There are some important definitions and terminologies in biology which reappear every year in NEET examinations. Here we bring to you a collection of all such terminologies and definitions for a super quick revision for your Biology NEET 2023 preparations.
Table of Contents
Chapter 2 – Biological Classification
Chapter 5 – Morphology of Flowering Plants
Chapter 6 – Anatomy of Flowering Plants
Chapter 8 – Cell: The Unit of Life
Chapter 10 – Cell Cycle and Cell Division
Chapter 11 – Transport in Plants
Chapter 12 – Mineral Nutrition
Chapter 13 – Photosynthesis in Higher Plants
Chapter 14 – Respiration in Plants
Chapter 15 – Plant Growth and Development
Chapter 16 – Digestion and Absorption
Chapter 17 – Breathing and Exchange of Gases
Chapter 18 – Body Fluids and Circulation
Chapter 19 – Excretory Products and their Elimination
Chapter 21 – Neural Control and Coordination
Chapter 1 – The Living World
- Nomenclature: The process of naming an organism such that it is known by the same name all over the world is known as nomenclature. A need for standardising the naming procedure came up when the local names of all organisms started creating confusion and ambiguity in the scientific world.
- Taxonomy: The science of classifying, naming and describing an organism based on its morphological, genetic, behavioural and biochemical characteristics is referred to as taxonomy. The taxonomic hierarchy consists of the following groups: Species → Genus → Family → Order → Class → Phylum/Division → Kingdom.
Chapter 2 – Biological Classification
- Heterocyst: Heterocysts are specialised cells found in eubacteria (true bacteria) that help in fixing atmospheric nitrogen. Example – Nostoc and Anabaena. These cells maintain an anaerobic conditions that help in proper functioning of the nitrogenase enzyme and hence nitrogen fixation takes place. Other vegetative cells have an aerobic condition for photosynthesis and hence they cannot support nitrogen fixation.
- Planktons: Planktons are minute microscopic organisms that are found floating passively with the water currents.
- Dikaryon: Dikaryon is an intervening stage found in fungi where two compatible fungi hyphae fuse together to form a condition of n+n, i.e., two nuclei in one cell. Normally, the nuclei fuse together to give rise to diploid cells, but sometimes an intervening dikaryon is formed that eventually fuses to become a diploid cell.
- Viroids: Viroids are small infectious agents that have a free RNA that is devoid of any protein coat. It is smaller than a virus, has a low molecular weight and was first discovered when it caused potato spindle tuber disease.
- Zoospore: Zoospores are motile, asexual and flagellated structures that help in locomotion and asexual reproduction in fungi. It is pyriform or pear-shaped and is found packed in a zoosporangium.
- Aplanospore: Aplanospores are asexual, non motile spores. They do not have flagella.
- Types of Gametic Fusion
- Isogamy: The gametes that fuse are similar in shape, size and all other characteristics.
- Anisogamy: The gametes are totally dissimilar from each other in every aspect.
- Oogamy: It is a specific type of fusion where the female gamete is large and non-motile and the male gamete is small and motile.
Chapter 3 – Plant Kingdom
- Antheridium and Archegonium: Antheridium and archegonium are male and female sex organs found in bryophytes, respectively. Appearance-wise, the archegoniophore of the archegonium has a leafy look while the antheridiophore of the antheridium looks like a scattered fried egg.
- Sporophylls: Sporophylls are structures found in pteridophytes that bear sporangia on leaf-like appendages.
- Prothallus: The thalloid, heart shaped gametophytic body found in pteridophytes is known as prothallus. It is heart-shaped, haploid and bears both the antheridium and archegonium.
- Strobili/Cones: Strobili or cones are reproductive structures that are borne on bryophytes. They are spiral or overlapping arrangements of sporophylls developed along a central axis. The male cones are found in lower branches whereas female cones are found on upper branches for easy pollination.
- Embryo Sac: Embryo sac is a 7-celled and 8-nucleated structure that is found in the ovary of angiosperms. It consists of a central cell that has two nuclei in n+n position. The chalazal end has three antipodal cells and the micropylar end has two synergids and one egg cell. The antipodal cells degenerate but the synergids help in the fertilisation of the egg cell on arrival of the pollen grain.
