1 - CELL STRUCTURE Flashcards
What is magnification?
It describes how much bigger an image appears compared with the original object.
How is magnification calculated?
Total magnification = magnifying power of objective lens x magnifying power of eyepiece lens
Magnification = Image size/ Actual size of image
What is resolution?
It is the ability of an optical instrument to see or produce an image that shows detail clearly.
Describe optical microscopes.
- use visible light
- relatively cheap
- easy to use
- portable
- able to be used in the field as well as in laboratories
- able to be used to study whole living specimens
- maximum magnification = x1500-x2000
- limited resolution = 0.2um which means organelles cannot be differentiated
What is a photomicrograph?
It is the photograph of the image seen using an optical microscope.
Describe laser scanning/ confocal microscopes.
- use laser light to scan an object point by point
- pixels are assembled into one image by computer
- have depth selectivity and so can focus on structures at different depths/ planes within a specimen
- can be used to observe whole living specimens
- used in the medical profession
- maximum magnification resolution
Describe SE microscopes.
- specimen must be fixed (dead) and coated in film of metal in a vacuum to be viewed
- produces a 3-D B&W image
- magnification ranges from x15000 to x20000
- maximum resolution is 0.002um
- electrons are knocked off of specimen and gathered in a cathode ray tube to form the image
Describe TE microscopes.
- specimen must be chemically fixed by dehydration and staining with metal salts to be viewed
- maximum magnification = x2 million (or x50 mil)
- maximum resolution is 0.0002um
- produces 2D B&W image - colour can be added to it by computer software
- electrons pass through specimen after being focused in beams by electromagnet
What are the disadvantages of both types of electron microscopes?
They are very large, expensive, and require skill and training to be used.
How are specimens prepared to be viewed under microscopes?
- Slides are dry mounted or wet mounted
- Dehydration
- Embedding in wax (prevents distortion when slicing)
- Making into sections which are differentially stained
What is differential staining?
Using coloured chemicals to identify different structures/ organelles within different cells under different microscopes
List all types of stains.
- Methylene blue (all-purpose)
- Acetic orcein - binds to DNA and stains chromosomes dark-red
- Eosin - stains cytoplasm
- Susan red - stains lipids
- Iodine in potassium iodide solution:
- stains cellulose (in cell walls) yellow
- stains starch granules blue/black
(appear violet under microscopes)
How are unstained specimens observed?
Using light interference to illuminate a colourless specimen against a dark background
What organelles are membrane-bound?
Nucleus, nuclear envelope , RER, SER, Golgi apparatus, mitochondrian lysosomes, chloroplasts, cell surface mebrane, flagella, cilia, and vacuole.
NUCLEUS
- Has a double membrane
- Houses all of th cell’s genome
- Contains chromatin which consists of DNA wound around histone proteins
- Has instructions for making proteins
NUCLEAR ENVELOPE
- Has 2 membranes with fluid in between them
- Surronds the nucleus
- Has pores which allow the passage of relatively large molecules
ROUGH ENDOPLASMIC RETICULUM
- Has cisternae - flattened membrane sacs
- Continuous with outer nuclear membrane
- Studded with ribosomes which enables transportation of proteins to plasma membrane or outside of cell
SMOOTH ENDOPLASMIC RETICULUM
- Has cisternae - flattened membrane sacs
- Continuous with outer nuclear membrane
- Not studded with ribosomes
- Invovled in essential lipid production
GOLGI APPARATUS
- Has a double membrane
- Stack of membrane-bound falttened sacs
- Recieves proteins from RER and modifies them by adding sugar - glycoproteins
- Packages modified proteins into vesicles for transportation or secretion from cell
MITOCHONDRIA
- Double membrane speprated by a fluid filled space
in the centre called the matrix - Highly folded inner membrane forms cristae
- Site of ATP production which drives almost all cell activites
LYSOSOMES
- Abundant in phagocytic cells
- Conatin powerful digestuve enzymes which break down materials
- Engulf old organelles and foreign matter
CHLOROPLASTS
- Double membrane seperated by fluid-filled space
- Inner membrane is continuous with falttened sacs called thylakoids forming granum which are repented by chlorophyll
- Site of photosynthesis in plant cells
- Found in some protoctists
FLAGELLA
- Long extension or tail
- Contains microtubules in 9+2 arrangement
- Enables movement
CILIA
- Short hair-like extensions
- Contains microtubules in 9+2 arrangement
- Enables fro movement of substances
