formulation & testing of hypothesis in scientific investigations

Formulation & Testing Formulation & Testing of Hypothesis in of Hypothesis in

Scientific Scientific InvestigationsInvestigations

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

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 “what is what is the relationship / how to be the relationship / how to be affected affected ” usually requires ” usually requires making objective making objective observations. observations. No hypothesis is needed.No hypothesis is needed.

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？

水的溫度與受熱時間的關係？

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?



• 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?



• 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 is the respiration rate of What is the respiration rate of

mealworms?mealworms?


I think that the respiration rate I think that the respiration rate (oxygen uptake) is constant. (oxygen uptake) is constant.

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?


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 effect of light intensity What is the effect of light intensity on the rate of photosynthesis?on the rate of photosynthesis?


The photosynthetic rate rises The photosynthetic rate rises with increase in light intensity. with increase in light intensity.

What is the osmotic potential of What is the osmotic potential of the cell sap in red onion epidermal the cell sap in red onion epidermal cells?cells?

Hypothesis:Hypothesis:When 50% of the observed cells is plaWhen 50% of the observed cells is plasmolysed, the O.P. of the cells is the ssmolysed, the O.P. of the cells is the same as that of the surrounding sucrosame as that of the surrounding sucrose solution. e solution.

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:• 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:•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.

Posing an investigatable questionPosing an investigatable 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 assumptions that you need to make in What are the assumptions 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 potometerTo measure transpiration rate using a bubble 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

Assumptions made in the controlled variables?Assumptions 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