.Write two differences observed between tomato skin and human skin, when seen under a microscope.
Answers
Explanation:
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The substance in a tomato that causes this change from green to red is the gas ethylene.
Ethylene ensures that the vacuoles in the cell produce red colouring agents causing
chromoplasts to arise. The chromoplast used to be a chloroplast. (Inside the chloroplasts of
plants photosynthesis takes place.) As the tomato is ripening the chloroplast receives
signals from its environment (by signalling molecules), these signals urge the chloroplast
to change into a chromoplast. Furthermore, the build-up of red colouring agents in the
vacuole is also responsible for the nice red colour of the tomato, which is also dependent
on ethylene. Even tomatoes lying in the dark can turn red, which means that light/UV is
not essential to this process. Light and warmth do have an influence on the production of
ethylene.
Next to the fact that due to this mechanism we know when the tomato is ripe and tasty
there is also an advantage for the plant. That has to do with the spreading of the seeds of
the plant. When the tomato turns red it stands out more in its green environment.
Birds/animals and people will therefore see the tomato more quickly, eat it and excrete the
seeds elsewhere. These seeds can then germinate and grow into new tomato plants.
Human cells in the skin have a very different construction. Humans have pigment cells in
their skin and these pigment cells are very different from chloroplasts, which makes it
impossible to compare them. The human skin bronzes through pigment produced by
melanocytes. Melanocytes are located in the epidermis and they produce melatonin under
the influence of UV light. The mechanisms and the underlying chemical reactions that
cause this are completely different from the ones taking place in tomato cells.
Under a low power microscope, the cell membrane is observed as a thin line, while the cytoplasm is completely stained. The cell organelles are seen as tiny dots throughout the cytoplasm, whereas the nucleus is seen as a thick drop.
Tomato cells are floating in the juice and hence are not connected to each other. The thick black circles are air bubbles that got trapped between slide and cover slip. I was not able to get rid of them after couple of tries.