2.1 - Basic Components of Living Systems Flashcards
Define magnification
How many times larger an image is than the actual size of the object
Define resolution
The closest distance between two points where they are both still clear and distinguishable
How does a compound light microscope work?
Has 2 lenses:
• objective lens - placed near specimen
• eyepiece lens - through which specimen is viewed
Both magnify the specimen
Double lens configuration allows for much higher magnification and reduced chromatic aberration
Illumination usually provided by light underneath samples, but some microscopes allow form opaque objects to be illuminated from above
What are the different types of sample preparation?
- dry mount
- wet mount
- squash slides
- smear slides
What is a dry mount?
Solid specimens are viewed whole or cut into very thin slices with a sharp blade (called SECTIONING)
Specimen is placed on the centre off the slide and a cover slip is placed over the sample
Eg hair, pollen, dust, insect parts can be viewed whole
Muscle tissue or plants can be sectioned and viewed this way
What is a wet mount?
Specimens are suspended in liquid eg water, immersion oil
A cover slip is placed on from an angle
Eg aquatic samples and other living organisms cam be viewed this way
What are squash slides?
A wet mount is first prepared, then a lens tissue is used to press down the cover slip
Potential damage to the cover slip can be avoided by squashing the sample between 2 microscope slides
Care needs to be taken so that the cover slip doesn’t break when being pressed
Eg root tip squashes are used to look at cell division
What are smear slides?
The edge of a slide is used to smear the sample, creating a thin, even coating on another slide.
A cover slip is then placed over the sample
Eg smearing blood on a slide to look at cells in the blood
Why do we use stains?
The cytoskeleton and other cell structures are often transparent
Stains increase contrast as different components within a cell take up stains to different degrees
The increase in contrast allows components to become visible so they can be identified
What are crystal violet and methylene blue?
Positively charged dyes
Attracted to negatively charged materials in the cytoplasm, leading to the staining of cell components
What are nigrosin and Congo red?
Negatively charged dyes
Repelled by negatively charged cytosol
These dyes stay outside cells , leaving fresh cells unstained, which then stand out against the stained background
This is a negative stain technique
What is differential staining?
Using specific stains to distinguish between different types of cells or between different organelles of a single organism
What is the gram-staining technique?
Used to differentiate bacteria into Gram-positive and Gram-negative bacteria.
Gram-positive bacteria take up a crystal violet stain and look blue/purple
Gram-negative bacteria don’t retain crystal violet stain and are then counter stained with safranin dye, turning it red
What processes may be involved in the production of pre-prepared slides?
- fixing - chemicals like formaldehyde are used to preserve specimens in as near-natural state as possible
- sectioning - specimens are dehydrated with alcohols to form a hard block and then placed in a mould with wax or resin to form a hard block, which can then be sliced thinly with a microtome
- staining - specimens are often treated with multiple stains to show different structures
- mounting - specimens are secured to a microscope slide and a cover slip placed on top
What are the features of a proper biological drawing?
- title
- state magnification
- use sharp pencil for drawing and labels
- use white, unlined paper
- use as much paper as possible for drawing
- draw smooth, continuous lines
- no shading
- draw clearly defined structures
- ensure proportions are correct
- label lines shouldn’t cross and shouldn’t have arrowheads
- label lines should be parallel to the top of he page and drawn with a ruler
What’s the equation for magnification?
M = I/A
M = magnification I = size of image A = actual size
What is an eyepiece graticule?
A glass disc marked with a scale 1-100
Doesn’t have units
Found on the objective lens of a microscope
What is a stage micrometer?
A microscope with a very accurate scale in micrometers (um) engraved on it
The scale marked is usually 100 divisions = 1mm, so 1 division = 10 um
It is used to calibrate the eyepiece graticule for each magnification separately
What is a transmission electron microscope (TEM)?
- a beam of electrons is transmitted through a specimen and focused to produce an image (similar to light microscopy)
- produces a 2D image
• resolution = 0.5nm
magnification = x 500,000
What is a scanning electron microscope (SEM)?
- a beam of electrons is sent across the surface of the specimen, and reflected electrons are detected
- produces a 3D image
•resolution = 3-10nm
magnification = x100,000
What is an artefact?
An object or structure seen through the microscope that have been created during the processing of a specimen (eg an air bubble)
Features of light microscopy
- inexpensive to buy and operate
- small and portable
- simple sample preparation
- sample preparation doesn’t usually lead to distortion
- natural colour of sample can be seen
- vacuum not required
- specimen can be alive or dead
- resolution = 200nm
- magnification = up to x2000
Features of electron microscopy
- expensive to buy and operate
- large and not portable (must be installed)
- complex sample preparation
- sample preparation can lead to distortion/artefacts
- black and white images produced (but can be coloured digitally)
- vacuum required
- specimen must be dead
- resolution = 0.5 nm (TEM) or 3-10nm (SEM)
- magnification = over x500 000
What are laser scanning confocal microscopes?
