B2 - Foundations in biology Flashcards
1
Q
What is the cell theory?
A
- both plants/animal tissue is composed of cells
- cells are the basic unit of all life
- cells only develop from existing cells
2
Q
What are the two lenses of a compound light microscope?
A
- objective (near specimen)
- eyepiece (specimen viewed)
3
Q
How are samples prepared for light microscopy?
A
- dry mount:
- solid specimens are viewed whole/cut into very thin slices (sectioning)
- cover slip is placed over the sample
- wet mount:
- specimens are suspended in liquid (water/immersion oil)
- cover slip is placed at an angle to prevent any air bubbles
- ** living organisms can be viewed this way **
- squash slides:
- wet mount prepared first and lens tissue is used to press down cover slip
- can be used for soft samples (e.g. root tip squashes)
- smear slides:
- edge of slide is used to smear a sample
- creates a thin, even coating on another slide
- cover slip is placed on top (can be used for blood samples)
4
Q
What are the types of electron microscopes?
A
- transmission electron (TEM)
- scanning electron (SEM
5
Q
What is a TEM?
A
- beam of electrons is transmitted through the specimen
- resolving power = 0.5 nm
- (2D images)
6
Q
What is a SEM?
A
- beam of electrons is sent across the surface of the specimen
- the reflected electrons are collected
- resolving power = 3-10 nm
- (3D images)
7
Q
What are the differences between a light and electron microscope?
A
- l = cheap/easy to use
- e = expensive/difficult to use
- l = no sample distortion
- e = sample prep causes distortion
- l = no vacuum required
- e = vacuum required
- l = natural colour/staining
- e = b/w images
- l = x2000 mag
- e = x 500 000 mag
- l = 200 nm (resolving power)
- e = 0.5/3-10 nm (resolving power)
- l = living/dead specimen
- e = dead specimen
8
Q
What is laser confocal microscopy?
A
- single spot of focused light is moved across specimen
- causes fluorescence from components labelled with a dye
- emitted light is filtered through pinhole (only light from close to focal plane is detected)
- non-invasive and used to diagnose eye diseases
- produces 2D/3D images
9
Q
Why is staining used for light microscopy?
A
- increases the contrast of cells
- different cells take up stains to different degrees
- allows for the cell components to be more visible
10
Q
What are the types of stains?
A
- crystal violet/methylene blue:
- positively charged
- attracted to negatively charged materials in cytoplasm (cell components)
- nigrosin/Congo red:
- negatively charged
- repelled by the cytosol (stay outside the cells)
- stand out against the stained background
11
Q
What is differential staining?
A
- helps to distinguish between two types of organisms
- gram stain technique
- acid-fast technique
12
Q
What is the gram stain technique?
A
- separates bacteria into gram +ve and -ve
- crystal violet is added, then iodine (fixes dye)
- it is then washed with alcohol
- the gram +ve retains the stain (blue/purple)
- gram -ve have thinner cell walls so they lose the stain
- (then stained with safranin dye)
- gram +ve are more susceptible to penicillin (inhibits cell wall formation)
- gram -ve are not susceptible
13
Q
What is the acid-fast technique?
A
- used to differentiate species of Mycobacterium from other bacteria
- lipid solvent carries carbolfuchsin dye into cells
- cells are washed with dilute acid-alcohol solution
- Mycobacterium are able to retain the carbolfuchsin stain (bright red)
14
Q
What are the stages of producing pre-prepared slides?
A
- fixing
- sectioning
- staining
- mounting
15
Q
What is magnification?
A
- how many times larger the image is than the actual size of the object
16
Q
What is resolution?
A
- the ability to distinguish between two close points of an object
17
Q
How do you calculate magnification?
A
- size of image / actual size of object
18
Q
What is an eyepiece graticule?
A
- glass marked with fine scale from 1 to 100 (no units)
19
Q
What is a stage micrometer?
A
- slide with accurate scale in micrometres (um)
- 1 division = 10 um
20
Q
What are prokaryotic cells?
A
- single-celled organisms
- simple structure with undivided internal area (cytoplasm)
21
Q
What are eukaryotic cells?
A
- multicellular organisms
- e.g. plants, animals, and fungi
- more complicated internal structure
- membrane-bound nucleus
- cytoplasm (with membrane-bound organelles)
22
Q
What is metabolism?
A
- the synthesis and breaking down of molecules
23
Q
What are membranes?
A
- selectively permeable barriers
- they control the movement of substances into and out of cells/organelles
24
Q
What are the cellular components of eukaryotic cells?
A
- nucleus (nucleolus/nuclear envelope)
- RER/SER
- Golgi apparatus
- ribosomes
- mitochondria
- lysosomes
- plasma membrane
- cell wall
- chloroplasts
- flagella
- cilia
- centrioles
24
What is the nuclear envelope?
