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ocr a level biology > module 2 - cell structure > Flashcards

module 2 - cell structure Flashcards

1
Q

what is meant by the ‘ultrastructure’ of a cell?

A
  • refers to the finer structural details of a cell which are only observable by looking through an electron microscope
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2
Q

what are the features and function of the nucleus in eukaryotic cells?

A
  • FUNCTION : contains genetic information
  • FEATURES : surrounded by the double membrane called nuclear envelope, contains pores which enables molecules to enter and leave nucleus
  • contains chromatin made up of DNA and histone proteins
  • contains a nucleolus which produces ribosomal RNA (rRNA)
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3
Q

CELL STRUCTURE - what are the features and function of mitochondria?

A
  • FUNCTION : produces ATP through aerobic respiration
  • FEATURES : has a double membrane, inner folds to form cristae
  • internal fluid within is named the matrix, contains all enzymes needed for respiration
  • usually oval shaped, bound by double membrane called the envelope
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4
Q

what are the features and function of lysosymes?

A
  • FUNCTION : break down waste such as old organelles
  • FEATURES : made up of specialised vesicles which are membranous sacs
  • vesicles contain hydrolytic ((digestive) acceptable) enzymes
  • bound by a single membrane
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5
Q

what are the features and function of smooth endoplasmic reticulum (SER)?

A
  • FUNCTION : synthesises & processes lipids and carbohydrates
  • FEATURES : made up of flattened membrane-bound sacs called cisternae
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6
Q

what are the features and function of rough endoplasmic reticulum (RER)?

A
  • FUNCTION : synthesises proteins (folds & processes) made on ribosomes
  • FEATURES : made up of cisternae (series of flattened sacs) bound to ribosomes (on surface)
  • these are made up of RNA and ribosomes can also appear loose in the cytoplasm
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7
Q

what are the features and function of golgi apparatus?

A
  • FUNCTION : modifies proteins & lipids and packages them into vesicles
  • also produces lysosymes
  • FEATURES : made up of flattened, fluid filled & curved sacs with vesicles surrounding the edges
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8
Q

what are the features and function of the cytoskeleton?

A
  • FUNCTIONS : maintains cell shape
  • controls cell and organelle movement
  • provides mechanical strength
  • FEATURES : made up of microfilaments which are made up of actin and control cell movement and cytokinesis
  • made up of microtubules which are made up of tubulin and regulate shape and organelle movement
  • these then form centrioles and spindle fibres
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9
Q

what are the features and function of centrioles?

A
  • FUNCTION : involved in cell division
  • FEATURES : hollow cylinders
  • contain a ring of microtubules arranged at right angles to each other
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10
Q

what are the features and function of flagella/flagellum?

A
  • FUNCTION : allow cell movement
  • FEATURES : made up of a cylinder with 11 microtubules, with 9 encircling 2 which are in the centre
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11
Q

what are the features and function of cilia/cilium?

A
  • FUNCTION : allow substances to move across surfaces
  • FEATURES : made up of a cylinder with 11 microtubules, with 9 encircling 2 of which are in the centre
  • shorter than the flagella
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12
Q

define the term ‘organelles’

A
  • membrane-bound compartments that exist within most cell types
  • many different functions but some involve the production and secretion of proteins
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13
Q

describe the interrelationship between the organelles involved in the production and secretion of proteins

A
  • proteins produces on the ribosomes
  • proteins which re produced on the surface on RER are folded and processed in the RER
  • the proteins are then transported from the RER to the golgi apparatus in vesicles
  • they are then modified in the golgi apparatus
  • golgi apparatus packages proteins into vesicles to be transported around the cells to where they are required
  • some proteins such as extracellular enzymes leave the cell by exocytosis
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14
Q

PROKARYOTIC CELLS - what is the difference between prokaryotic and eukaryotic cells?

A
  • prokaryotic cells are uniformly uni-cellular, meaning they are each made up of a single cell
  • whereas, eukaryotic cells are made up of multiple cells
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15
Q

what are some similar features in the structures and ultrastructures of prokaryotic and eukaryotic cells? (1)

A
  • REPRODUCTION : prokaryotes undergo asexual reproduction (binary fission)
  • eukaryotes undergo asexual or sexual production
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16
Q

what are some similar features in the structures and ultrastructures of prokaryotic and eukaryotic cells? (2)

A
  • CELL WALL : prokaryotes have a cell wall made up of peptidoglycan (or muerin) —> this is a polymer made up of sugars and amino acids
  • eukaryotic plant cells have a cell wall made of cellulose
  • eukaryotic fungal cells have a cell wall made up of chitin
17
Q

what are some similar features in the structures and ultrastructures of prokaryotic and eukaryotic cells? (3)

A
  • CILIA & FLAGELLA : prokaryotes have a flagella sometimes but with a different structure to eukaryotes
  • eukaryotes have flagella and they are most often present in animal cells
18
Q

what are some different features in the structures and ultrastructures of prokaryotic and eukaryotic cells?

