6.3.1 - Ecosystems

Question 1

What is an ecosystem?

Answer 1

The community of organisms (biotic) and non-living (abiotic) components of an area and their interactions

They are dynamic, and are influenced by both biotic and abiotic factors

Can be a range of sizes (eg oak tree, rock pool, playing field)

Question 2

What are biotic factors?

Answer 2

Living factors of an ecosystem

Eg:
• predation
• competition for space, food, water, light etc
• cooperation between organisms (same/different species)
• parasites
• pathogenic diseases caused by microorganisms
• mankind (hunting, farming, habitat loss)

Question 3

What are abiotic factors?

Answer 3

Non-living/physical factors affecting an ecosystem

Eg:
• light
• temperature
•water availability
• oxygen availability
• soil composition (

Question 4

How does light affect ecosystems?

Answer 4

• most plants are directly affected as light needed for photosynthesis
• in general, greater light availability = greater success of a plant species

Question 5

How does temperatures affect ecosystems?

Answer 5

• increased temperature increases enzyme activity
• plants and ectotherms develop more rapidly in warmer temperatures (endotherms less affected by external temperature)

• changes in temp of an ecosystem (eg due to changing seasons) can trigger migration/hibernation

Question 6

How does oxygen availability affect ecosystems?

Answer 6

• in aquatic ecosystems, cold, fast running water beneficial due to high concentration of oxygen. If water too warm/slow, organisms may suffocate
• in waterlogged soil, air spaces between oil particles are filled with water, reducing oxygen available for plants

Question 7

What is is a trophic level?

Answer 7

The position of an organism in a food chain

Question 8

What is a producer?

Answer 8

Photosynthetic organisms that convert light energy into chemical energy + produce biomass

Start of the food chain (first trophic level)

Question 9

What is a consumer?

Answer 9

Organism that feed on other organisms to obtain energy

Primary consumer - eats producer
Secondary consumer - eats primary consumer
Tertiary consumer - eats secondary consumer
Quaternary consumer - eats tertiary consumer

Food chains rarely have more trophic levels as there is insufficient biomass/stored energy left to support further organisms

Question 10

What is biomass?

Answer 10

The mass of living material present in a particular place/particular organisms

It’s important in the study of food chains/webs as it can be equated to energy content

Measured in kgm-2yr-1 (land) / kgm-3yr-1 (water)
• per year allows for changes, as biomass isn’t constant (due to seasonal changes, consumer feeding patterns etc)

Question 11

How is biomass calculated?

Answer 11

Multiply biomass in each organism by total number of organisms in that trophic level

Only represents biomass at a particular time - doesn’t take into account seasonal changes

Question 12

How is biomass measured?

Answer 12

Dry mass of organisms calculated

Organisms killed, placed in an oven at relatively low temperature (to prevent burning and loss of biomass, and dried until all water has evaporated (at least 2 identical mass readings)

A small sample is taken to minimise destruction

Advantages:
No water, so all mass is biomass

Disadvantages:
Organisms must be killed
Sample is small to minimise damage, but this may not be representative of population

Question 13

Why does biomass decrease as you move through the trophic levels (consumers)?

Answer 13

• not all of the biomass is eaten by the consumer
• not all of the biomass consumed is digested (lots passes through as faeces)
• the consumer converts a lot of the biomass (chemical energy) into movement and heat

Therefore, only a small proportion of biomass consumed is converted into new tissue (biomass)

Question 14

What is ecological efficiency?

Answer 14

The efficiency at which biomass/energy is transferred from one trophic level to the next

Question 15

Why is ecological efficiency between the sun and producers low?

Answer 15

• not all solar energy can be used for photosynthesis - most is reflected, some transmitted and some is an unusable wavelength
• some of the energy is used for photosynthetic reactions, respiration, etc
• other factors may limit the rate of photosynthesis (eg water availability)

Question 16

How can ecological efficiency be calculated?

Answer 16

Efficiency = (biomass transferred/biomass intake) x 100

Where:
• Biomass transferred = biomass that has passed to the higher trophic level
• Biomass intake = biomass of the lower trophic level that has been consumed

Question 17

How can net productivity of producers be calculated?

