Unit 2

Question 1

Define the terms eukaryotic and
prokaryotic cell. 2

Answer 1

Eukaryotic: DNA is contained in a
nucleus, contains membrane-bound
specialised organelles.

Prokaryotic: DNA is ‘free’ in cytoplasm,
no organelles e.g. bacteria & archaea

Question 2

State the relationship between a system and specialised cells.

Answer 2

Specialised cells → tissues that perform
specific function → organs made of
several tissue types → organ systems

Question 3

State an equation to calculate the actual size of a structure from microscopy

Answer 3

actual size

image size
/
magnification

Question 4

Define magnification and resolution 2

Answer 4

Magnification: factor by which the
image is larger than the actual specimen.

Resolution: smallest separation
distance at which 2 separate structures
can be distinguished from one another

Question 5

what is the structure 1 and function2 of a cell surface membrane

plus tails strucutre

Answer 5

f: control which substances enter and leave the cell
- involved in rapid signaling ad cell recognition
-partially permeable

s:phospholipid bilayer with intrinsic proteins embedded

hydrophilic phosphate head facing outside, hydrophobic fatty acid tails inside

Question 6

Explain the role of cholesterol,glycoproteins & glycolipids in the cellsurface membrane.
3

Answer 6

Cholesterol: steroid molecule connects phospholipids & reduces fluidity.

Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together.

Glycolipids: cell signalling & cell recognition

Question 7

Describe the structure of the nucleus. 4

Answer 7

● nuclear envelope, a
semi-permeable double membrane (control in and out)

● Nuclear pores mRNA/ ribosomes to
enter/exit.

● nucleolus made of RNA & proteins
assembles ribosomes.

*nucleoplasm

chromatin : squiggle of DNA = chromosomes made wound around proteins called histones

Question 8

Describe the function of the nucleus 2-3

Answer 8

*site of DNA replication and transcription

*contains genetic code for each cell

● Controls cellular processes: gene
expression determines specialization & site
of mRNA transcription, mitosis,
semiconservative replication.

Question 9

Describe the structure of a mitochondrion
2

function site of aerobic respiration in
eukaryotic cells
site of ATP production
(dna code for enzymes needed in respiration)

Answer 9

● Surrounded by double membrane folded
inner membrane forms folds cristae (increase sarea)

● Fluid matrix: contains mitochondrial DNA,
respiratory enzymes, lipids, proteins

Question 10

Describe the structure of a chloroplast.2

Chloroplasts: site of photosynthesis
to convert solar energy to chemical
energy.

Answer 10

s:double membrane
Thylakoids: stack to form grana; contain photosystems with chlorophyll

Stroma: fluid-filled matrix

Question 11

Describe the structure and function of the Golgi apparatus 2

Answer 11

f= make lysosomes, modifies proteins by adding carbohydrates (glycoproteins), make lipids

molecules are processes in cisternae

s=Flattened sacs of membrane with vessicles circles

Question 12

describe the structure and function of the golgi vessicle

Answer 12

s= fluid filled sac in cytoplasm
produced in the golgi apparatus

f= stores lipids and proteins made by the golgi apparatus and transports them out of the cell

Question 13

Describe the structure and function of a
lysosome.

Answer 13

-vessicle containing hydrolytic enzyme (enzymes which hydrolyase enzymes)

-hydrolayse bacteria, viruses, damage cells

Question 14

Describe the structure and function of a ribosome 2

Answer 14

formed by protein and rRNA
-free in cytoplasm or attached to (R)ER
site of protein synthesis via translation

Question 15

Describe the structure and function of the
endoplasmic reticulum (ER).
2

Answer 15

Cisternae: folded cell membrane through cytoplasm &
connects to nuclear envelope:

Rough ER: many ribosomes attached for protein synthesis & transport.
● Smooth ER: lipid synthesi

Question 16

State the srtucture and functions of the cell wall 4 bacteria and plants

Answer 16

-structural strength and support

● Bacteria:
Made of the polysaccharide murein.

