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St Ninian’s High School
Life on Earth
National 5 Biology
Learning Outcomes
Food Chains
Food chains show the direction of energy flow.
Only 10% of energy is passed on at each stage of a food chain.
Energy is lost as heat and movement.
All food chains start with a plant (producer).
Producers can make their own food from the sun (photosynthesis).
Consumers (animals) need to eat other organisms to gain energy.
Primary consumers eat producers and secondary consumers eat primary consumers.
Herbivores eat plants, omnivores eat animals and plants and carnivores only eat animals.
Predators and prey must be animals with the prey (primary consumer) being the animal hunted and the predator
(secondary consumer) being the animal that hunts.
As the prey increase the predators decrease and vice versa on graphs.
Pyramids
A pyramid of numbers is a diagram that represent the number of organisms at each stage of a food chain.
A pyramid of biomass is a diagram that represents the mass of organisms at each stage of a food chain.
A pyramid of energy is a diagram that represents the total energy in the bodies of organisms at each stage of a
food chain.
A pyramid of numbers is less reliable as its base can be shorter when the producer is a tree or the
top consumer can appear larger than it should when it is an insect like a flea..
Pyramids of biomass and energy always retain their pyramid shape.
A producer always the largest biomass and energy and usually has the largest number.
Learning Outcomes
Food Webs & Competition
Interconnected food chains make up food webs.
When one organism is removed this will affect ALL other organisms by increasing/decreasing their numbers.
Competition is when organisms want the same/similar resource.
Intraspecific competition is between organisms of the same species for the same resource.
Interspecific competition is between organisms of different species for similar resources.
Intraspecific competition is fiercer as the resources required are the exact same.
Competition leads to natural selection (survival of the fittest) where one species increases and the other decreases.
To reduce competition, members of a species occupy different niches.
An organism’s niche is the role it plays in the community e.g. birds have different beaks to eat different food.
Nitrogen Cycle
This is a process where nitrogen is recycled between the air, plants & animals and the soil.
Nitrogen is very important as it is needed to make protein.
Proteins include enzymes, hormones, antibodies, receptors and structural proteins.
Three bacteria control the nitrogen cycle.
Nitrogen gas is converted into protein by nitrogen fixing bacteria.
Legumes are plants (peas/clover) that have nitrogen fixing bacteria in their root nodules and naturally increase the
nitrate
content of the soil, making it more fertile (natural fertiliser).
Lightening also allows nitrogen fixation to occur (nitrogen gas converted into nitrate in soil to make protein).
Denitrifying bacteria remove the nitrate from the soil and recycle this back into the air.
Animals eating plants (food chain) is the only step in the Nitrogen cycle that does not involve bacteria in the cycle.
Some food chains involve decomposition where dead animals/plants are broken down into ammonia.
Decomposers are involved in this process.
Decomposers include bacteria and fungi.
The third bacteria (nitrifying bacteria) convert ammonia into nitrite and then into nitrate.
Nitrification is the only 2 step process in the nitrogen cycle.
Plants then absorb/uptake the nitrate in the soil to make protein.
Learning Outcomes
Ecosystems & Biomes
Habitat is where an organism lives.
Community consists of all the animals/plants living in one area.
Population is one particular species.
Ecosystem is made up of living (community) and non living (habitat) parts.
Biomes are large ecosystems.
There are 9 biomes worldwide dependent on the climate (temperature and rainfall) e.g. Tundra, Sahara.
Biomes have specific flora (plants), fauna (animals) and climate (rainfall and temperature).
Biomes must be preserved to have a stable planet as they increase the biodiversity.
Biodiversity is the variety and abundance of organisms present.
Biomes are affected by biotic, abiotic and human factors.
Human factors have the biggest impact on biome biodiversity.
Biotic factors are living factors and include predators and grazing.
Predator and prey numbers are the opposite of each other and can be shown as waves on a graph.
Abiotic factors are non living factors and include moisture, light intensity pH and temperature.
Human impact factors include exploitation (overfishing/hunting), deforestation, poaching and pollution.
