B4: Community level systems
Chapter 4.1: Ecosystems
Ecosystems
● Made up of living organisms and physical conditions of area
○ Organisms: community
○ Area they live in: habitat
● Population: number of organisms of each species
● Community groups:
○ Producers: make own food by photosynthesis
○ Consumers: cannot make own food, must eat other organisms for energy
○ Decomposers: gain energy by feeding on dead/decaying material
● Food chains display what an organism eats
○ Arrows show transfer of biomass
○ Trophic level: each step in food chain
○ Consumers can be classified by position in food chain
● Food web has series of interlinked food chains to show whole community
Biotic and abiotic factors
● Biotic factors: living factors eg. number of trees in woodland ecosystem (typically competition)
● Abiotic factors: non-living/physical factors eg. rainfall
● Light intensity (abiotic):
○ Required for photosynthesis
○ Higher light availability = higher success of plant
○ Plants evolve to grow in different light intensities
● Temperature (abiotic):
○ Affects enzymes controlling metabolic reactions
○ Cold-blooded animals and plants grow faster in warmer temperatures
● Moisture level (abiotic):
○ Lack of water = death
○ Required for photosynthesis and blood (plasma)
● Soil pH (abiotic):
○ Affects biological activity in soil and availability of minerals
○ Some plants grow best in acidic or alkaline soil
Competition and interdependence
● Plants and animals need different materials from surroundings
● If limited, they have to compete for resources
● What plants need to survive: light, minerals, space, water, CO2
● What animals need to survive: food, water, space, shelter, breeding partners
● Competition has direct effect on population eg. lots of food = population can increase
● Interdependence: how different organisms depend on each other in a community
● Interactions between organisms known as ecological relationships
● 3 types of relationships:
○ Predation: prey+predator relationship, predator pop. directly affects prey pop.
○ Mutualism: both organisms benefit from relationship
○ Parasitism: only parasite gains and host suffers
Pyramids of biomass
● Show population at each trophic level
, ● Producer at base, then next above
● Typically pyramid shaped (as size of organism increases, number decreases)
● By plotting biomass instead of population number and size of organism are factored
● Calculating biomass:
○ Ample of organisms taken from each trophic level
○ Measure average mass of each of these organisms and multiply by quantity
○ Scientists typically calculate dry mass of organisms since water content can vary
(requires death and then dried)
Efficiency of biomass transfer
● Biomass decreases at each trophic level
● Plants:
○ Only 1% of energy is transferred to plant from sun (mostly reflected from leaf)
○ <50% energy transferred by photosynthesis is transferred in respiration
○ Remaining energy transferred for biomass
● Animals:
○ About 10% of chemical energy in food is converted to new body tissue
○ Not all of organism is eaten eg. bones or roots
○ Some of biomass used in respiration
○ Some parts cannot be digested - removed as faeces (egestion)
○ Waste products produced by body removed by excretion eg. urine
● At each stage of food chain energy transferred becomes less
● Few food chains have 4+ trophic levels since not enough energy can be transferred
𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑎𝑓𝑡𝑒𝑟 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟
● Efficiency of biomass transfer (%) = 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟
Nutrient cycling
● Plants obtain nutrients needed for growth from soil
● Passed onto animals when plant is eaten
● When plants lose material or organisms die,
decomposers release trapped nutrients
● Many released back into soil (absorbed by plants),
some into atmosphere
● Materials are passed between biotic and abiotic parts
of ecosystem (nutrient cycling)
● 3 materials are cycled
● Carbon:
○ One of most common elements in organisms
○ Used to make carbohydrates, fats, proteins and DNA
○ Cycles between atmosphere, living organisms and
fossil fuels and can be trapped in oceans
and rocks
● Nitrogen:
○ Makes up <80% of atmosphere
○ Organisms use it for DNA and proteins
usually when in compound eg. nitrate
○ Exists in soil as nitrates dissolved in water
○ Water containing nitrates is taken by plant
and then used for proteins
○ Nitrogen compounds passed to animal
when eaten
○ When plants/animals die, compounds are broken down and released into soil as
