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AQA A LEVEL COMPUTER SCIENCE PAPER 2 MARK SCHEME 7517

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AQA A LEVEL COMPUTER SCIENCE PAPER 2 MARK SCHEME 7517 The following annotation is used in the mark scheme: ; -means a single mark // -means alternative response / -means an alternative word or sub-phrase A.- means acceptable creditworthy answer R.- means reject answer as not creditworthy NE. - means not enough I.- means ignore DPT. - in some questions a specific error made by a candidate, if repeated, could result in the loss of more than one mark. The DPT label indicates that this mistake should only result in a candidate losing one mark on the first occasion that the error is made. Provided that the answer remains understandable, subsequent marks should be awarded as if the error was not being repeated. Examiners are required to assign each of the candidates’ responses to the most appropriate level according to its overall quality, then allocate a single mark within the level. When deciding upon a mark in a level examiners should bear in mind the relative weightings of the assessment objectives. eg In the following questions, the marks available are as follows: Question 02 (max 3 marks) AO1 (knowledge) – 1 mark AO1 (understanding) – 2 marks Question 05.4 (max 7 marks) AO2 (analyse) – 5 marks AO3 (programming) – 2 marks Question 11.5 (max 6 marks) AO1 (knowledge) – 2 marks AO1 (understanding) – 4 marks Question 14.3 (max 4 marks) AO1 (knowledge) – 2 marks AO1 (understanding) – 2 marks Qu Pt Marking guidance Total marks 01 1 All marks AO2 (apply) Award 3 marks if correct final answer is shown: 16 // 24 If final answer is not given then award 3 marks if correct calculation is shown: ××× If final answer is not correct or overall calculation is not clear then award up to 2 marks for working, one for each of the points listed below: • multiplying 400 by 1000 // 400 000 shown in working; • dividing 3 200 000 or 400 000 or 8000 or 3200 or 400 or 8 by a number; • multiplying 1000 by 800 // 800 000 shown in working; • multiplying by 8 to convert from bytes to bits; • colour depth calculated as 4; • showing 2x as the last stage of the working, where x is the value calculated so far; 3 Qu Pt Marking guidance Total marks 01 2 All marks AO1 (understanding) Bitmap images store the colour of each pixel // vector graphics do not need to store the colour of each pixel; A. data about pixel instead of colour, but R. just storing pixels The image contains 800 000 pixels // images can contain lots of pixels; Vector graphics store information about / properties of the objects that an image is composed of; A. “shapes” for “object” R. “equations” for “object” R. “instructions” for “object” unless clear that instructions are descriptions of objects A. examples of properties/information instead of the actual words, if there are at least two valid examples NE. vector graphics are composed of objects without reference to properties/information It takes only a small amount of memory to store the properties of an object; (Large) images can be composed of relatively few objects // there will be fewer objects than there would be pixels // a single object might be equivalent to many pixels; Max 3 3 Qu Pt Marking guidance Total marks 01 3 All marks AO1 (understanding) Individual objects / components / parts of the image can be manipulated / edited / duplicated / copied independently; NE. images are easy to edit The image / individual objects / components / parts of the image can be enlarged / scaled without loss of quality / without becoming pixelated // vector graphics are resolution independent; A. zoomed in” for enlarged NE. easy to scale If an object / component is deleted, the software knows what is behind it // no “hole” is left in the image; R. faster transmission times (as a direct consequence of fewer bytes, given in question) Max 2 2 Qu Pt Marking guidance Total marks 02 1 mark AO1 (knowledge) and 2 marks AO1 (understanding) What it is (1 mark): Processing is carried out // applications/programs are executed on an application server (A. server); NE. Resources are stored on the server Why selected (Max 2 marks): Clients are cheaper to purchase // clients can have lower hardware specification; NE. cheaper without further explanation Less configuration of clients is necessary // easier to configure/add a new client // easier to replace a client; Simpler installation/updating of software (as only done on server); R. if implication that software is on client Impossible to install unauthorised software on workstations // more secure as fewer settings can be changed; Workstations consume less electricity/power; Licensing can be cheaper (as licence per active user not per client); Longer MTBF for workstations // workstations do not fail/break as often // workstations need less maintenance

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AQA A LEVEL
COMPUTER
SCIENCE
A-level
COMPUTER
SCIENCE 7517/2
Paper 2

Mark scheme
June 2021
Version: Final 1.1




*216A7517/2/MS*

,Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant
questions, by a panel of subject teachers. This mark scheme includes any amendments made at the
standardisation events which all associates participate in and is the scheme which was used by them in
this examination. The standardisation process ensures that the mark scheme covers the students’
responses to questions and that every associate understands and applies it in the same correct way.
As preparation for standardisation each associate analyses a number of students’ scripts. Alternative
answers not already covered by the mark scheme are discussed and legislated for. If, after the
standardisation process, associates encounter unusual answers which have not been raised they are
required to refer these to the Lead Examiner.

It must be stressed that a mark scheme is a working document, in many cases further developed and
expanded on the basis of students’ reactions to a particular paper. Assumptions about future mark
schemes on the basis of one year’s document should be avoided; whilst the guiding principles of
assessment remain constant, details will change, depending on the content of a particular examination
paper.


Further copies of this mark scheme are available from aqa.org.uk

, Level of response marking instructions
Level of response mark schemes are broken down into levels, each of which has a descriptor. The
descriptor for the level shows the average performance for the level. There are marks in each level.

Before you apply the mark scheme to a student’s answer read through the answer and annotate it (as
instructed) to show the qualities that are being looked for. You can then apply the mark scheme.

Step 1 Determine a level
Start at the lowest level of the mark scheme and use it as a ladder to see whether the answer meets the
descriptor for that level. The descriptor for the level indicates the different qualities that might be seen in
the student’s answer for that level. If it meets the lowest level then go to the next one and decide if it
meets this level, and so on, until you have a match between the level descriptor and the answer. With
practice and familiarity you will find that for better answers you will be able to quickly skip through the
lower levels of the mark scheme.

When assigning a level you should look at the overall quality of the answer and not look to pick holes in
small and specific parts of the answer where the student has not performed quite as well as the rest. If
the answer covers different aspects of different levels of the mark scheme you should use a best fit
approach for defining the level and then use the variability of the response to help decide the mark within
the level, ie if the response is predominantly level 3 with a small amount of level 4 material it would be
placed in level 3 but be awarded a mark near the top of the level because of the level 4 content.

Step 2 Determine a mark
Once you have assigned a level you need to decide on the mark. The descriptors on how to allocate
marks can help with this. The exemplar materials used during standardisation will help. There will be an
answer in the standardising materials which will correspond with each level of the mark scheme. This
answer will have been awarded a mark by the Lead Examiner. You can compare the student’s answer
with the example to determine if it is the same standard, better or worse than the example. You can then
use this to allocate a mark for the answer based on the Lead Examiner’s mark on the example.

You may well need to read back through the answer as you apply the mark scheme to clarify points and
assure yourself that the level and the mark are appropriate.

Indicative content in the mark scheme is provided as a guide for examiners. It is not intended to be
exhaustive and you must credit other valid points. Students do not have to cover all of the points
mentioned in the Indicative content to reach the highest level of the mark scheme.

An answer which contains nothing of relevance to the question must be awarded no marks.

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