● Plants:
Made of cellulose microfibrils= high tensile strength
-lots of hydrogen bonds between straight chains

Question 17

Describe the structure and function of the cell
vacuole in plants.
2

Answer 17

Surrounded by single membrane: tonoplast
contains cell sap

Controls turgor pressure.
● Absorbs and hydrolyses potentially harmful
substances to detoxify cytoplasm.

Question 18

Explain some common cell adaptations. 3

Answer 18

● Folded membrane or microvilli increase
surface area e.g. for diffusion.
● Many mitochondria = large amounts of ATP for
active transport.
● Walls one cell thick to reduce distance of
diffusion pathway.

Question 19

State the role of plasmids in prokaryotes.2

Answer 19

● Small ring of DNA that carries non-essential genes.
● genes that aid in survival of bacteria ( has enzymes that break down antibodies>

Question 20

State the role of flagella in prokaryotes 2

Answer 20

-aids movement of bacteria (RiGID COHESION SHAPE+ROTATING BASE)
-helps cell spin through fluids

Question 21

State the role of the capsule in prokaryotes 2

Answer 21

polysaccharide layer
-extra protective layer]helps groups of bacteria stick together

Question 22

Compare eukaryotic and prokaryotic cells
3

Answer 22

both have:
● Cell membrane.
● Cytoplasm.
● Ribosomes (don’t count as an
organelle since not membrane-bound).

Question 23

Contrast eukaryotic and prokaryotic cells 3-4 compare

Answer 23

Prokaryotic
-small cells, unicellular
-no membrane-bound organelles & no nucleus
-circular DNA not associated with proteins
-small ribosomes (70S)
-binary fission - always asexual reproduction
-capsule, sometimes plasmids & cytoskeleton
-murein cell walls

Eukaryotic
- larger cells,often multicellular
- always have organelles & nucleus
-linear chromosomes associated with histones
-larger ribosomes (80S)
-mitosis & meiosis - sexual and/or asexual
-cellulose cell wall (plants)/ chitin (fungi)
-no capsule, no plasmids, always cytoskeleton

Question 24

describe the strucutre of viruses 2-4

invade ad replicate in other host cells

Answer 24

-Acellular
-nucleic acids surrounded by protein coat (capsid)

-no cell membrane, ribosomes, plasmid, flagella, cell wall

Question 25

Describe the structure of a viral particle 2

Answer 25

● Linear genetic material (DNA or RNA) & viral enzymes e.g. reverse transcriptase. ● Surrounded by capsid (protein coat made of capsomeres).

Question 26

describe viral replication 4

Answer 26

-attachment proteins on its surface bind to complementary receptor proteins on the surface of a host cell -genetic material is released into host cell -gentic material and protein are replicated by host cell ribosomes to synthesize viral proteins/ nucleic acid Replicated viruses burst from host cell

Question 27

structure of HIv 5

Answer 27

-two RNA strands -capsid (protein coat) -attachment proteins on surface -reverse transcriptase (viral enzymes surrounded by capsid) -viral envelope (lipid bilyaer and glycoproteins)

Question 28

State the role of the capsid on viral particles 2

Answer 28

● Protect nucleic acid from degradation ● Surface sites enable viral particle to bind to & enter host cells or inject their genetic material

Question 29

State the role of attachment proteins on viral particles

Answer 29

-Enable viral particle to bind to complementary sites on host cell : entry via endosymbiosis.

Question 30

Outline how a student could prepare a temporary mount of tissue for an optical microscope 4

Answer 30

1. Obtain thin section of tissue 2. Place plant tissue in a drop of water. 3. Stain tissue iodine on a slide to make structures visible. 4. Add coverslip using mounted needle at 45° to avoid trapping air bubbles

Question 31

Suggest the 3advantages and 2limitations of using an optical microscope

Answer 31

+ colour image + can show living structures + affordable apparatus - 2D image - lower resolution than electron microscopes = cannot see ultrastructures

Question 32

Suggest the 2 advantages and 2limitations of using a TEM -electrons pass through specimen -detected as more dense structures= darker =absorb more electrons -Focus image onto fluorescent screen or photographic plate using magnetic lenses.

