basic components of living systems Flashcards
What 3 things does Cell Theory state?
• Both plant and animal tissue is composed of cells • Cells are the basic unit off all life • Cells only develop from existing cells
Define ‘compound light microscope
A light microscope which uses two lenses to magnify an object; the objective lens, which is placed near to the specimen and an eyepiece lens, through which the specimen is viewed.
List the 4 ways of preparing a sample for examination by light microscopy
List the 4 ways of preparing a
sample for examination by light
microscopy
Describe the dry mount sample preparation method
• Solid specimens are viewed whole or cut into very thin slices (sectioning) • Specimen placed in centre of slide and cover slip is placed over the sample • e.g. hair, pollen, dust, insect parts; muscle tissue or plants can be sectioned and viewed this way
Describe the wet mount sample preparation method
• Specimen are suspended in liquid e.g. water or oil • Cover slip is placed on from an angle • E.g. aquatic samples and other living organisms
Describe the squash slides sample preparation method
• Wet mount is prepared first • Lens tissue is used to gently press down cover slip • Squash sample between 2 microscope slides to avoid damage to coverslip • Good technique for soft samples • e.g. root tip squashes are used to look at cell division
Describe the smear slides sample preparation method
Edge of slide is used to smear sample creating thin even coating on another slide • Cover slip then placed over sample • E.g. for sample of blood to view cells in the blood
Give 3 reasons why stains are used in samples in light
microscopy
• Images tend to have low contrast as most cells don’t absorb lots of light • The cytosol (aqueous interior) of cells and other cell structures are often transparent • Stains increase contrast as different components in the cell take up stains to different degrees
How do you prepare a sample for staining?
• Place the sample on a slide and allow it to air dry • Heat fix the sample by passing through a flame • The specimen will adhere to the microscope slide and will then take up stains
List and describe 4 different types of stains
Crystal violet & Methylene blue are \+ve dyes attracted to and staining cell components • Nigrosin & Congo red are negatively charged dyes that are repelled by the -ve cytosol so stay outside cells
Define differential staining
Using specific stains to distinguish
different types of cell
Describe the gram stain technique
• Used to separate bacteria into gram-positive and gram-negative bacteria • Crystal violet is first applied to a bacterial specimen on a slide, then iodine which fixes the dye, then the slide is washed with alcohol
What are the 2 types of bacteria in gram staining?
• Gram negative bacteria - Bacteria with cell walls that stain red with Gram stain • Gram positive bacteria - Bacteria with cell walls that stain purpleblue with Gram stain
What is the acid-fast technique?
• Used to differentiate species of Mycobacterium • Lipid solvent is used to carry carbolfuchsin dye into the cells, which are then washed with dilute acid-alcohol solution • Mycobacterium are not affected by the acid-alcohol and retain the carbolfuchsin stain which is bright red
Define magnification
The number of times larger an image
appears, compared with the size of
the object
Define resolution
The clarity of an image; the high the
resolution, the clearer the image
What is the formula for calculating magnification?
Magnification = size of image /
. actual size of object
In a light microscope, what is resolution limited by?
The diffraction of light as it passes through samples (and lenses). • Diffraction is the tendency of light waves to spread as they pass close to physical structures • Light reflected from individual structures can overlap due to diffraction • Structures are no longer seen as separate entities and detail is lost • In optical microscopy, structure closer than 1/2 the wavelength of light can’t be seen separately
Why does using electron beams instead of light produce a better resolution?
Beams of electrons have a wavelength thousands of times shorter than light, so they are still diffracted, but individual beams can be a lot closer before they overlap. Therefore objects that are smaller and closer together can be seen separately without diffraction blurring the image
What is an eyepiece graticule?
A glass disc marked with a fine scale of 1 to 100. The scale has no units. The scale on the graticule at each magnification is calibrated using a stage micrometer
What is a stage micrometer?
A microscope slide with an accurate scale in micrometers marked on it. The scales usually 100 divisions = 1mm, so 1 division = 10 micrometers
What are the steps in using a graticule to calibrate a light microscope?
For each objective lens: 1. Put stage micrometer in place and the eyepiece graticule in the eyepiece 2. Get the scale on the micrometer slide in clear focus 3. Align the micrometer scale with the scale in the eyepiece. Take a reading from the 2 scales
Give the equation that links measurement (micrometers), graticule divisions, and
magnification factor
Measurement (micrometers) =
Graticule divisions x magnification
factor
Define ‘electron microscopy’
Microscopy using a microscope that uses a beam of electrons to illuminate a specimen. As electrons have a smaller wavelength than light, they produce images with higher resolutions.
