Cell Structure - AS Level Biology 2021
I = Image size
A = Actual size of image
M = Magnification
1µm = 1000nm
Eyepiece Graticules & Stage Micrometers
Number of Micrometers ÷
Number of Graticule Division
= 1 Graticule Division
Graticule Divisions x
= Measurement (µm)
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.
Eyepiece Lens Magnification x Objective Lens Magnification
= Total Magnification
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
Large and installations = Can't move.
Small and easy to carry.
No Vacuum Needed.
Easy sample preparation.
Over X 500 000
Up to X 2000 Magnification.
Resolution = 0.5nm
Resolution = 200nm
Specimens = Dead
Specimens = Dead/Living
Images obtained from a light microscope, these are used for specimens above 200 nm.
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.
Contains the cells DNA
Contains nuclear envelope = separates nucleus from cytoplasm.
Site where ribosomes are made.
Powerhouse of the cell.
Site of aerobic respiration.
Has 70s Ribosomes & Circular DNA.
Chloroplast (Plant Only)
Can't live on their own.
Where photosynthesis happens.
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.
60s & 40s subunits.
Found in Eukaryotic Cells
50s & 30s subunits.
Ribosomes in Prokaryotes.
In Mitochondria & Chloroplast.
Has 2 Types
Rough endoplasmic reticulum (RER):
Round sacs transport substances.
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)
Around vacuole in plants.
Large Permanent Vacuole (Plant Only)
Regulates osmotic properties.
Used to keep plants stiff.
Where pigment (petal colour) is found.
Cleaners of the cell.
Contains concentrated mixtures of digestive enzymes:
Attached to the vacuole of cells.
Discharged/removed from cell.
Involved in making the cilia.
Not found in flowering plants & fungi.
Involved in movement of components within the cell.
Guid & direct organelles.
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.
In anabolic reactions.
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.
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
A protein coat called a ‘capsid’
A nucleic acid core (their genomes are either DNA or RNA, can be single or double-stranded)