Transcript Slide 1
EOCT Review The first thing you need to know about science is the scientific method. The scientific method is used to acquire, organize, and apply new knowledge. The steps in the scientific method are as follows: * Define the problem. This means figuring out exactly what the problem is. It must be worded so that an investigation can take place. For instance, you wouldn’t decide to investigate the favorite band of every 15 year old human in the world. That problem is too big for one person to investigate. However, you COULD investigate the favorite band of 15 year old students in a single school. * Investigate previous research about the problem. Look up this problem in scientific journals, the internet, Interview researchers, etc. and find out what has already been researched about this question. Use that information as a basis to design your research. * Form a hypothesis about the answer. A hypothesis is an educated guess. Based on everything you have learned thus far, what would you logically expect to happen during this investigation. * Design and carry out an experiment. This experiment will test your predictions. * Record all data from the experiment. This is a really important step. Write down EVERYTHING you observe during the experiment. Sometimes the most important data comes from unexpected results. For instance if you were expecting a color to change and in addition the reaction starts bubbling, write the bubbling down too! * Draw conclusions from your data. Based on what you observed, what can you decide. Let’s say you observe 100 students. You allow 50 to chew gum during tests and the other 50 cannot chew gum. The 50 students who chew gum scored 25% better than the non-gum chewing students. It is logical to conclude that chewing gum allows the students to concentrate better during the test and therefore score better. Scientists often use the terms hypothesis, theory, laws/principles, and facts. But what is the difference between the terms. A HYPOTHESIS is an educated guess. Based on the information you have right now, this is what you think will happen in a given set of circumstances. (It is hypothesized that if cockroaches are sprayed with sulfuric acid they will die.) A THEORY is formed when a tremendous amount of information has been tested many times and hypotheses verified about the natural world. (Four hundred scientists noticed that if you drop an object it falls to the ground. Therefore, it was theorized that there is a force called gravity.) A LAW or PRINCIPLE is when a hypothesis is tested over and over again without ever being inaccurate. ( Newton demonstrated that if a chair is sitting on the floor, it will sit there unless something happens to turn it over [a human, earthquake, etc] and similarly if a ball is flying through the air it will continue to do so unless something stops it [a hand catching it, gravity, etc.]. This became known as Newton’s Law of Inertia, which states that an object at rest tends to remain at rest and an object in motion tends to remain in motion unless acted upon by some outside force.) A FACT is close agreement by highly qualified observers who make the same identical observations of the same occurrence. ( FACT – the moon is NOT made of green cheese!) 90 80 70 60 50 40 30 20 10 0 1st Qtr Insects Vertebrates Plants 2nd Qtr 3rd Qtr 4th Qtr 1st Qtr 2nd 3rd Qtr 4th Qtr Qtr Simple method to compare data. They are a good tool to use for comparing data. Good method to show percents or to compare parts to a whole. Best way to show how one variable changes with respect to another • Wear goggles to protect your eyes, and an apron to protect your clothes and your body from chemicals • Locate and know how to use an eye wash station, shower, fire blanket, fire extinguisher, and safety kit. • Do not eat, drink, or chew gum in the lab. • Report all accidents to your teacher. • Use a fume hood when working with toxic or flammable chemicals. • Pull long hair back so that it does not get into flames or chemicals. • Do not touch hot equipment, glassware, etc. Turn off heating equipment when it is not in use. • Do not taste or smell chemicals. • Read and reread labels before using chemicals. • Dispose of chemicals only under the supervision of the teacher. • NEVER change the instructions, mix chemicals to “see what happens”, or create your own experiments. • Do not put chemicals into their original containers. • ADD ACID TO WATER, not water to acid. • Make sure glassware has no chips or cracks. Do NOT force glassware into stoppers. Beaker – used to measure liquids that Measured in grams, kilograms are 100’s of milliliters. Graduated Cylinder – used to measure small amounts of liquids. Read Equipment is a triple beam balance or a digital balance. the amount at the meniscus (bottom curved part of the liquid. Volumetric flask – has one line to show the measurement of one amount. For example, it might have a line at 300 mL. Burette – used for titrations. They are filled with liquid which is then measured out. Pipette – has a suction bulb to draw fluid into it. When weighing a solid chemical you place it on top of a weighing paper. Weigh the paper, then add the chemical. Record the weight of the chemical plus the paper. Then subtract weight of the weighing paper from the total weight to find the weight of the chemical by itself. Cells Robert Hooke described and named cells in 1665, however he never recognized the importance of his discovery. It was van Leeuwenhoek who discovered living, single celled organisms. Almost 200 years later two German scientists recognized that all organisms are composed of cells. Specifically, Schwann stated that all animals are composed of cells and Schleiden concluded that all plants are composed of cells. These discoveries, plus others led to the cell theory. There are two major kinds of cells, prokaryotic cells and eukaryotic cells Cell Theory a) All organisms are composed of cells. b) All cells come from all other cells. c) The ability of cells to divide to form new cells is the basis for all reproduction and for the growth and repair of multicellular organisms, including humans. What Is A Eukaryotic Cell? A eukaryote is an organism with complex cells, in which the genetic material is organized into membrane-bound nuclei. Eukaryotes include animals, plants, and fungi (which are mostly