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A-level Aqa Biology > (2) cells: cell structure > Flashcards

(2) cells: cell structure Flashcards

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1
Q

Advantages of light microscopes?

A
  • can examine live specimens
  • cheap
  • portable (can take into field)
  • coloured images can be seen
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2
Q

Disadvantages of light microscope?

A

limited powers of magnification (x1500)
limited power of resolution (200nm)
staining of specimens may lead to artefacts

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3
Q

Advantages of an electron microscope?

A

high level of magnification (x500000)
excellent power of resolution

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4
Q

disadvantages of electron microscope?

A

specimen’s must be dead (observed in a vacuum)
preparations of specimens likely to produce artefacts
V expensive (£75000)
cannot be moved
images only in black and white

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5
Q

process of using an transmission electron microscope?

A
  1. Specimens covered in resin and frozen to form a solid block
  2. thinly sliced and stained with heavy metals (gold)
  3. As electrons pass through specimen, E’s absorbed by stained parts and the ones that pass focused by electromagnets onto a fluorescent screen/photograph film (only views dead samples)
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6
Q

process of using a scanning electron microscope?

A
  1. Specimen coated with a thin layer metal to improve conductivity and contrast
  2. electrons are reflected from the surface of the specimen producing a 3D image
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7
Q

properties of prokaryotic cells

A
  • 0.1-10 micrometer in diameters
    dna is circular and free in cytoplasm
    small ribosomes 70s
    very few organelles and not membrane bound
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8
Q

properties of eukaryotic cells

A
  • 10-100 micrometer in diameter
  • DNA inside distinct membrane bound nucleus
  • dna = linear, at rewatched to his tones and condensed into visible chromosomes before cell division
  • large ribosomes 80s
  • complex membrane system many organelles
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9
Q

cell membrane

A

made of many phospholipids
holds a cell together and regulated what enters and leaves the cytoplasm as it is a selectively permeable barrier

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10
Q

cytoplasm
(cytosol + organelles minus nucleus)

A

comprises a liquid called and all the organelles suspended in it

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11
Q

what are the features of the nucleus?

A

nuclear envelope: double membrane often with ribosomes on its surface, controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it

nuclear pores: allows passage of large molecules out of the nucleus (3000 in each)

nucleoplasm: granular jelly like material that makes up the bulk of the nucleus

chromosomes with protein bound linear DNA

nucleolus: small spherical region sin nucleoplasm, manufactures ribosomal RNA and assemblies ribosomes

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12
Q

what is the function of the nucleus?

A

acts as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis

retains the genetic material of the cell in the form of DNA and chromosomes

manufactures ribosomal RNA and ribosomes

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13
Q

what structures make up a mitochondrion?

A

double membrane that controls the entry and exit of material
inner membrane is folded to form extensions known as Cristae, provide a large surface area for the attachment of enzymes and other proteins involved in respiration

matrix: liquid the cristae projects into
contains proteins lipids and ribosomes and DNA and enzymes used in respiration to produce ATP

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14
Q

what is the function of mitocondria?

A

they are the sites of aerobic respiration and produce ATP

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15
Q

what are the main features of chloroplasts?

A

chloroplast envelope: double plasma membrane, highly selective in what it allows to enter / leave cells

grana: stacks of thylakoids, which contains chlorophyll
where first stage of photosynthesis takes place

stroma: fluid filled matrix where 2nd stage of photosynthesis takes place

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16
Q

how are chloroplasts adapted to their function of carrying out photosynthesis?

A

granal membrane provide a large surface area for attachment of chlorophyll, electron carriers and enzymes that carry our the first stage of photosynthesis

fluid of stoma possessesall the enzymes needed to make sugars in the second stage of photosynthesis

chloroplasts contain both DNA and ribosomes so they can quickly n easily manufacture proteins needed for photosynthesis

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17
Q

feature of the rough endoplasmic reticulum and its function?

A

series of cisternae with ribosomes present on the outer surface of the membrane

provides a large surface area for the synthesis of proteins and glycoproteins
packages new protein into a vehicle for transport

provides a pathway of for the transport of materials esp. proteins throughout the cell

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18
Q

feature of the smooth endoplasmic reticulum and its function?

A

series of branching tubes
synthesises and stores and transports lipids and carbohydrates

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19
Q

what is the function of Golgi apparatus?

A

stacks of cisternae and formed through the fusing of vesicles

secrets carbohydrates
transports modifies and stores lipids
adds carbohydrates to proteins to form glycoproteins
forms lysosomes

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20
Q

what are the functions of lysosomes?

A

vesicles containing digestive enzymes

hydrolyse material ingested by phagocytise cells
release enzymes to the outside of the cell to destroy material around the cell
digest worn out organelles so that useful chemicals they’re made of can be reused
autolysis: completely break down cells after they have died

21
Q

features and function of ribosomes?

A

small non-membranous organelles responsible for protein synthesis
2 subunits, one large n one small each containing ribosomal RNA and protein
80S found in eukaryotic cells
70S found in prokaryotic cells, slightly smaller

22
Q

features of the cell wall and its function?

A

consists of a number of polysaccharides such as cellulose
middle lamella (thin layer) marks boundary between adjacent cell walls and cements adjacent cells together

function: provide mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water

23
Q

what is cell fractionation and what are the 3 stages?

