Ecosystems

Question 1

Define ecosystem

Answer 1

All interacting living organisms and the non-living conditions in an area

Question 2

Define community

Answer 2

All the populations of living organisms in a particular habitat.

Question 3

Define habitat

Answer 3

The area inhabited by a species

Question 4

Define population

Answer 4

A group of organisms of one species that live in the same place at the same time

Question 5

Define species

Answer 5

The smallest and most specific taxonomic group

Question 6

Define ecology

Answer 6

Ecology is a branch of biology that deals with the distribution, abundance and interactions of living organisms at the level of communities, populations, and ecosystems, as well as at the global scale.

Question 7

Explain what is meant by the phrase “ecosystems are dynamic”.

Answer 7

Means they are constantly changing

Question 8

Define the term biotic factor

Answer 8

The living components of an ecosystem e.g the presence of organisms, the size of the populations of organisms and the competition between the organisms

Question 9

Define the term abiotic factor

Answer 9

The non-living conditions in a habitat e.g. amount of rainfall and yearly temperature range, light, water and oxygen availability.

Question 10

Define the term “edaphic factor” and give 3 examples.

Answer 10

Soil factors- soil types have different particle sizes :

1. clay- fine particles, is easily waterlogged and forms clumps when wet
2. loam- this has different sized particles, retains water but does not become waterlogged.
3. sandy- this has coarse, well-separated particles that allow free draining- doesn’t retain water and is easily eroded.

Question 11

Define food web

Answer 11

Systems of interlinked food chains used to show the transfer of biomass and therefore energy through the organisms in an ecosystem.

Question 12

Define food chain

Answer 12

Chains used to show the transfer of biomass and therefore energy through organisms in an ecosystem. Each stage in the chain is known as a trophic level.

Question 13

Define trophic level

Answer 13

Stages in a food chain- starting with producer the rest are consumers.

Question 14

Define the term heterotroph

Answer 14

Organisms that acquire nutrients by the ingestion of other organisms.

Question 15

Explain what the arrows represent in a food web.

Answer 15

Arrows represent the transfer of energy- they point in the direction that energy is being transferred.

Question 16

Define consumer

Answer 16

Organisms that obtains its energy by feeding on another organisms.

Question 17

Define producer

Answer 17

Organism that converts light energy into chemical energy.

Question 18

Define detritovore

Answer 18

1. Organisms that speeds up decay by breaking down detritus into smaller pieces e.g woodlice- wood, earthworm-dead leaves
2. Increase the surface area of organic material for decomposers to work on.
3. Perform internal digestion

Question 19

Define decomposer

Answer 19

1. Organism that breaks down dead organisms releasing nutrients back into the ecosystem. e.g primarily microscopic fungi and bacteria like oyster mushrooms - wood
2. Obtain their energy by saprobiotic nutrition- digest waste externally by secreting enzymes onto dead organisms or organic waste matter.
3. This releases stored inorganic compounds and elements back into the environment.

Question 20

Define the term biomass

Answer 20

Mass of living material

Question 21

Define the term dry mass

Answer 21

The mass of living material without its water content

Question 22

Explain why dry mass is a better indicator of biomass than fresh mass.

Answer 22

Dry mass excludes fluctuating water concentration which would affect the mass.- unreliable.

Question 23

Explain how to calculate the dry mass of each tropic level in a food chain.

Answer 23

1. Multiply the dry mass present in each organism by the total number of organisms in that trophic level.
2. To work out dry mass organisms have to be killed and then placed in an oven at 80 degrees until all water has evaporated- two identical mass readings.
3. Biomass is measured in grams per square metre for land and grams per cubic metre for water.

Question 24

Explain how to experimentally measure the energy content of organic matter.

Answer 24

1. The energy available at each trophic level is measure in kilo joules per metre squared per year
2. To allow for changes in photosynthetic production and consumer feeding patterns throughout the year.

Question 25

Explain how pyramids of numbers, biomass and energy represent data about an ecosystem and the relative merits of each.