Pollution of the air resulting from burning fossil fuels, increasing the sulfur dioxide in the air.
Lichens are an example of an indicator species as they only grow where there is little air pollution.
Indicator species indicate the level of pollution by their presence/absence.
Pollution of the water is caused by fertiliser dissolving in rain water and being washed into lochs
This increases the nitrate causing an algae bloom. Decomposer bacteria then feed on the algae and reduce the oxygen leve
the water (respiration) causing fish to die.
Learning Outcomes
Sampling Techniques
Biotic and Abiotic Factors can be sampled.
Biotic factors include sampling animals (pitfall trap & tree beating) and plants (quadrat).
Pitfall trap are dug level with the soil and alcohol placed in the bottom and animals such as woodlice are sampled.
Tree beating is where a tree is lightly tapped and organisms that fall off are caught in a bucket e.g. spider.
Problems with pitfall traps include failure to check the trap regularly or place alcohol in the trap and therefore the insects eat
each other.
In tree beating organisms can fly away or not fall into the bucket (use a larger bucket).
Quadrats allow the abundance of a certain plant to be measured by counting the number of squares that contain the plant
NOT the number of plants e.g. 20/25 squares.
Quadrats must be thrown randomly.
All techniques can be made more reliable by repeating the technique.
Abiotic factors to be sampled include light intensity, temperature, pH and moisture.
Light intensity is measured by pointing a light meter at the maximum light and being careful not to cast a shadow.
pH and moisture meters involve placing a probe in the soil and wiping the probe between measurements.
Temperature can be measured with a thermometer with care taken to read the scale properly and to hold the thermometer
at the top to prevent body temperature being measured by accidently holding the bulb.
Line transects involve using a quadrat at REGULAR intervals e.g. every metre and looking at the effect of a plant’s distribution
with a certain abiotic factor e.g. effect of light intensity on grass growth.
The higher the light intensity, the greater the growth of grass (plants need light for photolysis in photosynthesis).
Mutations & Adaptations
Mutations are a random change to DNA/genetic information.
Mutations are ROLF: randomly occurring and at low frequency.
Mutations can be disadvantageous (genetic disease), advantageous or neither.
Disadvantageous mutations include down syndrome where individuals have 3 copies of chromosome 21.
Advantageous mutations create a new allele (form of a gene) increasing biodiversity. This is not very common (black squirrel)
and leads to natural selection and formation of a new species (speciation).
Adaptations are features that organisms have, occurring often after a mutation that increase their chance of survival.
Adaptations can be structural (shell), physiological (rat does not sweat) or behavioural (nocturnal)
Mutagenic agents increase the likelihood of a mutation occurring e.g. Radiation, mustard gas & high temperatures.
Learning Outcomes
Speciation
Natural variation exists in any population due to different alleles which is caused by random mutations.
Speciation is the formation of two or more species from 1 original species.
Darwin’s Finches in the Galapagos Islands are one example of speciation—all the birds have different beaks to eat
different food (niche).
The definition of a species is that it can interbreed to produce fertile offspring.
Speciation is a three step process: isolating mechanism, mutation, natural selection.
Isolating mechanisms prevent gene flow between two sub populations.
Examples of isolating mechanisms include geographical, ecological and reproductive.
Mutations are random and therefore occur only on 1 side of the barrier OR different mutations occur either side
of the barrier.
Natural selection increases the selection pressure for those with a selective advantage and these successful organisms reproduce and pass on their successful alleles and the weaker organisms die out.
Peppered moth is one example of natural selection where the peppered moth died out as the black moth had
camouflage as a selective advantage.
Resistant bacteria are another example of natural selection as is human skin colour with darker skin caused by
melanin pigment offering a selective advantage in warmer climates .
Learning Outcomes
Intensive Food Production Solutions
Increasing human population requires increased food yield.
Three main solutions to the food crisis are intensive farming, biological control and Genetically Modified Crop.
All of these have the advantage of increasing food production to cope with increasing demand but all have
disadvantages also.
Intensive farming involves fertilisers, pesticides, growth of 1 type of plant (monoculture), ploughing fields and
battery farms.
