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Biology: protists: diatoms

The tutor mentions a few points about diatoms.

In my Feb 4 post I introduced protists, which constitute a kingdom of eukaryotic, mainly single-celled organisms. Protists are divided into plantlike and animal-like ones.

Diatoms, from phylum Chrysophyta, are among the golden brown algae. They are plantlike protists, perhaps the most numerous of them. In the oceans, their abundance makes them a major food source at the base of the ecosystem. Furthermore, they are prominent producers of oxygen on Earth.

Diatoms have a two-valve structure, rather like the base and lid of a box. They are well known for having glass (silica) in their cell walls, which show striking patterns under a microscope.

Diatoms have been even more abundant in the past; today, those fossils constitute diatomaceous earth, which is mined for applications such as soundproofing, filtration, and scouring powders.

HTH:)

Source:

Mader, Sylvia S. Inquiry into Life, 9th ed. Toronto: McGraw-Hill, 2000.

Ritter, Bob et al. Biology. Scarborough: Nelson Canada, 1996.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

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Biology: protists (Kingdom Protista) vs bacteria (Kingdom Monera)

The tutor makes some comparisons between protists and bacteria.

Members of Kingdom Protista are generally single-celled organisms that live in water. They form a significant part of ocean plankton. Bacteria are typically single-celled as well, and are found virtually everywhere that supports life.

Unlike a Moneran (bacterium), a protist has a nucleus and organelles each separated from the cytoplasm by its own membrane. This distinction means that Monerans are prokaryotes, while Protists are eukaryotes.

While Protists may have appeared around 1.5 billion years ago, Monerans are much older, having possibly emerged 3.5 billion years ago.

I’ll be talking more about Monerans and Protists in coming posts:)

Source:

Mader, Sylvia. Inquiry into Life, 9th ed. Toronto: McGraw-Hill, 2000.

Ritter, Bob et al. Biology, BC ed. Scarborough: Nelson, 1996.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

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Biology: winter survival

The tutor shares a fact that surprises him.

Winter here is fairly mild; I think the mean daily temp in Jan might be around 5 deg Celsius, with the mean nightly low being around -1 deg Celsius. That being said, this place is a rarity in Canada; even places further south than here, but east of the Rockies, are typically much colder. For places both east of the Rockies, and north of here as well, winter might as well be spent in a deep-freeze. How do the animals living there cope with it?

Recent reading informs me that some amphibians – e.g., frogs – actually freeze solid during winter as a survival mechanism. The wood frog and chorus frog are two examples given.

I’ve spent time around Prince George and know that, in May, the temp can reach 15 deg Celsius during the day but still plunge to -5 deg Celsius at night. In spite of the hard nightly freeze, flies abound in forest clearings. They must, I’ve always suspected, freeze at night, yet thaw the next day and live on. This Biology text confirms my suspicion. However, I wouldn’t have known for sure that frogs could do so as well.

To me, the point is surprising, yet makes a lot of sense. After all: how could those frogs avoid freezing solid through weeks in Jan or Feb, during which the temperature may not climb above -5 deg C, and certainly plunges below -20 deg C most nights?

Source:

Ritter, Bob et al. Nelson Biology. Scarborough: Nelson Canada, 1996.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

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Cell Biology: Containment: vesicles, vacuoles, and lysosomes

Tutoring biology, the cell is fundamental.  Heading towards another weekend Biology 12 workshop, the biology tutor recalls Bruce Willis’s advice in Last Boy Scout: “Be prepared.”

A cell, like anyone, needs storage.  More than that, it needs storage for different purposes.  While you keep your food in the pantry, you store your clothes in the bedroom closet.  The cell faces similar storage challenges.

The three main types of storage vessels a cell uses are vesicles, vacuoles, and lysosomes.  Each has its own particular use and features:

Vesicles are often used for transport.   For example, they are used to store molecules or food arriving from outside the cell.  Vesicles are also used to hold partially completed molecules the cell is making as they are moved to different “work sites”. Then, when a molecule is to be secreted from the cell, it is shipped to the outer membrane in a vesicle, then released outside.

A vacuole is larger than a vesicle.  Vacuoles are meant for storage until use – or even permanent storage.  Water, sugars, and even pigments are stored in vacuoles.  In the case of pigment, it will remain in the vacuole for the life of the cell, giving the cell color. A water vacuole holds a large amount of water in order to “fill out” the cell, giving it the proper shape.  Plants derive their rigid shape partially from the water in their cells’ vacuoles.  Vacuoles can also hold toxic by-products until the cell gets around to destroying them.  Although both plant and animal cells contain vacuoles, plants use them more.

A lysosome is a special type of vesicle that stores digestive enzymes (see my previous post). A vesicle containing food will be fused with a lysosome for digestion to take place.

A cell can be a busy place. Any such place needs ample storage. Fortunately for the cell, it can make new vesicles, vacuoles, or lysosomes as needed:)

Source: Inquiry into Life, 11th Edition. Mader, Sylvia. New York: McGraw-Hill, 2006.

Jack or Oracle Tutoring by Jack and Diane, Campbell River, BC.

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Biology: Alternation of Generations

I’ve always found this topic a bit tricky.  As a biology tutor, it’s time to give my own explanation.

Alternation of generations refers to the idea that the life cycle of a moss, for instance, comprises two distinct phases:  one in which the cells are haploid (n), and the other in which they are diploid (2n).  Haploid means they have half the number of chromosomes; diploid means they have the full possible number.

Although all plants have it, moss provides a good example of alternation of generations.  People may not notice as they walk over it, but moss looks different depending on the time of its cycle.  Most often you are probably seeing the gametophyte (n) generation – likely the green, soft carpet you imagine in forests or bogs.  However, if the carpet has brown stalks rising from it, you might well be walking over the sporophyte (2n).

Let’s enter the cycle at the spore stage.  A spore is a haploid (n) cell, often borne on the wind, which can land and grow into a new individual – specifically, a new gametophyte.  If the spore is male, it grows into a sperm-producing gametophyte; if female, an egg-producing one.  In wet conditions, sperm swim from the male stalks to the female ones.  (This is why moss needs dampness at least some of the time.)  Like you’d expect, the union of sperm with egg produces a zygote.  While the sperm and egg were each n, the zygote is 2n, since it receives n chromosomes from the sperm and n from the egg.

The zygote starts to divide, eventually becoming a sporophyte found on top of what was the female gametophyte (which is where the sperm joined the egg).  Cells in the mature sporophyte undergo meiosis, a special kind of division in which each cell produced receives only one chromosome from each set of two available.  Whether it receives the chromosome the sperm brought, or the one from the egg, is determined by chance:  hence the variability of sexual reproduction.  Either way, these new cells are haploid (n):  in fact, they will mature into spores.  The spores are released when it’s dry and windy, and the life cycle begins anew.

I’ll be mentioning more about this topic in future posts;  this was just a toe in the water:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.