what is a hypothesis? posing a question proposing a hypothesis a tentative explanation
TRANSCRIPT
What is a What is a hypothesis?hypothesis?
Posing a questionPosing a question
Proposing a hypothesisProposing a hypothesis
A tentative explanationA tentative explanation
Why need a Why need a hypothesis?hypothesis?
If the hypothesis is correct, what predictions can be
made?
Design experiments or
plan observations.
If the hypothesis is If the hypothesis is correct, we should correct, we should
observe observe xxxxxx when a when a certain test is certain test is
conductedconducted [predictions][predictions]
This guides us to plan This guides us to plan observations or design observations or design
experimentsexperiments
What hypothesis should be put What hypothesis should be put forward for the following forward for the following
investigations?investigations?
降落傘的大小如何影響其下降速度?
降落傘的形狀如何影響其下降速度?
• A hypothesis is NOT needed in such cases!
• An ‘expected’ result from the investigator will affect the objectivity of observation
水的溫度與受熱時間的關係?
• A hypothesis is NOT needed in such cases!
• An ‘expected’ result from the investigator will affect the objectivity of observation
水的溫度與受熱時間的關係?
用玻璃瓶蓋著燃燒的蠟燭,你會觀察到什麼?
為什麼火焰會熄滅?
A question that asks “A question that asks “whywhy” ” usually requires a usually requires a hypothesis.hypothesis.
A question that asks “A question that asks “whatwhat” ” usually requires making usually requires making objective observations. objective observations. No hypothesis is needed.No hypothesis is needed.
Do we need to suggest a Do we need to suggest a hypothesis for the following hypothesis for the following
questions?questions?
What is the W.P. of potato What is the W.P. of potato cells?cells?
Why does a potato become Why does a potato become more soft after storing for a more soft after storing for a long time?long time?
Do we need to suggest a Do we need to suggest a hypothesis for the following hypothesis for the following
questions?questions?
• What is the optimum What is the optimum temperature for salivary temperature for salivary amylase?amylase?
• Why is salivary amylase still Why is salivary amylase still very active at 70very active at 70ooC?C?
Do we need to suggest a Do we need to suggest a hypothesis for the following hypothesis for the following
questions?questions?
• What is the effect of light What is the effect of light intensity on the rate of intensity on the rate of photosynthesis?photosynthesis?
• Why does the rate of Why does the rate of photosynthesis becomes photosynthesis becomes constant with increase in light constant with increase in light intensity when the light intensity intensity when the light intensity is high?is high?
What food constituents are present in What food constituents are present in peanut, banana, grape, potato and peanut, banana, grape, potato and biscuit?biscuit?
Hypothesis:Hypothesis:
I think that peanut, banana, I think that peanut, banana, grape, potato and biscuit all grape, potato and biscuit all have proteins and lipids. have proteins and lipids.
What food constituents are present in What food constituents are present in peanut, banana, grape, potato and peanut, banana, grape, potato and biscuit?biscuit?
Hypothesis:Hypothesis:
I think that peanut, banana, I think that peanut, banana, grape, potato and biscuit all grape, potato and biscuit all have proteins and lipids. have proteins and lipids.
A hypothesis Not needed!!A hypothesis Not needed!!
What is the respiration rate of What is the respiration rate of
mealworms?mealworms?
Hypothesis:Hypothesis:
I think that the respiration rate I think that the respiration rate (oxygen uptake) is constant. (oxygen uptake) is constant.
What is the respiration rate of What is the respiration rate of
mealworms?mealworms?
Hypothesis:Hypothesis:
I think that the respiration rate I think that the respiration rate (oxygen uptake) is constant. (oxygen uptake) is constant.
A hypothesis Not needed!!
What is the transpiration rate of a What is the transpiration rate of a plant outside and inside the plant outside and inside the laboratory?laboratory?
Hypothesis:Hypothesis:
The plant outside the lab should The plant outside the lab should have a higher transpiration rate have a higher transpiration rate than the plant inside the lab. than the plant inside the lab.
