2.1 Flashcards
Electron micrograph
Photograph of an image seen using an electron microscope
Magnification
Number of times larger an image appears, compared with size of object
Organelles
Small structure within cells, each of which has specific function
Photomicrograph
Photograph of an image seen using optical microscope
Resolution
Clarity of an image, higher the resolution, the clearer the image
What is magnification
How much bigger ab image appears compared to original object
What type of magnification do microscopes produce
Linear magnification
Why do we say that microscopes magnification is linear
Is specimen is magnified by x100, then it is seen as 100times wider and longer than it is
What is resolution
Ability of optical instruments to see/ produce an image that shows fine detail clearly
Give an example of something with high resolution
UHD television is extremely clear and sharp images on the screen
What are optical microscopes useful in understanding
Basic cell structure
Where are optical microscopes used
Schools, hospitals and research labs
Why are optical microscopes used in schools and hospitals
Cheap, easy to use, portable and able to study a living specimen
What does optical microscope rely on to work
Lenses focusing a beam of light
What is an optical microscope magnification
x1500-x2000
What does optical microscope enable use to see
Larger cell structures
What does optical microscopes limited resolution mean
They can’t magnify more whilst producing a clear image
How does an optical microscope work
They use visible light on electromagnetic spectrum (400-700nm), so structures closer together than 200nm will appear one object such as ribsomes which are only 20nm
How would you analyse a specimen on a light microscope
1.put specimen on slide and clip into place with stage clips 2.rotate nose piece till low power objective lens is over specimen 3.adjust coarse focus knob and fine focus knob whilst looking into eyepiece until image is clear and focused 4.adjust iris diaphragm for optimum light 5.make sure specimen is directly over hole on the stage and turn to x10 lens and refocus with knobs 6.repeat step 5 with x40 objective lense
What is the equation for total magnification
Magnifying power of objective lens x magnifying power of eyepiece lense
What is a photomicrograph
Photo of image seen using optical microscope
How does a laser scanning microscope work
Uses laser to scan object point by point and assemble by computer pixel information into one image, displayed on a computer screen
Are image high or low resolution on laser scanning microscope and do they show contrast
High resolution and show contrast
How can laser scanning microscopes observe whole living specimen as well as individual cells
They have depth selectivity so can focus on structures at different depths in specimen
Where and when are laser scanning microscopes used
Used in medical professions, to observe fungal filament within cornea of eye in patients who have fungal infection, used in branches of biological research
What must be done to the specimen before using it in a transmission electron microscope
Specimen must be chemically fixed by being dehydrated and stained
How does transmission electron microscope work
Beam of electrons pass through specimen (stained with metal salts which can harm user) some electrons pass through and are focused on screen or photographic plate
What kind of image does a transmission electron microscope form
A 2D b&w image, when photographed called an electron micrograph
What magnification does transmission electron microscope have
x2,000,000 - x50,000,000
What happens in scanning electron microscope
Electrons don’t pass through specimen but causes secondary electrons to reflect off specimen surface and then be focused onto a screen
Does scanning electron microscope produce 2/3D image
3D
What is magnification of scanning electron microscope
x15 - x200 000
In scanning electron microscope what colour is the image
B&w but computer software adds false colours to make it easier to see different structures
What must specimen be dead before being used in scanning electron microscope
As specimen must be placed in a vacuum and often coated with a fine film of metal
How does an electron microscope work
Beams fast travelling electrons with wavelength of 0.004nm, electrons fired from cathode and focused by magnet rather than glass lenses onto screen or photographic plate
Why is electron microscope better than optical microscope
Greater resolution so used to giver clear and highly magnified images
Why is fast travelling electrons have better resolution than optical microscope
They have x125000 smaller wavelength than central part of visible light spectrum
Why are electron microscopes not as commonly used
Both types require lots of training, are expensive and large so cannot be moved easily
What size is an atom and what microscope can see it
0.1nm and electron microscope
What size is lipid and what microscope can see it
1nm and electron microscope
What size is ribosomes and what microscope can see It
10nm and electron microscope
What size if influence virus and what microscope can see it
100nm and light and electron microscope
What size are mitochondria, chloroplast and bacterium and what microscope can see it
1um and electron and light microscope
What size is human cheek cell and human ovum and what can see it
10um and electron and light microscope
Down to what size can the human eye see
1m - 1mm
