Ecosystems and sustainability

Question 1

what is an ecosystem?

Answer 1

a stable self-maintaining unit consisting of the community of populations (biotic factors) and the physical habitat (abiotic factors) and their reactions

Question 2

what is meant by the fact that ecosystems are dynamic?

Answer 2

they are constantly fluctuating e.g. a population size can rise or fall, affecting other populations via food chains - e.g. nitrogen-fixing plants increase nitrate soil level, and other plants take up nitrates decreasing the level

Question 3

What are biotic factors? name some biotic factors in an ecosystem

Answer 3

Factors that involve other living organisms including:

• feeding of herbivores on plants
• predation of predators on prey
• competition between species for shared resources
• parasites living on hosts
• mutualistic relationships where 2 species benefit from each other

Question 4

What are abiotic factors? name some abiotic factors in an ecosystem and how they affect the organisms in the environment

Answer 4

Factors involving the non-living physical habitat such as:

• temperature: rate of reactions in endotherms and ectotherms
• light intensity: rate of photosynthesis (plants) and behaviour (animals)
• O2 concentration in water: aerobic respiration
• water supply
• wind speed: plant transpiration, lowers temperatures
• atmospheric humidity: water loss by sweating/transpiration
• ion availability: nitrates affect plant growth
• soil type: drainage and water content for plants

Question 5

what is the energy input into an ecosystem? why is it needed

Answer 5

light energy from the sun. Ecosystems need a flow of energy through it to be self-maintaining

Question 6

What is a producer? e.g.

Answer 6

autotrophic organisms - e.g. plants convert light energy into chemical energy in photosynthesis
a few convert chemical energy into usable chemical energy

Question 7

What are consumers

Answer 7

organisms that obtain energy feeding on other organisms

Question 8

what are decomposers

Answer 8

organisms which obtain their energy feeding on dead matter/animal waste

Question 9

What is a trophic level?

what do arrows in food chains represent

Answer 9

each step in a food chain is called a trophic level. Arrows represent flow of energy from one trophic level to another

Question 10

What is the number of organisms in an ecosystem fundamentally determined by?

Answer 10

The efficiency of energy flow through the ecosystem

Question 11

What are some reasons for energy lost to the environment at each step in a food chain? (4)

Answer 11

• respiration of molecules to produce ATP for life processes such as protein synthesis
• heat loss from respiration and other chemical reactions
• loss of plant parts which die/shed (this energy is available only to decomposers)
• plants parts - cellulose - that cannot be digested
• energy lost in animal waste e.g. urine, faces (this energy is available only to decomposers)

Question 12

What are 3 ways to measure the efficiency of energy transfers in an environment?

Answer 12

• pyramids of biomass: dry mass of all organisms at a trophic level
• pyramids of energy: calorimetry used to measure energy released
• productivity: energy available in a particular trophic level per square metre per year

Question 13

How do you work out the net primary productivity (NPP) available to a consumer in a habitat?

Answer 13

gross primary productivity (the rate at which plants convert light energy into chemical energy) take away respiratory losses
GPP - respiratory losses

Question 14

what are the problems associated with measuring efficiency of energy transfers using pyramids of biomass, pyramids of energy, and NPP?

Answer 14

pyramids of biomass: destructive to the ecosystems when organisms are dried in an oven at 80 degrees, and the alternative method of collecting wet mass and converting it to dry mass using published data is also unreliable because different species may contain different amount of energy per unit mass.
pyramids of energy: destructive, time-consuming, doesnt take into account fluctuation in population sizes over time
NPP: varies in different habitats and even areas of the same habitat according to factors affecting rate of photosynthesis

Question 15

How can humans manipulate environmental factors to increase primary productivity (i.e. plant crops)?

Answer 15

• light intensity: artificial light in greenhouses/planting erlier in the year
• water: irrigation/development of drought-resistant crops
• temperature: higher in glasshouses
• ion availability: nitrate levels increased by crop rotation, use of nitrogen-fixing plants, inorganic fertilisers
• pests: use of pesticides, selective breeding/genetic modification to create pest-resistant strains
• competition reduced: use of herbicides

Question 16

How can humans manipulate energy transfer from producers to consumers to increase secondary productivity (i.e animals)?

