ODWS icon

The Open Door Web Site
HOMEPAGE CHEMISTRY PHYSICS ELECTRONICS HISTORY HISTORY OF SCI & TECH MATH STUDIES LEARNING FRENCH STUDY GUIDE  PHOTO GALLERY
BIOLOGY HOMEPAGE  IB BIOLOGY WEB TOPIC CHAPTERS FACTS & FIGURES LABORATORY WORK QUESTIONS & QUIZZES ECOLOGY CLUB PLAYS

 

Reference chapter

Question 3
HTML version
PDF version

 

 

 

 

HOW PLANTS FEED

Custom Search

Question 3

Duckweed is a simple plant which grows in ponds. Its leaves float on the surface of the water and its roots hang down in the water. The minerals that the duckweed needs for growth are absorbed from the water that surrounds its roots.

 

Duckweed

 

The following experiment was carried out on duckweed growing in two different mineral waters (Contrix and Hevion), distilled water and Knop's solution. (Knop's solution is a solution of minerals especially prepared for growing plants. It has been used since 1865.)

The numbers of leaves which the duckweed plants grew were counted regularly over four weeks. The results are shown as a graph:

 

Graph

 

1. In which solution did the duckweed grow the most leaves?

2. How many leaves are there in each of the solutions after 14 days?

3. Describe in your own words how the duckweed grows in Hevion. (Hint: Explain the shape of the graph)

 

On each bottle of mineral water is a label which gives the concentrations of the different minerals in cubic decimetres of water. The table below shows these concentrations and also the minerals found in Knop's solution and distilled water.

 

Minerals

Concentration of minerals
(mg/dm3)

  

Contrix

Hevion

Knop's

Distilled
water

Nitrate

4

4

1000

0

Potassium

3

1

400

0

Phosphate

0

0

300

0

Calcium

467

78

800

0

Sulphate

1192

10

200

0

Magnesium

84

24

200

0

Note: Nitrates are mineral salts which contain nitrogen, sulphates contain sulphur and phosphates contain phosphorus.

 

4. (a) Which mineral is present in Knop's solution but is missing from the other solutions?
(b) Perhaps it is the absence of this mineral which is stopping the plants from growing so well in the other solutions. How could you carry out an experiment to prove this idea?

5. Give the name of another mineral which plants need for their growth, which is not given in the table above.

6. Distilled water contains no minerals at all.
(a) How can you explain the growth of the duckweed in distilled water during the first seven days?
(b) What happens to the duckweed in the distilled water after 14 days?

7. If you grew duckweed in rain water do you think that it would grow very well?

8. Compare the minerals in Knop's solution with a bottled mineral water which you drink. Do you think that an animal, such as a human, needs the same minerals as a plant?

 

The Open Door Web Site is non-profit making. Your donations help towards the cost of maintaining this free service on-line.

Donate to the Open Door Web Site using PayPal

SITE MAP
WHAT'S NEW?
ABOUT

PRIVACY

COPYRIGHT

SPONSORSHIP

DONATIONS

ADVERTISING

© The Open Door Team 2017
Any questions or problems regarding this site should be addressed to the webmaster

© Paul Billiet and Shirley Burchill 2017

Hosted By
Web Hosting by HostCentric


SiteLock