Answer 17

Net production = gross production - respiratory losses

Where:
•net production = energy available to the next trophic level
• gross production = total solar energy that plants convert to organic matter
• respiratory losses = energy used for respiration

Question 18

Why do humans manipulate the transfer of biomass through ecosystems?

Answer 18

• having complex food chains with many trophic levels reduces the biomass available for consumption at the top
• in agriculture of plants, there are only 2 trophic levels - the producer (crops) and the primary consumer (humans)
• in agriculture of animals/animal produce, there are 3 tropic levels - producer (animal feed), primary consumer (animal), secondary consumer (human)

The best way to maximise the efficiency is to maximise agricultural productivity

Question 19

How can arable farmers maximise agricultural productivity?

Answer 19

• Providing artificial light in greenhouses on overcast days
• Irrigation to maximise growth in dry weather
• Use of fertilisers
• Selective breeding for fast growth
• Use of fungicides/pesticides
• Fencing to exclude grazers
• Ploughing and herbicides to kill weeds
• Plant crops that store energy in edible form e.g. seeds, fruit, tubers

Question 20

How can livestock farmers maximise productivity

Answer 20

• Use of good quality feeds / food supplements
• Use antibiotics and vaccines to reduce disease
• Control predation with fencing or with indoor animal husbandry
• Reduce competition for grazing e.g. rabbits, deer
• Indoor husbandry to reduce energy loss from movement or from getting cold outside

Question 21

Why can biomass be equated to energy?

Answer 21

Biomass consists of the cell and tissues within an organism, including carbohydrates and other carbon compounds within them

Bcs carbon compounds are a store of energy, biomass can be equated to energy

Question 22

What is decomposition?

Answer 22

A chemical process in which a compound is broken down into small we molecules/constituent elements

Important because nitrogen/carbon often cant be used directly in dead/waste matter

Question 23

What is a decomposer?

Answer 23

An organism that feeds on and breaks down dead plant/animal matter into nutrients photosynthetic producers can use

Primarily microscopic fungi and bacteria

Question 24

What is saprobiotic nutrition?

Answer 24

The method of obtaining nutrients from dead/waste organic material via extra cellular digestion

Question 25

What are saprotrophs?

Answer 25

Organisms that obtain nutrients via saprobiotic nutrition (eg decomposers) The enzymes secreted by the decomposers break down complex organic molecules into simple soluble molecules they can absorb Not all of these molecules are absorbed by the decomposers and are absorbed by other organisms (eg plants)

Question 26

What are detritivores?

Answer 26

Speed up the decay process by feeding on dead/decaying matter Perform internal digestion By breaking it down into smaller materials, the increase the SA decomposers can work on

Question 27

Why does nitrogen need to be recycled?

Answer 27

* it is important for making amino acids and nucleic acids * animals obtain N from what they eat, but plants must obtain it from the environment *  N is abundant in atmosphere (78%) but N2 cant be taken up by plants - it must be combined with other elements eg H or O * bacteria converts into a form usable by plants

Question 28

What is the nitrogen cycle?

Answer 28

The cycle through which nitrogen moves between living organisms and the environment Involves ammonification, nitrification, nitrogen fixation and denitrification

Question 29

What is nitrogen fixation?

Answer 29

The conversion of atmospheric nitrogen gas into ammonia by nitrogen fixing bacteria in the soil (azotobacter) or root nodules of legumes (rhizobium) Can also happen by non-living processes eg lightning, Haber process

Question 30

What are nitrogen-fixing bacteria?

Answer 30

Microorganisms responsible for the conversion of atmospheric nitrogen gas into nitrogen-containing compounds Can be free living (azotobacter) or mutualistic (rhizobium)

Question 31

How do azotobacter and rhizobium work?

Answer 31

They contain the enzyme nitrogen are which combines N2 with H2 to form ammonia (NH3) Azotobacter is free living in the soil Rhizobium live inside rooot nodules of legumes and have a symbiotic mutualistic relationship: • the plant gains amino acids from rhizobium, which are produced by fixing N2 to ammonia • the bacteria gains carbs produced but plant during photosynthesis

Question 32

What is nitrification?