Describe electron microscopes
• Use beam of fast-travelling electrons with wavelength < 1nm to illuminate the specimen • Electrons fired from a cathode and focused by magnets onto screen or photographic plate • Produce images with magnification up to x500 000 and still have clear resolution • Show more detail of cell ultrastructure because electrons have shorter wavelengths
What are the 2 types of electron microscope? Describe
both.
Transmission Electron Microscope • Beam of electrons transmitted through a specimen and focused to produce an image • Specimen must be chemically fixed by being dehydrated and stained then thinly sliced • 2D grey scale image is produced • Best resolving power (0.5nm) • Can produce magnification up to 2 million times Scanning Electron Microscope • Beam of electrons sent across surface of specimen; reflected electrons focused onto a screen • 3D grey scale image • Resolving power (3-10nm) • Magnification x15 to x200 000
Summarise light microscopes/microscopy
• Inexpensive to buy and operate • Small and portable • Simple sample preparation • Sample preparation doesn’t usually lead to distortion • Vacuum is not required • Natural colour of sample is seen (or stains are used) • Up to x2000 magnification • Resolving power is 200nm • Specimens can be living or dead
Summarise electron microscopes/ miscroscopy
• Expensive to buy and operate • Large and needs to be installed • Complex sample preparation • Sample preparation often distorts material • Vacuum is required • Black and white images produced (but can be coloured digitally) • Over x500 000 magnification • Resolving power of TEM is 0.5nm and of SEM is 3-10nm • Specimens are dead
What are artefacts?
Objects or structures seen through a microscope that have been created during the processing of the specimen e.g. air bubbles trapped under coverslip in light microscopy
How is electron microscopy affected by artefacts?
When preparing specimen, changes in the ultrastructure of cells are inevitable in the processing that sample must undergo. e.g. loss of continuity in membranes, distortion of organelles and empty spaces in the cytoplasm of cells
Define a ‘laser scanning microscope’
A microscope that employs a laser
beam and a pin-hole aperture to
produce an image with a very high
resolution
Describe laser scanning microscopes
• Use laser light to scan an object point by point and assemble (by computer) the pixel information into 1 image displayed on a computer screen • High resolution images that show high contrast • Have depth selectivity and can focus on structures at different depths within a specimen
Give 3 instances in which laser scanning confocal
microscopes are used
• To clearly observe whole living specimens as well as cells • Used in many branches of biological research • Used in medical profession e.g. to observe fungal filaments within cornea of the eye of a patient with a fungal cornea infection, so that diagnosis is earlier and treatment is more effective
What are eukaryotes?
Multicellular organisms like animals,
plants, fungi and single-celled
protoctista
What are eukaryotic cells?
Cells with a nucleus and other
membrane-bound organelles
Describe the structure of the plasma membrane
• The membrane found on the surface of animal cells and just inside the cell walls of plant cells and prokaryotic cells • Mainly made of lipids and proteins
What is the function of the plasma membrane?
• Regulates the movement of substances into and out of the cell • Also has receptor molecules on it, which allow it to respond to chemicals like hormones
Describe the structure of the nucleus
• Large organelle surrounded by a nuclear envelope (double membrane), which contains many nuclear pores • Contains coded genetic information in the form of DNA molecules • Contains chromatin (made from DNA and proteins called histones) • Often contains a nucleolus
What is the function of the nucleus?
• Controls the cell’s activities (by controlling DNA transcription) • DNA controls the metabolic activities of the cell • Provides the instructions for protein synthesis • The pores allow mRNA to leave the nucleus and substances e.g. steroid hormones to enter • Chromatin coils and condenses to form chromosomes which contain the organism’s genes
Describe the structure of the nucleolus
• An area within the nucleus
• Does not have an membrane
around it
• Composed of proteins and RNA
What is the function of the nucleolus?
• RNA is used to produce ribosomal RNA (rRNA) which is combined with proteins to form the ribosomes necessary for protein synthesis
Describe the structure of the rough endoplasmic reticulum (RER)
• Network of membranes containing fluid-filled cavities called cisternae • Connected to the outer membrane of the nucleus • Coated with ribosomes • Secretory cells have more RER than cells that don’t release proteins
What is the function of the rough endoplasmic reticulum?
