimulus that occurs without conscious effort. |
| Renal tubule | The portion of the nephron where urine is produced. |
| Replication | Process by which DNA is duplicated prior to cell division. |
| Reproductive system | A human system that is responsible for reproduction and thus the survival of the species. |
| Respiration | The controlled release of energy from food. |
| Respiratory system | A human system that moves oxygen from the external environment into the internal environment and removes carbon dioxide from the body. |
| Restriction enzymes | A series of enzymes that attach to DNA molecules at specific nucleotide sequences and cut both strands of DNA at those sites. |
| Retina | The inner, light-sensitive layer of the eye. It contains the rods and cones. |
| Ribonucleic acid (RNA) | The single stranded molecule transcribed from one strand of DNA during protein synthesis. There are three types of RNA, tRNA (transfer RNA), mRNA (messenger RNA) and rRNA (ribosomal RNA). RNA is made up nucleotides containing the sugar ribose, a phosphate |
| Ribose | Sugar found in nucleotides of RNA and in ATP. |
| Ribosomal RNA | It is the structural component in ribosomes. |
| Ribosomes | Small organelles made of rRNA and protein in the cytoplasm of prokaryotic and eukaryotic cells. They form amino acids. They are the site of protein synthesis. |
| Rods | Light receptors in the eyes that provide vision in dim light. |
| Root cap | Structure that covers and protects the apical meristem in plant roots |
| Root hairs | Extensions of the root epidermis that increase the root's ability to absorb water. |
| Roots | Organs, usually occurring underground, that absorb nutrients and water and anchor the plant |
| Root system | The part of the plant below ground level. |
| Saprophytes | Organisms that obtain their nutrients from decaying plants and animals. |
| Schwann cells | Specialized cells that form the myelin sheath that coats many axons. |
| Scientific method | The way in which knowledge about the world is obtained. Steps include observation, hypothesis, experimentation and evaluation. If hypothesis is supported by many experiments over time, it forms a theory. If a theory can be proven true under absolutely all |
| Secretion | The release of a substance in response to the presence of food or specific neural or hormonal stimulation. |
| Seed coat | The tough outer layer of the seed. |
| Segregation | Separation of replicated chromosomes to opposite sides of the cell. |
| Semen | A mixture of sperm and various glandular secretions. |
| Semi-lunar valve | A valve between each ventricle of the heart and the artery connected to that ventricle. |
| Seminal vesicles | Glands that contribute fructose to sperm. The fructose serves as an energy source. |
| Sensory neurons | Neurons carrying messages from sensory receptors to the spinal cord. |
| Sex chromosomes | Chromosomes that determine the gender (sex) of the individual. Human males have a large X and a smaller Y sex chromosomes, while human females have two X sex chromosomes. |
| Sex hormones | A group of steroid hormones produced by the adrenal cortexand also in the gonads which promote development and maintainence of the secondary sex characteristics and structures, prepare the female for pregnancy, and aid in development of gametes. Males pro |
| Sex linkage | A condition in which the inheritance of a sex chromosome is coupled with that of a given gene; e.g., red-green colour blindness and haemophilia in humans. |
| Shoot system | The part of the plant that is above the ground. |
| Sickle cell anaemia | Human autosomal recessive disease that causes production of abnormal red blood cells that collapse (or sickle) and cause circulatory problems. |
| Sieve plates | Pores in the end walls of sieve elements that connect them together |
| Sino-atrial (SA) node | A region of modified muscle cells in the right atrium that sends timed impulses to the heart's other muscle cells, causing them to contract. It is also known as the pacemaker. |
| Skeletal muscle | Muscle that is generally attached to the skeleton and causes body parts to move. These muscles control skeletal movements and are normally under conscious control. |
| Skeletal system | A system in humans that supports the body, protects internal organs, and, with the muscular system, allows movement and locomotion. |
| Small intestine | A coiled tube in the abdominal cavity that is the major site of chemical digestion and absorption of nutrients. It is composed of the duodenum, jejunum, and ileum. |
| Species | A group of similar organisms capable of interbreeding with each other to produce fertile offspring. |
| Sperm | The male gamete. |
| Spinal cord | A cylinder of nerve tissue extending from the brain stem that receives sensory information and sends output motor signals. |
| Spongy bone | The inner layer of bone. It is found at the ends of long bones and is less dense than compact bone. Some spongy bone contains red marrow. |
| Sporangium | The structures in which spores are produced. |
| Stamens | The male reproductive structures of a flower, composed of a filament and anther. |
| Stem cells | Cells in bone marrow that produce lymphocytes by mitotic division. They are unspecialised cells that can grow into virtually any type of tissue. |
| Sternum | The breastbone. |
| Stigma | Part of the female reproductive structure of the carpel of a flower where the pollen grains attach. |
| Stomach | The muscular organ between the oesophagus and small intestine that stores, mixes, and digests food and controls the passage of food into the small intestine. |
| Stomata | Pores on the underside of leaves that can be opened or closed to control gas exchange and water loss. |
| Stroma | The matrix surrounding the grana in the inner membrane of chloroplasts. The area between membranes (thylakoids, grana) inside the chloroplast. |
| Style | Part of the female reproductive structure in the carpel of a flower to which pollen grains attach. |