multicellular) as well as various other groups that are collectively classified as protists (many of which are unicellular). In contrast, other organisms, such as bacteria, lack nuclei and other complex cell structures; such organisms are called prokaryotes. The eukaryotes share a common origin, and are often treated formally as a superkingdom, empire, or domain. The name comes from the Greek eus (meaning true) and karyon (meaning nut, referring to the cell nucleus). Internal Membrane of Eukaryotes • • Eukaryotic cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. Simple compartments, called vesicles or vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles. The nucleus is surrounded by a double membrane, with pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form what is called the endoplasmic reticulum or ER, which is involved in protein transport. It includes the Rough ER where ribosomes are attached, and the proteins they synthesize enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the Smooth ER. In most eukaryotes, the proteins may be further modified in stacks of flattened vesicles, called Golgi bodies or dictyosomes. Mitochondria and Plastids • • • Mitochondria are organelles found in nearly all eukaryotes. They are surrounded by double membranes, the inner of which is folded into invaginations called cristae, where aerobic respiration takes place. They contain their own DNA and are only formed by the fission of other mitochondria. They are now generally held to have developed from endosymbiotic prokaryotes, probably proteobacteria. The few protozoa that lack mitochondria have been found to contain mitochondrion-derived organelles, such as hydrogenosomes and mitosomes. Plants and various groups of algae also have plastids. Again, these have their own DNA and developed from endosymbiotes, in this case cyanobacteria. They usually take the form of chloroplasts, which like cyanobacteria contain chlorophyll and produce energy through photosynthesis. Others are involved in storing food. Although plastids likely had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion. Endosymbiotic origins have also been proposed for the nucleus and eukaryotic flagella, but this is not generally accepted, both from a lack of cytological evidence and difficulty in reconciling this with cellular reproduction. Cytoskeletal Structures • • • Many eukaryotes have slender motile projections, usually called flagella when long and cilia when short, that are variously involved in movement, feeding, and sensation. These are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a basal body, also called a kinetosome or centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs or mastigonemes, scales, connecting membranes and internal rods. Their interior is continuous with the cell's cytoplasm. Centrioles are often present even in cells and groups that do not have flagella. They generally occur in groups of one or two, called kinetids, that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles may also be associated in the formation of a spindle during nuclear division. Some protists have various other microtubule-supported organelles. These include the radiolaria and heliozoa, which produce axopodia used in flotation or to capture prey, and the haptophytes, which have a peculiar flagellum-like organelle called the haptonema. Structure of Eukaryotic Cells Eukaryotic cells are generally much larger than prokaryotes, typically a thousand times by volume. They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules and microfilaments, which play an important role in defining the cell's organization. Eukaryotic DNA is divided into several bundles called chromosomes, which are separated by a micro tubular spindle during nuclear division. In addition to asexual cell division, most eukaryotes have some process of sexual reproduction via cell fusion, which is not found among prokaryotes. Summary of eukaryotic organelles and functions What Is A Prokaryote? Prokaryotes are organisms without a cell nucleus, or indeed any other membrane-bound organelles, in most cases unicellular (in rare cases, multicellular). This is in contrast to eukaryotes, organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. The arrangement of Eukaryote, Bacteria, and Archaea is called the three-domain system. Evolution of Prokaryotes • • • It is generally accepted that the first living cells were some form of prokaryote. Fossilized prokaryotes 3.5 billion years old have been discovered, and prokaryotes are perhaps the most successful and abundant organism even today. In contrast the eukaryote only appeared approximately 1.5 billion years ago. While earth is the only known place where prokaryotes exist, some have suggested structures within a Martian meteorite should be interpreted as fossil prokaryotes, but this is extremely doubtful. Prokaryotes diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct types of prokaryotes. For example, in addition to using photosynthesis or an organic form of carbon for energy like eukaryotes do, prokaryotes may obtain energy from inorganic chemicals such as hydrogen sulfide. This has enabled the bacteria to thrive and reproduce. Today, bacteria can be found in the cold of Antarctica and in the hot Yellowstone springs. Structure of Prokaryotes • • The cell structure of prokaryotes differs greatly from eukaryotes in many ways. The defining characteristic is, of course, the absence of a nucleus or nuclear envelope. Prokaryotes also were previously considered to lack cytoskeletons and do lack membrane-bound cell compartments such as vacuoles, endoplasmic reticulum, mitochondria and chloroplasts. In eukaryotes, the latter two perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare. Prokaryotes also have cell walls, while some eukaryotes, particularly animals, do not. Both eukaryotes and prokaryotes have structures called ribosomes, which produce protein. Prokaryotes are usually much smaller than eukaryotic cells. Prokaryotes have a single circular (only exceptionally linear, as in Borrelia burgdorferi) chromosome, contained within a region called nucleoid, rather than in a membrane-bound nucleus, but may also have various small circular pieces of DNA called plasmids spread throughout the cell. Reproduction is exclusively asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.