midterm review how scientists work; cell structure
TRANSCRIPT
Midterm Review
How Scientists Work; Cell Structure
Designing an Experiment
State the Problem
Form a Hypothesis
Set Up a Controlled Experiment
Record Results
Analyze Results
Draw a Conclusion
Publish 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
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
Controlled Variables:jars, type of meat,location, temperature,time
Manipulated Variables:gauze covering thatkeeps flies away from meat
Uncovered jars Covered jars
Several days pass
Maggots appear No maggots appearResponding Variable: whether maggots appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.
Drawing a Conclusion
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
When do you reject a hypothesis? If you reject your hypothesis did you
waste time? What happens next?
Cell Structure and Function
Prokaryotic Cell
Cell membrane
Cell membrane
Cytoplasm
Cytoplasm
Nucleus
Organelles
Eukaryotic Cell
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
Plant Cell
Nuclearenvelope
Ribosome(attached)
Ribosome(free)
Smooth endoplasmicreticulum
Nucleus
Rough endoplasmic reticulum
Nucleolus
Golgi apparatus
Mitochondrion
Cell wall
CellMembrane
Chloroplast
Vacuole
Eukaryotic Cells
Animal Cell
Centrioles
NucleolusNucleus
Nuclearenvelope
Rough endoplasmic reticulum
Golgi apparatus
Smooth endoplasmicreticulum
Mitochondrion
CellMembrane
Ribosome(free)
Ribosome(attached)
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
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
bilayerSuch 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. 7-12Outsideof cell
Insideof cell(cytoplasm)
Cellmembrane
Proteins
Proteinchannel Lipid bilayer
Carbohydratechains
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
Key points about diffusion:
1) Particles move from an area of high concentration to an area of low
concentration2) Diffusion will occur until equilibrium is
reachedequilibrium – 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
Protein channel
Glucose molecules
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 TransportMolecule tobe carried
Moleculebeing carried
Energy
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