Responsible for the synthesis and transport of proteins • Intracellular transport system: cisternae form channel for transporting substances within the cell • Large surface area for ribosomes which assemble proteins than then actively pass through the membrane into the cisternae and are taken to the Golgi apparatus
Describe the structure of the smooth endoplasmic reticulum
• Network of membranes containing
fluid-filled cavities called cisternae
• No ribosomes on its surface
What is the function of the smooth endoplasmic
reticulum?
• Responsible for lipid and carbohydrate synthesis, and storage • Contains enzymes that catalyse reactions involved with lipid metabolism
Describe the structure of the Golgi apparatus
Consists of a stack of fluid-filled,
membrane-bound flattened sacs
• Vesicles are often seen at the
edges of the sacs
What is the function of the Golgi apparatus?
• Processes and packages new
lipids and proteins
• Makes Lysosomes
Describe the structure of mitochondria
• Surrounded by two membranes (double membrane) with a fluidfilled space between them • Inner membrane is highly folded into cristae, and the fluid interior is called the matrix • Membrane forming the cristae contains the enzymes used in aerobic respiration
What is the function of mitochondria?
• The site of ATP production during aerobic respiration • Contain mitochondrial (mt) DNA and so can produce their own enzymes and reproduce themselves
Describe the structure of chloroplasts
• Large organelles • Found only in plant cells and in some protoctists • Surrounded by a double membrane • Internal network of membranes which form flattened sacs called thylakoids that contain chlorophyll • Each pile of thylakoids is called a grana (pl. granum) • Fluid enclosed in the chloroplast is called the stroma • Contain loops of DNA and starch grains
What is the function of chloroplasts?
• The site of photosynthesis • Internal membranes give large surface area needed for the enzymes, proteins and pigment molecules in photosynthesis • Stage 1: Light energy is trapped by chlorophyll and used to make ATP. Water is split into hydrogen ions. Happens in the grana • Stage 2: Hydrogen reduces CO2 using energy from ATP, to make carbohydrates. Happens in the stroma
Describe the structure of vacuoles
• Membrane lined sacs in the cytoplasm containing cell sap • Only plant cells have a permanent vacuole (some animal cells have transient vacuoles) • Membrane of a vacuole in a plant cell is called the tonoplast
What is the function of vacuoles?
• Filled with water and solutes, and maintains cell stability because when full it pushes against cell wall, making the cell turgid • The membrane is selectively permeable • Turgid plant cells helps to support the plant, esp in non-woody plants
Describe the structure of lysosomes
• Specialised forms of vesicles that contain hydrolytic (digestive) enzymes • Each is surrounded by a single membrane
What is the function of lysosomes?
• Keep the powerful hydrolytic enzymes separate from the rest of the cell • Responsible for breaking down waste material in cells e.g. old organelles and foreign matter • Digest waste material then return digested components to the cell for reuse • Play an important role in apoptosis (programmed cell death)
Describe the structure of cilia
Small hair-like structs that protrude from some cell types • Each cilium contains two central microtubules surrounded by 9 pairs of microtubules arranged like a wheel • Pairs of parallel microtubules slipover each other causing the cilia to move in a beating motion
What is the function of cilia?
Stationary cilia have an important function in sensory organs e.g. the nose • Mobile cilia beat in a rhythmic manner, creating a current and causing fluids or close objects to move, e.g. in the trachea moving mucus away from the lungs
Describe the structure of flagella
Whip-like extensions that protrude from some cell types • Stick out from the cell surface and are surrounded by the plasma membrane • 2 microtubules in the centre and 9 pairs around the edge
What is the function of flagella?
• Microtubules contract to make the flagellum move • Used primarily to enable cells motility, e.g. when a sperm swims • In some cells they are used as a sensory organelle detecting chemical changes in the cell’s environment
Describe the structure of the cytoskeleton
• Network of fibres • 3 components: • Microfilaments - contractile fibres formed from the protein actin • Microtubules - globular tubulin proteins polymerise to form tubes • Intermediate fibres
What is the function of the cytoskeleton?