Answer 32

The conversion of ammonium ions in nitrate ions by nitrifying bacteria Done in 2 stages: 1) nitrifying bacteria (eg nitrosomonas) oxidise ammonium compounds into nitrites (NO2-) 2) another nitrifying bacteria (eg nitrobacter) oxidise nitrites into nitrates (NO3-) Nitrates are highly soluble and are teh form in which most nitrogen is absorbed into he plant

Question 33

What is denitrification?

Answer 33

The conversion of nitrate ions into nitrogen gas by denitrifying bacteria Done in anaerobic conditions as a source of energy for respiration

Question 34

What is ammonification?

Answer 34

Teh production of ammonium compounds when decomposers feed on organic nitrogen-containing molecules

Question 35

Why does carbon need to be recycled?

Answer 35

C is a component of all major organic molecules eg fats, carbs, proteins ``` It is stored in various forms: • atmosphere • sedimentary rocks • fossil fuels eg coal, oil, gas • soil and other organic matter • vegetation (eg cellulose) • dissolved in oceans ```

Question 36

How is photosynthesis involved in the carbon cycle?

Answer 36

* autotrophs use the energy of sunlight to ‘fix’ CO2, turning the carbon into sugars and other organic molecules * this removes CO2 from the atmosphere/oceans where it is dissolved

Question 37

How is feeding involved in the carbon cycle?

Answer 37

* carbon containing molecules are passed to primary consumers when they feed on producers * carbon is passed up the food chain when the consumer is consumes

Question 38

How is respiration involved in the carbon cycle?

Answer 38

All organisms respire Aerobic respiration releases CO2 into the atmosphere (ink reaction and kerbs cycle) Anaerobic respiration releases CO2 into atmosphere via fermentation of yeast, mould, bacteria

Question 39

How are decomposers involved in the carbon cycle?

Answer 39

Dead plants/animals are fed upon by detritivores and decayed by saprotrophs, which: • releases CO2 into surroundings • supplies C to detritivores and saprotrophs Waste matter can also be decayed and releases CO2 back into the air

Question 40

How is sedimentation involved in the carbon cycle?

Answer 40

* if organisms aren’t fully decomposed, their bodies can form layers of sediment that build up over millions of years, locking the carbon they store into the ground * this sediment can form fossil fuels like peat, coal, oil and gas containing carbon

Question 41

How do fossil fuels affect the carbon cycle?

Answer 41

* when fossil fuels are burnt, CO2 is released back into the atmosphere at a faster rate than its absorbed by plants and aquatic producers * CO2 level in atmosphere has risen dramatically * warmer temperatures mean less CO2 an be dissolved in oceans, so its released into atmosphere * this has caused dramatic climate change

Question 42

Why do CO2 levels fluctuate?

Answer 42

• photosynthesis requires light, so during the day, CO2 s removed from atmosphere • respiration occurs constantly (day and night) , releasing CO2 into the atmosphere Therefore, atmospheric CO2 levels are higher at night than during the day CO2 tends to be lower in summer than winter as rate of photosynthesis is higher

Question 43

What is succession?

Answer 43

The progressive replacement of one dominant type of species/community by another in an ecosystem until a stable climax community is established

Question 44

What is primary succession?

Answer 44

The prioress that occurs when newly formed/exposed land with no species present is gradually colonised by an increasing number of species New land includes: • New rock formed after a volcanic eruption • sand dunes in costal areas • sea level dropping/lake drying up

Question 45

What is a seral stage (sere)?

Answer 45

A step in the process of succession At each seral stage, key species can be identified that change he abiotic factors (esp soil) to make it more suitable for subsequent species At each seral stage, different species are better adapted to the current conditions in the ecosystem, which outcompete other species and become the dominant species

Question 46

What is a pioneer community?

Answer 46

* primary succession begins with the arrival of a pioneer species, which colonises the inhospitable environment * the species arrive as spores/seeds carried by wind from nearby environments, or by animal droppings (eg birds) *  examples of pioneer species = algae, lichen

Question 47

How are pioneer species adapted to colonise bare environments?

Answer 47

* produce large quantities of sees/spores which are blown by wind and deposited on new land * seeds germinate rapidly * can photosynthesise - light, rain and air (therefore CO2) often only abiotic factors present * tolerance to extreme environments * ability to fix nitrogen form atmosphere, adding to the mineral content

Question 48

How to pioneer species affect the conditions of an environment?

