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Plant Growth Factors

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• Plants response to external stimuli is through plant growth factors:
o They exert their influences by effecting growth which are produced by cells located throughout the plant and not a particular organ.
o Unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on a distant target
Indoleacetic Acid (IAA)

o IAA is produced in the tips of the shoots/roots
o IAA is initially transported evenly throughout all regions as it begins to move down the shoot

• Phototropism
o Light causes IAA to move away from it, and therefore move towards the shaded side of the shoot
o A greater concentration of IAA builds up on the shaded side compared to the light side causing the elongation of shoot cells (n.b. same number of cells, however now they are elongated)
o The increased growth on the shaded side causes the plant to grow towards the light
• Gravitropism
o Cells in the root tips produce IAA which is transported along the root
o The IAA is initially transport to all sides of the root
o Gravity causes the IAA molecules to move downwards to the bottom of the root
o IAA is a growth inhibitor when in roots causing the area which does not have IAA in it (the top side of the root) to elongated, causing the root to grow downwards.

Energy Transfer

Energy Transfer

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Measuring Biomass
• Biomass can be calculated by measuring the mass of carbon that an organism contains or by the draw mass of its tissue per unit area per unit time
• The dry mass is the total mass of an organism without any water. The water content in different organism greatly varies therefore a dry mass is more beneficial than a wet mass in reference to biomass
• In measuring the dry mass, a sample of an organism is dried (usually in an oven at a low temperature). This mass is then measured every day until the sample reaches a constant mass, this means that all the water has been removed. Approximately 50% of the total mass of the dry mass is carbon. Now that the dry mass is known multiply the figure to give the dry mass (biomass) of the total population or the area being investigated. The typical units for dry mass is kg m-2
• Biomass varies over a period of time, it is useful to carry out multiple biomass test over a time. The typical unit is kg m-2 yr-1
• Burning the chemical energy is a sample can also give an estimate to the biomass using a calorimeter
• The heat output determines how much energy is given off and thus how much energy was contained
• A sample of the dry biomass is burnt under a known volume of water, where the change in the temperature of the water is therefore calculated for the chemical energy of the dry biomass
Primary Production
• Gross Primary Production (GPP) is the total amount of chemical energy produced from light energy by plants in a given area over a given time
• Respiratory loss (R) is the approximate 50% of the gross primary production which is lost to the environment as heat when the plant respires
• Net Primary Production (NPP) is the remaining chemical energy
• NPP energy allows the plant to grow and reproduce as well as being the energy which is able to move up the trophic levels
Net Production in Consumers
• Consumers get their energy by the consumption of plant (primary) material or animals which have eaten plant materials
• Not all of the chemical energy is transferred to the next trophic level as around 90% of it is lost over different ways:
o Not all of the animal/plant is eaten such as bones or cellulose is digested
o Energy is wasted in the animal moving
o Energy is wasted in maintain homeostasis
o Etc
• Net Product is the amount of energy after the energy has been lost, the remaining amount is stored in the consumers biomass and is therefore available for the next trophic level
N = I – (F + R)
N = net production
I = Chemical energy in ingested food
F = Chemical energy lost in faeces and urine
R = Energy lost through respiration

Efficiency of Energy Transfer
• Energy transfer can be measured by comparing the net production of energy for the current trophic level to the previous trophic level:
Net production of trophic level x 100
Net production of previous trophic level
• Energy transfer generally becomes more efficient the higher up the trophic level is, this is greatly to do with plants being greatly indigestible however the consumer being an animal has a greater proportion of chemical energy it can transfer as more of it digestible

Energy loss in Food Chains

Energy loss in Food Chains

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Photosynthesis Limiting Factors
• >90% of sun’s energy is reflected or absorbed by clouds/dust
• Not all wavelengths of sunlight can be used
• Light may not fall on a chlorophyll molecule
• Low carbon dioxide levels
Gross Primary Productivity
• The total quantity of energy that the plants in a community convert to organic matter
• Plants use 20~50% of energy as respiration, where very little of it is stored
• The rate at which a plant stores energy is the net primary production