What is the smallest thing human eye could see
Amoeba
What is the resolving power
Minimum distance two points must be separated in order for them to be seen as two separate points like microscope resolution is 0.2um
Advantages of electron microscope
Use electron beam instead of light and use electromagnets instead of glass lenses
Resolution of electron microscope
1nm
Disadvantage of electron microscope
Material must be dead as it is done in a vacuum
What specimen can you view under light microscope
Living organisms like paramecium and amoeba and smear preparations of human blood and cheek cell and thin sections of animal, plant and fungi tissue such as bone, muscle, leaf, root, or fungal hayphae
Why must biological structures be stained before viewing
Many structures are colourless and transparent, such as single felled organisms (paramecium)
What do some light microscopes use instead of staining
Light interference such as using a dark background to illuminate specimen
When is light interference most useful
Useful for studying living specimens and you can observe this with school light microscopes by adjusting iris diaphragm to reduce illumination of specimen
What are stains
Coloured chemicals that bind to molecules or on the specimen that makes them easy to see
Give an example of an all purpose stain
Methylene blue
What is differential staining
Where some stains bind to specific cell structures, staining each differently so structure can be easily identified within a single preparation
What stain binds to DNA and stains chromosomes dark red
Acetic stains
What is eosin stain
Stains cytoplasm
What does Sudan red stain
Lipids
What stains cellulose yellow and starch granules blue/black which look violet under microscope
Iodine in potassium iodine
How do scientists in a lab make a prepared fixed slide for schools
Dehydrate the specimen, then embed them with wax preventing distortion during slicing, create sections(very thin slices) using special instruments, then stain and mount them onto special chemical which will preserve them
How do you work out actual size of object from a photosmicrogram if you know the magnification
Measure with of specimen on diagram in mm, convert to um by x1000, and divide by magnification
Equation for magnification
Image size/actual size
How do you draw biological drawing
Use sharp pencil, title drawing and write magnification, indicate how much bigger it is than actual size, use clear unbroken lines and no shading, label areas on low power plan, then draw high power of 2-3 cells and identify structures you can see, use a ruler to label
What is 2mm in um
2000um
What is 30 000um in mm
30mm
What is the microscope eye piece fitted with
A graticule
What is a graticule look like
Transparent with small ruler etched on it
Can you still see the eyepiece graticule when viewing specimen
Yes, it is superimposed on it and can measure diameter of specimen in eye piece unit
Why is the scale of the eyepiece graticule described as arbitrary
Represents different lengths as different magnifications, image of specimen looks bigger if magnification is higher but actual size doesn’t change
What must be done to each objective lens before measuring a specimen
Must be calibrated with the eyepiece graticule
How do you calibrate eyepiece graticule with stage graticule
Place stage graticule on microscope stage and focus using low power objective lens so magnification is x40, align eyepiece and stage graticule, ensure stage and eyepiece graticule correspond(1mm to 40eyepiece divisions), so each eyepiece division would be 1000/40=0.025mm, then use x10 (x100) and focus and align graticules (100eyepiece division is now 1mm) =0.01mm is one eyepiece division
What safety precaution should you take when observing and measuring starch grains in potato tubular cells
Wear eye protection
How would you observe and measure starch grains(amyloplats) In potato tubular cells
1.use sharp knife to scrape little material from surface of peeled potato and place in microscope slide (need very thin layer and will have tubular cells) 2. place 2 drops of iodine solution on them and add coverslip 3.examine under microscope starting with low power and going higher, amyloplats stained with iodine will appear violet 4.measure length and with of 3 amyloplats
What cells are eukaryotic
All animal, plant, fungal and protoctist cells
Features of eukaryotic cells nucleus
Nucleus surrounded by nuclear envelope and containing DNA organised and wound to linear chromosomes, inside nucleus there is nucleolus containing RNA where chromosomes unwind and also involved in making ribosomes
Features in eukaryotic cell
cytoskeleton:network of protein filaments within cytoplasm that move organelles around cell, plasma membrane, membrane bound organelles like nucleus, mitochondria, golgi, endoplasmic reticulum, secretory vesicles, ribosomes
Extra features in a plant cell
Amyloplats containing starch, chloroplast, vacuole, cell wall
Extra features in animal cells
Lysosomes containing digestive enzymes
Definition of cells
Cell are fundamental building blocks of all living organisms
What is within every cell
Organelles with a specific function
What does a membrane bound organelle mean
Keeps organelle separate from rest of the cell
Under what microscope can you see organelle membranes
Electron microscope
Do prokaryotes have membrane bound organelles
No
What is the nucleus structure (eularyotes)
Nucleus surrounded by double membrane called nuclear envelope which has pores and nucleus contains DNA, but the nucleolus doesn’t have a membrane around it
