ecosystem Flashcards
1
Q
What is an ecosystem?
A
All of the living organisms that interact with one another in a defined area, and also the physical factors present in that region • e.g. rock pool, large tree, playing field, or a particular stretch of river
2
Q
What are the 2 types of factors
that affect ecosystems?
A
Biotic and abiotic factors
3
Q
What are biotic factors?
A
The interactions between organisms that are living, or have once lived. Often involves competition, either within a population or between different populations, e.f. for food, space and breeding partners • Producers: Plants (and some photosynthetic bacteria), which supply chemical energy to all other organisms • Consumers: Primary consumers are herbivores which feed on plants, and which are eaten by carnivorous secondary consumers which are eaten by carnivorous tertiary consumers • Decomposers: e.g. Bacteria, fungi and some animals, feed on waste material or dead organisms
4
Q
What are abiotic factors?
A
The non-living or physical factors • Light • Temperature • Water availability • Oxygen availability • Edaphic (soil) factors
5
Q
Describe light as an abiotic
factor
A
In general the greater the availability of light, the greater the success of a plant species • Plants develop strategies to cope with different light intensities • In areas of low light they may have larger leaves • They may also develop photosynthetic pigments that require less light • They may have reproductive systems that only operate when light availability is at an optimum
6
Q
Describe temperature as an
abiotic factor
A
The greatest effect of temperature is on the enzymes controlling metabolic reactions • Plants and ectothermic animals will develop more rapidly in warmer temperatures • Changes in the temperature of an ecosystem (e.g. changing seasons), can trigger migration or hibernation of animal species, and leaf-fall, dormancy or flowering for plant species
7
Q
Describe water availability as
an abiotic factor
A
In most plant and animal populations, a lack of water leads to water stress, which, if severe, will lead to death • A lack of water will cause most plants to wilt as water is required to keep cells turgid and so keep the plant upright • Water is also required for photosynthesis
8
Q
Describe oxygen availability as
an abiotic factor
A
• In aquatic ecosystems, it is beneficial to have fast-flowing cold water as it contains high concentrations of oxygen • If water becomes too warm or the flow rate too slow, the resulting drop in oxygen concentration can lead to the suffocation of aquatic organisms • In waterlogged soil, the air spaces between the soil particles are filled with water, which reduces the oxygen available for plants
9
Q
Describe edaphic (soil) factors as abiotic factors
A
Different soil types have different particle sizes which affect the organisms that are able to survive: • Clay: fine particles, easily waterlogged and forms clumps when wet • Loam: different-size particles, retains water but doesn’t become waterlogged • Sandy: coarse, well-separated particles that allow free draining, doesn’t retain water and is easily eroded
10
Q
What is a trophic level?
A
The level at which an organism feeds in a food chain • Producers • Primary consumers • Secondary consumers • Tertiary consumers
11
Q
What is biomass?
A
The mass of living material present in a particular place or in particular organisms • Important measure in the study of food chains and webs, as it can be equated to energy content Biomass at trophic level = biomass in each organism x total number of organisms in trophic level • This represents the biomass present at a particular moment in time and does not take into account seasonal changes
12
Q
How is biomass measured?
A
By calculating the ‘dry mass’ of organisms present • Organisms have to be killed in order to be dried • Organisms are placed in an oven at 80°C until all the water has evaporated (2 identical mass readings) • Only a small sample is taken to minimise the destruction of organisms, but this may not be representative • Measured in grams per square metre (g m-2) for areas of land, and grams per cubic metre (g m-3) for areas of water
13
Q
Why does biomass decrease
as you move up trophic levels?
A
• Biomass consists of all the cells and tissues of the organisms present, including the carbohydrates and other carbon compounds • As carbon compounds are a store of energy, biomass can be equated to energy content • When animals eat, on a small proportion of the food they ingest is converted into new tissue • It is only this part of the biomass (and hence energy) that is available for the next trophic level to eat
14
Q
How is energy at trophic levels
measured?
