Circular Motion

By Corina Bot

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.

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.

http://www.microscopy-uk.org.ukhttp://en.wikipedia.org

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. 

Elodea cells displaying cyclosis, the movement of materialin a circular motion around the inside perimeter of the cell.

(Watch for the movement of chloroplasts along the inside of the cell wall.)

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 ?

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 ?

t

rad

r

l

diameterr

(deg))(180

2

q2

q1

Dl

r

Dq

diameter = 100 mmDl = 120 mm

= ? Dq rad = ? Dq deg

w = ?

srad

s

rad

t

radrad

radm

m

r

l

mmdiameter

r

096.025

4.2

5.1374.2180

)(180

(deg)

4.250

120

502

100

2

Solution: