Download A2 level Biology Revision Notes - A

A2 level Biology Revision Notes
Unit 4- Populations and the Environment
How to use this revision booklet:
1. Read through the section in your notes and the text book, before
completing the revision booklet. Complete the definitions and cloze
sections – come in and talk through each section to check it.
2. Each diagram has space around it for annotations: use it!
3. To embed information in your long-term memory, you must revisit the
material. Use each page as an aide-memoire to go over the next day and
then again a few days later. Keep this up and it will pay off.
4. Use the revision booklet, together with your notes and the textbook, to
produce mind maps: don’t just copy – you must interact with the topic
and change it in some way.
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1. Populations ........................................................................... 3
1.1 Populations and ecosystems .................................................. 3
1.2 Investigating populations ..................................................... 3
1.3 Variation in population size .................................................. 5
1.4 Competition ...................................................................... 7
1.5 Predation ......................................................................... 9
1.6 Human populations ...........................................................10
2. ATP ....................................................................................12
2.1 Energy and ATP ................................................................12
3. Photosynthesis ......................................................................14
3.1 Overview of Photosynthesis .................................................14
3.2 The Light- dependent reaction ..............................................16
3.3 The Light Independent Reaction ............................................17
3.4 Factors Affecting Photosynthesis ...........................................18
4. Respiration...........................................................................20
4.1 Glycolysis ........................................................................20
4.2 Link reaction and Krebs cycle ...............................................21
4.3 The electron transport chain ................................................23
4.4 Anaerobic respiration ........................................................24
5. Energy and Ecosystems ............................................................25
5.1 Food chains and Food webs ..................................................25
5.2 Energy Transfer between Trophic Levels .................................26
5.3 Ecological Pyramids ...........................................................27
5.4 Agricultural Ecosystems ......................................................28
5.5 Chemical and Biological Control of Agricultural Pests .................29
5.6 Intensive Rearing of Domestic Livestock ..................................31
6. Nutrient Cycles ......................................................................33
6.1 The carbon cycle ...............................................................33
6.2 The greenhouse effect and global warming...............................34
6.3 The Nitrogen Cycle .............................................................35
6.4 Use of Natural and Artificial Fertilisers....................................36
6.5 Environmental consequences of using nitrogen fertilisers ............37
7. Ecological Succession...............................................................37
Succession ...........................................................................37
7.2 Conservation of Habitats .....................................................39
8. Inheritance and Selection .........................................................40
8.1 Studying inheritance ..........................................................40
8.2 Monohybrid Inheritance .....................................................41
8.3 Sex Inheritance and Sex Linkage ............................................42
8.4 Co-dominance and Multiple Alleles ........................................43
8.5 Allelic Frequency and Population Genetics ...............................44
8.6 Selection .........................................................................45
8.7 Speciation .......................................................................46
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1. Populations
1.1 Populations and ecosystems: definitions
Ecosystem- _________________________________________________________________
Population- _________________________________________________________________
Community- ________________________________________________________________
Habitat -____________________________________________________________________
Ecological niche- _____________________________________________________________
___________________________________________________________________________
1.2 Investigating populations
To study habitat often necessary count no individuals of species in given space.
This known as a_____________.
Virtually impossible identify & count every organism.
To 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 v________.
No sampling techniques used in study of habitat, these include:
R______ sampling using frame or point quadrats.
S__________ sampling along transects.
Quadrats
Three factors to consider when using quadrats:
Size of quadrat to use: ________________________________________________________
________________________________________________________________
________________________________________________________________
No of sample quadrats to record within the study area: _____________________________
________________________________________________________________
________________________________________________________________
Position of each quadrat w/in study area: ________________________________________
________________________________________________________________
________________________________________________________________
Random Sampling
Important sampling random avoid any b___ in collecting data, avoiding bias ensures data
obtained v_____
A good method of random sampling is to:
1. Lay out two long tape measures @ r_____ angles, along 2 sides of study area,
2. Obtain series of coordinates by using random no taken from table or generated by
computer or calculator,
3. Place quadrat at intersection of each pair c____________ & record s______ w/in it.
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Systematic sampling along transects
Sometimes more informative to measure abundance & distribution of species in
s_________ rather than r_____ manner.
Particularly important where some form of t_________ in communities plants & animals
take place.
L___ t_______ comprises string or tape stretched across ground in straight line, any
organism over which line passes is recorded.
B___ t_______ is strip, usually meter wide, marked putting second line parallel to first,
species occurring w/in belt between lines recorded.
Size of quadrat and approach taken depends on size of habitat and purpose of survey.
Measuring abundance
Random sampling w/ quadrats & transects used to obtain measures of abundance.
Abundance: _________________________________________________________________
Can be measured several ways, depending on size species being counted & the habitat, e.g.:
Frequency: ______________________________________________________________
Method useful where species is hard to count, gives quick idea species present &
general distribution.
Does not provide info on density & detailed distribution species.
Percentage cover: _________________________________________________________
Useful where species is particularly abundant or difficult to count.
Advantage is data collected rapidly & individual plants do not need to be counted,
less useful where organisms occur several overlapping layers.
Results: necessary to ensure sample size is l____, many quadrats used & mean of samples
obtained. Larger the no samples, results will be more r_____________ of the community.
