1. Biology 4
•Populations
•ATP
•Photosynthesis
•Respiration
•Energy and Ecosystems
•Nutrient cycles
•Ecological succession
•Inheritance and selection

2. Back
•
•
•
•
•
•
•
•
•
•
Populations
Ecology- study of inter-relationships between organisms and
environment
Ecosystem- interacting biotic and abiotic factors in a specific area
Populations- group of inter-breeding organisms of 1 species
Community- all populations living and interacting in a specific area
Habitat- place where community of organism lives
Niche- how an organism fits into the environment (no two species
occupy same niche)
Abiotic- temperature, light, PH, water and humidity
Biotic- living organisms (competition and predation)
Intraspecific competition- same species for; food, water, breeding
site
Interspecific- Different species; food, light, water

3. Back
Investigating populations
• Quadrats- factors, size, number and position should be
considered
• Random Sampling- avoid bias
-1. long tape measures at right angles
-2. Co-ordinates from random number generator
-3. place quadrat on intersection
• Systematic sampling- distribution of species- straight line or
belt (two lines)
• Measuring abundance-Frequency: e.g. 15/30= 50%- useful for species such as grass
-Percentage Cover: estimate area within quadrat that
particular plant species covers, useful for abundance of hard
to count species

4. Back
Mark-Release-Recapture:
Estimated
population size =
Total no. of individuals in 1st sample
x
Total no. of individuals in 2nd sample
No. of marked individuals recaptured

5. Back
Human populations
• Immigration and emigration (leaving)
• Pop. Growth= (births+immigration) - (death+emmigration)
• %pop. Growth rate= pop. Change during period
pop. At start of period
x100

6. Back
Birth and Death rates
• Birth:
-Economic conditions
-cultural/ religious
-social pressures & conditions
-Birth control
-political factors
• Birth rate= no. of births per year x1000
total pop. In same year
• Death:
-age profile
-life expectancy at birth
- food supply
-safe drinking water and sanitation
-medical care
-natural disasters
-war
Death Rate= no. of deaths per year x1000
Tot. pop. In same year
Change in population=
demographic translation

7. Back
ATP & Energy
• ATP is an energy source for:
•
•
metabolism, maintenance, movement, active transport, repair and
division, production of substances, maintenance of body
temperature
• ATP+ H20  ADP + Pi + E
Hydrolysis reaction
Synthesis of ATP:
reversible reaction (Pi to ADP – condensation reaction)
ATP immediate energy source
-released in small bursts of energy from mitochondria
-manageable
-fast reaction

8. Back
•
Photosynthesis
6CO2 + 6H20  C6H O + 6O2
12
• Light energy  Electrical  Chemical energy
• Chloroplasts:
Grana (Thylakoids) – light dependant stage- pigment
chlorophyll
Stroma- fluid-filled matrix – light independent stage- starch
grains
• Factors effecting photosynthesis rate:
light intensity
CO2
Temperature

9. Light- dependant reaction
• Involves capture of light for:
-to add Pi to ADP for ATP
-to split H+ ions (protons) and OH- ions by light known as photolysis
• Making of ATP:
-Chlorophyll molecules absorb light energy, boosts energy of electrons
raising energy level (excited state)- then leave chlorophyll
-electrons taken up by electron carrier
-Having lost electrons the chlorophyll has been oxidised- electron
carrier gains electrons (reduced)
-In thylakoids they pass through oxidation-reduction reactions
-energy along is lost for ATP production
• Photolysis of water:
-2H O  4H+ + 4e- + O
protons electrons
• H+ ions (protons) taken up by electron carrier NADP. NADP
becomes reduced
2
2
• Reduced NADP aand electrons from chlorophyll enters light
independent reaction
• Oxygen waste product/ used for respiration
Back

