Topic 2: Cells, Viruses and Reproduction of Living
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summary of Topic 2: Cells, Viruses and Reproduction of Living Things
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Topic 2: Cells, Viruses and Reproduction of Living
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Topic 2: Cells, Viruses and Reproduction of Living
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2.1 Eukaryotic and prokaryotic cell structure and function
i Understand that cell theory is a unifying concept that states that cells are a fundamental
unit of structure, function and organisation in all living organisms.
Cell theory states that are cells are a fundamental unit of structure , function and
organisation in all living organisms .New cells are formed from other existing cells
ii Understand that in complex organisms, cells are organised into tissues, organs, and organ
systems.
Cells later on are organised into tissues,tissues into organs and organs into organ systems
Tissue-group of cells working together to perform a particular function
iii Know the ultrastructure of prokaryotic cells and the structure of organelles, including:
nucleoid, plasmids, 70S ribosomes and cell wall.
Ultrastructure of prokaryotic cell
,Function of organelles
Nucleoid- The area in which the single length coiled of DNA is found
Plasmid-Small circular pieces of DNA that code for specific aspects of DNA phenotype
(genes that aid bacteria survival)
70s ribosomes- This is where proteins are created. In prokaryotes ribosomes are 70s .The
letter “s” is a measure of size. (made from 50s and 30s) subunit
Cell walls-these are made from peptidoglycan which provide mechanicals for the cell wall.
Mesosome-infolding of the cell membrane
Pilli-thread of protein projection
, iv Be able to distinguish between Gram positive and Gram negative bacterial cell walls and
understand why each type reacts differently to some antibiotics.
Even though all bacterial cell walls contain peptidoglycan there are two types , gram-positive
and gram-negative bacterial cell walls. These can be distinguished by a process known as
gram staining.
We use this as different types of bacteria are vulnerable to different types of antibiotics and
the factor that affects their vulnerability is the type of cell wall.
Before staining bacteria are colourless. The cell walls of gram positive bacteria have a thick
layer of peptidoglycan which contains teichoic acid. The crystal violet/iodine complex from
the gram stain is trapped within the thick peptidoglycan therefore the colour remains the
same.
The cell walls of gram negative bacteria have a thin layer of peptidoglycan and no teichoic
acid. The outer membrane is also made up from a lipopolysaccharide. When the crystal
violet/iodine. The lipopolysaccharide layer is dissolved in an ethanol solution leaving the thin
peptidoglycan layer behind. The peptidoglycan layer then takes a red counterstain so cells
appeared red
v Know the ultrastructure of eukaryotic cells and the functions of organelles, including:
nucleus, nucleolus, 80S ribosomes, rough and smooth endoplasmic reticulum, mitochondria,
centrioles, lysosomes, Golgi apparatus, cell wall, chloroplasts, vacuole and tonoplast.
Ultrastructure of eukaryotic cell
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