Biology Terms

Abdomen:  The abdomen refers to the region between the pelvis (pelvic brim) and the thorax (thoracic diaphragm) invertebrates, including humans. The space constituting the abdomen is termed the abdominal cavity. The borders of the abdominal cavity are comprised of the posterior peritoneal surface, the anterior abdominal wall, the inferior pelvic inlet, and the superior thoracic diaphragm. The abdomen functions to house the digestive system and provides muscles essential for posture, balance, and breathing.

Abiotic – nonliving, inanimate, characterized by the absence of life; of inorganic matter.

Activation energy – The energy required to complete a chemical reaction.

Aerobic: living or occurring only in the presence of oxygen.

Amino acid – The “building blocks” of proteins

Amino sugar – A sugar molecule with an amine group attached instead of one of its hydroxyl groups.

Anatomy: Anatomy is a branch of natural science which deals with the structural organization of living things. Anatomy is the study of the structure and relationship between body parts.

Angiosperm : Angiosperm, any of about 300,000 species of flowering plants, the largest and most diverse group within the kingdom Plantae. Angiosperms represent approximately 80 per cent of all the known green plants now living. The angiosperms are vascular seed plants in which the ovule (egg) is fertilized and develops into a seed in an enclosed hollow ovary. The ovary itself is usually enclosed in a flower, that part of the angiospermous plant that contains the male or female reproductive organs or both. Fruits are derived from the maturing floral organs of the angiospermous plant and are therefore characteristic of angiosperms. By contrast, in gymnosperms (e.g., conifers and cycads), the other large group of vascular seed plants, the seeds do not develop enclosed within an ovary but are usually borne exposed on the surfaces of reproductive structures, such as cones.

Antibiotic: any substance that can destroy or inhibit the growth of bacteria and similar microorganisms.

Antibody: A protein produced by the immune system meant to incapacitate and tag foreign bodies for disposal.

Antigen – A protein attached to the surface of a foreign body which can be recognized by proteins on immune cells.

Apoptosis – Programmed cell death that occurs in multicellular organisms, preceded by distinct changes to the morphology and biochemistry of the cell. Common during development and also used to prevent disease.

Apospory: Formation of gametophyte directly from sporophyte without meiosis and spore formation is apospory.

ATP – The “energy currency” of the cell. The chemical bonds in the ATP molecule store energy that can be used to accomplish life functions.

Bacteria: Bacteria are single-celled microorganisms with prokaryotic cells, which are single cells that do not have organelles or a true nucleus and are less complex than eukaryotic cells. Bacteria with a capital B refers to the domain Bacteria, one of the three domains of life. The other two domains of life are Archaea, members of which are also single-celled organisms with prokaryotic cells, and Eukaryota. Bacteria are extremely numerous, and the total biomass of bacteria on Earth is more than all plants and animals combined.

Binary fission – The method by which bacteria reproduce asexually through dividing.

Biodiversity – Large variety of organisms.

Biofilm: a thin film of mucus created by and containing a colony of bacteria and other microorganisms.

Biome – A large, naturally occurring community of life forms. Biomes can be thought of as “types of ecosystems.” Rainforest, tundra, savanna, temperate forest, and temperate grassland are examples of biomes.

Biomolecule – Biomolecule, also called biological molecule, any of numerous substances that are produced by cells and living organisms. Biomolecules have a wide range of sizes and structures and perform a vast array of functions. The four major types of biomolecules are carbohydrates, lipids, nucleic acids, and proteins.

Bioremediation: the use of biological organisms, usually microorganisms, to remove contaminants, especially from soil or polluted water.

Biotechnology: the use of living organisms (especially microorganisms) in industrial, agricultural, medical, and other technological applications.

Biotic factor – A living element of an ecosystem, such as a plant, animal, or bacteria. Biotic and abiotic factors together make up an ecosystem.

Biotransformation: the changes (both chemical and physical) that occur to a substance (especially a drug) by the actions of enzymes within an organism.


Capillary action – The mechanism by which trees draw water up through their roots to feed their leaves.

CarbohydatesA carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula Cm(H2O)n (where m may be different from n). This formula holds true for monosaccharides. Some exceptions exist; for example, deoxyribose, a sugar component of DNA, has the empirical formula C5H10O4. The carbohydrates are technically hydrates of carbon; structurally it is more accurate to view them as aldoses and ketoses.

