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Transcript
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 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 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 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 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 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