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The limiting factors of photosynthesis



Let us see now how protists and other little animals of ponds react to alteration to theirenvironment.
1 - Some microscopic algae, like the euglena, search out light (phototaxis) and to do thisthey use an organelle sensible to the light, named stigma. With a dark paper, cover thebottom part of a test tube holding a culture of euglena. The part of the test tube exposedto light should become green, rich with algae. Make the same experiment with othermicroscopic algae and with protozoa.
2 - Add two or three drop of distilled water to a little water drop collected in a pondand watch what happens to the protists. Very probably you will see them inflate and thenexplode. This occurs because of the different saline concentration inside and outside theprotists and the osmotic pressure which is produced inside their cells.
3 - Protists are sensitive to most chemicals and generally they react by running away; insome cases instead they approach them (chemotaxis). Prepare some microscope slides withprotists and observe through the microscope their behavior when you add acidic substances(i.e.: vinegar), basic substances (i.e.: backing soda), glucose, salt, sparkling water(rich of CO2), broth, milk, tiny grain of cheese, dyes, etc. At thebeginning use very low amounts of these substances, then increase their concentration.
4 - From a pond or an aquarium, collect a hydra and place it on a microscope slide with apair of water drops. Observing this tiny polyp through the microscope, probably you willsee some sucker shaped microorganisms (trichodina) moving on its body. Watch what happensafter adding a little drop of vinegar to their water! Trichodina will escape from thehydra and probably die. Hydra itself will have launched many of its harmful paralyzingdarts.
5 - Submit protists to different stimulus such as light, temperature, electric field(about 5 V in DC). In this last case, some protists will gather on the cathode (thenegative - pole). Also amebas are inclined to move towards the cathode. Change thepolarity of the current and observe the behavior of the protists.
Internet Keyword: phototaxis chemotaxis protists.



Until the end of the 17th century, people believed that little animals like flies andworms could spontaneously be born from substances in decomposition or from mud. FrancescoRedi, Lazzaro Spallanzani and Louis Pasteur made experiments which proved the idea of thespontaneous generation was wrong. At your home or in your school you can made suchexperiments too.
1 - Take two glass jars with a screw top. Put in each a little piece of cooked apple and aspoon of vinegar. For a night, leave one of these jars opened so it can be visited byvinegar (fruit) flies. Close the other jar with the lid and sterilize it by placing it inboiling water in a pressure cooker for a half an hour. After removing it from the cooker,let it cool, leaving it closed. The morning after, let the possible bugs present into thefirst jar leave and then close it with a fine gauze or a plastic sheet on which you willmake some pinholes to allow oxygen to enter. After a few days, you should see some bugs inthe first jar, and none in the second one. What has happened in the first jar which hasnot happened in the second? Some vinegar flies laid eggs in the first jar and from themsome new flies are born. In the second jar, even if there had been eggs, these are deadbecause of high temperature in the pressure cooker. More eggs were not laid because thejar was kept closed. With experiments like this one, you can realize that living beingscannot born from nothing, but they are born from other organisms like them. Fall is themore suited season to do this experiment because vinegar flies are particularly active.
2 - Anyway you can try to adapt this experiment to organisms present at other times of theyear. For example, if you place some dry grass in a water glass, in few days a deal ofprotists will appear. If instead you will put the same material in a close glass pot andif you boil it, nothing will be born. Only some rare thermoresistant microorganisms,bacteria which resist the high temperature of boiling water.
... Uhm, and still there is something which is not working: if any living being comes fromanother living being, from where has come the first living being from which all others arederived? Can we consider completely falsified the theory of the spontaneous generationwith these experiments? Is it possible to assert that, even if the spontaneous generationis not the usual way with which living creatures are born, at least at one time duringbillions of years it has happened on the Earth or another place in the Universe? It is noaccident that there are scientists who study how life began in the first place.
Spontaneous Generation
Spontaneous Generation
Internet keywords: spontaneous generation.

What is the factor which is limiting the rate of photosynthesis at point X on the graph?

Absorption spectrum of chlorophyll

Photosynthesis consists of light-dependent and light-independent reactions.

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The enzymes controlling photosynthesis are nearer or at their optimum temperature.

It is not easy to write a conclusion for such a heterogeneous series ofexperiments. However, we hope you have appreciated this technique of gathering manybriefly described experiments in a single article. At least it offers you many choices. Wenow ask for your help: please report to us the links which are not working any more; tellus about other interesting sites; tell us what experiments you would like to see treatedin a more detail; send us other comments and suggestions. You can use the evaluation cardbelow. Will you help us?

