2.1.1 - Cell Structure Flashcards
How does a light microscope work?
It uses light to form an image. Light that passes through or reflects from the surface of the specimen is seen.
What images are produced by light microscopes?
- Poor resolution due to the long wavelength of light (200nm)
- Low magnification (2000x)
- Colour image
- 2D
Which specimens can be examined by light microscopes?
Living and non-living specimens
How does a transmission electron microscope work?
It uses electrons to form an image. The electrons that pass through the specimen are detected.
What images are produced by transmission electron microscopes?
- High magnification (1000000x)
- High resolution due to short wavelength of electrons (0.2nm)
- Black and white
- 2D
Which specimens can be examined by transmission electron microscopes?
Only non-living specimens as the microscope must be in a vacuum so the air doesn’t absorb the electrons.
How does a scanning electron microscope work?
It uses electrons to form an image. Electrons that are reflected from the surface on the specimen are detected.
What images are produced by scanning electron microscopes?
- High magnification (1000000x)
- High resolution due to short wavelength of electrons (3-20nm)
- Black and white
- 3D
Which specimens can be examined by scanning electron microscopes?
Only non-living specimens as the microscope must be in a vacuum so the air doesn’t absorb the electrons.
How does a laser scanning microscope work?
It uses a laser beam to scan an object pixel by pixel creating an image of the reflected photon.
What images are produced by laser scanning confocal microscopes?
- High resolution
- 2D and 3D images
- Black and white/computer generated colour
What are dry mounts?
When thin slices or whole specimens are viewed with just the coverslip placed on top
What are wet mounts?
When water is added to the specimen before lowering the coverslip with a mounted needle to prevent air bubbles from forming. This is used for aquatic organisms.
What are squash slides?
Wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer to enable light to pass through. This is used for a root tip to view the chromosomes in mitosis.
What are smear slides?
When you use the edge of another slide to smear the sample across the slide to create a smooth, thin and even coated specimen. A cover slip is placed on top after smearing. This is used when examining blood cells in a blood sample.
How do you calibrate an eye piece graticule?
- Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece
- Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale
- Each division on the micrometer is 10μm so this can be used to calculate what one division on the eyepiece graticule is
Why are stains used in microscopy?
- To make cells more visible
- Increase contrast
- Identify different cell components
What is the formula for magnification?
Magnification = image size/object size
What is magnification?
The number of times greater the size of the image is than the size of the real object
What is resolution?
The ability to distinguish between two objects that are very close together. A higher resolution means more detail.
What is the structure of the nucleus?
- Nuclear envelope which is a double membrane that has nuclear pores to control exchange between the nucleus and cytoplasm
- Nucleoplasm which is a granular jelly like material
- Chromosomes which are protein bound linear DNA
- Nucleolus which is a smaller sphere inside which is the site of rNA production and makes ribosomes
What is the function of the nucleus?
- Site of DNA replication and transcription
- Contains the genetic code for each cell
- Site of ribosomal synthesis
What is the structure of flagella?
Long whip like structure
What is the function of flagella?
Involved in mobility and sometimes as sensory organelle for chemical stimuli