Answer 25

1. Pyramid of numbers- producers are always placed at the bottom of the diagram with subsequent trophic levels added above. Shows the actual number of organisms. 2. Pyramids of biomass- usually always pyramid shape , show, it is almost always less biomass than the trophic level before. 3. Biomass consists of all cells and tissue of the organisms present, including the carbohydrates and the other carbon compounds the organism contain. As carbon compounds are a store of energy, biomass can be equated to energy content.

Question 26

Explain how energy is transferred from one trophic level to the next.

Answer 26

1. When animals eat only a small proportion of food they ingest is converted into new tissue- part of the biomass which is available for the next trophic level to eat.

Question 27

Define the term “ecological efficiency” and write an equation to calculate it.

Answer 27

1. Efficiency with which energy or biomass is transferred from one trophic level to the next 2. Energy or biomass available after the transfer/ energy or biomass available before the transfer *100

Question 28

Explain 3 reasons why only 1-3% of the sunlight producers receive is converted into chemical energy.

Answer 28

1. Not all of the solar energy available is used for photosynthesis- approx 90% is reflected, some is transmitted through the leaf and some is of unusable wavelength. 2. Other factors may limit photosynthesis 3. A proportion of energy is lost as it is used for photosynthetic reactions.

Question 29

Define net production

Answer 29

Plants use 20-50% of the gross production in respiration. | 2. The rest of the energy is converted into biomass- this is the energy available to the next trophic level.

Question 30

Define respiratory losses

Answer 30

1. Energy lost in respiration (heat?)

Question 31

Write an equation for net production

Answer 31

Net production= gross production - respiratory losses

Question 32

Define primary production

Answer 32

The generation of biomass in a producer

Question 33

Define secondary production

Answer 33

The generation of biomass in a consumer

Question 34

Explain 4 reasons why consumers at each trophic level convert only a small amount of the biomass in the trophic level below to their own organic tissue.

Answer 34

1. Not all the biomass of an organism is eaten e.g plant roots or animal bones. 2. Some energy is transferred to the environment as metabolic heat, as a result of movement and respiration. 3. Some parts of an organism are eaten but are indigestible - these parts (and their energy content) are egested as faeces. 4. Some energy is lost from the animal in excretory materials such urine. `

Question 35

Draw, label and annotate, a diagram showing the flow of energy through trophic levels and out of the food chain.

Answer 35

Look at p 613. 1. Sun→produces→primary consumer etc 2. Arrow up pointing to decomposers and detritivores 3. Arrow down to energy lost as heat during respiration

Question 36

Explain why food chains with more than 4 trophic levels are rare.

Answer 36

As by the time it gets to the 4th trophic level there is not sufficient biomass and stored energy left to support any further organisms.

Question 37

Describe how humans have manipulated energy transfer through trophic levels in the farming of plants and animals to our advantage.

Answer 37

1. Plants are provided with the abiotic conditions they need to thrive 2. Competition from other species is removed- pesticides 3. As well as threat from predators.- creating barriers. 4. Agriculture creates simple food chains - so in farming animals or animal produce for human consumption, only 3 trophic levels are present. So less energy is less. 5. In plants for humans- only 2 trophic levels. 6. This means that the minimum energy is lost as there are fewer trophic levels than in the natural ecosystem, 7. This ensures as much energy as possible is transferred into biomass that can be eaten by humans.

Question 38

Compare the movement of energy through an ecosystem with the movement of elements such as nitrogen and carbon.

Answer 38

1. Energy has a linear flow through the ecosystem- enters from the sun and is ultimately transferred to the atmosphere as heat. As long as there is sun it is good. 2. Nutrients constantly have to be recycled throughout the ecosystems in order for plants and animals to grow. 3. This is because they are used up by living organisms and there is no large external source constantly replenishing nutrients in the way the Sun supplies energy.

Question 39

Draw, label and annotate a diagram of the nitrogen cycle.

Answer 39

1. Processes of nitrogen fixation, nitrification, denitrification and ammonification all form part of the nitrogen cycle. 2. Memorise it

Question 40

Explain the importance of decomposers and detritivores in the recycling of matter in ecosystems

Answer 40

1. Decomposition is a chemical process in which a compound is broken down into smaller molecules to its constituent elements. 2. These are often essential elements e.g. nitrogen or carbon, which cannot be directly used by an organism in the organic form it is in, in dead or waste matter 3. So they need to be broken down into inorganic elements and compounds, which are a more usable form and returned to the environment.

