Edexcel GCSE Computer Science (1CP2) exam questions

Build a practice paper from 693 exam-style questions, each with its mark scheme and example answers. Print it, or answer it on paper and then open the mark schemes. Or browse the questions by topic.

Practice paper

4 questions · 12 marks

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1Short recall2 marksImages Swap Remove

Bitmap images are stored as a grid of pixels.

Define the term pixel.

[2 marks]

Mark scheme

Award one mark for any of the following up to a maximum of two marks:

The smallest element/area of a bitmap image (1)
The smallest identifiable part of an image (1)
Stores/represents a single colour as a binary value (1)
Stores/represents a single colour using a number of bits/colour depth (1)

Allow 'picture element' for element/part in the first two bullets, but not on its own

Allow 'bit depth' for colour depth

Do not accept 'picture element'/'pixel' on its own

Do not accept 'a group of pixels' or 'a dot' on its own; allow 'dot' only when it is described as the smallest element/area of the image

Do not accept 'single colour' on its own for the second mark; it must be linked to a binary value/number of bits

Do not accept 'lots of coloured dots' (it contradicts a single colour)

Example answers and how they were marked

Full marks2/2

The smallest identifiable area of a bitmap image, which has one colour stored as a binary value.

Why: Smallest identifiable area (1) and single colour stored as a binary value (1)

Some marks1/2

The smallest part of a bitmap image, made of one colour.

Why: Smallest part (1); no credit for the second mark because the single colour is not linked to a binary value or number of bits

No marks0/2

A picture element made from lots of coloured dots.

Why: 'Picture element' on its own is not accepted and 'lots of coloured dots' contradicts a single colour

2Describe2 marksCharacter Sets Swap Remove

A computer uses 7-bit ASCII to store text.

Describe why 7 bits are needed to represent each character, rather than 6 bits.

[2 marks]

Mark scheme

Award up to two marks for a linked description such as:

6 bits give only 64 different codes (1) which is fewer than the number of letters, digits and symbols that must be represented (1)
7 bits give 128 different codes (1) which is enough to represent every letter, digit and symbol that is needed (1)
Adding a bit doubles the number of different codes from 64 to 128 (1) so that every character needed can have its own code (1)
There are more than 64 characters that must be represented (letters, digits and symbols) (1) so 6 bits cannot give each one a different code (1)

A statement of the number of codes without a development can earn one mark only; the development must be linked to the statement for the second mark.

Do not accept responses that only say computers use binary (1s and 0s).

Do not accept that 7 bits are needed because 7 is a bigger number than 6, with no reference to the number of codes or characters.

Do not accept responses about 8 bits, extended ASCII or Unicode.

Example answers and how they were marked

Full marks2/2

6 bits can only give 64 different codes, which is not enough for all the letters, digits and symbols that have to be represented.

Why: Gives the number of codes 6 bits can make (1) linked to the number of characters that must be represented (1).

Some marks1/2

7 bits give 128 different codes.

Why: States the number of codes available from 7 bits (1) but gives no linked development, so the second mark is not earned (0).

No marks0/2

Because computers only use binary and 7 is a bigger number than 6.

Why: Says only that computers use binary and compares the numbers, which the mark scheme tells markers not to accept; no creditworthy point about codes or characters.

3Explain2 marksCharacter Sets Swap Remove

A computer system uses a 4-bit code to represent the characters typed on its keyboard.

Explain one limitation of using 4 bits to represent characters.

[2 marks]

Mark scheme

Award up to two marks for a linked explanation such as:

Only 16 different characters can be represented (1) so there are not enough characters codes for every letter of the alphabet (1)
4 bits give only 16 different combinations (1) which is not enough for the uppercase letters, lowercase letters, digits and symbols on a keyboard (1)
More than 16 characters are needed on a keyboard (1) so some letters, digits or symbols cannot be represented (1)
The number of character codes available is limited to 16 (1) because 4 bits give 2 to the power of 4 combinations (1)

For both marks, the expansion must follow/associate with the statement.

Calculating that 4 bits give 2 to the power of 4 = 16 combinations can earn either the point or the linked reason, provided the other half of the answer says what this means (too few characters/codes).

Allow an expansion that names only the letters of the alphabet, e.g. there are not enough character codes for the 26 letters (1).