Answer 48

* when organisms of a pioneer species die and decompose, small organic products are released - this organic component is called humus * over time, bare rock weathers and combines with the humus to form a soil * the soil becomes able to support secondary colonisers (eg moss) which arrive as spores or seeds. This is because the soil contains nitrates and can retain some water *  pioneer species may also provide a food source for consumers, so some animal species will start to colonise the area

Question 49

What is an intermediate community?

Answer 49

* pioneer species alter the environment, making to possible for secondary colonisers to settle * as environmental conditions continue to improve, tertiary colonisers (eg ferns) arrive *  at each stage, rock continues to be eroded and mass of organic matter increases * when organisms decompose, they contribute to a deeper, nutrient rich soil which makes abiotic conditions more favourable for small flowers, later shrubs and eventually trees * in many cases, multiple seral stages evolve during the intermediate period

Question 50

What is deflected succession?

Answer 50

Changes to the natural flow of succession due to human activity that result in a stable community called a plagioclimax

Question 51

Why does deflected succession occur?

Answer 51

AGRICULTURE • grazing and trampling of vegetation by domesticated animals resulting in large areas remaining as grassland • removing existing vegetation to plat crops - crop becomes final community • burning as a means of forest clearance - often leads to an increase in biodiversity as it provides space and nutrient-rich ash for other species to grow CONSERVATION • intermediate stages of succession often hold a distinctive diversity that wouldn’t exist if climax community was reached • these environments also provide food and habitat for a high diversity of animals which may also be of conservation importance • deflected succession can maintain an environment at an intermediate level eg heathland

Question 52

Hoe cam distribution of organisms within an ecosystem be measured?

Answer 52

LINE TRANSECT • lay a line/surveyors tape along the ground and take samples at regular intervals BELT TRANSECT • 2 parallel lines are marked • samples taken of the area between these specified points Both are systematic sampling techniques

Question 53

Why may systematic sampling be better than random sampling when measuring the distribution of organisms?

Answer 53

* in SS, different areas within a habitat are identified and sampled separately * this allows scientists to study how the differing abiotic factors in different areas may affect the distribution of species

Question 54

What is the distribution of organisms within an ecosystem?

Answer 54

Refers to where individual organisms are found within an ecosystem

Question 55

What is abundance?

Answer 55

The number of individuals of a species in a specific area at any given time This may fluctuate daily due to immigration, emigration, birth and death

Question 56

Why can populations rarely be counted accurately?

Answer 56

* Some animals elude capture * May be too time-consuming to count all members of the population *  Counting process could damage environment They are therefore estimated using sampling techniques

Question 57

What is a population?

Answer 57

All organism of the same species living with one another in a habitat at the same time

Question 58

How can you increase the accuracy of a sample?

Answer 58

* use a large sample size - greater number of individuals studied = lower probability chance will influence results * use random sampling to reduce the effect of sampling bias

Question 59

How is plant abundance measured?

Answer 59

* quadrats are placed randomly in an area * abundance in that area is measured by counting the no. Of individual plants contained within quadrat P = N÷A Where: • P = estimated number in population (m^-2) • N = number of individuals in sample • A = area of sample (m^2)

Question 60

How can animal abundance be measured?

Answer 60

Using the capture-mark-release-recapture technique P = (F x S)/R Where: • P = estimated population size • F = number of individuals in first sample • S = number of individuals in the second sample • R = number of recaptured marked individuals

Question 61

What is the capture-mark-release-recapture technique?

Answer 61

1) capture as many individuals as possible in a sample area 2) mark/tag each individual 3) release the marked animals back into the sample area and allow them to redistribute themselves through the habitat 4) recapture as many individuals as possible in the original sample area 5) record the number of marked and unmarked individuals present, then release back into their habitat 5) use the Lincoln index to estimate population size

Question 62

What is Simpson’s index?

Answer 62

Used to calculate biodiversity in a habitat Value of 0-1, with higher values = higher biodiversity D = 1- Σ(n/N)² Where: • D = Simpson’s index • n =number of individuals in each species • N = total number of organisms in the ecosystem