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1.3 Variation in population size
Population: _________________________________________________________________
Number of individuals in population is population size.
All populations are different organisms that live & interact together are known as a
c_________.
Population Growth Curves
Usual pattern of growth for natural population has 3 phases:
1. Period of s___ g_____ as the initially small number of individuals reproduce to slowly build up
their number
2. Period of r____ g_____ where the ever-increasing number of individuals continue to reproduce.
The population size doubles during each interval of time
3. Period when population growth d_______ until its size remains more or less s_____. The
decline may be due to food supply limiting numbers or to increased population. Graph
therefore levels out with only c_____ f____________ due to variations in factors such as food
supply or the size of the predator population.
Population Size
Imagine situation in which single algal cell, capable asexual reproduction, is placed in a
newly created pond:
Summer & so plenty light & temp of water around 12oC, mineral nutrients being added
to water,
In these circumstances algal cell divides rapidly as all factors needed for growth of
population present,
There are no l_______ f_______.
In time, things change:
1. M_______ i____ used up as population becomes larger,
2. 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 some these species
may use algae as food or compete for light or minerals,
4. Winter brings l_____ t__________ & l_____ i_________ during days of shorter duration.
As result population slows and may possibly diminish, ultimately population likely reach
relatively c________ size.
There many factors (both b_______ & a________) will affect the ultimate size.
Changes these factors will influence rate growth & final size population.
SUMMARY: no population continues grow indefinitely as certain factors limit growth, e.g.
availability of f_____, l______ i_________, w_____, o_______ & shelter & accumulation of toxic
w______, d________ & predators
Each population has max size can be sustained over relatively long period, this is determined
by limiting factors.
Various limiting factors affect size population are of 2 types:
1. Abiotic Factors: non-living part
2. Biotic factors: activities living organisms
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Abiotic Factors
Abiotic features that influence size population include:
____________: each species has different optimum at which best survive. Further away
from optimum small population be supported. In plants enzymes work more slowly &
metabolic rate reduced. Populations grow more slowly. Above optimum, enzymes work less
efficiently as gradually undergo denaturation. AGAIN population grows more slowly.
Warm-blooded animals, birds & mammals, maintain relatively c________ body temp
regardless of e________ temp. Might think population growth & size unaffected by temp.
BUT further external environment gets from their optimum more energy expend to
maintain normal temp. Leaving less energy individual growth & so mature more slowly &
r___________ rate slows. Population size therefore smaller.
______: the ultimate source of energy for ecosystems. Rate of p______________ increases
as intensity increases. Greater rate photosynthesis, the faster plants grow & more
s_______/s_____ produced. Their population growth & size therefore potentially greater. In
turn population animals that feed on plants potentially larger.
___: this affects action of enzymes. Each enzyme has optimum at which operates most
effectively. Population of organisms is larger where conditions suit & smaller, or nonexistent where very different from optimum.
W_______ & H___________: where it is scarce, populations are small & consist only of
species that are well adapted living in dry conditions. Affects t______________ rates in
plants & e____________ of water from bodies of animals. Again, in dry air conditions,
populations of species adapted to tolerate low h__________ will be larger than those with
no such adaptation.
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1.4 Competition
When 2 or more individuals share any resources (e.g. light, food, space, oxygen) that is
insufficient satisfy all requirements fully = C______________.
Where competition arises between same species: i____________ competition.
Where competition arises between different species: i_____________ competition.
Intraspecific Competition
Intraspecific competition occurs when individuals of the s_____ s______ compete w/ one
another for resources.
It is availability of r_________ that determines size of population.
Greater availability  larger the population, lower the availability  smaller the population.
Examples
Limpets competing for a_____, their main food. More algae available, larger limpet
population becomes.
Oak trees competing for resources, in large population small oak trees some grow larger
& restrict availability of l_____, w_____ & m________ to rest, which then die. In time
population be reduced to relatively few large dominant oaks.
Robins competing for b________ territory. Female birds normally only attracted males
w/ territories, each territory provides adequate food for 1 family. When food scarce
territories have to become larger to provide enough food. Therefore fewer territories
given area = fewer breeding pairs = smaller population.
Interspecific Competition
Occurs when individuals of d__________ s_______ compete for resources.
Where populations of 2 species initially occupy same n______, 1 normally 1 species has
competitive advantage:
Population of this species gradually increase size while population other will diminish,
If conditions remain same, will lead complete removal of one species,
Known as competitive exclusion principle – where 2 species competing for limited
resources, one uses resources most effectively, ultimately eliminating the other.
No two species can occupy same niche indefinitely when resources limiting:
Cormorant & Shags (sea birds) appear occupy same n_____ – 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 d_________ niches.
In order to affect population size, the factor must affect b_____ r____ &/or d_____ r____
(must describe link explicitly):
E.g. i_________ food supply does not necessarily mean more individuals; just results in
bigger individuals,
E.g. decrease food supply leads to individuals dying of s__________, resulting in
reduction of population,
E.g. increase food supply means more likely individuals survive & so increased
p___________ will produce o_________ & population will increase.
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Application – Correlation and cause for effects of interspecific competition
In many cases ecologists suspect interspecific competition is reason for v__________ in
population. A causal link must be established to show that competition is the cause of
observed correlation.