10. Light- independent reaction
•
•
•
ATP and reduced NADP from light dependant reaction used to reduce CO2
Calvin cycle in stroma
Stages:
1. CO2 diffuses into leaf through stomata
2. In stroma CO2 combines with 5-carbon compund (RUBp) using an enzyme
3.Combination of CO2 & RuBP produces 2x molecules of glycerate 3
phosphate (GP)
4. ATP & reduced NADP from light-dependant reaction used to reduce
activated glycerate 3-phosphate to triose phosphate (TP)
5. NADP re-formed and goes back to light dependant reaction to be reduced
by accepting Hydrogen
6. Some triose phosphate molecules are converted to useful organic
substances, such as glucose
7. Most triose phosphate used to regenerate ribulose biphosphate using ATP
from light dependant
Site of light independent reaction:
fluid of stroma- contains all enzymes for Calvin cycle
stroma fluids surrounds grana, so products of light dependant reaction in grana can
easily diffuse
Contains both DNA and ribosome's, so quickly and easily manufacture proteins for
Calvin cycle

11. Back
Respiration
• Aerobic respiration- needs O2, produces CO2, water and
ATP
• Anaerobic respiration (fermentation)- takes place without
O2, produces lactate in animals and or ethanol/CO2 in plants
but only a little ATP in both cases
• Aerobic can be divided in to four stages:
1.Glycolysis- splitting 6-carbon glucose to two 3-carbon
pyruvate
2.link reaction- conversion of 3-carbon pyruvate molecule into
CO2 and a 2-carbon molcule= acetylcoenzyme A
3.Krebs cycle-acetylcoenzyme A into cycle of oxidationreduction reactions that yield ATP and a large no. of
electrons
4.electron transport chain-use of electrons produced by
krebs to synthesise ATP (water is by-product)

12. Back
•
•
Glycolysis
Initial stage of aerobic and anaerobic respiration. Occurs in
cytoplasm of all living cells
Four stages:
1.activation of glucose by phosphorylation- glucose more reactive by
adding 2 phosphate molecules so it can split. Phosphate comes from
hydrolysis of ATP to ADP- provides energy to activate glucose
2.splitting phosphorylated glucose- split into 3-carbon molecules
known as triose phosphate.
3.Oxidation of triose phosphate- Hydrogen removed from each 2
triose phosphate & transferred to hydrogen-carrier molecule known
as NAD to form reduced NAD
4.production of ATP- ezyme controlled reactions convert each
triose phosphate to another 3-carbon molecule- pyruvate. In process
two molecules of ATP regenerated from ADP.
Energy yield from Glycolysis:
-two ATP molecules (two were used for phosphorylation)
-two molecules of reduced NAD (has potential to produce more ATP
-two molecules of pyruvate

13. Back
Link Reaction
• Pyruvate produced during glycolysis can only release energy using
oxygen in krebs cycle.
-1st oxidised in link reaction
-Krebs & Link take place in eukaryotic cells inside mitochondria
• Link reaction: Pyruvate actively transported to matrix of
mitochondria.
-Pyruvate oxidised by removing hydrogen- hydrogen is accepted
by NAD to form reduced NAD (later used to produce ATP)
-2-carbon molecule, called acetyl group, combines with a
molecule called coenzyme A (COA) to produce acetylcoenzyme
A
- a CO2 molecule is formed from each pyruvate
Pyruvate + NAD + COA  acetyleCOA +reduced NAD + CO2

14. Back
1.
Krebs Cycle
2-Carbon acetylcoenzyme A combines with 4-carbon molecule to
produce 6-carbon molecule
2.
6- Carbon loses CO2 and hydrogens to give a 4-carbon molecule &
single ATP
3.
The 4-carbon molecule can now combine with new molecule
acetylcoenzyme A to begin cycle again
Link & Krebs produce:
-reduced coenzymes NAD & FAD potential to produce ATP
-one molecule of ATP
-3 molecules of CO2
Because 2 pyruvate molecules are produced for each original glucose,
yield is double of quantities above
Significance of Krebs:
-break down macromolecules into smaller ones
-production of ATP provides metabolic energy
-regenerates 4-carbon molecules which would otherwise
-accumulate
-source of intermediate compounds used by cells in manufacture
of fatty acids, amino acids and chlorophyll