Fertilisers wash into rivers, increasing algae blooms which increases decomposer bacteria deoxygenating the
water and killing fish
Pesticides (DDT) cannot be broken down and accumulate in the bodies of organisms as you move up the food
chain to lethal levels.
Intensive farming also destroys habitats of animals/deforestation due to necessity of large fields and reduces
biodiversity.
Biological control is a natural alternative that does not involve chemicals.
Viruses/Predators are deliberately spread to control pests and reduce numbers e.g. Virus Myoxma or ladybirds to
kill greenfly.
Advantages of biological control include that the predator is specific to the pest, no resistance builds up, no
chemicals enter rivers or accumulate in animals and it is cheap to run after initial set up.
Disadvantages include lack of success on a large scale, predators can increase to a level that they become the
pest, initial set up costs are high and it is not possible to eliminate all pests meaning some crops will still be lost.
Genetically modified crops involves genetic engineering where a foreign gene is transferred into a plant to confer
an advantage.
Examples include blight resistant potatoes, golden rice and GM fruits e.g. tomatoes to prevent spoilage.
GM food surrounded in controversy due to health concerns.
1.1
Food Chains
Terms
Producer – makes their own food (by photosynthesis).
Consumers – needs to eat other organism to obtain food.
Food Chains
All food chains start with a producer (green plant).
The arrows show the direction of energy flow.
Food Chain Terms
Primary consumer
first consumer.
Secondary consumer
second consumer.
Tertiary consumer
third consumer.
Predators
animals who hunt other animals for food.
Prey
animals who are hunted by other animals.
***(note prey cannot be PLANTS)***
Carnivores
eat animals only
Herbivores
eat plants only
Omnivores
eat animals & plants
1.2
Energy transfer in Food Chains
All energy comes from the sun.
Plants absorb a small percent of this energy and use this to make food
(photosynthesis)
Likely Percentage Calculation 1
4% of the light energy reaching the sun is converted into new plant
material.
How much energy did the Oak tree Receive?
(4%) = 4/100 x 4,000,000 = 160,000 units of energy
Likely Calculation 2
Only 10% of energy is passed on at each stage of a food
How is the energy lost from the food web?
1. Heat
2. Movement
3. Undigested material (faeces)
1.3
Pyramids & Food Chains
Three types of Pyramids *** learn definitions ***
1.
Pyramids of Numbers
Show the number of organisms at each
stage of a food chain.
2.
Smallest amount of
energy/biomass/
numbers
Pyramid of Biomass
Shows the mass of organisms at each stage of a
food chain.
Largest amount of energy/biomass/numbers
3.
Pyramids of Energy
Shows the energy received by organisms at each
stage of a food chain.
Problem with pyramids of numbers
Pyramid does not resemble a true pyramid shape when a tree is a
consumer (smaller at bottom) OR insect at the top!
****Pyramids of biomass & energy always remain true pyramid ****
1.4
Food Webs
All organisms are connected in a food web. Removing one organism from the food
web destroys the delicate balance.
When an organism is removed it will ALWAYS affect other organisms in a good or
bad way, dependent on the circumstances.
Common Exam Question
What would happen to the phytoplankton and fish if the krill were
removed?
A)
Phytoplankton —increase
Why—Less krill eating the phytoplankton therefore can grow more.
B)
Fish—decrease
Why—Less krill to eat.
1.5
Competition & Niche
When animals/plants want same/similar resources
Examples of Resources
1. Space
2. Food
3. Light (plants only)
4. Mates (animals only)
Inter specific Competition
Intra specific Competition
Between different species
Within the same species who want the
who want similar resources.
same resources.
e.g. grey & red squirrels
Much fiercer competition
E.g. red squirrels
Competition Graphs
Results in the survival of the fittest
(Natural Selection)
1 species increases
1 species decreases
Niche
The role an organism plays in its community
Example;
Different beak SHAPE for different food.
Having different niches reduces competition.