In practice difficult to prove for number reasons:
Many other f________ influence population size, such as abiotic factors,
T____ lag in many cases relating to competition & so population change may due
competition that took place years earlier,
Data on natural population sizes hard to obtain & not always r_______.
HINT
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 causal link
for the observed correlation.
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1.5 Predation
Predation: ________________________________________________________________________
Effect of predator-prey relationship on population size
Predators eat their p____, thereby reducing the population.
With fewer prey available the predators are in greater c____________ 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 s________.
With fewer p_________ left, less prey is eaten.
The prey p__________ therefore increases.
With more prey now available as f____, the predator population in turn increases.
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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 ag_________.
The development of manufacturing and trade that created the i__________ r__________.
Factors affecting the growth and size of human populations
The basic factors that affect the growth rate of human populations are b_____ r____ and d_____
r____.
Individual populations are further affected by m__________, which occurs when individuals move
from one population to another. There are two types:
_____________: where individuals join a population from outside.
_____________: where individuals leave a population.
Population growth = (b______ + i___________) - (d______ + e__________)
Factors affecting birth rate
Economic conditions - countries with a low per capita income tend to have _______ birth
rates.
Cultural and religious backgrounds - some countries encourage larger families and some
religions are opposed to b_____ c_______.
Social pressures and conditions - in some countries a large family improves social standing.
Birth control - the extent to which c_____________ and a________ are used markedly
influences the birth rate
Political factors - governments influence b_____ r_____ through education and taxation
policies.
Birth rate = (number of births per year  total population in the same year) x 100
Factors affecting death rate
A___ profile - the greater the proportion of elderly people in a population, the higher the death
rate is likely to be.
L____ e__________ at birth - the residents of economically developed countries live longer
than those of economically less developed countries.
Food supply - an adequate and balanced ____ reduces death rate
Safe drinking water and effective s__________ - reduce death rate by reducing the risk of
contracting water-borne diseases, such as cholera.
Medical care - access to healthcare and education ________ the death rate.
Natural disasters - the more prone a region is to a drought, famine or disease the _______its
death rate.
War - deaths during wars produce an immediate drop in population and a longer term fall as
a result of fewer f_______ adults.
Death rate = (number of deaths per year  total population in the same year) x 100
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Population structure
Age population pyramids:
There are three typical types of population pyramids:
S_______ population - where the birth rate and the death rate are in balance and so there is
no increase or decrease in the population size.
I__________ 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.
D__________ 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 s________ c_____ plots the number of people alive as a function of t____. 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: __________________________________________
_________________________________________________________________________________
It follows that life expectancy can be calculated from a survival curve, by finding this % and reading
off the life expectancy.
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2. ATP
2.1 Energy and ATP
In most ecosystems the initial source of e_______ is the sun (light energy).
Plants use solar energy for photosynthesis to make o_______ molecules, this takes place
inside chloroplasts which are mainly found in the m_________ layer of a leaf.
Carbon dioxide is taken in through the ________.
Water is taken in through the _____.
Light is absorbed by the green pigment ____________.
Oxygen is released into the atmosphere through the ________.
Glucose is transported in solution for use or is stored as _______.
Energy is defined as the ability to do _____:
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 ________ or __________
Measure in _______ (J).
Organisms need energy for:
M__________ - reactions within living organisms,
M________ e.g. circulation of blood and locomotion,
A______t_________ - the net movement of particles against a concentration gradient
across a plasma membrane,
Maintenance, repair and di_______ of cells and organelles,
Production of substances e.g. e_______ and hormones,
Maintenance of body t___________ 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 _______________, the chemical energy in
the form of organic molecules is converted into ____ during respiration in all cells, this is
then used to perform useful _____.
Adenosine triphosphate has _ phosphate groups, a _ carbon ribose and _ adenine group.
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The bonds between the phosphate groups are unstable and have a low activation energy so
they are easily broken, when they are they _______ energy, it is the terminal phosphate
that is removed. This is known as a h__________ reaction. The reaction can also be reversed
to make A_P from A_P through a condensation reaction.
The synthesis of ATP from ADP occurs in 3 different ways:
1. ______phosphorylation- takes place in chlorophyll-containing plant cells during
photosynthesis.
2. __________ phosphorylation- occurs in the mitochondria of a plant and animal cells
during the process of electron transport.
3. _________-_____ phosphorylation- occurs in plant and animal cells when phosphate
groups are transferred from donor molecules to ADP to make ATP.
ATP is not a good store of energy due to u________ bonds, but good as an immediate
source of energy for same reason. Each ATP molecule releases _____ energy than each
glucose molecule therefore released in smaller more manageable amounts. The hydrolysis
of ATP to ADP is a single reaction that releases immediate energy whereas the breakdown
of g_______ is a long series of reactions.
ATP is the source of energy for:
(1) Metabolic processes: p_____________ synthesis from monosaccharide,
p__________ synthesis from amino acids and DNA/RNA synthesis from
n___________.
(2) Movement: muscle c___________.
(3) Active transport: ATP provides energy to change the shape of the c_______ proteins,
allows molecules or ions to be moved against a c_____________ gradient.
(4) S_________ : needed to form the lysosomes
(5) Activation of molecules: lowers the a__________ energy of molecules so they are
more reactive; so enzyme-catalysed reactions can occur more readily.
