Here i have some super detailed flashcards on the module 'Population size and ecosystem' which i used to achieve an A* in A-Level Biology.
The exam board i used was Eduqas/WJEC, however OCR and Eduqas are very similar boards and the flashcards will still be applicable.
Q: Define ecosystem:
A characteristic community of interdependent species interacting with the abiotic
components of their habitat.
Q: Define habitat:
The place in which an organism lives.
Q: Define community:
Interacting populations of two or more species in the same habitat at the time.
Q: Define niche:
The role and position a species has in its environment, including all interactions with
the biotic and abiotic factors of its environment.
Q: Why are ecosystems dynamic?
The intensity of energy flowing through the ecosystem varies.
Biological cycles, such as the nitrogen cycle, vary the mineral availability.
Habitats change over time as succession occurs.
New species arrive and some species are no longer present.
Q: What is a fugitive species?
Species that are poor at competition. Instead, they rely on a large capacity for
reproduction and dispersal to increase their number. Example = algae
Q: Describe the 4 phases of the one-step growth to model the population size in an
equilibrium species:
1. Lag Phase = initially, population does not increase but then there is a period of slow
growth. Period of adaptation or preparation for growth with intense metabolic
activity. Represents the time for individuals to reach sexual maturity.
2. The exponential phase = as numbers increase, as long as there is no factor limiting
growth, more individuals become available for reproduction. However, as numbers
increase, environmental resistance starts to be a factor, as there will be less food
available, not enough space and waste products tend to build up and reach toxic
levels. Biotic factors also set in, for example, predation and parasitism.
3. Stationary phase = occurs when birth rate is equal to the death rate. The population
has reached its maximum size, which is the carrying capacity.
4. Death phase.
Q: What factors regulate population growth?
, Population Size and Ecosystems:
1. Density-dependent factors: factors that affect a greater proportion of the population
if the population is dense. These are generally biotic factors and include disease,
parasitism and depletion of food supply.
2. Density-Independent factors: the effect of abiotic factors does not depend on the
density of the population. An example is sunlight.
Q: What is abundance?
The number of individuals in a species in a given area or volume.
Q: How can animal abundance be assessed?
Capture-mark-recapture experiments, using Lincoln index calculation.
Kick sampling in a stream and counting aquatic invertebrates.
Q: How can plant abundance be measured?
Using a quadrat to calculate the mean number of individuals in several quadrats of
known area.
Estimating percentage cover of a plant in which individuals are hard to recognise.
Estimating percentage frequency.
Q: What is distribution?
The area or volume in which the organisms of a species are found.
Q: How do you measure distribution?
If a habitat is uniform, the positions of the outermost plant can be marked on a map
and the area they surround can be measured. A small area may indicate that a
species is under threat of extinction.
If a habitat is not uniform, a transect is a useful technique for displaying the variation
in organisms and its correlation with a changing abiotic factor.
Q: What are the two different type of transects?
1. Line Transect = shows the organisms that lie on a line, at measured intervals.
2. Belt Transect = shows abundance data for a given area at measured distances along
the transect. A quadrat is placed at each coordinate along the transect and readings
are taken for, the density of the species, percentage frequency and cover.
Q: What is the source of energy for an ecosystem?
The sun in the form of light energy, trapped by photosynthesis is the source of
energy for most ecosystems, other than those based on chemosynthesis, e.g.
hydrothermal vents.
Q: What is a trophic level?
Feeding levels; the number of times that energy has been transferred between the
sun and successive organisms along a food chain.
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