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Topic 1: Cell Theory
Topic 2: M...
Topic 1 - Cell Biology
Understandings: 1.1
1. Explain cell theory.
- The cell theory builds on three premises.
1. All living organisms are composed of cells.
2. A cell is the smallest living unit.
3. Cells come from pre-existing cells by cell division.
Thus everything alive we see today may be rooted back into one single cell.
Then there are some characteristics a cell always has (since we need to
define what a cell is we also need to know their characteristics). They have a
membrane, a genetic blueprint (DNA), a chemical metabolism and some kind of
energy processor.
2. Explain unicellular organisms.
● Uni means one and cellular means a small unit so a unicellular organism
is one cell that can carry out all the functions of life all alone.
● The functions of life every organism needs to execute are: Movement,
Reproduction, Sensibility, Growth, Respiration, Excretion and nutrition
(MRS GREN).
3. Explain the importance of surface area to volume ratio.
➢ The ratio between SA:V grows significantly as the measurement
increases in a 3D object.
➢ If it grows too much, its rate of metabolism will expand faster than the
amount of molecules going through the membrane.
➢ Volume corresponds to metabolism, and surface area the absorption but
also the secretion through the membrane.
➢ So the cell will be overheated and should undergo cell division when the
cell is too big. The cell cannot be too small though because the
organelles have to fit.
4. Explain multicellular organisms and explain emergent property.
● Humans are multicellular organisms because we are made up of more
than one cell.
● A multicellular organism is bounded with an external membrane like the
skin to make “one organism”.
● An important concept is the emergent property. “The whole is greater
than the sum of the parts”.
○ SO individual cells may be important, but it is the interactions
between them that make the organism.
5. Explain specialized tissues that have developed by cell differentiation.
● Cells become specialized by expressing different genes to become more
efficient of what they do.
● Erythrocytes (RBCs) do not have a nucleus to fit more hemoglobin.
6. Explain that differentiation involves the expression of some genes and not
others in a cell’s genome.
● As we said above, specialization requires gene expression.
● All cells in our body have the same genetic sequence because they
fundamentally came from one zygote.
○ But it is what is getting expressed that determines the role of the
cell.
7. Explain stem cells.
● Stem cells are cells that are not fully differentiated.
● Distinguish between embryonic stem cell and adult/somatic stem cell.
● Simply said, embryonic (baby) stem cells have a broader possibility of
different cells than somatic (adult) stem cells.
● Understanding stem cells has the potential to solve many problems such
as food (differentiating into muscles for meat) and spinal cord recovery
and other injuries.
1. Be able to question the cell theory using atypical examples, including
striated muscle, giant algae and aseptate fungal hyphae.
● Striated muscles have more than one nucleus, has long fibres (shows
cells don't always function autonomously)
● Aseptate hyphae also has more than one nucleus, divided by septa,
● Giant algae are up to 100mm but are unicellular, (shows cells aren't
always made up of microscopic cells)
All seems to defy the characteristics of a cell.
2. Explain the functions of life in Paramecium and one named photosynthetic
unicellular organism.
3. Explain the use of stem cells to treat Stargardt’s disease and one other
named condition.
● Stem cells have a wide register of potentially curing diseases.
● Stargardt’s disease is a genetic disorder from a recessive gene- This
impairs the active transport of cells on the retina
○ so basically, the eye cannot receive the light properly. It may
ultimately lead to blindness.
○ Well, we use embryonic stem cells to become cells on the retina! It
seems like the results were promising with no side effects).
- Leukemia is a cancer of white blood cells
- Well, the source is in the bone marrow, so one would extract stem
cells, kill the stem cells in bone marrow and insert the healthy
ones back in. It works!
4. Discuss the ethics of the therapeutic use of stem cells from specially
created embryos, from the umbilical cord blood of a new-born baby and from
an adult’s own tissues.
● When it comes to stem cells, ethical issues are inevitable.
● Why?
○ Well, stem cells are found in young organisms and extremely
fragile. So, the higher risk we have of killing it - its more plastic
○ Cord blood stem cells (from umbilical cord) are less fragile, easily
obtained but are not as plastic as embryonic stem cells.
○ Adult/Somatic stem cells are not fragile but they are difficult to
obtain and not so plastic. But hey, it does not kill the adult.
5. Be able to use a light microscope to investigate the structure of cells and
tissues, with drawing of cells. Be able to calculate the magnification of
drawings and the actual size of structures and ultrastructures shown in
drawings or micrographs.
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