Answer 32

+ electrons have shorter wavelength than light = high resolution,(small) ultrastructure visible + high magnification (x 500000) - 2D image - requires a vacuum = dead structures - extensive preparation may introduce artefacts - no colour image

Question 33

Suggest the 2 advantages and 2 limitations of using an SEM. -electrons focused by magnets -reflected electrons hit collecting device and produce a image

Answer 33

+ 3D image + electrons have shorter wavelength than light = high resolution - requires a vacuum = cannot show living structures - no colour image - only shows outer surface

Question 34

Outline what happens during cell fractionation and ultracentrifugation. 1-3a-c

Answer 34

1. homogenize tissue to break open cells & release organelles. 2. Filter homogenate to remove debris. 3. Perform differential centrifugation: a) Spin homogenate in centrifuge. b) The most dense organelles in the mixture form a pellet. c) Filter off the supernatant and spin again at a higher speed

Question 35

Explain why fractionated cells are kept in a ice cold, buffered, isotonic solution. 3

Answer 35

ice cold: slow the action of enzymes so they don't digest organelles buffered: maintain constant pH. (protein/enzymes not damaged in 3* isotonic: so they all have the same water potential and prevent osmosis of organelles

Question 36

State what the cell cycle is and outline its stages

Answer 36

cycle of division with intermediate growth periods 1. interphase 2. mitosis or meiosis (nuclear division) 3. cytokinesis (cytoplasmic division)

Question 37

Outline what happens during interphase. G0= dormancy period 3

Answer 37

G1: making new organelles (ATP) -cell synthesises proteins for replication e.g. tubulin for spindle fibres & cell size doubles S: DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere G2: organelles divide

Question 38

State the purpose of mitosis. 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Answer 38

produces 2 genetically identical daughter cells for: ● Growth ● Cell replacement/ tissue repair ● Asexual reproduction

Question 39

what happens at prophase 2

Answer 39

1. Chromosomes condense, becoming visible. 2. Centrioles move to opposite poles of cell (animal cells) & mitotic spindle fibres form. 3. Nuclear envelope & nucleolus break down = chromosomes free in cytoplasm

Question 40

Outline what happens during metaphase 2

Answer 40

-chromatids line up at cell equator -spindle fibres attach to centromeres and pull to the end poles

Question 41

Outline what happens during anaphase 3 requires energy from ATP hydrolysis

Answer 41

1. Spindle fibres contract (shorten) -centromeres divide. - chromatids separate and pulled to opposite poles of cell (looks like ‘V’ shapes facing each other). 3. Spindle fibres break down.

Question 41

Outline what happens during telophase 2

Answer 41

1. Chromosomes decondense, becoming invisible again. 2. New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome

Question 42

difference in benign and malignant tumours

Answer 42

benign -less likely to be life threatening -grow more slowly -more compact malignant -more likely to be life threatening grow more rapidly less compact

Question 43

Suggest how cancer treatments control the rate of cell division. -Dna replication distrupt spindle formation

Answer 43

Disrupt the cell cycle: ● prevent DNA replication -by inibiting DNA helicase / polymerase -in s phase of interphase -prevent the synthesis of enzymes needed for DNA replication -disrupts cell cycle= forcing cell to kill itself ● disrupt spindle formation = inhibit metaphase / anaphase NB: can also damage healthy cells

Question 44

how does binary fission happen in prokaryotic cells 3-4

Answer 44

-Circular DNA replicates once and plasmids replicate in any amount in the cytoplasm -Cell elongates and cytoplasm splits by cytokinesis *produces two daughter cells = single copy circular DNA molecule and a variable number of plasmids

Question 45

Why is it so difficult to develop effective treatments against viruses?

Answer 45

Replicate inside living cells = difficult to kill them without killing host cells.

Question 46

Describe the fluid mosaic model of membranes. 2

Answer 46

Fluid: phospholipid bilayer in which individual phospholipids can move =membrane has flexible shape. Mosaic: extrinsic & intrinsic proteins of different sizes and shapes are embedded.

Question 47

Explain the functions of extrinsic and intrinsic proteins in membranes. 2 for each ?