| Suppressor T cells | T cells that slow down and stop the immune response of B cells and other T cells. Immune system cells that shut off the antibody production when an infection is under control. |
| Symbiosis | An interactive association between two or more species living together. This association may be parasitic, commensal, or mutualistic. |
| Synapse | The space between neurons. |
| Synaptic cleft | The space between the end of a neuron and an adjacent cell. |
| Synovial joint | The most movable type of joint in which the bones are covered by connective tissue, the interior of which is filled with synovial fluid, and the ends of the bones are covered with cartilage. |
| Systemic circuit | The loop of the circulatory system that carries blood through the body and back to the heart. |
| Systolic pressure | The peak blood pressure when ventricles contract. |
| Tap root | A primary root that grows vertically downward and gives off small lateral roots. They usually occur in dicots. |
| Tarsals | The bones that make up the ankle joint. |
| T cells | The type of lymphocyte responsible for cell-mediated immunity. They protect against infection by parasites, fungi, and protozoans and can kill cancerous cells. |
| Tendons | Fibrous connective tissue that connects muscle to bone. |
| Terminal buds | Buds located at the end of a plant shoot. |
| Testes | Male gonads in mammals. Paired organs that contain seminiferous tubules in which sperm are produced. |
| Testosterone | Male sex hormone that stimulates sperm formation, promotes the development of the male duct system in the foetus, and is responsible for secondary sex characteristics such as facial hair growth. |
| Thigmotropism | Plants' response to contact with a solid object; e.g., tendrils' twining around a pole. |
| Thoracic cavity | The chest cavity in which the heart and lungs are located. |
| Thylakoids | The specialized membrane structures in which photosynthesis takes place. Internal membranes in the chloroplast where the light reaction chemicals are embedded. Collections of thylakoids form the grana. |
| Thyroid-stimulating hormone | A hormone produced by the anterior pituitary that stimulates the production and release of thyroxin. |
| Trace element | An element needed in very small amounts in a living organism. |
| Trachea | The air-conducting duct that leads from the pharynx to the lungs. |
| Tracheids | Long, tapered cells that form a system of tubes in the xylem and carry water and solutes from the roots to the rest of the plant. |
| Transcription | The making of RNA from one strand of the DNA molecule. |
| Transfer RNAs (tRNAs) | Small, single-stranded RNA molecules that bind to amino acids and carry the specified amino acid to the ribosome during photosynthesis. |
| Translation | The making of a polypeptide sequence by translating the genetic code of an mRNA molecule associated with a ribosome. |
| Transpiration | The loss of water from the leaves of a plant. |
| Trophoblast | The outer layer of cells of a blastocyst that stick to the endometrium during implantation. |
| Tropism | The movement of an organism in response to an environmental stimulus. |
| Tubal ligation | A contraceptive procedure in women in which the oviducts are cut, preventing the ova from reaching the uterus. |
| Tumour Suppressor Genes | Genes that normally keep cell division under control, preventing the cell from responding to internal and external commands to divide. |
| Turgor pressure | Pressure caused by the cytoplasm pressing against the cell wall. |
| Umbilical cord | The structure that connects the placenta and the embryo. |
| Ureter | A muscular tube that transports urine by peristaltic contractions from the kidney to the bladder. |
| Urethra | A narrow tube that transports urine from the bladder to the outside of the body. In males, it also conducts sperm and semen to the outside. |
| Urine | Fluid containing various wastes that is produced in the kidney and excreted from the bladder. |
| Uterus | The organ that houses and nourishes the developing embryo and foetus. |
| Vacuoles | Membrane-bound fluid-filled spaces in plant and animal cells that remove waste products and store food. |
| Vascular bundle | Groups of xylem, phloem and cambium cells in stems of plants |
| Vascular cambium | A layer of lateral meristematic tissue between the xylem and phloem in the stems of woody plants |
| Vascular plants | Group of plants having lignified conducting tissue (xylem vessels or tracheids). |
| Vascular system | tissues for transporting fluids and nutrients in plants. It also supports the plant. |
| Vas deferens | The duct that carries sperm from the epididymis to the ejaculatory duct and urethra. |
| Vasectomy | A contraceptive procedure in men in which the vas deferens is cut tied to prevent the transportation of sperm. |
| Veins | Thin-walled vessels that carry blood to the heart. They have valves to prevent back-flow of blood. |
| Ventricle | The lower chamber of the heart through which blood leaves the heart. |
| Venules | Small veins that connect a vein with capillaries. |
| Vertebrae | The segments of the spinal column. They are separated by disks made of connective tissue. |
| Villi | Finger-like projections of the lining of the small intestine that increase the surface area available for the absorption of food. |
| Virus | Infectious chemical agent composed of a nucleic acid (DNA or RNA) inside a protein coat. |
| Vitamins | A diverse group of organic molecules that are required for metabolic reactions. |
| X-chromosome | One of the sex chromosomes. |
| Xylem | Tissue in the vascular system of plants that moves water and dissolved nutrients from the roots to the leaves. |
| Zygospore | In fungi, a structure that forms from the diploid zygote created by the fusion of haploid hyphae of different mating types. After a period of dormancy, the zygospore forms sporangia, where meiosis occurs and spores form. |
| Zygote | A fertilized egg. A diploid cell resulting from fertilization of an egg by a sperm cell |
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