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1. Cell Structure - AS Level Biology 2021 Cheat Sheet by

Cell Structure - AS Level Biology 2021

Magnif­ication Calcul­ations

I = Image size
A = Actual size of image
M = Magnif­­ic­ation

1m=1000mm
1mm=1000µm
1µm = 1000nm

Eyepiece Graticules & Stage Microm­eters

Number of Microm­­eters ÷
Number of Graticule Division
= 1 Graticule Division
Graticule Divisions x
Magnif­ication Factor
= Measur­­ement (µm)

Magnif­ication

How many times bigger the image of a specimen observed is in compared to the actual size of the specimen.
A light microscope has two types of lens:
An eyepiece lens.
A series of objective lenses.
Total
Magnif­ica­tion:
Eyepiece Lens Magnif­­ic­ation x Objective Lens Magnif­­ic­ation
= Total Magnif­­ic­ation

Resolution

 
The ability to distin­­guish between two separate points.
Resolution of a light microscope is limited by the wavelength of light.
Electron micros­­copes have a higher resolution and magnif­­ic­ation as electrons have a much smaller wavelength than visible light.

Electron Microscope VS Light Microscope

Electron Micros­cope
Light Microscope
Large and instal­lations = Can't move.
Small and easy to carry.
Vacuum Needed.
No Vacuum Needed.
Compli­cated sample
preparation.
Easy sample preparation.
Over X 500 000
Magnification.
Up to X 2000 Magnification.
Resolution = 0.5nm
Resolution = 200nm
Specimens = Dead
Specimens = Dead/Living

Photom­icr­ographs

Images obtained from a light micros­cope, these are used for specimens above 200 nm.

Electron microg­raphs

Images obtained from electron micros­copes, both scanning and transm­ission, these are used for specimens above 0.5 nm

Electron Microg­raphs: Animal Cells

Electron Microg­raphs: Plant Cells

 

Cell Surface Membrane

Controls exchange of material between the internal and external cell enviro­nment.

Cell Wall (Plant Only)

Used to enclos­e/p­rot­ect­/su­pport.
Fully permeable = Lets anything through.

Nucleus

Gives instru­ction.
Contains the cells DNA
Contains nuclear envelope = separates nucleus from cytoplasm.

Nucleolus

Site where ribosomes are made.

Mitoch­ondrion

Powerhouse of the cell.
Site of aerobic respir­ation.
Produces ATP.
Has 70s Ribosomes & Circular DNA.

Chloro­plast (Plant Only)

Contain DNA.
Can't live on their own.
Where photos­ynt­hesis happens.

Ribosome

Built of 2 subunits.
Do ont have a membrane.
Ones found in cytosol = always attached to ER
Ones found freely in cytoplasm or as part of the Rough endopl­asmic reticulum in Eukaryotic cells.
Is a complex of ribosomal RNA & Proteins.
Site of transl­ation.

80s Ribosomes

60s & 40s subunits.
Found in Eukaryotic Cells
In cytoplasm

70s Ribosomes

50s & 30s subunits.
Ribosomes in Prokar­yotes.
In Mitoch­ondria & Chloro­plast.

Endopl­asmic Reticulum

Has 2 Types
Rough endopl­asmic reticulum (RER):
Round sacs transport substa­nces.
 
Processes proteins.
Smooth endopl­asmic reticulum (ER):
Involved in the produc­tio­n/p­roc­ess­ing­/st­orage of lipids­/ca­rbo­hyd­rat­es/­ste­roids.
 
Site where substances needed by the cell are made.
 
Has no ribosomes.

Golgi body (Golgi appara­tus­/co­mplex)

Synthe­sises specific functions:
Hormones & enzymes.
Modifies proteins and packages them into vesicles or lysosomes.

Tonoplast (Plant Only)

Controls exchange.
Around vacuole in plants.

Large Permanent Vacuole (Plant Only)

Regulates osmotic proper­ties.
Used to keep plants stiff.
Where pigment (petal colour) is found.

Lysosomes

Cleaners of the cell.
Single membrane.
Contains concen­trated mixtures of digestive enzymes:
Hydrolytic enzymes
Attached to the vacuole of cells.
Discha­rge­d/r­emoved from cell.

Centrolie

Involved in making the cilia.
Not found in flowering plants & fungi.

Microt­ubules

Involved in movement of components within the cell.
Guid & direct organe­lles.

Plasmo­desmata

Important for transp­ort­/co­mmu­nic­ati­on/­sig­nalling between cells.
Controls movement & created paths between cells.
 

The vital role of ATP

Adenosine Tripho­sphate is a nucleo­tide.
Provides energy to cells.
It is produces in mitoch­ondria & chloro­plasts.
This energy
is required:
In anabolic reactions.
Active Transport.
In animals.
ATP from respir­ation = used to transfer energy in all energy­-re­quiring prosesses in the cells.

Structural features of Typical Prokar­yotic Cells

Bacteria are a type of prokar­yote.
Unicel­lular
100s/1000s of times smaller than eukaryotic cells.
Genetic material is not packaged within a membra­ne-­bound nucleus and is usually circular.

Prokar­yotic vs Eukaryotic Cell Structures

Viruses

Non-ce­llular struct­ures.
They have:
A protein coat called a ‘capsid’
 
A nucleic acid core (their genomes are either DNA or RNA, can be single or double­-st­randed)
               
 

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