7/30/2019 Unit 4.1 Biology
1/45
Page 1 of 45
A2 level Biology notes
Unit 4- Populations and the Environment
7/30/2019 Unit 4.1 Biology
2/45
Page 2 of 45
1. Populations ............................................................................ 31.1 Populations and ecosystems .................................................. 3
1.2 Investing populations........................................................... 31.3 Variation in population size ................................................... 5
1.4 Competition....................................................................... 71.5 Predation.......................................................................... 91.6 Human populations ........................................................... 10
2. ATP.................................................................................... 122.1 Energy and ATP ................................................................ 12
3. Photosynthesis ...................................................................... 143.1 Overview of Photosynthesis ................................................. 143.2 The Light- dependent reaction.............................................. 16
3.3 The Light Independent Reaction ........................................... 173.4 Factors Affecting Photosynthesis ........................................... 18
4. Respiration .......................................................................... 204.1 Glycolysis........................................................................ 204.2 Link reaction and Krebs cycle............................................... 214.3 The electron transport chain................................................ 23
4.4 Anaerobic respiration ........................................................ 245. Energy and Ecosystems ............................................................ 25
5.1 Food chains and Food webs.................................................. 255.2 Energy Transfer between Trophic Levels................................. 265.3 Ecological Pyramids........................................................... 27
5.4 Agricultural Ecosystems ..................................................... 285.5 Chemical and Biological Control of Agricultural Pests ................. 29
5.6 Intensive Rearing of Domestic Livestock................................. 316. Nutrient Cycles ...................................................................... 33
6.1 The carbon cycle ............................................................... 33
6.2 The greenhouse effect and global warming .............................. 346.3 The Nitrogen Cycle ............................................................ 356.4 Use of Natural and Artificial Fertilisers ................................... 36
6.5 Environmental consequences of using nitrogen fertilisers ........... 367. Ecological Succession .............................................................. 37
Succession ........................................................................... 37
7.2 Conservation of Habitats ..................................................... 38
8. Inheritance and Selection ......................................................... 398.1 Studying inheritance.......................................................... 398.2 Monohybrid Inheritance ..................................................... 408.3 Sex Inheritance and Sex Linkage ........................................... 41
8.4 Co-dominance and Multiple Alleles ........................................ 428.5 Allelic Frequency and Population Genetics............................... 438.6 Selection......................................................................... 44
8.7 Speciation ....................................................................... 45
7/30/2019 Unit 4.1 Biology
3/45
Page 3 of 45
1. Populations1.1 Populations and ecosystems
Ecosystem- It is made up of all the interacting biotic and abiotic features in aspecific area
Population- A group of interbreeding organisms of one species in a habitat.
Community- All the populations of different organisms living and interacting
in a particular place at the same time.
Habitat -The place where a community of organisms lives.
Ecological niche- All the biotic and abiotic conditions required for an
organism to survive, reproduce and maintain a viable population. No 2
species occupy exactly the same niche.
1.2 Investing populations
To study habitat often necessary count no
individuals of species in given
space
This known as abundance
Virtually impossible identify & count every organism
Do so would time consuming & cause damage habitat being studied
SO small samples usually studied in detail
As long as samples representative of habitats as whole any conclusion drawn
from findings will be validN
osampling techniques used in study of habitat, these include:
Random sampling using frame or point quadrats
Systematic sampling along transects
Quadrats
Three factors to consider when using quadrats:
Size quadrat use: depend upon size plants or animals being counted & how
they distributed within area. Large species = larger quadrat
Where species occurs in series group rather being evenly distributed
throughout area, a large no
small quadrats will give more representative
results than small n
o
large onesN
oof sample quadrats to record within the study area: larger n
oof sample
quadrats the more reliable results will be.
Recording species w/in quadrat is time-consuming task, needs balance
between validity results & time available.
Greater no
different species present in area studied = greater no
quadrats
required valid results
Position each quadrat w/in study area: produce statistically significant
results technique random sampling must used.
Random Sampling
Important sampling random avoid any bias in collecting data, avoiding bias
ensures data obtained valid
7/30/2019 Unit 4.1 Biology
4/45
Page 4 of 45
A good method of random sampling is to:
1. Lay out two long tape measures @ right angles, along 2 sides of studyarea
2. Obtain series of coordinates by using random no taken from table orgrated by computer or calculator
3. Place quadrat at intersection of each pair coordinates & record speciesw/in it
Systematic sampling along transects
Sometimes more informative measure abundance & distribution of species in
systematic rather random manner
Particularly important where some form transition in communities plants &
animals take place
Line transect comprise string or tape stretched across ground in straight line,
any organism over which line passes is recorded
Belt transect is strip, usually meter wide, marked putting second line parallelto first, species occurring w/in belt between lines recorded
Measuring abundance
Random sampling w/ quadrats & transects used obtain measures abundance
Abundance no
individuals of species w/in given space
Can measured several ways, depending on size species being counted & the
habitat, e.g.:
Frequency: likelihood of particular species occurring in quadrat, e.g. a
species occurs 15/30 quadrats frequency is 50%. Method useful where
species is hard count, gives quick idea species present & general
distribution. Does not provide info on density & detailed distributionspecies
Percentage cover: an estimate area w/in quadrat that particular plant
species covers. Useful where species is particularly abundant or diff
count. Advantage is data collected rapidly & individual plants not need
counted, less useful where organisms occur several overlapping layers.
