1.
Biology
A2
Unit
4
Revision
Notes
AQA

2. Biology
Unit
4
–
3.4.1
Definitions
Word
Ecosystem
Definition
An
ecosystem
is
made
up
of
all
the
interacting
biotic
(living)
and
abiotic
(non-­‐living)
factors
in
a
specific
area
Population
Is
a
group
of
interbreeding
organisms
of
one
species
in
a
habitat
Community
All
the
populations
of
different
organisms
in
a
given
area
at
a
given
time
Habitat
Place
where
a
community
of
organisms
lives
(e.g.
decaying
log)
Ecological
Niche
How
an
organism
fits
into
the
environment,
refers
to
both
where
an
organism
lives
and
what
it
does
there.
No
two
species
occupy
the
same
niche
Investigating
populations
Quadrats
3
factors
to
consider:
1. The
size
of
quadrat
to
use
–
this
will
depend
on
the
size
of
whatever
you’re
sampling
and
how
they
are
distributed
within
the
sample
area
2. The
number
of
quadrats
to
record
within
the
sample
area
–
for
questions
asking
about
this
10
or
more
should
be
used
within
each
area
to
get
a
big
enough
sample
size,
basically
more
is
better
3. The
position
of
each
quadrat
within
the
sample
area
–
random
sampling
should
be
used
Random
sampling
• This
is
used
to
prevent
bias
–
as
someone
might
pick
to
place
a
quadrat
where
there
is
a
large
amount
of
clover
for
example
but
this
may
not
be
representative.
You
should:
•
•
•
Place
two
tape
measures
at
right
angles
along
two
sides
of
the
area
you’re
studying
Obtain
co-­‐ordinates
using
a
random
numbers
table
Place
quadrats
at
the
intersection
of
each
pair
of
co-­‐ordinates
Systematic
sampling
using
transects
• Transect
is
a
line
or
tape
• This
can
be
used
more
effectively
than
quadrats
for
measuring
things
such
as
abundance
of
species
as
you
enter
a
forest
or
measuring
the
abundance
of
species
comared
with
how
far
away
from
the
sea
you
are

3. They
can
be
used
in
two
ways:
Any
organism
over
which
the
line
passes
is
recorded
You
can
put
a
quadrat
down
every
however
many
meters
down
the
transect
•
•
Measuring
abundance
Sampling
is
used
to
get
a
measure
of
abundance.
This
is
the
number
of
individuals
of
a
species
within
a
given
space.
Two
ways
of
measuring
this:
•
•
Frequency
–
counting
individual
animals
or
plants
Percentage
cover
–
an
estimate
of
the
area
within
the
quadrat
that
one
species
covers
Mark-­‐release-­‐recapture
This
is
carried
out
to
determine
the
population
size.
This
method
is
used:
•
•
•
•
A
known
number
of
animals
are
caught
These
are
marked
in
some
way
These
are
then
released
back
into
the
community
Later
more
animals
are
caught
and
the
number
of
marked
individuals
are
recorded
Then
this
formula
is
used
to
determine
population
size
(needs
to
be
remembered
for
exam):
𝑒𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 1 × 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 2
=
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑎𝑟𝑘𝑒𝑑 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 2
This
technique
relies
on
a
number
of
assumptions:
•
•
•
•
•
The
marked
individuals
distribute
themselves
evenly
amongst
the
other
individuals
in
the
population.
No
deaths
or
births
in
the
population
No
emigration
or
immigration
effecting
the
population
The
method
of
marking
is
non-­‐toxic
to
the
individual
and
it
doesn’t
make
them
more
liable
to
predation
The
mark
isn’t
rubbed
off
or
lost
during
the
investigation

