Unit 4 A2 Biology Notes AQA

1. Biology
Unit 4
AQA

2. Ecology Definitions
Habitat – The place where an organism lives
Population – A group of organisms belonging to the same species
Community – All the populations of different organisms living and interacting
in the same space at the same time
Ecosystem – A community of living organisms and the abiotic factors which
affect them
Abiotic – The physical and chemical features of the environment
Biotic – The biological features of the environment (living)
Niche – A species role within it’s habitat
Adaptation – A feature that members of a species have to increase their
chance
of survival

3. Investigating
Populations
Quadrats:
- Set out 2 tape measure at right angles, forming the axes for the
chosen area
- Generate 2 random numbers (using calculator) to use as coordinates
- Place quadrat where co-ords meet
- Find mean number of species per quadrat
- Multiply by size of area being sampled
Transects:
- It’s a line through an area to be studied to identify changes through
an area
- Line Transects – a tape measure is placed along the transect and
the
species that touch the tape measure are recorded
- Belt Transects – quadrats are placed next to each other along the
transect to work out species frequency &
percentage
cover along a transect

4. Measuring Abundance
Quadrats:
- Have a known dimension
- Used to:
- Estimate population density
- Estimate % cover of an organism
- Estimate the frequency of an organism
Factors:
- Size of quadrat – More small quadrats = more representative results
- Number of quadrats – more quadrats = more reliable results
- Position of quadrat – must be placed randomly to avoid bias
At least 20 samples taken. Eventually a sample size is big enough that the
number of species doesn’t increase much more the sample is said to be
representative.

5. Mark-Release
Recapture
A known number of animals are caught and marked. They’re then released back.
Later another sample are caught and the number of marked individuals is recorded
Assumptions:
- No reproduction
- No migration
- Enough time for both marked & unmarked animals to mix
- Marking doesn’t affect behaviour

6. Variation in Population Size
Abiotic Factors:
- Affected by factors such as temperature, light, space, water etc…
- When conditions are ideal an organism will thrive and vice versa
Biotic Factors:
- Interspecific Competition:
-
Competition between different species
- Intraspecific Competition:
-
Competition between the same species
- Predation – Predator & Prey populations are linked
-
Prey increases, more food, so predator increases.
Predator eats prey, prey decreases as they’re eaten
Predator decreases due to lack of food
Predator peaks after prey

7. Human Populations
Population Growth = (BR + Immigration) – (DR + Emigration)
% Population Growth Rate =
Population Change
Population Start
x 100
Demographic Transition Model:
- Shows the change in BR, DR & population size over along period of time

8. Survival Curves
Show the percentage of all individuals that were born in a population that are still
alive at a given age.
Life Expectancy – is the age someone is expected to live to
- it’s the age at which 50% of the population are still alive
e.g. the life expectancy of this example is
81 as that is the age when 50% of the
population are still alive

9. Age-Sex Population
Pyramids
West Europe:
-
West Africa:
-
High BR
Short Life Expectancy
High DR
Developing Country
Lower BR
Long Life Expectancy
Lower DR
Developed Country

10. Ecosystem Definitions
Producer – They’re photosynthetic organisms that manufacture organic
substances using light energy, water and CO2
Consumer – They’re organisms that obtain their energy by feeding on other
organisms
Decomposers – When consumers & producers die, the energy can be used
by
organisms that break down the complex materials into single
components again
Food Chains – Describes a feeding relationship in which the producer are
eaten
by the primary consumers. They’re then eaten by secondary
consumer
Trophic Level – The level between each stage in the food chain
Food Web – More than one food chain linked together
Trophic Level
Grass  Sheep  Human
(Producer)
(1° Consumer)
(2° Consumer)

11. Energy Transfer Between
Trophic Levels
Little solar energy converted to chemical energy in PS:
- Some is reflected due to wrong wavelength/frequency/colour
- Doesn’t hit chlorophyll molecule
- Lost as heat during evaporation
Energy is lost along a food chain:
- Not all the organism is eaten
- Not all organism digested – lost in faeces
- Urine
- Heat in respiration
- Movement
- Birds & Mammals – energy used to maintain a constant body temperature
(homeostasis)
Not enough energy to support further trophic levels, so rarely more than 4
trophic levels present in a food chain