Carbon cycle: the physical cycle of carbon through the earth’s biosphere, geosphere, hydrosphere, and atmosphere that includes such processes as photosynthesis, decomposition, respiration and carbonification.

Carcinoma: Carcinoma is a term used to describe cancer derived from epithelial cells that line various tissues throughout the body. In addition, malignant tumours that have an unknown primary origin, but share histological characteristics with epithelial cells (e.g., stratification, pseudostratification, cytokeratin production, mucin, etc.) are also classified as carcinomas. Depending on the location, carcinomas can be surgically removed, or treated with conventional radiation or chemotherapy.

Cell: The cell (meaning “small room”) is the basic structural, functional, and biological unit of all known living organisms. All living organisms are made up of building blocks we call the cell. Many living things consist of vast numbers of cells working in concert with one another.

Cell Biology: Cell biology is the study of cell structure and function, and it revolves around the concept that the cell is the fundamental unit of life. Focusing on the cell permits a detailed understanding of the tissues and organisms that cells compose

Cell membrane – A membrane made up of phospholipids, and which separates from the inside of a cell from the outside.

cell surface membrane: a very thin membrane (about 7nm diameter) surrounding all cells; it is partially permeable and controls the exchange of materials between the cell and its environment.

Cell wall : A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes (except mollicute bacteria), in algae, fungi and eukaryotes including plants but are absent in animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters.

Cellular respiration – Energy from nutrients is converted into ATP.

Centriole: one of two small, cylindrical structures, made from microtubules, found just outside the nucleus in animal cells, in a region known as the centrosome; they are also found at the bases of cilia and flagella

Chemosynthetic: Using chemical reactions as energy source. Eg: Nitrosomonas Bacteria.

Chemotroph – An organism that obtains energy mainly from carbon dioxide and from other inorganic chemicals through a process called chemosynthesis

Chloroplast: an organelle found in the cells of green plants and photosynthetic algae where photosynthesis takes place.

Chromatin: the loosely coiled form of chromosomes during interphase of the cell cycle; chromatin is made of DNA and proteins and is visible as loosely distributed patches or fibres within the nucleus when stained.

Classification: Grouping of organisms into categories on the basis of similarities & differences.

Coenzyme – A complex enzyme contains a non-protein part, called a prosthetic group or co-enzymes. Co-enzymes are very essential for the biological activities of the enzyme.

Cohesion – The tendency of molecules to stick to other molecules like themselves.

Convergent evolution – occurs when unrelated life forms evolve very similar solutions to environmental problems.

Conjugation: the temporary fusion of organisms, especially as part of sexual reproduction.

Crista: cristae (singular crista) are the internal compartments formed by the inner membrane of a mitochondrion.

Cyanobacteria: photosynthetic prokaryotic microorganisms, of phylum Cyanobacteria, once known as blue-green algae.

Cytoplasm – Cytoplasm is a thick solution that fills each cell and is enclosed by the cell membrane. It is mainly composed of water, salts, and proteins. In eukaryotic cells, the cytoplasm includes all of the material inside the cell and outside of the nucleus. All of the organelles in eukaryotic cells, such as the nucleus, endoplasmic reticulum, and mitochondria, are located in the cytoplasm. The portion of the cytoplasm that is not contained in the organelles is called the cytosol. Although cytoplasm may appear to have no form or structure, it is actually highly organized. A framework of protein scaffolds called the cytoskeleton provides the cytoplasm and the cell with their structure.


Daughter Cells: Daughter cells are produced after a single cell undergoes cell division. During mitosis, one pair of daughter cells is created after one round of DNA replication. During meiosis, a single round of DNA replication is followed by 2 rounds of cell division. This creates two sets of daughter cells, each of which has a haploid genome.

Ear: The ear is the organ found in animals which are designed to perceive sounds. Most animals have some sort of ear to perceive sounds, which are actually high-frequency vibrations caused by the movement of objects in the environment. The human ear picks up and interprets high-frequency vibrations of air, while the sound-sensing organs of aquatic animals are designed to pick up high-frequency vibrations in the water. Most vertebrates have two ears: one on either side of the head.

