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AQA A-LEVEL BIOLOGY > 2. Cells > Flashcards

2. Cells Flashcards

1
Q

Eukaryotic cells

A

contain a distinct nucleus and membrane-bound organelles

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2
Q

Cell wall

A

not in animal cells, cellulose in plants and algae, chitin in fungi, murein in bacteria, provides structural support, strength and rigidity, helps resist osmotic pressures preventing cell lysis

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3
Q

Cell membrane

A

phospholipid bilayer with embedded intrinsic and extrinsic proteins, selectively permeable barrier (only small, lipid-soluble, non-polar molecules can pass directly through), controls movement of substances in/out the cell

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4
Q

Nucleus

A

nucleolus, chromatin, nuclear envelope and nuclear pores, contains genetic information, site of transcription and splicing, site of DNA replication, nucleolus makes ribosomes, nuclear pores control movement of substances in/out the cytoplasm

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5
Q

Mitochondria

A

double membrane with inner membrane folded into cristae, 70s ribosomes in matrix, small circular DNA, site of aerobic respiration producing ATP

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6
Q

Chloroplast

A

thylakoid membranes staked into grana linked by lamellae, stroma contains enzymes, starch granules, 70s ribosomes and small circular DNA, site of photosynthesis producing glucose

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7
Q

Golgi apparatus

A

fluid-filled membrane-bound sacs, vesicles at edge, modifies proteins and lipids and packages them into vesicles to transport out the cell membrane via exocytosis, makes lysosomes

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8
Q

Lysosomes

A

contain digestive enzymes (lysozymes) which hydrolyse pathogens or worn down cell components

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9
Q

Rough endoplasmic reticulum

A

system of membranes with bound ribosomes, folds and processes proteins made at ribosomes on surface and packages them into vesicles to transport to Golgi

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10
Q

Smooth endoplasmic reticulum

A

system of membranes with no bound ribosomes, synthesises and processes lipids

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11
Q

Ribosome

A

small and large subunits made of protein and rRNA, 70s in prokaryotes, 80s in eukaryotes, site of translation in protein synthesis

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12
Q

Vacuole

A

fluid filled sack surrounded by tonoplast membrane, helps maintain pressure in cell keeping it rigid, involved in isolation of unwanted chemicals inside the cell

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13
Q

Prokaryotic cells

A

smaller, don’t contain membrane-bound organelles, 70s ribosomes, no nucleus, circular DNA which floats free in cytoplasm, murein cell wall, occasional plasmids, capsule and flagella

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14
Q

Binary fission

A

circular DNA (and plasmids) replicate, cell grows and cytoplasm divides to produce two daughter cells, each daughter cell has one copy of circular DNA and variable number of plasmids

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15
Q

Magnification

A

how many times larger the image is compared to the object, calculated by dividing image size by actual size

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16
Q

Resolution

A

minimum distance between two objects for them to appear as separate objects, determined by wavelength of light/electrons

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17
Q

Optical microscope

A

use light rays to form an image, glass lens for focussing, 2D colour image produced, poorer resolution as light has a longer wavelength, lower magnification

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18
Q

Preparing microscope slide

A

pipette a small drop of water onto slide, use tweezers to place a thin section of specimen onto the droplet, stain (eg. iodine) to highlight organelles, lower cover slip using a mounted needle

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19
Q

Transmission electron microscope

A

beam of electrons focused onto specimen using a condenser electromagnetic, denser parts of the specimen absorb more electrons so appear darker, 2D black and white image produced, highest resolution as electrons have shorter wavelength, higher magnification, complex staining process, can’t view live specimens due to vacuum

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20
Q

Scanning electron microscope

A

beam of electrons scanned across specimen, knocking off electrons from the surface of the specimen which are gathered in a cathode ray tube, 3D black and white image produced, high resolution as electrons have shorter wavelength, higher magnification, complex staining process, can’t view live specimens due to vacuum

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21
Q

Cell fractionation

A

process of isolating of a sample of organelles

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22
Q

Homogenisation

A

chop and grind to break open cell membrane and release organelles in an ice-cold (to reduce activity of enzymes that digest organelles), isotonic (prevent damage to organelles by osmosis), buffered solution (to maintain pH, preventing enzymes denaturing), isotonic solution (prevent damage to organelles by osmosis)