Chapter 4 – Animal Kingdom
- Metamerism: In animals, the body is externally and internally divided into segments with repetition of organs, this phenomenon is known as metamerism. For example, earthworms.
- Metagenesis: The alternation of generation between polyp and medusa in cnidarians is referred to as metagenesis.
- Monoecious & Dioecious: In animals, monoecious organisms are those that reside both the male and female sex organs in the same body. They are also known as hermaphrodites. Conversely, dioecious animals are those that have separate sexes. The same goes for plants as well.
- Notochord: Notochord is a mesodermally derived solid structure that separates the alimentary canal from the nerve cord. Animals that possess the notochord are known as chordates and those that do not have a notochord are referred to as non-chordates.
Chapter 5 – Morphology of Flowering Plants
- Phyllotaxy: The arrangement of leaves on a stem or branch is known as phyllotaxy. Alternate phyllotaxy is observed in Hibiscus where only one leaf is borne on one node and they are alternatively placed. Opposite phyllotaxy is observed in guava where two leaves are found opposite to each other on a single node. Lastly, whorled phyllotaxy is seen in Alstonia where more than one or a bunch of leaves are observed arising from a single node.
- Aestivation: The arrangement of sepals and petals arranged in a floral bud with respect to other whorls of the flower is referred to as aestivation. It is of four types: valvate aestivation – where the sepals or petals merely touch each other at the margin; twisted aestivation – where the sepals and petals overlap each other on the margin; imbricate aestivation – where the sepals and petals overlap each other but one sepal has both the margins inside and one sepal and both the margins outside; and lastly vexillary aestivation – where one bigger sepal encloses the other sepals inside it as seen in pea plants.
- Placentation: The arrangement of ovules inside the ovary of a flower is known as placentation. When the ovules are present in the centre of the ovary and the ovary is compartmentalised with septa, it is called axile placentation. When the ovules are present on the ventral suture of the ovary, it is referred to as marginal placentation. When the ovules are found on the periphery of the ovule, it is referred to as parietal placentation. When the ovules are found in the centre of the ovary, and the ovary is not compartmentalised, it is referred to as free central placentation. Lastly, when there is a single ovule present at the base of the ovary, it is called as basal placentation.
Chapter 6 – Anatomy of Flowering Plants
- Exarch and Endarch: The xylem that is formed before is known as protoxylem and the one that is formed later is referred to as metaxylem. On the basis of arrangement of protoxylem and metaxylem there are two types of vascular bundles – endarch and exarch. Endarch is the condition when the protoxylem is situated at the centre and the metaxylem is situated at the periphery, normally seen in plant stems. Exarch condition is observed when the protoxylem is present at the periphery and metaxylem is present in the centre as seen in plant roots.
- Conjoint Vascular Bundle: When the xylem and phloem lie on the same radius, they are referred to as conjoint vascular bundles. If cambium is found between the xylem and phloem, they are referred to as an open-type bundle. On the other hand, if cambium is absent between the xylem and phloem, it is referred to as a closed bundle.
- Adaxial and abaxial: When epidermis is found on the upper surface of leaves, it is considered as the adaxial surface. On the other hand, when epidermis is found on the lower surface of leaves, it is referred to as the abaxial surface.
- Bark: Bark is a non-technical term for the layer present beyond vascular cambium. It includes secondary phloem and periderm (it consists of phellogen, phelloderm and phellem).
Chapter 8 – Cell: The Unit of Life
- Glycocalyx: it is the outermost layer of the cell envelope that is made up of carbohydrates embedded with proteins and lipids. The composition of the layer varies among different bacteria.
- Nucleoid: Nucleoid as seen in prokaryotes is a primitive structure that is not well defined and consists of dense areas of genetic material.
- Endomembrane System: It is a system that consists of single membrane bound organelles such as endoplasmic reticulum, Golgi apparatus, vacuoles and lysosomes. These organelles are involved in the packaging and transport of materials.
