chp 4 organisms and their environment Flashcards
what is a population
A population is defined as a group of organisms of one species, living in the same area at the same time
What is a community
A community is defined as all of the populations of different species in an ecosystem
what is an ecosystem
An ecosystem is defined as a unit containing the community of organisms and their environment, interacting together (eg a decomposing log, a lake)
how do populations expand at the expense of others
Those which are the best adapted to their environments generally increase their populations at the expense of those less well adapted
factors affecting population
Food supply
Predation
Disease
changing temperature or light
immigration (individuals moving into the area)
emigration (individuals moving out of the area)
reasons fro human population grwoth
Improved technology leading to an abundance of food = rapid increase in birth rate
Improved medicine, hygiene and health care = decrease in death rate
phases of sigmoid growth curve
lag
log
stationary
death
what is lag phase
organisms are adapting to the environment before they are able to reproduce; in addition, at this stage there are very few organisms and so reproduction is not producing larger numbers of offspring
what is log phase
food supply is abundant, birth rate is rapid and death rate is low; growth is exponential and only limited by the number of new individuals that can be produced
what is stationary phase
population levels out due to a factor in the environment, such as a nutrient, becoming limited as it is not being replenished; birth rate and death rate are equal and will remain so until either the nutrient is replenished or becomes severely limited
what is death phase
– population decreases as death rate is now greater than birth rate; this is usually because food supply is short or metabolic wastes produced by the population have built up to toxic levels
what is nitrogen fixing bacteria
Bacteria which can absorb nitrogen as a gas from air spaces in the soil and build it into compounds of nitrogen
what are decomposers
Organisms which break down dead animal and plant material, releasing the nutrients into the soil
what is nitrfying bacteria
Bacteria which convert ammonium compounds into nitrate
what is denitrifying bacteria
Bacteria that use nitrate ions in their metabolism and release nitrogen gas
describe the carbon cycle
Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis
It is passed on to animals (and microorganisms) by feeding
It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration
If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies can be converted, over millions of years and significant pressure, into fossil fuels
When fossil fuels are burned (the process is known as combustion), the carbon combines with oxygen and carbon dioxide is released into the atmosphere
what leads to excess co2 in the atmosphere
Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere
In addition, mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis
This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they are burnt down, releasing yet more carbon dioxide into the atmosphere
Describe the water cycle
ater molecules move between various locations – such as rivers, oceans and the atmosphere – by specific processes
This is possible because water changes state at a relatively low temperature
Water enters the atmosphere as water vapour in one of two processes:
Energy from the Sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes
Transpiration from plants releases water vapour into the air
The warmer air of the lower atmosphere rises, taking the water vapour with it
The moist air cools down as it rises
Water vapour condenses back into liquid water, forming clouds
Water returns to Earth in the form of precipitation
As the water droplets in the cloud get bigger and heavier, they begin to fall as rain, snow and sleet
This is called precipitation
what is nitrogen required for
Nitrogen as an element is required to make proteins
why cant nitrogen be easily absorbed
Neither plants nor animals can absorb it from the air as N2 gas is very stable and the bonds holding the nitrogen atoms together would need massive amounts of energy to break (the two nitrogen atoms in a nitrogen molecule are held together by a triple covalent bond)
how is nitrogen absorbed
Nitrogen fixing bacteria found ‘free living’ in soil and also in the root nodules of certain plants (peas, beans, clover – we call them leguminous plants) take N2 gas and change it into nitrates in the soil
Lightning can ‘fix’ N2 gas, splitting the bond between the two atoms and turning them into nitrous oxides like N2O and NO2 that dissolve in rainwater and ‘leach’ into the soil
describe the nitrogen cycle
Plants absorb the nitrates they find in the soil and use the nitrogen in them to make proteins
Animals eat the plants (or other animals) and get the nitrogen they need from the proteins in the plant or animal
Waste (urine and faeces) from animals sends nitrogen back into the soil as ammonium compounds (the urea in urine contains nitrogen)
When the animals and plants die, they decay and all the proteins inside them are broken down into ammonium compounds and put back into the soil by decomposers
The plants can’t absorb ammonium compounds though, so a second type of soil bacteria, nitrifying bacteria, convert the ammonium compounds to nitrites and then to nitrates, which can then be absorbed by plants – and so the cycle goes on
Finally, there is a third, unhelpful type of (anaerobic) bacteria called denitrifying bacteria found in poorly aerated soil (ie not much oxygen)
These bacteria take the nitrates out of the soil and convert them back into N2 gas
Farmers can help reduce the amount of these unhelpful bacteria by ploughing and turning over soil
what are producers
organisms that produce their own nutrients usually using energy from sunlight