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23
Q

Filtration

A

filter homogenate through gauze to remove large cell debris

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24
Q

Ultracentrifugation

A

centrifuge filtrate at low speed to start, densest organelles (nuclei) flung to bottom form a pellet, remaining organelles stay suspended in the supernatant, recentrifuge supernatant at higher speed, next densest organelles form a pellet (chloroplasts)

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25
Q

Cell cycle

A

interphase, mitosis, cytokinesis

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26
Q

Interphase

A

divided into G1 where organelles replicate and proteins are made, synthesis where DNA replicates and G2 where cell grows and ATP content increases

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27
Q

Mitosis

A

cell divides to produce two genetically identical diploid daughter cells, needed for growth of multicellular organisms and repair of damaged tissues

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28
Q

Prophase

A

chromosomes condense and become visible (appearing as two sister chromatids joined by a centromere), centrioles move to opposite poles and form spindle, nuclear envelope breaks down

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29
Q

Metaphase

A

chromosomes line up along equator of the cell, spindle fibres attach to centromeres

30
Q

Anaphase

A

centromere divides, spindles contract (using ATP) pulling chromatids to opposite poles, centromere first (V-shaped)

31
Q

Telophase

A

chromatids reach opposite poles and uncoil, spindle fibres disintegrate, nuclear envelope reforms, cytokinesis finishes

32
Q

Mitotic index

A

proportion of cells undergoing mitosis, calculated by dividing number of cells undergoing mitosis by total number of cells observed

33
Q

Tumour

A

a mass of cells as a result of uncontrolled cell division, can lead to cancer

34
Q

Fluid mosaic model

A

phospholipids align as a bilayer, hydrophobic phosphate head faces outwards, hydrophilic fatty acid tails face inwards, channel and carrier proteins, glycoproteins, glycolipids and cholesterol scattered through

35
Q

Cholesterol

A

present in eukaryotic organisms, binds to hydrophobic fatty acid tails making membrane more rigid, giving the membrane stability so it’s more resistant to high temperatures

36
Q

Investigating membrane permeability

A

cut five equal size pieces of beetroot, place in five different test tubes each containing same volume of water, place each test tube in water bath of different temperature for same length of time, remove beetroot, transfer liquid into colorimeter, record absorbance (higher absorbance indicates higher permeability)

37
Q

Simple diffusion

A

net movement of molecules down concentration gradient (from an area of higher concentration to lower concentration), passive proves, continues until equilibrium is reached

38
Q

Facilitated diffusion

A

net movement of molecules down concentration gradient (from an area of higher concentration to lower concentration) via channel or carrier proteins, passive process, continues until equilibrium is reached

39
Q

Channel proteins

A

tubes filled with water enabling water-soluble ions to pass through membrane, highly selective

40
Q

Carrier proteins

A

bind with molecule (eg. glucose) causing protein to change shape so molecule is released on the other side of the membrane

41
Q

Osmosis

A

net movement of water molecules down water potential gradient (from an area of higher water potential to lower water potential) across a partially permeable membrane

42
Q

Water potential

A

pressure created by water molecules measured in kPa, pure water has a water potential of 0, adding more solutes lowers water potential

43
Q

Hypertonic solution

A

lower water potential than cell, water moves out cell by osmosis so cell shrivels

44
Q

Hypotonic solution

A

higher water potential than cell, water moves into cell by osmosis so cell becomes turgid or bursts

45
Q

Isotonic solution

A

same water potential as cell, no net movement of water, cell remains same mass

46
Q

Investigating water potential

A

make five serial dilutions of sucrose solution, cut five equal size pieces of potato, measuring starting mass of each chip, place each chip into different concentration sucrose solution for same length of time, remove chips, pat dry and reweigh, plot calibration curve (point at which curve crosses x-axis is when isotonic)

47
Q

Active transport

A

movement of molecules/ions against concentration gradient (from an area of lower concentration to higher concentration) via carrier proteins using energy from ATP

48
Q

Co-transport

A

movement of two molecules across a membrane together via a carrier protein using energy from ATP