What is the transpiration rate of a What is the transpiration rate of a plant outside and inside the plant outside and inside the laboratory?laboratory?
Hypothesis:Hypothesis:
The plant outside the lab should The plant outside the lab should have a higher transpiration rate have a higher transpiration rate than the plant inside the lab. than the plant inside the lab.
A hypothesis is NOT neededA hypothesis is NOT needed
Why is the transpiration rate of a Why is the transpiration rate of a plant differ outside and inside the plant differ outside and inside the laboratory?laboratory?
Hypothesis:Hypothesis:
Why is the transpiration rate of a Why is the transpiration rate of a plant differ outside and inside the plant differ outside and inside the laboratory?laboratory?
Hypothesis:Hypothesis:
The light intensity is higher The light intensity is higher outside the lab.outside the lab.•The CO2 conc is higher outside The CO2 conc is higher outside the lab.the lab.•The UV light intensity is higher The UV light intensity is higher outside the lab……….outside the lab……….
In the In the ColeusColeus leaf, more stomata are leaf, more stomata are present on the lower epidermis than on present on the lower epidermis than on the upper epidermis. the upper epidermis.
What is the significance of this uneven What is the significance of this uneven
distribution of stomata?distribution of stomata? Hypothesis:Hypothesis:
In the In the ColeusColeus leaf, more stomata are leaf, more stomata are present on the lower epidermis than on present on the lower epidermis than on the upper epidermis. the upper epidermis.
What is the significance of this uneven What is the significance of this uneven
distribution of stomata?distribution of stomata? Hypothesis:Hypothesis:• To reduce the rate of water loss due To reduce the rate of water loss due
to transpiration when sunlight shines to transpiration when sunlight shines directly from above.directly from above.
• To allow a faster rate of To allow a faster rate of photosynthesis as more carbon photosynthesis as more carbon dioxide can be taken in. dioxide can be taken in.
If a potted plant is placed outside the If a potted plant is placed outside the laboratory for two days without any laboratory for two days without any water supply, it becomes wilted. A water supply, it becomes wilted. A similar plant inside the laboratory will similar plant inside the laboratory will not show wilting. How would you not show wilting. How would you
explain these observations?explain these observations? Hypothesis:Hypothesis:
If a potted plant is placed outside the If a potted plant is placed outside the laboratory for two days without any laboratory for two days without any water supply, it becomes wilted. A water supply, it becomes wilted. A similar plant inside the laboratory will similar plant inside the laboratory will not show wilting. How would you not show wilting. How would you
explain these observations?explain these observations? Hypothesis:Hypothesis:• The plant outside the laboratory The plant outside the laboratory
becomes wilted because it has a becomes wilted because it has a higher transpiration rate due to the higher transpiration rate due to the windy conditions outside.windy conditions outside.
• The plant outside the laboratory The plant outside the laboratory becomes wilted because it is hotter becomes wilted because it is hotter outside.outside.
Potatoes stored for a long Potatoes stored for a long time becomes soft to the time becomes soft to the touch. touch.
Why does this occur?Why does this occur? Hypothesis:Hypothesis:
Potatoes stored for a long Potatoes stored for a long time becomes soft to the time becomes soft to the touch. touch.
Why does this occur?Why does this occur? Hypothesis:Hypothesis:•The longer the time of storage, the The longer the time of storage, the
more water is lost through more water is lost through transpiration.transpiration.
•The cell membrane is damaged The cell membrane is damaged during storage. So the cells lose during storage. So the cells lose their turgidity.their turgidity.
Posing a question (Posing a question (Why Why ……??))
Proposing a hypothesisProposing a hypothesis
A tentative explanationA tentative explanation
A tentative idea that A tentative idea that generates predictions – for generates predictions – for
testing the idea.testing the idea.
