✅ 7. Required Practical: Investigating Population Size (B16)

Question 1

Aim Of The Practical

Answer 1

In this practical you will plan and carry out an experiment to measure the population size of a common species in a habitat. You will also use sampling techniques to investigate the effect of a factor on the distribution of this species.

Question 2

What do You Sample Quadrats along a Transect to see?

Answer 2

You sample quadrats along a transect to see a change in species distribution in a line from A to B.

Question 3

What do You Sample Quadrats on Coordinates from a Number Generator to count

Answer 3

You sample quadrats on coordinates from a random number generator to count the number of a species in an area.

Question 4

What’s the Simplest Way to Count the Number of Organisms in an Area

Answer 4

The simplest way to count the number of organsisms is to use a sample area called a quadrat. We often use a square frame laid on the ground to outline our sample area. People refer to these frames as quadrats too.

Question 5

What are Transects used for?

Answer 5

Transects are often used across a rocky shore, across a pathway, or down a hillside. Transects are often done where you expect a change is linked to a particular abiotic factor. You sample the organisms along that line at regular intervals using a quadrat. This shows you how the distribution of organisms changes along that line. You can also measure some of the physical factors, such as light levels, and soil pH, that might affect the growth of the plants along a transcet.

Question 6

Safety Measures for this Practical

Answer 6

• Follow local rules on working in an outside environment and wash hands after the lesson.
• When any fieldwork is undertaken, work in groups and be aware of any hazards in that specific environment.
• Sensible footwear and clothing should be worn. If the weather is hot and sunny, sunscreen and hats are required.

Question 7

Equipment for the Practical

Answer 7

• two 20 m measuring tapes
• table of random numbers or other generator of random numbers
• 50 x 50 cm gridded quadrat frame
• notebook and pencil
• identification sheet- optional equipment to measure abiotic factors, such as light meter, pH meter/ universal indicator paper, anemometer

Question 8

How do You Ensure The Results Are As Valid As Possible?

Answer 8

You use the same size quadrat every time, and sample as many areas as you can. This makes your results as valid as possible. Sample sizes is very important. You must choose your sample areas at random. This ensures that your results reflect the true distribution of the organisms and that any conclusion that are made will be valid.

Question 9

How Do You Ensure The Samples You Take Are Random?

Answer 9

A more scientific way of deciding where to drop the quadrat can be numbering each section/area, and then use a random number generator to generate numbers that decide what areas you’re sampling. This gives each section an equally chance of being picked.

Question 10

What is Quantitative Sampling and What can you use it for?

Answer 10

Several random readinsg need to be taken, and then the mean number or organisms per m^2 can be found. This technique is known as quantitative sampling.

• You can use quantitative sampling to compare the distribution of the same organism in different habitats.
• You can use it to compare the variety of organisms in several different habitats.
• Sampling is also used to measure changes in the distribution of organisms over

Question 11

How Do You Estimate The Population Of Plants

Answer 11

Estimated Population Size = (Total Area / Area Sampled) x Total Number Of __________ Counted

Question 12

What are the 2 Main Ways to Study The Distribution of an Organism

Answer 12

There are a couple of ways to study the distribution of an organism. You can:

• Measure how common an organism is in two sample areas (e.g using quadrats) and compare them.
• Study how the distribution changes across an area, e.g by placing quadrats along a transect.

Both of these methods give quantitative data.

Question 13

How is Where an Organism is found be Affected by Environmental Factors

Answer 13

Where an organism is found is affected by enviornmental factors. An organism might be more common in one area than another due to differences in evironmental factors between the two areas. For example, in the playing field, you might find that dasies are more common in the open than under trees, because there’s more light avaliable in the open.

Question 14

Method:

Using Quadrats to Study The Distribution of Small Organisms

Answer 14

1. Place a 1cm^2 quadrat on the ground at a random point within the first sample area. E.g, divide the area into a grid and use a random number generator to pick coordinates.
2. Count all the organisms within the quadrat.
3. Repeat steps 1 and 2 as many times as you can
4. Work out the mean number of organisms per quadrat within the first sample area.
5. Repeat steps 1-4 in the second sample area.
6. Finally, compare the two means. E.g, you might find 2 daisies per m^2 in the shade, and 22 daisies per m^2 (lots more) in the open field.

Question 15

Method:

Using Transects to Study The Distribution of Small Organisms Along A Line

Answer 15

1. Mark out a line in the area you want to study using a tape measure.
2. Then collect data along the line
3. You can do this by just counting all the organisms you’re interested in that touch that line.
4. Or, you can collect data by using quadrats. These can be placed next to each other along the line or at intervals, for example, every 2m.

Question 16

Independant, Dependant, And Control Variables

Answer 16

Independant Variable: Quadrat Number

Dependant Variable: Daisies

Control Variables: The same grid area, The same sized quadrat, The same day, The same time of day

Question 17

Describe And Explain (for the Number of Daises in the Trampled Field vs Un-Trampled Field)

Answer 17

On the whole, there were more diases found on the trampled field than the un-trampled field in this practical, with a mean of 2.6 dasies counted per 0.25m^2 in the trampled area, compared to the 0.2 daises counted per 0.25m^2 in the un-trampled area. This means that overall, there were around 1.3 times more daises in the trampled field. This may be due to the fact that the trampled field is cut regularly and the daises there recieve lots of sunlight, allowing more daises to grow there, along with the fact that there is less competition from other organisms with the daises than in the un-trampled area which is around a shaded area where the daises don’t recieve as much light and the grass isn’t cut as often. In addition, daisy plants have their stems and leaves spread across the ground. Meaning that they don’t break when they get stepped on, as most of the plant is already spead across the floor, meaning few will be damaged due to being stepped on. As a result, these reasons contribute to more daises being found on the trampled field than the non-trampled field.

Question 18

State 2 examples of abiotic factors and biotic factors

Answer 18

Abiotic Factors: Temperature, Light

Biotic Factors: Competition from other plants (Plants), Humans trampling on them (Animals)

Question 19

What is the function of a quadrat

Answer 19

It is used to sample an organism in a specific area.

Question 20

Why is it important for samples to be random when estimating the population of an organism over an area of land

Answer 20

It is important for the samples to be random so that there is no bias that may affect the results in any way.

Question 21

Comment on the advantages and advantages and disadvantages of completing a transect over rabdom sampling of an area

Answer 21

Advantages of completing a transect over sample of a random area is that it removes any bias from where you take your measurements from, while you are able to get a mean number of plants. Disadvantages of this include the fact that random sampling might not give an accurate representation of the number of flowers in a field, as a random number generator could just generate coordinates that don’t give an accurate representation of the rest of the field.