4. Population
growth
curves
1. Lag
phase
–
slow
growth
–
small
numbers
initially
so
reproduction
slow
–
organisms
are
getting
used
to
the
conditions
2. Log
phase
–
rapid
growth
and
optimum
conditions
3. Stationary
phase
–
stable
state
–
no
population
growth
–
small
fluctuations
due
to
changes
in
factors
such
as
food
supply
Abiotic
factors
•
•
•
•
Temperature
–
each
species
has
an
optimum
–
the
further
away
from
this
you
go
the
smaller
the
population
that
can
be
supported
Light
–
ultimate
source
of
energy
for
ecosystems
–
rate
of
photosynthesis
increases
as
light
intensity
increases
–
this
allows
a
larger
primary
consumer
population
to
be
supported
pH
–
this
effects
the
action
of
enzymes
–
a
population
of
organisms
is
larger
where
the
optimum
pH
is
water
and
humidity
–
where
water
is
scarce
populations
are
small
and
only
well
adapted
organisms
survive
–
humidity
effects
the
later
loss
from
plants
(transpiration)
and
animals
in
dry
air
conditions
only
those
individuals
with
adaptations
to
this
will
survive
Competition
Intraspecific
•
•
•
•
Individuals
of
the
same
species
Competing
for
resources
such
as
food,
space,
light
etc.
Availability
of
the
resources
that
determines
population
size
Lower
the
availability
smaller
the
population
size
and
vice
versa
Interspecific
•
•
•
Individuals
of
different
species
Competing
for
resources
such
as
food,
space,
light
etc.
Competitive
advantage
determines
which
population
will
grow

5. •
If
conditions
remain
the
same
this
will
lead
to
the
complete
removal
of
one
species
as
they
can’t
compete
in
this
niche
Predation
•
Occurs
when
one
organism
is
consumed
by
another
Data
can
be
inaccurate
on
this
as
it
has
to
be
measured
in
the
wild
by
sampling
which
is
only
as
good
as
the
methods
used.
None
of
these
methods
guarantee
complete
accuracy
so
caution
is
advised
with
any
data
produced
this
way
Predator-­‐prey
relationship
•
•
•
•
•
•
Predators
eat
their
prey
therefore
reducing
the
population
size
of
the
prey
With
fewer
prey
available
the
predators
are
in
greater
competition
with
each
other
for
the
remaining
prey
The
predator
population
is
reduced
as
some
individuals
are
unable
to
consume
enough
prey
to
survive
and
reproduce
With
fewer
predators
left
less
prey
is
consumed
The
prey
population
increases
More
prey
are
now
available
so
predator
population
increases
This
is
a
cycle
and
carries
on
and
as
the
graph
shows
The
human
population
Factors
effecting
population
size
•
•
•
•
Birth
rate
Death
rate
Immigration
Emigration
𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑔𝑟𝑜𝑤𝑡ℎ = 𝑏𝑖𝑟𝑡ℎ𝑠 + 𝑖𝑚𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛 − (𝑑𝑒𝑎𝑡ℎ𝑠 + 𝑒𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛)

6. 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑔𝑟𝑜𝑤𝑡ℎ =
𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑐ℎ𝑎𝑛𝑔𝑒 𝑑𝑢𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑝𝑒𝑟𝑖𝑜𝑑
×100%
𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑎𝑡 𝑡ℎ𝑒 𝑠𝑡𝑎𝑟𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑒𝑟𝑖𝑜𝑑
Factors
effecting
birth
rates
•
•
•
•
•
Economic
conditions
Cultural
and
religious
backgrounds
Social
pressures
and
conditions
Birth
control
Political
factors
𝐵𝑖𝑟𝑡ℎ 𝑟𝑎𝑡𝑒 =
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑟𝑡ℎ𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟
×1000
𝑡𝑜𝑡𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑎𝑚𝑒 𝑦𝑒𝑎𝑟
Factors
effecting
death
rate
•
•
•
•
•
•
•
Age
Life
expectancy
Food
supply
Availability
of
safe
drinking
water
and
effective
sanitation
Access
to
medical
care
Natural
disasters
War
𝐷𝑒𝑎𝑡ℎ 𝑟𝑎𝑡𝑒 =
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟
×1000
𝑡𝑜𝑡𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑎𝑚𝑒 𝑦𝑒𝑎𝑟
Demographic
Transition
(©
Nelson
Thornes
A2
AQA
Biology
text
book)
This
summarises
a
pattern
that
different
countries
have
gone
through
as
they
have
developed

7. Age
population
pyramids
These
fit
into
the
demographic
transition
stages
based
on
the
shape
of
the
pyramid:
Stage
1
Pyramid
Shape
explanation
Bigger
bars
at
the
bottom
and
less
at
the
top
as
high
birth
rate
so
lots
of
children
but
also
high
death
rate
so
less
older
people
2
Still
high
birth
rate
so
big
bars
at
the
bottom
but
decreasing
death
rate
so
more
in
the
middle
and
more
people
living
longer.
3
Low
death
rate
so
bigger
bars
in
the
middle
and
more
people
reaching
the
top
of
the
pyramid.
Birth
rate
is
decreasing
so
less
at
the
bottom
of
the
pyramid