Answer 47

extrinsic: ● binding sites/ receptors e.g. for hormones ● antigens (glycoproteins) ● bind cells together ● involved in cell signalling intrinsic: ● electron carriers (respiration/photosynthesis) ● channel proteins (facilitated diffusion) ● carrier proteins (facilitated diffusion/ active transport)

Question 48

what is mitotic index

Answer 48

mitotic index = number of cells with visible chromosomes ÷ total number of cells

Question 49

(extra info ) Explain the functions of membranes within cells

Answer 49

● Provide internal transport system. ● Selectively permeable to regulate passage of molecules into / out of organelles. ● Provide reaction surface. ● Isolate organelles from cytoplasm for specific metabolic reactions

Question 50

Explain the functions of the cell-surface mebrane 3

Answer 50

● Isolates cytoplasm from extracellular environment. ● Selectively permeable to regulate transport of substances. ● Involved in cell signalling/cell recognition.

Question 51

Name and explain 3 factors that affect membrane permeability.

Answer 51

● Temperature: -high temperature denatures membrane (carrier/channel) proteins / phospholipid molecules - have more kinetic energy & move further apart / can change shape ● pH: changes tertiary structure of membrane proteins. ● Use of a solvent: may dissolve membrane.

Question 52

Define osmosis

Answer 52

net movement of water across a partially permeable membrane from an area of higher water potential to a area of lower water potential -(untik dynamic equilibrium is reached

Question 53

What is water potential (ψ)? 3

Answer 53

● pressure created by water molecules measured in kPa ● Ψ of pure water at 25℃ & 100 kPa: 0 ● more solute = ψ more negative

Question 54

How does osmosis affect plant and animal cells?

Answer 54

● osmosis INTO cell: plant: protoplast swells = cell turgid animal: lysis (hypotonic) ● osmosis OUT of cell: plant: protoplast shrinks = cell flaccid animal: crenation (hypotonic)

Question 55

Suggest how a student could produce a desired concentration of solution from a stock solution

Answer 55

● volume of stock solution = required concentration x final volume needed / concentration of stock solution. ● volume of distilled water = final volume needed -volume of stock solution.

Question 56

Define simple diffusion 2

Answer 56

-net movement of small/non polar molecules down a concentration gradient (high to low) -passive

Question 57

define facilitated diffusion

Answer 57

-diffusion large/ polar lolecules/ ions via carrier/ channel proteins down a concetration gradient (has complementary binding sites) -passive

Question 58

Explain how channel and carrier proteins work 2

Answer 58

Channel: hydrophilic channels bind to specific ions = one side of the protein closes & the other opens Carrier: binds to complementary molecule = conformational change releases molecule on other side of membrane; ( in active transport, requires energy from ATP hydrolysis)

Question 59

Name 5 factors that affect the rate of diffusion.

Answer 59

● Temperature= more KE ● Diffusion distance ● Surface area= more channel/carrier, lipid soluble ● Size of molecule ● Difference in concentration (how steep the concentration gradient is)

Question 60

State Fick’s law.rate of diffusion proprtional to

Answer 60

surface area x difference in concentration / diffusion distance

Question 61

How are cells adapted to maximise the rate of transport across their membranes? 2

Answer 61

● many carrier/ channel proteins ● folded membrane increases surface area

Question 62

Explain the difference between the shape of a graph of concentration (x-axis) against rate (y-axis) for simple vs facilitated diffusion. 2

Answer 62

Simple diffusion: straight diagonal line; rate of diffusion increases proportionally as concentration increases. Facilitated diffusion: straight diagonal line later levels off when all channel/ carrier proteins are saturated

Question 63

Define active transport. 2

Answer 63

against a concentration gradient via carrier proteins using ATP ATP hydrolysed and attached tocarrier protein= protein changes shape Specific carrier protein transports molecules/ ions from area of low concentration to area of higher concentration (i.e. against concentration gradient).

Question 64

Compare and contrast active transport and facilitated diffusion 3

Answer 64

● Both may involve carrier proteins. ● Active transport requires energy from ATP hydrolysis; facilitated diffusion is a passive process. ● Facilitated diffusion may also involve channel proteins.

Question 65

Define co-transport.

Answer 65

co-transport of 2 different substances using a carrier protein Substances bind to complementary intrinsic protein: symport: transports substances in same direction antiport: transports substances in opposite direction e.g. sodium-potassium pump.

