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Biology A-Level -James > Chapter 2.1-Cell Structure > Flashcards

Chapter 2.1-Cell Structure Flashcards

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1
Q

What does magnification mean?

A

the number of times larger an image appears compared to the original object

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2
Q

What does resolution mean?

A

ability of an optical instrument to see or produce an image that shows fine detail clearly

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3
Q

How does optical microscopes produce an image?

A

-the eyepiece lens magnifies the image from the objective lens

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4
Q

What are the benefits of using a optical (light)microscope?

A
  • relatively cheap
  • easy to use
  • portable and able to be used in the field as well as in laboratories
  • study whole living specimens
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5
Q

What is the maximum magnification of a optical(light) microscope?

A

x1500

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6
Q

In light microscopes, what is the wavelength of visible light and how does this affect the resolution?

A
  • optical microscopes use part of the electromagnetic spectrum called visible light which has a wavelength of between 400 and 700nm
  • resolution is very low, structures closer together than 200nm(0.2 micrometers) will appear as one object
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7
Q

What organelle cannot be seen under a optical microscope(light)?

A

ribosomes(20nm in diameter)

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8
Q

On an optical(light) microscope, what is the fine focus knob, objective lens, stage, course adjustment knob and eyepiece lens?

A
  • fine focus knob: focuses the image
  • objective lens: usually there are 3/4 on a microscope, they have different magnifying powers
  • stage:flat platform where the slides with the specimen on are placed
  • course adjustment knob: moves the objective lens closer or further away from the slide
  • eyepiece lens: lens at the top of the microscope that you look through
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9
Q

Whats the formula for calculating magnification?

A

total magnification= magnifying power of the objective lens x magnifying power of the eyepiece lens

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10
Q

What is the photograph called that is produced by a optical (light) microscope?

A

photomicrograph

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11
Q

How doe electron microscopes work?

A
  • use a beam of fast travelling electrons with a wavelength of about 0.004nm.
  • electrons are fired from a cathode and focused, by magnets rather than glass lenses, on to a screen or photographic plate
  • some electrons are absorbed by the specimen but some electrons pass through the specimen
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12
Q

How do transmission electron microscopes produce an image?

A
  • specimen has to be chemically fixed by being dehydrated and stained
  • beam of electrons passes through the specimen, which is stained with metal salts
  • denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
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13
Q

What type of image is formed in a transmission electron microscope and what is the name of the photograph that is produced?

A
  • 2D black and white image

- electron micrograph

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14
Q

What is the maximum magnification of transmission electron microscopes?

A

-up to 2 million times

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15
Q

How do scanning electron microscopes produce an image?

A
  • beam of electrons are scanned across the specimen, which knocks off electrons from the specimen (secondary electrons) and then are gathered in a cathode ray tube to form an image
  • the specimen is fixed(dead) and coated with a fine film of metal
  • specimen has to be placed in a vacuum
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16
Q

What is the maximum magnification of a scanning electron microscope?

A

x15 up to x200,000

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17
Q

What type of image is formed in a scanning electron microscope?

A
  • 3D image

- image black and white, but computer software programmes can add false colour

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18
Q

What are two disadvantages to using electron microscopes?

A
  • large and very expensive

- need a great deal of skill and training to use

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19
Q

What are two advantages to using electron microscopes?

A
  • high magnification

- high resolution

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20
Q

How do laser scanning (confocal) microscopes produce an image?

A

-use a beam of light to scan an object point by point and assemble, by computer, the pixel information onto one image, displayed on a computer screen

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21
Q

What are the advantages of using a laser scanning (confocal) microscope?

A
  • high resolution images with show high contrast
  • depth selectivity and can focus on structures at different depths within a specimen
  • used to examine cells or whole living specimens
  • used in the medical profession as well as many branches of biology
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22
Q

What specimens can be seen using a light microscope?

A
  • living organisms, such as Paramecium and Amoeba
  • smear preparations of human blood and cheek cells
  • thin sections of animal, plant, and fungal tissue, such as bone, muscle,leaf,root or fungal hyphae
  • mitochondria and chloroplast
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23
Q

What are stains?

A

coloured chemicals that bind to molecules in or on the specimen, making the specimen easier to see

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24
Q

What are ways in which organisms which are transparent or colourless be seen under a light microscope other than using stains?