2.0
Nitrogen Cycle
Decomposers
Decomposers are bacteria & fungus that feed on dead animals/plants and
return nutrients (nitrogen) to the soil.
Shown in food chains as a backwards loop on the food chain.
Grass
Bird
Cat
Fox
Decomposers
Decomposition
Living material broken down by bacteria/fungi (decomposers)
Useful material returned to soil (recycling)
Why Recycle Nitrogen by decomposers?
To make proteins in plants.
Nitrogen Cycle
2.0
Bacteria
3 Bacteria control the recycling of nitrogen in a cycle.
1.
Nitrogen fixing bacteria
Nitrogen gas
(air)
Protein (plants/animals)
Two Natural examples of Nitrogen Fixing
A) Lightning
2.
B) Legumes (peas/clover)
Denitrifying bacteria
Nitrate
(soil)
Nitrogen Gas (air)
3. Nitrifying Bacteria (two steps)
Ammonia (dead bodies)
Nitrite
Nitrate
2.0
Nitrogen Cycle
Other Steps to the Nitrogen Cycle:
Death & Decomposition
Death & Decomposition may appear as separate steps in an exam question
or may appear as the same step.
Death—when animals/plant die.
Dec—when dead bodies then turn into ammonia.
Uptake by roots/absorption
Plants convert nitrate (soil) plant protein (growth)
Nitrate = fertiliser for plants to make protein.
Eating
Food chain where animals eat plants.
Plant
Animals
Eating is the only step in the cycle which does not involve bacteria.
2.0
Nitrogen Cycle
Name of Step
Process
Nitrogen fixing bacteria
(legumes in root nodules)
Nitrogen gas to protein in plants (sometimes via
nitrate)
Denitrifying bacteria
Nitrate (soil) to nitrogen gas in air
Nitrifying bacteria
Ammonia to nitrite to nitrate
Decomposing bacteria/fungi
Organic remains forming ammonia
Absorption/uptake by roots
Nitrate in soil to plant protein
Biodiversity
3.1
Variety and relative abundance (amount) of living organisms.
Importance of Biodiversity
Variety of organisms needed for a stable planet as all food webs are linked
together.
If one type of organism dies out, others will be
affected.
Ecosystem Terms
Term
Definition
Example
Habitat
Where an organism lives.
Pride Rock/Caves
Population
One type of species.
Lions
Community All the different species living
together .
Ecosystem Made up of living (community) and non
living (habitat) parts.
Lions, hyenas,
monkeys
Desert
3.2
Biomes & Biodiversity
Biomes
Biomes are very large ecosystems— 9 worldwide
Depend on flora (plants), fauna (animals ) & climate (rainfall & temperature)
Examples: Tundra
Rainforest
Sahara Desert
Factors Affecting Biomes
Having a variety of Biomes is very important to
ensure biodiversity and a stable planet.
3 Factors affect the Distribution of Biomes.
Factor affecting Biome
Definition
Examples
1. Biotic Factors
Living factors
Predators, & Grazing,
2. Abiotic Factors
3. Human Influences
Non Living factors
Man made
influences
Rainfall and Temperature
Overfishing/hunting
Poaching
(biggest
Deforestation/Desertification
influence)
Pollution
A) fossil fuels release SO2 (air)
B) fertiliser produce algae bloom—
(water)
3.3
Biotic Factors
Predation/Prey Graphs
Explaining the Graph
Prey are high when predators are
low
Why—less predators to eat prey
Prey are low when predators are
high
Grazing & Biodiversity Graph
Why—prey eaten by predators
Explaining the Graph
Low Grazing/Low biodiversity
Dominant species are not kept in
check (survival of the fittest).
Medium Grazing/high biodiversity
Dominant species eaten, allowing
other weaker plants to grow.
High Grazing
Only dominant plants can handle
very high levels of grazing.
3.4
Human Impact on Biodiversity
Air Pollution
When fossil fuels are burned, sulphur dioxide (SO2) is released , polluting the
air.
Water pollution
Fertiliser (nitrate) washes into water
Increased algae bloom (plants grow)
Algae rotted by decomposer bacteria
Water deoxygenated
Fish/Other species die
Indicator Species
Presence or absence determines the level of pollution.