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3. Photosynthesis
3.1 Overview of Photosynthesis
Site of photosynthesis - the leaf
Structure of the leaf
is adapted to bring together the three raw materials of photosynthesis. (______, _______ ________
and ______) and remove its products (_______ and ________). These adaptations include:
A large ________ _____ that collects as much sunlight as possible.
An arrangement of leaves on the plant that minimises overlapping and so avoids the
s_________ of one leaf by another.
T____, as most light is absorbed in the first few millimetres of the leaf and the diffusion
distance is thus kept short.
A t___________ cuticle and epidermis that let light through to the photosynthetic
mesophyll cells beneath.
Long narrow, upper mesophyll cells packed with c____________ that collect sunlight.
Numerous s_______ for gaseous exchange.
Stomata that open and close in response to changes in l______ i_________.
Many air spaces in the lower mesophyll layer to allow d_________ of CO2 and oxygen.
A network of x______ that brings water to the leaf cells and p______ that carries away the
sugars produced in photosynthesis.
Outline of photosynthesis
Capturing of light energy - by chloroplast p_______, 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 of light on chlorophyll and this
causes water to split (__________) into protons, electrons and oxygen. The products are
reduced N___P, A__P and oxygen.
The light-independent reaction - in which these protons (_________ ions) are used to
reduce carbon dioxide to produce sugars and other organic molecules.
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Structure and role of Chloroplasts in photosynthesis
Photosynthesis takes place inside the chloroplasts.
They are surrounded by a _______ membrane.
Inside the chloroplast membrane there are 2 distinct regions:
- The ______ - stacks of thylakoids 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 _______ - fluid-filled matrix where the light independent stage takes place,
contains starch grains.
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3.2 The Light- dependent reaction
Requires l______.
Requires w_____.
Requires photosynthetic p________.
Occurs in the t___________.
Light strikes chlorophyll and e_________ are excited to a higher energy level where they are
accepted by an electron carrier.
P___________ (splitting of water) occurs.
Electrons pass down the electron transfer chain to NADP forming ATP
(P__________________n- process by which ATP is made during the light reaction).
Products are N____H, ATP and O2.
O______ produced comes from water.
NAPDH and ATP are then used in the Calvin cycle (______ ____________reaction) .
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3.3 The Light Independent Reaction
Does not require light (can occur in both l_____ and d____).
Occurs in the _______ of the chloroplast.
C_______ d_______ from the atmosphere diffuses into the leaf through the stomata and
dissolves in water around the walls of the m_________ cells. It then diffuses across the
plasma membrane, cytoplasm and chloroplast membranes into the stroma of the
c___________.
In the stroma, the CO2 combines with the __-carbon R___P using the enzyme RuBisCo.
Combination produces __ molecules of glycerate 3-phosphate.
ATP and NADPH from light dependent reaction are used to reduce the activated glycerate 3phosphate to t______ phosphate.
The N___P is re-formed and goes back to light dependent reaction.
Some triose phosphate are converted to useful organic substrates such as g_______ .
Most are used to regenerate RuBP using ____ from the light dependent reaction.
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3.4 Factors Affecting Photosynthesis
Limiting 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 l_____ i_________, c______ d_______
concentration and t___________.
Light intensity
No light - no photosynthesis. The l_____ d_________ r_______ does not take place.
Increasing the light intensity to value A causes photosynthesis to i________. The more light
the greater the LDR and the greater the production of A__P to the LIR.
At light intensity A the rate of photosynthesis reaches its maximum and levels off. Some
factor other than light intensity is limiting the rate of p______________: 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 's__________ p_____' - 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 n_ e_______ on the new limiting factor so photosynthesis
stays the same.
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Carbon dioxide concentration
No carbon dioxide - no p______________.
Increasing the carbon dioxide concentration to value A causes photosynthesis to i________.
The greater the supply of CO2, the faster the rate of enzyme activity.
At A the rate of photosynthesis reaches its m_______ and levels off. Some factor other than
CO2 is limiting the rate of photosynthesis: it may be low temperature, low light intensity.
The rate of photosynthesis remains constant at maximum beyond A. Increase in CO2 has no
effect on the new limiting factor so photosynthesis s_____ the s_____.
Temperature
At 0°C the rate of photosynthesis is low. Enzyme activity is low. Photosynthesis is an
e______-c__________ process.
Increasing the temperature to 30°C i_________ the rate of photosynthesis. Enzyme activity
increases.
M_______ photosynthesis at 30°C. Enzyme activity at it maximum - maximum collision
frequency between native enzymes and substrates.
Photosynthesis declines beyond 30°C. Enzyme activity slowing due to d____________ of
enzymes.
No photosynthesis at ___°C. No enzyme activity - enzymes are denatured.
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4. Respiration
4.1 Glycolysis
The splitting of the __C glucose molecule into two __C pyruvate molecules.
Occurs in the cytoplasm of the cells. – Is an anaerobic process.
Net production of __ ATP molecules.
__ molecules of pyruvate produced.
__ molecules of reduced NAD produced (then used in the electron transport chain).
Takes place in cytoplasm as glucose cannot enter the m____________ due to size and
e_______ used in the breakdown of glucose are found in the cytoplasm.