A
  • light interference

- dark background against the illuminated specimen

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25
Q

What is the name of the all-purpose stain?

A

methylene blue

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26
Q

What does acetic orcein bind to and what colour is seen?

A
  • binds to DNA

- stains chromosomes dark red

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27
Q

What part of the specimen does eosin stain and what colour is seen?

A
  • cytoplasm

- pink

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28
Q

What part of the specimen does Sudan red stain and what colour is seen?

A
  • lipids

- red

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29
Q

What two parts of the specimen does iodine stain and what colours are seen?

A
  • stains cellulose in plant cell walls yellow

- stains starch granules blue/black

30
Q

What is meant by differential staining?

A

each structure within the specimen can be stained with a different colour and each one can be easily seen within a single preparation

31
Q

How are slides prepared before use?

A
  • the specimen is dehydrated
  • embedding them in wax to prevent distortion during slicing
  • using a thin instrument to make very thin slices called sections-these are stained and mounted in a special chemical to preserve them.
32
Q

What is the formula linking, actual image size, image size and the magnification?

A

Magnification=Image size/Actual size

33
Q

How do you convert from a millimetre(mm), to a micrometre (μm) and then to a nanometre(nm)?

A

millimetre to a micrometre x1000
micrometre to a nanometre x1000
to convert back just divide by 1000

34
Q

What is the eyepiece graticule?

A

a measuring device. It is located in the eyepiece of a microscope and acts as a ruler when you view an object under the microscope

35
Q

What is a stage graticule?

A

a precise measuring device. It is small scale that is placed on a microscope stage and used to calibrate the value of eyepiece divisions at different magnifications

36
Q

What is a cell?

A

fundamental units or building blocks of all living organisms

  • within each cell there are various organelles, each having specific functions
  • they become specialised to do a particular job
  • this provides a division of labour, which means that every cell can carry out its many functions efficiently
37
Q

What type of organisms have eukaryotic cells?

A
  • animal
  • plant
  • fungal
  • protoctist cells
38
Q

In animal cells (eukaryotic), what organelles are present?

A
  • nucleus(surrounded by a nuclear envelope) and containing DNA
  • nucleolus, which is inside the nucleus, which contains RNA
  • jelly-like cytoplasm
  • cytoskeleton
  • plasma membrane
  • membrane-bound organelles(e.g. mitochondrion, RER)
  • small vesicles
  • ribosomes
39
Q

In plant cells (eukaryotic) , what organelles are present?

A
  • chloroplast
  • membrane bound organelles (e.g. mitochondrion, RER)
  • amyloplast containing starch
  • vacuole
  • CELL WALL
40
Q

What are membrane bound organelles?

A
  • organelles within eukaryotic cells which are covered by a membrane
  • this keeps each organelle separate from the rest of the cell, so that is is a discrete compartment
41
Q

What is the maximum resolution of transmission electron microscopes?

A

0.0002(μm)

42
Q

What is the maximum resolution of scanning electron microscopes?

A

0.002(μm)

43
Q

What are the steps in using a light microscope?

A
  1. Clip the slide containing the specimen you want to look at onto the stage
  2. Select the lowest powered objective lens (lowest magnification)
  3. Use the course adjustment knob to move the objective lens down to just above the slide
  4. Look down the eyepiece (contains the ocular lens) and adjust the focus with the fine adjustment knob, until you get a clear image of whatever on the slide
44
Q

Whats the function and structure of the nucleus?

A

Structure
-surrounded by a double membrane called the nuclear envelope. There are pores in the nuclear envelope.
- nucleolus is at the centre and is where ribosomes are made
Function
-control centre of the cell
- stores genome (chromatin is the genetic material, consisting of DNA wound around histone proteins)
-transmits genetic info
- provides instruction for protein synthesis

45
Q

What is the function of the nuclear envelope?

A
  • separates the contents of the nucleus from the rest of the cell
  • pores within the envelope enable larger substances, such as messenger RNA (mRNA) to leave the nucleus. Substances such as steroid hormones can enter the nucleus via these pores.
46
Q

Whats the function of the nucleolus

A
  • ribosomes for protein synthesis are made here

- contains RNA

47
Q

What is the structure and function of the rough endoplasmic reticulum (RER)?

