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cells

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1
Q

what are the groups of eukaryotic cells?

A

-fungi
-animal
-plants
-protists
(algal and fungal cell are similar to plant cells)

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2
Q

what are the distinguishing features of eukaryotic cells?

A
  • cytoplasm containing membrane-bound organelles
  • so DNA enclosed in a nucleus
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3
Q

what are the structures found in animal cells?

A
  • cell membrane
    -mitochondrion
    -nucleus
    -ribosomes
    -rough endoplasmic reticulum (RER)
    -Smooth endoplasmic reticulum (SER)
    -Golgi apparatus and vesicles
    -lysosomes
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4
Q

what are the structures found in a plant cell?

A
  • cell membrane
    -mitochondrion
    -nucleus
    -ribosomes
    -rough endoplasmic reticulum (RER)
    -Smooth endoplasmic reticulum (SER)
    -Golgi apparatus and vesicles
    -lysosomes
    -chloroplast
    -cell wall
    -cell vacuole
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5
Q

diagram of a plant and animal cell with labelled structures

A
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6
Q

describe the structure of the cell surface membrane

A
  • found in all cells phospholipid bilayer embed within and attached on the outside (proteins, carbohydrates and cholesterol)
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7
Q

describe the function of the cell-surface membrane

A
  • selectively permeable so enables control of passage of substance in/out of cell
    -molecules/receptors/antigens on surface allows cell recognition/signalling
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8
Q

describe the structure of the nucleus

A

-nuclear envelope: double membrane that surrounds the nucleus - controls entry/exit of materials
-nuclear pores: allow passage of larger molecules
-nucleoplasm: granular, jelly like material that makes up the bulk of the nucleus
-nucleolus(dense region): site of rRNA production and makes ribosomes
-chromosomes(highly condensed)/ chromatin (condensed) : consists of protein/histone-bound, linear DNA

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9
Q

describe the function of a nucleus

A
  • holds/stores genetic information which codes for polypeptide (proteins) in the form of DNA and chromosomes
    -site of DNA replication
  • site of transcription (part of protein synthesis) producing mRNA
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10
Q

describe the structure of ribosomes

A

-not a membrane bound organelle
-made of ribosomal RNA and protein ( two subunits)- 80s found in eukaryotic cells, 70s found in prokaryotic cells

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11
Q

describe the function of a ribosome

A
  • site of protein synthesis
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12
Q

describe the structure of rER and sER

A

-both have folded membranes called cisternae
-rER has ribosomes on cisternae (outer membrane)
-sER lacks ribosomes on surface, more tubular in appearance
- single membrane

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13
Q

describe the function of rER + sER

A

rER:
● Ribosomes on surface synthesise proteins
● Proteins processed / folded / transported inside rER
● Proteins packaged into vesicles for transport e.g.. to Golgi apparatus
sER:
● Synthesises and stores lipids and carbs
● E.g.. cholesterol and steroid hormones

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14
Q

describe the structure of Golgi apparatus and Golgi vesicles

A

-Golgi apparatus: flattened membrane sacs, has a single membrane
- Golgi vesicles: small membrane sac

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15
Q

describe the function of Golgi apparatus and Golgi vesicles

A

Golgi apparatus:
-modifies protein, e.g. adds carbohydrates to produce glycoproteins
- modifies lipids, e.g. adds carbohydrates to make glycolipids
- packages proteins/ lipids into Golgi vesicles
-produces lysosomes (a type of Golgi vesicles)

Golgi vesicles:
-transports proteins/lipids to their required destination
- e.g. moves to and fuses with cell-surface membrane

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16
Q

describe the structure of lysosomes

A
  • bags of digestive enzymes
  • has hydrolytic enzymes
  • single membrane
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17
Q

describe the function of lysosomes

A

-release hydrolytic enzymes (lysozymes) to break down/hydrolyse pathogens or worn out cell components (organelles) for reuse of materials