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4.2 Link reaction and Krebs cycle
The link reaction
No energy is stored or removed in this reaction.
Occurs in the m______ of the mitochondria
Pyruvate is converted into a_____________ A in this reaction.
This occurs twice so... __ molecules of Acytlycoenzyme A, __ reduced NAD and __
molecules of carbon dioxide are produced.
The Krebs cycle
Occurs in the m______ of the mitochondria.
Provides a continuous support of e_________ to fuel the electron transport chain.
Produces a SMALL amount of A__P.
Occurs t_____ due to 2 acytylcoenzyme A molecules.
__ molecules of NADH produced (reduced NAD).
__ molecules of FADH2 produced (reduced FAD).
__ molecules of ATP produced.
__ 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 o_________
p_____________n.
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4.3 The electron transport chain
Energy from h_________ 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 ch__________s.
Occurs on the c________ of mitochondria. Hydrogen from glycolysis is used.
Reduced NAD and FAD are oxidised, releasing Hydrogen atoms. The H atoms are split into
__+ and __-.
The regenerated N___ and F___ are reused in Krebs cycle.
The electrons move along the electron transport chain (made up of 3 electron carriers), in a
series of o________n-r________n reactions, losing energy at each stage.
Some of this energy is used to combine an inorganic phosphate with A__P to make A__P.
The remaining energy is released as heat.
The p_______ (H+) 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 o______ to form
H2O.
Oxygen is the f_____ a________ of electrons in the electron transport chain.
Without oxygen acting as the final acceptor of electrons, the H+ ions and electrons would
‘back up’ along the chain and r___________ would come to a halt.
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4.4 Anaerobic respiration
Only g__________ can occur in the absence of oxygen.
There are 2 forms of anaerobic respiration: a_________ f____________ in plants and
l_______ f____________ in animals
The production of ethanol is exploited in the brewing process.
Pyruvate is converted to ethanal by decarboxylation; reduced NAD is then oxidised by the
ethanal to give e______l.
In animals, lactate is formed by the oxidation of reduced NAD by p________.
The production of lactate regenerates the N___ and so glycolysis can continue: a small
amount of ATP is still produced to keep biological processes going.
An oxygen _____ is created, lactate broken back down by oxygen at end.
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5. Energy and Ecosystems
5.1 Food chains and Food webs
Organisms can be divided into 3 groups depending on how they obtain their e______.
_________ - photosynthetic organisms that manufacture organic substances using
light energy, water and CO2 by photosynthesis
_________ - obtain their energy by consuming other organisms. Primary consumers
feed directly off plants (producers). These are then consumed by secondary
consumers and then tertiary consumers (usually predators can be scavengers or
parasites).
___________ - 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 (detritivores).
Food chains
Describes a feeding relationship by showing the t________ of e______ between
producers and consumers.
Each stage is referred to as a t_______ l_____.
Arrows represent the d_________ of energy flow.
Food webs
Most organisms in a c_________ do not just feed upon one animal, and one 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: it is just a model.
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5.2 Energy Transfer between Trophic Levels
Most energy is not converted by plants because
most of the sun’s light is r_________ back into the atmosphere by clouds,
not all w___________ can be absorbed,
light may not fall on the c___________ molecules,
a l________ factor may stop the rate of photosynthesis e.g. low CO2 levels.
The rate at which plants store energy is called ____ 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 e______
2. Some parts cannot be d________ so lost in faeces
3. Lost in e_________ materials (urine)
4. Lost as heat, maintaining body t___________
5. M_______t during hunting etc
Most food chains don’t have more than 4/5 trophic levels due to so much e______ lost,
insufficient energy to support more.
Total mass of organisms is less at h______ trophic levels.
Total amount of energy stored is less at each trophic level.
Energy transfer (%) between each trophic level can be calculated by:
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5.3 Ecological Pyramids
Pyramids are drawn to show changes in n______, b_______ or e______.
Pyramid of number
Shows the number of organisms at each ________ _____.
The width of the block is p___________l to the number of organisms present at each level
Disadvantage: ___________________________________________________________
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
Units for biomass: ____________________________________________________________
Disadvantages:
Live (wet) mass can be used but gives un_________ results.
Not always practical/desirable to kill organisms find the d___ mass (e.g. mass of whales).
S________l differences are not present.
Pyramid of energy
Shows the flow of energy through each trophic level of an ecosystem during a fixed period
of t_____.
Always a fixed p_______ shape.
Units for energy: _____________________________________________________________
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5.4 Agricultural Ecosystems
Made up of largely domesticated animals and plants used to produce _____ for humans.
Tries to ensure that as much of the available e______ from the sun is transferred to
humans.
Aims to increase the p___________ of the human food chain.
Net productivity = gross productivity – respiratory loss
E_________y affected by the efficiency of the crop at photosynthesising and the area of the
ground covered by the leaves of the crop.
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
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Artificial community prevented from
reaching its climax
Natural climax community
Energy input
To prevent an agricultural ecosystem from developing they remove all other s______s 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, f____ for the farmers and f______ f_____ for the machines.
Productivity
Additional energy input increases productivity, controlling photosynthesis within a
greenhouse would also do this as maximum photosynthesis can be achieved (c______
d_______ levels controlled, t___________ controlled, w_____ controlled, m________ i____
controlled etc).
