2.1c Prokaryotic & Eukaryotic Cells

28/08/2012 § Leave a comment

When scientists started studying the cell structure in detail back in the 1950s, they discovered the ultrastructure of the cell, or the fine detailed structure of the cell. Cells can be divided into two types based on their structure, and that there is the topic of our blog post today – the prokaryotic and eukaryotic cell.

First we have the prokaryotes or prokaryotic cells. They were the first organisms to ever evolve on this planet and to this day have the simplest cell structure amongst all organisms. Prokaryotes are small in size, unicellular and are everywhere, including the soil, our skin, water and intestines. Yes, our intestines. Note that bacteria are prokaryotes (single-celled organisms!) and yup, that means there are bacteria living in our intestines. The good part is most of those prokaryotes (usually the bacterium Escherichia coli or E. coli) are harmless. The bad news is not all of them are.

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2.1b Cell Theory: Differentiation

28/08/2012 § Leave a comment

I’d first like to point out that I found an editing error in the IB Biology Course Companion textbook (p. 16, section Multicellular organisms and cell differentiation, para. 3, line 3). It prides me to know this. That is all.

The next topic of discussion in this season of IB Biology is multicellular organisms and cell differentiation. To start off, cell differentiation is [quote] the development of cells in different ways to perform different functions [end quote], or the method in which cells alter themselves and branch out in order to accomplish different tasks for the body, which is how I understand it. Cells in a multicellular organism can do this by using the information programmed into the organism’s genome (or set of information in their DNA). Different cell types use different parts of the genes in its nucleus but omits the rest of the information. Note that when cells are using information from certain genes, those genes are being expressed. Furthermore, when genes are expressed, it’s like a switch goes off that instructs the cell to produce a particular protein or other product that the cell will need.

There are unicellular and multicellular organisms. An example of a unicellular organism is a toe of alga called Volvox aureus, which live together in spherical colonies. Though they live in colonies, the volvox aureus is still a unicellular organism because they are not fused to form one single mass of cells, like humans are. (Spoilers: humans are multicellular organisms, if our something-trillion number of cells are of any indication.)

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2.1a Cell Theory: Limitations on cell size

25/08/2012 § Leave a comment

A cell’s surface area-to-volume ratio

As mentioned in my previous blog, one of the six functions of life is Metabolism, which, in a cell, are chemical reactions that release energy for the cell to accomplish multiple tasks. The rate of the reactions that occur within the cell (also known as the metabolic rate of the cell) is proportional to the volume of the cell.

This makes complete sense because know that all substances that are used for chemical reactions must pass through the plasma membrane, as does all the waste that the cell produces. The plasma membrane’s surface area is a large factor in the rate at which these substances and waste move into and out of the cell.

Linking the two together, the surface area of the cell is also directly related to the volume of the cell. If the cell’s volume is too large and the surface area too small, then the metabolic rate of the cell will be overwhelming for the cell to handle. With a ratio that is too small and imbalanced, substances and waste will struggle to enter and leave the cell at safe rates. The same goes for the production and loss of heat. A ratio that is too small won’t allow the cell to release heat fast enough and the cell could overheat.

Biology and Graphs

In a nutshell, graphs, in biology, are used to explain and visually display the relationship between two variables. The x-axis is used to represent the independent variable and the y-axis represents the variable that is affected by the independent variable.

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2.1 Cell Theory

23/08/2012 § 2 Comments

We begin the year with the topic of cell theory, which is composed of three major points.

  • The cell is the smallest unit of life.
  •  All living things are made up of one or more cells.
  •  All cells come from pre-existing cells, which means new cells cannot be formed through non-living chemical substances.

Although there are different levels of order in life, everything begins with the cell. We can have an entire ecosystem or population filled with many kinds of species, then perhaps a certain individual of a particular species. In that individual, one will find that they are made of many systems that help regulate and control the body. These systems are made up of different organs, those organs are made of tissues, which are made of cell muscles that are made of tissue cells. Even if we start from a very large group, still the cell is the building block that starts it all.

Cells are also responsible for carrying out all the functions of life. As mentioned earlier, some living things are made up of just one cell, which means that that one cell is in charge of accomplishing the six functions of life:

  • Growth – always increasing in size
  • Homeostasis – maintaining balanced conditions inside the organism
  • Metabolism – chemical reactions to release energy
  • Nutrition – obtaining food to produce energy needed to grow
  • Reproduction – sexually or asexually producing offspring
  • Sensitivity – responding and reacting to the cell’s environment

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Test

23/08/2012 § Leave a comment

Testing, testing.

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