Do not accept '4 bits can only store 4 characters' (the number of bits is not the number of characters).

Do not accept 'it can only store 16 bits' (16 is the number of character codes/combinations, not the number of bits).

Do not accept 'not enough memory/storage' (the limitation is the number of character codes, not the amount of storage).

Do not accept 'it is limited/smaller' without saying how many characters/codes are available or what cannot be represented.

Example answers and how they were marked

Full marks2/2

Only 16 different characters can be represented, so there are not enough character codes for all 26 letters.

Why: Gives the point that only 16 characters can be represented (1) and links it to the reason that this is fewer than the letters needed (1).

Some marks1/2

Only 16 different characters can be represented.

Why: Gives the point that only 16 characters can be represented (1) but does not explain what cannot be represented.

No marks0/2

It can only store 4 characters because there are 4 bits.

Why: Misconception that the number of bits equals the number of characters, which the mark scheme says not to accept; no creditworthy point.

4Discuss6 marksSound Swap Remove

A developer is creating a voice memo app for a phone. The app records speech and saves it as a digital audio file. The developer can choose the bit depth used for each sample.

Discuss how the bit depth affects how the amplitude of the speech is represented in binary and the size of the saved file.

Your answer should include:

how the amplitude of a sample is stored using bits
how the bit depth affects the accuracy of each sample
the effect of the bit depth on the file size.

[6 marks]

Mark scheme

Indicative content

Storing amplitude

Each sample records the amplitude of the sound wave at that moment, and the amplitude is stored as a binary number.
The bit depth is the number of bits used to store each sample, so it sets how many different amplitude values can be represented.
With a bit depth of 8, there are 2^8 = 256 possible values for the height of the wave.
The binary value for each sample tells the computer how loud the speech is at that point.

Accuracy

A higher bit depth gives more possible values, so the recorded amplitude can be closer to the true amplitude of the speech.
With a low bit depth, the amplitude must be rounded to the nearest available value, which adds quantisation error and makes the speech sound rough.
A higher bit depth reduces the difference between the original wave and the digital version.
Quiet parts of the speech may be lost or inaccurately recorded if the bit depth is too low.

File size

A higher bit depth uses more bits for every sample, so the voice memo file is larger.
A lower bit depth reduces the number of bits per sample, so the file is smaller and uses less storage on the phone.
The developer must balance clear speech against storage space and download time.

Levels

Level 0 (0 marks): No rewardable content.
Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Level 3 responses must link the bit depth to both the accuracy of the amplitude and the file size.

Do not accept bit depth defined as the number of samples taken per second.

Example answers and how they were marked

Full marks6/6

Each sample measures the amplitude of the speech wave and stores it as a binary number. The bit depth is the number of bits used for each sample, so with 4 bits there are only 16 possible amplitude values, but with 16 bits there are 65,536. A higher bit depth therefore lets the app record the loudness of the speech more accurately, because each sample can be closer to the real wave and quiet sounds are less likely to be rounded away. This makes the voice memo sound clearer. However, every sample uses more bits, so a higher bit depth creates a larger file, which takes up more storage on the phone and may take longer to send. The developer should choose a bit depth that keeps speech clear without making the files unnecessarily large.

Why: Level 3 (6 marks): explains amplitude stored in binary, how bit depth gives more values and accuracy, and the file-size trade-off, applied to the voice memo app.

Some marks3/6

The bit depth is the number of bits used for each sample. A higher bit depth means the amplitude can be stored more accurately because there are more values. But it makes the file larger. The app should use a high bit depth for clear speech.

Why: Level 2 (3 marks): covers bit depth, accuracy and file size briefly with some linkage, but lacks detailed reasoning.

Some marks1/6

The bit depth is the number of samples taken per second. A higher bit depth means more samples are taken, so the file is smaller and the speech is more accurate.

Why: Level 1 (1 mark): a basic idea that more accuracy is linked to higher bit depth, but bit depth is confused with sample rate and the file-size effect is wrong.

Edexcel GCSE Computer Science (1CP2) Exam Questions

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Questions by topic

2.1 Binary

2.2 Data representation

2.3 Data storage and compression

3.1 Hardware

3.2 Software

3.3 Programming languages

4.1 Networks

4.2 Network security

5.1 Environmental

5.2 Ethical and legal

5.3 Cybersecurity

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