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A lot of organisms emit light. Of course you know fireflies, but there are also otherluminescent organisms such as some fishes, mushrooms, bacteria, dinoflagellates, andshellfishes. The culture of luminescent bacteria is not difficult. What you have to do isto get a strain of luminescent and harmless bacteria and raise it in a suitable culturemedium. A bacterium widely cultured and used also for lessons in schools is the Photobacteriumphosphoreum, now renamed: Vibrio phosphoreum.
Search for information about the mechanism of the bioluminescence. You can findinformation for this culture and general information on the Internet at sites listedlater. There is a lot of information on bioluminescence on the Internet. There are evenamateur sites devoted to this topic. You can buy the Vibrio phosphoreum at commercially,such as the ATCC (American Type Culture Collection) .You can find other firms of this type on the Internet, using the keywords: culturecollection. Also try the links for the protists experiment. These companies also supplythe culture media and in their sites you can often read their composition.
: In these experiments, need thehelp of a biologist to avoid culturing dangerous microorganisms. Even with help, keep thecultures only for a short time, wash your hands, wash and disinfect all tools which havebeen in contact with the cultures.
Utilisation Pedagogique de Bacteries Luminescentes (in French)
Luminescent Bacteria
Bioluminescence in Plankton and Nekton (there is a list of luminescent organisms)
Flash! Bacterial illumination
Isolation of Pure Cultures Of Bacteria (Please, read the safety warnings present inthis website)
Bioluminescence Web sites
Internet Keyword: luminous bacteria luminescent bioluminescence luciferin luciferase.
To find companies which sell strains of microorganisms use the keywords: culturecollection.



Are the insects which fly around lamps at night attracted by light or heat? To find out,use a clothing iron and an electric lamp. The electric lamp produces light with a littleheat, the iron produces only heat. Put both on a table. Keep them at least a meter (abouta yard) apart and with the emitting surfaces turned away from you. Note the differentbehavior of insects. Mask the lamp with plastic sheets of different colors and verify ifbugs are more attracted to a particular color. This is also a method to capture nighttimeinsects, particularly moths, so you can observe them with a lens or a stereoscopicmicroscope.

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If placed in a suitable nutrient environment, cells and tissues of many organisms are ableto reproduce and form new plants or animals. Now, we will deal with vegetable tissues,whose culture is simpler than that of animal cellules and tissues. It is necessary toprepare a nutritive and sterilized culture medium for the piece of plant tissue. Keep theculture in the suitable conditions of light and temperature and which vary from plant toplant. Over many days, you will observe the growth of a callus or roots or shoots. In thisway you can obtain even whole plants (cloning). These experiments show that special cellskeep all the information necessary to generate the whole plant.
As we have mentioned, it is necessary avoid bacteria and moulds in the cultures. For thisyou will need sterilize tools, vials, tubes, and nutrient medium. Place each in anautoclave for a ten minutes or, lacking an autoclave, a pressure cooker. The tissues aswell have to be free from microorganisms and they have to be sterilized with bleach (40%solution for 15 min) or with alcohol.
The transfer of the tissues into the test tubes has to be made in aseptic conditions,using a sterile box. Lacking that, make your first trials in a quiet place, as devoid ofwind and dust as possible. The culture medium should contain water, vitamins (particularlythose of the B-complex. For this, use yeast extract), sugars, mineral salts. To enrich thewater with mineral salts, boil some water with a handful of soil, then let settle andfilter it. Usually, people also insert 0.5-0.8% of agar-agar to "solidify" themedium. As culture medium, coconut milk has been used. It contains mineral salts, sugars,vitamins and growth hormones.
1 - For yours first tests of micropropagation, use strawberries tissues.
2 - If this simple experiment interests you, you can continue on the way of the invitro culture of vegetable tissues. In fact you can propagate a lot of plants in thisway. Plants easy to culture are the following: tomato, potato, strawberry, chrysanthemum,geranium, sunflower, tobacco, carrot and onion. You can use tissues obtained from seeds,such as the embryo, but you can use also tissues taken from adult plants, such as tissuesof roots, stems, apical buds, shoots, leaves, even single cells. Each plant and tissue hasits own needs. They are different from each other. You can try the influence of thevegetable hormones, special nutrients, etc.
This field is very broad and complex so, if you are interested in continuing with theseexperiments, you can buy special books and you should build a sterile box.
Plant Tissue Culture for the Gardener
Basic Principle in Plant Tissue Culture Technique
Plant Tissue Culture Kit Manual
Plant Micropropagation Using African Violet Leaves
Plant Tissue Culture (links)
Internet keywords: in vitro culture plant tissue micropropagation.

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Contrary to what people think, lungs do not have muscles of their own, but they are dilated or compressed by means of the movements of chest and diaphragm. The device of figure 19 shows how a diaphragm causes air to enter and leave the lungs. In the phase A, the balloons have to be as empty as possible. If you are a teacher, ask to your pupils what would happen if there was a hole in the bottle. Then make a hole, so everybody will see that, even if the diaphragm is lowered, the lungs will not fill with air. Yet it is easy to close the hole and restore the functioning of the lungs. To prove this, seal the hole of the bottle with some sticking tape and move the diaphragm again. This simple experiment shows how a hole in the chest could be fatal. Also how you could save a person by simply plugging the hole. If you have difficulties in finding the Y tube to build the model of the lungs, just use a tube. You will only have one lung, but the principle is the same and you know that in reality there are two.
Do-It-Yourself Lung Model

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