15. Back
Coenzymes
• Coenzymes are molecules that some enzymes acquire for
energy
• Carry Hydrogen atoms from one molecule to another
Examples:
NAD- important throughout respiration
FAD- important in Krebs cycle
NADP- important in photosynthesis
• In respiration NAD is most important carrier. Works with
dehydrogenase enzymes that catalyse removal of hydrogen
ions from substrates and transfer them to other molecules

16. Back
•
•
•
•
•
•
Electron transport Chain
Cristae (inner folds) in mitochondria is the sight of electron
transport chain
Hydrogen carried by coenzymes NAD and FAD to electron
transport chain from Krebs are 1st attached to cristae
Releases protons from H-atoms- protons actively transported across
inner membrane
Electrons meanwhile pass along chain in oxidation-reduction
reactions- elec. Lose energy down chain- some used to combine ADP
and Pi. Remaining energy released as heat
Protons accumulate in space between 2 mitochondrial membranes
before diffusing back into matrix through protein channels
End of chain electrons & protons and O2 combine to form H2O. O2
is the final acceptor of electrons in chain
Importance of O2:
H-atoms (protons) and electrons would otherwise back- up- respiration
would come to a halt
Cyanide (non-competitive inhibitor)

17. Back
•
•
•
•
Anaerobic Respiration
In eukaryotic cells:
plants convert ethanol to CO2
animals pyruvate to lactase
Pyruvate + reduced NAD ethanol + CO2 + NAD (plants)
When O2 is low:
lactate production occurs mostly in muscle
reduced NAD must be removed for glycolysis- each pyruvate takes
up 2 H-atoms from reduced NAD
pyruvate + reduced NAD  lactate + NAD
(animals)
Lactate can cause cramp and muscle fatigue- must be oxidised back
to pyruvate
Energy Yields from anaerobic and aerobic respiration:
Substrate level phosphorylation in glycolysis and Krebs produces ATP
Oxidative phosphorylation- electron transport chain- ATP
In aerobic respiration Krebs or electron chain can’t take place.
Less ATP for anearobic- only from glycolysis

18. Back
Energy and ecosystems
• Consumers (Primary, secondary and tertiary)
• Decomposers- fungi and bacteria
• Detritivores- certain animals such as earthworms
• Each stage in the food chain is a Trophic level

19. Back
Energy transfer between trophic levels
• Energy losses in food chains:
90% of suns energy reflected back in space by clouds and
dust
not all wavelengths can be absorbed
light may not fall on chlorophyll
low CO2 may limit photosynthesis
• Gross production= total quantity of energy that plants in
community convert to organic matter
• Net production= gross production – respiratory losses

20. Low percentage energy transferred at each stage:
-some of organism is not eaten
-some parts are eaten but can’t be digested & therefore lost
in faeces
-some energy is lost in excretory materials, such as urine
-Heat respiration/ body to environment
Must food chains have 4/5 trophic levels, insufficient energy for
more
Total mass of organisms (biomass) is less at higher trophic levels
Total amount of energy stored is less at each level
Calculating efficiency of energy transfers:
Energy transfer= energy available after transfer x100
energy available before transfer
Back

21. Back
Ecological pyramids
• Pyramids of numberno account is taken for size
no. of individuals is so great that its impossible to represent
them accurately
• Pyramids of biomasswater in organism may make it unreliable
no seasonal difference apparent in both pyramids
• Pyramids of energyenergy through food chain
difficult and complex to obtain the results

22. Back
Agricultural ecosystems
• Gross productivity- rate plants assimilate chemical energy
• Net productivity= gross productivity- respiratory losses
• Net productivity is affected by:
-efficiency of crop carrying out photosynthesis
-are of ground covered by leaves/crops
• Comparisons of natural & agricultural ecosystems:
• Energy input – only source is sun- additional energy- food and
or fossil fuels
• Productivity- Natural eco. Prod. Is low, fertilisers and
pesticides added

