Unit 4.1 Biology

7/30/2019 Unit 4.1 Biology

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A2 level Biology notes

Unit 4- Populations and the Environment


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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


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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


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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


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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


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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.


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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 = 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


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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


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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.


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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 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:


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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.


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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


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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 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


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(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


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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


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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)


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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


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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


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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.


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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


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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


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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


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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.


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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


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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


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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:


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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


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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)


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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


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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.


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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


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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


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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.


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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


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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.


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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


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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


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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


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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.


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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


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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


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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


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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


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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


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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

Unit 4.1 Biology

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