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