Question 41

Define nitrogen fixation

Answer 41

Conversion of nitrogen gas to ammonium compounds

Question 42

Define nitrification

Answer 42

Conversion of ammonium compounds into nitrites and nitrates.

Question 43

Define denitrification

Answer 43

Conversion of nitrates to nitrogen gas

Question 44

Define ammonification

Answer 44

Conversion of nitrogen compounds in dead organic matter or waste into ammonium compounds by decomposers.

Question 45

Name the micro-organisms involved in the nitrogen cycle and state the nitrogen-containing molecule they use and the nitrogen-containing molecule they produce.

Answer 45

1. Nitrogen fixing bacteria e.g Azotobacter (free-living soil bacteria) and Rhizobium (live inside root nodules) - contain nitrogenase which combines atmospheric nitrogen with hydrogen to produce ammonia. 2. Nitrifying bacteria e.g Nitrosomonas- oxidise ammonium compounds into nitrates 3. Nitrifying bacteria e.g Nitrobacter- oxidise nitrites into nitrates 4. Denitrifying bacteria- use nitrates as a source of energy for respiration and nitrogen gas is released. 5. Decomposers convert nitrogen-containing matter in dead organisms, faeces and urine into ammonium compounds.

Question 46

Draw, label and annotate a diagram of the carbon cycle.

Answer 46

see p619

Question 47

Explain why carbon dioxide levels in the atmosphere may vary throughout a 24 hour period, seasonally and over many years.

Answer 47

1. Photosynthesis only takes place in the light- in day lower levels of CO2 than in night 2. Lower CO2 in summer than winter days as photosynthesis is higher 3.

Question 48

Suggest two reasons why carbon dioxide levels in the atmosphere have increased significantly over the last 200 years

Answer 48

1. Combustion of fossil fuels- release CO2 that was trapped below Earth's surface 2. Deforestation- removed significant quantities of photosynthesising biomass from Earth.- less CO2 is removed from atmosphere and cleared forest is burnt releasing more CO2 3. CO2 raises temperature, amount of CO2 dissolved in seas and oceans is affected by the temperature (high temp means less CO2 is dissolved) - global warming reduces the carbon bank in the atmosphere- further contributing in a positive feedback loop

Question 49

Define succession

Answer 49

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

Question 50

Define primary succession

Answer 50

The predictable change in a community of organisms over time starting in a location where terrestrial life has not previously colonised. - newly formed land or exposed such as bare rock- no soil or organic material present.

Question 51

Define secondary succession

Answer 51

The predictable change in a community of organisms over time starting in a location where terrestrial life had previously colonised but the larger plant and animal life is no longer present. - soil is present but no plant or animal species- e.g bare earth after forest fire.

Question 52

Define deflected succession

Answer 52

1. Succession is prevented from proceeding due to some external factor, usually human activity 2. Succession is halted before it reaches the climax community.

Question 53

Define pioneer species

Answer 53

The first organisms to colonise an area

Question 54

Define seral species/ sere

Answer 54

The steps in succession

Question 55

Define climax community

Answer 55

1. The final stage in succession, where the community is said to be in a stable state 2. Not further succession occurs as long as the abiotic conditions remain the same.

Question 56

Define plagioclimax

Answer 56

1. Stage in succession where artificial or natural factors prevent the natural climax community from forming. 2. The final stage in deflected succession

Question 57

Give 5 adaptations that some species have for being pioneer species.

Answer 57

1. The ability to produce large quantities of seeds or spores, which are blown by the wind and deposited on the new land 2. Seeds that germinate rapidly 3. The ability to photosynthesise to produce their own energy- light, rainfall and air are often the only abiotic factors present. 4. Tolerance to extreme conditions 5. The ability to fix nitrogen from the atmosphere, so adding to the mineral content of the soil.

Question 58

Describe the effect pioneer species have on the environment.