What is chromatin
Genetic material, consists of DNA wound linearly around histone proteins and when cell doesn’t divide chromatin is spread out or extended but when cell about to divide chromatin bonds tightly into chromosomes, chromatin makes up nearly all organisms genome
What is nuclear envelope function
Separates content of nucleus from rest of the cell, in some regions outer and inner nuclear membranes fuse together, then some dissolve substances and ribosomes can pass through as pores allow larger substances (mRNA) to leave nucleus and steroid hormones may enter nucleus from cytoplasm via these pores
What is overall function of nucleus
Is the control centre of cells, stores organisms genome, transmits genetic information, provides instructions for protein synthesis
Structure of rough endoplasmic reticulum
System of membranes with fluid filled caverties called cisternae that are continuous with nuclear membrane and coated with ribosomes
Function of rough endoplasmic reticulum
It is a ultra cellular transport system, cisterns form channels for transport in cells and provide large SA for ribosomes which turn amino acids to proteins which then actively pass through membrane into cisternae and transported to Golgi apparatus
Structure of smooth endoplasmic reticulum
System of membranes containing fluid filled cavities called cisternae that are continuous with nuclear membrane but has no ribosomes on it surface
Function of smooth endoplasmic reticulum
Contains enzymes that catalyse reactions involved with lipid metabolism like synthesis of cholesterol, lipids and phospholipids needed by cell and synthesis of steroid hormones, involved with absorption, synthesis and transport of lipids from gut
Structure of Golgi apparatus
Consists of stack of membrane bound flattened sacs, secretory vesicles bring materials to and from Golgi apparatus
Function of Golgi apparatus
Protein modified by adding sugar molecules to make glycoproteins, or adding lipids to make lipoproteins or being folded into their 3D shape, proteins are packed into vesicles which are pinched off and then stored in cell or moved to plasma membrane to be incorporated in membrane or exported outside of cell
Structure of mitochondria
Spherical rod shaped or branched, surrounded by two membranes with fluid filled space between them, inner membrane highly folded into cristae making inner part of mitochondria a fluid filled matrix
Function of mitochondria
Site of ATP produced in aerobic respiration, self-replicating, so more can be made if cells energy needs increasing, abundant in cells where much metabolic activity takes place such as liver cells and at synapsis between neurone where neurotransmitter is synthesised and released
Structure of chloroplast
Large organelle, found in plants and some protoctists, surrounded by double membrane/ envelope, inner membrane continuous with stacks of flattened membrane stacks called thylakoids which contain chlorophyll(each stack called granum, fluid filled matrix called stroma, also contains loops of DNA and starch grains
Function of chloroplast
Site of photosynthesising, 1st stage of photosynthesis when light energy trapped by chlorophyll and used to make ATP which occurs in the grana. Water also split to supply hydrogen ions, 2nd stage, hydrogen reduces CO2 using energy from ATP to make carbohydrates which occurs in stroma, chloroplast abundant in leaf cells usually in palisade mesophyll layer
Structure of vacuoles
Surrounded by membrane called tonoplast and contains fluid
Function of vacuoles
Only plant cells have large permeant vacuoles, filled with water and solutes and maintains cells stability, as when it is full it pushes against cell wall making it turgid, if all plant cells turgid it helps to support plants, especially non woody ones
What is the structure of lysosomes
Small bags formed from Golgi apparatus each surrounded by a single membrane, contains powerful hydrolytic (digestive) enzymes, abundant in phagocyte cells (wbc) that can ingest and digest invading pathogens like bacteria
Function of lysosomes
Keep powerful hydrolytic enzymes from rest of the cell, can engulf old cell organelles and foreign matter, digest them and return digested components to cell for reuse
Structure of cilia and undulipodia
Protrusions from cell and surrounded by cell surface membrane, each contain microtubules and are formed from centrioles
Examples of organelles without membranes
Ribosomes and cytoskeletons like centrioles
Structure of ribosomes
Small spherical organelles made of ribosomal RNA, made in nucleolus as two separate subunits, which pass through nuclear envelope into cell cytoplasm then combine, but some remain free in cytoplasm and some attach to endoplasmic reticulum
Ribosomes function
Bound to exterior of rough endoplasmic reticulum for synthesising proteins that will be exported outside the cell, ribosomes free in cytoplasm, single or cluster, primarily site of assembly of proteins that will be used inside the cell
Structure of centrioles
Consists of 2 bundles of microtubules at right angle to each other, microtubules made of tubulin protein subunits and arranged to form cylinders
Centrioles function before cells divide
Spindle made of thread of tubulin forms from centrioles, chromosomes attach to middle part of spindle and motor protein walks along tubulin threads which pulls chromosomes to opposite ends of the cell
