Seed Dispersal: Parachuting Fruits
Students’ Sheet
Introduction
Some plants spread their seeds by producing fruits with a seed attached
to a ‘parachute’. The dandelion is a well-known example.
Mile-a-minute (Mikania cordata) is another example. The plant is found
in Southeast Asia and Eastern Africa. It is extremely invasive,
smothering other plants, shrubs and even trees. It has a number of
uses, including covering areas to prevent erosion.
Parachute fruits are dispersed by the wind. They drift easily in the air
and can be carried long distances even by a gentle breeze.
You can see that there are similarities and differences between the fruits
of a dandelion and mile-a-minute. One difference is the distance
between the parachute and the seed.
Dandelion fruit
In this activity you will use models to investigate the way parachute fruits
behave when released into the air.
In this activity you will investigate the design of parachuting fruits and
seeds.
How slowly do they descend slowly through the air?
Do they spin or not when they fall?
Mile-a-minute fruit
Activities
Activity 1: Watching dandelions flower, fruit and disperse their seeds
Watch these videos or others than you can find on the Internet:
Time lapse Dandelion flower to seed head
Dandelion seed head forming and seeds blowing away timelapse
Dandelion seeds blowing in the wind: slow motion reveal!
If you are doing this activity in the spring you could experiment with some dandelions.
Questions
1. Describe how dandelion fruits move in the air.
2. Explain why a fruit that falls more slowly is likely to be dispersed further than one that falls
rapidly to the ground.
Science & Plants for Schools: www.saps.org.uk
Parachuting Fruits: p. 1
Activity 2: Two alternative models of parachute fruit
Making model 1
Cut a piece of paper 14 cm x
7 cm. Draw a pencil line 3 cm
from one of the 7 cm edges.
Using a pair of scissors cut
strips about 2-3 mm wide
down 11 cm down to the line.
Roll the paper to make a 14
cm long tube, allowing a slight
overlap. Gently splay out the
thin strips. It should look
something like the picture on
the far right.
14
cm
3
cm
7
cm
Cut a circle of paper about 15 cm in diameter. Fold it to make a pleated cone.
Making model 2
Fold the cut out circle
four times, one each
along the dotted lines
For example, across
the horizontal line
Now make pleats by
folding each section in
the opposite direction
pleated
paper cone
blobs of
plasticine
toothpick
It should look something like the picture on the left above.
Push a toothpick through the point of the cone of the funnel and use a small ball of plasticine,
about 2-3 mm in diameter, to hold it in place. At the other end of the toothpick stick another small
ball of plasticine (see drawing on right above).
Testing the models
Take both models somewhere that they can be dropped safely from a height of 2-3 metres (or
preferably more, especially if you want to time them).
Observe the way each model descends.
If possible, you could try videoing their descents. You might also want to time their descents.
Questions
1. Describe the movement of each model when they are dropped and fall to the ground.
2. Which is the better model of a dandelion fruit? Give your reasoning.
Science & Plants for Schools: www.saps.org.uk
Parachuting Fruits: p. 2
Activity 3: Investigating parachute design
Plan and carry out an investigation of model 2 to find out the effect of changing these variables:
•
•
•
mass on bottom of toothpick
length of toothpick
surface area of parachute
While you are planning what to do remember that you should only change one variable at a time.
If you change two of more you won’t know which caused any differences in the way your model
parachuting seed falls to ground.
Questions
1. Which design features ensure a slow smooth descent?
2. Try to explain how parachute fruits are able to stay longer in the air and be dispersed by the
wind.
Note: The aerodynamics of flight are complicated, so don’t expect to be able to give a ‘right’
answer. Just think about gravity, the arrangements and movement of particles in solids and
gases, and air resistance.
Activity 4: The effect of wind
As the name suggests, wind dispersal depends on wind blowing a descending fruit further away
from the plant that it fell from (its parent plant).
Plan and carry out an investigation of the effect of wind on a parachuting fruit. You could try using
dandelions or one of the model parachute fruits you made. You could do this outdoors on a windy
day or simulate the outdoor conditions on a windy day using a fan.
Questions
1. Explain what causes wind.
Hint: The density of air is not the same throughout the atmosphere. It varies from place to place.
Particles are closer together in regions of high pressure than in regions of low pressure.
2. Sketch a diagram to show the forces acting on a falling object when the wind is blowing.
3. Explain why parachute fruits are dispersed further on a windy day than on a still day (little or no
wind).
Science & Plants for Schools: www.saps.org.uk
Parachuting Fruits: p. 3