Answer 58

1. It changes the conditions of the environment to make it more suitable for a different community of organisms. 2. They are poor competitors and get out-competed by organisms that arrive once the abiotic conditions are less harsh.

Question 59

Describe how the conditions of the soil change as succession occurs (and why).

Answer 59

1. Over time weathering of bare rock produces particles that form the basis of soil- cannot support other species on its own. 2. When organisms of the pioneer species die and decompose small organic products are released into the soil. 3. This organic component of soil is known as humus. 4. The soil becomes able to support the growth of new species of plant- secondary colonisers- as it contains minerals including nitrates and has an ability to retain some water.

Question 60

Describe how succession occurs

Answer 60

1. Soil becomes able to support the growth of new species of plant- secondary colonisers 2. Secondary colonisers arrive as spores or seeds e.g. mosses- pioneer species also provide a food source for consumers, so some animal species will start to colonise. 3. As the environmental conditions continue to improve, new species of plant arrive e.g ferns- tertiary colonisers. 4. Tertiary colonisers- have waxy cuticles that protects them from water loss- can survive without the abundance of water- but need to obtain most of their water and mineral salts from the soil. 5. At each stage the rock continues to be eroded and the mass of organic matter increases. 6. When organisms decompose they contribute to a deeper more nutrient-rich soil, which retains more water.- makes abiotic conditions more favourable initially for small flowering plants such as grasses, then shrubs and then trees. 7. This period is intermediate community and many seral stages evolve during this period until climax community is attained. 8. At each seral stage plant and animal species are better adapted to the current conditions in the ecosystem. They out-compete many of the species that were previously present and become the dominant species.- most abundant species (by mass) present in the ecosystem at a given time.

Question 61

Define dominant species

Answer 61

The most abundant species in an ecosystem at a given time.

Question 62

Describe and explain the change in niche number and number of species (and so biodiversity) present as succession progresses.

Answer 62

1. General increase in biodiversity- Abiotic conditions become less harsh and so more plant species can survive. More plants provides more different food sources for primary consumers. More primary consumers provide more different food sources for secondary consumers etc. More food sources provide more niches and more species arrive to fill each niche, increasing biodiversity. 2. But often it decreases as it gets towards the climax community- dominant species is out-competing pioneer and other species, resulting in their elimination. The more successful the dominant species the less biodiversity in a given ecosystem.

Question 63

Explain why secondary succession is likely to occur more quickly than primary succession.

Answer 63

1. Soil is already present so there doesn't need to be time for soil to develop up to the condition required for a climax community. 2. Often tehre are seeds already present in the soil and so chance colonisation doesn't need to occur. 3. Often the location of sites of secondary succession are near sites that are already colonised and so colonisation of this site is quick.

Question 64

Give 3 reasons why deflected succession might occur

Answer 64

1. Grazing and trampling of vegetation may occur by domesticated animals- results in large areas remaining as grasslands 2. Removing existing vegetation (such as shrub land) to plant crops- the crop become the final community. 3. Burning as a means of forest clearance- this often leads to an increase in biodiversity as it provides space and nutrient-rich ash for other species to grow such as shrubs.

Question 65

Define the term “sampling” and explain why it is important.

Answer 65

Sampling means taking measurements of a limited number of individual organisms present in a particular area. 1. Can be used to estimate the number of organisms in an area without having to count them all- abundance 2. Can be used to measure particular characteristic of an organism- measuring height of plants and taking an average

Question 66

State the two general ways in which sampling can be undertaken.

Answer 66

Random and non-random

Question 67

Define random sampling

Answer 67

Sampling where each individual in the population has an equal likelihood of selection.

Question 68

Define non-random sampling

Answer 68

The sample is not chosen at random, it can be opportunistic, stratified or systematic.

Question 69

Outline how to randomly sample an area.

Answer 69

Random number tables or computers can be used. 1. Mark out a grid on the grass using two tape measures laid at right angles. 2. Use random numbers to determine the x coordinate and the y coordinate on your rid 3. Take a sample at each of the coordinate pairs generated

Question 70

Name and describe the 3 main techniques of non-random sampling.

