Important and Difficult Keywords with Definitions
Cell — The basic structural and functional unit of life. All living organisms are made of cells.
Unicellular organism — An organism made up of only one cell, such as bacteria or yeast.
Multicellular organism — An organism made up of many cells, such as plants, animals, and humans.
Tissue — A group of similar cells that perform a similar function.
Organ — A structure formed by different tissues working together to perform a specific function.
Organ system — A group of organs working together to perform a major life function.
Resolution — The ability to distinguish two very close points as separate and distinct.
Limit of resolution — The minimum distance at which two points can still be seen separately by the eye or an instrument.
Magnification — The process of making an object appear larger than its actual size.
Microscope — An instrument used to see tiny objects that cannot be seen clearly with the naked eye.
Light microscope — A microscope that uses visible light and lenses to magnify small objects.
Electron microscope — A very powerful microscope that uses a beam of electrons to see very tiny structures in great detail.
Cell membrane / Plasma membrane — A thin outer boundary of the cell that surrounds and protects the cell contents and controls movement of substances in and out.
Selectively permeable membrane — A membrane that allows only certain substances to pass through it while blocking others.
Diffusion — The movement of particles from a region of higher concentration to a region of lower concentration.
Osmosis — The movement of water through a selectively permeable membrane from a region of higher water concentration to lower water concentration.
Concentration gradient — The difference in concentration of particles between two regions.
Isotonic solution — A solution in which the concentration outside the cell is equal to the concentration inside the cell.
Hypotonic solution — A solution in which the concentration outside the cell is lower than inside the cell.
Hypertonic solution — A solution in which the concentration outside the cell is higher than inside the cell.
Fluid-mosaic model — The model that explains the structure of the cell membrane as a lipid bilayer with proteins embedded in it.
Lipid bilayer — The double layer of lipid molecules that forms the basic structure of the cell membrane.
Protein — A complex biological molecule that helps in structure, transport, movement, and many functions inside living cells. In membranes, proteins help substances pass through.
Cell wall — A rigid outer covering outside the cell membrane in plants, fungi, and bacteria that gives shape, support, and protection.
Permeable — A condition in which substances such as water and some dissolved materials can pass through.
Cellulose — A carbohydrate that forms the main part of the plant cell wall.
Cytoplasm — The jelly-like semi-fluid substance inside the cell in which cell organelles are present.
Organelle — A specialised structure inside the cell that performs a particular function.
Prokaryotic cell — A cell that does not have a well-defined nucleus and lacks membrane-bound organelles, such as a bacterial cell.
Eukaryotic cell — A cell that has a well-defined nucleus and membrane-bound organelles, such as plant and animal cells.
Membrane-bound organelles — Organelles that are surrounded by their own membranes.
Nucleoid — The region in a prokaryotic cell where genetic material is present without a surrounding membrane.
Cytoskeleton — A network of fine fibres in eukaryotic cells that gives support, maintains shape, and helps movement and transport.
Cell inclusions — Stored materials in the cytoplasm such as starch or crystals.
Nucleus — The control centre of the cell that contains genetic material and directs cell activities.
Nuclear membrane — The double-layered covering around the nucleus.
Nuclear pore — Small openings in the nuclear membrane through which materials move between the nucleus and cytoplasm.
Nucleolus — The dense round body inside the nucleus where ribosomal subunits are formed.
Chromatin — The thread-like form of DNA present in a non-dividing cell.
Chromosome — A condensed rod-shaped structure formed from chromatin during cell division; it carries genetic information.
DNA (Deoxyribonucleic acid) — The molecule that carries genetic information in living organisms.
Gene — A functional segment of DNA that carries information for inherited traits.
Inheritance — The passing of characters from parents to offspring.
Ribosome — A tiny cell structure that is the site of protein synthesis.
Protein synthesis — The process by which proteins are made in the cell.
Endoplasmic Reticulum (ER) — A network-like organelle that helps in the synthesis and transport of proteins, lipids, and some hormones.
