BI 152 Week 11 Spring 2011

Investigation and data collection:

Does position on branch affect pine needle length?

Since plants use sunlight to power their growth, it makes sense that leaves that receive more light would be larger than those that receive less light. Does position on a branch affect leaf length?

Conjecture: Leaves of a tree that are at the outer edge of the branch are exposed to the sun more and will be longer in length than needles that receive less sun because they are further in toward the trunk.

1. Variables: What is the independent variable?

What is the dependent variable?

2. Write the research, null and alternate hypotheses in the possible outcomes table below.

3. Possible outcomes and interpretation table

. Complete the following table

Statements of Hypotheses / Predicted results of that hypothesis / Interpretation
H0 / H0
HR
HA
HR / H0
HR
HA
HA / H0
HR
HA1

We will focus on the outermost 10 cm of a branch (outermost zone) and the innermost 10 cm of the same branch (closest to the trunk), the innermost zone. We will choose 5 needles to measure in each 10 cm zone.

So, how do we decide which 5 needles to measure in each zone????

We need to take a RANDOM SAMPLE

There are too many needles on even one pine tree to measure them all. What scientists do is take a Random Sample. This means that the sample ofneedles to be measured are chosen by a method thatremoves prejudice or bias that might affect a scientists’ choice of specimens to be measured. You can’t just pick the first specimens that you see.
So, if we wanted to take a random sample of students in this class, we might choose one person per table, sitting in the southeastern-most seat at each table.
Or, we might count off by threes and choose all the number 2 people.
Or we might use the last four digits of your SE id number, and choose all those that end in an even number
Or those that end in 6 or 4
Or 1
Etc.
We could give each person a number, put the numbers in a jar and choose 7 of them.

In pines (genus: Pinus) the leaves are needle shaped and are attached to the branch in groups called fascicles. The number of needles in a fascicle is pretty much uniform for a given species, but can vary among species. Fascicles are bundles of pine needles (see arrows)

For the pine needles, we will measure in mm the longest needle in each sampled fascicle.

So, how can we randomly sample the fascicles on the branches?

  1. Examine the branch your table has been given.
  2. If your branch has several branchlets, choose the longest one and measure off 10 cm inward from its tip. This will be the “outermost zone”
  3. Then, starting at the tip of the branchlet, remove every 4th fascicle for 10 cm of length.
  4. Lay them out in the spaces below for the “outermost zone.”Stop when you have 5 fascicles.
  5. For the innermost zone, measure off 10 cm, starting at the first fascicle closest to the cut end of the branch and working inward. Remove every 4th fascicle and place them in the spaces below for the “innermost zone.”Stop when you have 5 fascicles.

Fascicles from outermost zone / Fascicles from innermost zone
1 / 2 / 3 / 4 / 5 / 1 / 2 / 3 / 4 / 5

Now, choose the longest needle within each fascicle. Discard the others. Measure its length in mm.

Length of needles in outermost zoneLength of needles in innermost zone

1 / 2 / 3 / 4 / 5 / 1 / 2 / 3 / 4 / 5

Go up to the computer and insert your data into the excel spread sheet. We will use this next week.

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