paper 2: Populations and Ecosystems

Question 1

define population

Answer 1

individuals of the same species occupying one area at one time that can potentially interbreed

Question 2

define habitat

Answer 2

an area where an organism lives

Question 3

define community

Answer 3

all the populations of all the species in one area at one time

Question 4

define niche

Answer 4

the role an organism plays in the ecosystem and how it interacts with the biotic and abiotic factors

Question 5

define biotic factor

Answer 5

a living factor which affects the distribution of an organism

Question 6

define abiotic factor

Answer 6

a non-living factor which affects the distribution of an organism

Question 7

define carrying capacity

Answer 7

the maximum population size of a species that an ecosystem can support

Question 8

define ecosystem

Answer 8

consists of the community and the non-living components of its environment

Question 9

explain why sampling should be carried out at random

Answer 9

to ensure that all data collected is not biased

Question 10

describe how you would retrieve reliable and representative data when sampling

Answer 10

you must take a large sample

Question 11

define interspecific competition

Answer 11

competition between different species

Question 12

define intraspecific competition

Answer 12

competition between the same species

Question 13

define predation

Answer 13

how the populations of predators and prey affect each other

Question 14

describe intraspecific competition

Answer 14

• members of the same species compete for the same resources e.g. food
• if population gets too big then intraspecific competition increases so population falls again
• if population gets too small, intraspecific decreases so population size increases again

Question 15

draw and label a graph showing intraspecific competition

Answer 15

Question 16

describe interspecific competition

Answer 16

one species will outcompete the other one if they occupy the same niche

Question 17

draw a graph showing interspecific competition

Answer 17

Question 18

explain predation

Answer 18

• prey population increase so food source increases for the predator so predator population increases shortly after
• more predators so more prey are killed so prey population decreases
• less prey to eat so predator population decreases because they die of starvation
• less prey eaten so prey population increases and the cycle starts again

Question 19

draw a graph showing predation

Answer 19

Question 20

why is there a delay in time between increase prey population and increased predator population

Answer 20

give time for reproduction of predators

Question 21

why must a sample be random

Answer 21

prevent bias

Question 22

why must a sample be large

Answer 22

• sample is more representative
• calculate more reliable mean
• allows use of stats test

Question 23

what are quadrats used for

Answer 23

estimate size of population of a particular species in a certain area

Question 24

describe the step-by-step method of random sampling with quadrats

Answer 24

1. split area into a grid and asign coordinates
2. pick coordinates randomly using a random number table
3. place quadrat at coordinates and count number of individuals or % cover
4. repeat a large number of times and calculate a mean
5. multiply this mean by the number of times the quadrat fits ino the area

Question 25

for sample seaweed with a quadrat, explain which method you would use

Answer 25

% cover less time consuming than counting individual plants / cannot identify individual plants/ too many individuals

Question 26

how can you find the correct number of quadrats to use to get representative data

Answer 26

calculate a running mean until the mean stays constant

Question 27

what are transects used to show

Answer 27

show chnages down an environmental gradient

Question 28

what is a limitation of using transects

Answer 28

single transect might not go through a representative data

Question 29

how would you make sure that you have a representative sample of the area when using transects

Answer 29

- select position of transects at random - use a large number of parallel transects and calculate the mean at each distance

Question 30

decsribe the step-by-step method of using a transect

Answer 30

1. several belt transects are placed at parallel across an area and numbered 2. a transect is chosen at random using a random number generator button on a calculator 3. a quadrat is placed along the line at regular intervals 4. the % cover or number of each species are counted in each quadrat 5. this is repeated across a large number of parallel transects and a mean at each interval

Question 31

what is the mark, release, recapture method used for

Answer 31

used to estimate the sizes of populations of motile organisms

Question 32

equation for mark, release, recapture

Answer 32

Question 33

equation for mark, release, recapture

Answer 33

Question 34

what are the assumptions made with the mark, release, recapture method

Answer 34

- birth rate = death rate - marking does not influence survival such as increasing chances of predation and is non-toxic - no immigration/ emmigration - long enough time for marked individuals to evenly distribute into the population between release and recapture

Question 35

describe the stages of succession

Answer 35

1. starts with colonisation of pioneer species in hostile conditions 2. pioneer species change abiotic conditions e.g. from soil/ humus 3. environment becomes less hostile and more suitable for new species to colonise 4. new species out-compete the pioneer species so pioneer number decrease 5. from stage to stage, genetic diversity increases 6. eventually a climax community is reached

Question 36

what does primary siccession start with

Answer 36

bare rock or sand

Question 37

what does secondary succession start with

Answer 37

soil and some vegetation

Question 38

what is the ecosystem like in a climax community

Answer 38

- stable populations - abiotic conditions are constant - same species are present

Question 39

explain why species diversity may decrease slightly in a climax community

Answer 39

- trees block light reaching the ground, so less photosynthesis - only plants which can photosynthesise at low light intensities survive

Question 40

what is turbidity

Answer 40

a measure of how much solid is in a solution

Question 41

what piece of equipment measures turbidity

Answer 41

spectrophotometer

Question 42

how does a spectrophotometer measure turbidity

Answer 42

- light passed through the solution - absorbance is measured - the more turbid the solution the more light is absorbed

Question 43

why is a log scale used when measuring turbidity

Answer 43

when there is a large range of numbers