Biology A2 Revision

Biology A2.

This is specifically for AQA Biology A2, containing special sections for both Unit 4 and Unit 5.

A complete revision guide for Unit 4 and Unit 5, and multiple choice questions for every syllabus unit.


The topics covered in the revision guide and multiple choice question section are detailed here:

Unit 4

3.4.1 The dynamic equilibrium of populations is affected by a number of factors. 
3.4.2 ATP provides the immediate source of energy for biological processes. 
3.4.3 In photosynthesis, energy is transferred to ATP in the light-dependent reaction and the ATP is utilised in the light-independent reaction. 
3.4.4 In respiration, glycolysis takes place in the cytoplasm and the remaining steps in the mitochondria. ATP synthesis is associated with the electron transfer chain in the membranes of mitochondria.
3.4.5 Energy is transferred through ecosystems and the efficiency of transfer can be measured. 
3.4.6 Chemical elements are recycled in ecosystems. Microorganisms play a key role in recycling these elements.
3.4.7 Ecosystems are dynamic systems, usually moving from colonisation to climax communities in the process of succession.
3.4.8 Genetic variation within a species and geographic isolation lead to the accumulation of different genetic information in populations and the potential formation of new species.


Unit 5

3.5.1 Stimuli, both internal and external, are detected and lead to a response. 
3.5.2 Coordination may be chemical or electrical in nature. 
3.5.3 Skeletal muscles are stimulated to contract by nerves and act as effectors. 
3.5.4 Homeostasis is the maintenance of a constant internal environment.
3.5.5 Negative feedback helps maintain an optimal internal state in the context of a dynamic equilibrium. Positive feedback also occurs.
3.5.6 The sequence of bases in DNA determines the structure of proteins, including enzymes.
3.5.7 Gene expression is controlled by a number of features.
3.5.8 Gene cloning technologies allow study and alteration of gene function in order to better understand organism function and to design new industrial and medical processes.