- moves a single spot of focused light across a specimen (point illumination)
- this causes fluorescence from the components labelled with a ‘dye’
- the emitted light from the specimen is filtered through a pinhole aperture
- only light radiated form very close to the focal plane (the distance that gives the sharpest image) is detected
How do you prepare a sample for laser scanning confocal microscopy?
You treat it with a fluorescent chemical (dye)
This means that when the laser (high intensity light) passes over the specimen, there is fluorescence, which is then detected to produce a magnified image
Features of laser scanning confocal microscopy
- high resolution, as very thin sections of specimen are examined and light from elsewhere is removed
- 2D and 3D images can be produced
- non invasive
What are prokaryotes and prokaryotic cells?
PROKARYOTES:
• single-called prokaryotic organisms from the kingdom Prokaryotae
PROKARYOTIC CELLS:
•cells with no membrane bound nucleus or organelles
What are eukaryotes and eukaryotic cells?
EUKARYOTES:
•multicellular eukaryotic organisms like animals, plants and fungi
•single-celled protoctista
EUKARYOTIC CELLS:
• cells with a nucleus and other membrane-bound organelles
What are the components of an animal cell?
- nucleus
- nucleolus
- nuclear envelope
- rough endoplasmic reticulum (RER)
- smooth endoplasmic reticulum (SER)
- Golgi apparatus/body
- vesicles
- lysosomes
- mitochondria
- ribosomes
- cytoplasm
- cytoskeleton
- plasma cell membrane/cell-surface membrane
- food vacuole (temporary)
- cilia and flagella (sometimes)
- centrosome (2 centrioles)
What are the components of a plant cell?
- nucleus
- nucleolus
- nuclear envelope
- rough endoplasmic reticulum (RER)
- smooth endoplasmic reticulum (SER)
- Golgi apparatus/body
- vesicles
- lysosomes
- mitochondria
- ribosomes
- cytoplasm
- cytoskeleton
- plasma cell membrane/cell-surface membrane
- cellulose cell wall
- permanent vacuole
- tonoplast
• chloroplast
What is the nucleus?
- largest organelle, diameter roughly 5-10 μm
- contains genetic information (DNA), which directs protein synthesis, and in this way, controls all the metabolic processes of the cell
What is the nucleolus?
- area within the nucleus
- approx 0.2-3.5μm in diameter
- responsible for producing ribosomes
- made of proteins and RNA
- RNA is used to make ribosomal RNA (rRNA), which is combined with proteins to form ribosomes
What is the nuclear envelope?
- a double membrane around the nucleus
- protects nucleus from damage in the cytoplasm
- contained nuclear pores which allow molecules to move into/out of nucleus
What is endoplasmic reticulum (ER)?
A network of membranes enclosing flattened sacs called cisternae
ROUGH ENDOPLASMIC RETICULUM (RER):
• has ribosomes bound to its surface
• is responsible for synthesis and transport of proteins
SMOOTH ENDOPLASMIC RETICULUM (SER):
• doesn’t have ribosomes on the surface
•responsible for lipid and carbohydrate synthesis, and storage
Wheat is the Golgi apparatus?
- aka Golgi body
- approx 2-5 μm
- made of cisternae (similar ion structure to SER)
- plays a role in modifying proteins after translation and packaging proteins into vesicles
What are vesicles?
- membranous sacs which story and transport substances within the cell
- are a single membrane with fluid inside
- 30nm - 100 nm in diameter
What are lysosomes?
- specialised vesicles which contain hydrolytic enzymes
- break down waste material, eg old organelles, and pathogens in cytoplasm
- important for apoptosis (programmed cell death)
What are mitochondria?
- site of cellular respiration, where ATP is a produced
- have a double membrane - inner one is highly folded into cristae, increasing surface area for respiration
- the fluid interior is called the matrix
- contains a small amount of DNA called mtDNA
- can produce their own enzymes and reproduce themselves
• approx size 0.5-1 μm
What are ribosomes?
- made from rRNA and proteins
- site of protein synthesis
- not surrounded by a membrane
- found free floating in cytoplasm, on the RER, in mitochondria and chloroplasts
- approx size 25-30nm
What is the cytoplasm?
Internal fluid of cells
Made of:
• cytosol (water, salts and organic molecules)
•organelles
• cytoskeleton
What is the cytoskeleton?
Made of:
•microfilaments
•microtubules
• intermediate fibres
Functions:
• whole cell support/ maintains shapes of cell
• movement of cilia and flagella
•change shapes of cell (cytokinesis, phagocytosis, exocytosis, endocytosis)
•provides tracks for organelles to move across, and holds organelles in place
• movement of chromatids during mitosis
What are microfilaments?