ammonia
, ○ Animals put nitrogen back into soil by faeces and urine
● Water:
○ Essential for any ecosystem
○ Determines physical characteristics of habitats
necessary for organism
○ Eg. polar bears rely on ocean ice to hunt and
capture seals
○ Water cycle moves water and nutrients through
atmosphere, soil, rivers, etc
○ Brings fresh water and nutrients to people, animals
and plants
Carbon cycle
● Process by which carbon is cycled through atmosphere, earth, plants and animals
● How carbon is removed from atmosphere:
○ Photosynthesis (converts CO2 and water into
oxygen and glucose)
○ Glucose: simple sugar usable for complex carbs
(grow and develop (biomass)
○ Carbon is transferred to animal when plant is eaten
○ Some used to produce fats and proteins in animal’s
body
● How carbon is released into atmosphere:
○ Respiration: CO2 is produced and released
○ Decomposition: when plants/animals/algae die decomposers break down remains
(releasing CO2)
○ Burning fossil fuels:store of carbon, when burnt carbon is released
● Why level of atmospheric CO2 varies:
○ Photosynthesis happens only during day
○ Respiration is carried out day and night by all organisms
○ Over past 200 years, average has risen significantly (human activities)
Decomposers
● Microorganisms eg. bacteria and fungi that break down/decay dead organic material at
microscopic level
● Also break down animal waste
● Nutrients are released which can be recycled
● Saprophytes: organisms that feed on dead material this way
● Detritivores: small animals that speed up process - shreds material into small pieces
● Creates larger surface area for decomposers to work on
● How decomposers release nutrients:
○ Bacteria and fungi release enzymes to break down substances in matter
○ Then absorb soluble nutrients into body and used for growth and energy store
○ Many bacteria/fungi may be eaten by other organisms (nutrients passed on)
○ Some nutrients released directly into soil or environment
● Factors affecting rate of decomposition:
○ High temperatures denature enzymes, low temperatures make less reactions
○ Insufficient water reduces/stops reactions in microorganism
○ Oxygen needed for respiration
𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑚𝑎𝑠𝑠
● Rate of decay (g/day) = 𝑡𝑖𝑚𝑒
, B5: Genes, inheritance and selection
Chapter 5.1: Inheritance
Variation
What it is
● Phenotype: appearance of an organism eg. eye colour
● Variation: differences within a species eg. height
● Two causes of variation:
○ Genetic variation: generic material inherited from parents
○ Environmental variation: environment in which living thing lives
● Most characteristics in humans are caused by environmental factors eg. personality
● Very few characteristics in humans are caused by genetic variation alone eg. eye colour
● Some characteristics in humans can be affected by both eg. height
● Some characteristics controlled by one gene but most features controlled by multiple genes
Continuous and discontinuous variation
● Variation of a characteristic displayed within a species can be divided into two further groups
Continuous Discontinuous
definition can be any value in a range can only be one of
specific (discrete) values
example height blood group
cause of variation genetic and environmental genetic
genetic control multiple genes one or few genes
type of graph used histogram (sometimes just bar chart
trend line)
Sexual and asexual reproduction
Asexual reproduction
● Organism created from one parent and genetically identical to parent (clone of parent)
● Bacteria reproduce asexually - replicate their genetic material and divide in half by process of
mitosis
● Many plants can reproduce asexually eg. :
○ Potato plants produce many tubers, each of which can grow into new plant
○ Spider plants produce long stems (runners) with tiny plants (plantlets) on the end
○ Daffodils produce an underground storage organ (bulb) at end of each growing
season - following year new flower will grow from a bud on this bulb
● Small number of animals (including sea anemones and starfish) can reproduce asexually
Sexual reproduction
● Organism created from two parents and genetic info taken from both parents - offspring
produced aren’t identical (creates variation)
● Most animals reproduce sexually
● Organisms produce sex cells (gametes)
○ Sperm: male sex cells
○ Ova: female sex cells
● The gametes fuse together in fertilisation and fertilised egg then develops into offspring
● Many plants reproduce sexually - to create a new seed (to grow into plant), pollen cell (male)
has to fuse with an egg (female) in ovule