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18
Q

describe the structure of mitochondria

A
  • double membrane that controls the entry/exit of material
  • inner membrane is folded to form extension of cristae
  • matrix: contains small ribosomes(70s) and circular DNA which allows the mitochondria to control the production of their own proteins
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19
Q

describe the function of mitochondria

A
  • site of aerobic respiration
  • to produce ATP for energy release (energy carrier molecule)
    -e.g. for protein synthesis/vesicle movement/active transport
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20
Q

describe the structure of chloroplasts in plants and algae

A
  • chloroplast envelope: double plasma membrane that surrounds the organelle- highly selective in what can be entered/exit the chloroplast
    -grana: stacks of thylakoid(folded membrane embedded with pigments and is the 1st stage of photosynthesis)
    -lamella: thylakoids linking grana
    -stroma: fluid filled matrix where the 2nd stage of photosynthesis takes place. contains thylakoid membranes, small 70s ribosomes, circular DNA and within the stroma are a number of other structures e.g. starch granules and lipid droplets
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21
Q

describe the function of chloroplasts in plants and algae

A
  • absorbs light energy for photosynthesis to produce organic substances e.g. carbohydrates/lipids
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22
Q

describe the structure of the cell wall in plants, algae and fungi

A
  • composed mainly of cellulose ( a polysaccharide) in plants/algae
  • composed of chitin ( a nitrogen-containing polysaccharide) in fungi
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23
Q

describe the function of the cell wall in plants, algae and fungi

A
  • provides mechanical strength to cells
  • so prevents cell changing shape or bursting under pressure due to osmosis
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24
Q

describe the structure of the cell vacuole in plants

A

a large shaped organelle that varies in shape containing cell sap
- single membrane

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25
Q

describe the function of the cell vacuole in plants

A
  • maintains turgor pressure in cell (stopping plant wilting)
  • contains cell sap - stores sugars, amino acids, pigments and any waste chemicals
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26
Q

describe how eukaryotic cells are organised in complex multicellular organisms

A

in multicellular organisms, eukaryotic cells become specialised for specific functions
- tissue: group of specialised cells with a similar structure working together to perform a specific function, often with the same origin
- organ: aggregations of tissues performing specific functions
- organ system: group of organs working together to perform specific functions

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27
Q

what are the distinguishing features of prokaryotic cells? and examples

A
  • cytoplasm lacking membrane-bound organelles
    -so genetic material not enclosed in a nucleus
  • prokaryotic organisms e.g. bacteria and archaea (always unicellular)
28
Q

what are the structures that are sometimes present in a prokaryotic cell?

A
  • capsule: additional protection, slimy layer made out of proteins which prevents cell from desiccating (drying out)
  • plasmids: small rings of DNA
    -flagella: rotates to enable the bacteria to move
29
Q

what are the structures that are always present in a prokaryotic cell?

A
  • cell surface membrane
  • cell wall: contains murein, a glycoprotein
  • cytoplasm
  • small 70s ribosomes
  • circular DNA: free in cytoplasm, not associated with proteins
30
Q

compare and contrast the structure of eukaryotic and prokaryotic cells

A
  1. eukaryotic has membrane bound organelles e.g. mitochondria, ER but in prokaryotic there’s no membrane bound organelles e.g. no mitochondria and ER
  2. eukaryotic has a nucleus containing DNA but the DNA in prokaryotic is free in the cytoplasm instead
  3. eukaryotic: DNA is long and linear and associated with histone proteins
    prokaryotic: DNA is short and circular and isn’t associated with proteins
  4. eukaryotic has larger 80s ribosomes in cytoplasm. prokaryotic has smaller 70s ribosomes
  5. eukaryotic: cell walls only in plant, fungi and algae containing chitin or cellulose.
    prokaryotic: all cells have cell walls containing murein, a glycoprotein
  6. eukaryotic: plasmids/ capsules are never present (sometimes flagella)
    prokaryotic: plasmids, flagella and capsules are sometimes present
  7. eukaryotic: larger overall size
    prokaryotic: smaller in overall size
31
Q

describe why viruses are described as acellular and non-living

A
  1. acellular: not made of cells, no cell membrane/ cytoplasm/organelles
  2. non-living: have no metabolism, cannot independently move/respire/replicate/ excrete
32
Q

describe the general structure of a virus particle

A

-nucleic acids surrounded by a capsid (protein coat)
- attachment proteins allow attachment to specific host cells
- no cytoplasm, ribosomes, cell wall, cell surface membrane etc.
- some also surrounded by a lipid envelope e.g. HIV ( not all viruses have a lipid envelope but HIVs do)

33
Q

what’s the difference between bacterial capsules and virus capsids?

A
  • bacterial (‘slime’) capsules provide protection and help with adhesion
  • virus capsid (‘protein coat’) protect genetic material
34
Q

how does prokaryotic cells make ATP?

