This document provides an in-depth, complete, and well-written set of notes for the AQA A-level Year Two Biology syllabus. Designed to assist students in their preparation for examinations and enhance their understanding of the subject, these notes cover all key topics, concepts, and principles req...
o Frequency of measurable/observable characteristics
o Base sequence of DNA/mRNA
o Amino acid sequence of proteins encoded by DNA and mRNA
Quantitative investigations of variation within a species involve:
o Collecting data from random samples
o Calculating a mean value of the collected data and standard deviation
o Interpreting mean values and their standard deviations
Energy transfers in and between organisms
Photosynthesis
,6CO2 + 6H2O (+ energy) C6H12O6 + 6O2
Environmental factors can limit the rate of photosynthesis: light intensity, temperature and
carbon dioxide concentration can all be limiting factors
There are two stages that make up photosynthesis:
The light-dependent reaction NB final products in
Occurs in thylakoid membranes of chloroplast green
Non-cyclic photophosphorylation
1. Photo-ionisation of photosystem II (PSII)
Light energy excites electrons
move to higher energy level
released from chlorophyll
move down the electron transport chain to photosystem I (PSI)
2. Photolysis of water: H2O 2H+ + 2e- + ½O2
Replaces electrons lost by photoionisation
3. Chemiosmosis:
Electrons lose energy as they move down electron transport chain
This energy is used to transport H+ ions into thylakoid
Electrochemical gradient across thylakoid membrane
H+ diffuse into stroma via ATP synthase
energy from this used to synthesise ATP: ADP + Pi ATP
4. Photo-ionisation of photosystem I (PSI)
Light energy excites electrons
move to higher energy level
transferred to NADP along with a H+
formation of redNADP
Cyclic photophosphorylation
Electrons from PSI are not passed to NADP
Instead, they are passed back to PSI via electron carriers and are recycled,
repeatedly flowing through PSI
production of a small amount of ATP
The light-independent reaction (aka Calvin Cycle)
Occurs in stroma of chloroplasts
,1. CO2 diffuses into stroma
rubisco catalyses combination of CO2 with ribulose biphosphate (RuBP)
unstable 6C compound formed
forms 2 glycerate 3-phosphate (GP) (3C compound)
2. GP reduced to triose phosphate (TP) (3C compound) NB 6 turns of the Calvin
Uses ATP from LDR Cycle 1 hexose sugar
Uses H+ from redNADP from LDR
3. 5 of 6 TP used to regenerate RuBP
Uses rest of ATP from LDR
4. Remaining TP converted into useful organic compounds
Respiration
Respiration produces ATP, which is the immediate source of energy in cells.
, C6H12O6 + 6O2 6CO2 + 6H2O (+ energy)
It can be done aerobically or anaerobically. Both start with glycolysis:
Oxidation
1. Oxidation of TP (loses 2H+) 2 pyruvate
2. NAD collects 2H+ 2 redNAD
3. Production of 4 ATP (so net gain* of 2 ATP)
If anaerobic
Pyruvate converted into ethanol or lactate using redNAD
NAD formed which is used in further glycolysis
Production of 2 ATP
Process is rapid but inefficient
If aerobic, pyruvate enters the mitochondrial matrix by active transport:
The link reaction
1. Decarboxylation of pyruvate release of CO2
2. Oxidation of pyruvate acetate
3. NAD redNAD
4. Acetate combines with coenzyme A (CoA) acetylcoenzyme A
NB happens twice
The Krebs cycle
1. Acetylcoenzyme A combines with oxaloacetate (4C) citrate (6C)
2. CoA returns to the link reaction
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