Answer 16

• slaughtered before adulthood so less energy used in growth
• selective breeding can produce breeds with faster growth rates, increased egg production or higher milk yields
• antibiotics can be given to prevent energy losses to combat diseases
• animals can be kept indoors to minimise heat loss and restrict energy losses due to movement
• increased food availability e.g. protein supplements to increase muscle growth

Question 17

describe primary succession

Answer 17

the sequence of plant and animal populations that colonise a new area over a period of time. Each population changes the physical conditions, making it possible for other species to colonise the area and out-compete and replace the previous community

Question 18

why is nitrogen so important for living organisms?

Answer 18

involved in many important biological molecules such as nucleic acids, proteins, ATP and are required in the form of nitrates

Question 19

what is the only way nitrogen in the atmosphere can be accessed? what type of bacteria are involved anywhere might they be found?

Answer 19

NITROGEN-FIXATION: nitrogen-fixing bacteria such as Rhizobium convert N2 gas into ammonium compounds. Can be found free living in the soil or inside root nodules of leguminous plants

Question 20

describe ammonification

Answer 20

Nitrogen containing compounds e.g. proteins in dead animals are converted to amino acids then ammonia compounds by decomposer bacteria/fungi

Question 21

describe the process by which ammonium compounds are converted into materials which are accessible to plants. Bacteria involved?

Answer 21

NITRIFICATION: ammonium compounds –> nitrites (uses Nitrosomonas) –> nitrates (uses Nitrobacter)
Requires oxygen, so aerated soil required.
Plants can take up the nitrates from the soil by active transport

Question 22

what is denitrification?

Answer 22

conversion of nitrates in the soil to N2 gas by denitrifying bacteria. Occurs in anaerobic soils and makes the soil less fertile as fewer nitrates are available for plant growth

Question 23

Discuss the efficiency of energy transfers between trophic levels

Answer 23

At each step in a food chain, some enegry is lost to the environment and so is not available to the next trophic level.
This means there are rarely more than 5 trophic levels in a food chain.
Reasons for energy losses:
- respiration of molecules to produce ATP for life processes e.g. protein synthesis
- heat loss from respiration and other chemical reactions
- loss of plant parts e.g leaves/flowers - energy available to decomposers only
- indigestible plant parts such as cellulose
- excreted energy in urine, faeces only available to decomposers

Question 24

how can the distribution and abundance of organisms in a habitat be measured?

Answer 24

using sampling techniques such as line transects, belt transects, quadrats and point quadrats

Question 25

When are quadrats used and how?

Answer 25

Used for sampling uniform habitats, e.g. grasslands.
Coordinates selected using random number generators and quadrats placed.
Dichotomous keys used to identify species in each quadrat.
No. large individuals counted, % cover for small individuals estimated. Means are calculated from 10+ quadrats.

Question 26

What are point quadrats?

Answer 26

Linear frames with holes at regular intervals. They are placed within a quadrat and pins are pushed through the holes. Species touched by the pins are recorded, and the number of hits is proportional to the percentage cover.

Question 27

When are transects used instead of quadrats?

Answer 27

Used to investigate changing habitats over a distance, a.g. up a hill, along a shore.

Question 28

Describe the 2 types of transects

Answer 28

Line transects:
A line is marked out along a region using tape/string. At regular intervals, the species touching the line are identified and recorded.
Belt transects:
quadrats are placed at regular intervals along the line (interrupted belt transect) or side by side along the line (continuous belt transect). The percentage cover of each species is measured, showing the changing distribution of each species. Other measures can be taken e.g. soil samples, water content, pH. The transect is repeated further on.

Question 29

describe one example of primary succession resulting in a climax community

Answer 29

succession on sand dunes:

1. pioneer plants are tolerant of salt spraay and a lack on nutrients and watre colonise bare sand - have xerophytic features e.g. sunken stomata, thick waxy cuticle to reduce water loss
2. The pioneer plants change the conditions allowing other plants to grow. Death of plants provides humus which traps water and releases nutrients as it decays.
3. Sea couch grass and marram grass stabilise the sand with underground roots
4. nitrogen-fixing plants colonise the base of the dunes where more water is available and add nitrates to the newly forming soil
5. This allows a wider range of grasses to grow and the top of the dunes becomes grassland
6. eventually this may be succeeded by a woodland climax community which outcompete the grassland plants by shading them and obtain more water and nitrates with their longer roots