A

has no membrane bound organelles so doesn’t have mitochondria but will still perform respiration to make ATP

35
Q

required practical 4: describe a method to investigate the effect of a named variable (e.g. temp) on the permeability of cell-surface membranes

A
  1. cut equal size/identical cubes of plant tissue (e.g. beetroot) of same age/type using a scalpel
  2. rise to remove pigment released during cutting or blot on paper towel
  3. ass same number of cubes to 5 different test tubes containing same volume of water (e.g. 5cm^3)
  4. place each test tube in water bath at a different temperature (e.g. 10,20,30,40,50°C)
  5. leave for same length of time
  6. remove beetroot and measure pigment release by measuring intensity of colour or concentration of surrounding solution semi-quantitively or quantitively
36
Q

describe 2 methods to estimate pigment concentration in a solution

A
  1. semi-quantitative:
    - use a known concentration of extract and distilled water to prepare a dilution series
    - compare results with these ‘colour standards’ to estimate concentration
  2. quantitative:
    - measure absorbance of light of known concentration using a colorimeter
    - draw a calibration curve - plot a graph of absorbance (y) against concentration (x) and draw a line/curve of best fit
    -read off sample absorbance value on curve to find associated concentration
37
Q

explain why the beetroot is washed before placing it in water

A
  • wash off any pigment on surface
  • to show that released is only due to (named variable)
38
Q

explain why each test tube containing cubes of beetroot is regularly shaken

A
  • to ensure all surface of cubes remain in contact with liquid
  • to maintain a concentration gradient for diffusion
39
Q

explain why the volume of water needs to be controlled

A
  • too much water would dilute the pigment so solution will appear lighter/ more light passes through in colorimeter than expected
  • so results are comparable
40
Q

explain how you could ensure beetroot cylinders were kept at the same temperature throughout the experiment

A
  • take readings in intervals throughout experiment of temperature in tube using a digital thermometer/ temperature sensor
  • use corrective measure if temperature has fluctuated
  • keep all at room temperature in the same room
41
Q

describe the issues with comparing to a colour standard

A
  • matching to colour standards is subjective
  • colour obtained may not match any of colour standards
42
Q

what does a high absorbance suggest about the cell-membrane?

A
  • more permeable/damaged
  • as more pigment leaks out making surrounding solution more concentrated (darker)
43
Q

explain how temperature affects permeability of cell-surface membranes

A
  1. as temperature increases, cell membrane permeability increases:
    - phospholipids gain kinetic energy so fluidity increases
    - transport proteins denature at high temperatures as hydrogen bonds break, changing their tertiary structure
  2. at very low temperatures, cell membrane permeability increases:
    - ice crystals can form which pierce the cell membrane and increase permeability
44
Q

explain how pH affects permeability of cell-surface membranes?

A

high or low pH increases cell membrane permeability : transport proteins denature as H / ionic bonds break, changing tertiary structure

45
Q

explain how lipid-soluble solvents e.g. alcohol affects permeability of cell-surface membranes

A
  • as concentration increases, cell membrane permeability increases
  • ethanol ( a lipid soluble solvent) may dissolve phospholipid bilayer (creating gaps)
46
Q

what is cell fractionation used for?

A

-cells are broken open to release the contents and organelles are then separated
-used to isolate different organelles so they can be studied. This enables individual organelle structures and functions to be studied
-before cell fractionation can begin, the tissue is placed in a cold, buffered, isotonic solution
-there are 2 stages: homogenisation and ultracentrifugation

47
Q

what happens in stage 1 of cell fractionation: homogenisation?

A

1.homogenise tissue/use a blender: disrupts the cell membrane, breaking open cells to release contents/organelles
2.placed in a cold, isotonic, buffered solution:
-cold: reduce enzyme activity so organelles not broken down/damaged
-isotonic: water doesn’t move in or out of organelles by osmosis so they don’t burst
- buffered: to keep pH constant so enzyme doesn’t denature
3. filter homogenate: remove large, unwanted debris e.g. whole cells, connective tissue

48
Q

what happens in stage 2 of cell fractionation: ultracentrifugation

A

ultracentrifugation: separates organelles in order of density/mass
- centrifuge homogenate in a tube at a low speed
-remove pellet or heaviest organelle and respin supernatant at a higher speed
-repeat at increasing speeds until separated out, each time the pellet is made of lighter organelles (nuclei → chloroplast/mitochondria→ lysosomes → ER → ribosomes

49
Q

what is the summarised stages of the cell cycle in the eukaryotic cell?