Obtain results, necessary ensure sample size is large, many quadrats used &
mean all samples obtained. Larger the no
samples, more representative
community as whole will be results
7/30/2019 Unit 4.1 Biology
5/45
Page 5 of 45
1.3 Variation in population size
A population is group interbreeding individuals of same species in a habitat
Number individuals in population is population size
All populations are different organisms that live & interact together areknown as a community
Population Growth Curves
Usual pattern of growth for natural population has 3 phases:
1. Period of slow growth as the initially small number of individuals reproduce toslowly build up their number
2. Period of rapid growth where the ever-increasing number of individuals continueto reproduce. The population size doubles during each interval of time
3. Period when population growth declines until its size remains more or lessstable. The decline may be due to food supply limiting numbers or to increase
population. Graph therefore levels out with only cyclic fluctuations due to
variations in factors such as food supply or the population size of predators
Population Size
Imagine situation in which single algal cell, capable asexual reproduction,
placed newly created pond
Summer & so plenty light & temp water around 12oC, mineral nutrients been
added to water
These circumstances algal cell divides rapidly as all factors needed for growth
population present
Are no limiting factors
In time, things change:
1. Mineral ions used up as population becomes larger2. Population becomes so large that the algae at surface prevent light reaching
those at deeper levels
3. Other species introduced into pond, carried by animals or wind, and somethese species may use algae as food or compete for light or minerals
4. Winter brings lower temp & light intensity of shorter durationAs result population slows and may possibly diminish, ultimately population
likely reach relatively constant size
There many factors (both biotic & abiotic) will affect the ultimate size
Changes these factors will influence rate growth & final size population
SUMMARY: no population continues grow indefinitely as certain factors limitgrowth, e.g. availability food, light, water, oxygen & shelter & accumulation
toxic waste, disease & predators
Each population has max size can be sustained over relatively long period,
this is determined limiting factors
Various limiting factors affect size population are of 2 types:
1. Abiotic Factors: non-living part2. Biotic factors: activities living organisms
Abiotic Factors
Abiotic features that influence size population include:
Temperature: each species has different optimum temp at which bestsurvive. Further away from optimum small population be supported. In plants
7/30/2019 Unit 4.1 Biology
6/45
Page 6 of 45
enzymes work more slowly & metabolic rate reduced. Populations grow
more slowly. Temp above optimum, enzymes work less efficiently as
gradually undergo deterioration. AGAIN population grows more slowly
Warm-blooded animals, birds & mammals, maintain relatively constant body
temp regardless external temp. Might think population growth & size unaffected
temp. BUT further temp external environment gets from their optimum more
energy expend to maintain normal temp. Leaving less energy individual growth &
so mature more slowly & reproductive rate slows. Population size therefore
smaller
Light: as ultimate source energy for ecosystems, light basic necessity life.
Rate photosynthesis increases as light intensity increases. Greater rate
photosynthesis, the faster plants grow & more spores/seed produced. Their
population growth & size therefore potentially greater. In turn population
animals that feed on plants potentially larger
pH: this affects action enzymes. Each enzyme has optimum pH at which
operates most effectively. Population of organisms is larger whereappropriate pH exists & smaller, or non-existent where pH very different
from optimum
Water & Humidity: where water is scarce, populations are small & consistent
only of species that are well adapted living in dry conditions. Humidity affects
transpiration rates in plants & evaporation water from bodies of animals.
Again, in dry air conditions, populations species adapted to tolerate low
humidity will be larger than those with no such adaption.
7/30/2019 Unit 4.1 Biology
7/45
Page 7 of 45
1.4 Competition
When 2 or more individuals share any resources (e.g. light, food, space,
oxygen) that is insufficient satisfy all requirements fully = COMPETITION
Where competition arises between same species: intraspecific competitionWhere competition arises between different species: interspecific
competition
Intraspecific Competition
Intraspecific competition occurs when individuals same species compete w/
one and other for resources
It is availability of resources that determines size population
Greater availability, larger the population, lower the availability smaller the
population
Examples
Limpets competing for algae, main food. More algae available, largerlimpet population becomes
Oak trees competing resources, in large population small oak trees some
grow larger & restrict availability light, water & minerals to rest which die.
In time population be reduced relatively few large dominant oaks
Robins competing breeding territory. Female birds normally only
attracted males w/ breeding territories, each territory provides adequate
food for 1 family. When food scarce territories have become larger
provide enough food. Therefore fewer territories given area = fewer
breeding pairs = smaller population
Interspecific CompetitionOccurs when individuals ofdifferentspecies compete for resources
Where populations 2 species initially occupy same niece, 1 normally have
competitive advantage
Population this species gradually increase size while population other will
diminish
Conditions remain same, will lead complete removal one species
Known as competitive exclusion principle where 2 species competing
limited resources, one uses resources most effectively ultimately
eliminate other
No two species can occupy same niece indefinitely when resources limitingCormorant & Shags (sea birds) appear occupy same niece living &
nesting same type cliff face & eating fish from sea
Analysis food shows shags feed largely on sand eels & herring,
cormorants eat mostly flat fish, gobies & shrimps
Therefore occupy different niches
Show how factor influences size of population necessary like birth rate &
death rate of individuals to population
E.g. increase food supply not necessarily mean more individuals; just result
bigger individuals
Therefore important show how factor, such as change in food supply, affectsnumber individuals in population
7/30/2019 Unit 4.1 Biology
8/45
Page 8 of 45
E.g. decrease food supply lead individuals dying starvation, resulting in
reduction population
Increase food supply means more likely individuals survive & so increased
probability will produce offspring & population will increase
Effect therefore takes longer influence population
Application Effects Interspecific competition
Many cases we suspect competition is reason variations in population.
Practice difficult prove for number reasons:
Many other factors influence population size, such as abiotic factors
Casual like be established show that competition is cause of observed
correlation
Time lag in many cases competition & so population change may due
competition took place years earlier
Data natural population sizes hard to obtain & not always reliableHINT
Although population of 1 species may increase as another decrease, this does not
prove that this is due to direct competition between them. To be certain, it is
necessary to establish a casual like for the observed correlation
7/30/2019 Unit 4.1 Biology
9/45
Page 9 of 45
1.5 Predation
Predation occurs when one organism is consumed by another.
Effect of predator-prey relationship on population size
Predators eat their prey, thereby reducing the population of prey.With fewer prey available the predators are in greater competition with each
other for the prey that are left.
The predator population is reduced as some individuals are unable to obtain
enough prey for their survival.
With fewer predators left, less prey is eaten.
The prey population therefore increases
With more prey now available as food, the predator population in turn
increases.
7/30/2019 Unit 4.1 Biology
10/45
Page 10 of 45
1.6 Human populations
Human population size and growth rate
Most of our history has been kept in check by food availability, disease, predators
and climate. Two recent events have lead to an explosion in human population:The development of agriculture
The development of manufacturing and trade that created the industrial
revolution.
Factors affecting the growth and size of human populations
The basic factors that affect the growth rate of human populations are birth rate
and death rate.
Individual populations are further affected by migration, which occurs when
individuals move from one population to another. There are two types:
Immigration, where individuals join a population from outside.
Emigration, where individuals leave a population.
