Unit 3 Biology: Cell Structure and Functions

Vocabulary flashcards covering the key structures, organelles, and historical discoveries in cell biology based on Chapter 8 of Unit 3.

Reductionist Biology

A physico-chemical approach to study and understand living organisms by applying the concepts and techniques of physics and chemistry to describe processes in molecular terms.

G.N. Ramachandran

The founder of the ‘Madras school’ of conformational analysis of biopolymers who discovered the triple helical structure of collagen in 1954 and developed the ‘Ramachandran plot’.

Cell

The fundamental structural and functional unit of all living organisms; anything less than a complete structure of a cell does not ensure independent living.

Antonie Von Leeuwenhoek

The scientist who first saw and described a live cell.

Robert Brown

The scientist who discovered the nucleus.

Matthias Schleiden

A German botanist who in 1838 observed that all plants are composed of different kinds of cells which form the tissues of the plant.

Theodore Schwann

A German Zoologist (1839) who reported that animal cells have a thin outer layer called the ‘plasma membrane’ and concluded that the cell wall is a unique character of plant cells.

Rudolf Virchow

The scientist who in 1855 first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula).

Cell Theory

A theory stating that (i) all living organisms are composed of cells and products of cells and (ii) all cells arise from pre-existing cells.

Prokaryotic Cells

Cells that lack a membrane bound nucleus and membrane bound organelles; examples include bacteria, blue-green algae, mycoplasma, and PPLO.

Eukaryotic Cells

Cells that possess membrane bound nuclei and other membrane bound organelles like the endoplasmic reticulum, mitochondria, and Golgi complex.

Cytoplasm

A semi-fluid matrix that occupies the volume of the cell and is the main arena of cellular activities in both plant and animal cells.

Ribosomes

Non-membrane bound organelles found in all cells (prokaryotic and eukaryotic) that serve as the site of protein synthesis.

Mesosome

A specialized differentiated form of cell membrane in prokaryotes formed by the extensions of plasma membrane into the cell in the form of vesicles, tubules, and lamellae.

Plasmids

Small circular DNA molecules found in many bacteria outside the genomic DNA which confer unique phenotypic characters like resistance to antibiotics.

Glycocalyx

The outermost layer of the bacterial cell envelope; it can be a loose sheath called the slime layer or a thick and tough layer called the capsule.

Gram Positive Bacteria

Bacteria that take up the staining procedure developed by Gram.

Chromatophores

Membranous extensions into the cytoplasm of some prokaryotes like cyanobacteria that contain pigments.

Polysome (Polyribosome)

A chain formed by several ribosomes attached to a single mRNA which translates the mRNA into proteins.

Inclusion bodies

Non-membrane bound reserve materials stored in the cytoplasm of prokaryotic cells, such as phosphate granules, cyanophycean granules, and glycogen granules.

Fluid Mosaic Model

An improved model of cell membrane structure proposed by Singer and Nicolson in 1972, where the quasi-fluid nature of lipid enables lateral movement of proteins within the bilayer.

Passive Transport

The movement of molecules briefly across the membrane without any requirement of energy along the concentration gradient.

Active Transport

An energy dependent process involving the utilization of ATP to transport molecules across a membrane against their concentration gradient, such as the $Na^+/K^+$ Pump.

Middle lamella

A layer mainly of calcium pectate which holds or glues different neighbouring plant cells together.

Endomembrane System

A group of membranous organelles whose functions are coordinated, including the endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles.

Rough Endoplasmic Reticulum (RER)

Endoplasmic reticulum bearing ribosomes on their outer surface; it is frequently involved in protein synthesis and secretion.

Smooth Endoplasmic Reticulum (SER)

Endoplasmic reticulum without ribosomes on its surface; it is the major site for the synthesis of lipids and lipid-like steroidal hormones in animal cells.

Golgi apparatus

A densely stained reticular structure first observed by Camillo Golgi (1898) consisting of flat, disc-shaped sacs called cisternae; it packages materials and forms glycoproteins and glycolipids.

Lysosomes

Membrane bound vesicular structures formed in the Golgi apparatus, rich in hydrolytic enzymes (hydrolases) that digest carbohydrates, proteins, lipids, and nucleic acids.

Tonoplast

The single membrane that binds the vacuole in plant cells.

Mitochondria

Double membrane-bound organelles known as the 'power houses' of the cell; they are the sites of aerobic respiration and produce ATP.

Cristae

The inner membrane infoldings of a mitochondrion that increase the surface area.

Chloroplasts

Double membrane-bound plastids containing chlorophyll and carotenoid pigments responsible for trapping light energy for photosynthesis.

Leucoplasts

Colourless plastids that store nutrients: amyloplasts (starch), elaioplasts (oils and fats), and aleuroplasts (proteins).

Stroma

The space limited by the inner membrane of the chloroplast which contains enzymes for carbohydrate and protein synthesis, circular DNA, and ribosomes.

Thylakoids

Flattened membranous sacs present in the stroma of chloroplasts; they are arranged in stacks called grana.

Cytoskeleton

An elaborate network of filamentous proteinaceous structures (microtubules, microfilaments, intermediate filaments) involved in mechanical support, motility, and cell shape maintenance.

Axoneme

The core of eukaryotic cilia or flagella, possessing a 9+2 array of microtubules.

Centrosome

An organelle containing two perpendicular cylindrical structures called centrioles, which are made of nine triplets of tubulin protein.

Chromatin

A loose and indistinct network of nucleoprotein fibres in the interphase nucleus containing DNA, histones, non-histone proteins, and RNA.

Centromere

The primary constriction of a chromosome that holds two chromatids together and possesses disc-shaped structures called kinetochores.

Metacentric Chromosome

A chromosome with a middle centromere forming two equal arms.

Microbodies

Membrane bound minute vesicles containing various enzymes, present in both plant and animal cells.