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Cell Structure - AS Level Biology 2021
Magnification CalculationsI = Image size
A = Actual size of image
M = Magnification
1m=1000mm
1mm=1000µm
1µm = 1000nm |
Eyepiece Graticules & Stage MicrometersNumber of Micrometers ÷
Number of Graticule Division | = 1 Graticule Division | Graticule Divisions x
Magnification Factor | = Measurement (µm) |
MagnificationHow 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 MicroscopeElectron 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 |
PhotomicrographsImages obtained from a light microscope, these are used for specimens above 200 nm. |
Electron micrographsImages 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 MembraneControls exchange of material between the internal and external cell environment. |
Cell Wall (Plant Only)Used to enclose/protect/support. | Fully permeable = Lets anything through. |
NucleusGives instruction. | Contains the cells DNA | Contains nuclear envelope = separates nucleus from cytoplasm. |
NucleolusSite where ribosomes are made. |
MitochondrionPowerhouse 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. |
RibosomeBuilt 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 Ribosomes60s & 40s subunits. | Found in Eukaryotic Cells | In cytoplasm |
70s Ribosomes50s & 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. |
LysosomesCleaners of the cell. | Single membrane. | Contains concentrated mixtures of digestive enzymes: | Hydrolytic enzymes | Attached to the vacuole of cells. | Discharged/removed from cell. |
CentrolieInvolved in making the cilia. | Not found in flowering plants & fungi. |
MicrotubulesInvolved in movement of components within the cell. | Guid & direct organelles. |
PlasmodesmataImportant for transport/communication/signalling between cells. | Controls movement & created paths between cells. |
| | The vital role of ATPAdenosine 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 CellsBacteria 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
VirusesNon-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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