A

Structure:
-coated with ribosomes
-system of membranes containing fluid-filled cavities called cisternae that are continuous with the nuclear membrane
Function:
-protein synthesis
- provides a large surface area for ribosomes, which assemble amino acids into proteins. These proteins then actively pass through the membrane into the cistern and are transported to the Golgi apparatus for modification and packaging.
-intracellular transport system

48
Q

What is the structure and function of the smooth endoplasmic reticulum?

A

Structure:
- system of membranes, containing fluid-filled cavities (cistern) that are continuous with the nuclear membranes
-no ribosomes on its surface
Function:
-lipid metabolism
-synthesis of lipids, cholesterol and steroid hormones
-absorption and transport of lipids from the gut

49
Q

What is the function and structure of the Golgi apparatus?

A

Structure:
- stack of membrane-bound flattened sacs.
-Secretory vesicles bring materials to and from the Golgi apparatus
Function:
- protein modification:
adding sugar to make glycoproteins
adding lipid molecules to make lipoproteins
being folded into their 3D shape
-proteins are packaged into vesicles that are ‘pinched off’ and then:
stored in the cell
moved to the plasma membrane, either to be incorporated into the plasma membrane, or exported outside the cell

50
Q

What is the function and structure of mitochondria (singular:mitochondrion)?

A

Structure:
-may be spherical, rod-shaped or branched, and are 2-5 micrometers long
-surrounded by two membranes with a fluid filled space between them. The inner membranes is highly folded into cristae
- inner part of the mitochondrion is a fluid-filled matrix
Function:
-site of ATP production during aerobic respiration
- self-replicating, so more can be made if the cell’s energy needs to increase
- abundant in cells where a lot of metabolic activity takes place

51
Q

What is the function and structure of chloroplasts?

A

Structure:
- large organelles, 4-10 micrometres long
-found only in plant and in some protoctists
- surrounded by a double-membrane. Inner membrane is continuous with stacks of flattened membrane sacs called thylakoids (resembling piles of plates), which contain chlorophyll.
- each stack or pile of thylakoids is called a granum (plural:grana). The fluid-filled matrix is called the stroma.
-chloroplasts contain loops of DNA and starch grains
Function:
- site of photosynthesis
- first stage of photosynthesis takes place in the grana where light energy is trapped by chlorophyll and used to make ATP. Water is also split so supply hydrogen ions
-second stage of photosynthesis occurs in the stroma where hydrogen reduces C02, using energy from ATP, to make carbohydrates.
-Chloroplasts are abundant in leaf cells, particularly the palisade mesophyll layer

52
Q

What is the structure and function of lysosomes?

A

Structure:
- small bags, formed from the Golgi apparatus. Each is surrounded by a single membrane
- contain powerful hydrolytic (digestive) enzymes
- abundant in phagocytic cells such as neutrophils and macrophages(white blood cells) that can ingest and digest pathogens such as bacteria
Function:
-keep powerful hydrolytic enzymes separate from the cell
- engulf foreign matter
-return digested components to the cell for reuse

53
Q

What is the structure and function of the vacuole?

A

Structure:
-surrounded by a membrane called the tonoplast and contains fluid
Function:
- only plant cells have vacuoles
- It is filled with water and solutes and maintains cell stability, because when the cell is full is pushes against the cell wall, making the cell turgid
- helps support the plant, especially in non-woody plants

54
Q

What is the structure and function of cilia and undulipodia?

A

Structure:
-potrusions from the cell and are surrounded by the cell surface membrane
- each contains microtubules
-they are formed from centrioles
Function:
-moving mucus
- cilium have receptors and allows the cell to detect signals about its immediate environment
- only type of human cell to have an undulipodium ( a longer cilium) is a spermatozoon. Enables it to move

55
Q

What organelles do not have membranes?

A
  • ribosomes

- cytoskeleton

56
Q

What is the structure and function of ribosomes?

A

Structure:
- small spherical organelles, about 20 nm in diameter.
-made of ribosomal RNA
- made in the nucleolus, as two separate subunits, which pass through the nuclear envelope into the cell cytoplasm and then combine
- some remain free in the cytoplasm and some attach to the endoplasmic reticulum
Function:
- ones bound to the RER are mainly for synthesising proteins that will be exported outside the cell.
-free ribosomes in the cytoplasm, either strongly or in clusters, are primarily the site of assembly of proteins that will be used inside the cell

57
Q

What is the structure and function of centrioles?

