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The call theory
1) All living things are made of cells
2) Cells are the smallest unit of life
3) Cells come from preexisting cells
Types of cells
- Multicellular. Ex: Humans, dogs
- Unicellular. Ex: Bacteria, yeast, paramecium (looks like a shoe),
Chlamydomonas
Differentiation: A cluster of cells specified to do a specific function.
Exceptions where the cell is the smallest unit of life
- Giant algae
- Striated muscle fiber
- Fungal hyphae
- Red blood cell
,Characteristics of living organisms
1) Metabolism: all reactions in a cell guided by enzymes. (Anabolic + Catabolic
reactions).
2) Response: Living things can respond and interact with the environment.
3) Homeostasis: The maintenance of internal cell conditions (temperature and water).
4) Growth: Living things can grow or change shape and size.
5) Reproduction: Living things produce offspring either sexually or asexually.
6) Exertion: the removal of metabolic waste.
7) Nutrition: Feeding by photosynthesis or by the absorption of organic molecules
needed for growth.
Surface area to volume ratio
- It is the rate of material passing in and out.
- A small volume that has a big surface area has a fast rate.
- As the volume increases, the ratio decreases, therefore, the rate of the material
passing in and out of the call decreases.
- If the cell grows beyond a limit, materials won't be able to cross the membrane
efficiently. Thus, growing cells tend to divide and remain small in order to
maintain a high surface area-to-volume ratio.
- For example, the alveoli in the lungs have many folds so have a big surface area.
This is important for cell diffusion.
Emergent property: the whole is greater than the sum of the parts.
No chemical reactions happens without enzymes.
The only source of energy for living organisms is ATP.
,Cell differentiation and gene expression
- Specialized tissues can develop by cell differentiation in multicellular organisms.
- Different cells perform different functions.
- Cells are specialized by the expressed genes
- Certain genes become activated (switched on) and others are switched off.
Stem cells: are cells that are not fully differentiated but have the ability to divide and
differentiate into different types of cells
- Stem cells are necessary for embryonic development as all the cells in the adult
organism stem from the embryonic stem cells.
- There are three types of stem cells; embryonic, cord blood, and adult stem cells.
(Oxford Biology, 2014)
Pluripotent cells are not differentiated (aren’t specialized to do a specific function)
Embryonic stem cells are derived from the pluripotent cell. It can be used to transplant
organs.
Embryonic Stem cell features:
- Not differentiated so they can differentiate into any type of cell. (potency)
- High potential to divide.
SCID disease
- Genetic disorder
- Mutation
- Carried on the X chromosome (Female XX, male XY)
, - Most cases are due to a recessive mutation of a gene called ABCA4 which
causes a membrane protein used for transport in retina cells to malfunction. This
leads to a loss of vision when the photoreceptive cells die.
- The cure is embryonic stem cells. The new stem cells move to the retina where
they attach themselves and remain.
Leukemia
- It is a type of cancer that involves the production of a large number of white blood
cells.
- Adult stem cells are extracted from the bone marrow before chemotherapy and
then are returned to the body. They start to produce a normal amount of white
blood cells.
Magnification rules of conversion
1m=102 cm
1m=103 mm
1m= 106 µ
1m= 109 nm
QB questions of 1.1
Explain how cells are limited in size.
Why can’t nerve cells divide?
Nerve cells can't divide because they don't have a centriole. Therefore, they are unable
to perform mitosis and meiosis. Hence, these cells don’t divide.
What is the real size of the mitochondria in mm if the image measurement is 2 cm?
Magnification=10,000 X
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