Population growth = (births + immigration) - (deaths + emigration)
Factors effecting birth rate
Economic conditions - countries with a low per capita income tend to have higher
birth rates.
Cultural and religious backgrounds - some countries encourage larger families and
some religions are opposed to birth control.
Social pressures and conditions - in some countries a large family improves social
standing.
Birth control - the extent to which contraception and abortion are used markedly
influences the birth rate
Political factors - governments influence birth rates through education and taxation
policies.
Birth rate = number of births per year x100
total population in the same year
Factors effecting death rate
Age profile - the greater the proportion of elderly people in a population, the higher
the death rate is likely to be.
Life expectancy at birth - the residents of economically developed countries
live longer than those of economically less developed countries.
Food supply - an adequate and balanced diet reduces death rate
Safe drinking water and effective sanitation - reduce death rate by reducing
the risk of contracting water-borne diseases such as cholera.
Medical care - access to healthcare and education reduces the death rate.
Natural disasters - the more prone a region is to a drought, famine of disease
the higher its death.
War - deaths during wars produce an immediate drop in population and a
longer term fall as a result of fewer fertile adults.
Death rate = number of deaths per year x100 total population in the same
year
Population structure
Age population pyramidThere are three typical types of population pyramids:
7/30/2019 Unit 4.1 Biology
11/45
Page 11 of 45
Stable population - where the birth rate and the death rate are in balance
and so there is noincrease of decrease in the population size.
Increasing population - where there is a high birth rate, giving a wider base to
the population pyramid (compared to a stable population) and fewer older
people, giving a narrower apex to the pyramid. This type of population is
typical of economically less developed countries.
Decreasing population - where there is a lower birth rate (narrower base of
the population pyramid) and a lower mortality rate leading to more elderly
people (wider apex to pyramid). This type of population occurs in certain
economically more developed countries, such as Japan.
Survival rates and life expectancy
A survival curve plots the number of people alive as a function of time. Typically it
plots the percentage of a population still alive at different ages but it can also be
used to plot the percentage of a population still alive following a particular event,
such as a medical operation or the onset of a disease.
The average life expectancy is the age at which 50 per cent of the individuals in aparticular population are still alive. It follows that life expectancy can be calculated
from a survival.
7/30/2019 Unit 4.1 Biology
12/45
Page 12 of 45
2. ATP
2.1 Energy and ATP
In most ecosystems the initial source of energy is the sun (light energy)Plants use solar energy for photosynthesis to make organic molecules, this
takes place inside the chlorophyll inside chloroplasts which are mainly found
in the spongy mesophyll of a leaf
Carbon dioxide is taken in through the stomata
Water is taken in through the roots
Light is absorbed by the green pigment chlorophyll
Oxygen is released into the atmosphere through the stomata
Glucose is transported in solution for use or is stored as starch
Energy is defined as the ability to do work
Takes a variety of different forms- light, heat, sound, electrical, magnetic,
mechanical, chemical and atomic
Can only be changed form one form to another, cannot be created ordestroyed
Measure in joules (J)
Organisms need energy for
Metabolism- reactions within living organisms
Movement e.g. circulation of blood and locomotion
Active transport- the net movement of particles against a concentration
gradient across a plasma membrane
Maintenance, repair and division of cells and organelles
Production of substances e.g. enzymes and hormones
Maintenance of body temperature in birds and mammals (endothermic
organisms)
The flow of energy through living organisms occurs in 3 stages: Light energy
from the sun is converted by plants into chemical energy during
photosynthesis, the chemical energy in the form of organic molecules is
converted into ATP during respiration in all cells, this is then used to perform
useful work
Adenosine triphosphate has 3 phosphate groups, a 5 carbon ribose and an
adenine group
7/30/2019 Unit 4.1 Biology
13/45
Page 13 of 45
The bonds between the phosphate groups are unstable and have a low
activation energy so they are easily broken, when they are they release
energy, it is the terminal phosphate that is removed.
This is known as a hydrolysis reaction
The reaction can also be reversed to made ATP from ADP through a
condensation reaction
The synthesis of ATP from ADP occurs in 3 different ways
1. Photophosphorylation- takes place in the chlorophyll containing plantcells during photosynthesis
2. Oxidative phosphorilation- occurs in the mitochondria of a plant andanimal cells during the process of electron transport
3. Substrate level phosphorilation- occurs in plant and animal cells whenphosphate groups are transferred from donor molecules to ADP to make
ATP
not a good store of energy due to unstable bonds, but good as an immediate
source of energy for same reason
Each ATP molecule releases less energy than each glucose molecule therefore
released in smaller more manageable amounts
The hydrolysis of ATP to ADP is a single reaction that releases immediateenergy whereas the breakdown of glucose is a long series of reactions
ATP is the source of energy for:
(1)Metabolic processes polysaccharide synthesis from monosaccharide,polypeptide synthesis from amino acids and DNA/RNA synthesis from
nucleotides
(2)Movement- muscle contraction(3)Active transport- ATP provides energy to change the shape of the
carrier proteins, allows molecules or ions to be moved against a
concentration gradient
(4)Secretion- needed to form the lysosomes
7/30/2019 Unit 4.1 Biology
14/45
Page 14 of 45
(5)Activation of molecules- lowers the activation energy of molecules sothey are more reactive so enzyme catalysed reactions can occur more
readily
3. Photosynthesis3.1 Overview of Photosynthesis
Site of photosynthesis - the leaf
Structure of the leaf
is adapted to bring together the three raw materials of photosynthesis. (Water,
carbon dioxide and light) and remove its products (oxygen and glucose). These
adaptations include.
A large surface area that collects as much sunlight as possible.
An arrangement of leaves on the plat that minimises overlapping and so
avoids the shadowing of one leaf by another.
Thin, as most light is absorbed in the first few millimetres of the leaf and the
diffusion distance is thus kept short.
A transparent cuticle and epidermis that let light through to the
photosynthetic mesophyll cells beneath.
Long narrow, upper mesophyll cells packed with chloroplasts that collect
sunlight.
Numerous stomata for gaseous exchangeStomata that open and close in response to changes in light intensity
Many air spaces in the lower mesophyll layer to allow diffusion of CO2 and
oxygen.
