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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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