Two Examples
1.
Lichen (air pollution)
2. Stone fly nymph (water pollution)
Lichen Only grow where air is clean
Nymphs only live where water is
(lacks sulfur dioxide)
Oxygenated
(lacks bacteria)
3.5
Biotic Sampling Techniques
Sampling Animals
Pitfall Trap
Hole dug level with ground to ensure
insects fall in.
Covered in stones to ensure nothing eats
the insects.
Alcohol placed at bottom to stop insects
eating each other
E.g. woodlice
Tree Beating
Branch given few sharp taps at specific
height.
Insects fall into bucket/sheet below.
Use a large bucket/rimmed edges to be
to observe as many insects as possible
E.g. spider
Errors associated with Techniques
1.
Repeat for more reliable results (both)
2.
Trap not level with ground (pitfall trap)
3.
Alcohol not placed in trap (pitfall trap)
4.
Insects fly out of bucket (tree beating)
3.5
Sampling Plants:
Biotic Sampling Techniques
Quadrats
Error— quadrat not thrown randomly or mistake in classification when counting.
Thrown at random and number of
squares that have plants in the
square counted (abundance
score).
Example
Dandelion 12/25
*** Handy Hint ***
To increase Reliability
Repeat the experiment
3.5
Sampling Plants:
Biotic Sampling Techniques
Quadrats
Line transect.
Quadrat NOT THROWN RANDOMLY but placed every metre to determine the effect.
To determine the effect of an abiotic factor e.g. (light intensity) on the growth of a plant
i.e. plants need light to photosynthesise.
3.6
Abiotic Sampling Techniques
Light Intensity
Measured with a light meter.
Meter held at maximum light intensity & care taken
not to cast a shadow over meter
pH/Moisture
Measured with a pH/moisture meter
Simply place probe into soil and take reading. Care
taken to wipe probe between readings.
Temperature
Measured with a thermometer.
Measure air, soil or water temperature by holding
thermometer at top, avoiding the bulb at the bottom
to prevent you measuring body temperature
Care taken to read scale properly.
Errors
1.
Repeat for more reliable results (all).
2.
Cast shadow over meter (light meter)
3.
Failure to wipe between readings (moisture/pH meter)
4.
Holding thermometer at bulb/not reading scale correctly (temperature)
4.1
Mutations
Change to DNA base sequence (A, G, C, T)
Remember
Change to DNA base sequence
Changes the Amino Acid sequence at the
ribosome
Changing the protein produced (non functional)
E.g. enzyme, hormone, antibody etc
Mutations are ROLF!!!
Randomly Occurring (unpredictable)
Low frequency (do not occur often)
Mutagenic Agents
•Environmental factors that increase the frequency of a mutation occurring.
1. Radiation (UV, X-ray etc)
2. Chemical agents e.g. mustard gas
3. High Temperatures
Types of Mutations
1.
Disadvantageous—cause genetic disease
2.
Advantageous—help to increase variety & biodiversity
(cause natural selection & formation of new species)
3.
Neither—no effect
4.1
Types of Mutations
1. Disadvantageous Mutations—genetic disease
Down Syndrome
3 copies of chromosome 21
Symptoms
Causes physical & mental
development problems.
2.
Advantageous Mutations (not often)
Create new alleles (versions of a gene).
Increases variety & biodiversity.
Leads to Survival of the Fittest (natural selection) & formation of a
new species (speciation).
Example 1—black & grey squirrel
Black more aggressive
Example 2—black & peppered moth
black camouflaged against polluted lichen
4.2
Adaptations
A characteristic which an organism has which makes it well suited
to survive in its environment (survival of fittest)
Often result of a favourable mutation leading to Natural selection
and often formation of a new species who have a selective
advantage.
Adaptations increase biodiversity.
Types of Adaptations
1.