Ecology:  The prefix ‘eco’ has become synonymous with environmentally-friendly living. This green fad, however, has more to do with conservation biology than with ecology, where the prefix is borrowed from.

All organisms, no matter their size, their species, or where they live, need to interact with other organisms in their ‘neighbourhood’ and with their environment in order to survive. Ecology is the scientific study of the interactions between organisms and their environment. The term comes from the Greek ‘study of house’, or the study of the place we live in.

The scope of ecology is huge, and it encompasses all organisms living on Earth and their physical and chemical surroundings. For this reason, the field is usually divided into different levels of study including organismal ecology, population ecology, community ecology and ecosystem ecology.

Ecosystem – A biological community of organisms and their environment. “Ecosystem” and “biome” are very similar terms, although “biome” usually refers to a specific type of ecosystem such as a rainforest, tundra, etc.

Electron Transport Chain(ETC):

The sequence of reactions whereby the reduced forms of the coenzymes are reoxidized by molecular O2 known as electron transport chain

The chain has principle electron carriers

  • NADH dehydrogenase.
  • Succinate dehydrogenase.
  • Coenzyme Q.
  • Cytochromes b2, bH, b560, c1, c, a, & a3 and iron sulphur proteins.

Each of them functions as a redox system with its prosthetic group or metal ions changing alternatively to reductant and oxidant – forms during electron transport.

Energy Pyramid – A graphic illustration which is used to show how energy flows through an ecosystem. These pyramids typically have plants, which efficiently and directly harvest sunlight, at the “bottom” and the top predator at the top, with herbivores and intermediate prey species in the middle.

Endocrinology: The study of the medical aspects of hormones, including diseases and conditions associated with hormonal imbalance, damage to the glands that make hormones, or the use of synthetic or natural hormonal drugs.

Endomembrane: all the membraneous components inside a eukaryotic cell, including the nuclear envelope, endoplasmic reticulum, and Golgi apparatus

Endosymbionts – Organisms that live within other organisms.

Flagellum – A flagellum (plural: flagella) is a long, whip-like structure that helps some single-celled organisms move. It is composed of microtubules. They help propel cells and organisms in a whip-like motion. The flagellum of eukaryotes usually moves with an “S” motion, and is surrounded by cell membrane. Flagella are structurally almost identical with the much smaller Cilia. So much so that it has been proposed protists bearing either should be unified in the Phylum Undulipodia.

Genome – A genome is an organism’s complete set of genetic instructions. Each genome contains all of the information needed to build that organism and allow it to grow and develop. Our bodies are made up of millions of cells (100,000,000,000,000), each with their own complete set of instructions for making us, like a recipe book for the body. This set of instructions is known as our genome and is made up of DNA.

Glucose: Glucose (also called dextrose) is a simple sugar with the molecular formulaC6H12O6. Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight. There it is used to make cellulose in cell walls, which is the most abundant carbohydrate. In energy metabolism, glucose is the most important source of energy in all organisms. Glucose for metabolism is partially stored as a polymer, in plants mainly as starch and amylopectin and in animals as glycogen. Glucose circulates in the blood of animals as blood sugar. The naturally occurring form of glucose is d-glucose, while l glucose is produced synthetically in comparatively small amounts and is of lesser importance.

Golgi body (Golgi apparatus, Golgi complex): an organelle found in eukaryotic cells; the Golgi apparatus consists of a stack of flattened sacs, constantly forming at one end and breaking up into Golgi vesicles at the other end; Golgi vesicles carry their contents to other parts of the cell, often to the cell surface membrane for secretion; the Golgi apparatus chemically modifies the molecules it transports; for example, sugars may be added to proteins to make glycoproteins.

Haemoglobin – Hemoglobin (American English) or haemoglobin (British English) abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells (erythrocytes) of almost all vertebrates (the exception being the fish family Channichthyidae) as well as the tissues of some invertebrates. Hemoglobin in blood carries oxygen from the lungs or gills to the rest of the body (i.e. the tissues). There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism. A healthy individual has 12 to 20 grams of hemoglobin in every 100 ml of blood.

Histology – Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy which looks at larger structures visible without a microscope. Although microscopic anatomy may be divided into organology, the study of organs, histology, the study of tissues, and cytology, the study of cells, modern usage places these topics under the field of histology. In medicine, histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue. In the field of paleontology, the term paleohistology refers to the histology of fossil organisms.