A network of xylem that brings water to the leaf cells and phloem that
carries away the sugars produced in photosynthesis
Outline of photosynthesis
Capturing of light energy - by chloroplast pigments such as chlorophyll
The light dependent reaction- in which light energy is converted into
chemical energy. During the process an electron flow is created by the effect
7/30/2019 Unit 4.1 Biology
15/45
Page 15 of 45
of light on chlorophyll and this causes water to split (photolysis) into protons,
electrons and oxygen. The products are reduced NADP, ATP and oxygen.
The light-independent reaction - in which these protons (hydrogen ions) are
used to reduce carbon dioxide to produce sugars and other organic
molecules.
Structure and role of Chloroplasts in photosynthesis
Photosynthesis takes place inside the chloroplasts
They are surrounded by a double membrane
Inside the chloroplast membrane there are 2 distinct regions:
- The grana- stacks of thylokoids where the light-dependent reaction
takes place, contains the chlorophyll and can have tubular like structures
to join them together called inter-granal lamellae
- The stroma- fluid filled matrix where the light independent stage takes
place, contain starch grains
7/30/2019 Unit 4.1 Biology
16/45
Page 16 of 45
3.2 The Light- dependent reaction
Requires light
Requires water
Requires photosynthetic pigmentsOccurs in the thylokoids
Light strikes chlorophyll and electrons are excited to a higher energy level
where they are accepted by an electron carrier
Photolysis occurs
Electrons pass down the electron transfer chain to NADP firming ATP
(Photophosphorylation- process by which ATP is made during the light
reaction)
Products are NADPH, ATP and O2
Oxygen produced comes from water
NAPDH and ATP are then using in the Calvin cycle (light independent reaction)
7/30/2019 Unit 4.1 Biology
17/45
Page 17 of 45
3.3 The Light Independent ReactionDoes not require light (can occur in both light and dark)
Occurs in the stroma of the chloroplast
Carbon dioxide from the atmosphere diffuses into the leaf through the
stomata and dissolves in water around the walls of the mesophyll cells. It
then diffuses into the plasma membrane, cytoplasm and chloroplast
membranes into the stoma of the chloroplastIn the stroma, the co2 combines with the 5-carbon RuBP using the enzyme
RuBisCo
Combination produces 2 molecules of glycerate 3-phosphate
ATP and NADPH from light dependent reaction are used to reduce the
activated glycerate 3-phosphate to triose phosphate
The NADP is re-formed and goes back to light dependent reaction
Some triose phosphate are converted to useful organic substrates such as
glucose
Most are used to regenerate RuBP using ATP from the light dependent
reaction
7/30/2019 Unit 4.1 Biology
18/45
Page 18 of 45
3.4 Factors Affecting PhotosynthesisLimiting Factors
The law of limiting factors can be expressed as:
At any given moment, the rate of a physiological process is limited by the factor
that is at its least favourable value.Limiting factors of photosynthesis include light intensity, carbon dioxide
concentration and temperature.
Light intensity
No light - no photosynthesis. The light phase does not take place.
Increasing the light intensity to value A causes photosynthesis to increase.
The more light the greater the light phase and the greater the production of
ATP to the Dark Phase.
At light intensity A the rate of photosynthesis reaches its maximum and levels
off. Some factor other than light intensity is limiting the rate ofphotosynthesis: it may be low temperature, low carbon dioxide, low
chlorophyll content or the enzyme system is deficient (enzymes at maximum
turnover number).
Light intensity A is known as the 'saturation point' - the value beyond which
light intensity is not a limiting factor.
The rate of photosynthesis remains constant at maximum beyond light
intensity A. The Increase in light intensity has no effect on the new limiting
factor so photosynthesis stays the same.
Carbon dioxide
concentration
No carbon dioxide - no photosynthesis.
Increasing the carbon dioxide concentration to value A causes photosynthesis
to increase. The greater the supply of CO2, the faster the rate of enzyme
activity
At A the rate of photosynthesis reaches its maximum and levels off. Some
factor other than CO2 is limiting the rate of photosynthesis: it may be low
temperature, low light intensity
7/30/2019 Unit 4.1 Biology
19/45
Page 19 of 45
The rate of photosynthesis remains constant at maximum beyond A. Increase
in CO2 has no effect on the new limiting factor so photosynthesis stays the
same.
Temperature
At 0C the rate of photosynthesis is low. Enzyme activity is low.
Photosynthesis is an enzyme-controlled process.
Increasing the temperature to 30C increases the rate of photosynthesis.
Enzyme activity increases.
Maximum photosynthesis at 30C. Enzyme activity at it maximum - maximum
collision frequency between native enzymes and substrates.
Photosynthesis declines beyond 30C. Enzyme activity slowing due to
denaturing of enzymes.
No photosynthesis at 50C. No enzyme activity - enzymes are denatured.
7/30/2019 Unit 4.1 Biology
20/45
Page 20 of 45
4. Respiration4.1 Glycolysis
The splitting of the 6C glucose molecule into two 3C pyruvate molecules.Occurs in the cytoplasm of the cells. Is an anaerobic process.
Net production of 2 ATP molecules
2 molecules of pyruvate produces
2 molecules of reduced NAD produced (then used in the electron transport
chain)Takes place in cytoplasm as glucose cannot enter the mitochondria due to
size and enzymes used in the breakdown of glucose are found in the
cytoplasm
7/30/2019 Unit 4.1 Biology
21/45
Page 21 of 45
4.2 Link reaction and Krebs cycleThe link reaction
No energy is stored or removed in this reaction
Occurs in the matrix of the mitochondria
Pyruvate is converted into acytlycoenzyme A in this reaction
This occurs twice so... 2 molecules of Acytlycoenzyme A, 2 reduced NAD and
2 molecules of carbon dioxide are produced
The Krebs cycle
Occurs in the matrix of the mitochondria
Provides a continuous support of electrons to fuel the electron transport
chain
Produces a SMALL amount of ATP
7/30/2019 Unit 4.1 Biology
22/45
Page 22 of 45
Occurs twice due to 2 acytylcoenzyme A molecules
6 molecules of NADH produced (reduced NAD)
2 molecules of FADH2 produced (reduced FAD)
2 molecules of ATP produced
4 molecules of carbon dioxide produced
The NAD works with dehydrogenase enzymes that catalyse the removal of
hydrogen ions and transfers then to other molecules such as hydrogen
carriers involved in oxidative phosphorilation
7/30/2019 Unit 4.1 Biology
23/45
Page 23 of 45
4.3 The electron transport chainEnergy from hydrogen atoms removed from compounds can be used to make
ATP
Energy carried by electrons, from reduced coenzymes (reduced FAD and
NAD) is used to make ATP, involves electron transport chain and
chemiosmosis.
