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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 5 marks

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1Multiple choice1 markImages Swap Remove

Identify the term for the number of bits used to store the colour of each pixel.

[1 mark]
  • AColour depth
  • BImage size
  • CResolution
  • DStorage size
Mark scheme
  • A Colour depth (1)
  • The only correct answer is A. The correct answer is colour depth.
  • B is not correct because image size is the width and height of the image in pixels
  • C is not correct because resolution is the number of pixels per unit length, such as pixels per inch
  • D is not correct because storage size is the amount of storage the image file uses
Example answers and how they were marked
Full marks1/1

A Colour depth

Why: Correct option; colour depth is the number of bits used to store the colour of each pixel (1).

No marks0/1

B Image size

Why: Image size is the width and height of the image in pixels, not the number of bits used per pixel; no mark.

No marks0/1

D Storage size

Why: Storage size is the amount of storage the image file uses, not the colour depth; no mark.

2Short recall2 marksCharacter Sets Swap Remove

ASCII is a character set that uses 7 bits to represent each character.

Give two limitations of 7-bit ASCII when it is used to represent text.

[2 marks]
Mark scheme

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

  • (Only) 128 different characters can be represented / 7 bits give 2^7 = 128 different codes (1)
  • It cannot represent characters from languages other than English / non-English alphabets, e.g. Greek, Chinese (1)
  • It cannot represent accented characters, e.g. é, ñ (1)
  • It cannot represent symbols or emoji that are not in the ASCII character set (1)

Award a maximum of one mark for the last three bullets, as they are all examples of characters that fall outside the 128 ASCII codes.

Allow 'it can only represent 128 characters, so some characters are missing' for the first bullet.

Do not accept 'it uses 7 bits' / 'it only uses 7 bits' on its own, without saying what this limits.

Do not accept 'it can only store a limited amount of text' / 'it can only store short messages', as 7 bits limits the number of characters available, not the length of a message.

Do not accept 'it can only represent the characters in the ASCII character set', as this repeats the question.

Do not accept 'it is old/out of date' or 'it cannot store numbers'.

Example answers and how they were marked
Full marks2/2

Only 128 different characters can be represented, so it cannot store characters from other languages such as Greek.

Why: 128 character limit (1) and characters from other languages (1); two separate creditworthy limitations.

Some marks1/2

It cannot show accented characters like é and it only uses 7 bits.

Why: Accented characters (1); 'only uses 7 bits' is not qualified, so scores 0.

No marks0/2

It only uses 7 bits, so it can only store a small amount of text.

Why: Scores 0: text length is not a limitation of 7-bit ASCII, and 'only uses 7 bits' is unqualified; both Do not accept lines apply.

3Describe2 marksImages Swap Remove

A bitmap image of a logo is stored in binary.

Describe how the pixels in the logo are represented in binary, and how the number of bits available for each pixel can limit the image.

[2 marks]
Mark scheme

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

  • Each pixel is a single colour (1) that is stored/given as a binary value (1)
  • Each pixel is represented by a binary value (1) which gives/represents its colour (1)
  • The pixels are stored in order/rows (1) so the binary values can be read back to recreate the image (1)
  • Each pixel uses a fixed number of bits/colour depth (1) so only a limited number of colours can be represented (1)
  • The number of bits available for each pixel is fixed (1) so some colours cannot be stored/shown (1)

Allow '1s and 0s' for binary value.

For the first mark, accept a statement that a pixel is stored/represented by a binary value; do not award the first mark for 'grid of pixels' or 'a pixel is a single colour' alone unless it is linked to a binary value.

Do not accept 'a pixel is a small dot' alone.

Do not accept responses that only describe file size or resolution.

Example answers and how they were marked
Full marks2/2

Each pixel is a single colour and its colour is stored as a binary value. The number of bits for each pixel is fixed, so only a limited number of colours can be represented.

Why: Linked point (1) that each pixel is a single colour and development (1) that its colour is stored as a binary value; the colour-depth limitation is also creditworthy but the answer is capped at 2.

Some marks1/2

Each pixel is stored as a binary value.

Why: Point (1) that each pixel is stored as a binary value, but no linked development about the colour it represents.

No marks0/2

A bitmap image is made of lots of dots called pixels.

Why: No credit: 'a pixel is a small dot' alone is not accepted because it does not link a pixel to a binary value.

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