Chapter 4.1: Ecosystems
Ecosystems
● Made up of living organisms and physical conditions of area
○ Organisms: community
○ Area they live in: habitat
● Population: number of organisms of each species
● Community groups:
○ Producers: make own food by photosynthesis
○ Consumers: cannot make own food, must eat other organisms for energy
○ Decomposers: gain energy by feeding on dead/decaying material
● Food chains display what an organism eats
○ Arrows show transfer of biomass
○ Trophic level: each step in food chain
○ Consumers can be classified by position in food chain
● Food web has series of interlinked food chains to show whole community
Biotic and abiotic factors
● Biotic factors: living factors eg. number of trees in woodland ecosystem (typically competition)
● Abiotic factors: non-living/physical factors eg. rainfall
● Light intensity (abiotic):
○ Required for photosynthesis
○ Higher light availability = higher success of plant
○ Plants evolve to grow in different light intensities
● Temperature (abiotic):
○ Affects enzymes controlling metabolic reactions
○ Cold-blooded animals and plants grow faster in warmer temperatures
● Moisture level (abiotic):
○ Lack of water = death
○ Required for photosynthesis and blood (plasma)
● Soil pH (abiotic):
○ Affects biological activity in soil and availability of minerals
○ Some plants grow best in acidic or alkaline soil
Competition and interdependence
● Plants and animals need different materials from surroundings
● If limited, they have to compete for resources
● What plants need to survive: light, minerals, space, water, CO2
● What animals need to survive: food, water, space, shelter, breeding partners
● Competition has direct effect on population eg. lots of food = population can increase
● Interdependence: how different organisms depend on each other in a community
● Interactions between organisms known as ecological relationships
● 3 types of relationships:
○ Predation: prey+predator relationship, predator pop. directly affects prey pop.
○ Mutualism: both organisms benefit from relationship
○ Parasitism: only parasite gains and host suffers
Pyramids of biomass
● Show population at each trophic level
, ● Producer at base, then next above
● Typically pyramid shaped (as size of organism increases, number decreases)
● By plotting biomass instead of population number and size of organism are factored
● Calculating biomass:
○ Ample of organisms taken from each trophic level
○ Measure average mass of each of these organisms and multiply by quantity
○ Scientists typically calculate dry mass of organisms since water content can vary
(requires death and then dried)
Efficiency of biomass transfer
● Biomass decreases at each trophic level
● Plants:
○ Only 1% of energy is transferred to plant from sun (mostly reflected from leaf)
○ <50% energy transferred by photosynthesis is transferred in respiration
○ Remaining energy transferred for biomass
● Animals:
○ About 10% of chemical energy in food is converted to new body tissue
○ Not all of organism is eaten eg. bones or roots
○ Some of biomass used in respiration
○ Some parts cannot be digested - removed as faeces (egestion)
○ Waste products produced by body removed by excretion eg. urine
● At each stage of food chain energy transferred becomes less
● Few food chains have 4+ trophic levels since not enough energy can be transferred
𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑎𝑓𝑡𝑒𝑟 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟
● Efficiency of biomass transfer (%) = 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟
Nutrient cycling
● Plants obtain nutrients needed for growth from soil
● Passed onto animals when plant is eaten
● When plants lose material or organisms die,
decomposers release trapped nutrients
● Many released back into soil (absorbed by plants),
some into atmosphere
● Materials are passed between biotic and abiotic parts
of ecosystem (nutrient cycling)
● 3 materials are cycled
● Carbon:
○ One of most common elements in organisms
○ Used to make carbohydrates, fats, proteins and DNA
○ Cycles between atmosphere, living organisms and
fossil fuels and can be trapped in oceans
and rocks
● Nitrogen:
○ Makes up <80% of atmosphere
○ Organisms use it for DNA and proteins
usually when in compound eg. nitrate
○ Exists in soil as nitrates dissolved in water
○ Water containing nitrates is taken by plant
and then used for proteins
○ Nitrogen compounds passed to animal
when eaten
○ When plants/animals die, compounds are broken down and released into soil as
ammonia
