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Biology > 2 - Basic components of living systems > Flashcards

2 - Basic components of living systems Flashcards

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1
Q

What is a light microscope, what are the names of its parts?

A
  • It uses light to view an image
  • its has an objective lense, an eyepiece lense a course-focusing knob and a fine-focusing knob
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2
Q

Why is resolution limited?

A

it cant produce an image of an object that is half the size of the wavelength of light. The wavelength of light ifs 500-650 nm so objects <250 cannot be distinguished.

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3
Q

What is the resolution and magnification of light microscopes?

A
  • maximum resolution is 200nm
  • maximum magnification is x1500
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4
Q

What is resolution?

A

The ability to distinguish between two separate points

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5
Q

What is magnification

A

How many times bigger the image of aa specimen is observed

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6
Q

What can/n’t light microscopes observe?

A

Large objects such as eukaryotic cell, nuclei and possibly mitochondria and chloroplast.

Small organelles such as ribosomes, ER or lysosomes

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7
Q

What is a dry mount? Give sample examples

A
  • Solid specimens are viewed whole of cut into thin slices (sectioning)
  • it is placed on the slide and a cover slip is added
  • E.g. hair, pollen, muscle tissue or plants
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8
Q

What is a wet mount? Give sample examples

A
  • Specimens are suspended in a liquid such as water or an immersion oil
    -a cover slip is placed from an angle and blotting paper is used to remove excess liquid
  • E.g. aquatic samples and other living organisms
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9
Q

What is a squash slide? Give sample examples

A
  • A wet mount is first prepared and lens tissue is used to press down the cover slip or between two slides
  • soft samples
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10
Q

What is a smear slide? Give sample examples

A
  • The edge of a slide is used to smear the sample, creating a thin and even coating. a cover slip is placed on top
  • blood
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11
Q

What is diffraction?

A

The bending of light as it passes close to the edge of an object

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12
Q

How do you prepare a sample for staining?

A

-placed on a slide and airdried
- then it is heat fixed to pass through a flame

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13
Q

What are two negatively charged stains? How do they work?

A
  • Nigrosin or Congo red
  • they are repelled by the negatively charged cytosol, so they stay outside of cells, leaving the inside unstained. Cells stand out against the stained background
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14
Q

What are two positively charged stains? How do they work?

A
  • Crystal violet and methylene blue that are attracted to the negatively charged cytosol
  • so they stain cell components
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15
Q

What is differential staining?

A
  • can distinguish between two types of organisms ad organelles
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16
Q

What is the gram stain technique

A

It is used to separated bacteria into Gram-positive and Gram-negative bacteria
1) Crystal violet is applied so specimen
2) iodine is added to fix the dye
3) slide is washed with alcohol
Gram-positive bacteria retain the crystal violet stain and appear blue/purple. Gram negative have thinner walls and therefore lose the stain
4)They are then stained with safranin dye, which is called a counterstain. Now gram-negative appear red

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17
Q

What is Acid-fast technique

A

It is used to differentiate species of mycobacterium from other bacteria
- A lipid solvent is use to carry carbolfuchsin dye into the cells
- cells are washed with dilute acid-alcohol solution
- mycobacterium are not affected by the acid-alcohol solution and retain carbolfuchsin stain (which is red)

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18
Q

What is fixing?

A

chemicals such as formaldehyde are used to preserve specimens in their near-natural state

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19
Q

What is sectioning?

A

Specimens are dehydrated with alcohols then placed in a mould with wax or resin to form a hard block. they can then be sliced with a microtomes

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20
Q

How do you do a scientific drawing?

A

titles
state magnification
use sharp pencil
smooth, continuous lines
no shade
clearly defined structures
parallel label lines

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21
Q

What is an electron microscope?

A
  • A beam of electrons with a wavelength of less than 1nm is used to illuminate
22
Q

Why do light microscopes have a higher resolution compared to light microscopes?

A

A beam of electrons has a much smaller wavelength than light, so an electron microscope can resolve (distinguish between) two objects that are extremely close together

23
Q

What is a Transmission electron microscope? State res and mag

A
  • Electrons are transmitted through a specimen and focused to produce an image
  • Resolution of 0.05-2 nm
  • Mag of x500 000
24
Q

Describe the image of a TEM

A

-shows image of cell interior
- 2D image
- Organelles visible
- High mag and res

25
Q

What are the disadvantages of TEM?

A
  • only be used with very thin specimens or - thin sections of the object
  • They cannot be used to observe live specimens (as there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed, meaning that specimens must be dead, unlike optical microscopes that can be used to observe live specimens)
  • The lengthy treatment required to prepare specimens means that artefacts can be introduced

-They do not produce a colour image (unlike optical microscopes)

26
Q

What is a Scanning electron microscope? What is its res?

A
  • scans a beam of electrons across the specimen
  • This beam bounces off the surface of the specimen and the electrons are detected, forming an image
  • res of 3-10nm
27
Q

Describe the image of SEM

A

-3D image of the specimens surface

28
Q

What are the disadvantages of SEMs?

A

-They give lower resolution images than TEMs

-They cannot be used to observe live specimens (unlike optical microscopes)

-They do not produce a colour image (unlike optical microscopes)

29
Q

What is an artefact?

A

A visible structural detail caused by the processing of the specimen and not a feature of the specimen

30
Q

What is a laser scanning confocal microscope?

