scientific method

hypothesis

an educated guess based on observations.

experiment

an investigation carried out to test a hypothesis

double-blind testing

neither the patients nor medical staff know who is getting the placebo and who is getting the real drug

placebo

an ineffective pill given to patients to mimic a trial drug

explain the necessity of random selection

ensures a fair test and reduces bias

good experimental design

• a control

• large sample size

• only one variable

• able to be repeated

why is it important that scientists publish the results of their research?

- so that others can learn from their work

- so that others can repeat it

how can a scientist avoid bias in an experiment?

• large sample size

• random selection

what is the purpose of replicates in a scientific experiment?

to ensure reliability

how would you ensure that pH remains constant?

pH buffer

how to maintain constant temperature?

water bath

replicate

an exact repeat of a previous experiment

purpose of replicates

verify results

limitations of a scientific method

• the extent of our knowledge

• accidental discoveries

• ethical issues (e.g. animal testing)

why is a control used/essential when carrying out an experiment?

to provide a standard against which the actual experiment can be compared

theory

a hypothesis proven to be accurate by many different experiments

law

a theory that has been observed over a long period of time

how does a hypothesis differ from a theory?

a hypothesis is an educated guess based on observations. a hypothesis can develop into a theory if proven by many different experiments

data

results of an experiment

Q1 scientist investigated the effect of a certain mineral on the growth of wheat.* suggest a reason why all the seeds were taken from one parent plant.

to ensure they have similar genes and prevent genetic variation

Q1 the compost in which the wheat plants were grown were sterilised at the start of the investigation* suggest a way in which the scientist may have sterilised the compost.

using the natural HEAT from the sun

Q1. state one reason why it was important to sterilise the compost.

• to kill micro-organisms

• prevent contamination

Q1. why did the scientist divide the young wheat plants into two equal groups?

as a control

Q1. during the investigation, the scientist kept the two groups of plants under identical conditions. why?

only have one variable

Q1. name two conditions the scientists would have kept constant during the investigation.

• light

• temperature

• pH

• CO2

• water

Q1. why did the scientists repeat the investigation several times before publishing their results in a scientific journal?

to ensure reliability

Q2. if a scientist wished to determine the effect of a certain herbicide on weed growth she would include a control in the investigation.* suggest a suitable control in this case.

no herbicide. use water in place.