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

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