A
  • CYTOSKELETON : prokaryotes have a cytoskeleton made up of different proteins to the eukaryotic one
  • MEMBRANE-BOUND ORGANELLES : prokaryotes do not have them whereas eukaryotes do
  • RIBOSOMES : prokaryotes have smaller ribosomes than eukaryotes
  • DNA : prokaryotes have one main molecule of circular DNA which is naked in the cytoplasm and additional DNA can also be stored in plasmids
  • EUKARYOTES & DNA : have linear DNA in the form of chromosomes and are associated with the histone proteins in the nucleus and additional DNA can be stored in mitochondria and chloroplasts
19
Q

MICROSCOPY - what is the use of microscopy to observe and investigate different types of cells and cell structures in a range of eukaryotic organisms?

A
  • the purpose of microscopes is to magnify specimens and, ideally, to give a clear, detailed image of the organelles and structures within a cell
20
Q

state the formula for magnification

A

actual size = image size/magnification

21
Q

what is the difference between magnification and resolution?

A
  • magnification is the size of the image divided by the actual size of the object
  • resolution is the shortest distance between two objects that can be distinguished as separate and individual structures
22
Q

describe what a light microscope is like

A
  • uses a light to form the image
  • has a maximum resolution of 0.2 micrometers : can’t view organelles smaller than this e.g ribosomes, ER and lysosomes. mitochondria may be visible but not clear, nucleus visible
  • maximum useful magnification of light microscope is about x1500
23
Q

describe what an electron microscope is like

A
  • uses electrons to form an image
  • has a higher resolution than optical microscopes to give a more detailed image (and can be used to view all organelles)
  • maximum resolution of about 0.0002 micrometers - about 1000 times higher than light
  • maximum useful magnification of an electron microscope is about x1,500,000
24
Q

how does a transmission electron microscope work?

A
  • uses electromagnets to focus a beam of electrons, which is transmitted through a specimen
  • the densest parts of the specimen absorb more electrons, which makes them look darker
  • TEMs produce a high resolution image to see internal structure of organelles
  • they can only be used on thin specimens
25
Q

how does a scanning electron microscope work?

A
  • scans a beam of electrons over the specimen that knocks off electrons that are gathered in a cathode ray tube to form an image
  • the images show the surface of the specimen and can be 3D
  • good for use on thick specimens
  • SEMs give a lower resolution image than TEMs
26
Q

MICROSCOPY PRACTICAL SKILLS - how are microscope slides prepared for use in light microscopy?

A
  • by staining for examination of organelles, for instance
27
Q

what is the use of staining in light microscopy?

A
  • as the cytoplasm is transparent, it is necessary to add stains (and counter-stains) to the slide holding the specimen being viewed under a light microscope because light goes through everything on the surface
28
Q

describe the gram stain test

A
  • stain used for bacteria
  • the bacteria in the sample are dyed with crystal violet before being rinsed with a decolorizing solution to remove any remaining dye
  • immediately thereafter, a counter stain is applied (e.g safranin and fuchsine)
  • under a microscope, gram-positive bacteria retain the violet stain, but gram-negative bacteria do not and they look red/pink
29
Q

describe the composition of gram-negative bacteria

A
  • have only a thin layer of peptidoglycan and an additional outer membrane composed of lipopolysaccharides and proteins, which prevents the cell from retaining the counterstain as strongly
30
Q

what colours can a gram negative bacteria cell turn?

A

(continued from last card)
- consequently, the cell appears red (safranin) or pink (fuchsine) as it retains the counterstain
- fuchsine and safranin are able to stain all cells, and because the stain is lighter than that of a crystal violet, it does not interfere with cells that have already been stained

31
Q

what are artefacts and why do you sometimes spot them under the microscope?

A
  • frequently, artefacts can be found on the slides
  • they are not true components of the specimen and may be identified as such upon closer examination with a microscope
  • they are merely imperfections (accidental material, like a hair or piece of dust) that have been accentuated by the staining process
32
Q

CALCULATING CELL SIZE - what is an eyepiece graticule and how is it used ?

A
  • eyepiece graticule is a ruler with no units
  • needs to be calibrated with the stage micrometer (true ruler)
  • by calibrating the two, you can determine what each length on the eyepiece graticule corresponds to in terms of actual micrometer measurements on the stage micrometer

ocr a level biology (7 decks)

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