Module 2 Foundations in Biology Flashcards
Compound microscopes led to new discoveries essential for cell theory to be fully explained. Explain the benefit of having two lenses in a microscope. (4 marks)
- Objective lens and eyepiece lens
- Objective lens magnifies the specimen
- Eyepiece lens magnifies image (from objective lens)
- Higher magnification produced than with just one lens
Outline how a student could prepare a temporary mount of tissue for a light microscope.
1) Obtain thin section of tissue e.g. using ultratome or by maceration.
2) Plant plant tissue in a drop of water.
3) Stain tissue on a slide to make structures visible.
4) Add coverslip using mounted needle at 45* to avoid trapping air bubbles.
Describe how light microscopes work.
- Lenses focus rays of light and magnify the view of a thin slice of specimen.
- Different structures absorb different amounts and wavelengths of light.
- Reflected light is transmitted to the observer via the objective lens and eyepiece.
Describe how a transmission electron microscope (TEM) works.
- Pass a high energy beam of electrons through a thin slice of specimen.
- More dense structures appear darker since they absorb more electrons.
- Focus image onto fluorescent screen of photographic plate using magnetic lenses.
Describe how a scanning electron microscope (SEM) works.
- Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses.
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
Describe how a laser scanning confocal microscope works.
- Focus a laser bean onto a small area on a sample’s surface using the objective lenses.
- Fluorophores in the sample emit photons.
- Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order.
Why do samples need to be stained for light microscopes?
Coloured dye binds to the structures.
Facilitates absorption of wavelengths of light to produce image.
Differential staining: contrast between heavily and lightly stained areas distinguishes structures.
Outline how a student could prepare a temporary mount of tissue for a light microscope.
1) Obtain thin section of tissue e.g. using ultratome or by maceration.
2) Plant plant tissue in a drop of water.
3) Stain tissue on a slide to make structures visible.
4) Add coverslip using mounted needle at 45* to avoid trapping air bubbles.
Describe how light microscopes work.
- Lenses focus rays of light and magnify the view of a thin slice of specimen.
- Different structures absorb different amounts and wavelengths of light.
- Reflected light is transmitted to the observer via the objective lens and eyepiece.
Describe how a transmission electron microscope (TEM) works.
- Pass a high energy beam of electrons through a thin slice of specimen.
- More dense structures appear darker since they absorb more electrons.
- Focus image onto fluorescent screen of photographic plate using magnetic lenses.
Describe how a scanning electron microscope (SEM) works.
- Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses.
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
Describe how a laser scanning confocal microscope works.
- Focus a laser bean onto a small area on a sample’s surface using the objective lenses.
- Fluorophores in the sample emit photons.
- Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order.
Why do samples need to be stained for light microscopes?
Coloured dye binds to the structures.
Facilitates absorption of wavelengths of light to produce image.
Differential staining: contrast between heavily and lightly stained areas distinguishes structures.
State the magnification and resolution of a compound optical microscope.
Magnification - x 2000
Resolution - 200nm
State the magnification and resolution of a TEM.
Magnification - x 500,000
Resolution - 0.5 nm
State the magnification and resolution of an SEM.
Magnification - x 500,000
Resolution - 3 ^- 10 nm
Describe the structure of the nucleus.
- Surrounded by a nuclear envelope, a semipermeable double membrane.
- Nuclear pores allow substances to enter/exit.
- Dense nucleolus made of RNA and proteins assembles ribosomes.
Describe the function of the nucleus.
- Contains DNA coiled around chromatin into chromosomes.
- Controls cellular processes: gene expression determines specialisation, site of mRNA transcription, mitosis, and semiconservative replication.
Describe the structure and the function of the endoplasmic reticulum (ER).
Cisternae structure: Network of tubules and flattened sacs extends from cell membrane and connects to nuclear envelope.
ROUGH ER - Many ribosomes attached for protein synthesis and transport.
SMOOTH ER - Lipid synthesis.
Centrioles
Structures found in the cytoplasm made of microtubules that produce the spindle fibres during mitosis.
Chloroplast
Organelles found in plants and algae that are the site of photosynthesis.
Cilia
Small hair-like structures that project from the surface of cells.
Confocal Microscopy
A type of microscopy that uses lasers to scan a specimen point by point to produce an image.
Cytoskeleton
A mesh of protein fibres found in the cytoplasm of eukaryotic cells used for structural support and intracellular transport.
Differential Staining
Using multiple different stains to distinguish different parts of a specimen.
Eukaryotic Cell
A type of cell that contains a nucleus along with membrane bound organelles.
Flagella
A whip-like structure found on bacterial cells that is used for cell movement.
Golgi Apparatus
An organelle found in eukaryotic cells that is involved in the modification and packaging of proteins.
Light Microscope
A type of microscope that uses a series of lenses to magnify the visible light reflecting off a specimen.
Lysosomes
Membrane-bound vesicles found in the cytoplasm that contain a hydrolytic enzyme called lysozyme.
Magnification
How much bigger an image appears compared to the original object calculated using the following formula:
image size = actual size x magnification
Mitochondrion
An organelle found in eukaryotic cells that is the site of aerobic respiration.
Nuclear Envelope
A double membrane that surrounds the nucleus.
Nucleolus
A structure found inside the nucleus that contains proteins and RNA and is involved in synthesizing new ribosomes.
Nucleus
An organelle found in eukaryotic cells that stores the genetic information of the cell as chromosomes and is surrounded by a membrane called the nuclear envelope.
Plasma Membrane
A semipermeable lipid bilayer studded with proteins that surrounds the cell and many organelles.
Prokaryotic Cell
A type of cell that does not contain any membrane bound organelles or a nucleus.
Resolution
The ability to distinguish two different points in a specimen.
Ribosomes
Organelles found either free in the cytoplasm or membrane bound that are
involved in the synthesis of proteins.
Rough Endoplasmic Reticulum (RER)
A membrane-bound organelle that is involved in the synthesis and packaging of proteins.
Scanning Electron Microscope (SEM)
A type of microscope that passes a beam of electrons over the surface of a specimen to produce an image.
Smooth Endoplasmic Reticulum (SER)
A membrane-bound organelle involved in lipid
synthesis.
Transmission Electron Microscope (TEM)
A type of microscope that passes a beam of electrons through a sample to produce an image.
Adhesion
A property of water molecules that creates an attraction between them and surfaces that they are in contact with.
Amino Acid
The monomers containing an amino group (NH2), a carboxyl group (COOH) and a variable R group that make up proteins.
Amylopectin
A branched polysaccharide made up of alpha glucose monomers joined by α-1,6 glycosidic bonds that makes up starch along with amylose.
Amylose
An unbranched polysaccharide made up of alpha glucose monomers joined by α-1,4 glycosidic bonds that makes up starch along with amylopectin.
Anions
An ion with a negative charge.
Benedict’s Test
A biochemical test used to detect the presence of a reducing sugar in a solution and distinguish between solutions of different reducing sugar concentrations.