A

the process of separating cell organelles from each other
3 stages:
homogenisation
filtration
ultracentrifugation

24
Q

why must the sample of tissue be placed in a cold isotonic buffer solution before being homogenised?

A

ice cold - to reduce the activity of enzymes that break down organelles
isotonic - to prevent water moving organelles which would cause them to expand and become damaged
buffered solution - prevents enzymes from becoming denatured

25
Q

what is the process of homogenisation?

A

tissue containing solution is homogenised where the machine grinds the cell up and breaks the plasma membrane of the cells and releases the organelles into a solution called homogenate

26
Q

what happens during filtration?

A

homogenate is filtered through a gauze to separate any large cell debris or tissue debris that were not broken up
leaves the filtrate that contains a mixture of organelles

27
Q

what happens in ultracentrifugation?

A

filtrate is placed into a tube and into the centrifuge where it is spun on a low speed to separate the heaviest organelles (nuclei)
which settle at the booth known as the pellet and the solution on top is the supernatant

supernatant placed into another tube and spun at a higher speed to extract a different organelle in the pellet

28
Q

what is the order of mass from heaviest to lightest in ultracentrifugation

A

nuclei
chloroplasts
mitochondria
lysosomes
endoplasmic reticulum
ribosomes

29
Q

what are the 2 groups of prokaryotes?

A

bacteria and archea

30
Q

what is the role and characteristic of the mesosome in a prokaryotic cell?

A

it is the unfolding of the cell membrane and thought to be involved in respiration, attachment and replication of DNA and secretion

31
Q

what is the cells wall made of in prokaryotic cells?

A

peptidoglycan
a polymer of aminoacids and sugars in

32
Q

what are the characteristics of the DNA in a prokaryotic cell?

A

not associated with proteins but is freely suspended in the cytoplasm usually coiled up and referred to as the nucleoid or genephore

33
Q

what can only some prokaryotic cells have and what are the roles of them?

A
  • plasmid: possesses genes that may aid the survival of bacteria in adverse conditions
  • pili (spikes in outside of cell): hollow protein structures used during bacterial conjugation
  • flagellum: long helical tube, which rotate to provide locomotion powered by protein motors
34
Q

what are the characteristics of viruses?

A

smaller than bacteria (20-300nm)
contain nuclei acid (single or double strand) -> can have DNA or RNA depending on species
contains capsid which is a protein coat that holds the nuclei acid

35
Q

what is the difference between mitosis and meiosis?

A

mitosis produces 2 daughter cells that are genetically identical to the parent cells and each other
meiosis produces 4 daughter cells that are genetically different, and have half the amount of chromosomes of the parent cells

36
Q

why do cells divide?

A

development: increase in complexity from a single zygote
growth: involves an increase in size through an increase in cell number
replacement: many cells within a multicellular organism are constantly dying and being repaired
asexual reproduction: process that produces identical clones

37
Q

what are the 3 phases of the cell cycle?

A

interphase:
Nuclear division
cytokinesis

38
Q

what are the stages in interphase and what happens in each one?

A

G1: the new cell grows and carries out its normal cell functions such as protein synthesis and respiration
S phase: cells DNA is replicated so that each chromosome is double structured
-> energy is also saved up in the form of ATP, ready for process of cell division
G2: (second gap/growth phase): followed by a central checkpoint, where the cell checks and repairs damage to its DNA before proceeding to mitosis

39
Q

mitosis: what happens during prophase?

A

prophase: chromatin condenses and becomes inactive, centrioles migrate in pairs to opposite poles and the nuclear and nucleolus break up

40
Q

mitosis: what happens during metaphase?

A

mitotic spindle grows further and attaches to the centromere of each chromosome
the fibres then, arrange the chromosomes to line up along the cell equator

41
Q

mitosis: what happens during anaphase?

A

centromere of each chromosome breaks, sister chromatids separate into daughter chromosomes
the cell starts to elongate as cytokinesis begins

42
Q

mitosis: what happens during telophase?

A

the new nuclear membranes and nucleoli form
chromosome start to unwind back into chromatin and are no long visible under the microscope

43
Q

what happens during cytokinesis?

A

the cell will completely divide in to two daughter cells as the cytoplasm and cell membrane separates

44
Q

what is the process that allows prokaryotic cells to divide?
explain

A

binary fission
circular DNA molecule replicated and both copies attach to the cell membrane , plasmids also replicated
the cell membrane begins to grow between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm into 2
a new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of circular DNA and a variable number of copies of the plasmids

45
Q

how do viruses replicate?

A

cannot go under cell division as they are non living

they replicate by:
attaching to their host cell with the attachment proteins on the surface
then they inject their nuclei acid into the cell, and the genetic info on the injected viral nuclei. Acid then provides the ‘instructions’ for the hosts cell metabolic processes to start producing the viral components, nuclei acid, enzymes and structural proteins, which are assembled into new viruses

46
Q

what is cancer a result of and what does it lead to?

A

result of damage to the genes that regulate mitosis and the cell cycle
leads to uncontrolled growth and division of cells, and as a consequence a group of abnormal cells called a tumour develops and expands in size
becomes cancerous if it changes from benign to malignant

47
Q

how does chemotherapy disrupt the cell cycle and treat cancer?

A

prevents DNA from replicating
inhibiting the metaphase stage of mitosis by interfering with spindle formation

48
Q
A

A-level Aqa Biology (9 decks)

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