8. 4
Low
birth
rate
and
death
rate
so
smaller
bars
at
the
bottom
and
bigger
bars
in
the
middle
also
more
people
reaching
the
top
so
larger
bars
there

9. Biology
Unit
4
–
Section
3.4.2
Why
do
organisms
need
energy
•
•
•
•
•
•
Metabolism
–
all
the
reactions
that
take
place
in
living
organisms
involve
energy
Movement
Active
transport
Maintenance,
repair
and
division
of
cells
Production
of
enzymes
and
hormones
Maintenance
of
body
temperature
Hydrolysis
(ATP
+
Water)
ATP
ADP
+
Pi
Energy
from
respiration
Synthesis
of
ATP
from
ADP
This
requires
the
addition
of
a
phosphate
to
ADP.
There
are
3
ways
this
occurs:
•
•
•
PHOTOPHOSOHORYLATION
–
This
occurs
in
chlorophyll
containing
plant
cells
during
photosynthesis
OXIDATIVE
PHOSPHORYLATION
–
Which
occurs
in
the
mitochondria
of
plant
and
animal
cells
during
the
process
of
the
electron
transport
chain
SUBSTRATE
–
LEVEL
PHOSPHORYLATION
-­‐
Occurs
in
plant
and
animal
cells
when
donor
molecules
donate
phosphate
to
the
ADP
to
make
ATP
like
in
the
formation
of
pyruvate
ATP
IS
AN
IMMEDIATE
ENERGY
SOURCE
AND
ISN’T
A
GOOD
LONG
TERM
STORE
OF
ENERGY.
IT
RELEASES
ENERGY
IN
MANAGABLE
Q UANTITIES
F OR
C ELL
R EACTIONS
A ND
C AN
Q UICKLY
B E
R EFORMED
M AKING
I T
A
G OOD
IMMEDIATE
ENERGY
SOURCE

10. Biology
Unit
4
–
Section
3.4.3
Overview
of
photosynthesis
1. Capturing
of
light
energy
by
chloroplast
pigments
2. Light
dependent
reaction
3. Light
independent
reaction
Structure
of
a
chloroplast
(image
from
passscience.blogspot.com)
•
•
Light
dependent
reaction
takes
place
in
the
thylakoids
Light
independent
reaction
takes
place
in
the
stroma
Light
dependent
reaction
Two
purposes:
•
•
Add
phosphate
to
ADP
making
ATP
(photophosphorylation)
Split
water
into
H+
ions,
electrons
and
Oxygen
(photolysis)
Oxidation
and
reduction
Oxidation
–
The
loss
of
electrons,
the
loss
of
hydrogen
or
the
gain
of
oxygen
Reduction
–
The
gain
of
electrons,
the
gain
of
hydrogen
or
the
loss
of
oxygen
Wordy
Explanation
of
what
happens
• When
chlorophyll
molecules
absorb
light
energy
a
pair
it
boosts
the
energy
of
a
a
pair
of
electrons
which
raises
them
to
a
higher
energy
level
• These
electrons
have
so
much
energy
that
they
leave
the
chlorophyll
molecule
• They
are
taken
up
by
an
electron
carrier
• The
pair
of
electrons
are
now
passed
along
a
series
of
electron
carriers
in
oxidation
reduction
reactions
(located
in
the
membrane
of
the
thylakoids)
• Each
carrier
is
at
a
slightly
lower
energy
level
than
the
last
and
the
electrons
lose
energy
• This
energy
is
used
to
add
a
phosphate
to
ADP
to
make
ATP
• The
photolysis
of
water
also
happens
• This
is
due
to
chlorophyll
molecules
losing
two
electrons
so
these
need
to
be
replaced

