Edexcel GCSE Computer Science (1CP2) Exam Questions

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)

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

• The computer looks up the character in the ASCII character set/table (1) to find the code that represents it (1)
• Each character has its own unique ASCII code (1) so the letter A is converted to and stored as a 7-bit binary pattern (1)
• ASCII uses 7 bits for each character (1) so A is stored as its ASCII code 1000001 (binary) / 65 (denary) (1)

The second mark requires a linked expansion, so a point on its own (e.g. 'A has the code 65') can only earn one mark.

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

Accept an 8-bit pattern with a leading 0 (e.g. 01000001) as the binary code for A.

Do not accept 'the character is stored as text' without saying it is changed into a code/binary.

Do not accept a binary value on its own (e.g. 1000001) without saying that it is the ASCII code/that the character is converted to it.

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

• More samples are taken every second / the sample rate is higher (1) so the digital wave follows the shape of the analogue wave more closely (1)
• The amplitude is measured more often / at shorter intervals (1) so fewer changes in the sound are missed between measurements (1)
• The sample interval is shorter (1) so less of the sound wave is lost/goes unrecorded between samples (1)
• More data points are recorded for the same length of sound (1) so the digital representation is a closer copy of the original sound (1)

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

Do not accept 'the quality is better/higher' or 'the sound is clearer' as a point on its own without a reason such as more samples or more detail.

Do not accept 'the samples are more accurate' or 'more data is collected' without saying what becomes more accurate or what the extra data records.

Do not accept 'the file size is larger' as a reason for improved quality.

Do not accept answers about using more bits per sample, as these describe bit depth, not the sample rate.

Indicative content

Number of colours

• 4 bits give 2^4 = 16 different binary values, so at most 16 colours can be stored for each pixel.
• The console cannot store every shade that the designers want; colours outside the 16 must be approximated or left out.
• Adding more bits per pixel would allow more colours, but this may not be possible on the console's hardware.

Effect on appearance

• The sprite may show banding where a smooth change from green to blue should be.
• A sprite that needs many shades, such as a detailed landscape, will look unrealistic or have blocks of colour.
• Simple sprites with flat colours, such as a retro character, can still look acceptable.
• The limitation is in the number of colours, not the number of pixels; resolution is a separate issue.

Managing the limitation

• Designers can choose a palette of 16 colours that includes the most important greens and blues for the game.
• They can design sprites with flat colours rather than smooth gradients.
• They can use more bits per pixel for important sprites if the console allows it.
• They can accept that some shades will be approximated and check that the sprite still looks clear on the console's screen.

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 cover the number of colours and the effect on appearance.

Do not accept 4 bits give 4 colours or 8 colours.