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SCI1183 Origins

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SCI1183 Origins & Evolution of Life
Short answer examination questions
S2, 2015
1. Describe the concepts of sterility, contamination and spontaneous generation in a biological
context.
Sterility is the lack of a physiological ability of a living thing to effect reproduction sexually. Sterility has a
wide range of causes, which may be an inherited trait as seen in the mule, or it could be acquired from
the environment through physical injury, disease or also by exposure to different forms of radiation. Its
synonymous to barrenness, fruitlessness or infertile conditions.
Contamination is the accidental introduction of "foreign" material known as the contaminant .For
instance contaminants can seriously distort all the results of experiments where the samples used are
small. In case the contaminant is a living organism it can often multiply and take over the experiment,
this often occurs in cultures and eventually make them useless.
Spontaneous generation is the proposed processes in which different types of life might
repeatedly emerge from specific sources apart from the seeds, parents or eggs .It also includes
the theoretical principles that were presented in support of any such phenomena. spontaneous
generation puts emphasis on the idea that life comes from non-life and that no causal agent like
parent ,egg or seed is needed to come up with life.. A good example of abiogenesis is the
supposed seasonal generation of mice and other animals from the mud of the Nile. spontaneous
generation can be divided into two processes namely; abiogenesis where life emerges from non
living matter in a given time scale and heterogenesis in which one form of life has been
supposed to arise in different form and from a given time scale such as tapeworms from the
bodies of their hosts.
[8]
2. Describe resolving power, contrast and illumination in microscopy.
Resolving power is the ability of a microscope lens to show two adjacent objects as discrete entities. Its
the capability of a microscope distinguish two images that are close together as being separate.
Contrast is the difference in light intensity between the image and the adjacent background relative to the
overall background intensity.
Illumination is the provision of light or lighting up of the sample that is mounted on the microscope to
enable clear observation.
3. Describe osmosis and its effects in animal and plant cells.
Osmosis is the spontaneous net movement of solvent molecules through a semi permeable membrane
into a region of higher solute concentration in the direction that tends to equalize the solute
concentrations on the two sides. It may also be used to describe a physical process in which any solvent

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moves across a membrane only permeable to the solvent but not the solute that separates two
solutions of different concentrations.
When an animal cell or a plant cell is placed in a medium, which is a water solution , the
following occurrences shall be observed ;
If the of the cell cytoplasm concentration is lower than that of the medium ,a condition called
hypotonic , then osmosis will result in the cell obtaining and gaining water. This will make the
cell to swell.
If cell cytoplasm concentration is the same as that in the surrounding medium a, condition
called isotonic there will exist a dynamic equilibrium between the number of molecules of water
entering and leaving the cell and so the cell retains its original size.
If the cell cytoplasm concentration is higher than that of the medium entering the
cell[hypertonic]the number of the water molecules diffusing out will be more than that diffusing
inside and the cell shrinks and shrivel due to osmosis.
When the plant cell is placed in a hypotonic solution , it takes up water by osmosis and starts to
swell, but the cell wall prevents it from bursting. The plant cell becomes turgid.[swollen and
hardWhen a plant cell is placed in a hypertonic solution , the water from inside the cell
cytoplasm diffuses out and the plant cell becomes flaccid due to plasmolysis.When a plant cell is
placed in an isotonic solution incipient plamolysis occurs.
Animal cells do not have cell walls. In hypotonic solutions, animal cells swell up and lyse as
they cannot become turgid because there is no cell wall to prevent the cell from lysis.In
hypertonic solutions, water diffuses out of the cell due to osmosis and the cell shrinks. The animal cell
has always to be surrounded by an isotonic solution so as to maintain its original size
4. Describe the consequences of size and shape on diffusion rates and the implications on body
size and shape.
The source of energy for the movement of particles in diffusion is the heat in the environment. At a
given temperature, a smaller particle or molecule moves faster than a larger one. Hence the rate of
diffusion is inversely proportional to the size of the particle. There for a smaller particle will diffuse
faster than a larger one. The distance to be travelled by the diffusing component also affects diffusion.
The longer the distance the slower the rate of diffusion
Larger organisms such as mammals have a relatively small surface area compared to their
volume so they need special systems such as the lungs in order to get enough oxygen.By
increasing the surface area the rate of diffusion will go up,this is by reducing the body size

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SCI1183 Origins & Evolution of Life Short answer examination questions S2, 2015 1. Describe the concepts of sterility, contamination and spontaneous generation in a biological context. Sterility is the lack of a physiological ability of a living thing to effect reproduction sexually. Sterility has a wide range of causes, which may be an inherited trait as seen in the mule, or it could be acquired from the environment through physical injury, disease or also by exposure to different forms of radiation. Its synonymous to barrenness, fruitlessness or infertile conditions. Contamination is the accidental introduction of "foreign" material known as the contaminant .For instance contaminants can seriously distort all the results of experiments where the samples used are small. In case the contaminant is a living organism it can often multiply and take over the experiment, this often occurs in cultures and eventually make them useless. Spontaneous generation is the proposed processes in which different types of life might repeatedly emerge from specific sources apart from the seeds, parents or eggs .It also includes the theoretical principles that were presented in support of any such phenomena. spontaneous generation puts emphasis on the idea that life comes from non-life and that no causal agent like parent ,egg or seed is needed to come up with life.. A good example of abiogenesis is the supposed seasonal generation of mice and other animals from the mud of the Nile. spontaneous ...
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