49
Q

Co-transport and absorption of glucose

A

Na+ actively transported out epithelial cell into blood by the sodium-potassium pump, Na+ diffuse down step concentration gradient from ileum into the epithelial cell bringing a molecule of glucose via co-transport proteins, increasing concentration of glucose in epithelial cell, glucose diffuses out cell into blood by facilitated diffusion

50
Q

Pathogen

A

microorganism that can cause disease by releasing toxins or killing cells

51
Q

Virus

A

acellular and non-living pathogen, contain a core of genetic material, protein capsid, lipid envelope and attachment proteins

52
Q

Viral replication

A

viral attachment proteins bind to complementary receptor proteins on the cell membrane of host cell, injecting its genetic material into the host cell, reverse transcriptase makes complementary DNA from viral RNA template, DNA inserted into host cells DNA, transcribed into viral mRNA and translated into viral proteins, viral particles assemble are released

53
Q

HIV

A

infects and destroys T helper cells, host immune system becomes so weak, host becomes susceptible to opportunistic infections and thus develops AIDS

54
Q

Antibiotics

A

kill bacteria by interfering with their metabolic reactions, don’t kill viruses as they have no metabolic reactions and are unreachable inside host cells

55
Q

Antigens

A

proteins on the cell-surface membrane that trigger an immune response when detected

56
Q

Antigenic variation

A

pathogenic DNA mutates causing antigens on surface to change shape, specific antibody no longer complementary to antigen, makes it difficult to develop vaccines

57
Q

Phagocytosis

A

first stage of immune response, phagocyte recognises foreign antigens on pathogen and engulfs pathogen into a phagosome, lysosomes fuse with phagosome releasing lysozymes which hydrolyse pathogen, phagocyte presents pathogens antigens on cell-surface membrane

58
Q

T lymphocytes

A

made in bone marrow and mature in thymus gland, involved in the cellular response

59
Q

Cellular response

A

T cell with specific receptor proteins on surface binds to antigen on APCs, activating the T cell (clonal selection), T helper cells activate B cells, cytotoxic T cells destroy infected cells causing cell death

60
Q

B lymphocytes

A

made in bone marrow and mature in bone marrow, involved in the humoural response

61
Q

Humoural response

A

B cell with complementary antibody on surface binds to antigen on APCs, activating the B cell to divide by mitosis into many cloned plasma cells (clonal selection and expansion)

62
Q

Plasma cells

A

secrete many antibodies complementary to a specific antigen (monoclonal antibodies)

63
Q

Antibodies

A

quaternary structure proteins, highly specific variable regions form antigen binding sites only complementary to one specific antigen, two binding sites so cause agglutination of pathogens, all antibodies have the same constant region

64
Q

Active immunity

A

immune system makes its own antibodies after exposure to antigen, long term immunity (memory cells made), slower acting, can be natural through catching a disease or artificial through vaccination

65
Q

Passive immunity

A

given antibodies produced by another organism, short term immunity (no memory cells made), fast acting, can be natural through placenta a disease or artificial through injection

66
Q

Vaccination

A

small amounts of dead or weakened pathogens injected, stimulating the primary immune response

67
Q

Primary immune response

A

first exposure to pathogen, slower response as there are no memory T or B cells

68
Q

Secondary immune response

A

second exposure to pathogen, faster and stronger response as there are memory T and B cells

69
Q

Herd immunity

A

when enough of the population is vaccinated so the pathogen is less likely to come across and so spread easily, provides protection for those who are unvaccinated

70
Q

Monoclonal antibodies

A

identical antibodies produced from a single group of cloned B cells, used in medical treatment and diagnosis

71
Q

Direct ELISA test

A

detects whether patient has specific antigen, immobilised antibodies are attached to well, sample added, complementary antigen binds to antibody forming an AAC, rinse to remove unbound antibodies, second antibody with enzyme attached binds to complementary antigen, substrate added, colour change if positive

72
Q

Indirect ELISA test

A

detects whether patient has specific antibody, specific antigens are attached to well, sample added, complementary antibody binds to antigen forming an AAC, rinse to remove unbound antibodies, second antibody with enzyme attached binds to complementary antibody, substrate added, colour change if positive

AQA A-LEVEL BIOLOGY (8 decks)

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