Rough Endoplasmic Reticulum (RER) — The type of ER that has ribosomes on its surface and mainly makes proteins.
Smooth Endoplasmic Reticulum (SER) — The type of ER that lacks ribosomes and mainly makes and stores fats and some hormones.
Golgi apparatus — A stack of flattened sacs that modifies, sorts, packages, and transports proteins and lipids.
Vesicle — A small membrane-bound sac used for transport or storage of materials inside the cell.
Lysosome — A membrane-bound sac containing digestive enzymes that breaks down wastes and worn-out cell parts.
Enzyme — A biological substance that speeds up chemical reactions in living organisms.
Mitochondrion / Mitochondria — The organelle that releases energy from food and is called the powerhouse of the cell.
Cristae — Finger-like folds of the inner membrane of mitochondria that increase surface area for energy-producing reactions.
Cellular respiration — The process by which food is broken down to release energy in the cell.
ATP (Adenosine Triphosphate) — The energy currency of the cell that stores and supplies usable energy.
Plastid — A type of organelle found in plant cells that helps in food synthesis, storage, or colour formation.
Chloroplast — A green plastid containing chlorophyll that performs photosynthesis.
Chlorophyll — The green pigment that absorbs sunlight for photosynthesis.
Photosynthesis — The process by which green plants prepare food in the presence of sunlight.
Stroma — The semi-fluid substance inside a chloroplast.
Chromoplast — A plastid containing coloured pigments such as yellow, orange, or red.
Leucoplast — A colourless plastid that stores food such as starch, oils, or proteins.
Pigment — A coloured substance present in cells or plastids.
Vacuole — A membrane-bound storage sac in the cell that stores water, minerals, sugars, and wastes.
Cell sap — The watery fluid present inside the vacuole of a plant cell.
Wilted — The drooping condition of a plant when its cells lose water and firmness.
Cell division — The process by which new cells are formed from pre-existing cells.
Mitosis — A type of cell division that produces two genetically identical daughter cells with the same number of chromosomes as the parent cell.
Meiosis — A type of cell division that produces four daughter cells with half the number of chromosomes; it forms gametes.
Daughter cells — The new cells formed after cell division.
Gamete — A reproductive cell such as sperm or egg having half the number of chromosomes.
Fertilisation — The fusion of male and female gametes to form a new individual.
Genetic diversity — Differences in genetic makeup among individuals of the same species.
Cell cycle — The controlled and orderly sequence of events through which a eukaryotic cell grows and divides.
Cell culture — The process of growing plant or animal cells outside the body under special conditions.
Synthetic biology — A field of science in which scientists design or build biological systems or parts artificially.
Cell Theory — The theory stating that all living organisms are made of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.
Contact inhibition — The process in which many animal cells stop dividing when they come in contact with neighbouring cells.
Tumour — A mass of abnormal cells formed due to uncontrolled cell division.
Cancer cell — An abnormal cell that divides uncontrollably and may form tumours.
Programmed Cell Death (PCD) — A genetically controlled process in which cells die in an orderly way for proper growth and balance in the body.
Totipotency — The ability of a living plant cell to develop into a complete plant under suitable conditions.
Thermophiles — Heat-loving bacteria that can survive in very hot environments like hot springs.
Acellular — Not made up of cells.
Virus — A tiny acellular infectious agent made of genetic material and a protein coat.
Viroid — A tiny infectious agent made only of genetic material and lacking a protein coat.
Prion — An infectious misfolded protein that lacks genetic material.
Most Important Keywords to Memorise First
For quick revision, these are the most important terms from the chapter:
Cell, Cell membrane, Osmosis, Diffusion, Cell wall, Cytoplasm, Nucleus, Chromosome, DNA, Gene, Prokaryotic cell, Eukaryotic cell, Ribosome, ER, Golgi apparatus, Lysosome, Mitochondria, ATP, Plastid, Chloroplast, Chromoplast, Leucoplast, Vacuole, Cell division, Mitosis, Meiosis, Gamete, Cell Theory, Contact inhibition, Tumour.