Answer 70

Opportunistic- This is the weakest form of sampling, as it may not be representative of the population - uses organisms that are conveniently available. Stratified- Some populations can be divided into a number of strata based on a particular characteristic.- a random sample is then taken form each of theses strata proportional to its size. Systematic- Different areas within an overall habitat are identified which are then sampled separately.

Question 71

Define the term Frame quadrat

Answer 71

A square rigid structure of fixed size used to identify an area to be sampled. It is usually dived in to a grid of equal sections

Question 72

Define the term point quadrat

Answer 72

A frame containing a horizontal bar. At set intervals along the bar, long pins can be pushed through the bar to reach the ground. Each species of plant the pin touches is recorded.

Question 73

Define the term line transect

Answer 73

This involves marking out a line along the ground between two poles and taking samples at specified points.

Question 74

Define the term belt transect

Answer 74

Provides more information than the line transect; two parallel lines are marked and samples are taken of the area between the two lines

Question 75

Define the term interrupted belt transect

Answer 75

Sampling using a frame quadrat at specific intervals along a line transect.

Question 76

Describe 5 ways to sample animals.

Answer 76

1. Pooter- catch small insects by sucking on a mouthpiece, draws insects into the holding chamber via the inlet tube 2. Sweep nets- catch insects in long grass 3. Pitfall traps- catch small crawling invertebrates in a hole that is dug in the ground- deep enough so they can come out and is covered with a roof structure to stop drowning. 4. Tree beating- a large white cloth is stretched out under the tree, the tree is shaken or beaten to dislodge invertebrate. 5. Kick sampling- the river bank and bed is kicked for a period of time to disturb the substrate. The net is held downstream for a set period of time in order to capture any organisms released into the flowing water

Question 77

Describe 2 ways to sample plants (and sessile, or very slow moving, animals).

Answer 77

1. point quadrat | 2. Frame quadrat

Question 78

Describe 3 ways of collecting data using a frame quadrat (that could be applied to either random or non-random sampling

Answer 78

1. Density- Count the number of plants in a quadrat- density per square metre- absolute measure not an estimate 2. Frequency- individual members of a species are hard to count like grass or moss. Using small grids within a quadrat count the number of squares a particular species is present in. 3. Percentage cover- for speed as lots of data can be collected quickly. Useful when a particular species is abundant or difficult to count. An estimate by eye of the area withing a quadrat that a species covers.

Question 79

Name, and state the equipment used to measure, 6 abiotic factors that could be measured when studying the abundance and distribution of organisms in an area.

Answer 79

1. Wind speed- anemometer ms-1 2. light intensity- light meter lx 3. Relative humidity- humidity sensor- mg dm-3 4. pH- pH probe 5. Temperature- temperature probe degrees Celsius 6. Oxygen content in water- dissolved oxygen probe mg dm-3

Question 80

Explain why a temperature probe linked to a data-logger may be advantageous over the use of a thermometer when investigating factors affecting the abundance and distribution of organisms in an area.

Answer 80

1. Rapid changes can be detected 2. Human error in taking a reading is reduced. 3. A high degree of precision can often be obtained. 4. Data can be stored and tracked on a computer

Question 81

Describe how the abundance of plants can be estimated (and then how population size can be calculated from this).

Answer 81

1. Quadrats are placed randomly in the area. 2. The abundance of the organisms in that area is measured by counting the number of individual plants contained within the quadrat. 3. Estimated population number (m-2) = Number of individuals in sample/ Area of sample (m2)

Question 82

Describe the capture-mark-release-recapture technique can be used to estimate the population size of an animal species.

Answer 82

1. Capture as many individuals as possible in a sample area 2. Mark or tag each individual- not detrimental to animals 3. Release the marked animals back into the sample area and allow time for them to redistribute themselves throughout the habitat 4. Recapture as many individuals as possible in the original sample area. 5. Record the number of marked and unmarked individuals present in the sample (release all individuals back into their habitat) 6. Lincoln index to estimate population size: (number of individuals in first sample * number of individuals in second sample)/ number of recaptured marked individuals.