A-Level Biology Year 1 – Cells, Microscopes, Cell Cycle & Immunity: Complete Answers

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AQA, OCR, Edexcel

A Level

A Level Biology
Cells, Microscopes, Cell Cycle
and Immunity Answers

Name:




Total Marks:


Page 1

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M1.

(a)
Protein synthesis L;

Modifies protein H;

Aerobic respiration N;
3

(b) 1800−2200;
1.8, 2.0 or 2.2 in working or answer = 1 mark.
Ignore units in answer.

1 mark for an incorrect answer in which student clearly divides measured length by
actual length (of scale).
Accept I / A or I / O for 1 mark but ignore triangle.
Accept approx 60mm divided by 30μm for 1 mark 2 [5]

M2.(a) Any five from:
1. Cell homogenisation to break open cells;
1. Accept suitable method of breaking open cells.

2. Filter to remove (large) debris / whole cells;
2. Reject removes cell walls.

3. Use isotonic solution to prevent damage to mitochondria / organelles;
3. Ignore to prevent damage to cells.

4. Keep cold to prevent / lreduce ldamage lby lenzymes l/ luse lbuffer lto
lprevent lprotein l/ lenzyme ldenaturation;


5. Centrifuge l(at llower lspeed l/ l1000 lg) lto lseparate lnuclei l/ lcell lfragments l/
lheavy lorganelles; 5. lIgnore lincorrect lnumerical lvalues.


6. Re-spin l(supernatant l/ lafter lnuclei l/ lpellet lremoved) lat lhigher lspeed lto
lget lmitochondria lin lpellet l/ lat lbottom.
6. lMust lhave llocation
Reject lref lto lplant lcell lorganelles lonly lonce 5 lmax

(b) Principles:
1. Electrons lpass lthrough l/ lenter l(thin) lspecimen;
2. Denser lparts labsorb lmore lelectrons;
3. (So) ldenser lparts lappear ldarker;
4. Electrons lhave lshort lwavelength lso lgive lhigh lresolution;
Principles: Allow lmaximum lof l3 lmarks

Limitations:
5. Cannot llook lat lliving lmaterial l/ lMust lbe lin la lvacuum;
6. Specimen lmust lbe l(very) lthin;
7. Artefacts lpresent;
8. Complex lstaining lmethod l/ lcomplex l/ llong lpreparation ltime;
9. Image lnot lin l3D l/ lonly l2D limages lproduced.
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Limitations:Context lof llimitation lmust lbe lclear, lnot lsimply
lexplaining lhow lTEM lworks
E.g l“allows lyou lto lsee lorganelles las la lthin lsection lis lused” lis lnot
la llimitation
Allow lmaximum lof l3 lmarks
Ignore lref lto lcolour 5 lmax [10]

M3.(a) 1. How lto lbreak lopen lcells land lremove ldebris;
2. Solution lis lcold l/ lisotonic l/ lbuffered;
3. Second lpellet lis lchloroplast. 3

(b) 1. A lstroma;
2. B lgranum. Accept lthylakoid 2



(c) μm 1

(d) Two lof lthe lfollowing lfor lone lmark:
Mitochondrion l/ lribosome l/ lendoplasmic lreticulum l/ llysosome l/ lcell-surface
lmembrane. 1 lmax [7]

M4.(a) (i) Anaphase 1

2. 1. Sister l/ lidentical lchromatids l/ lidentical lchromosomes;
Reject: lHomologous lchromosomes lseparate.
Allow lany lreference lto lchromatids l/ lchromosomes lbeing lidentical
e.g. lsame lDNA

2. To l(opposite) lpoles l/ lends l/ lsides; 2

(b) (i) 1. 8.4 l/ lcells lwith ltwice lDNA lcontent l= lreplicated lDNA l/ llate
linterphase l/ lprophase l/ lmetaphase l/ lanaphase;
Any lreference lto linterphase lmust lsuggest ltowards lend lof
linterphase.
'Chromosomes lreplicate' lis lnot lenough lfor lDNA lreplicates.

2. 4.2 l= lDNA lnot lreplicated l/ l(early) linterphase l/ ltelophase l/ lcell
ljust ldivided l/ lfinished lmitosis; 2

(ii) 2.1; 1 l6]

M5. (a) 1. Growth l/ lincrease lin lcell lnumber;
Ignore lgrowth lof lcells

2. Replace lcells l/ lrepair ltissue l/ lorgans l/ lbody;
Ignore lrepair lcells
lReject lbacteria


3. Genetically lidentical lcells;
‘Produces l2 lgenetically lidentical lcells’ ldoes lnot lreach lMP1 las
lwell las lMP3


4. Asexual lreproduction l/ lcloning;
Allow lexample lor ldescription
2 lmax



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