Question 66

Explain how co-transport is involved in the absorption of glucose / amino acids in the small intestine. 5

Answer 66

1.Na+ions leave epithelial cell and enter blood;. 2. (Transport out is by) active transport / pump / via carrier protein using ATP. 3. So, Na+conc. in cell is lower than in lumen (of gut) 4.Sodium/Na+ions enter by facilitateddiffusion 5.Glucose absorbed with Na+ions against their concentration

Question 67

what is a pathogen 2

Answer 67

Organisms that cause disease -they have antigens on their surface -bacteria -fungi -viruses

Question 68

What is a antigen

Answer 68

(foreign) -cell surface molecule/(glyco)protein/(glyco)lipid/ polysaccharide. -which stimulates a immune response

Question 69

Explain how phagocytosis destroys pathogens? (non-specific response, carried out by macrophages)

Answer 69

1. Phagocyte recognises foreign antigen 2.Phagocyte moves round and engulfs pathogen by endocytosis to form phagosome 3.Phagosome fuses with lysosome and is enclosed in vacoule (phagolysosome) 4. Lysoszymes digest pathogen (hydrolysed) 5. Presents antigen on surface = antigen presenting cell (APC)

Question 70

explain the role of antigen-presenting cells (APC) in the cellular response

Answer 70

-Macrophage displays antigen from the pathogen on its surface (after hydrolysis in phagocytosis). Enhances recognition by THelper cells, which cannot directly interface with pathogens/ antigens in body fluid.

Question 71

Give 2 differences between specific and nonspecific immune responses (2for each)

Answer 71

-nonspecific (inflammation, phagocytosis) = same for all pathogens -specific (B & T lymphocytes) = complementary pathogen -nonspecific = immediate -specific = time lag

Question 72

Name 2 types of specific immune response 2

Answer 72

-Cell-mediated immunity= T lymphocytes (responds to foreign material inside body cell= responds to own cells altered by (cancer, viruses, organ transplanted) Humoral immunity= B lymphocytes (responds to foreign material outside body cells)= responds to bacteria and viruses by producing antibodies

Question 73

explain cell mediated response (t cells) 3

Answer 73

-Complementary T h cells bind to foreign antigen on APC (after phagocytosis has happened) -T h cells produce a clone of daughter cells that release cytokines -clonal selection of complementary T h cells (rapid mitosis) become *memory T cells *Cytotoxic T cells *T helper cells= secrete cytokines that stimulate B cells to divide and form.... -

Question 74

explain the role of t helper cells 2

Answer 74

-secrete cytokines that stimulate B cells to divide by rapid mitosis and clonal selection and differentiate to *plasma cells *memory B cells

Question 75

Outline the process of the humoral response B cells 3

Answer 75

-Complementary T H cells bind to foreign antigens on antigen-presenting T cells -Release cytokines that stimulate clonal selection and rapid mitosis of complementary B cells -B cells differentiate into plasma cells and memory cells -plasma cells secret antibodies with complementary variable region to antigen

Question 76

define antibody 2 describe levels of protein strucutre structure

Answer 76

-protein specific to antigen, produced by B cells -s=Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen. -The rest of the molecule is known as the constant region 1* proteins with chains of amino acids 3*Unique 3D shape with further folding and H, ionic bonds,Disulfide bridge in hinge region 4* 4 polypeptide chains

Question 77

How do antibodies lead to the destruction of a pathogen? 2

Answer 77

-Formation of antigen-antibody complex -results in agglutination, which enhances phagocytosis.

Question 78

What are monoclonal antibodies?

Answer 78

Antibodies produced from a single clone of B cells

Question 78

What are memory cells?

Answer 78

● Specialised TH/ B cells produced from primary immune response. ● Remain in low levels in the blood. ● Can divide very rapidly by mitosis if organism encounters the same pathogen again.

Question 79

Contrast the primary and secondary immune response 3

Answer 79

secondary response: ● Faster rate of antibody production. ● Shorter time lag between exposure & antibody production. ● Higher concentration of antibodies. ● Antibody level remains higher after the secondary response. ● Pathogen usually destroyed before any symptoms.