A

Stage 1:Interphase
-cell grows and organelles are synthesised
-DNA replicates semi-conservatively (S phase)
-Leading to 2 chromatids (identical copies) joined at a centromere
-chromosomes are not visible
-Number of organelles & volume of cytoplasm increases, protein synthesis (G1 / G2)
Stage 2: Mitosis
-Nucleus divides
-To produce 2 nuclei with identical copies of DNA produced by parent cell
Stage 3: Cytokinesis
-Cytoplasm and cell membrane (normally) divide
-To form 2 new genetically identical daughter cells

50
Q

what happens in stage 1 of prophase?

A
  • Nuclear envelope breaks down
    -Chromosomes condense, becoming shorter / thicker so visible
    ○ Appear as 2 sister chromatids joined by a centromere
  • Centrioles move to opposite poles forming spindle network
  • Spindle fibres start to attach to chromosomes by their centromeres
51
Q

what happens in stage 2 of metaphase?

A

-Spindle fibres attach to chromosomes by their centromeres
-Chromosomes align along equator

52
Q

what happens in stage 3 of anaphase?

A
  • Spindle fibres shorten / contract
  • Centromere divides
  • Pulling chromatids (from each pair) to opposite poles of cell
53
Q

what happens in stage 4 of telophase?

A
  • Chromosomes uncoil, becoming longer / thinner and are no longer visible
  • Nuclear envelopes reform = 2 nuclei
    -chromatids have reached opposite poles
  • Spindle fibres / centrioles break down
54
Q

diagram of the different stage of cell cycle

A
55
Q

why do some eukaryotic cells not undergo the cell cycle?

A

-within multicellular organisms, not all cells retain the ability to divide (e.g. neurons)
-Only cells that do retain this ability go through a cell cycle

56
Q

Explain the importance of mitosis in the life of an organism

A

Parent cell divides to produce 2 genetically identical daughter cells for:
● Growth of multicellular organisms by increasing cell number
● Replacing cells to repair damaged tissues
● Asexual reproduction

57
Q

Describe how tumours and cancers form

A

Mitosis is a controlled process so:
● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour = cancerous, can spread (metastasis)
○ Benign tumour = non-cancerous

58
Q

Suggest how cancer treatments control rate of cell division

A

-Some disrupt spindle fibre activity / formation
○ So chromosomes can’t attach to spindle by their centromere
○ So chromatids can’t be separated to opposite poles (no anaphase)
○ So prevents / slows mitosis
-Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents / slows mitosis

59
Q

Describe how prokaryotic cells replicate

A

Binary fission:
1. Replication of circular DNA
2. Replication of plasmids
3. Division of cytoplasm to produce 2 daughter cells
○ Single copy of circular DNA
○ Variable number of copies of plasmids

60
Q

Describe how viruses replicate

A

Being non-living, viruses do not undergo cell division
1. Attachment proteins attach to complementary receptors on host cell
2. Inject viral nucleic acid (DNA/RNA) into host cell
3. Infected host cell replicates virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein / capsid / enzymes
c. Virus assembled then released

61
Q

true or false: mitosis repairs cells?

A

mitosis creates new cells to replace damaged or dead ones, therefore
repairing the tissue, but not the cells themselves.

62
Q

when does DNA replication occur?

A

in the interphase which is before mitosis

63
Q

what are chromatids?

A

A chromatid is one of the two identical halves of a chromosome that
has been replicated. These are held together by a centromere.

64
Q

what’s the difference between centromeres and centrioles?

A

Centromeres join sister chromatids, while centrioles are organelles
involved in spindle formation.

65
Q

true or false: “Cytokinesis always happens.”

A

Some cells (eg. muscle cells) undergo mitosis (nuclear division) without
cytokinesis (cytoplasmic division), so have multiple nuclei.

66
Q

true or false: “In binary fission in prokaryotic cells,
bacterial chromosomes replicate.”

A

Chromosomes consist of linear DNA associated with histones and are
only found in eukaryotic cells. Bacteria have circular DNA (no histones).

biology paper 1 (7 decks)

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