Cell as a Unit of Life- Important Terms

Cell as a Unit of Life:

• Cell- is a structural and functional unit of living beings that consists of a membrane-covered mass of protoplasm. Cell was discovered by Robert Hooke in 1665.
• Cytology- is the study of the form and structure of cells as well as their organelles with the help of a microscope.
• Cytoplasm- A part of protoplasm filled within the space of nuclear membrane and cell membrane having cell organelle.
• Hyaloplasm- Cytoplasm without cell organelle.
• Compound- A substance that is formed by the chemical combination of two or more than two substances.
• Protoplasm- The living substance present in the living cells. The cytoplasm and nucleoplasm together form protoplasm.
• Amino Acid- Organic compounds with carboxyl and amino groups. These are the basic building block of protein.
• Carbohydrate- Organic molecules containing carbon, hydrogen and oxygen in the ratio of CH₂O. Example- glucose, starch, glycogen, sugar, cellulose.
• Nucleus- A dense body in the centre of the cell having the nucleoplasm and chromosomes. It was discovered by Robert Brown in 1831 and is commonly called as ‘director of the cell‘.
• Monosaccharide- Simple sugar, not digestible by hydrolysis. Example- glucose, fructose.
• Disaccharide- A complex molecule of sugar having two molecules of glucose.
• Polysaccharide- These are composed of several molecules of glucose joined together by glycosidic bonds.
• Mucopolysaccharides- These are polysaccharides formed galactose and mannose. The most common example is mucilage which is produced by the plant as a slimy substance.
• Callus- An unorganized and undifferentiated mass of tissue.
• Totipotency- It is the inherent capacity of living cells to develop into different kinds of cells.
• Adenosine Triphosphate (ATP)– An energy-rich compound that is found in all cells and serves as an energy source for various cellular functions.
• Aster- Bundle of microtubule fibres radiating out from each cell pole during metaphase.
• Basal Body- Cylindrical microtubule containing cell organelle lying at the base of cilia and flagella and similar in structure to centrioles.
• Simple Proteins- These are the proteins that are composed of amino acids only. They form small globular molecules soluble in water or larger globular molecules insoluble in water.
• Conjugated Proteins- These are formed by the binding of a simple protein with a non-protein called the prosthetic group. Example- nucleoproteins.
• Nucleic Acid- Macromolecule or polymer of nucleotides in an unbranched chain; DNA and RNA.
• Ribonucleic Acid (RNA)- A nucleic acid containing phosphate, ribose sugar and the nitrogen base, uracil, besides adenine, guanine and cytosine. Functions in protein synthesis.
• Deoxyribonucleic Acid (DNA)- Genetic material; deoxyribose containing a nucleic acid that stores hereditary information in the form of code words and makes chromosomes and genes.
• Purine- It is a nitrogenous base having 9 membered double ring.
• Pyrimidine- It is a base that has a single 6 membered ring.
• Translation- The synthesis of protein according to the information coded on mRNA.
• Transcription- The process of RNA synthesis on a DNA template.
• Cell Membrane- also called plasma membrane or plasmalemma is a delicate, thin elastic and semi-permeable membrane that surrounds all living cells.
• Permeable Membrane- is one that allows all the substances (solvents) to pass through it.
• Semi-permeable Membrane- also called selectively permeable membrane is one that allows only some selected solvents to pass through it.
• Impermeable- A membrane that does not allow any substance to pass through it.
• Osmosis– The tendency of water to move across a differentially permeable membrane from a dilute to a concentrated solution.
• Differentially Permeable Membrane- Selectively permeable membranes found in living systems.
• Diffusion- It is the movement of particles from a medium of higher concentration to a medium of lower concentration till the concentration of both media become equal.
• Endocytosis- Intaking of large-sized liquid or solid macromolecules inside the cell through the plasma membrane.
• Exocytosis-Expelling of cellular secretions or wastes out of the cell through the plasma membrane.
• Pinocytosis- It is the process of taking liquid substance by a plasma membrane.
• Phagocytosis (cell eating)- It is the process of engulfing solid particles.
• Active Transport- It is the movement of the ions or molecules across a membrane against concentration gradients.
• Passive Transport- It is the movement of ions or molecules across a membrane from high to low concentration along the chemical or electrochemical gradient.
• Tonicity- The external osmotic environment of a cell forms the tonicity.
• Isotonic- When the relative concentration of water and solutes on either side of the cell membrane is the same, the solution is called isotonic.
• Hypertonic- Solution exerting greater osmotic pressure than the cytoplasm.
• Hypotonic- Solution exerting lesser osmotic pressure than the cytoplasm.
• Exosmosis- If during osmosis the water or solvent from the living cell diffuses out, the phenomenon is termed exosmosis.
• Endosmosis-If during osmosis, the flow of water from surroundings into a living cell take place, the process is known as endosmosis.
• Plasmolysis- As a result of exosmosis, the cytoplasm of the cell gets shrunk and moves towards the centre of the cell.
• Crenation- The shrunken appearance caused by exosmosis in erythrocytes.
• Lysosome- is a cell organelle that releases enzymes to hydrolyze the cell contents. Lysosomes also called suicide bags.
• Cytokinesis- The division of cytoplasm during cell division.
• Prokaryote- Organisms lacking a nucleus and membrane-bounded organelles in their cells. Example- bacteria, blue-green algae.
• Eukaryotes- Organisms such as plants and animals, with a well-defined nucleus enclosed in a nuclear envelope and having one or more membrane-bounded organelles in their cells.
• Tonoplast- The membrane surrounding the vacuole.
• Suberin- A water-proofing material secreted by cork cells and endodermal cells.
• Stroma- The granular matrix of the chloroplast.
• Centromere- Region of the chromosome at which spindle fibril is attached during cell division.
• Chlorophyll- Green photosynthetic, light-capturing pigment of plant cells, typically located in the chloroplasts.
• Chloroplasts- are green plastids.
• Chromoplasts- Yellow, orange, or red-coloured plastids containing various pigments like carotenes and xanthophyll, etc. 
• Leucoplats- A colourless plastid that stores proteins, lipids and starch.