• Network of fibres necessary for the shape and stability of a cell • Holds organelles in place, controls cell movement, and the movement of organelles within cells • Microfilaments - Responsible for cell movement and cell contraction during cytokinesis • Microtubules - Form a scaffold-like structure that determines the shape of the cell. Act as tracks for the movement of organelles, including vesicles around the cell. Spindle fibres are made of microtubules • Intermediate fibres - Give mechanical strength to cells ad help maintain their integrity
Describe the structure of centrioles (*not in flowering
plants and most fungi)
• 2 bundles of microtubules at right angles to each other • The microtubules are made of tubulin protein subunits and are arranged to form a cylinder
What is the function of centrioles?
• 2 associated centrioles form the centrosome, which is involved in the assembly and organisation of spindle fibres during cell division • In organisms with cilia and flagella, centrioles play a role in the positioning of these structures
Describe the structure of ribosomes (* mitochondria,
chloroplasts and prokaryotic cells also contain ribosomes)
Can be free-floating in the cytoplasm or attached to the ER, forming RER • Not surrounded by a membrane constructed by of RNA molecules made in the nucleolus
What is the function of ribosomes?
• Site of protein synthesis • On the RER are mainly for synthesising proteins that will be exported outside the cell • Free in the cytoplasm are mainly for assembling proteins that will be used inside the cell
Describe the structure of the cellulose cell wall (*fungi have cell walls that contain chitin not cellulose)
• On the outside of the plasma membrane • Made from bundles of cellulose (complex carbohydrate) fibres • Contain plasmodesmata
What is the function of cellulose cell walls?
• Permeable and allow solutions to pass through • Provide strength and support for cell and plant + maintain the cell’s shape • Defence mechanism, protecting the cell from pathogens
Describe the structure of vesicles
• Membranous sacs
• A single membrane with fluid
inside
What is the function of vesicles?
• Storage and transport roles
• Used to transport materials inside
the cell
List all of the components of a eukaryotic cell
- Cytosol
- Plasma membrane
- Nucleus
- Nucleolus
- Rough endoplasmic reticulum
- Smooth endoplasmic reticulum
- Golgi apparatus
- Mitochondria
- Chloroplasts (plants)
- Vacuoles (mostly plants)
- Lysosomes
- Flagella
- Cytoskeleton
- Centrioles
- Ribosomes
- Cell wall (cellulose and chitin )
- Vesicles
1. Proteins are synthesised on the ribosomes bound to the ER 2. They then pass into the cisternae and are packaged into transport vesicles 3. vesicles containing newly synthesised proteins move towards the GA via the transport function of the cytoskeleton 4. Vesicles fuse with cis face of GA and the proteins enter 5. The proteins are structurally modified before leaving GA in vesicles from its trans face 6. Secretory vesicles carry proteins tone taken out of the cell; the vesicles move towards and fuse with cell surface membrane releasing their contents by exocytosis 7. Some vesicles form lysosomes that contains enzymes for use in the cell
What are prokaryotes?
Single-celled prokaryotic organisms from the kingdom Prokaryotae. They first appeared 3.5 billion years ago and can be classed into either Archaea or Bacteria
What are prokaryotic cells?
Cells a relatively simple structure w
with no membrane-bound nucleus,
and few organelles which are also
not membrane-bound.
Describe DNA in prokaryotic cells
• The structure of DNA is fundamentally the same as in eukaryotic cells, but packed differently • Only 1 molecule of DNA,a chromosome, which is supercoiled to make it more compact
Describe ribosomes in prokaryotic cells
• Smaller than those in eukaryotic cells (70S vs 80S) • Both types of ribosome are necessary for protein synthesis, but 80S are involved in more complex proteins
Describe the cell wall in prokaryotic cells
• Made from peptidoglycan (also
known as murein)
• Complex polymer formed from
amino acids and sugars
Describe flagella in prokaryotic cells
• Thinner than those in eukaryotes,, and doesn’t have the 9+ 2 arrangement • Energy to rotate the filament that forms the flagellum comes from chemiosmosis not ATP as in eukaryotic cells • A molecular motor causes the flagellum to rotate giving it a whiplike movement that propels the cell
Summarise the differences between prokaryotic and eukaryotic cells: • Nucleus • DNA • DNA organisation • Extra chromosomal DNA • Organelles • Cell wall • Ribosomes • Cytoskeleton • Reproduction • Cell type • Cell-surface membrane