A tentative idea that A tentative idea that generates predictions – for generates predictions – for
testing the idea.testing the idea.ExamplesExamples
• Light intensity affects Light intensity affects photosynthesisphotosynthesis
• Water is necessary for seed Water is necessary for seed germinationgermination
Posing an ‘testable’ questionPosing an ‘testable’ question
Is it necessary to put Is it necessary to put forward a hypothesis ?forward a hypothesis ?
Designing Designing
experiment/observationexperiment/observation
Designing Designing
experiment/observationexperiment/observation Biological principleBiological principle Designing method of Designing method of
investigationinvestigation What is the independent What is the independent
variable?variable?How to change it?How to change it?
What is the dependent What is the dependent variable?variable?
How to measure it?How to measure it?
What are the assumptions made?What are the assumptions made?
Designing Designing
experiment/observationexperiment/observation What are the controlled What are the controlled variables?variables?
Any assumptions made?Any assumptions made?
Is it necessary to set up a Is it necessary to set up a control experiment?control experiment?If yes, how to do it?If yes, how to do it?
What are the What are the assumptionsassumptions that you need to make in that you need to make in
order to draw a valid conclusion from your results?order to draw a valid conclusion from your results? To measure transpiration rate using a bubble To measure transpiration rate using a bubble potometer:potometer:rate of water absorptionrate of water absorption = =
To find the W.P. using the % change in mass To find the W.P. using the % change in mass method:method:
change in mass of potato cylinderchange in mass of potato cylinder
To find the growth rate of a plant by measuring To find the growth rate of a plant by measuring the change in dry mass:the change in dry mass:
To compare the sugar content of green, red and To compare the sugar content of green, red and dark grapes using Benedict’s test:dark grapes using Benedict’s test:
What are the What are the assumptionsassumptions that you need to make in that you need to make in
order to draw a valid conclusion from your results?order to draw a valid conclusion from your results? To measure transpiration rate using a bubble To measure transpiration rate using a bubble potometer:potometer:rate of water absorptionrate of water absorption = = rate of transpirationrate of transpiration To find the W.P. using the % change in mass To find the W.P. using the % change in mass method:method:
change in mass of potato cylinderchange in mass of potato cylinder amount of amount of water water uptake/loss by uptake/loss by osmosisosmosis To find the growth rate of a plant by measuring To find the growth rate of a plant by measuring the change in dry mass:the change in dry mass:change in dry masschange in dry mass amount of cytoplasm amount of cytoplasm formedformedTo compare the sugar content of green, red and To compare the sugar content of green, red and dark grapes using Benedict’s test:dark grapes using Benedict’s test:amount of reducing sugar amount of reducing sugar totaltotal amount of amount of sugarsugar
AssumptionsAssumptions made in the controlled variables? made in the controlled variables?
Effect of light intensity on photosynthesis:Effect of light intensity on photosynthesis:rate of respiration remains constant in different rate of respiration remains constant in different light intensity; gas bubbles are identical in size light intensity; gas bubbles are identical in size
To compare the vitamin C content of different To compare the vitamin C content of different food samples using DCPIP:food samples using DCPIP:
To compare the rate of anaerobic respiration of To compare the rate of anaerobic respiration of yeast using different substrates:yeast using different substrates:
AssumptionsAssumptions made in the controlled variables? made in the controlled variables?
Effect of light intensity on photosynthesis:Effect of light intensity on photosynthesis:rate of respiration remains constant in different rate of respiration remains constant in different light intensity; gas bubbles are identical in size light intensity; gas bubbles are identical in size
To compare the vitamin C content of different To compare the vitamin C content of different food samples using DCPIP:food samples using DCPIP:Each drop of solution has the same volume; the Each drop of solution has the same volume; the end points are the sameend points are the same
To compare the rate of anaerobic respiration of To compare the rate of anaerobic respiration of yeast using different substrates:yeast using different substrates:air temperature & pressure unchanged; the air temperature & pressure unchanged; the yeast samples are identical yeast samples are identical