11. •
These
replacement
electrons
are
provided
by
the
splitting
of
water
molecules
as
shown
below:
2𝐻! 𝑂 → 4𝐻! + 4𝑒 ! + 𝑂!
•
The
H+
is
taken
up
by
NADP
to
form
reduced
NADP
(or
NADPH2)
this
then
enters
the
light
independent
reaction
Diagrammatic
explanation
(©
Nelson
Thornes
AQA
A2
Biology
Text
Book)
Light
independent
reaction
•
•
Products
of
light
dependent
reaction
(reduced
NADP
and
ATP)
are
used
Takes
place
in
the
stroma
of
the
chloroplasts
Wordy
explanation
1. Carbon
dioxide
diffuses
from
the
air
eventually
into
the
stroma
of
the
chloroplast
2. Here
it
combines
with
the
5
carbon
Ribulose
Bisphosphate
(RuBP)
3. This
produces
two
molecules
of
glycerate-­‐3-­‐phosphate
(GP)
4. ATP
and
reduced
NADP
from
the
light
dependent
reaction
are
then
used
to
reduce
GP
into
triose
phosphate
(TP)
5. NADP
(non-­‐reduced)
is
reformed
and
goes
back
into
the
light
dependent
reaction
to
accept
more
hydrogen
6. Some
triose
phosphate
molecules
are
used
to
make
other
useful
substances
such
as
glucose
7. Most
triose
phosphate
molecules
are
used
to
regenerate
RuBP
using
ATP

12. Diagram
(©
Nelson
Thornes
AQA
A2
Biology
Text
Book)
Limiting
factors
on
photosynthesis
At
any
given
moment
the
rate
is
limited
by
the
factor
that
is
at
its
least
favourable
value
Factors
that
limit
photosynthesis
•
•
•
Light
intensity
Temperature
CO2
Concentration
Temperature
is
a
factor
as
it’s
an
enzyme
controlled
reaction
so
higher
temperature
gives
the
molecules
more
energy
and
therefore
they
collide
with
the
right
amount
of
energy
with
the
enzyme
and
form
more
enzyme
substrate
complexes.

13. Biology
Unit
4
–
Section
3.4.4
Aerobic
respiration
4
stages:
•
•
•
•
Glycolysis
Link
reaction
Krebs
Cycle
Electron
Transport
Chain
Glycolysis
• Phosphorylation
of
Glucose
• Splitting
of
phosphorylated
glucose
• Oxidation
of
triose
phosphate
(by
removal
of
hydrogen)
• Hydrogen
accepted
by
NAD
to
form
NADH2
• Production
of
ATP
• Formation
of
pyruvate

14. Link
Reaction
• Pyruvate
oxidised
by
removal
of
hydrogen
• Hydrogen
accepted
by
NAD
to
form
NADH2
• De-­‐carboxylation
occurs
producing
carbon
dioxide
• Acetyl
group
formed
(2-­‐carbon)
• Combines
with
coenzyme
A
to
form
the
2
carbon
acetylcoenzyme
A
Krebs
Cycle
• Acetylcoenzyme
A
feeds
into
this
from
the
link
reaction
• Acetylcoenzyme
A
combines
with
a
4
carbon
compound
to
form
a
6
carbon
compound
• This
then
undergoes
2
decarboxylation’s
removing
two
molecules
of
carbon
dioxide
• It
also
reduces
two
hydrogen
carriers:
NAD
and
FAD
forming
reduced
NAD
and
reduced
FAD
• This
then
is
the
4
carbon
compound
needed
to
combine
with
another
acetylcoenzyme
A
molecule
and
so
it
keeps
on
going

15.
Electron
transport
chain
• Hydrogen
atoms
collected
by
coenzymes
NAD
and
FAD
are
used
• These
are
split
into
electrons
and
protons
• The
electrons
get
passed
down
the
electron
transport
chain
where
as
they
are
passed
from
carrier
to
carrier
they
lose
energy
• This
energy
is
used
to
combine
a
phosphate
with
ADP
to
make
ATP
• The
protons
are
pumped
into
the
inter-­‐membrane
space
of
the
mitochondria
(the
space
between
the
cristae
and
the
outer
membrane
• As
they
accumulate
here
they
diffuse
back
through
special
channels
• At
the
end
of
the
chain
the
electrons
combine
with
these
protons
and
oxygen
to
form
water
Anaerobic
Respiration
•
•
•
•
•
When
there
is
little
or
no
oxygen
neither
the
krebs
cycle
or
electron
transport
chain
can
take
place
Only
glycolysis
can
So
lots
of
pyruvate
produced
in
order
to
produce
the
2
ATP
molecules
glycolysis
yields
(net
yield)
NAD
must
be
regenerated
so
pyruvate
accepts
this
hydrogen
However
this
happens
differently
in
animals
and
plants
In
plants
and
some
microorganisms
𝑝𝑦𝑟𝑢𝑣𝑎𝑡𝑒 + 𝑟𝑒𝑑𝑢𝑐𝑒𝑑 𝑁𝐴𝐷 → 𝑒𝑡ℎ𝑎𝑛𝑜𝑙 + 𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 + 𝑁𝐴𝐷