12. Net Primary Productivity
Gross Primary Productivity (GPP) – Amount of light energy that plants
convert
to chemical energy
Net Primary Productivity (NPP) – Total amount of energy stored in a plant
that
is available to the next trophic level
NPP = GPP - Respiration
Measured in
Energy
=
Transfer (%)
kJ m-2 Year -1
Energy after Transfer
X 100
Energy before Transfer

13. Production of ATP
•
ATP- Adenine TriPhosphate
•
Made from ADP + Pi
•
Energy stored in the phosphate bond
•
ATPase catalyses the breakdown of ATP into ADP + Pi
•
ATP synthase catalyses the production of ATP
•
The ADP + Pi is recycled and the process starts again
Properties:
• Small compound – easily transported around the
cell
• Easily broken down (Hydrolysed)
• Cell has instant energy supply

14. Photosynthesis
2 Photo Systems capture light in a chloroplast PSI (best at 700nm) & PSII (best at
680nm)
Thylakoid
Stroma Starch Grain
6CO2 + 6H2O + Energy = C6H12O6 + 6O2
Granum
Contains
Chlorophyll
Substomatal
Cavity
Inner &
Outer
membrane
Waxy Cuticle
Loop of DNA
Lamellae (Membrane
joining Thylakoids)
Absorption Spectrum
Number of
Chloroplasts
Upper Epidermis
Airy Cells,
lots of
space
Palisade Layer
Spongy Mesophyll
Lower Epidermis
Plants absorb red & blue
wavelengths only
reflecting green. It’s why
they’re green

15. LDS (Non-Cyclic Photophosphorylation)
Electron Acceptor
Electron Carrier
Photolysis Of Water:
2H2O = 4H+ + 4e- + O2
Requires a photon to split water
Occurs in the Thylakoids of
chloroplasts
Thylakoids adapted for their function:
•
•
•
•
Large SA, large area for attachment of chlorophyll, electron carriers and enzymes
Proteins in grana hold chlorophyll to allow max light intake
Granal membranes contain enzymes that help make ATP
Chloroplast contain DNA & Ribosomes to manufacture proteins for LDS quickly

16. Cyclic Photophosphorylation
Happens when lack of NADP
No light wasted
Only uses Photo System 1
Only ATP produced

17. LIS (Calvin Cycle)
In Stroma
RuBp – Ribulose
Bisphosphate
TP – Triose Phosphate
(GALP)
GP – Glycerate 3-Phosphate
RUBISCO – Enzyme used in
CO2 Fixation
ATP and rNADP from LDS
6 Cycles = 1 Glucose
Molecule

18. Respiration
C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy
1. Glycolysis:
• Makes Pyruvate from Glucose
• In cytoplasm
• Anaerobic Process
• Net Yield of 2ATP
Dehydrogenation – Removal of H2
- Using dehydrogenase enzyme
Substrate Level Phosphorylation
- ADP + Pi  ATP

19. 2. Link Reaction:
•
•
•
Pyruvate oxidised by removing H
Acetyl CoEnzyme A produced
Per Pyruvate a CO2 molecule produced
Decarboxylation – Removal of CO2
- Using Decarboxylase enzyme
Pyruvate + NAD + CoA = Acetyl CoA + rNAD + CO2

20. 3. Krebs Cycle:
•
•
•
Acetyl CoA + oxaloacetate (4C) = Citrate
Citrate converted to 5C compound ( 2H+ & CO2 removed)
5C to 4C Produces:
• 2 x rNAD
• ATP
NAD – Nicotinamide Adenine Dinucleotide
• rFAD
FAD – Flavine Adenine Dinucleotide
• CO2

21. Electron Transfer Chain
When rFAD & rNAD are oxidised they release 2H & 2eElectrons used in transfer chain Hydrogen used in chemiosmosis
Energy/ATP produced in ETC is used to power chemiosmosis
Oxygen is the last electron acceptor.
O2 + 2e- + 2H  H2O

22. Chemiosmosis
In Photosynthesis & Respiration Energy (ATP) from ETC used to power Chemiosmosis
If ATP synthase
not present energy
lost in the form of
Heat instead of
forming ATP
Electro – Chemical
Gradient
Active Transport

23. Respiration

24. Anaerobic Respiration
Instead of pyruvate being converted into Acetyl CoA it’s
converted into ethanol (in plants and yeast) and lactic acid (in
animals and some bacteria)