Cambridge IGCSE™

COMBINED SCIENCE 0653/43

Paper 4 Theory (Extended) October/November 2024
MARK SCHEME
Maximum Mark: 80

Published

This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the
examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the
details of the discussions that took place at an Examiners’ meeting before marking began, which would have
considered the acceptability of alternative answers.

Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for
Teachers.

Cambridge International will not enter into discussions about these mark schemes.

Cambridge International is publishing the mark schemes for the October/November 2024 series for most
Cambridge IGCSE, Cambridge International A and AS Level components, and some Cambridge O Level
components.

This document consists of 11 printed pages.

© Cambridge University Press & Assessment 2024 [Turn over

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Generic Marking Principles

These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the
specific content of the mark scheme or generic level descriptions for a question. Each question paper and mark scheme will also comply with these
marking principles.

GENERIC MARKING PRINCIPLE 1:

Marks must be awarded in line with:

• the specific content of the mark scheme or the generic level descriptors for the question
• the specific skills defined in the mark scheme or in the generic level descriptors for the question
• the standard of response required by a candidate as exemplified by the standardisation scripts.

GENERIC MARKING PRINCIPLE 2:

Marks awarded are always whole marks (not half marks, or other fractions).

GENERIC MARKING PRINCIPLE 3:

Marks must be awarded positively:

• marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond
the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate
• marks are awarded when candidates clearly demonstrate what they know and can do
• marks are not deducted for errors
• marks are not deducted for omissions
• answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the
question as indicated by the mark scheme. The meaning, however, should be unambiguous.

GENERIC MARKING PRINCIPLE 4:

Rules must be applied consistently, e.g. in situations where candidates have not followed instructions or in the application of generic level
descriptors.

© Cambridge University Press & Assessment 2024 Page 2 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
GENERIC MARKING PRINCIPLE 5:

Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may
be limited according to the quality of the candidate responses seen).

GENERIC MARKING PRINCIPLE 6:

Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or
grade descriptors in mind.

Science-Specific Marking Principles

1 Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks
should not be awarded if the keywords are used incorrectly.

2 The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for
any correct statement that is contradicted within the same question part. Wrong science that is irrelevant to the question should be ignored.

3 Although spellings do not have to be correct, spellings of syllabus terms must allow for clear and unambiguous separation from other
syllabus terms with which they may be confused (e.g. ethane / ethene, glucagon / glycogen, refraction / reflection).

4 The error carried forward (ecf) principle should be applied, where appropriate. If an incorrect answer is subsequently used in a scientifically
correct way, the candidate should be awarded these subsequent marking points. Further guidance will be included in the mark scheme
where necessary and any exceptions to this general principle will be noted.

5 ‘List rule’ guidance

For questions that require n responses (e.g. State two reasons …):

• The response should be read as continuous prose, even when numbered answer spaces are provided.
• Any response marked ignore in the mark scheme should not count towards n.
• Incorrect responses should not be awarded credit but will still count towards n.
• Read the entire response to check for any responses that contradict those that would otherwise be credited. Credit should not be
awarded for any responses that are contradicted within the rest of the response. Where two responses contradict one another, this
should be treated as a single incorrect response.
• Non-contradictory responses after the first n responses may be ignored even if they include incorrect science.

© Cambridge University Press & Assessment 2024 Page 3 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
6 Calculation specific guidance

Correct answers to calculations should be given full credit even if there is no working or incorrect working, unless the question states ‘show
your working’.

For questions in which the number of significant figures required is not stated, credit should be awarded for correct answers when rounded
by the examiner to the number of significant figures given in the mark scheme. This may not apply to measured values.

For answers given in standard form (e.g. a  10n) in which the convention of restricting the value of the coefficient (a) to a value between 1
and 10 is not followed, credit may still be awarded if the answer can be converted to the answer given in the mark scheme.

Unless a separate mark is given for a unit, a missing or incorrect unit will normally mean that the final calculation mark is not awarded.
Exceptions to this general principle will be noted in the mark scheme.

7 Guidance for chemical equations

Multiples / fractions of coefficients used in chemical equations are acceptable unless stated otherwise in the mark scheme.

State symbols given in an equation should be ignored unless asked for in the question or stated otherwise in the mark scheme.

