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The
Gram staining allowed us to identify whether the bacteria were gram positive or
gram negative, what shape the bacterial cells were and how they were gathered on
the slide. Two of the samples (A & B) contained cocci bacteria, and one
sample (C) contained bacilli shaped bacteria. All of the samples contained
bacteria that were gathered in ‘irregular clusters’, rather than in chains or
pairs.

Bacteria
in samples A and B were stained blue/violet, which would suggest they were
gram-positive, as the blue crystal violet stain has been retained by the thick
peptidoglycan layer. The bacteria in sample C were stained pink, which would
suggest they were gram-negative, as the crystal violet stain would have been
washed out of the thin peptidoglycan layer and the red safarin counter-stain
taken up.

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The
Gram stain is mainly used to identify if there is a significant number of bacteria
in a sample. As well as Gram-negative and Gram-positive bacteria, there are
also Gram-variable bacteria, which can react to the stain differently within
the same sample. This could cause confusion as the same species of bacteria
could then look like two different species, and so therefore the Gram staining
technique cannot be used to identify a bacteria species.

 

Question
2

 

Bacterial cultures
usually have four growth phases: lag, log, stationary and death. The bacterial
growth phases can be presented in a bacterial growth curve.  The lag phase involves a period of no
bacterial replication (however the cells may grow in volume), as the cells are adapting
to the environment and synthesizing RNA and proteins, such as enzymes. The
second 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 the
graph by a straight line when converted to the natural log. In theory, this
exponential growth would continue, however in practice the bacterial cells
begin to die in the culture (Zwietering, Rombouts and Riet, 1992). This is
because of a limiting factor, such as toxic waste products from the cells beginning
to build up in the growth medium (unless removed), and the nutrients the cells
need to grow and divide becoming less numerous as they continue to be used up
by other dividing cells. In the stationary phase, the graph levels off, as the
number of cells dying equals the number of cells being produced through
division. This continues until the cells dying begin to outnumber the cells
being produced, which starts the death phase of the graph. The bacterial cells
continue to die in large numbers as the nutrients are extremely scarce and
there are large quantities of toxic waste materials in the culture (produced
from the bacteria) (Maier, 2000).

 

 

Question
3

 

Paramecium
is a genus of the phyla protozoa of the kingdom Protista, and contains
unicellular eukaryotic organisms. They are ciliated and live in freshwater
bodies, and can be divided into two groups based on shape (Wichterman, 2014). One
group is the Bursaria, which tend to be ‘slipper’ shaped, and the other is the Aurelia
group, which are an oblong shape. The organisms are heterotrophic, and the
cilia lining the outer membrane of the organisms to transport the organism’s food
source, bacteria, into the oral groove (and help to move the cell). Contractile
vacuoles 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 be
somatic or reproductive, and are interconnected by strands of cytoplasm (Ikushima
et al.,1968). Somatic cells have two flagella, which can move the whole colony
around when the movements are coordinated. Volvox colonies are also found in
freshwater (Powers, J.H., 1908), but are autotrophs, unlike Paramecium. As they
are algae, Volvox species contain chloroplasts that have chlorophyll a and b,
along with other accessory pigments (Burrows, 1991) and have ‘eyespots’, which
allow the cells to sense light direction and intensity, thus allowing the
colony to move towards light. Volvox species are primary producers, but
Paramecium, however, are heterotrophs, and so are consumers.

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