What is the goal of science?
1. Investigate and understand the
natural world.
2. Explain the natural world.
3. Predict events in the natural
world.
Science is a way of knowing.
What does that mean?
Biology is the study of living
things.
Bio: Living
Abio: Non-living
Thinking like a scientist.
Thinking like a scientist
• Observation
• Data
– Quantitative
– Qualitative
• Inference
Scientific Method
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Asking a question
Research
Forming a hypothesis
Setting up a controlled environment
only one variable is changed at a time
• Recording and analyzing the results
• Drawing a conclusion
• Repeating the investigation
The hypothesis of spontaneous
generation
• Aristotle – Developed the theory of
Spontaneous Generation (Abiogenesis) which
states that:
living things come from non-living things
ie. Flies came from a dead cow
Frogs come from mud
Mice come from dirty rags
Fransesco Redi
page 11
In 1668, Fransesco Redi, an Italian physician
attempted to disprove the theory of
Spontaneous Generation.
Controlled Experiment
Whenever possible, a hypothesis should be
tested by an experiment in which only one
variable is changed at a time. All other variables
should be kept unchanged or controlled.
The variable that is deliberately changed is
called the manipulated variable.
Look at Redi’s experiment and figure out what
his hypothesis was and which was the
manipulated variable.
Redi’s Experiment
John Needham
• Mid 1700s
• British
• Needham tried to prove that spontaneous
generation could occur in the right
circumstances. (He disagreed with Redi.)
John Needham’s Experiment
He boiled broth, claiming to have killed all of he
“animalcules” in it. After a few days, he used a
newly developed microscope to have a look and
saw many of the little animals.
What was wrong with his experiment?
Lazzaro Spallanzani
• Italian
• Felt that Redi was right and that Needham’s
experiment had failed because he did not boil
the broth long enough or did not have a tight
enough stopper.
• He boiled 2 containers of gravy, sealed one
and left the other open.
Spallanzani
• After a few days:
- the open container was teeming with
microorganisms and was cloudy.
- the sealed container remained free of
organisms.
• Conclusion:
The broth did not produce living things. The
microorganisms in the open container were the
offspring of microorganisms that had entered
through the air.
Louis Pasteur
• 1864
• French
• Designed a flask that would disprove
spontaneous generation once and for all.
Pasteur
“Theory”
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In science, a theory is a well-tested
explanation that unifies a broad range of
observations.
What’s the difference between a theory and a
hypothesis?
Studying Life
• Page 15
• Biology uses the scientific method to study
living things.
Living things share the following
characteristics:
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•
•
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Made up of units called cells
Reproduce
Are based on a universal genetic code
Grow (life span) and develop (life cycle)
Obtain and use materials and energy
Respond to their environment
(stimulus/response)
• Maintain a stable internal environment
(homeostasis)
• As a group, change over time (evolve)
Life is Cellular
• Without the instruments that made them
visible, cells remained out of sight and
unknown.
• The microscope changed all that!
Microscope
Mid-1600s:
- Anton van
Leeuwenhoek
- Holland
- Single lens microscope
to examine pond water
- What did he see?
• Robert Hooke
England
1665
• Compound microscope
(2 lenses) to examine a
thin slice of cork.
• “Cells”
Cell theory
• Soon different observations about cells were
being made by scientists all over.
1. Matthias Scheiden, German botanist: all
plants are made of cells
2. Theodor Schwann, German biologist: all
animals are made of cells.
3. Rudolf Virchow, German physician: new cells
are produced only from the division of
existing cells.
In the mid-1800s these observations were
combined to form the cell theory, a
fundamental concept of biology.
Cell theory states:
• All living things are composed of cells.
• Cells are the basic units of structure and
function in all living things.
• New cells are produced from existing cells.
Cells
There are two categories of cells:
1. Prokaryotic
2. Eukaryotic
Complete the handout on the two cells.
Prokaryotic cells: (from the Greek
meaning before nuclei)
1. lack a membranebound nucleus
• genetic information is in
the cytoplasm.
Prokaryotic cells (prokaryotes):
2.
3.
4.
5.
Are bacteria
Are smaller than eukaryotes (usually)
Contain fewer organelles
Do not contain organelles that have their
own membranes
Eukaryotic cells (from the Greek
meaning truly nuclear)
1. All living things except
bacteria.
2. Have a membranebound nucleus where
DNA (deoxyribonucleic
acid) is stored.
3. Usually bigger than prokaryotes
4. Have more organelles, including some that
have their own membranes
5. Are often specialized (i.e. skin cells, liver cells,
heart cells)
The main difference between eukaryotic and
prokaryotic cells is that eukaryotic cells have a
nucleus with a membrane around it (a
membrane-bound nucleus) that holds almost all
of the cell’s DNA and prokaryotic cells don’t
have a nucleus. Their DNA floats around in the
cytosol (the liquidy stuff).
Eukaryotic cells (cheek cells)
Organelles
• An organelle (which means “little organ”) is a
specialized structure with a specific function
within the cell.
• All living material within the cell is called
protoplasm