- DNA is located within this *double membrane*
- protects it from damage in the cytoplasm
- contains nuclear pores that allow molecules to move into/out of the nucleus
- ** DNA is too large to leave the nucleus so it is converted into RNA (protein synthesis) **
24
What is the nucleus?
- contains coded genetic info in the form of DNA
- directs the synthesis of proteins required by the cell
- DNA controls the metabolic activities of the cell
- DNA associates with *histones* (proteins) to form *chromatin*
- this coils/condenses to form *chromosomes*
25
What is the nucleolus?
- area within the nucleus that produces *ribosomes*
- it is composed of proteins and RNA
- RNA is used to produce *ribosomal RNA* (rRNA)
- this combines with proteins to form ribosomes
26
What is mitochondria?
- site of final stages of cellular respiration (energy stored in bonds of complex organic molecules made available for ATP)
- they have a double membrane
- inner membrane = *cristae* (contains enzymes used in aerobic respiration)
- fluid interior = *matrix*
- contain small amount of DNA (mitochondrial DNA)
- they are able to produce own enzymes and reproduce themselves
27
What are vesicles?
- membranous sacs that have storage/transport roles
- they consist of a *single* membrane with fluid inside
28
What are lysosomes?
- specialised vesicles that contain *hydrolytic* enzymes
- they break down waste material in cells
- ** in the immune system, they break down pathogens ingested by phagocytic cells **
- they also play a role in programmed cell death/apoptosis
29
What is the cytoskeleton?
- a network of fibres responsible for the shape/stability of a cell
- e.g. organelles are held in place by the cytoskeleton
- microfilaments:
- *contractile fibres* formed from actin (protein)
- cell movement/contraction (cytokinesis)
- microtubules:
- polymerised globular tubulin proteins
- act as tracks for movement of organelles
- intermediate fibres:
- give mechanical strength to cells
- helps to maintain integrity
30
What are centrioles?
- composed of *microtubules*
- two centrioles form *centrosome* (assembly/organisation of spindle fibres)
31
What is flagella?
- whip-like extension
- used for cell's motility
- can also be used as a *sensory* organelle to detect chemical changes
32
What is cilia?
- hair-like extension
- can be either stationary or mobile
- stationary = surface of cells, important function in *sensory* organs
- mobile = create a current, cause fluids/objects to move
- each cilium contains *two central microtubules* surrounded by nine pairs of microtubules
- known as the 9+2 arrangement
33
What organelles are involved in protein synthesis?
- endoplasmic reticulum (rough/smooth)
- ribosomes
- Golgi apparatus
34
What is the endoplasmic reticulum?
- a network of membranes enclosing (flattened sacs) *cisternae*
35
What is the smooth ER?
- responsible for lipid/carbohydrate synthesis and storage
- it *does not* contain ribosomes
36
What is the rough ER?
- has *ribosomes*
- responsible for the synthesis/transport of proteins
37
What are ribosomes?
- constructed of RNA molecules produced in nucleolus of cell
- site of *protein synthesis*
38
What is the Golgi apparatus?
- compact structure formed of *cisternae*
- does not contain ribosomes
- modifies proteins and packages them into *vesicles*
- secretory vesicles = leave cell
- lysosomes = stay in the cell
39
How are proteins produced?
- 1) synthesised on ribosomes on RER
- 2) passed into *cisternae* and packaged into (transport) vesicles
- 3) move towards the Golgi apparatus via the *cytoskeleton*
- 4) vesicles fuse with Golgi and proteins enter
- 5) they are structurally modified before leaving
- 6) *secretory vesicles* fuse with the cell-surface membrane and release their contents (exocytosis)
40
What does a plant cell wall consist of?
- made of cellulose
- *freely permeable* which allows substances to pass into/out of the cell
- gives the cell its shape
- supports both the individual cell and the plant
- acts as a *defence mechanism*
41
What are vacuoles?
- membrane lined sacs containing cell sap
- help to maintain *turgor*
- tonoplast = membrane (selectively permeable)
42
What are chloroplasts?
- responsible for photosynthesis
- found in green areas of a plant
- fluid = stroma
- thylakoids = flattened sacs
- granum = stacks of thylakoids
- grana contain *chlorophyll* pigments for photosynthesis
43
What are prokaryotic organisms?
- unicellular with a relatively simple structure
- do not have DNA or membrane-bound organelles
44
What are the differences between eukaryotes and prokaryotes?
- DNA:
- packaged differently
- in prokaryotes, they have one molecule of DNA which is *supercoiled*
- a no. of genes are switched on/off at the same time
- ribosomes:
- much smaller in prokaryotes (70S) than eukaryotes (80S)
- cell wall:
- prokaryotes have a cell wall made from *peptidoglycan*/*murein*
- flagella:
- prokaryotes have a much thinner flagella
- attached to the bacterium cell by *basal body* and rotated by a molecular motor
- reproduction:
- prokaryotes = binary fission
- eukaryotes = asexual/sexual