Question 80

What causes antigen variability? 4

Answer 80

1. Random genetic mutation changes DNA base sequence. 2. Results in different sequence of codons on mRNA ( 3. Different primary structures of antigen = H-bonds,ionic bonds & disulfide bridges form in different places in tertiary structure. 4. Different shape of antigen.

Question 81

Explain how antigen variability affects the incidence of disease 2

Answer 81

● Memory cells no longer complementary to antigen = individual not immune = can catch the disease more than once. ● Many varieties of a pathogen = difficult to develop vaccine containing all antigen types

Question 82

Compare 2 and contrast passive 4 and active 4 immunity. Give examples of both types. passive natural: antibodies in breast milk/ across placenta passive artificial: anti-venom, needle stick injections active natural: humoral response to infection active artificial: vaccination

Answer 82

● both involve antibodies ● can both be natural or artificial active= exposure to antigen, take while for protection to develop, memory cells produced -long term protection as antibodies produced complementary to antigen pass= doesn't require exposure to antigen, protection immediate, memory cells not produced -short term protection as antibodies broken down

Question 83

Explain the principles of vaccination 4

Answer 83

1. Vaccine contains dead/ inactive form of a pathogen or antigen. 2. Triggers primary immune response (B plasma cells). 3. Memory cells are produced and remain in the bloodstream, so secondary response is rapid & produces higher concentration of antibodies. 4. Pathogen is destroyed before it causes symptoms.

Question 84

What is herd immunity?

Answer 84

Vaccinating large proportion of population reduces available carriers of the pathogen. Protects individuals who have not been vaccinated e.g. those with a weak immune system.

Question 85

Suggest some ethical issues surrounding the use of vaccines 4

Answer 85

● production may involve use of animals= animal tested ● potentially dangerous side-effects ● clinical tests may be fatal ● compulsory vs opt-out ( may not be able to get vaccine)

Question 86

Suggest the clinical applications of monoclonal antibodies 3

Answer 86

● Pregnancy tests by detecting HCG hormones in urine. ● Diagnostic procedures e.g. ELISA test ● Targeted treatment by attaching drug to antibody so that it only binds to cells with abnormal antigen e.g. cancer cells due to specificity of tertiary structure of binding site.

Question 87

Explain the principle of the a direct ELISA test 5

Answer 87

detects presence of a specific antigen 1. Monoclonal antibodies bind to bottom of test plate. 2. Antigen molecules in sample bind to antibody. Rinse excess. 3. Mobile antibody with ‘reporter enzyme’ attached binds to antigens that are ‘fixed’ on the monoclonal antibodies. Rinse excess. 4. Add substrate for reporter enzyme. Positive result: colour change.

Question 88

Explain the principle of an indirect ELISA test 5

Answer 88

detects presence of an antibody against a specific antigen 1. Antigens bind to bottom of test plate. 2. Antibodies in sample bind to antigen. Wash away excess. 3. Secondary antibody with ‘reporter enzyme’ attached binds to primary antibodies from the sample. 4. Add substrate for reporter enzyme. Positive result: colour change.

Question 89

Suggest some ethical issues surrounding the use of monoclonal antibodies.

Answer 89

● Production involves animals. (Animals are often used to produce cells from which monoclonal antibodies are produced) ● Drug trials against arthritis & leukaemia resulted in multiple organ failure.

Question 90

How does HIV result in the symptoms of AIDS?

Answer 90

1. Attachment proteins bind to complementary CD4 receptor on TH cells. 2. HIV particles replicate inside TH cells, killing or damaging them. 3. AIDS develops when there are too few TH cells for the immune system to function. 4. Individuals cannot destroy other pathogens & suffer from secondary diseases/ infections.

Question 91

Why are antibiotics ineffective against viruses? 2 antibiotics destroy murein cell wall (bacteria), viruses have no cell wall

Answer 91

Antibiotics often work by damaging murein cell walls to cause osmotic lysis. Viruses have no cell wall. Viruses replicate inside host cells = difficult to destroy them without damaging normal body cells.

Question 92

two ways pathogens cause disease 2

Answer 92

release toxins kill cells

Question 93

two ways pathogens cause disease 2

Answer 93

release toxins kill cells