16.
In
animals
𝑝𝑦𝑟𝑢𝑣𝑎𝑡𝑒 + 𝑟𝑒𝑑𝑢𝑐𝑒𝑑 𝑁𝐴𝐷 → 𝑙𝑎𝑐𝑡𝑎𝑡𝑒 𝑙𝑎𝑐𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 + 𝑁𝐴𝐷
In
both
cases
this
is
very
inefficient
as
only
2
ATP
molecules
are
produced
by
glycolysis
and
there
is
a
much
greater
quantity
produced
by
Aerobic
respiration

17. Biology
Unit
4
–
Section
3.4.5
Food
Chains
and
Food
Webs
Producers
Photosynthetic
organisms
that
manufacture
organic
substances
using
light
energy
Consumers
Organisms
that
obtain
their
energy
by
feeding
on
other
organisms.
Those
that
directly
eat
plants
are
called
primary
consumers.
The
animals
eating
those
organisms
are
called
secondary
consumers
and
so
on.
Not
normally
more
than
4
consumers
in
a
food
chain
Decomposers
When
producers
and
consumers
die
these
organisms
make
the
energy
contained
in
the
other
organisms
available
for
the
food
chain
again
by
breaking
down
the
producer/consumer.
These
nutrients
can
then
be
absorbed
by
plants
and
used
in
the
food
chain
Food
webs
In
reality
many
animals
don’t
rely
on
a
single
food
source
and
in
a
habitat
many
food
chains
link
together
forming
a
food
web
with
lots
of
different
organisms
interacting
Energy
Losses
in
food
chains
Producers:
• Over
90%
of
the
suns
energy
reflected
back
into
space
by
clouds
and
dust
or
absorbed
by
the
atmosphere
• Not
all
wavelengths
of
light
can
be
absorbed
and
used
for
photosynthesis
• Light
may
not
fall
of
a
chlorophyll
molecule
• A
factor
such
as
low
carbon
dioxide
levels
may
limit
the
rate
of
photosynthesis
Formula
to
work
out
NP
(net
production)
𝑁𝑒𝑡 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 = 𝑔𝑟𝑜𝑠𝑠 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 − 𝑟𝑒𝑠𝑝𝑖𝑟𝑎𝑡𝑜𝑟𝑦 𝑙𝑜𝑠𝑠𝑒𝑠
Losses
by
primary
consumers:
• Some
of
the
organism
isn’t
eaten

18. •
•
•
Some
parts
can’t
be
digested
Energy
lost
in
excretory
products
such
as
urine
Energy
losses
due
to
heat
loss
Why
are
food
chains
short?
• Most
food
chains
only
have
4
or
5
trophic
levels
as
there
isn’t
enough
energy
available
to
support
a
population
at
another
level
• The
total
mass
of
the
organisms
in
a
particular
place
(biomass)
is
less
at
higher
trophic
levels
• The
total
amount
of
energy
stored
is
less
at
each
level
as
you
move
up
the
food
chain
Calculating
efficiency
of
energy
transfer
𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 =
𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑎𝑓𝑡𝑒𝑟 𝑡ℎ𝑒 𝑡𝑎𝑛𝑠𝑓𝑒𝑟
×100%
𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑡ℎ𝑒 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟
Ecological
pyramids
Numbers
• The
actual
numbers
of
organisms
proportional
to
each
other
• Drawbacks:
o No
account
is
taken
of
size
so
a
large
oak
tree
is
just
1
even
though
lots
of
aphids
can
feed
on
it
o This
will
create
an
inverted
pyramid
shape
o Number
of
individuals
can
be
so
great
that
it
is
impossible
to
represent
them
accurately
on
the
same
scale
Biomass
• Measure
of
the
total
mass
of
plants/animals
in
a
particular
place
• More
reliable
and
quantitative
• Only
the
organisms
present
at
a
particular
time
are
measured
so
this
doesn’t
take
into
account
seasonal
differences
Energy
• Most
accurate
representation
of
energy
flow
through
an
ecosystem
• This
measures
the
energy
stored
in
organisms
• Collecting
data
however
can
be
difficult
and
complex
• Always
a
pyramid
shape
How
productivity
is
effected
by
farming
practices
Fertilisers
Fertilisers
are
substances
farmers
spread
on
the
soil
to
replace
nutrients,
normally
nitrogen,
which
plants
get
from
the
soil.
Natural
fertilisers
Natural
fertilisers
are
the
faeces
of
animals
which
can
be
spread
onto
the
soil
to
increase
the
nutrients
available
to
the
plants.
The
advantages
are
that
this
is
free
and
readily
available
to
the
farmer,
however
the
disadvantage
is
that
it
has
to
be
left
in
the
soil
to
rot
down
so
that
the
nutrients
are
available
to
the
plants,
which
takes
time.
They
may
also
contain
pathogens
which
can
be
harmful
to
the
plant

