Transcript Midterm Review

Midterm Review
How Scientists Work; Cell
Structure
Designing an Experiment
State the Problem
Analyze Results
Form a Hypothesis
Draw a Conclusion
Set Up a Controlled Experiment
Publish Results
Record Results
How do scientists test hypotheses?

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.
Setting Up a Controlled Experiment

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The variable that is deliberately
changed is called the manipulated
variable.
The variable that is observed and that
changes in response to the
manipulated variable is called the
responding variable.
Redi’s Experiment Fig. 1-8
OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.
PROCEDURE
Uncovered jars
Controlled Variables:
jars, type of meat,
location, temperature,
time
Covered jars
Several
days pass
Manipulated Variables:
gauze covering that
keeps flies away from
meat
Responding Variable:
whether maggots
Maggots appear
No maggots appear
appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous
generation of maggots did not occur.
Drawing a Conclusion

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Scientists use the data from an
experiment to evaluate a hypothesis
and draw a valid conclusion.
Redi’s results supported the
hypothesis that maggots were
produced by flies, not spontaneous
generation.
Drawing a Conclusion

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When do you reject a hypothesis?
If you reject your hypothesis did you
waste time?
What happens next?
Cell Structure and Function
Cell membrane
Cytoplasm
Prokaryotic Cell
Cell membrane
Cytoplasm
Nucleus
Eukaryotic Cell
Organelles
Cell Theory
1) All living things are composed of cells.
2) Cells are the basic units of structure
and function in living things
3) New cells are produced from existing
cells
All Cells have:
1) Cell Membranes
2) Genetic Information (DNA)
Eukaryotic Cells



contain DNA in a nucleus (at some time in
there life cycle)
generally larger and more complex than
prokaryotic cells
many are highly specialized
example: neurons
Eukaryotic Cells continued…
contain many structures and internal
membranes → eukaryotic organelles
 Make up a great variety of organisms
Examples: Plants, Animals, Fungi,
Protists

Prokaryotic Cells
do not contain nuclei (they do have
DNA)
 generally smaller and simpler than
eukaryotic cells
Example: Bacteria

Prokaryotic or Eukaryotic?
Eukaryotic Cells
Smooth endoplasmic
reticulum
Vacuole
Ribosome
(free)
Chloroplast
Ribosome
(attached)
Cell
Membrane
Nuclear
envelope
Cell wall
Nucleolus
Golgi apparatus
Nucleus
Mitochondrion
Rough endoplasmic reticulum
Plant Cell
Eukaryotic Cells
Nucleolus
Nucleus
Ribosome
(attached)
Nuclear
envelope
Ribosome
(free)
Cell
Membrane
Mitochondrion
Smooth
endoplasmic
reticulum
Rough
endoplasmic
reticulum
Centrioles
Golgi apparatus
Animal Cell
Eukaryotic Cell Structure


Eukaryotic cells contain many
structures that act as specialized
organs known as organelles
Eukaryotic cells are classified into two
major parts: 1) the nucleus, and 2) the
cytoplasm – the portion of the cell
outside of the nucleus
Nucleus


is the control center of the cell
contains the genetic material known as
DNA (deoxyribonucleic acid)


DNA provides the instructions for making
proteins and other important molecules
contains chromatin - consists of DNA
bound to protein → condenses to form
chromosomes
Ribosomes

Proteins are assembled (synthesized)
on the ribosomes

produce proteins by following coded
instructions that come from the nucleus
* Cells that synthesize a lot of proteins
are filled with ribosomes
Analogy: a machine in a factory /
construction workers
Mitochondria and Chloroplasts

All living things require a source of
energy

most cells get energy in one of two ways:
from food molecules or from the sun
* Both organelles contain their own
genetic information
Mitochondria

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convert chemical energy stored in food
into compounds that are more
convenient for the cells to use
enclosed by two membranes
Analogy: Coal-Burning Power Plant
Chloroplasts
contained in plant cells and some
other organisms
 capture energy from the sunlight and
convert it into chemical energy through
a process called photosynthesis
 enclosed by two membranes
Analogy: Solar Powered Cells

Cell Membrane
Function: 1) To regulate what enters
and leaves the cell
2) To provide protection and
support
Cell Membrane
Structure: 1) Takes the form of a lipid bilayer →
both flexible and strong
2) Many different molecules are
embedded in the lipid bilayer
Such as: Proteins and Carbohydrates
 Proteins often form channels to allow certain
molecules to pass in and out of the cell
 Carbohydrates act as markers to identify the
cell
Cell Membrane - Fig. 7-12
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Cell Wall
Present in many types of organisms, such
as: plants, algae, fungi, and many
prokaryotes
Function: To provide protection and
support
Structure: Primarily made of cellulose →
tough carbohydrate fiber; the cell
wall is not flexible like the cell
membrane
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Key points about diffusion:
1) Particles move from an area of high
concentration to an area of low
concentration
2) Diffusion will occur until equilibrium is
reached
equilibrium – the concentration of a solute is
the same throughout a system
3) Substances diffuse across a membrane
without requiring the cell to use energy
Facilitated Diffusion
Glucose
molecules
Protein
channel
Active Transport

Sometimes cells move materials in the
opposite direction from which the
materials would normally move—that
is against a concentration difference.
This process is known as active
transport.

Active transport requires energy
Osmosis
Water passes quite easily across most
membranes, even though many solute
molecules cannot → this results in
osmosis
osmosis – the diffusion of water through
a selectively permeable membrane


osmosis usually occurs until equilibrium
is reached
Active Transport
Molecule to
be carried
Energy
Molecule
being carried
Levels of Organization

Used to make it easier to describe
multicellular organisms
Individual Cells → Tissues → Organs → Organ Systems
Levels of Organization
Muscle cell
Smooth muscle tissue
Stomach
Digestive system