- Semi-Autonomous Organelles: The organelles that can produce their own genetic material are referred to as semi-autonomous organelles. Such organelles include mitochondria and chloroplast. They are able to synthesise almost half of the proteins by themselves and remain dependent on the nucleus for the other half, that is why they are referred to as semi-autonomous organelles.
- Histone Proteins: The positively charged proteins that bind the negatively charged DNA into chromosomes are referred to as histone proteins. H1 protein is a linker protein that binds the multiple nucleosomes together. H2A, H2B, H3 and H4 form a histone octamer around the DNA helix for binding.
- Centromere: A constricted point that joins two chromatids of a chromosome together is referred to as a centromere.
- Kinetochore: It is a specialised structure found on the centromere that becomes the site for attachment of spindle fibres during cell division.
Chapter 10 – Cell Cycle and Cell Division
- Karyokinesis & Cytokinesis: Karyokinesis is the division of the nucleus whereas cytokinesis is the division of cells.
- Quiescent stage/ G0 stage: The inactive stage of the cell cycle where the cell does not divide at all is referred to as the quiescent or G0 stage.
- Metaphase Plate: The chromosomes align in a plane during the metaphase stage of cell cycle and form a plate-like structure called the metaphase plate.
- Synaptonemal Complex: The synaptonemal complex is a proteinaceous structure formed between two homologous sister chromatids in eukaryotes during meiosis I that brings out synapsis and recombination of the chromosomes.
Chapter 11 – Transport in Plants
- Translocation: The biological mechanism of transport of water and other important nutrients by xylem and phloem from one plant part (source) to another (sink) is known as translocation. The xylem transports water from the roots to different parts of the plant, whereas the phloem transports food prepared by the leaves to all the parts of the plant.
- Porins: Porins are proteins that form large pores in the external membrane of mitochondria and chloroplasts and allow diffusion of molecules across the membrane. Example – Aquaporins are water channels that allow the diffusion of water molecules across the membrane.
- Uniport, Symport and Antiport: The movement of a single molecule in one direction across a membrane is referred to as uniport transport. The movement of two molecules in the same direction across a membrane is referred to as symport transport. Antiport on the other hand is the movement of two molecules in opposite directions across a membrane.
- Water Potential: The potential energy of water in a system as compared to pure water when both are kept at same temperature and pressure is referred to as water potential. It is denoted by Ψw. The water potential of pure water is always 0.
- Solute Potential: The pressure that is required to stop the inward flow of water through a semipermeable membrane is referred to as solute potential. It is denoted by Ψs. Since the water potential of pure water is always 0, adding any solute to it makes the potential negative.
Chapter 12 – Mineral Nutrition
- Hydroponics: The science of cultivating plants in a soil-free environment is known as hydroponics. In this technique, the plants are grown in a nutrient enriched solution with or without the support of inert materials like perlite, sand or gravel.
- Critical Concentration: The concentration of essential elements below which the growth of the plants get retarded is known as critical concentartion. The concentration of elements above this level can lead to toxicity.
Chapter 13 – Photosynthesis in Higher Plants
- Light Harvesting Complex (LHC): A complex of chlorophyll and protein molecules that is implanted in the thylakoid membrane of the chloroplast is referred to as the light harvesting complex. It is made up of a reaction centre that is surrounded by numerous accessory pigments. It helps in the transfer of light energy. The chlorophyll a in the reaction centre excites the electron and helps in the formation of ATP.
- Z-scheme: The movement of electrons in a non-cyclic manner for the production of ATP (phosphorylation) is known as non-cyclic phosphorylation. The movement of electrons takes places from the photosystem II to photosystem I in a unidirectional manner forming a Z, hence it is also known as the Z-scheme.
- Kranz Anatomy: The specialised arrangement of mesophyll cells clustered around the bundle sheath cells in a ring like manner in C4 plants is referred to as Kranz anatomy. It is mainly found in grasses such as maize but has also been seen in a few dicots. This is an adaptation by the C4 plants to prevent photorespiration.