19. Artificial
fertilisers
Artificial
fertilisers
contain
nitrogen
compounds
such
as
ammonia
which
are
spread
onto
the
soil
normally
in
soluble
granules
to
increase
nitrogen,
and
other
nutrients,
concentrations
in
the
soil.
The
advantages
are
that
the
nitrogen
is
readily
available
for
plants
to
take
up
and
use.
Farmers
can
also
buy
types
which
have
special
controlled
release
technology
which
means
there
is
a
constant
stable
nitrogen
content
going
into
the
soil.
The
disadvantages
are
the
cost,
as
the
fertiliser
is
very
expensive
whereas
natural
fertilisers
are
free.
Also
after
long
term
use
as
the
fertiliser
doesn’t
replace
the
trace
mineral
content
in
the
soil,
these
can
run
out
and
aren’t
present
in
the
crop
or
the
fruit
so
humans
or
animals
aren’t
consuming
these
trace
elements
which
can
be
bad
for
health.
Fertilisers
add
nutrients
to
the
soil
to
help
increase
the
productivity
of
plants
Pesticides
There
are
two
types,
chemical
and
biological,
both
do
the
job
of
killing
pests
which
feed
on
food
crops
and
fruit
which
ultimately
can
mean
that
farmers
don’t
get
the
maximum
yield
from
their
crops.
A
pesticide
should
be:
•
•
•
•
Specific
–
only
target
the
plant/insect/fungus
it
is
supposed
to
not
the
crop
or
any
other
organisms
Biodegrade
–
so
once
it
has
been
used
it
doesn’t
go
into
the
soil
and
kill
the
crop,
however
it
also
needs
to
have
a
long
shelf
life
Cost-­‐effective
–
developing
a
pesticide
costs
a
lot
and
new
pesticides
only
are
effective
for
a
short
length
of
time.
Not
accumulate
–
so
it
doesn’t
build
up
in
the
food
chain
and
cause
problems
for
other
organisms
Biological
control
This
is
using
the
predator
of
the
pest
to
control
the
numbers
of
the
pest.
Its
advantages
are:
•
•
•
Very
specific
Once
introduced
the
predator
breeds
so
keeps
numbers
up
so
has
a
long
term
effect
Pests
can’t
become
resistant
The
ideal
situation
is
for
the
predator
to
exist
in
balance
with
the
pest
keeping
the
pest
at
a
level
where
it
has
no
or
little
effect.
There
are
however
some
disadvantages
with
this
method
these
are:
•
•
They
do
not
act
as
quickly,
as
the
predator
has
to
build
up
its
numbers
so
there
is
a
lag
between
introducing
the
predator
and
seeing
a
significant
drop
in
the
pest
numbers
The
predator
may
become
a
pest
for
example
if
there
are
few
natural
predators
to
it
or
as
the
pest
population
decreases
it
may
use
the
crops
as
a
food
source.
Integrated
systems
Integrated
control
involves:
•
•
•
Choosing
animal
or
plant
varieties
which
are
as
pest
resistant
as
possible
Managing
the
environment
to
provide
habitats
for
natural
pest
controlling
organisms
to
live
Regularly
checking
crops
for
signs
of
pest
activity