5.5 Chemical and Biological Control of Agricultural Pests
A pest is :_________________________________________________________
________________________________________________________________
A pesticide should:
1. Be _________- harmless to humans and other organisms,
2. ___________- 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 _____-effective,
4. Not ___________ - does not pass along food chain and harm other species
higher up the food chain.
Biological control
Controlling a pest by using its natural p________ or pa________ of the pest.
Aim to c_______ not eradicate - could be counterproductive, not enough pest for predator
pest can increase in number again as predator dies.
Disadvantages:
1. _______________________________________________________________
2. _______________________________________________________________
Biological Control
Very Specific
Once introduced, control organism
reproduces itself
Chemical Pesticides
Always have some effect on other
species
Must be reapplied – very expensive
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Pests do not become resistant
Risk that control organism becomes a
pest – as pest population is reduced
control feeds on crops
Pests can develop genetic resistance
– so new pesticides have to be
developed
Risk of accumulation in species or
polluting nearby rivers
Integrated pest control systems
Involves using all methods of pest control (c_________, b__________ and natural) to
CONTROL the amount of pest.
Involves:
1.
2.
3.
4.
5.
6.
Choice of crop: a plant/animal that is immune as possible to the pest,
Manage the environment to provide h________ suitable for predators,
Monitor the crops for early signs of p_____,
Remove pests by hand if exceeds acceptable amount,
Use b__________ control if necessary and available,
Use p_________s as a last resort.
Such systems can be effective with minimum impact on the e___________.
Pests reduce productivity in agricultural ecosystems:
weeds c_______ with crop plants for water, minerals etc,
insects can d______ leaves of crops needed for photosynthesis,
insects can reduce crop q_______,
pests can be in direct competition by eating the crops themselves.
Monoculture: _______________________________________________________________
___________________________________________________________________________
Disadvantages: ___________________________________________________________
___________________________________________________________
___________________________________________________________
Improved productivity requires balance between:
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the cost of pest control,
the benefits of pest control,
the demand for c_____ food,
farmers making a living,
the c____________n of natural habitats,
sustainability of systems.
5.6 Intensive Rearing of Domestic Livestock
Designed to produce the maximum y_____ of meat, eggs and milk at the lowest cost
possible.
They do this by using methods to convert the smallest amount of food e______ into the
greatest amount of animal m____.
They do this by minimising the energy loss by keeping animals in confined spaces to
increase energy conversion rate, it does this because:
1. Movement is restricted so less energy is used in m______ contraction,
2. Environment can be kept _____ so energy not used to maintain body heat,
3. Feeding can be controlled for maximum g______,
4. Pr________ are excluded so no loss to other organisms in food web.
Other means include s_________ breeding of animals to produce varieties that are more
efficient at converting food into body mass and using h________ to increase growth rates.
Main features of intensive rearing are:
1. E_________ energy conversion,
2. L___ cost,
3. L____ land is used leaving more natural habitats,
4. High density animal population more at risk to spread of d_______, but easier to
isolate if this happens,
5. Animals are regularly given a___________ to prevent spread of disease,
6. Over use of drugs leads to a__________r__________ and can also alter the flavour
of food or pass into the foods then into humans affecting their health,
7. Maintains a higher level of animal welfare but can lead to aggressive behaviour from
being in unnatural conditions,
8. Produces large concentrations of waste in a small area: rivers and ground waters
may become p________, pollutant gases can be dangerous and smell, larger farms
have own waste facilities,
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9. Reduced g_______ d_________ due to selective breeding,
10. High energy-conservation rates due to use of f_______ fuels: CO2 levels released
leading to increased global warming.
Economic and environmental issues
Economic- desire for cheap food conflicts with the conservation of the environment.
Managing the physical environment leads to reduced species d_________ due to:
1. removal of h______ and woodland,
2. creation of m___________s,
3. filling in ponds and d________ marshes and other wetlands,
4. over-g_______ of land preventing regeneration of woodland.
Indirect effects also reduce species diversity:
1. use of pesticides and in________ fertilisers,
2. escape of farm wastes into water courses,
3. absence of crop r________ leading to poor soil structure.
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Conservation techniques include:
1. using crop rotation with a nitrogen fixing crop
2. creating natural meadows and using hay for silage
3. leaving the cutting of verges and field edges until after flowering and
seeds have dispersed
4. ____________________________________________________________
5. ____________________________________________________________
6. ____________________________________________________________
7. ____________________________________________________________
8. ____________________________________________________________
9. ____________________________________________________________
10. ____________________________________________________________
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 p_____________, becoming carbon
compounds in plants.
2. Carbon is passed along the f____ c_____ through consumption.
3. When organisms die, carbon compounds are digested by microorganisms and
returned to the air as they carry out r_____________.
4. If any dead organic matter ends in places where there aren’t any decomposers,
their carbon compounds can be turned into f______ f_____. The carbon in these
is released when they are burnt for fuel.
CO2 c_____________ falls during the day as it is removed by plants as they carry out
photosynthesis. It then increases at night as it’s no longer being removed by photosynthesis
but all organisms continue to respire and add CO2.
