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TheGram staining allowed us to identify whether the bacteria were gram positive orgram negative, what shape the bacterial cells were and how they were gathered onthe slide. Two of the samples (A & B) contained cocci bacteria, and onesample (C) contained bacilli shaped bacteria. All of the samples containedbacteria that were gathered in ‘irregular clusters’, rather than in chains orpairs.Bacteriain samples A and B were stained blue/violet, which would suggest they weregram-positive, as the blue crystal violet stain has been retained by the thickpeptidoglycan layer.

The bacteria in sample C were stained pink, which wouldsuggest they were gram-negative, as the crystal violet stain would have beenwashed out of the thin peptidoglycan layer and the red safarin counter-staintaken up.TheGram stain is mainly used to identify if there is a significant number of bacteriain a sample. As well as Gram-negative and Gram-positive bacteria, there arealso Gram-variable bacteria, which can react to the stain differently withinthe same sample. This could cause confusion as the same species of bacteriacould then look like two different species, and so therefore the Gram stainingtechnique cannot be used to identify a bacteria species.  Question2 Bacterial culturesusually have four growth phases: lag, log, stationary and death. The bacterialgrowth phases can be presented in a bacterial growth curve.

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 The lag phase involves a period of nobacterial replication (however the cells may grow in volume), as the cells are adaptingto the environment and synthesizing RNA and proteins, such as enzymes. Thesecond phase is the log, or exponential phase, where the cells begin to divide.The bacterial cell number doubles per time period, which is represented in thegraph by a straight line when converted to the natural log. In theory, thisexponential growth would continue, however in practice the bacterial cellsbegin to die in the culture (Zwietering, Rombouts and Riet, 1992). This isbecause of a limiting factor, such as toxic waste products from the cells beginningto build up in the growth medium (unless removed), and the nutrients the cellsneed to grow and divide becoming less numerous as they continue to be used upby other dividing cells.

In the stationary phase, the graph levels off, as thenumber of cells dying equals the number of cells being produced throughdivision. This continues until the cells dying begin to outnumber the cellsbeing produced, which starts the death phase of the graph. The bacterial cellscontinue to die in large numbers as the nutrients are extremely scarce andthere are large quantities of toxic waste materials in the culture (producedfrom the bacteria) (Maier, 2000).

  Question3 Parameciumis a genus of the phyla protozoa of the kingdom Protista, and containsunicellular eukaryotic organisms. They are ciliated and live in freshwaterbodies, and can be divided into two groups based on shape (Wichterman, 2014). Onegroup is the Bursaria, which tend to be ‘slipper’ shaped, and the other is the Aureliagroup, which are an oblong shape.

The organisms are heterotrophic, and thecilia lining the outer membrane of the organisms to transport the organism’s foodsource, bacteria, into the oral groove (and help to move the cell). Contractilevacuoles release water taken up by the cell so cell lysis does not accidently occur(New World Encyclopedia, 2017). Volvox is the genus of species of green algae.Colonies of Volvox form circular groups of spherical cells, which can either besomatic or reproductive, and are interconnected by strands of cytoplasm (Ikushimaet al.,1968). Somatic cells have two flagella, which can move the whole colonyaround when the movements are coordinated.

Volvox colonies are also found infreshwater (Powers, J.H., 1908), but are autotrophs, unlike Paramecium. As theyare algae, Volvox species contain chloroplasts that have chlorophyll a and b,along with other accessory pigments (Burrows, 1991) and have ‘eyespots’, whichallow the cells to sense light direction and intensity, thus allowing thecolony to move towards light. Volvox species are primary producers, butParamecium, however, are heterotrophs, and so are consumers.

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