Mark scheme abbreviations

; separates marking points

/ separates alternative responses for the same marking point
ecf error carried forward
AVP alternative valid point
ORA or reverse argument
AW alternative wording
underline actual word given must be used by candidate (grammatical variants accepted)
() the word / phrase in brackets is not required but sets the context

© Cambridge University Press & Assessment 2024 Page 4 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

1(a)(i) grasshopper / rabbit / caterpillar ; 1

1(a)(ii) hawk AND owl ; 1

1(a)(iii) snake AND hawk AND (blue) jay ; 1

1(b) energy is lost at each trophic level ; 3

named example of energy loss, e.g. heat / respiration / excretion / protein synthesis / metabolism / not all organism is eaten ;
not enough energy left (to support trophic level five) ;

Question Answer Marks

2(a)(i) Zn(s) + ...2...HCl (aq) → ZnCl 2 (aq) + ...H2...(g) 2

2 added for balancing ;

H2 as product ;

2(a)(ii) any two from: 2

solid zinc reduces in size / AW ;
fizzing / bubbles (of gas) ;
AVP ;

2(a)(iii) by filtration ; 1

2(a)(iv) heat ; 2
evaporate / remove water ;

2(b) sodium has a +1 charge AND zinc has a +2 charge ; 2

chloride ions have a -1 charge AND idea that charges must balance ;

© Cambridge University Press & Assessment 2024 Page 5 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

3(a) vibrating ; 3
20 ;
gases ;

3(b) (because of its) change in speed / different speeds ; 1

3(c) 2

two columns correct ;

four columns correct ;

evidence of, v = f / 3.0  10 ÷ 1.2  10 ;

3(d) 8 7 2
25 (m) ;

© Cambridge University Press & Assessment 2024 Page 6 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

4(a)(i) (most) enzyme denatured; 3

active site changes shape / substrate no longer fits active site ;
rate of photosynthesis decreases (so fewer bubbles) ;

4(a)(ii) gas exchange takes place through stomata / carbon dioxide enters through stomata / oxygen exits through stomata ; 2
carbon dioxide is needed for photosynthesis / oxygen is produced in photosynthesis ;

4(a)(iii) iodine (solution) ; 2

colour changes (from brown) to blue-black ;

4(b) amylase ; 4
(simpler) sugars ;
salivary ;
pancreas ;

Question Answer Marks

5(a) compound ; 2
electricity ;

5(b) 2e– ; 2
H2 ;

5(c) (hydroxide ions) lose electrons / ions are discharged; 2

water (also) formed ;

5(d) acid remains / acid is not used up / only water is electrolysed ; 1

© Cambridge University Press & Assessment 2024 Page 7 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

6(a)(i) 0.40 (m / s) ; 1

6(a)(ii) (calculation of any relevant area) 160 / 1280; 3

(all three relevant areas) 160 + 1280 + 160 / 1600 (m) ;
1.6 (km) ;

6(b)(i) evidence of, W = Fd / 462 000 ÷ 1100 ; 2

420 (m) ;

6(b)(ii) idea that some energy is also transferred to the surroundings ; 2

as, thermal / sound / AVP ;

6(b)(iii) evidence of, P = W ÷ t / 792 000 ÷ 330 ; 3

2400 ;
W / watt(s) ;

© Cambridge University Press & Assessment 2024 Page 8 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

7(a)(i) A pulmonary artery ; 2

B vena cava ;

7(a)(ii) left atrium labelled ; 1

7(a)(iii) reference to contraction ; 2

(muscles of) ventricles (contract) ;

7(b)(i) any two from: 2

diet ;
stress ;
smoking ;
genetic predisposition ;
age ;
AVP ;

7(b)(ii) any two from: 3

both / male / female / number of people increasing AND then decreasing ;
males higher (than females) ORA ;
AVP ;

plus one for:

correct use of supporting data, e.g. both graphs reach peak in 2004 / 10 000 females and 22 000 males in 1978 ;

© Cambridge University Press & Assessment 2024 Page 9 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

8(a) 3

four pairs bonding electrons around carbon correct ;

one bonding pair between oxygen and hydrogen (O-H bond) correct ;
four non-bonding electrons on oxygen shell AND no extra electrons (on hydrogen) ;

8(b)(i) ethene, has a double bond / shares 4 electrons OR 1

ethane, has only single bonds / has single bond between carbons / shares 2 electrons ;

8(b)(ii) 2

two correct ;
three correct ;

8(c) alkene C5H10 ; 2

alkane C4H10 ;

8(d) alkene no colour / colourless ; 2

alkane orange ;

© Cambridge University Press & Assessment 2024 Page 10 of 11

0653/43 Cambridge IGCSE – Mark Scheme October/November 2024
PUBLISHED
Question Answer Marks

9(a) fuse ; 1

9(b)(i) (current in headlight branch = 11.0 – 1.0 =) 10.0 (A) ; 1

9(b)(ii) (current in one headlight = ½  10.0) = 5.0 (A) ; 3

evidence of, R = V ÷ I / 12 ÷ 5.0 ;
2.4 () ;

alternative method:
evidence of, R = V ÷ I or 12 ÷ 10.0 or 1.2() ;
(resistance of parallel arrangement) 1.2  2 OR double the calculated resistance ;
2.4 (Ω) ;

9(c) resistance of wire proportional to length / 3 longer gives 3 resistance / 3  3 or 9 ; 3

resistance of wire inversely proportional to cross-sectional area / half cross-sectional area gives 2 resistance / 2  3 or 6 ;
(resistance of rear lamp is 6 resistance of headlamp =) 18 () ;

© Cambridge University Press & Assessment 2024 Page 11 of 11