CO2 concentration ___________ in the summer in some climates as it is used rapidly when
light intensity is greatest – more photosynthesis can occur. More CO2 is removed as more
plants are photosynthesising.
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6.2 The greenhouse effect and global warming
Global warming is where the mean temperature of the Earth has increased.
The g__________ e______ is a natural process that occurs all the time: without it the
average temperature on earth would be -18°C. The gases that surround the earth in the
atmosphere trap the heat from the sun keeping it warm at an average of 17°C.
The most important greenhouse gas is c______ d_______ because it remains in the
atmosphere for much longer than other greenhouse gases: 50-70% of global warming is due
to CO2.
Human activities, such as _____________ and _____________ increase the amount of
carbon dioxide in the atmosphere enhancing the greenhouse effect.
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________ is also a greenhouse gas. It 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.
Consequences of global warming:
1. Melting of polar ice caps which could cause the e__________ of some plants and
animals and also a rise in sea level,
2. Rise in sea level could cause flooding, s____water would extend further up rivers
making cultivation of crops difficult,
3. Higher t_____________ and less r________ lead to failure of crop growth in
some areas, distribution of wild plants change and so animal distribution would
change,
4. Greater rainfall and storms in some areas cause change in d___________n of
plants and animals,
5. Life-cycles and populations of insect pests would change as they adapt, tropical
diseases could then spread further up north as the insects m______.
Could also see benefits as i__________ rainfall would fill reservoirs, i__________
temperature allows for growing crops in places where originally too cold, r____ of
photosynthesis increases, may be possible to harvest t_____ a year.
6.3 The Nitrogen Cycle
Plants and animals need nitrogen to make p________ and n_______ a_____ (DNA/RNA).
Although the atmosphere has 78%, can't use it in that form, need s__________c bacteria to
convert it into nitrogen compounds first.
Nitrogen Cycle includes:
1. Nitrogen Fixation (Can also happen when lightning passes through the atmosphere)
Nitrogen gas in the atmosphere is turned to ________ by _________-_______ bacteria
Free-living nitrogen-fixing bacteria reduce gas to _________ which is then used to
manufacture a_____ acids. Nitrogen rich compounds released when they decay.
M___________ bacteria e.g. Rhizobium is found in root nodules of leguminous plants (peas,
beans).
They form a mutualistic relationship with the plants- they provide the plant with
n_________ compounds and the plant provides them with c_____________.
2. Ammonification
Nitrogen compounds from dead organisms are turned into ammonium compounds by
d___________.
Animal waste also contains compounds and are turned into a_________m.
3. Nitrification
This is the conversion of ammonium ions to nitr_te ions by nitrifying bacteria, to be used by
the plant.
Firstly nitrifying bacteria oxidise ammonium ions to nitr_te ions (N02-)
Secondly other nitrifying bacteria oxidise nitr_te ions to nitr_te ions (N03-)
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The bacteria require o_______, 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 r___________ and produce nitrogen gas.
Happens under an_________ conditions - no oxygen e.g. waterlogged soil.
Parts of the cycle can be carried out artificially on an industrial scale. H_____ process
produces ammonia from atmospheric nitrogen to make fertilisers.
6.4 Use of Natural and Artificial Fertilisers
All p______ need mineral ions, especially nitrogen.
I_________ 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
micro__________ on its death.
In agricultural ecosystems the plants are harvested and transported for consumption and
are rarely returned to the same area, making it necessary to replenish the minerals or they
will become a l_________ f______ to the plants’ growth.
To do this 2 different types of fertilisers are added:
1. Natural (organic) fertilisers: ________________________________________________
_______________________________________________________________________
2. Artificial (inorganic) 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 p____________.
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6.5 Environmental consequences of using nitrogen
fertilisers
Reduced species diversity can occur- nitrogen-rich soils favour the growth of grasses, nettles
and other rapidly growing species. This causes more c___________ for other species, which
then die out and this reduces species diversity.
Leaching: ___________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
If nitrogen fertiliser is leached it can cause eutrophication:
1. Nitrates leached from fertilised fields stimulate g______ of algae in ponds etc.,
2. Large amounts of algae block l_____ from reaching plants below,
3. Plants die as they are unable to p_______________,
4. B________ feed on the dead plant matter,
5. Increased numbers of bacteria reduce the o_______ concentration in water by
carrying out aerobic respiration,
6. Fish etc. die as there isn't enough d_________ oxygen.
Organic manures, animal s______, human s______, ploughing old grass land and natural
leaching can also cause eutrophication, but artificial is main cause.
7. Ecological Succession
7.1Succession
Succession:
________________________________________________________________
________________________________________________________________
Pioneer species:
________________________________________________________________
________________________________________________________________
Climax community:
________________________________________________________________
________________________________________________________________
Primary succession:
________________________________________________________________
________________________________________________________________
Secondary succession:
________________________________________________________________
________________________________________________________________
Pioneers:
1. rapidly g__________ seeds,
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2.
3.
4.
5.
reach isolated areas easily,
have the ability to p________________,
have the ability to fix n________,
have tolerance to e_______ conditions.
Succession takes place in a series of stages (seres)  at each stage certain species can be
identified which c______ the environment  therefore the environment becomes more
suitable for other species  these other species out c________ current species  this
forms a new c_________.
During any succession, common features are:
1.
2.