A 
Structure:
- consists of two bundles of microtubules at right angles to each other. The microtubules are made of tubular protein subunits, and are arranged to form a cylinder
Function:
-cell division:
chromosomes replicate (S phase)
pulled apart (mitosis)
"mitotic spindle"
- involved in the formation of cilia and undulipodia
58
Q

What is the structure of the cytoskeleton?

A
  • network of protein structures within the cytoplasm
  • consits of:
  • microfilaments made of subunits of the protein actin
  • tubulin
  • various proteins; myosin, kinesics and dyneins
59
Q

Why is the cytoskeleton important?

A
  • provides mechanical strength to the cells(microfilaments)
  • aids transport within cells(microtubules)
  • enables cell movement (microfilaments)
  • movement of Cilla/flagella
60
Q

What is the structure and function of the cell wall?

A 
Structure:
-only found in plants
- found on the outside of the plants plasma membrane
-made of bundles of cellulose fibres
Function:
- strength and support
-prevents cell from bursting when turgid
-permeable and allow solutions (solute and solvent) to pass through
61
Q

What are the cell walls in Fungi made of?

A

chitin

62
Q

What are the steps in making and secreting a protein?

A
  1. mRNA makes a copy of the instructions(gene) for insulin in the nucleus by transcribing.
  2. mRNA leaves the nucleus through a nuclear pore
  3. mRNA attaches to a ribosome, in this case attached to RER. Ribosome reads the instructions to assemble the protein(insulin) translation.
  4. Insulin molecules are ‘pinched off’ in vesicles and travel towards the Golgi apparatus. They move along microtubules and are carried by motor proteins
  5. Vesicle fuses with the Golgi apparatus
  6. Golgi apparatus processes and packages insulin molecules ready for release
  7. Packaged insulin molecules are ‘pinched off’ in vesicles from Golgi apparatus and move towards the plasma membrane
  8. vesicles fuses with the plasma membrane
    9 Plasma membrane opens to release insulin molecules outside
63
Q

What type of transport is the production and secretion of proteins?

A

bulk transport called exocytosis

64
Q

What have prokaryotic cells?

A

bacteria(microorganisms)

65
Q

What are some similarities between prokaryotic and eukaryotic cells?

A
  • plasma membrane
  • cytoplasm
  • ribosomes for assembling amino acids into proteins
  • DNA and RNA
66
Q

How are prokaryotic cells different from eukaryotic cells?

A
  • much smaller
  • much less well-developed cytoskeleton with no centrioles
  • do not have a nucleus
  • do not have membrane-bound organelles such as mitochondria, endoplasmic reticulum, chloroplasts or Golgi apparatus
  • have a wall that is made of peptidoglycan and not cellulose
  • smaller ribosomes
  • naked DNA which is not wound around histone proteins but floats free in the cytoplasm, as a loop(not linear chromosomes)
67
Q

What are some features of prokaryotic cells?

A
  • protective waxy capsule surrounding their cell wall
  • small loops of DNA, called plasmids, as well as the main large loop of DNA
  • flagella-long whip-like projections that enable them to move. The structure of these flagella differs from that of eukaryotic undulipodia
  • pili- smaller hair-like projections that enable the bacteria to adhere to host cells or to each other, and allow the passage of plasmid DNA from one cell to another
68
Q

How do prokaryotic cells divide?

A
  • binary fission

- dont have linear chromosomes so cannot carry out mitosis.

69
Q

How do eukaryotic cells divide?

A

mitosis

70
Q

Do prokaryotic cells have any membrane bound organelles?

A

NO

71
Q

What type of microorganisms have eukaryotic cells?

A
  • yeast (single celled fungus)

- amoebae

72
Q

What is the endosymbiont theory?

A
  • explains how eukaryotic cells evolved from prokaryotic cells
  • some prokaryotic cells with infolded membranes were engulfed by, some other prokaryote, but not digested. As the invaded prokaryote’s plasma membrane folded inwards around the invading cell, this produced the double membrane of what are now chloroplasts and mitochondria. Both chloroplasts and mitochondria share characteristics with prokaryotic cells. They:
  • have small ribosomes
  • have loops of DNA
  • contain RNA
  • can divide by binary fission

Biology A-Level -James (18 decks)

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