20. •
•
•
Removing
pest
mechanically
(hands,
vacuum,
making
barriers)
Using
biological
agents
Only
using
chemical
pesticides
as
a
last
resort
All
pests
damage
or
compete
with
plants
or
animals
leading
to
reduced
productivity
Intensive
rearing
of
livestock
Intensive
farming
is
about
converting
the
smallest
possible
amount
of
food
energy
into
the
largest
possible
amount
of
animal
biomass.
This
is
achieved
by
minimise
the
energy
lost
by
animals
during
their
lifetime.
Ways
in
which
this
is
achieved:
•
•
•
•
•
•
Movement
is
restricted
–
less
energy
used
in
muscle
contraction
Keeping
the
environment
warm
(for
warm
blooded
animals)
–
reduced
heat
loss
from
body
Feeding
controlled
–
animals
receive
the
optimum
amount
and
type
of
food
for
maximum
growth
Predators
are
excluded
–
no
loss
to
other
organisms
Selective
breeding
–
produces
animals
which
are
the
most
efficient
at
converting
the
food
they
eat
into
biomass
Using
hormones
to
increase
growth
rates

21. Biology
Unit
4
–
Section
3.4.6
See
pages
at
the
end
of
the
carbon
and
nitrogen
cycle
diagrams,
as
these
are
the
first
bit
of
this
section.
Also
see
section
3.4.5
first
as
there
is
some
overlap
with
the
use
of
fertilisers
Effects
of
nitrogen
fertilisers
Reduced
species
diversity
This
is
because
nitrogen
rich
soils
favour
the
growth
of
fast
growing
species,
these
out
compete
many
other
species
which
causes
these
other
species
to
die
as
a
result
Leaching
This
is
a
process
where
nutrients
are
removed
from
the
soil.
Rain
water
will
dissolve
any
soluble
nutrients
and
carry
them
deep
into
the
soil
eventually
beyond
the
reach
of
the
plant
roots.
These
eventually
find
their
way
into
water
courses.
They
can
have
a
harmful
effect
on
humans
if
they
drink
them
and
can
also
cause
eutrophication.
Eutrophication
• In
most
lakes
and
rivers
there
is
naturally
very
little
nitrate
and
so
this
is
the
limiting
factor
for
plant
and
algal
growth
• Ass
the
amount
of
nitrate
increases
due
to
leaching,
plants
and
algae
grow
massively
• As
algae
mostly
grow
on
the
surface
massive
algal
blooms
form
and
this
absorbs
the
light
and
stops
it
reaching
the
lower
depths
• Light
can’t
reach
the
plants
at
the
bottom
so
these
die
• The
increase
in
dead
plant
matter
causes
decomposers
to
grow
• These
are
aerobic
so
require
a
large
amount
of
oxygen
from
the
water
• This
massively
increases
the
BOD
(biochemical
oxygen
demand)
• Oxygen
then
becomes
the
limiting
factor
for
aerobic
organisms
such
as
fish
• If
these
can’t
swim
away
(e.g.
they
are
in
a
pond)
they
will
die
• There
is
less
competition
for
anaerobic
organisms
whose
populations
rise
massively
• These
organisms
further
digest
the
plant
waste
and
this
leads
to
more
nitrates
in
the
water
and
also
toxic
substances
such
as
hydrogen
sulphide

22. Biology
Unit
4
–
Section
3.4.7
During
succession
a
number
of
common
things
happen:
•
•
•
•
•
The
non-­‐living
(abiotic)
environment
becomes
less
hostile
–
soil
forms,
nutrients
are
more
plentiful
and
plants
provide
shelter
Greater
number
and
variety
of
habitats
Increased
biodiversity
–
as
different
species
occupy
the
habitats
More
complex
food
webs
Increased
biomass
–
especially
during
the
mid-­‐stages
(©
nelson
thornes
AQA
Biology
A
text
book)
Managing
succession
•
•
•
•
•
•
To
reach
the
climax
community
the
land
has
gone
through
a
lot
of
stages
Most
of
the
species
present
in
the
earlier
stages
are
no
longer
present
However
to
get
grass
to
allow
cattle
to
graze
we
need
grass,
this
is
at
one
of
the
earlier
stages
of
succession
To
do
this
we
manage
succession
by
not
allowing
it
to
proceed
past
this
point
This
can
be
achieved
by
mowing
or
allowing
cattle
to
eat
the
grass
If
this
was
simply
left
shrubs
would
develop
and
then
trees
such
as
oaks
to
make
deciduous
woodland
This
is
one
example
but
there
are
many.
Succession
is
managed
to
allow
the
plants
to
grow
that
we
want/
are
useful
rather
than
letting
everything
develop
to
the
climax
community.