A
Kiljoules per metre squared per year (kJ m-2 yr-1) • This allows for changes in photosynthetic production and consumer feeding patterns throughout the year
15
Q
What is ecological efficiency?
A
The efficiency with which biomass or energy is transferred from one trophic level to the next Biomass transferred x 100 Biomass intake
16
Q
Describe efficiency at producer
level
A
Producers only convert 1-3% of solar energy they receive into chemical energy and hence biomass • Not all of the solar energy available is used for photosynthesis - 90% is reflected, some is transmitted through the leaf, and some is of unusable wavelength • Other factors limit photosynthesis • A proportion of the energy is used as it used for photosynthetic reactions
17
Q
What is net production?
A
Net production = gross production - respiratory losses • The total solar energy that plants convert to organic matter is gross production • Plants use 20-50% of this energy in respiration • The rest is converted into biomass
18
Q
Describe efficiency at
consumer levels
A
Consumers convert at most 10% of the biomass in their food into their own organic tissue • Not all of the biomass of an organism is eaten e.g. plant roots and animal bones may not be consumed • Some energy is transferred to the environment as metabolic heat as a result of movement and respiration • Some parts of an organism are eaten but are indigestible - these are digested as faeces • Some energy is lost from the animal in excretory materials e.g. urine
19
Q
How do human activities
manipulate biomass through
ecosystems?
A
Agriculture involves planting species that we can eat (crops), and rearing animals for their food or produce • Plants and animals get the abiotic conditions they need to thrive e.g. watering, greenhouse use and stabling animals • Competition from other species is removed (pesticides) as well of the threat of predators (fences) • Agriculture creates very simple food chains, so the minimum energy is lost since there are fewer trophic levels than in the natural ecosystem • This ensures that as much energy as possible is transferred in biomass that can be eaten by humans
20
Q
What is decomposition?
A
A chemical process in which a compound is broken down into smaller molecules, or its constituent elements • Organic material must be processed into inorganic elements and compounds, which are a more usable form, and returned to the environment
21
Q
What is a decomposer?
A
An organism that feeds on and breaks down dead plant or animal matter, turning organic compounds into inorganic ones (nutrients) available to photosynthetic producers in the ecosystem. • Primarily microscopic fungi and bacteria, but also include large fungi e.g. toadstools
22
Q
Why are decomposers
saprotrophs?
A
They obtain their energy from dead
or waste organic material
(saprobiotic nutrition)
23
Q
How do decomposers digest
their food?
A
Externally by secreting enzymes onto dead organisms or organic waste matter • The enzymes breakdown complex organic molecules into simpler soluble molecules • The decomposers then absorb these molecules • Through this process, decomposers release stored inorganic compounds and elements back into the environment
24
Q
What are detritivores?
A
Another class of organism involved in decomposition • They help to speed up the decay process by feeding on detritus (dead and decaying material) • They break it down into smaller pieces of organic material, which increases the surface area for the decomposers to work on • They perform internal digestion • e.g. woodlice that breakdown wood, earthworms that help break down dead leaves
25
Q
What is nitrogen fixation?
A
The combination of atmospheric nitrogen (N2) with hydrogen (H2) to produce ammonia (NH3) by nitrogenfixing bacteria such as Azotobacter and Rhizobium.
26
Q
Describe 2 examples of
nitrogen-fixing bacteria
A
• Azotobacter is a free-living soil bacterium • Rhizobium live inside root nodules - these are growths on the roots of leguminous plants e.g. peas, beans and clover • They contain the enzyme nitrogenase for nitrogen-fixing
44
Q
What are seral stages (or
sere)?
A
The steps involved in succession
• Pioneer community
• Intermediate community
• Climax community
66
Q
How is the biodiversity present
in a habitat calculated
A
Simpson’s Index of Diversity (D): D = diversity index N = total number of organisms in the ecosystem N = number of individuals of each species • Always results in a value between 0 and 1. 0 represents no diversity, and 1 represents infinite diversity