23. • Pesticides effectiveness:
specific
biodegrade
cost-effective
not accumulate
• Biological control:
not as quick
control organism may itself become pest
• Intensive rearing and energy conversion:
Movement restricted (less energy used by muscle
contraction)
Environment kept warm
Feeding controlled
Predators excluded
Selective breeding
Hormones to increase growth rates
Back

24. Back
Nutrient Cycles
• Basic sequence for nutrient cycles:
-nutrient taken up by plants (producers) as simple, inorganic
molecules
-producer incorporates nutrient into complex organic
molecules
-when producer eaten, nutrients pass into consumers
-passes along food chain
-when producers/consumers die, complex molecules broken
down by saprobiotic microorganisms that release nutrient in
simple form

25. Carbon Cycle
Back
CO2 in
atmosphere
& dissolved in
oceans
Photosynthesis
Combustion
Fossil
Fuels
Respiration
Carbon containing
compounds in
producers
(plants)
Feeding
Carbon-containing
compounds in
consumers
(animals)
Death
Decay
Living component
Carbon-containing
compounds in
Decomposers (saprobiotic microorganisms)
Non- Living component
Basic sequence
Additional pathways
Decay Prevented

26. Greenhouse effect & Global warming
• Greenhouse effect- solar radiation reflected back into space,
some reflected back- gas traps heat near earths surface
• Global Warming:
-melting of ice caps
-rise in sea level
-faliure of crops
-disease may spread
Back

27. Nitrogen Cycle
•
Four main stages: Ammonification, nitrification, nitrogen fixation
and denitrification each involving saprobiotic organisms A>N>N>D
Nitrogen fixation by free- living bacteria
Nitrification
Nitrite
Ions
Nitrification
Ab
so
rp
t
io
n
Ammonium
ions
Nitrate
ions
Denitrification
Nitrogen in
atmosphere
ion
ia
ixat
nf
c t er
oge
c ba
N it r
lis t i
t ua
mu
By
AmmoniumAmmonium- containing
containing molecules Feeding and molecules e.g. proteins
e.g. proteins, in producers digestion
in consumers
Death
Ammonification
Back
Ammonium- containing
molecules e.g. proteins
in decomposers
saprobiotic microorganisms
Death &
excretion

28. Ammonification:
Production of ammonia from organic ammonium containing compounds
Sprobiotic microorganisms (fungi/bacteria) release ammonia which forms
ammonium ions in soil. Returns to non living component.
Nitrification:
Conversion of ammonium ions to nitrate ions, using oxidation
reactions (release energy)- carried out by free-living soil
microorganisms called: nitrifying bacteria. 2 stages:
1.Oxidation of ammonium ions to nitrite ions (NO 2-)
2.Oxidation of nitrite ions to nitrate ions (NO3-)
Needs O2 so ploughing (aerated) and good drainage (no water)
Nitrogen fixation:
Nitrogen gas is converted to nitrogen-containing compounds, carried out by:
free-living nitrogen-fixing bacteria: reduce gaseous nitrogen to ammonia,
used to manufacture amino acids
mutualistic nitrogen fixing bacteria: Nodules of roots/plants- obtain
carbohydrates plant and plant acquires amino acids from bacteria
Denitrification:
Soil becomes waterlogged, so short of O2= few nitrogen fixing bacteria and
increase denitrifying bacteria (convert soil nitrates to gaseous nitrogen)
Back

