ACTUAL 2025 AQA A-LEVEL COMPUTER SCIENCE Paper
2 Question Paper & Mark Scheme (Merged)
Exam
AQA A-Level Computer Science: Paper 2 Revision Q&A
(1-100)
1. What is the difference between Baud Rate and Bit
Rate?
A: Baud rate is the number of signal changes per second
on a transmission line. Bit rate is the number of bits
transmitted per second. They are only equal if each signal
change represents one bit.
2. Define the term 'Real Number' in computing.
A: Any number that can represent a quantity along a
continuous line, including both rational and irrational
numbers.
3. What is a 'Record' data structure?
A: A data structure that can store multiple values (fields)
of different data types under a single identifier (e.g.,
a Student record with fields for name [String], ID [Integer],
and grade [Char]).
4. How does a Procedure differ from a Function?
A: A procedure performs a task but does not return a
value. A function performs a task and must return a value.
,5. Explain the difference between Definite and
Indefinite Iteration.
A: Definite iteration repeats a set number of times (e.g.,
a FOR loop). Indefinite iteration repeats until a condition
is met, so the number of iterations is unknown beforehand
(e.g., a WHILE loop).
6. What does the 'XOR' (Exclusive OR) logical
operation return as true?
A: It returns TRUE only if exactly one of the two inputs
is TRUE. It is false if both are true or both are false.
7. What is the purpose of Exception Handling (e.g.,
Try-Catch)?
A: To anticipate, detect, and recover from runtime errors
(exceptions) without causing the entire program to crash,
improving robustness.
8. Explain the difference between passing a
parameter ByVal and ByRef.
A: ByVal passes a copy of the variable's value; changes
inside the subroutine do not affect the
original. ByRef passes a reference/memory address;
changes inside the subroutine affect the original variable.
9. What is Recursion?
A: A programming technique where a subroutine
(function/procedure) calls itself as part of its solution,
,typically with a smaller subset of the problem, until a base
case is reached.
10. What is meant by 'Object Instantiation'?
A: The creation of a specific instance of a class using
the new keyword. Memory is allocated for that object's
attributes.
11. Define 'Inheritance' in OOP.
A: A mechanism where a new class (child/subclass) is
created from an existing class (parent/superclass),
inheriting its attributes and methods. The child can then
extend or override them.
12. What is 'Polymorphism'?
A: The ability for objects of different classes to be treated
as objects of a common superclass, and to respond
differently to the same method call (e.g., a draw() method
behaving differently for Circle and Square objects).
13. Describe the 'Queue' abstract data type.
A: A FIFO (First-In, First-Out) data structure. Elements are
added (enqueued) to the rear and removed (dequeued)
from the front.
14. Describe the 'Stack' abstract data type.
A: A LIFO (Last-In, First-Out) data structure. Elements are
added (pushed) and removed (poped) from the same end,
called the top.
, 15. What is a 'Graph' in computer science?
A: A set of vertices (nodes) connected by edges (arcs).
Used to model relationships or networks.
16. What is an advantage of an Adjacency List over an
Adjacency Matrix for representing a graph?
A: An adjacency list is more memory-efficient for sparse
graphs (graphs with few edges compared to nodes), as it
only stores existing connections.
17. What is a 'Binary Tree'?
A: A tree data structure where each node has at most two
children, typically referred to as the left child and right
child.
18. When would you use a Post-Order tree traversal?
A: To delete or free all nodes in a tree safely (processing
children before the parent), or to evaluate postfix
expressions.
19. What is a 'Hash Table'?
A: A data structure that implements an associative array
using a hash function to compute an index (hash) into an
array of slots, from which the desired value can be found.
Used for fast data retrieval.
20. What is a 'Thin Client'?
A: A networked computer that relies heavily on a central
2 Question Paper & Mark Scheme (Merged)
Exam
AQA A-Level Computer Science: Paper 2 Revision Q&A
(1-100)
1. What is the difference between Baud Rate and Bit
Rate?
A: Baud rate is the number of signal changes per second
on a transmission line. Bit rate is the number of bits
transmitted per second. They are only equal if each signal
change represents one bit.
2. Define the term 'Real Number' in computing.
A: Any number that can represent a quantity along a
continuous line, including both rational and irrational
numbers.
3. What is a 'Record' data structure?
A: A data structure that can store multiple values (fields)
of different data types under a single identifier (e.g.,
a Student record with fields for name [String], ID [Integer],
and grade [Char]).
4. How does a Procedure differ from a Function?
A: A procedure performs a task but does not return a
value. A function performs a task and must return a value.
,5. Explain the difference between Definite and
Indefinite Iteration.
A: Definite iteration repeats a set number of times (e.g.,
a FOR loop). Indefinite iteration repeats until a condition
is met, so the number of iterations is unknown beforehand
(e.g., a WHILE loop).
6. What does the 'XOR' (Exclusive OR) logical
operation return as true?
A: It returns TRUE only if exactly one of the two inputs
is TRUE. It is false if both are true or both are false.
7. What is the purpose of Exception Handling (e.g.,
Try-Catch)?
A: To anticipate, detect, and recover from runtime errors
(exceptions) without causing the entire program to crash,
improving robustness.
8. Explain the difference between passing a
parameter ByVal and ByRef.
A: ByVal passes a copy of the variable's value; changes
inside the subroutine do not affect the
original. ByRef passes a reference/memory address;
changes inside the subroutine affect the original variable.
9. What is Recursion?
A: A programming technique where a subroutine
(function/procedure) calls itself as part of its solution,
,typically with a smaller subset of the problem, until a base
case is reached.
10. What is meant by 'Object Instantiation'?
A: The creation of a specific instance of a class using
the new keyword. Memory is allocated for that object's
attributes.
11. Define 'Inheritance' in OOP.
A: A mechanism where a new class (child/subclass) is
created from an existing class (parent/superclass),
inheriting its attributes and methods. The child can then
extend or override them.
12. What is 'Polymorphism'?
A: The ability for objects of different classes to be treated
as objects of a common superclass, and to respond
differently to the same method call (e.g., a draw() method
behaving differently for Circle and Square objects).
13. Describe the 'Queue' abstract data type.
A: A FIFO (First-In, First-Out) data structure. Elements are
added (enqueued) to the rear and removed (dequeued)
from the front.
14. Describe the 'Stack' abstract data type.
A: A LIFO (Last-In, First-Out) data structure. Elements are
added (pushed) and removed (poped) from the same end,
called the top.
, 15. What is a 'Graph' in computer science?
A: A set of vertices (nodes) connected by edges (arcs).
Used to model relationships or networks.
16. What is an advantage of an Adjacency List over an
Adjacency Matrix for representing a graph?
A: An adjacency list is more memory-efficient for sparse
graphs (graphs with few edges compared to nodes), as it
only stores existing connections.
17. What is a 'Binary Tree'?
A: A tree data structure where each node has at most two
children, typically referred to as the left child and right
child.
18. When would you use a Post-Order tree traversal?
A: To delete or free all nodes in a tree safely (processing
children before the parent), or to evaluate postfix
expressions.
19. What is a 'Hash Table'?
A: A data structure that implements an associative array
using a hash function to compute an index (hash) into an
array of slots, from which the desired value can be found.
Used for fast data retrieval.
20. What is a 'Thin Client'?
A: A networked computer that relies heavily on a central