Chapter 14 – Respiration in Plants
- Respiratory Quotient: The ratio of volume of CO2 produced to the volume of O2 consumed during respiration is termed as the respiratory quotient.
| Substrate | Respiratory Quotient |
|---|---|
| Carbohydrates | 1 |
| Organic Acids | >1 |
| Fats | 0.7 |
| Proteins | 0.5 – 0.9 |
Chapter 15 – Plant Growth and Development
- Differentiation: Meristematic cells are dividing cells that divide throughout their life. In plants, root apical and shoot apical meristems are such cells that keep dividing. When these cells divide and mature to become specialised cells that perform particular functions and do not divide further, it is called differentiation.
- Dedifferentiation: When the differentiated cells regain their ability to divide, i.e., become meristematic again, it is called dedifferentiation.
- Redifferentiation: When the dedifferentiated cells divide and mature to become specialised cells, it is known as redifferentiation.
- Plasticity: The ability of plants to form different structures to cope and adapt with the changing environment is known as plasticity.
- Apical Dominance: The dominance of the apical buds over the lateral buds is known as apical dominance. In this condition, the growing apical buds inhibit the growth of lateral buds so that the plant only grows in height to gain more light for photosynthesis.
- Vernalisation: The artificial procedure of exposing the plants (or seeds) to cooler temperatures to accelerate the flowering process is known as vernalisation.
Chapter 16 – Digestion and Absorption
- Thecodont: Any animal that possesses a morphological arrangement where the base of the tooth is completely embedded in the socket of jaw bone is referred to as a thecodont. Examples – crocodiles and dinosaurs
- Heterodont: Animals that have different types of tooth in the same dentition are known as heterodonts. Example – dog, tiger, etc.
- Diphyodont: Animals that develop two sets of teeth in their lifetime are known as diphyodont. Example – Human is a diphyodont that develops deciduous teeth and eventually a permanent set of teeth as an adult.
| Note: Humans can also be called as heterodonts because the permanent teeth are of different morphology such as canines, incisors, molars and premolars. |
|---|
- Chyme: Chyme is a semi-fluid mass of partially digested food that is passed from the stomach to the intestines.
- Chyle: Chyle is milky white fluid formed during digestion in the intestines. It is mainly made up of fats and lymph fluids.
Chapter 17 – Breathing and Exchange of Gases
- Bohr’s Effect: Bohr’s effect is the phenomenon of change in the oxygen affinity of haemoglobin in response to the pH change and concentration change of CO2 in blood.
Chapter 18 – Body Fluids and Circulation
- Pericardium: A conical sac of serous membranes that encloses the heart and roots of great blood vessels is referred to as pericardium.
- Sinoatrial Nodes: The sinoatrial nodes or the SA nodes are specialised myocardial structures that are located in the walls of the atrium of the heart between the superior caval vein and right atrium. It functions to send electrical impulses along the electrical conduction system of the heart and stimulate contraction.
Chapter 19 – Excretory Products and their Elimination
- Columns of Bertini: The columns of Bertini, also known as renal column, are medullary extensions between the renal cortex and renal pyramids in the kidney. It consists of urinary tubes, blood vessels and fibrous material.
- Glomerular Filtration Rate: The volume of filtrate formed by the kidney per minute is referred to as glomerular filtration rate (GFR). It is 125 ml/min.
- Atrial Natriuretic Factor (ANF): ANF is a peptide hormone released from the cardiac atria in response to atrial stretch from hypervolemia and hypertension.
Chapter 21 – Neural Control and Coordination
- Resting Potential: The electric potential across a resting plasma membrane is termed as resting potential. Its value is -70mV.
- Action Potential: A sudden rise or fall in the electric potential across the resting plasma membrane is called the action potential. Its value lies between +30 to +45mV.
- Thalamus: Thalamus is an egg shaped grey matter present in the centre of the brain. It functions as a hub for the exchange of sensory motor information such as sight, taste, hearing and touch.
- Rods and Cones: Rods and cones are photoreceptor cells found in the retina of the eye. Rods have rhodopsin that help in scotopic or dim light vision, whereas cones have iodopsin that help in photopic or day light vision.
This sums up important terminologies of Class 11 for Biology NEET 2023 preparations. Stay tuned to BYJU’S for more information related to NEET.
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