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Edexcel GCSE Computer Science (1CP2) Exam Questions

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2 questions · 8 marks

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1Explain2 marksImages Swap Remove

An image uses a colour depth of 2 bits per pixel. The original image contains 12 different colours.

Explain why the image cannot be represented accurately at this colour depth.

[2 marks]
Mark scheme

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

  • Only 4 colours can be represented (1) because 2 bits give 2^2 = 4 possible values (1)
  • Some of the 12 colours cannot be stored (1) so they are lost/replaced with a colour that can be represented (1)
  • The image will not match the original exactly (1) because there are fewer colour codes than the number of colours needed (1)
  • Many colours will share the same binary value (1) so the image will lose colour detail (1)

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

Allow 'four colours' or '2^2'.

Do not accept 'only two colours' (confusing the number of bits with the number of values) or 'resolution is too low'.

Example answers and how they were marked
Full marks2/2

Only four colours can be represented (1) because two bits give four possible binary values (1).

Why: Linked point (1) and reason (1): 2 bits give 2^2 = 4 colour codes.

Some marks1/2

Only four colours can be represented.

Why: One mark for identifying that four colours can be represented; the linked reason about two bits giving four values is missing.

No marks0/2

Only two colours can be represented because each pixel has two bits.

Why: A common misconception: two bits give four possible values, not two, so no creditworthy point is given.

2Discuss6 marksImages Swap Remove

A school is creating a small logo to display on its website. The logo is stored as a bitmap image. Each pixel in the logo is stored as a binary value.

Discuss how the bitmap image of the logo is represented in binary.

Your answer should include:

  • pixels
  • binary values
  • the grid of pixels.
[6 marks]
Mark scheme

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.

Example answers and how they were marked
Full marks6/6

A bitmap is a grid of pixels. Each pixel is one small area of the logo and has a single colour. The width and height of the grid are measured in pixels, so the logo's dimensions tell us how many pixels it contains. Each pixel's colour is stored as a binary value. The number of bits used for each pixel is the colour depth, and with n bits there are 2^n possible values, so 2^n possible colours. For example, 3 bits per pixel would allow 8 colours. The binary values are stored row by row so that the computer can rebuild the grid. A larger grid stores more pixel values, but it can show more detail. More bits per pixel let the logo use more colours, such as the school's colours.

Why: Covers pixels as the smallest areas of a grid (AO1), binary values with colour depth and 2^n colours (AO1), and applies these to the logo's grid and colours (AO2). Sustained and structured, so Level 3.

Some marks4/6

A bitmap is a grid of pixels. Each pixel is a small square with one colour. Each pixel is stored as a binary value. The logo needs a binary value for every pixel, so a bigger logo has more values. More bits per pixel means more colours.

Why: Gives pixels and binary values, with a simple link to the logo's size. Points are mostly independent and not developed into a full discussion, so Level 2.

Some marks1/6

A bitmap image is a grid of pixels. Resolution is the number of colours in the image. Each pixel is stored as a letter, so the logo can use any colour.

Why: One basic point: a bitmap is a grid of pixels. The rest is incorrect: resolution is not the number of colours, and pixel values are stored as binary, not letters.

Questions by topic

2.1 Binary

Build a paper on this topic 58
Adding Binary Numbers 6 questions Binary and Hexadecimal Basics 10 questions Binary Shifts 6 questions Binary to Denary Conversion 6 questions Binary to Hexadecimal Conversion 6 questions Denary to Binary Conversion 6 questions Denary to Hexadecimal Conversion 6 questions Denary to Negative Binary Conversion 6 questions Hexadecimal to Binary Conversion 6 questions

2.2 Data representation

Build a paper on this topic 56
Character Sets 18 questions Images 19 questions Sound 19 questions

2.3 Data storage and compression

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Compression 18 questions Units & Conversion 6 questions

3.1 Hardware

Build a paper on this topic 77
Embedded Systems 17 questions Fetch Decode Execute Cycle 15 questions Primary Memory 15 questions Secondary Memory 15 questions Stored Program Computers 15 questions

3.2 Software

Build a paper on this topic 124
File Management 18 questions Memory Management 16 questions Peripheral Management 11 questions Process Management 12 questions Purpose & Function of Operating Systems 17 questions Software Basics 13 questions User Management 18 questions Utility Software 19 questions

3.3 Programming languages

Build a paper on this topic 37
Low and High Level Languages 19 questions Translators 18 questions

4.1 Networks

Build a paper on this topic 138
Addressing 16 questions LANs & WANs 16 questions Network Speed 5 questions Packet Switching 16 questions Protocols & Layers 17 questions The Internet 16 questions Topologies 17 questions Wired Connections 17 questions Wireless Connections 18 questions

4.2 Network security

Network Security Risks 16 questions

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