Structural
Shell, horns
2. Physiological (desert rat)
dry nose & mouth
does not sweat
Very efficient large intestine
3. Behavioural (desert rat)
nocturnal as too hot during day
4.3
Natural Selection
Also called ―survival of the fittest‖ as proposed by Darwin for how
species evolve.
Process
1.
Variation occurs naturally due to different
alleles (mutations)
2.
Fierce competition for resources (inter/intra).
3.
Increased selection pressure for those with a
selective advantage.
4.
Those individuals with a selective advantage
reproduce and pass on the successful alleles.
5..
Weaker individuals die out
Example of Natural Selection
Alleles
Selective Advantage
Peppered Moth
Dark & Peppered moth
Black moth—camouflaged
against polluted lichen.
Antibiotic Resistance
Human Skin Colour
Sensitive & Resistant
Only resistant bacteria can
bacteria
survive antibiotics leading to
Light & Darker Skin
Darker skin advantage where
weather is warmer as melanin
4.4
Speciation
Species Definition
Can interbreed to produce fertile offspring.
Speciation: formation of a new species
1. Isolating Mechanisms
2. Mutations
3. Natural Selection
Isolating Mechanisms (barrier)
Importance: Prevent gene flow between sub populations.
2 sub populations
form
Type of Isolating mechanisms: (learn these)
1.
Reproductive
2. Geographical
3. Ecological
Exam Tip
Write Geographical NOT river in exam!
4.4
2.
Speciation
Mutations
As mutations are RANDOM—mutations occur on only 1 side of the barrier.
3. Natural Selection
Increased selection pressure for those with a selective advantage.
These individuals survive and reproduce & pass on successful alleles.
Weaker individuals die out.
Isolating Mechanism
Diagram
1 species split into 2 sub –populations by
isolating mechanism (no gene flow)
Mutations
Mutation occurs on 1 side of barrier and
not other OR
Different mutations occur either side.
Natural Selection
Increased selection pressure for those
with a selective advantage.
Successful individuals reproduce & pass
on their alleles.
Two species formed. They cannot
Interbreed to produce fertile
Offspring.
5.1
Problems of Food Production
World Food Problem
Population rising sharply, hence not
enough food.
Need to increase food yield.
3 solutions
1.
Intensive farming
2.
Biological Control
3.
Genetic Modification of crops
1. Intensive Farming
Two chemicals are used in intensive farming
Features Description
Problem
Alternative
Fertiliser Nitrates which
Algae bloom
GM crops
Pesticide builds
Biological control
increase the growth
Pesticide Kill insects which
eat crops,
up as you move up
food chain & kills
5.2
Intensive Farming
Problem with fertilisers (learn this process)
Fertiliser washes into water
Increased algae bloom due to fertilizers
This reduces light levels killing aquatic plants.
Increased bacteria as they feed on dead algae/plants
Water deoxygenated
Fish Die (reduces biodiversity)
Problems with Pesticides
Pesticides can accumulate in the bodies of organisms over time.
As they are passed along food chains, toxicity increases and can reach
lethal levels.
(lethal levels)
5.3
Alternative to Intensive Farming
3. Biological Control
Control achieved via natural methods (no chemicals)
1.
Introducing disease
2.
Introducing predator
Virus Myxoma & Rabbits
Virus introduced to limit rabbit population.
Ladybirds & greenfly
Ladybirds (predator) of greenfly, reduce their numbers.
Advantages
1.
Predators specific to prey, does not reduce biodiversity.
2.
No chemicals to accumulate up food chains.
Disadvantages
1.
Not very successful on a large scale.
2.
Predators can become the pests if their numbers rise.
5.2
3.
Intensive Farming
GM Crops (genetic engineering of plants)
When a foreign gene in inserted into a plant to produce a desirable
characteristic.
Desirable characteristics of GM crops:
a) Plants that are now Drought resistant
b) Plants that are now Disease resistant
Indicator species
Presence or absence determines the level of pollution.
Two Examples
1.
Lichen (air pollution)
2. Stone fly nymph (water pollution)
Lichen only grow where air is clean
Nymphs only live where water is
(lacks sulfur dioxide)
Oxygenated
(lacks bacteria)