Occurs on the cristae of mitochondria. Hydrogen from glycolysis is used.
Reduced NAD and FAD are oxidised, releasing Hydrogen atoms. The H atoms
are split into H+
and e-.
The regenerated NAD and FAD are reused in Krebs cycle.
The electrons move along the electron transport chain (made up of 3
electron carriers), in a series of oxidation-reduction reactions, losing energy
at each stage.
Some of this energy is used to combine an inorganic phosphate with ADP to
make ATP. The remaining energy is released as heat.
The protons accumulate in the space between the 2 mitochondrial
membranes before they diffuse back into the matrix of the mitochondria
through protein channels.
At the end of the chain, the electrons combine with these protons and
oxygen to form H2O.
Oxygen is the final acceptor of electrons in the electron transport chain.
Without oxygen acting as the final acceptor of electrons, the H
+
ions andelectrons would back up along the chain and respiration would come to a
halt.
7/30/2019 Unit 4.1 Biology
24/45
Page 24 of 45
4.4 Anaerobic respirationOnly Glycolysis can occur in the absence of oxygen
There are 2 forms of anaerobic respiration: alcoholic fermentation in plants
and lactate fermentation in animals
The production of ethanol if exploited in the brewing process
Pyruvate is converted to ethanal by decarboxillationn reduced NAD is thenoxidised by the ethanal to give ethanol
In animals, lactate is formed by the oxidation of reduced NAD by pyruvate
The production of lactate regenerate the NAD and so Glycolysis can continue,
a small amount of ATP is still produced to keep biological processes going
An oxygen dept is created, lactate broken back down by oxygen at end
7/30/2019 Unit 4.1 Biology
25/45
Page 25 of 45
5. Energy and Ecosystems
5.1 Food chains and Food websOrganisms can be divided into 3 groups depending on how they obtain
their energyProducers- Photosynthetic organisms that manufacture organic
substances using light energy, water and co2 by photosynthesis
Consumers- Obtain their energy by consuming other organisms. Primary
consumers feed directly of plants (producers) these are then consumed
by secondary consumers and then tertiary consumers (usually predators
can be scavengers or parasites)
Decomposers- feed off dead organic matter to obtain energy which is
trapped inside them. Majority of them fungi and bacteria (decomposers)
and to a lesser extent by animals such as earth worms (detritivors)
Food chains
Describes a feeding relationship by showing the transfer of energy
between producers and following consumers.
Each stage is referred to as a trophic level
Arrows represent the direction of energy flow
Food webs
Most organisms in a community do not just feed upon one animal, andone animal can be fed upon by many other animals, a food web shows
SOME of the feeding relationships within the community
Not all of the relationships can be shown as it would be too complex
7/30/2019 Unit 4.1 Biology
26/45
Page 26 of 45
5.2 Energy Transfer between Trophic LevelsMost energy is not converted by plants because, most of the suns light is
reflected back into the atmosphere by clouds, not all wavelengths can be
absorbed, light may not fall on the chlorophyll molecules and a limiting factor
may stop the rate of photosynthesis e.g. low co2 levels
The rate at which plants store energy is called net production:
Net production= gross production respiratory loss
Low % of energy transferred at each stage of the food chain is due to:
1. Some of the organism is not eaten2. Some parts cannot be digested so lost in faeces3. Lost in excretory materials (urine)4. Lost as heat, maintaining body temperature5. Movement during hunting etc
Most food chains dont have more then 4/5 trophic levels due to so much
energy lost, insufficient energy to support more
Total mass of organisms is less at higher trophic levels
Total amount of energy stored is less at each trophic level
Energy transfer (%) between each trophic level can be calculated by:
7/30/2019 Unit 4.1 Biology
27/45
Page 27 of 45
5.3 Ecological PyramidsPyramids are drawn to show changes in number, biomass or energy
Pyramid of number
Shows the number of organisms at each trophic level
The more the wider the section of pyramid, the width of the block is
proportional to the number of organisms present at each level
Disadvantage: the range of numbers can be large
Pyramid of biomass
The biomass of all living organisms at each trophic level can be calculated by:
Biomass = the number of individuals x mass of each individual
Live mass can be used but gives unreliable results
Not always practical/desirable to find the dry mass (mass of whales)
Seasonal differences are not present and animal must be killed to get dry
mass
Units for biomass
Pyramid of energy
Shows the flow of energy through each trophic level of an ecosystem during a
fixed period of time
Always a fixed pyramid shape
Units for energy
7/30/2019 Unit 4.1 Biology
28/45
Page 28 of 45
5.4 Agricultural EcosystemsMade up of largely domesticated animals and plants used to produce food
for mankind
Tries to ensure that as much of the available energy from the sun is
transferred to humans
Increases the productivity of the human food chain
Net productivity = gross productivity respiratory loss
Efficiency affected by the efficiency of the crop at photosynthesising and the
area of the ground covered by the leaves of the crop
Comparison of natural and agricultural ecosystems:
Natural Ecosystem Agricultural Ecosystem
Solar energy only Solar energy plus energy from food and
fossil fuels
Lower productivity Higher productivity
More species diversity Less species diversity
More genetic diversity within a species Less genetic diversity within a species
Nutrients are recycled naturally within
an ecosystem
Natural recycling is more limited and
supplemented by the addition of
artificial fertilisers
Populations are controlled by natural
means (competition, climate)
Populations controlled by both natural
and use of pesticides and cultivation
Natural climax community Artificial community prevented from
reaching its climax
Energy input
To prevent an agricultural ecosystem from developing they remove all other
species from a crop apart from the one they are growing
To remove or suppress unwanted species requires an additional input of
energy which comes in 2 forms, food for the farmers and fossil fuels for the
machines.
