AQA A2 Biology Unit 4: Populations

Charlotte Lloyd
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Charlotte Lloyd
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Question Answer
what is the difference between biotic and abiotic factors? abiotic factors of the non living component ecosystem, whilst biotic factors are the living components of an ecosystem
name two things that must be considered within an ecosystem the flow of energy through the system and the cycling of elements within the system
define population a group of interbreeding organisms of one species in a habitat
Define community all the populations of different organisms living and interacting in a given place at the same time
define habitat the place where a community of organisms live, within an ecosystem there are many habitats
what is an ecosystem made up of? all of the interacting biotin and abiotic features in a specific area
what is a niche describes how an organism fits into the environment, where are organisms lives and what it doesdoes. no two organisms occupy the same niche
why is random sampling used to avoid bias when collecting data
describe the process of random sampling layout to two tape measures at right angles octane coordinates using random numbers and place the quadrat at the intersection of the coordinates
name three factors to consider when using quadrats the size of the quadrat, depends on size of organism and how it is distributed. number of quadrats to use, generally the greater number the better. the position of the contract within the area, random sampling or systematic sampling
when would systematic sampling be appropriate to use when a transition is taking place
how would you carry out systematic sampling layout a straight line of string stretched over the area, either place quadrats along the string or record all organisms touching the string
define abundance number of individuals of a species within a given space
describe two methods of measuring abundance frequency, the likelihood of a species occurring in a quadratic. percentage cover, an estimate of the area within a quadrat that a plant species covers
when and how is mark release recapture be used is useful when investigating animal species. first a known number of animals are caught marked and released back into the community later organisms are recaptured and the number of marks recorded this information is used to estimate the population size
what equation is used to estimate population size using mark release recapture data population size equals (number in first sample x number in second samplesample) divided buy number of marked re captured x 100
describe for the simpsons that must be made when using mark release recapture estimate population size no migration or immigration, no birth or deaths, doesn't increase chance of predation, proportion of marked to unmarked individuals in the second sample is representative of the population, marked individualsindividuals distribute themselves evenly throughout the population
describe the three general periods Found on a population growth curve a period of slow growth, as the initially small number of individuals reproduce slowly. a period of rapid growth, where the growing number of individuals continue to reproduce. a period of decline until a more or less stabel number is achieved with cyclic fluctuations
name and explain for a biotic limiting factors temperature, each species has an optimum temperature for enzyme activity. light intensity determines the rate of photosynthesis, ph affects enzyme action, water and humidity affect transpiration and photosynthesis
when and why does competition occur Two or more individuals share resources are insufficient to satisfy all their requirements
what is intraspecific competition competition between individuals of the same species for resources such as food and water, the availability of such resources determines the population
What is interspecific competition competition between individuals of different species
what is the competitive exclusion principle where populations of two species occupy the same niche one will have a competitive advantage over the other, this population will increase over time whilst the other will diminish
what is a predator an organism which feeds on other organisms known as their prey
how have predators and prey evolved Predators have evolved to become better at catching prey whilst prey evolve to become better at a avoiding predators
summarise how are predators prey relationships or cyclic fluctuation in population size predators eat pray reducing prey population. Fewer prey so more intraspecific competition. Predator population reduced. Fewer predators so fewer prey eaten. Prey population increases. More prey available to eat so predator population increases.
How are population crashes advantageous to organisms? Important in evolution, as create a selection pressure, individuals which survive are better adapted to prevailing conditions.
How has human population size changed over time? Started very small, with large amount s of disease and famine causing regular crashes thus keeping population fairly constant. Population slowly increases however disease kept it fairly low. Population increases exponentially due to improved medicine, sanitation and food availability.
What two basic factors affect population growth? Birth and death rates
Distinguish between emigration and immigration Immigration is when individuals join a population Emigration is when individuals leave a population
Equation for population growth (Births + immigration) - (Deaths + emigration)
Equation for percentage population growth rate (Population growth during period) ÷ (population at the start of the period) × 100
Factors affecting birth rate Economic conditions Cultural and religious background Social pressures and conditions Birth control Political factors
Equation for birth rate (Number of births in a year) ÷ (total population in the same year) × 100
Factors affecting death rate Age profile Life expectancy at birth Food availability Safe drinking water availability Sanitation Medical care Natural disasters War
Equation for death rate (Number of deaths per year) ÷ (total population in the same year) × 100
Describe the shape of a stable population pyramid, and say what causes it Width of boxes gradually decreases towards the top. Caused by birth and death rates being in balance not no net increase or deacrease in population size.
Describe the shape of, and what causes an increasing population pyramid Bottom of pyramid much wider, decreases steeply to a lower maximum age. Caused by a high birth rate and few elderly people.
What does an decreasing population pyramid look like, and what causes it to occur. Steady width much of the way up, higher maximum. Caused by low birth and mortality rate.
What is average life expectancy? Age at which half of the population is still alive