, ○ Animals put nitrogen back into soil by faeces and urine
● Water:
○ Essential for any ecosystem
○ Determines physical characteristics of habitats
necessary for organism
○ Eg. polar bears rely on ocean ice to hunt and
capture seals
○ Water cycle moves water and nutrients through
atmosphere, soil, rivers, etc
○ Brings fresh water and nutrients to people, animals
and plants
Carbon cycle
● Process by which carbon is cycled through atmosphere, earth, plants and animals
● How carbon is removed from atmosphere:
○ Photosynthesis (converts CO2 and water into
oxygen and glucose)
○ Glucose: simple sugar usable for complex carbs
(grow and develop (biomass)
○ Carbon is transferred to animal when plant is eaten
○ Some used to produce fats and proteins in animal’s
body
● How carbon is released into atmosphere:
○ Respiration: CO2 is produced and released
○ Decomposition: when plants/animals/algae die decomposers break down remains
(releasing CO2)
○ Burning fossil fuels:store of carbon, when burnt carbon is released
● Why level of atmospheric CO2 varies:
○ Photosynthesis happens only during day
○ Respiration is carried out day and night by all organisms
○ Over past 200 years, average has risen significantly (human activities)
Decomposers
● Microorganisms eg. bacteria and fungi that break down/decay dead organic material at
microscopic level
● Also break down animal waste
● Nutrients are released which can be recycled
● Saprophytes: organisms that feed on dead material this way
● Detritivores: small animals that speed up process - shreds material into small pieces
● Creates larger surface area for decomposers to work on
● How decomposers release nutrients:
○ Bacteria and fungi release enzymes to break down substances in matter
○ Then absorb soluble nutrients into body and used for growth and energy store
○ Many bacteria/fungi may be eaten by other organisms (nutrients passed on)
○ Some nutrients released directly into soil or environment
● Factors affecting rate of decomposition:
○ High temperatures denature enzymes, low temperatures make less reactions
○ Insufficient water reduces/stops reactions in microorganism
○ Oxygen needed for respiration
𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑚𝑎𝑠𝑠
● Rate of decay (g/day) = 𝑡𝑖𝑚𝑒
, B5: Genes, inheritance and selection
Chapter 5.1: Inheritance
Variation
What it is
● Phenotype: appearance of an organism eg. eye colour
● Variation: differences within a species eg. height
● Two causes of variation:
○ Genetic variation: generic material inherited from parents
○ Environmental variation: environment in which living thing lives
● Most characteristics in humans are caused by environmental factors eg. personality
● Very few characteristics in humans are caused by genetic variation alone eg. eye colour
● Some characteristics in humans can be affected by both eg. height
● Some characteristics controlled by one gene but most features controlled by multiple genes
Continuous and discontinuous variation
● Variation of a characteristic displayed within a species can be divided into two further groups
Continuous Discontinuous
definition can be any value in a range can only be one of
specific (discrete) values
example height blood group
cause of variation genetic and environmental genetic
genetic control multiple genes one or few genes
type of graph used histogram (sometimes just bar chart
trend line)
Sexual and asexual reproduction
Asexual reproduction
● Organism created from one parent and genetically identical to parent (clone of parent)
● Bacteria reproduce asexually - replicate their genetic material and divide in half by process of
mitosis
● Many plants can reproduce asexually eg. :
○ Potato plants produce many tubers, each of which can grow into new plant
○ Spider plants produce long stems (runners) with tiny plants (plantlets) on the end
○ Daffodils produce an underground storage organ (bulb) at end of each growing
season - following year new flower will grow from a bud on this bulb
● Small number of animals (including sea anemones and starfish) can reproduce asexually
Sexual reproduction
● Organism created from two parents and genetic info taken from both parents - offspring
produced aren’t identical (creates variation)
● Most animals reproduce sexually
● Organisms produce sex cells (gametes)
○ Sperm: male sex cells
○ Ova: female sex cells
● The gametes fuse together in fertilisation and fertilised egg then develops into offspring
● Many plants reproduce sexually - to create a new seed (to grow into plant), pollen cell (male)
has to fuse with an egg (female) in ovule
