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

It is important that scientists include evidence for their ideas. Most of this evidence can be data gathered from past experiments. For example, the idea that nothing smaller than a cell can survive independently can be supported by the data from experiments in which cells are split open, and the individual subunits of the cell are left separated from each other. The data shows that the subunits won’t survive, and this supports the previous idea.

A large part of studying cells is understanding their size because cells are small, they’re so small we can’t see them with a typical magnifying glass and we have to invest some money for the science department to purchase a few advanced microscopes for the biology students to use to look at the cells. Looking at cells through microscopes means we also have to understand magnification, which is the size of the image we can see divided by the actual size of the specimen. The units of measurement that we’ll definitely need to know for this unit (and most likely for the rest of our biology career) are nanometers (nm) and micrometers (µm). A scale we can (and should) remember is the following:

  • 1 nm = molecules
  • 10 nm = cell membrane thickness
  • 100 nm = virus
  • 1 µm = bacteria
  • 10 µm = organelles
  • 100 µm = eukaryotic cells

A cell’s innards are barred inside by its plasma membrane, which is like a wall that separates the cell from outside. However, the cell produces components that leave the cell through the plasma membrane and form structures outside – this is why we aren’t a puddle of goo, fluids and flesh all the time. The extracellular components support a living organism’s tissues and holds all its parts together. (Components inside the plasma membrane are intracellular.)

An example of the extracellular matrix – the ECM – is the plant cell wall. Although it’s the cell wall of the plant, the cell constantly adds cellulose to the thickness of the wall so it can maintain its shape and support the growing cell. The wall prevents water from expanding the cell’s contents and bloating the plant. This maintains the rigidness of the plant and is what makes trees and stems stand so upright.

All living things are proof that life itself is an emergent property, which means to say that life can only exist as a product of independent parts working together.



1. a) The magnification of the string of Thiomargarita cells can only be found if we know the actual size of the line of Thiomargarita cells. As of now, we know that m (magnification) simply equals 0.3mm ÷ x (the missing value of the actual cell size).

b) The width of the string cells, based on what information we do have is still 0.3mm (x whatever magnitude).

2. a) magnitude = 87.5, b) the 5µm scale bar needs to be 0.4375mm long, c) width of mitochondrion = 2.29µm

3. a) 40mm, b) 2µm

4. a) the length of the ostrich’s egg is three times the width of the hen’s egg, b) I estimate about 0.001 magnification. It is smaller than it really is.

§ 2 Responses to 2.1 Cell Theory

  • cafergy says:

    Grade 5 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them in a variety of situations.

    1 a Magnfication = size of image / actual size of the specimen
    Size of the image (scale bar) = 20 mm
    Actual size = 0.2 mm
    Magnification 20 / 0.2 = 100 ×

    b Width of thiomargarita in the image (image size) = 26 mm
    magnification = 100 ×
    actual size = 26/100 = 0.26 mm

    2 a Magnification = length mitochondrion in the image
    (63 mm) / actual size of the specimen (8 µm / 0.008 mm)
    = 63 / 0.008 = × 7875

    b Scale bar 5 µm × 7875 = 39 375 µm (approx. 40 mm)

    c Width on the image 23 mm / magnification 7875
    = 0.0029 mm (2.9 µm)

    3 a 20 µm × 2000 (magnification) = 40, 000 µm
    (or 40 mm scale bar)

    b Actual size of specimen 34 mm/2000 = 0.017 mm

    4 a Hens egg is 16 mm in diagram. Ostrich egg is
    46 mm long in diagram. Real hen egg is about
    50 mm wide.
    Ostrich egg (50 × 46)/16 5 144 mm approx.

    b Magnification = size image / actual size of the
    Hens egg : Magnification 16 mm /50 mm = × 0.32

  • onesmo leonard says:

    do mean that cell theory limitation is only one?
    And how surface area to volume ratio related to cell theory as one of their limitation?

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