29. •
•
Levels of mineral ions in agriculture falls
To replenish this fertilisers are used:
Natural (organic) fertilisers- dead, decaying animals/plants
Artificial inorganic fertilisers- mined from rocks & deposits- contains
three compounds: nitrogen, phosphorus and potassium
• Effects of nitrogen fertilisers:
Reduced species diversity e.g. nettles and grasses out compete other
species
Leaching- may lead to pollution of watercourses
Eutrophication- caused by leaching of fertiliser
Leaching –
Nitrates with rain draining into streams/rivers then drain into
freshwater lakes- harmful effect to humans if source of drinking
water- cause eutrophication
Eutorphication –
In lakes/rivers a limiting factor for plants/algae is nitrate- as nitrate
increases the algae & plants grow
Upper layers of water become densely populated with algae (algal
bloom) Absorbs light and prevents light at bottom. Plants at bottom
die. Saprobiotic algae feed on dead plants but they need oxygen. O2
concentration is reduced in lake so fish has no O2 and die- further
decompose (dead organism) more nitrate water is putrid
Back

30. Back
Ecological succession
• First stage is colonisation of inhospitable environment by
organisms called pioneer species.
• The abiotic environment is continuously changing
• Climax community- final stage of ecological succesion
• During succession:
-non-living environment becomes less hostile- e.g. soil
-great number/variety of habitats produce:
-increased biodiversity
-more complex food webs
-increased biomass
• Primary colonisers secondary colonisers Tertiary
colonisers  shrubland  Climatic climax

31. Back
Conservation of habitats
• Main reasons for conservation:
Ethical- other species have inhabited earth longer
Economic- may be useful in long term
Cultural/ aesthetic- habitats/organisms enrich and
inspire lives (writer, artists and composers)
• Succession- changes over time

32. •
•
•
•
•
•
•
•
•
•
•
•
•
Inheritance and Selection
Genotype- genetic composition of organism
Phenotype- visible characteristics of an organism resulting from
genotype & environment
Gene-section of DNA that determines characteristics of DNA
Allele-different forms of a gene
Homologous chromosomes-pair of chromosomes that have same loci
therefore determine same features
Homozygous-alleles are identical for particular gene
Heterozygous-alleles of gene different
Dominant-allele that is always expressed in phenotype of organism
Recessive-allele only present in diploid phenotype if another identical
allele is present
Diploid- when nucleus contains 2 sets of chromosomes
Haploid-only contain 2 set of chromosomes e.g. Sex cell/ gametes
Co-dominant-both alleles code for one gene in heterozygous
individual
Multiple alleles-gene that has more than two possible alleles
Back

33. Monohybrid Inheritence
• Law of Segregation:
In diploid organisms, characteristics are determined by alleles
that occur in pairs. Only one of each pair of alleles can be
present in a single gamete”
• Sex Inheritance and Sex linkage:
As males have one X and one Y chromosome they produce 2
different types of gamete
-X chromosome is longer so there is no equivalent homologous
portion with Y. Haemophilia is inherited from the mother to
male
- Pedigree charts are a good representation of inheritance
Back

34. Co-dominance and multiple alleles
•
Co-dominance example: Red and white snapdragon = pink
snapdragon
• Multiple Alleles example: Blood groups
- Io is recessive in B.G
• Hardy Weinberg:
Frequencies of alleles- proportion of dominant and recessive
Five conditions:
-No mutation
-Population isolated
-No selection
-large population
-Random mating
p + q = 1.0
p2 + 2pq + q2 = 1.0
Heterozygote= 2pq
Back

35. Selection
• All organisms produce more organisms than food, light and
space can support
• Therefore Intraspecific competition
• Organisms with the better fitting alleles survive and then
reproduce
Types of Selection:
• Directional selection: individuals that vary in one direction to
the mean of population
some individuals that fall to left/right of mean will possess a
phenotype more suited to new conditions
-extreme of the populations
• Stabilising selection: favour average individuals- preserves
characteristics of a species
-If environmental conditions stay stable individuals with
closest phenotype to mean are favoured
Back

36. Speciation
• Speciation: evolution of new species from existing species
• Geographical Isolation:
When a physical barrier prevents 2 populations from breeding
with one another
-In the split Land A has organisms with more suitable
phenotypes and Land B has organisms with more suitable
phenotypes
-In time difference becomes so great in gene pools that they
become 2 separate species
-Once united they cannot breed
Back