A

-The cells being viewed must be stained with fluorescent dyes

-A thick section of tissue or small living organisms are scanned with a laser beam
The laser beam is reflected by the fluorescent dyes

-Multiple depths of the tissue section/organisms are scanned to produce an image

31
Q

Explain how to measure the diameter of the nucleus of one of the white blood cells, when observing the cells
through a light microscope

A

-use eyepiece graticule
-calibrate graticule, using stage micrometer / detail of
-calibration / calculate the length of one epu
-measure the diameter of the nucleus in, epu / graticule
units
-take repeat measurements and calculate a mean
diameter (in epu)
-use calibrated epu to calculate diameter (of nucleus) (in
μm) / described

32
Q

Both a transmission electron microscope (TEM) and a scanning electron microscope (SEM) can be used to
view the same cell. However, the images formed will be different.
Compare the resolutions of these microscopes and the images formed by them

A

TEM has, better / higher, resolution
TEM
(resolution figure in range) 0.05 - 2 nm
(shows) image of cell interior
(shows) ultrastructure / (two named) cell organelles
SEM
(resolution figure in range) 5 - 50 nm
(shows) 3D / three-dimensional, image
(shows cell) surface / topography

33
Q

Cells are usually stained before viewing under a light microscope.
Explain why cells need to be stained.

A

create / provide / increase contrast;
make, cells / (named) component(s), visible
OR
cells / (named) components, can be, identified /
distinguished / differentiated;

34
Q

Discuss the benefits of using stains when making slides for light microscopy

A

-contrast is high(er) (1)
-more (internal) structures visible (1)
-some (named) organelles / cell components more
-visible, because they bind to stain (1)
-clearer image can be obtained (1)

35
Q

Explain why it is important to use a differential stain when examining a blood smear under the
microscope

A

1 to, see / identify, (differences between) cells
2 to, see / identify, (differences between) organelles
3 red blood cells visible, anyway / without stain (due to
haemoglobin)
4 ref. contrast
5 allows, white cells / leucocytes, to be counted

36
Q

What is the Cell wall?

A

-The cell wall is freely permeable to most substances
-Found in plant cells but not in animal cells
-Cell walls are formed outside of the cell membrane and offer structural support to cell
-Structural support is provided by the polysaccharide cellulose in plants, and peptidoglycan in most bacterial cells
-Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells

37
Q

What is the nucleus

A

-Present in all eukaryotic cells (except red blood cells), the nucleus is relatively large and separated from the cytoplasm by a double membrane (the nuclear envelope) which has many pores
-Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in
-DNA associates with histones to form a complex called chromatin. chromatin then coils and condenses to form chromosomes. chromosomes are only visible when cells are preparing to divide

38
Q

What is the nucleolus?

A

An area within the nucleus that is responsible for synthesising ribosomes.
It is made of proteins and RNA. RNA is used tie make ribosomal RNA, rRNA, and then combined with proteins to form ribosomes

39
Q

What is the mitochondria?

A

-Surrounded by double-membrane with the inner membrane folded to form cristae
-The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP
- the inner membrane has protein complexes vital for the later stages of aerobic respiration embedded within it
-Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)

40
Q

What are vesicals?

A
  • membrane sacs for storage and transport roles
  • they are made of a single membrane with fluid inside
    -Found in plant and animal cells
41
Q

What are lysosomes?

A
  • Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down)
    -Break down waste materials such as worn-out organelles
    -Used extensively by cells of the immune system and in apoptosis (programmed cell death)
42
Q

What are centrioles?

A

-Hollow fibres made of microtubules
-Two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
-Not found in flowering plants and fungi
- in cells with a flagella/cillia, centrioles play a role in their positioning

43
Q

What are microtubules?

A

-Found in all eukaryotic cells
-Makes up the cytoskeleton of the cell about 25 nm in diameter
-Made of α and β globular tubulin combined to form dimers, the dimers are then joined into protofilaments
-Thirteen protofilaments in a cylinder make a microtubule
- act as tracks for organelles

44
Q

What are microfilaments?

A
  • contractile fibres formed from actin
    -responsible for cell movement and contraction during cytokinesis
45
Q

What are intermediate fibres?

A

give mechanical strength to cells and help maintain their integrity

46
Q

What is the rough endoplasmic reticulum?

A

-Found in plant and animal cells
-Surface covered in ribosomes
-Formed from continuous folds of membrane continuous with the nuclear envelope
- synthesis and transport of proteins

47
Q

What is the smooth endoplasmic reticulum?

A

-Found in plant and animal cells
-Does not have ribosomes on the surface,
-Involved in the production, processing and storage of lipids, carbohydrates and steroids

48
Q

What are ribosomes?

A

-Found in all cells
-Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
-They arnt surrounded by a membrane
-Each ribosome is a complex of ribosomal RNA (rRNA) and proteins
-80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells
-70S ribosomes (composed of 50S and 30S subunits) in prokaryotes, mitochondria and chloroplasts
-Site of translation (protein synthesis)

49
Q

What is the golgi apparatus?

A

-Found in plant and animal cells
-Flattened sacs of membrane similar to the smooth endoplasmic reticulum (cisternae)
-Modifies proteins and lipids before packaging them into Golgi vesicles
-The vesicles then transport the proteins and lipids to their required destination
-Proteins that go through the Golgi apparatus are usually exported (e.g. hormones such as insulin), put into lysosomes (such as hydrolytic enzymes) or delivered to membrane-bound organelles

50
Q

What is the large permanent vacuole?

A

A sac in plant cells surrounded by the tonoplast, selectively permeable membrane
- contains cell sap
-Vacuoles in animal cells are not permanent and small
-maintain turgor

51
Q

What is the chloroplast?

A
  • responsible for photosynthesis in plant cells
    -a double membrane structure and the fluid enclosed is called the stroma. they have an internal network of membranes which form flattened sacs called thylakoids. Several thylakoids are called granum
  • granum are joined by membranes called lamellae
  • starch made during photosynthesis is present as starch grains
  • they have DNA and ribosomes

Biology (24 decks)

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