In general, plants require nitrogen in the form of soil nitrates which their roots can absorb.
Cyanobacteria are the only organisms able to perform both oxygenic (oxygen-generating) photosynthesis and
They achieve both functions by a division of labour - vegetative cells carry-out photosynthesis,
whilst specialised cells called heterocysts carry out nitrogen-fixation.
Photosynthesis is a chemical process through which plants, some bacteria and algae, produce glucose and oxygen from carbon dioxide and water, using only light as a source of energy.
This process is extremely important for life on earth as it provides the oxygen that all other life depends on.
Just like humans and other living things, plants also need this food for many things. Let's see a few:
Glucose resulting from photosynthesis is used during respiration to release energy that the plant needs for other life processes.
The plant cells also convert some of the glucose into starch for storage. This can then be used when the plant needs them. This is why dead plants are used as biomass, because they have stored chemical energy in them)
Glucose is also needed to make other chemicals such as proteins, fats and plant sugars that are all needed for the plant to carry out essential growth and other life processes.
All living organisms are composed of cells. Multicellular organisms (example: humans) are composed of many cells while unicellular organisms (example: bacteria) are composed of only one cell. Cells are the basic unit of structure in all organisms.
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.
Internet keywords: spontaneous generation.
Ponds are among the richest and the most interesting natural environments to observe. Tomake a pond it is sufficient to have a garden or, a meadow or a wood near your home. It isnot necessary to be large, a square meter (9 square feet) of surface is sufficient, buttwo(18 sq. ft.) are better. Find a shady position in the garden. Dig a hole of about 2square meters, 50 cm(2 feet) deep. At least one side, the border has to gently slope downto allow to little animals to enter and leave, for hedgehogs and opossums to drink and tobirds to bath without being too deep. Put some sand in the bottom. Leave the grass on theside. Bare roots are okay. Waterproof the hole with a tarpaulin of white PVC. Why white?Because you can see aquatic animals better when they come near the shore. Cover the borderof the tarpaulin with the grass sod. Allow the tarpaulin to extend for at least 40 cm (16inches) beyond the sloping shore. In this position you can keep the water in such a way tocreate the typical conditions of a marsh. Fill up the pond with tap water and shovel somesand or soil in the bottom: they will benefit the aquatic plants. Go to a natural pond ormarsh and collect some aquatic plants. If it is possible, carry some gallons of water fromthe pond and pour them into your puddle, which will be enriched with microorganisms,algae, and animals, which live in ponds. In few days, your little pond will become greenwith algae and very rich of protozoa. Rapidly dragonflies will come to lay eggs, boatflies, coleoptera and aquatic spiders also will come. In the spring, frogs and newtswill come to lay eggs. The observation of the life in a pond is fascinating. You canremain for hours watching the organisms, which live in this ecosystem. Buy books torecognize the organisms that live in the ponds. See bibliography (5, 6). These texts willalso give you also useful information on the habits of these plants and animals. For anexercise, note your observations in a book, glue pictures, and sketch drawings. Everyyear, during the fall, you should clear out the pond. Shovel out the stinking mud, washthe tarpaulin, or changed it if it leaks, put some tap water, winter rain will supply theremaining part. In spite of what shopkeepers will tell you, your pond does not need pumpsto circulate water, nor aerators, nor falls, nor fountains, nor anything else. The pond isbetter to be as natural as possible. Little ponds of private gardens are very important toamphibians. Avoid introducing fish. They will eat the eggs of the amphibians and thetadpoles. Moreover, the newts will keep the pond free from the mosquito larvae. When thereare tadpoles, your pond will be visited by water snakes, with difficulty you will noticeof them!... and --- don't be frightened: they are harmless!
Multiple Microhabitat Pond Microcosm (good cross section of a pond)
A Large Pond
Building a Pond
"Pond" Cultures of Microscopic Invertebrates
Internet keywords: pond building homemade.
I will look at the various factors affecting the reaction and select one variable to change, while the others keep constant in order to carry out a detailed investigation....
I will look at the various factors affecting the reaction and select one variable to change, while the others keep constant in order to carry out a deta...
There are other
mechanisms of protecting nitrogenase from oxygen in cyanobacteria that are poorly understood.
Many strains are facultatively chemotrophic in the dark, but these maintain constituitve photosynthetic apparatus
and can photosynthesise immediately when light is introduced.