Populations and Communities

Question 1

what is a haemocytometer?

Answer 1

an instrument for counting cell density

Question 2

how is volume calculated?

Answer 2

area x depth

Question 3

what volume does a Type A square have?

Answer 3

0.1mm3

Question 4

what volume does a Type B square have?

Answer 4

0.004mm3

Question 5

what volume does a Type C square have?

Answer 5

0.00025mm3

Question 6

how is cell density counted using a haemocytometer?

Answer 6

-a suspension containing cells to be counted is placed on the grid on the haemocytometer.
-depending on the density, type A, B or C squares should be used
-follow the north-west rule

Question 7

what is the north-west rule?

Answer 7

cells touching or lying on the outer grid line at the top (north) and the left (west) side of the square should be counted.
those touching or overlying the grid lines on the right side (east) and the bottom (south) shouldn’t be counted.

Question 8

what are some important points when using the haemocytometer?

Answer 8

-mix yeast cell suspension thoroughly before taking a sample.
-use a sample from the same depth in the flask.
-if sampling from the ‘natural environment’ different samples should be taken from the same depth and the same time of day.
-avoid getting yeast suspension onto the top of the coverslip.
-carry out a number of replicates for reliability.

Question 9

what is serial dilution?

Answer 9

when the suspension is diluted

Question 10

what is the principle of the ‘capture-recapture’ technique?

Answer 10

a number of animals are trapped, counted, marked and then released.
after some time some of the target species r caught for a second time
-marked species should be caught both times.

Question 11

what is the equation for estimated population size?

Answer 11

s1 x s2
_______
r

s1= number caught in first sample.
s2= number caught in second sample
r= number recaptured

Question 12

what is the procedure for the ‘capture-recapture technique’?

Answer 12

-a large sample of the species is caught
-caught animals are marked
-the marking should not harm the animal or make it more likely to be predated
-marked animals are released.
-sufficient time should be given to allow captured animals to mix throughout the whole population.
-population is then resampled using the trapping process and population size is calculated.

Question 13

what are some assumptions with calculating population size?

Answer 13

-there are no significant gains or loses through immigration and emigration
-no significant gains or loses through births and deaths respectively
-the trapping process doesn’t affect the animal in any way
-the marked animals have mixed throughout the whole population before the re-sampling period