Healthy plants II

This task is about deciding which data to collect to see if a plant is healthy.

Ally and Jack each grew a tomato plant. They wanted to see who could grow the healthier plant. After three weeks they drew pictures of their plants.

Ally's plant	Jack's plant

Name ____________________

a)	What things could be measured or counted from the pictures of Ally's and Jack's tomato plants? Give as many different things that you can.

	---- Cut along this line and give the top part to your teacher ---- Name ____________________
Use the list which your teacher shows you to answer the next question.
b)	Which things on the list would be most useful to show which plant is healthier?

Teaching and learning:

This task requires students to draw on their science knowledge about what a healthy plant looks like to select which variables indicate a healthy tomato plant.

The task would be more authentic if students used data collected from their own investigations into growing healthy plants. Another alternative is to use this task after such an investigation to see if they can apply what they have learnt.

Note that the trial was not carried out in conjunction with a science investigation, i.e., the trial students completed the task "cold". Most students did seem to have some general concept of what a healthy plant looks like, but those who were able to draw on experiences or knowledge about plant needs provided more science-oriented justifications for their ideas. For example, a few students identified that the leaves of Jack's plant looked dry, perhaps indicating that they were aware plants need water.

Statistics Focus
Students are demonstrating their ability to perform part of the Statistical Enquiry Cycle (SEC) by:

Naming different types of data that can be collected from a science investigation. Data can be category data (e.g., leaf colour; height is described as tall or short), whole number (e.g., number of tomatoes), or measurement (e.g., height in cm). For more information, click on the link Types of data: Statistics.
Using their scientific knowledge to identify the most useful data to collect. These represent the Plan and the Data steps of the SEC. The full cycle is Pose – Plan – Data – Analyse – Communicate. For more information click on the link Statistical Enquiry Cycle.

Science Focus
Students in this resource are demonstrating beginning ideas about:

Fair testing. They do this by comparing variables between two similar plants and deciding how these variables can be measured. They also decide what variables might be different between the two plants that result in their different growth pattern.
Data in science can be measurements, e.g., 8 cm, or whole number, e.g., 3 tomatoes) and/or descriptive (e.g., short, tall, green, yellow, etc.).

Diagnostic and formative information:

Common response

Likely reasoning

Water, soil, food, sun, shade, "Chop off the unhealthy bits"

Ruler

Does not answer the question that was posed
Lists the requirements that a plant needs to be healthy rather than giving the features of the plant which indicate its health. Gives ways to measure aspects of the plant.

Height of the plant

Looks at one feature of a plant in isolation
The student ignores other unhealthy features of a plant, and sees "bigger as better".

Justifying answers
When this task was trialled we asked students to give reasons why they chose their answers for Question b). No students gave reasons that linked the variables chosen to the functions of the plants' parts. For example, even though many chose green leaves as an indication of health they did not link this to the fact that green leaves show that the plant is making food, or that it means that it is getting enough sunlight to make food. This is quite sophisticated science knowledge for students to have at this age, so it is not surprising that they could not do this. Instead they used their implicit understanding of what a healthy plant looks like to choose the most useful variables. This question has since been removed as it does not provide any extra information about their reasoning. Some students who gave the requirements of plants show that they have the building blocks for justifying their selection, but possibly need some scaffolding to help them to do so.

Next steps:

Does not answer the question that was posed
This may be a close reading issue. Get the student to re-read the question. If they can then answer the question correctly, they are achieving as expected. Careful reading and re-reading of mathematical situations is essential as the meaning often is very precise. If the student can still not give a written description, get them to respond orally.

Looks at one feature of a plant in isolation
Students need to take account of multiple features relating to health and weigh them up holistically. Many students included height with features that indicate health. Ask these ones why they included height, and what was it about the height (they may even see the shortness and overall shape of Ally's plant as healthier than Jack's tall thin one). These students may alternatively have a misconception that a greater height indicates health.

Justifying choices
While the question has been removed from the assessment task, students should always be encouraged to give reasons for their choices. The following prompts scaffold students to use their science understandings to justify their choice of data sets, although it should be remembered that, unless they have had experiences in this context, the knowledge they have to draw on is likely to be limited.

Response from trials	What they may know	Possible next step	Prompts to scaffold next step
Ally's [leaves] are darker green and Jack's are more yellow.	Dark green is a healthier colour than yellowy green.	Plants make their food in their leaves. The greenness helps them do this.	I wonder why tomato plants need to have green leaves.
Ally's plant is more green than Jack's and has more leaves and tomatoes.	All the variables need to be considered rather than each variable in isolation to decide whether a plant is healthy	Functions of the leaves	I wonder why tomato plants need to have green leaves. If Ally's plant had no tomatoes do you think it would be healthier than Jacks? Why? If Ally's plant had yellow leaves, whose plant do you think would be healthier? Why?
Ally's one has more tomatoes and Ally's one has 12 leaves. Ally's is healthier because there are more tomatoes	The number of leaves or tomatoes suggests that the plant is healthy	Functions of the leaves	Explain why "more" means healthier.
Ally's plant is healthy and small but Jack's is tall and unhealthy	Notices that height does not indicate health in this case.	Identify the other indicators of a healthy tomato plant. Plants need sunlight to grow into ealthy plants. Plants that are not getting enough sun grow tall to reach for the sun's light (energy).	I wonder why Jack's plant grew so tall even though it doesn't look healthy. What do you notice about Ally's plant that makes you think it is healthier? If Ally's plant grew taller than Jack's would it be unhealthy too? Why do you say that?

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Healthy plants II

Healthy plants II