Productivity
Additional energy input increases productivity, controlling photosynthesis
within a greenhouse would also do this as maximum photosynthesis can be
achieved (CO2 levels controlled, temp controlled, water controlled, minerals
controlled ect)
7/30/2019 Unit 4.1 Biology
29/45
Page 29 of 45
5.5 Chemical and Biological Control of
Agricultural PestsA pest is an organism that competes with humans for food or space,
pesticides are poisonous chemicals used to kill pestsA pesticide should:
1. Be specific- harmless to humans and other organisms2. Biodegrade- so it will break down into harmless substances in the
soil but also needs to be chemically stable so has a long shell life
3. Be cost effective4. Not accumulate- does not pass along food chain and harm other
species higher up the food chain
Biological control
Controlling a pest by using its natural predator or parasites of the pestAim to control not eradicate- could be counterproductive, not enough pest
for predator pest can increase in number again as predator dies
Disadvantages:
1. Do not act as quickly, so could be time between introductionand significant control
2. Control may become a pest itself
Biological Control Chemical Pesticides
Very Specific Always have some effect on other
species
Once introduced, control organism
reproduces itself
Must be reapplied very
expensive
Pests do not become resistant Pests can develop genetic
resistance so new pesticides
have to be developed
Risk that control organism becomesa pest as pest population is
reduced control feeds on crops
Risk of accumulation in species orpolluting nearby rivers
7/30/2019 Unit 4.1 Biology
30/45
Page 30 of 45
Integrated pest control systems
Involves using all methods of pest control (chemical, biological and natural)
to CONTROL the amount of pestInvolves:
1. Choose a plant/animal that is immune as possible to the pest2. Manage the environment to provide habitats suitable for
predators
3. Monitor the crops for early signs of pests4. Remove pests manually is exceeds acceptable amount5. Use biological control if necessary and available6. Use pesticides as a last resort
Such systems can be effective with minimum impact on the environment
Pests reduce productivity in agricultural ecosystems (weeds compete with
crop plants for water, minerals etc, insect can damage leaves of crops needed
for photosynthesis/ in direct competition eating the crops themselves)
Monoculture- a large area of land in which only 1 crop is grown, this enables
pests to spread rapidly, pests may cause disease, animals become unfit for
human consumption as do not grow rapidly which will lead to reduced
productivity
The effect of productivity is to balance the cost of pest control with the
benefits it brings the problem is that the farmer has to balance the demand
for cheap food while still making a living and the conservation of natural
habitats so we can have food in the future.
7/30/2019 Unit 4.1 Biology
31/45
Page 31 of 45
5.6 Intensive Rearing of Domestic LivestockDesigned to produce the maximum yield of meat, eggs and milk at the lowest
cost possible
They do this by using methods to convert the smallest amount of food energy
into the greatest amount of animal mass
They do this my minimising there energy loss by keeping them in confined
spaces to increase energy conversion rate, it does this because:
1. Movement is restricted so less energy is used in muscle contraction2. Environment can be kept warm so not used to maintain body heat3. Feeding can be controlled for maximum growth4. Predators are excluded so no loss to other organisms in food web
Other means include selective breeding of animals to produce varieties that
are more efficient at converting food into body mass and using hormones to
increase growth rates
Main features of intensive rearing are:
1. Efficient energy conversion2. Low cost3. Worst tasting food4. Less land is used leaving more natural habitats5. High density animal population more at risk to spread of disease but
easier to isolate if this happens
6.
Animals are regularly given antibiotics to prevent spread of disease7. Over use of drugs lead to antibiotic resistance and can also alter the
flavour of food or pass into the foods then into humans affecting their
health
8. Maintains a higher level of animal welfare but can lead to aggressivebehaviour from being in unnatural conditions
9. Produces large concentrations of waste in a small area rivers andground waters may become polluted, pollutant gases can be
dangerous and smell, larger have own waste facilities
10.Reduced genetic diversity due to selective breeding11.High energy-conservation rates due to use of fossil fuels, CO2 levels
released increased global warming
Economic and environmental issues
7/30/2019 Unit 4.1 Biology
32/45
Page 32 of 45
Economic- desire for cheap food conflicts with the conservation of the
environment
Environment- reduced species diversity due to:
1. removal of hedges and woodland2. creation of monocultures3. filling in ponds and draining marshes and other wetlands4. over-grazing of land preventing regeneration of woodland
Indirect effect to reduce species diversity-
1. use of pesticides and inorganic fertilisers2. escape of farm wastes into water courses3. absence of crop rotation leading to poor soil structure
Conservation techniques include:
1. maintaining existing hedgerows2. planting hedges as field boundaries3. maintaining existing ponds and where possible creating
new ones
4. leaving wet corners of fields rather than draining them5. planting native trees in low species diversity areas6. reduce use of pesticides using biological control where
possible
7. using organic rather than inorganic fertilisers8. using crop rotation with a nitrogen fixing crop9. creating natural meadows and using hay for silage10.leaving the cutting of verges and field edges until after
flowering and seeds have dispersed
7/30/2019 Unit 4.1 Biology
33/45
Page 33 of 45
6. Nutrient Cycles
6.1 The carbon cycle
Shows how carbon moves through living organisms and the non-living
environment.
1. Carbon (Co2) is absorbed by plants by photosynthesis, becomingcarbon compounds in plants.
2. Carbon is passed along the food chain through consumption.3. When organisms die, carbon compounds are digested by
microorganisms and returned to the air as they carry out
respiration.
4. If any dead organic matter ends in places where there arent anydecomposers, their carbon compounds can be turned into fossil
fuels. The carbon in these fossil fuels is released when they are
burnt for fuel.
CO2 concentration falls during the day as it is removed by plants as they carry
out photosynthesis. It then increases at night as its no longer being removed
by photosynthesis but all organisms continue to respire and add CO2.
CO2 concentration decreases in the summer in some climates as it is when
light intensity is greatest more photosynthesis can occur. More CO is
removed as more plants are photosynthesising.
7/30/2019 Unit 4.1 Biology
34/45
Page 34 of 45
The Sun gives heat to
Earth
and the heat
reflects from the
surface into space
but the greenhouses
gases stops the heat
from reflecting away
so the heat bounces
back in.
6.2 The greenhouse effect and global
warmingThe greenhouse effect is a natural process that occurs all the time without it
the average temperature on earth would be -18 degrees Celsius, the gasesthat surround the earth in the atmosphere trap the heat from the sun
keeping it warm at 17 degrees Celsius
The most important greenhouse gas is CO2 because it remains in
the atmosphere for much longer than other
greenhouse gases, 50-70% of global warming is due
to CO2.