Net Primary productivity = Gross Primary – Respiratory Losses
Energy Loss by Consumers

• Only 10% of this plant food stored is used by primary consumers for growth
o The low percentage is due to cellulose not being able to be broken down
• Secondary and tertiary consumers ae more efficient transferring about 20% available from the prey into their bodies
• Energy is lost through:
o Movements
o Some parts are not eaten (e.g. bones)
o Some parts are indigestible (e.g. cellulose)
o Excretory materials
o Heats from respiration
o Body temperature

Calculating the efficiency of energy transfers
• Data is given at each available trophic level
• The amount of energy available is commonly measured in kJ m-2 year-1

Energy Transfer Efficiency = Energy Available after the transfer x100
Energy Available before the transfer
e.g. Calculate the efficiency of the transfer of energy from a producer to a tertiary consumers
Trophic Level Productivity (kJ m-2 year-1)
Producers 9,000
Primary Consumers 1,500
Secondary Consumers 120
Tertiary consumers 12

12 x100 = 0.13%

Ecological Niche
• The role of a species within its habitat following:
o Biotic Interaction
o Abiotic Interaction
• It includes the position of the species within a food chain



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“Within any population there is a range of alleles which leads to a wider range of phenotypes.”
Cause of Variation
• Mutations
• Independent Segregation
• Meiosis
Types of Variation:
Discontinuous Variation
• Distinct Binary categories
e.g. Male or Female
• Categorical data can therefore use Chi Square
• Usually caused by genes
Continuous Variation
• A scale of categories
e.g. height, hand size
• Statistical tests depend on data, typical use of means uses T test
• Usually caused by environment

Variation due largely to Environmental Influences
• Environment exerts an influences on all organisms
• These influences affect the way the organism’s genes are expressed
• Whereas the genes does set limits, but it is largely the environment that determines where within those limits an organisms stays.
• Some characteristics of organisms grade into one another, forming a continuum
e.g. height and mass
• Characters that display this type of variation are controlled by several genes (polygenes)
• Environmental factors play a significant role in determining where on the continuum an organism lies
e.g. Height is determined by a gene mostly, however environmental factors such as died similarly affect height
• A graph formed from populations of distribution will likely form a normal distribution graph



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• Succession is the process by which an ecosystem changes over time
• Succession occurs in a series of stages of where each stage the plant and animal communities in an area slowly change the environmental conditions (both abiotic/biotic)
• These changes in environmental conditions aid the ability for other species with different adaptations
• Results in one community of organisms to be succeeded by another
Primary Succession
• Occurs on newly formed/exposed land
• There is no soil or organic materials to start with
Pioneer stage of succession
1) Species colonises a new land surface
2) Seeds and spores are brought in via the wind and thus begin to grow
3) First species to colonise the area are the pioneer species
4) Abiotic conditions are hostile and only pioneer species can grow because they are specially adapted for them
5) Pioneer species are able to change the abiotic condition making them less hostile
 When they die saprobiontic decompose the dead organc material which forms the (basic) soil
6) Therefore, conditions because less hostile so new organisms with different adaptations can live there
7) New organisms die and decompose
 Further adds organic matter and makes the soil deeper and rich in minerals so much so that nitrogen-fixing bacteria can turn nitrogen  ammonia
 Ammonium ions in a solution can be used in plants therefore increasing plant growth
8) Larger plants are able to grow in the nutrient rich soil
*Some species can increase the hostility of an area
Later stages of succession
1) Different plants and animals that are better adapted to the improved conditions are able t move in
o These outcompete pre-existing species and become the dominant species
2) Dominant species causes the greatest change to the abiotic environment (thus making it more suitable for other species to live with)
3) As succession continues the complexity of the ecosystem increases so biodiversity increases
4) Eventually, a climax community is reaches where the ecosystem is supporting the largest and most complex community of plants and animals it can
5) It will not change significantly from this point