Centrioles function in formation of cilia and undulipodia
Before cilia forms, centrioles multiply and line up beneath cell surface membrane, microtubules then spout outwards from each centriole forming cilia or undulipodium
Are centrioles found In plant cells
Not usually but sometimes in unicellular algae like chlamydomas
Structure of cytoskeleton
Network of protein structure within cytoplasm consisting of rod like micro filaments made of subunits of protein actin, polymers of actin(7nm diameter) with intermediate filaments 10nm diameter, straight cylindrical microtubules made of protein subunits called tubulin(18-30nm diameter)
Structure of cytoskeletal motor proteins
Myosins, kinesins, and dyneins are molecular motors, they are also enzymes which have a site that binds to and allows hydrolysis of ATP as an energy source
Function of cytoskeletons
Protein micro filaments within cell wall give support and mechanical strength to keep cel shape stable and allows cell movement, microtubules also provide shape and support and help substances and organelles move across cytoplasm by forming tracks along which motor proteins can walk/drag organelles from one to another part of a cell which forms spindle before cell divides enabling chromosomes to move within cell, microtubules also make up cilia, undulipodia and centrioles
Cytoskeleton intermediate filaments function
Made of a variety of proteins which anchor nucleus within cytoplasm, and extend between cells in some tissues between species junctions, enabling cell to cell signaling and allows cells to adhere to a basement membrane, therefore stabilising tissues
Cellulose in cell wall structure
Outside of plasma membrane and made from bundles of cellulose fibres
Function of cellulose in cell wall
Absent from animal cells but cell wall is strong and prevent plant cells bursting when turgid, the cell wall of plants provide strength and support, maintain cell shape, contribute to strength and support of whole plant and permeable and allows solutions (solutes and solvent) to pass through
What is fungi cell wall made of
Chitin
What is the first step in making a protein
The gene that has coded instructions for a protein such as insulin (housed in chromatin) in nucleus is transcribed to RNA called messenger RNA (mRNA)
What happens after mRNA is made in protein synthesis
Many copies of mRNA are made and passed out of pores in nuclear envelope to ribosomes
What happens at ribosomes in protein synthesis
Instructions are translated and insulin molecules are assembled
What happens after ribosomes translate mRNA to insulin
Insulin molecule passes to cisternae of rough endoplasmic reticulum and along hollow sacs
What happens in protein synthesis after protein molecule is in RER cisternae
Vesicles fuse with Golgi apparatus where insulin protein molecules may be modified for rerelease
What happens to vesicles at Golgi apparatus after protein has been processed and packaged
Inside vesicles pinched off from Golgi apparatus, then these molecules pass to plasma membrane and the vesicles and plasma membrane fuse and insulin is released outside of the cell
Where is mRNA copy of the instructions/gene for insulin made
The nucleus
How does mRNA leave nucleus
Nuclear pores in nuclear envelope
Where does mRNA attach to after it left nucleus
Ribosomes
What happens to protein molecule in Golgi apparatus
Processed and packages protein molecule ready for release
What is exocytosis
Type of bulk process which is active so energy is needed, to move protein molecule out of the cell
Where does exocytosis occur
Plasma membrane
What are bacteria and what cell do they have
Microorganisms with prokaryote cells
how are prokaryotes similar to eukaryotes
Have plasma membrane, cytoplasm, ribosomes for assembling amino acids to proteins, DNA and RNA
How are prokaryotes different from eukaryotes
Much smaller and less developed cytoskeleton with no centrioles, don’t have nucleus, don’t have membrane bound organelles like mitochondria, ER, chloroplasts or Golgi apparatus, they also have a peptidoglycan cell wall instead of cellulose, smaller ribosomes and naked DNA that isn’t wound around histone proteins but floats free in cytoplasm as a loop (not linear)
What are other extra features of prokaryotes
Have a waxy capsule surrounding cell wall, small loops of DNA called plasmids, flagella so they can move, pili which are smaller hair like structures so bacteria can adhere to host cell and to each other and allows passage of plasmid DNA from one cell to another
How do prokaryotes divide
Binary fission
Why don’t prokaryotes carry out mitosis
As they don’t have linear chromosomes
What happens before prokaryotes divide
Before they divide there DNA is copied so each new cell gets a large loop of DNA and any smaller plasmids
Do prokaryotes in bacteria have membrane bound organelles
No but they have non membrane bound organelles like ribosomes
Why are bacteria microorganisms
As they are small and prokaryotes due to their cell structure
Are all microorganisms prokaryotes
No, yeast is a single called fungus and amoeba have eukaryote cells
Why are viruses different
They are microscopic but do not have cells
What do plasmids serves as
Additional chromosomes to the nucleotoid and in many disease causing bacteria these plasmids are associated with resistance to antibiotics
How is a mesosome formed in prokaryotes cells
Formed by unfoldings in plasma membrane
What is function of waxy capsule on prokaryotes
To prevent phagocytes ingesting them or dehydration
