Biology IB HL - 1.2 Cell Structure

Prokaryotes are organisms whose cells lack a nucleus

archaebacteria

- eubacteria

found in extreme environments like high temperatures, salt concentrations or pH (i.e. extremophiles)

traditional bacteria including most known pathogenic forms (e.g. E. coli, S. aureus, etc.)

nucleoid

plasmids

slime capsule

flagella

pilli

region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)

autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)

70S

rigid outer covering made of peptidoglycan

a thick polysaccharide layer

used for protection against dessication (drying out) and phagocytosis

Long, slender projections containing a motor protein that enables movement

Hair-like extensions

enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)

Binary fission is a form of asexual reproduction used by prokaryotic cells

The circular DNA is copied in response to a replication signal

The two DNA loops attach to the membrane

The membrane elongates and pinches off (cytokinesis), forming two cells

organisms whose cells contain a nucleus

Eukaryotic cells are compartmentalised by membrane-bound structures (organelles) that perform specific roles

protista

fungi

plantae

animalia

unicellular organisms; or multicellular organisms without specialised tissue

have a cell wall made of chitin and obtain nutrition via heterotrophic absorption

have a cell wall made of cellulose and obtain nutrition autotrophically (via photosynthesis)

no cell wall and obtain nutrition via heterotrophic ingestion

Organelles are specialised sub-structures within a cell that serve a specific function

ribosomes

cytoskeleton

plasma membrane

Two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S)

Site of polypeptide synthesis (this process is called translation)

A filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol)

Provides internal structure and mediates intracellular transport (less developed in prokaryotes)

Phospholipid bilayer embedded with proteins (not an organelle per se, but a vital structure)

Semi-permeable and selective barrier surrounding the cell

Double membrane structure with pores; contains an inner region called a nucleolus

Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly

A membrane network that may be bare (smooth ER) or studded with ribosomes (rough ER)

Transports materials between organelles

| smooth ER = lipids ; rough ER = proteins

An assembly of vesicles and folded membranes located near the cell membrane

Involved in the sorting, storing, modification and export of secretory products

Double membrane structure, inner membrane highly folded into internal cristae

Site of aerobic respiration (ATP production)

Membranous sac containing a variety of catabolic enzymes

Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites

Microtubule organising centre (contains paired centrioles in animal cells but not plant cells)

Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)

chloroplast

vacuole (large, central and permanent)

cell wall

Double membrane structure with internal stacks of membranous discs (thylakoids)

Site of photosynthesis – manufactured organic molecules are stored in various plastids

Fluid-filled internal cavity surrounded by a membrane (tonoplast)

Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)

External outer covering made of cellulose (not an organelle per se, but a vital structure)

Provides support and mechanical strength; prevents excess water uptake

Membranous sacs filled with hydrolytic enzymes

Breakdown/hydrolysis of macromolecules (presence in plant cells is subject to debate)

Electron microscopes use electron beams focused by electromagnets to magnify and resolve microscopic specimens

Transmission electron microscopes (TEM)

| Scanning electron microscopes (SEM)

generate high resolution cross-sections of objects

display enhanced depth to map the surface of objects in 3D

They have a much higher range of magnification (can detect smaller structures)

They have a much higher resolution (can provide clearer and more detailed images)

Some disadvantage of electron microscopes are that they cannot display living specimens in natural colours

A micrograph is a photo or digital image taken through a microscope to show a magnified image of a specimen

Attempts can be made to deduce cell function based on the relative abundance of various organelles

Cells with many mitochondria typically undertake energy-consuming processes (e.g. neurons, muscle cells)

Cells with extensive ER networks undertake secretory activities (e.g. plasma cells, exocrine gland cells)

Cells rich in lysosomes tend to undertake digestive processes (e.g. phagocytes)

Cells with chloroplasts undergo photosynthesis (e.g. plant leaf tissue but not root tissue)

pili

flagella (except sperm)

slime capsule

plasmid

labelled as 70S

peptidoglycan, (thicker than cell membrane)