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1) Capture a sample of species using an appropriate technique
2) Mark them in a harmless way (e.g. a spot of paint/ID tags)
3) Release them back into the habitat
4) Wait a period of time (e.g. a week)
5) Take another sample from the same population
6) Count how many of the second sample have been marked

Total Population Size = Number caught in 1st sample x Number caught in 2nd sample
Number of marked in 2nd sample

• Marked samples has had enough time and opportunity to mix back in with population
• Marking has not affected the individuals chance of survival
• Making is still indistinguishable
• There are no changes in population size due to birth, deaths, immigration, emigration (during trial period)

• Stress put onto animal during capture/marking process
• Stress induced may causes animal to avoid trap in future
o Which would affect population results
• Stress may also inhibits animals ability to integrate back into population

Abundance and Distribution of a population

Abundance and Distribution of a population

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Test Method Positive Test Results Extra
Primary, Secondary, and tertiary Alcohols 1)      Add potassium dichromate solution


·        Primary and secondary alcohols can be oxidised by the Cr2O72-

·        Dichromate ions (Cr2O2-) are orange. On reduction Cr 3+ ions are formed which are green.

·        Primary + secondary remain green

·        Tertiary changes to orange


·        Primary alcohols are oxidised to aldehydes and the carboxylic acids

·        Secondary alcohols are oxidised to ketones.

·        Tertiary alcohols cannot be oxidised by the dichromate ions.


Primary and Secondary alcohols Using Tollens’ reagent

1)      diamminesilver(I) ion, [Ag(NH3)2]+ (containing silver(i) ions) is added

2)      drop of NaOH gives a precipitate of silver(i) oxide ions

3)      Add dilute NH3 to redissolve precipitate

4)      Few drops of aldehyde (primary) or ketone (secondary) is added

5)      Solution warmed gently in hot water bath for several minutes

·        Aldehyde (primary alcohol): Colourless solution producing silver mirror

·        Ketone (secondary alcohol): No change in the colourless solution

·        Large enough of aldehyde (from oxidation of primary alcohol) or ketone (from secondary alcohol) to be able to test them.
Carbocyclic Acids 1)      Add Sodium hydrogen carbonate

2)      Add limewater

·        Carbon Dioxide gas produced

·        Limewater turns cloudy

Halogenoalkanes 1)      Add Aqueous NaOH

2)      Warm the solution

3)      Acidify with nitric acid

4)      Add aqueous silver nitrate

·        Precipitate of silver halides formed
Alkenes 1)      Mix with bromine water ·        Solution changes from orange to colourless
Aldehyde and Ketones Using Tollens’ reagent

1)      diamminesilver(I) ion, [Ag(NH3)2]+ (containing silver(i) ions) is added

2)      drop of NaOH gives a precipitate of silver(i) oxide ions

3)      Add dilute NH3 to redissolve precipitate

4)      Few drops of aldehyde or ketone is added

5)      Solution warmed gently in hot water bath for several minutes


Fehling’s solution or Benedict’s solution

·        Both contain complexed copper(II) ions in an alkaline solution.

·        Fehling’s solution contains copper(II) ions complexed with tartrate ions in sodium hydroxide solution

·        Benedict’s solution contains copper(II) ions complexed with citrate ions in sodium carbonate solution.

1)      A few drops of the aldehyde or ketone are added to the reagent

2)      Mixture is warmed gently in a hot water bath for a few minutes.



·        Aldehyde: Colourless solution producing silver mirror

·        Ketone: No change in the colourless solution








·        Aldehyde: Blue solution -> Dark red ppt (Cu2O ppt)

·        Ketone: No change (blue solution)


Metal Halides 1)      Add dilute nitric acid

2)      Add a few drops of silver nitrate

·        Fluoride = no precipitate

·        Chloride = White precipitate (able to dissolve in dil. NH3)

·        Bromide = Cream precipitate (able to dissolve in conc. NH3)

·        Iodide = Yellow precipitate