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UNIT 1
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All living things are composed of cells

2
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All cells come from pre-existing cells



Caveats to the Cell Theory:
• certain types of cells/tissues do not conform to a standard notion of what constitutes a cell:

• Started Muscle Fibres:

◦ muscle cells fuse to form fibers that may be very long (>300 mm)

◦ consequently, they have multiple nuclei despite being surrounded by a single, continuous
plasma membrane

◦ challenges the idea that cells always function as autonomous units

• Aseptate Fungal Hyphae:
◦ fungi may have many filamentous structures called hyphae, which are separated into cells
by internal walls


called septa

◦ some fungi are not partitioned by septa and have have a continuous cytoplasm along the
length of the


hyphae

◦ challenges the idea that living structures are composed of discrete cells

• Giant Algae
◦ certain species of a unicellular algae may grow to very large sizes (e
...
Acetabulalria may
exceed 7 cm in


length)

◦ challenges the idea that larger organisms are always made of many microscopic cells

Functions of Life
Unicellular organisms (e
...
Euglena, amoeba) are the smallest organisms capable of independent
life



All living things carry out 7 basic functions integral to survival:

• Metabolism: living things undertake essential chemical reactions

• Reproduction: living things produce offspring, either sexually or asexually

• Sensitivity: living things are responsive to internal and external stimuli

• Homeostasis: living things maintain a stable internal environment

• Excretion: living things exhibit the removal of waste products

• Nutrition: living things exchange materials and gases with the environment

• Growth: living things can move and change shape or size




[MRSHANG]



As unicellular organisms are composed of a single cell, this cell must be able to carry out all the
life functions



How unicellular organisms fulfill these basic functions may differ according to structure and
habitat




1
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g
...
g
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Scendesmus (autotroph)
• exchange gases and other essential materials via diffusion (nutrition/excretion)

• chlorophyll pigments allow organic molecules to be produced via photosynthesis (metabolism)

• daughter cells form as non-motile nautospores via the internal asexual division of the parent
cell (reproduction)

• may exist as unicells or form colonies for protection (responsiveness)
SA:Vol Ratio
Cells need to produce chemical energy (via metabolism) to survive and this requires the
exchange of materials with the environment

• the rate of metabolism of a cell is a function of its mass/volume (larger cells need more energy
to sustain essential functions)

• the rate of material exchange is a function of its surface area (large membrane surface equates
to more material movement)



As a cell grows, volume (units3) increases faster than surface area (units 2) leading to a
decreased SA:Vol ratio

• if metabolic rate exceeds the rate of change

• growing cells tend to divide and remain small in order to maintain a high SA:Vol ratio suitable
for survival



Increasing SA:Vol Ratio

Cells and tissues are specialized for gas or material exchanges will increase their surface area to
optimize material transfer

• intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the surface
area of the inner lining

• alveoli within the lungs have membranous extensions called microvilli, which function to
increase the total membrane surface
Magnification
Calculation of Magnification:
To calculate the linear magnification of a drawing or image, the following equation should be
used:

• Magnification = Image size (with ruler) / Actual Size (according to the scale bar)
Light microscopes use visible light and a combination of lenses to magnify images of mounted
specimens

• living specimens can be view in their natural color but stains can be applied to pick out
specific structures




When drawing microscopic structures, the following should be followed:

• a title should be included to identify the specimen (e
...
name of organism, tissue or cell)

• magnification or scale should be included to indicate relative size

• identifiable structures should be clearly labelled (drawings should only reflect what is seen, not
idealized versions)





Emergent Properties
Emergent properties only arise when the interaction of individual components produce new
functions



Multicellular organisms are capable of completing functions that unicellular organisms could not
undertake - this is due to the collective actions of individual cells combining to create new
synergistic effects



In multicellular organisms:

• Cells can be grouped together to form tissues

• Organs are then formed from the function grouping of multiple tissues

• Organs that interact can form organ systems capable of carrying out specific body functions

• organ systems collectively carry out the life functions of the complete organism





Cell Differentiation
Differentiation: the process during development whereby newly formed cells become more
specialized and district from another as they mature



All cells of an organism share an identical genome (each cell contains the entire set of genetic
instructions for that organism)



The activation of different instructions (genes) within a given cell by chemical signals will cause it
to differentiate



Gene Packaging
Within the nucleus of a eukaryotic cell, DNA is packaged with proteins to form chromatin

• active genes: usually packaged in an expanded form called euchromatin

• inactive genes: packaged in a more condensed form called heterochromatin



Differentiated cells will have different regions of DNA packaged as euchromatin and
heterochromatin according to their specific function





Stem Cells
When cell differentiates and becomes specialized it cannot become an alternative cell type:

1
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Potency: there have the capacity to differentiate into specialized cell types



Use of Stem Cells:
Stem cells are necessary for embryonic development as they are undifferentiated cell source
from which all other cell types may be derived




Cell types that are not capable of self-renewal are not stem cells



As tissues are not able to regenerate or replace, them cells have become a viable therapeutic
option when those tissues become damaged



Stem Cell Therapy
Stem cells can be used to replaced damaged or diseased cells with healthy, function ones
...
Stargardt's Disease

• inherited form of juvenile macular degeneration that causes progressive vision loss to the point
of blindness

• caused by gene mutation that impairs energy transport in retinal photoreceptor cells which
causes them to degenerate

• treated by replacing dead cell in the retina with functioning ones derived from stem cells



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Other Therapeutic Examples

• Leukemia: bone marrow transplants for cancer patients who are immunocompromised as a
result of chemotherapy

• Diabetes: replace non-functioning islet cells with those capable of producing insulin in type I
diabetes



Stem cells can be derived from one of the three sources:

• Embryos

• Umbilical cord blood or placenta of a newborn baby

• Certain adult tissues like bone marrow

•

Ethical considerations associated with therapeutic use of stem cells will depend on the source:

• using multipoint adult tissues may be effective for certain conditions, but is limited in its scope
of application

• Stem cells derived from umbilical cord blood need to be stored and preserved at cost, raising
issues of availability and access

• the greatest yield of pluripotent stem cells come from embryos but requires the destruction of

a potential living organism




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