3.
4.
5.
the non-living environment becomes less hostile which leads to 
greater number and variety of habitats which produce 
increased biodiversity which lead to 
more complex food webs 
increased biomass
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7.2 Conservation of Habitats
Conservation:
_________________________________________________________________________________
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 adds interest to our every day lives.
Ways to manage succession:
1. Animals left to g_____ on land, so larger plants can't establish themselves and vegetation is kept
low.
2. Managed fires are lit, after fires s_________ succession will occur on the moorland, so the
pioneer species growing back will be the species that is being conserves e.g. heather.
3. Arriving s_______ are selectively removed to prevent succession from moving on to the next
sere.
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8. Inheritance and Selection
8.1 Studying inheritance
Dominant Allele: _____________________________________________________________
Recessive Allele: _____________________________________________________________
Co-dominance: ______________________________________________________________
Genotype: __________________________________________________________________
Phenotype: _________________________________________________________________
Heterozygous: _______________________________________________________________
Multiple Alleles: _____________________________________________________________
Homozygous: _______________________________________________________________
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8.2 Monohybrid Inheritance
Representing genetic crosses
Choose a single letter to represent each characteristic
Choose 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 (Always write the higher
case letter first)
State the g_______ produced by each parent, indicating meiosis.
Use a p______ square to show the result of the random crossing of gametes, label male and
female.
State the p__________ of each different genotype and indicate the number of each type.
Inheritance 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:
A similar cross can be done for cystic fibrosis which is the recessive gene coded for by the protein
CFTR.
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8.3 Sex Inheritance and Sex Linkage
Sex is determined by c___________ rather than genes.
As females only have X and males have either __ or __ 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 ____-_______.
Carried on the X chromosome, males either have the disease or don’t but women can be
c________.
Males can therefore only obtain a sex-linked disease from their m______ (since the gene is
not carried on the Y chromosome they inherit from their father).
If the mother does not have the disease but the son does, then she would be a c_______
and so h___________s for the condition.
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8.4 Co-dominance and Multiple Alleles
Co-dominance: _____________________________________________________________
__________________________________________________________________________
E.g. a plant that codes for red and white flowers, both are d________ so the colours would
be:
1. Homozygous for red = red CRCR
2. Homozygous for white = white CWCW
3. Heterozygous = pink CRCW
C= colour and then R= red and W= white:
Multiple alleles
Inheritance of the ABO blood group is one example.
3 genes carried on the I (immunoglobulin gene), which lead to the different production of
different a________ on the surface of red blood cells:
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8.5 Allelic Frequency and Population Genetics
Gene pool:
________________________________________________________________
________________________________________________________________
Allelic frequency:
________________________________________________________________
________________________________________________________________
Example:
Cystic fibrosis- C- dominant allele which codes for normal production of m_____.
c- Recessive allele which codes for production of thicker mucus and cystic fibrosis
Pairs of alleles for cystic fibrosis have 3 different combinations:
1. CC - h___________s d_______t
2. cc - h____________s r________e
3. Cc / cC- h___________s
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 h___________s then the frequency of C or c would be 0.5.
The Hardy-Weinberg Principle
A mathematical equation can be used to calculate the f_________of a_______.
Principle states that the proportion of dominant and recessive alleles stays the same from
generation to generation if:
(1) _______________________________________________________________
(2) _______________________________________________________________
(3) _______________________________________________________________
(4) _______________________________________________________________
(5) _______________________________________________________________
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 = 1.0
Therefore:
If 1 in 25000 people have a (recessive) then aa= 1/25000 therefore q squared = ________
If p + q = 1.0 and q is then equal to 0.00063, p = _________
To calculate heterozygous you then use 2pq = (2 x 0.9937 x 0.0063) = __________
So 125 in 10 000 carry the allele for the characteristic.
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8.6 Selection
Reproductive success and allele frequency
All organisms produce more o_________ than can be supported.
Despite overproduction most populations remain c________.
There is competition between members of a s_______ to survive.
Within the population there will be a wide variety of a_______ in the gene pool.
Some will possess the g_____ which make them better able to survive.
These individuals will obtain the available resources and grow more rapidly; as a result will
be more successful b________ and produce more offspring.
The more successful then pass on their g_____.
Offspring with advantageous alleles will then c______e better and will reproduce.
The number of individuals with the advantageous alleles will increase.
Over time, the f_________ of the allele increases.
The advantages will vary due to environment.
Types of selection
Selection is the process in which organisms that are better a______d will survive and breed.
Different e_____________ conditions favour different characteristics within a population.
Directional selection: _________________________________________________________
___________________________________________________________________________
Stabilising selection: __________________________________________________________
___________________________________________________________________________
Directional selection
Environmental conditions change so p_________ needed to survive changes.
New individuals become more adapted to survive at one end of the spectrum and so over
time the m____ 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 _____.
Mean are favoured, extremes are favoured against.
Eliminates extremes.
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8.7 Speciation
Speciation: _________________________________________________________________
___________________________________________________________________________
Species: ___________________________________________________________________
__________________________________________________________________________
If 2 populations become i________ in some way, there is no longer a flow of a________.
The environment for each group may differ and so 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
Can also occur if there is no specific extrnsic barrier, but just a large range over which mating could
occur.
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