Hormone: Hormone, organic substance secreted by plants and animals that functions in the regulation of physiological activities and in maintaining homeostasis. Hormones carry out their functions by evoking responses from specific organs or tissues that are adapted to react to minute quantities of them. The classical view of hormones is that they are transmitted to their targets in the bloodstream after discharge from the glands that secrete them. This mode of discharge (directly into the bloodstream) is called endocrine secretion. The meaning of the term hormone has been extended beyond the original definition of a blood-borne secretion, however, to include similar regulatory substances that are distributed by diffusion across cell membranes instead of by a blood system.

Hypothermia – Hypothermia is a medical emergency that occurs when your body loses heat faster than it can produce heat, causing a dangerously low body temperature. Normal body temperature is around 98.6 F (37 °C). Hypothermia (hi-poe-THUR-me-uh) occurs as your body temperature falls below 95 F (35 °C).

Magnification: Magnification is the number of times larger an image is, than the real size of the object. The number of times greater than an image is than the actual object; magnification = image size ÷ actual (real) size of the object

Mitochondrion (plural: mitochondria): the organelle in eukaryotes in which aerobic respiration takes place

Nucleolus: a small structure, one or more of which is found inside the nucleus; the nucleolus is usually visible as a densely stained body; its function is to manufacture ribosomes using the information in its own DNA.

Nucleus: a relatively large organelle found in eukaryotic cells, but absent from prokaryotic cells; the nucleus contains the cell’s DNA and therefore controls the activities of the cell

Organelle: a functionally and structurally distinct part of a cell, e.g. a ribosome or mitochondrion

Parthenogenesis: Parthenogenesis is the phenomenon of development of an embryo from an egg without fertilization. It is of two types haploid and diploid parthenogenesis. It occurs usually due to defective meiosis that results in the egg nucleus having the unreduced number of chromosomes.

Pilus: A pilus (plural: pili) is a hair-like appendage found on the surface of many bacteria and archaea. The terms pilus and fimbria (plural: fimbriae) can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation. All pili in the latter sense are primarily composed of pilin proteins, which are oligomeric. Dozens of these structures can exist on the bacterial and archaeal surface. Some bacteria, viruses or bacteriophages attach to receptors on pili at the start of their reproductive cycle.

Pollination: Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma. The goal of every living organism, including plants, is to create offspring for the next generation. One of the ways that plants can produce offspring is by making seeds. Seeds contain the genetic information to produce a new plant.

Prokaryote: A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle.The word prokaryote comes from the Greek  “pro” means before  and “karyon” means nut or kerne. Prokaryotes are divided into two domains, Archaea and Bacteria. Species with nuclei and organelles are placed in the third domain, Eukaryota. Prokaryotes reproduce without fusion of gametes. The first living organisms are thought to have been prokaryotes.

Protein- Any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism. They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.

Resolution: is the ability to distinguish between two objects very close together; the higher the resolution of an image, the greater the detail that can be seen.

Ribosome: A ribosome is a complex cellular mechanism used to translate genetic code into chains of amino acids. Long chains of amino acids fold and function as proteins in cells. The function of a ribosome in any cell is to produce proteins.

TCA Cycle: The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or theKrebs cycle– is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins, into adenosine triphosphate (ATP) and carbon dioxide. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically. Even though it is branded as a ‘cycle’, it is not necessary for metabolites to follow only one specific route; at least three segments of the citric acid cycle have been recognized.

Tissue: Tissue is a cellular organisational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.

Tropic hormone: Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary. The hypothalamus secretes tropic hormones that target the anterior pituitary, and the thyroid gland secretes thyroxine, which targets the hypothalamus and therefore can be considered a tropic hormone.

Unicellular: A unicellular organism is an organism that consists of a single cell. This means all life processes, such as reproduction, feeding, digestion, and excretion, occur in one cell. Amoebas, bacteria, and plankton are just some types of unicellular organisms. They are typically microscopic and cannot be seen with the naked eye.

Zygote: A zygote is the union of the sperm cell and the egg cell. Also known as a fertilized ovum, the zygote begins as a single cell but divides rapidly in the days following fertilization.

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