Tree roots

Tree roots

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Overview
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about interpreting diagrams.

Question 1Change answer

Part one: Review your knowledge 
 
a) Use your knowledge of plants to list two main functions carried out by the roots of trees.
Function 1:

Function 2: 
Part two: Interpret a model
Diagram A is a model that compares how the diameter of a tree's root system and branches changed over time.  The tree was less than 1m high when it was dug up and replanted somewhere else.
tree-cross-section-diagram-A.png

Question 1Change answer

b)  i)  What does each smooth circle on the model represent? 

Question

     ii)  How many years' growth in total does the model show? 

    • Less than 2 years

    • 2-3 years 

    • 3-4 years

    • At least 5 years

Question 3Change answer

     iii)  How long did the roots take to grow back to their original spread?

Question

Diagrams B and C show two types of tree root systems.
 
c)  i)  Which of these diagrams would be most like the tree modeled in diagram A?

    • tree-diagram-B.png

    • tree-diagram-C.png

Give a reason for your choice.

Question 1Change answer

Part three: Apply your knowledge
When trees are moved the effects on their root systems can be dramatic. When even quite small trees are moved it is impossible to dig up all the roots as well. This means trees need very careful attention for some time if they are to survive.
 
d)  Trees are often supported with sturdy stakes when they are first transplanted.
     How does this help them survive?

Question 2Change answer

e)  Use the information provided to recommend a suitable length of time for keeping the stakes in place.
 
Level:
5
Curriculum info: 
Science, Communicating in science, Living World
Key Competencies: 
Using language, symbols, and texts
Keywords: 
Life processes, functions, trees, roots, models, key competencies
Description of task: 
Task: Students apply both their knowledge of the functions of roots and information from a model to explain why care is needed when transplanting trees. Assessment focus: interpreting diagrams.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.
 
Capability: Interpret representations
This resource provides opportunities to discuss using and interpreting a model that represent something that can't be seen from the outside.
Science capabilities: 
Interpret representations
Answers/responses: 
 

Y10 (08/2006)
Part one
a)   Both of:

  • anchor the tree in the soil/support above ground parts of the tree; and
  • provide water and soil minerals to tree
 difficult
Part two
b) i)

ii)
iii)

 One year of root growth
or
At least a partial answer, e.g., one year
At least 5 years
3 years

very difficult

easy
difficult
c) i)
ii)		 Diagram C
The roots spread out much further than the top, to cover a much greater area of ground around the tree.

moderate
difficult
Part three
d)   For any 1 of:

  • Roots take time to grow;
  • Tree needs support until a sufficient spread of roots has been established.

or
Partial answers mention support risks (growing crooked, blowing over, without being explicit about role of roots)


difficult

moderate
e)   Time stated and justified with reference to:

  • Growth rate information provided by Diagram C; or
  • Knowledge of support functions of roots, e.g.,
    For about three years because the example of the tree in Diagram A took three years to get back to sequential growing of roots.

Time length stated as 2-5 years with no justification (partial answer)

difficult 
difficult

Trialled by 174 Year 10 students.

Teaching and learning: 

Key competencies
This task is relevant to the key competency in the draft curriculum Using language, symbols, and texts, which is expressed in the Communicating in science strand as: Students will use a wider range of science vocabulary, symbols, and conventions (including diagrams, graphs, and formulae).

This task assesses students' ability to interpret a deceptively simple model on three levels:

  • By identifying a single specific feature of the model [Question b) i)]
  • By describing a simple trend in the model [Question b) ii)]
  • By relating an abstract model to an actual object [(Questions c) i) and c) ii)].
Diagnostic and formative information: 
a) Roots "feed" plant nutrients – response made by 29 percent

  • They reach out to find food.

Believing that roots absorb ready-made food for plants is known to be a common misconception, perhaps supported by everyday use of terms such as "plant food" for fertiliser.

"Photosynthesis" as a function of roots
In some ways this is the opposite misconception – quite a few students, in several schools, seemed to think that roots can photosynthesise.

Students were more likely to identify the uptake of water and/or minerals (37 percent) as a root function than the anchorage of the plant (19 percent).
b) Very few students could identify each concentric circle on Diagram A as a symbol to represent one year's growth. The most common response was:

  • The diameter of the roots (i.e. a combination of all circles).

Some students seemed to think of Diagram A in terms of the more familiar growth rings of tree trunks:

  • The age after so many years
  • Rings of a tree (age)
c) 47 percent of students chose B for question c) i).
Believing that tree roots are usually the shape of an inverted treetop is another misconception known to be common. (Many trees have roots that spread as in Diagram C)

Some students brought their own views of what tree roots ought to look like to question c) and did not compare diagrams B and C to diagram A at all:

  • Roots go down.
  • Because the roots are deep
  • I think this [B] is a more realistic diagram of the way the roots are growing.
  • Because the roots go out like a triangle, making it like diagram A.

Their own preconceptions seemed to lead some students astray, even when they did recognise a potential mismatch between what the models were showing them and their own views of what trees roots should look like:

  • Because the diameter of roots spread increasingly on all sides not just outwards
  • Because the roots are getting bigger but rounder in size. Diagram C are long and wide.

Even some students who answered C because they did see the relationship to Diagram A seemed to think this was a temporary state of affairs:

  • The tree is only 5 years old and 1 m high so the roots wouldn't have grown as much as in Diagram B.
  • Because the tree has not been in the ground long enough to get such deep roots
d) 47 percent of students answered question d) in ways that implied a role for tree roots, without being explicit about this:

  • So the wind doesn't blow them over
  • Functions of plant parts – This resource is a simple matching task of structure and function of plants.  For root function it only addresses obtaining water.
  • Change or edit the resource as required. For example, add the second function of roots if this is a focus of your assessment.