Circular Motion
By Corina Bot
Elodea is a genus of aquatic plants often called the waterweeds. Elodea is native to
North America and is also widely used as aquarium vegetation.
If a chloroplast appears to be in the middle of a cell, it is not. If it is blurry, it is placed
at the bottom of the cell. If it is in focus, it is placed at the top of the cell.
Cyclosis is the circulation or streaming of the cytoplasm within some living cells.
In plant cells, chloroplasts may be moved around with the stream, possibly to a
position of optimum light absorption for photosynthesis. The rate of motion is
usually affected by light exposure, temperature, and pH levels.
http://www.microscopy-uk.org.uk
http://en.wikipedia.org
Elodea cells displaying cyclosis,
the movement of material
in a circular motion around the
inside perimeter of the cell.
(Watch for the movement of
chloroplasts along the inside of
the cell wall.)
Research Problem:
Assume we focus on a spherical cell inside another type of leaf. One chloroplast travels along
the cell wall through an arc length of 120 mm. If one cell has a diameter of approximately
100 mm, through what angular displacement does the chloroplast travel?
Calculate angular displacement in both radians and degrees.
What is the average angular speed for the chloroplast in 25s ?
Assume we focus on a spherical cell inside another type of leaf. One chloroplast travels along the cell
wall through an arc length of 120 mm. If one cell has a diameter of approximately 100 mm, through what
angular displacement does the chloroplast travel? Calculate angular displacement in both radians and
degrees. What is the average angular speed for the chloroplast in 25s ?
diameter = 100 mm
l = 120 mm
  ? rad
  ? deg
=?
2
1
r
r 
diameter
2
 
l
r
180

 
   ( rad )    (deg)

t
Solution:
r 
diameter

100 m m
2
 
l
2

120 m m
50 m m
r
  (deg) 
 

t
 50 m m

180

   ( rad ) 
2 . 4 rad
25 s
 2 . 4 rad
 0 . 096 rad
180

s
 2 . 4 rad  137 . 5 