- contractile fibres formed from the protein actin
- responsible for cell movement and cell contraction during cytokinesis
- average diameter 6nm
What are microtubules?
- globular tubulin proteins polymerise to form tubes
- used to form scaffold-like structures that determine the shape of the cell
- act as tracks for the movement of organelles around the cell
- form spindle fibres which are used in anaphase of cell division
- average diameter 25nm
What are intermediate filaments?
- multiple strands of fibrous proteins wound together
- give mechanical strength to cells and help maintain their integrity
- average diameter 8-10nm
What is the cell surface membrane?
- aka plasma membrane
- found on surface of cells
- made of a phospholipid bilayer and proteins embedded within it
- partially permeable membrane that’ll controls what enters/leaves the cell
What are cilia?
- found in animal cells
- stationary cilia are present on the surface of many cells and have an important any function in sensory organs eg nose
- mobile cilia beat in a rhythmic manner, creating a current, causing fluids or objects adjacent to the cell to move
- each cilia has 2 central microtubules surrounded by 9 pairs of microtubules (9+2) formation
- pairs of microtubules slide over each other, causing the cilia to move in a beating pattern
What are flagella?
- whip like structures protruding from a cell
- enables cell mobility
- can be used as a sensory organelle, detecting chemical changes in the cell’s environment
What are centromeres?
- made of 2 centrioles
- make spindle fibres made from microtubules for mitosis
- each centriole is approx 250nm in diameter and 500nm long
What is a vacuole?
- membrane-lined sacs containing cell sap
- permanent vacuoles found in plants are important in maintaining cell turgor, so that then contents of teh cell push against the cell wall and maintain a rigid framework for the cell
- membrane around the vacuole is called the tonoplast
- it is partially permeable, so controls what enters/leaves vacuole
- if vacuoles appear in animal cells, they are small and transient (not permanent)
- average size 1-10 μm
What is a cellulose cell wall?
- found in a plant cell
- made of cellulose
- freely permeable so substances can pass into and out of cell through her the cell wall
- acts as a defence mechanism, protecting the contents iof the cell against invading pathogens
What is a chloroplast?
- found in plant cells
- responsible for photosynthesis
- have a double membrane structures (similar to mitochondria)
- fluid enclosed in chloroplast is called the stroma
- they have an internal network of membranes which form flattened sacs called thylakoids, providing a large surface area
- several thylakoids stacked together are called granum (pl. grana)
- grana are joined together by membranes called lamellar
- grana contain the chlorophyll pigments, where light dependant reactions occur during photosynthesis
- starch produced by photosynthesis is present as starch grains
• chloroplasts contains their own ribosomes and DNA, so can produce their own proteins
Describe how organelles work together to produce proteins
1) nucleus contains the genes for protein synthesis and is the site of transcription where an mRNA molecule is produced
2) the mRNA leaves the nucleus via the nuclear pore and binds to the ribosomes on the rough endoplasmic reticulum (RER), where the protein is synthesised
3) protein passes through the cisternae of the RER and is packaged into a transport vesicle. The vesicle travels via the cytoskeleton to the Golgi apparatus
4) vesicle fuses to the cis-face of the Golgi apparatus and the proteins enter. The Golgi apparatus processes and modifies the protein.
5) the protein is packaged into a vesicle and leave the Golgi apparatus from the trans face. Some vesicles form lysosomes. Some vesicles form secretory vesicles, which carry the protein to the cell surface membrane. The vesicle fuses with the cell surface membrane and the protein is secreted via exocytosis
What components make up the ultra structure of a prokaryotic cell?
- cytoplasm
- cell surface membrane
- ribosome
- circular chromosome
- plasmid
- flagellum
- pili
- peptidoglycan cell wall
- slime capsule
What is a circular chromosome?
- a singular chromosome of DNA found in prokaryotes
- not contained in a nucleus - free floating in cytoplasm (within nucleoid region)
- supercoiled to make it more compact
What are plasmids?
- a small loop of DNA found in prokaryotes
* contain additional genes not included in circular chromosome
What is the difference between prokaryotic and eukaryotic ribosomes?
• prokaryotic ribosomes are smaller (70S/ 20nm) than eukaryotic ribosomes (80S/25nm)
What are prokaryotic flagella?
- thinner than eukaryotic flagella
- doesn’t have a 9+2 arrangement
- energy to rotate the flagella comes from chemiosmosis (not ATP)
- attached to the cell membrane of a prokaryote by a basal body
- rotated by a molecular motor
- moves in a whip like manner
- enables prokaryote to move
What are pili?
- hair like structures found on prokaryotes
* allow them to adhere to one another or to host cells
What is a peptidoglycan cell wall?
- found on prokaryotes
- aka murein
- polymer formed from amino acid and sugars
- provides strength and support to the cell
What is a slime capsule?
- a waxy, protective capsule found on the outside of prokaryotes
- prevents infection by viruses (bacteriophages)
