Populations

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What is a population?
Group of individuals of the same species living in the same place at the same time & interbreeding
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Why do individuals lie in populations?
Increases breeding chances, protection from predators & locate new food resources
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What are disadvantages of high population?
Lack of space & greater competition within or between species
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What influences population growth?
Birth rate, immigration, emigration & death
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What factors affect population growth?
Biotic potential of the population, environmental resistance & carrying capacity
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What is the biotic potential of the population?
When the population grows at its maximum e.g. birth rate exceeds dead rate
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What is another name for exponential growth phase?
Log phase
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When does the exponential growth phase occur?
In phase 2 of the growth curve
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Why is biotic potential rarely reached?
Environmental resistance
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What is environmental resistance?
Describes all factors that could limit population growth
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Give examples of limiting factors
Food, space, increased competition, build up of toxic chemicals, increase in disease
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What is carrying capacity?
Maximum population size that can be sustained over a relatively long period of time
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What does carrying capacity depend on?
Resources provided by the environment
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How long does the lag phase last?
A few minutes to several days
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What happens during the lag phase?
Adaptation & preparation for growth with intense metabolic activity (enzyme synthesis)
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What happens during the exponential phase?
Numbers increase providing there's no limiting factors, so more individuals can reproduce
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What is it called when the birth rate is equal to the death rate?
Stationary phase?
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Why does the stationary phase occur?
Factors limit the population growth
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What is the phase when the death rate is greater than the birth rate?
Decline phase
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What are abiotic factors?
Temperature, light & pH
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What is the name for factors whose effect increases as the density of population increases e.g. toxic waste, disease or depletion of food?
Density dependent
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Is carrying capacity density dependent or independent?
Density dependent
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What is the name for factors whose effect doesnt depend on the population density?
Density independent
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What is a density independent factor
A sudden or violent change e.g. freezing, flooding or fire
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What is another term used for "lie near an equilibrium"?
Set point
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What happens when the population rises above the set point?
A density dependent factor increases mortality or reduces breeding
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What happens if population falls below a set point?
Environmental resistant is temporarily relived so population rises
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How are population fluctuations/oscillations regulated?
By negative feedback
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What do plants compete for?
light, space, water & nutrients
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What do animals compete for?
food, shelter, reproductive partners
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What type of competition is it when individuals of the same species compete?
Intra-specific
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Is intra-specific competition density dependent & why?
Yes, because as population increases, greater proportion dies due to lack of resources
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What type of competition is it when individuals of different species compete?
Inter-specific competition
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What is a pest?
An organism that competes with or adversely affects a population of organisms that are of economic importance
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Name an environmental issue of using pesticidies?
Bioaccumulation
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How do pests reduce the yield of crops?
Feeding on crops & animals, competing with crops for nutrients, causing disease in crops, making infection by pathogens more likely, spoiling food whilst being stored or transported
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What is the name given to when pests cause so much economic damage it becomes worth spending money to control them
Economic injury level
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What should an effective chemical pesticide be?
Specific, not accumulate, biodegradable & cost-effective
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What kills pests?
Pesticide
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What kills weeds?
Herbicides
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What kills insects?
Insecticides
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What kills fungus?
Fungicides
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How can pesticides be applied?
Sprayed, powders, smokes (in enclosed areas) or added to feeds
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Why has resistance occured?
Overuse of pesticides
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What type of competition is used for biological control
Inter-specific competition
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Whats the name given to a beneficial organism?
Agent
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Whats the name given to an undesirable organism?
Target
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Why may eradicating a pest completely be counter-productive?
Wouldn't leave a food source for the predator, which would die out & if the pest re-invaded it would increase in numbers again
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What is integrated pest control?
Combination of biological control agents, pest-resistant crops, varying cultivation techniques & minimal, well-targeted application of highly selective pesticides
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Two advantages of biological control?
No pollution & long term method
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Another two advantages of biological control?
Highly specific to one pest & in the long term it's cheap
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Two advantages of biological control cont?
Good for large areas but can be used in small environments as well
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Two disadvantages of biological control?
Expensive initially as it requires a lot of time & research & no control over agent species
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Two more disadvantages of biological control?
May harm other things not just pests & agent could become a pest
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Two disadvantages of biological control cont?
Difficult to eradicate pests on a large scale & detailed knowledge of life cycle is required
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Two advantages of chemical control?
Very effective & relatively cheap
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Two more advantages of chemical control?
Applied on a small scale, doesn't require high level of skill
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Two disadvantages of chemical control?
Not specific and can kill beneficial insects & pests may become resistant
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Two more disadvantages of chemical control?
May contaminate food of other animals & long term over-exposure to pesticides can cause harm to humans e.g. cancer
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Where can carbon be found?
Carbs, fats, proteins, nucleic acids, rocks, shells of marine organisms, dissolved in water
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How do plants remove carbon dioxide from the air?
Photosynthesis and convert it to carbohydrates
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How is carbon dioxide returned to the atmosphere?
Respiration
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Why is there an increase in carbon dioxide?
Burning fossil fuels, releasing carbon dioxide that was locked up & deforestation, removing biomass that photosynthesises
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How can atmospheric nitrogen be converted directly into ammonia?
nitrogen-fixing bacteria
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Give an example of a free living nitrogen-fixing bacteria
Azotobacter - uses ammonia to manufacture amino acids
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Name a symbiotic nitrogen fixing bacteria
Rhizobium
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Where is Rhizobium found?
In root nodules of legumes
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Why are the nodules pink/red?
presence of haemoglobin
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What is ammonification also known as?
Putrefaction/deamination
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What are bacteria and fungi referred to?
Decomposers
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What is a decomposer?
Decay dead plants & animals, faeces & urine into ammonium ions
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What happens in nitrification?
Ammonia is converted into nitrites & then nitrates
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Which bacteria converts ammonia into nitrites?
Nitrosomonas
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Which bacteria converts nitrites into nitrates?
Nitrobacter
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What conditions do the bacteria in nitrification require?
Aerobic conditions
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What is the name given to the conversion of nitrate into nitrogen gas?
Denitrification
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Where is nitrogen loss a particular problem?
Waterlogged soils
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Waterlogged soils have anaerobic conditions, what does this mean?
Anaerobic bacteria reduces nitrates & ammonium ions back to nitrogen
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What is the nitrogen cycle?
The flow of organic & inorganic nitrogen in an ecosystem where there's an exchange between nitrogenous compounds & atmospheric nitrogen
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What happens when plants & animals die?
Minerals in their bodies & excretory products are decomposed to release minerals back into the soil
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How can human activities improve nitrogen circulation?
Fixing atmospheric nitrogen artificially using chemical processes & using animal waste and sewage disposal as manure to boost organic nitrogen
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How does draining land aid nitrogen circulation?
Reduces anaerobic conditions
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How does ploughing fields help?
Improves aeration of soil
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Other cards in this set

Card 2

Front

Why do individuals lie in populations?

Back

Increases breeding chances, protection from predators & locate new food resources

Card 3

Front

What are disadvantages of high population?

Back

Preview of the front of card 3

Card 4

Front

What influences population growth?

Back

Preview of the front of card 4

Card 5

Front

What factors affect population growth?

Back

Preview of the front of card 5
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