Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• The number of bits used to store/represent each pixel (1) which determines how many colours/shades it can have (1)
• The number of binary values/combinations available for each pixel (1) so a greater colour depth gives a wider range of colours/a larger colour palette (1)
• More bits are stored for each pixel (1) so each pixel can be one of more possible colours/shades (1)

Do not award 'the number of colours' alone, as it does not say that colour depth is the number of bits per pixel.

Do not accept responses about image resolution or the number of pixels.

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

Pixels

• A bitmap image is made up of picture elements, called pixels.
• Each pixel is the smallest identifiable area of the image and has a single colour.
• The logo is stored as a grid of pixels, and its width and height in pixels give its dimensions.
• Each pixel is stored separately, so a larger grid needs more pixel values to be stored.

Binary values

• Each pixel's colour is represented by a binary value.
• The number of bits used for each pixel is the colour depth.
• With n bits per pixel there are 2^n different binary values, so 2^n possible colours.
• A black-and-white image can use one bit per pixel, with 0 for white and 1 for black.
• More bits per pixel allow more colours to be represented in the logo.

Grid

• The binary values are stored in order, row by row, so the computer can rebuild the grid.
• The resolution is the number of pixels in the image, for example width × height.
• A higher-resolution grid stores more pixels, so the logo can show more detail.
• The image file stores the pixel values and data such as the image dimensions.

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 both pixels and binary values.

Do not accept resolution as the number of colours.