Hypothesis, Theories & Models about Plant Function
Photosynthesis
Investigations
Aim
17th Century
Plants eat soil for growth
Scientists
Jan Baptista van Helmont (1580 – 1644)
thought that soil formed plant matter
Experiments
Weighed 90kg of dried soil
planted a 2.25kg willow seedling
watered the plant for 5 years
separated the seedling from the soil
dried the soil
weighed both
Conclusion
soil weighed 89.9 kg
small decrease
plant weighed 76.1 kg
large increase
All of plant matter came from water
Evaluation
Conclusion was incorrect
tested whether soil provided matter
concluded it was water
Should be
very little of plant matter came from soil
Flawed
Mass of lost leaves
not included
No control
To test whether if water was only used
No Repetition
Only one plant was tested
Many Inaccuracies
description
incomplete
no measurement of water
weighing accurately
not possible
soil cannot separate from plant
Joseph Priestley (1733 – 1804)
Observations
Experiment
Enclosed space
candle would go out
mouse would die
Mint plant into enclosed space
Transpiration-Cohesion-Tension Theory
Extinguished candle
Put another mint plant
With a mouse
Conclusion
Plant present in enclosed space
candle lit
focused sunlight
remained alight
mouse survived
Plant restores to the air
Whatever candle & mouse removed
candle & mouse
breathing the air
'injured' the air
plant growth
Replacing factors
Mouse & Candle had removed
Evaluation
Well-designed
conclusion matched knowledge of the time
contributed greatly
photosynthesis
Jan ingenhousz (1730 – 1799)
Experiment
Similar to Priestley
candle and plant
covered bell jar
no light could enter
left it for number of days
in bell jar
submerged small aquatic plant
in water
exposed to light
set-up to darkness
candle did not light
Conclusion
light is necessary
Restoring air
after it has been 'fouled'
for plants
make oxygen
aquatic plant exposed to light
bubbles formed
around leaves
around green parts of the stem
In darkness
bubbles stopped
'purify' air
Took Priestley's work even further
credited with discovering photosynthesis
demonstrated
light and green sections of plant
required
produce oxgyen
Jean Senebier
Nicholas-Theodore de Saussure
F.F. Blackman
Cornelis van Niel
Samuel Ruben
Martin Kamen
Melvin Calvin
definition
explain how water and mineral ions
move in xylem tissue
developed based on investigations
scientists
John Joly
Henry Horatio Dixon
Stephen Hales
Eugen Askenasy
Steven Jansen
H. Jochen Schenk
Process of Investigations
experiments & results are analysed
basis for further investigation
Evaluation
Judgement made
Whether the scientific method was followed
Evidence
Claims or Conclusions
correct conclusion
results of investigation
supported
by experiments