Human activities increases the amount of carbon
dioxide in the atmosphere enhancing the greenhouse
effectMethane is also a greenhouse gas which is produced
when decomposers break down the dead remains of
organisms or then microorganisms in the intestines of
primary consumers digest the food that has been
eaten
Global warming is where the mean temperature of the Earth has increased
Consequences of global warming:
1. Melting of polar ice caps which could cause theextinction of some plants and animals and also a rise in
sea level
2. Rise in sea level could cause flooding, salt water wouldextend further up rivers making cultivation of crops
difficult
3. Higher temperatures and less rainfall lead to failure ofcrop growth in some areas, distribution of wild plants
change and so animal distribution would change
4. Greater rainfall and storms in some areas cause changein distribution of plants and animals
5. Life-cycles and populations of insect pests would changeas they adapt, tropical diseases could then spread
further up north as the insects migrate
Could also benefit as increased rainfall would fill reservoirs, increased
temperature grow crops in places where originally too cold, rate of
photosynthesis increase, may be possible to harvest twice a year
7/30/2019 Unit 4.1 Biology
35/45
Page 35 of 45
6.3 The Nitrogen CyclePlants and animals need nitrogen to make proteins and nucleic acids
(DNA/RNA)
Although the atmosphere has 78%, can't use it in that form, need saprobiotic
bacteria to convert it into nitrogen compounds first.Nitrogen Cycle includes:
1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification.
1. Nitrogen Fixation (Can also happen when lightning passes through the
atmosphere)
Nitrogen gas in the atmosphere is turned to ammonia by nitrogen-fixing
bacteria
Free-living nitrogen fixing bacteria reduce gas to ammonia which is then usedto manufacture amino acids. Nitrogen rich compounds released when they
decay
Mutualistic bacteria e.g. Rhizobium is found in root nodules of leguminous
plants. e.g. peas, beans
They form a mutualistic relationship with the plants- they provide the plant
with nitrogen compounds and the plant provides them with carbohydrates
2. Ammonification
Nitrogen compounds from dead organisms are turned into ammonium
compounds by decomposers
Animal waste also contains compounds and are turned into ammonium3. Nitrification
This is the conversion of ammonium ions to nitrate ions by nitrifying bacteria,
to be used by the plant.
Firstly nitrifying bacteria oxidise ammonium ions to nitrite ions (N02-)
Secondly other nitrifying bacteria oxidise nitrite ions to nitrate ions (N03-)
The bacteria require oxygen, so soil with lots of air spaces by ploughing and
good drainage so air spaces are not filled with water is needed.
4. Denitrification
Nitrates in the soil are converted into nitrogen gas by denitrifying bacteria
they use nitrates in the soil to carry out respiration and produce nitrogen gas
Happens under anaerobic conditions - no oxygen e.g. waterlogged soil.
Parts of the cycle can be carried out artificially on an industrial scale. Haber
process produces ammonia from atmospheric nitrogen to make fertilisers.
7/30/2019 Unit 4.1 Biology
36/45
Page 36 of 45
6.4 Use of Natural and Artificial FertilisersAll plants need mineral ions, especially nitrogen
Intensive food production makes large demands on soil because mineral ions
are continually being taken up by crops grown there
In natural ecosystems the minerals are returned when the plant is broken
down my microorganisms on its death
In agricultural the plants are harvested and transported for consumption and
are rarely returned to the same area, making it necessary to replenish these
minerals or it will become a limiting factor to the plants growth
To do this 2 different types of fertilisers are added:
1. Natural (organic) fertilisers- consist of dead and decayingplants and animals as well as animal waste (manure and bone
meal)
2. Artificial (inorganic) fertilisers- mined from rocks and depositsthen converted into different forms and blended to give the
appropriate amount of mineral needed for the land (NKP
fertilisers)
Plants need these minerals for grown e.g. nitrogen to make proteins and
DNA, when available plants are more likely to develop earlier, grow taller and
have a greener leaf area, this increases rate of photosynthesis and so
increases productivity
6.5 Environmental consequences of using
nitrogen fertilisersReduced species diversity can occur- nitrogen rich soils favour the growth of
grasses, nettles and other rapidly growing species which causes more
competition for other species which then die out and so reduces species
diversity.
Leaching- when water soluble compounds in soil are washed away, e.g. byrain / irrigation systems, into nearby ponds and lakes.
If nitrogen fertiliser is leached it can cause eutrophication:
1. Nitrates leached from fertilised fields stimulate growth of algae in ponds
etc.
2. Large amounts of algae block light from reaching plants below
3. Plants die as they are unable to photosynthesise
4. Bacteria feed on the dead plant matter
5. Increased numbers of bacteria reduce the oxygen concentration in water
by carrying out aerobic respiration
6. Fish etc. die as there isn't enough dissolved oxygen
7/30/2019 Unit 4.1 Biology
37/45
Page 37 of 45
Organic manures, animal slurry, human sewage, ploughing old grass land and
natural leaching can also cause eutrophication but artificial is main cause.
7. Ecological Succession
7.1SuccessionSuccession --> term to describe changes taking place over time
1st Step is --> colonisation of an inhospitable environment by organisms -->
called pioneer species --> their features suit them because they:
1. rapidly germinate seeds2. reach isolated areas easily3. have the ability to photosynthesise4. have the ability to fix nitrogen5.
have tolerance to extreme conditions
Succession takes place in a series of stages --> at each stage certain species
can be identified which change the environment --> therefore the
environment becomes more suitable for other species --> these other species
out compete current species --> this forms a new community
During any succession, common features are:
1. the non-living environment becomes less hostile which leads to -->2. greater number and variety of habitats which produce -->3. increased biodiversity which lead to -->4. more complex food webs5. increased biomass
7/30/2019 Unit 4.1 Biology
38/45
Page 38 of 45
7.2 Conservation of Habitats
Conservation is the management of the Earth's natural resources so that maximumuse of them can be made in the future.
Main reasons for conservation:
Ethical- other species have existed longer and so should be allowed to co-
exist
Economic- long term productivity is greater if ecosystems are maintained in
their natural balanced state
Cultural and aesthetic- Variety add interest to our every day lives
Ways to manage succession:
1. Animals left to graze on land, so larger plants can't establish themselves and
vegetation kept low
2. Managed fires are lit, after fires secondary succession will occur on the moorland,
so the pioneer species growing back will be the species that is being conserves e.g.
heather
7/30/2019 Unit 4.1 Biology
39/45
Page 39 of 45
8. Inheritance and Selection
8.1 Studying inheritance
Dominant Allele: allele that is always expressed in the phenotype.
