Cell: The Building Block of Life

Comprehensive vocabulary flashcards covering the structure, function, history, and division of cells based on the Grade 8/9 lecture materials.

Thermophiles

Heat-loving, unicellular bacteria found in environments like the hot springs of Puga Valley in Ladakh, where temperatures remain nearly at the boiling point of water.

Unicellular

Organisms that consist of only one cell, such as bacteria or yeast.

Multicellular

Organisms made up of millions of cells that work together, such as plants, fish, birds, or humans.

Tissue

A group of similar cells performing similar functions.

Organ

A structure formed by different tissues organized to perform specific functions.

Organ System

A collection of several organs that work together to perform a major body function, such as the respiratory system.

Limit of resolution of the human eye

The ability of the human eye to see two points as distinct, which is approximately $0.1\,mm$ when viewed from a distance of about $25\,cm$.

Robert Hooke

The first person to observe a cell in $1665$; he used a self-designed microscope to examine cork and named the small box-like compartments 'cells'.

Light Microscope

A tool used in school laboratories to observe objects using visible light and lenses to achieve magnification and resolution.

Magnification of a Microscope

The total magnifying power calculated by multiplying the power of the eyepiece by the power of the objective lens (e.g., $10\times$ eyepiece and $10\times$ objective equals $100\times$ total magnification).

Micrometre ($\mu m$)

A unit of length where $1\,millimetre\,(mm) = 1000\,micrometre\,(\mu m)$, often used to measure the size of cells.

Nanometre ($nm$)

A unit of length equal to one-billionth of a metre ($10^{-9}\,m$).

Electron Microscope

A powerful instrument that uses a beam of electrons instead of light to reveal fine details of cell structures at the nanometre scale.

Cell Membrane

Also called the plasma membrane, it is a thin boundary that protects the cell and is selectively permeable, controlling the movement of substances in and out.

Selectively Permeable

A characteristic of the cell membrane that allows some substances to pass through while blocking others.

Osmosis

The diffusion of water across a selectively permeable membrane from an area of higher water concentration (dilute solution) to lower water concentration (concentrated solution).

Diffusion

The net movement of particles from a higher concentration to a lower concentration due to a concentration gradient.

Isotonic Solution

A solution where the solute concentration outside the cell is equal to the solute concentration inside the cell.

Hypotonic Solution

A solution where the solute concentration outside the cell is lower than inside the cell, causing the cell to swell due to water intake.

Hypertonic Solution

A solution where the solute concentration outside the cell is higher than inside the cell, causing the cell to shrink as water moves out.

Fluid-Mosaic Model

A model of the cell membrane describing it as a lipid bilayer ($7$ to $10\,nm$ thick) with embedded proteins that can move sideways, rotate, or flip.

Cell Wall

An additional rigid layer outside the cell membrane found in plants, fungi, and bacteria that provides protection and maintains cell shape.

Cellulose

A type of carbohydrate formed by linked glucose units that makes up the plant cell wall and serves as roughage in the human diet.

Cytoplasm

A semi-fluid, jelly-like substance inside the cell containing the nucleus and various organelles.

Organelles

Sub-cellular components in the cytoplasm, most of which are membrane-bound, that perform specific functions like manufacturing, waste removal, and energy production.

Prokaryotic Cells

Primitive cells (e.g., bacteria) that lack a well-defined nucleus and membrane-bound organelles; their genetic material is kept in a region called the nucleoid.

Eukaryotic Cells

Complex cells (e.g., plants and animals) that have a well-defined nucleus and several membrane-bound organelles.

Cytoskeleton

A network of fine fibres in eukaryotic cells that providing structural support, maintains cell shape, and enables internal transport.

Cell Inclusions

Stored substances in the cytoplasm, such as starch in plant cells or crystals of calcium oxalate and silica.

Nucleus

The house of coded instructions in a cell, enclosed by a double-layered nuclear membrane with pores for material transfer.

Nucleolus

A dense round body within the nucleus where the synthesis of ribosomal subunits takes place.

Chromosomes

Rod-shaped structures visible during cell division composed of DNA and proteins, which carry genetic information from parents to offspring.

DNA (Deoxyribonucleic acid)

The molecule containing genetic information; its functional segments are called genes.

Chromatin

An entangled mass of thread-like structures composed of DNA and proteins found in the nucleus of a non-dividing cell.

Ribosomes

Tiny structures that serve as the protein factories of the cell; they can be free in the cytoplasm or attached to the ER.

Endoplasmic Reticulum (ER)

A large network of membranes continuous with the nuclear envelope involved in the synthesis and transport of proteins, lipids, and hormones.

Rough Endoplasmic Reticulum (RER)

ER with ribosomes attached to its surface; it is primarily involved in protein synthesis and secretion.

Smooth Endoplasmic Reticulum (SER)

ER without ribosomes on its surface; it is involved in the synthesis and storage of fats (lipids) and hormones.

Golgi Apparatus

A stack of flattened sacs that acts as the cell's 'post office,' modifying, sorting, and packaging proteins and lipids into vesicles.

Lysosomes

Single membrane-bound sacs filled with enzymes that break down unwanted proteins, fats, carbohydrates, and damaged organelle parts.

Mitochondria

The powerhouses of the cell where cellular respiration occurs to release energy in the form of ATP; they contain their own DNA and ribosomes.

ATP (Adenosine Triphosphate)

The energy currency of the cell used for most cellular activities.

Cristae

The finger-like folds of the inner mitochondrial membrane that increase surface area for chemical reactions.

Plastids

Organelles found in plant cells used for food synthesis and storage; they have their own DNA and ribosomes.

Chloroplasts

Double-membrane-bound plastids containing the green pigment chlorophyll; the site of photosynthesis.

Chromoplasts

Plastids containing yellow, orange, or red pigments that give bright colors to flowers and fruits.

Leucoplasts

Colorless plastids that store food materials like starch (in potatoes), oils, or proteins.

Vacuoles

Storage organelles filled with cell sap; they are large and central in plant cells to maintain pressure and firmness, and smaller/temporary in animal cells.

Mitosis

A type of cell division resulting in two genetically identical daughter cells with the same DNA and chromosome count as the parent cell; used for growth and repair.

Meiosis

A two-step cell division process that produces four daughter cells (gametes), each with half the number of chromosomes; used for sexual reproduction.

Cell Culture

The method of growing plant or animal cells outside the body in nutrient-rich media under sterile conditions.

Contact Inhibition

A process in normal animal cells where cell division stops once cells come into contact with neighboring cells.

Programmed Cell Death (PCD)

A genetically regulated, organized process of selective cell destruction essential for normal development and immune function.

Totipotency

The ability of a single plant cell to develop into a complete plant if provided with suitable nutrients and conditions; proposed by Gottlieb Haberlandt in $1902$.

Cell Theory

The unifying principle of biology 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.