Recessive Allele: allele that is expressed in the phenotype in the absence of a
dominant allele.
Co-dominance: both alleles are dominant and are expressed in the
phenotype.
Genotype: constitution of an organism comprising all the genes possessed by
an individual.
Phenotype: characteristics of an organism, often visible, resulting from the
genotype and the effects of the environment.Heterozygous: having two different alleles for a given gene.
Multiple Alleles: when a gene has more than 2 allelic forms
Homozygous: having two dominant/recessive alleles present for a given gene.
7/30/2019 Unit 4.1 Biology
40/45
Page 40 of 45
8.2 Monohybrid InheritanceRepresenting genetic crosses
Choose a single letter to represent each characteristicChoose the first letter of one of the contrasting features
Choose the letter in which the higher and lower case forms differ in shape as
well as size so they cannot be confused
Higher letter represents dominant gene, lower for recessive gene
State the gametes produces by each parent, indicating meiosis
Use a punnet square to show the result of the random crossing of gametes,
label male and female
State the phenotypes of each different genotype and indicate the number of
each type. Always write the higher case letter firstInheritance of pod colour in peas
Another example of a monohybrid cross is a person with Huntington disease, this is a
dominant gene: coded for by protein Huntington
7/30/2019 Unit 4.1 Biology
41/45
Page 41 of 45
A similar cross can be done for cystic fibrosis which is the recessive gene coded for
by the protein CFTR
8.3 Sex Inheritance and Sex LinkageSex is determined by chromosomes rather than genes
As females on have x and males have either x or y males determine the sex of
a child (xx for female, xy for male)
Sex Linkage- Haemophilia
A gene that is carried on the x or y chromosome is said to be sex linked
Carried on the X chromosome, males either have the disease or dont but
women can be carriers
Males can therefore only obtain a disease from their mothers as the gene is
not carried on the y chromosome they inherit from their fathers but the x
chromosome from the mother, if she does not have the disease but the son
does then she would be a carrier and so heterozygous for the condition
7/30/2019 Unit 4.1 Biology
42/45
Page 42 of 45
8.4 Co-dominance and Multiple AllelesCo-dominance occurs when both alleles are dominant so both are expressed
within the phenotype
E.g. a plant that codes for red and white flowers, both are dominant so the
colours would be:
1. Homozygous for red = red2. Homozygous for white = white3. Heterozygous = pink
C= colour and then R= red and W= white:
Multiple alleles
Inheritance of the ABO blood group is an example of this
3 genes carried on the I (immunoglobulin gene), which lead to the different
production of different antigens on the surface of red blood cells
7/30/2019 Unit 4.1 Biology
43/45
Page 43 of 45
8.5 Allelic Frequency and Population GeneticsGene pool- all of the genes of all the individuals of a population at any one
time
Allelic frequency- the number of times a gene appears within the gene pool
Example:
Cystic fibrosis- C- dominant allele which codes for normal production of
mucus
c- Recessive allele which codes for thinker production of mucus and cystic
fibrosis
Pairs of alleles for cystic fibrosis have 3 different combinations:
1. CC- heterozygous dominant2. cc- Homozygous recessive3. Cc / cC- Heterozygous
The total number of alleles is said to be 1.0, in a population if no one had
cystic fibrosis then the frequency of the gene c would be 0.0 whereas the
frequency of the gene C would be 1.0. If everyone was heterozygous then the
frequency of C or c would be 0.5
The Hardy-Weinberg Principle
A mathematical equation can be used to calculate the frequency of alleles
Principle states that the proportion of dominant and recessive alleles stays
the same from generation to generation if:(1)No mutations arise(2)The population is isolated(3)There is no selection(4)The population is large(5)Mating within the population is random
Let the frequency of allele A = p and the frequency of allele a = q
P + q = 1.0
4 possible arrangements (AA, Aa, aA and aa) the frequency of all 4 added
together = 1.0Therefore:
If 1 in 25000 people have a (recessive) then aa= 1/25000 therefore q squared
= 0.00004
If p + q = 1.0 and q is then equal to 0.00063, p = 0.9937
To calculate heterozygous you then use 2pq = (2 x 0.9937 x 0.0063) = 0.0125
So 125 in 10 000 carry the allele for the character
7/30/2019 Unit 4.1 Biology
44/45
Page 44 of 45
8.6 SelectionReproductive success and allele frequency
All organisms produce more offspring then can be supported
Despite overproduction most population remain constant
There is competition between members of a species to survive
Within the population thee will be a wide variety of alleles in the gene pool
Some will possess the genes which make them better able to survive
These individuals will obtain he available resources and grow more rapidly as
a result will have more successful breeding and offspring
The more successful then pass on their genes
The ones with advantageous alleles will then compete better and will
reproduce
The number of individuals with the advantageous alleles will increase
Over time, the frequency of the allele increases
The advantages will vary due to environment
Types of selection
Selection is the process in which organisms that are better adapted will
survive and breed
Different environmental conditions favour different characteristics within a
population
Selection that favours individuals in one direction from the mean population
is called directional selectionSelection that favours the mean population is called stabilising selection
Directional selection
Environmental conditions change so phenotype needed to survive changes
New individuals become more adapted to survive at one end of the spectrum
and so over time the mean changes to suit the new phenotype
This results in phenotypes at one extreme being favoured and the other
being favoured against
Stabilising selection
Environmental conditions remain the sameMean are favoured, extremes are favoured against
Eliminates extremes
7/30/2019 Unit 4.1 Biology
45/45
8.7 SpeciationSpeciation is the evolution of new species from an existing one
Species- a group of individuals with similar genes that can produce fertile
offspring
If 2 populations become isolated in some way, there is no longer a flow of
alleles, the environment with each group may differ and so one type of allele
frequency may change in time the gene pools will become so different that
they are no longer the same species
Geographical isolation:
Occurs when a physical barrier prevents 2 populations from breeding with
one another e.g. rivers, mountains and deserts
Example in a forest
Continued adaptationsLeads to evolution
Of new species Y and Z