Download TOPIC 2 – CELL THEORY 2.1.1 Outline the cell - McLain

TOPIC 2 – CELL THEORY
2.1.1 Outline the cell theory.
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Living organisms are composed of cells
Cells are the smallest unit of life
Cells come from pre-existing cells
Cells contain genetic material
Cells are the site of metabolism
2.1.2 Discuss the evidence for the cell theory.
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When scientists first devised microscopes they were able to look at tissues and
organisms up close. These samples showed that tissues were made up of little
chambers. Hooke the first to coin the term “cells” while looking at sample of cork
under his homemade compound microscope. Leeuwenhoek made an even more
powerful microscope which allowed him to see “animicules” such as protozoa and
bacteria.
Since the discovery of the electron microscopes scientist have been able to see
cells and their organelles even more clearly.
Scientists have confirmed through experimentation that the smallest component
able to live freely in a lab setting is a cell. Viruses, which usually are considered
nonliving can’t reproduce or metabolize without a host cell.
Louis Pasteur among others confirmed that cells only arise from other cells by
disproving “spontaneous generation”. He filled flasks with a sterilized broth,
exposed one of the flasks to the air and the other he protected from outside
contamination. Organisms grew only in the exposed flask.
We are able to see cells divide through the process of mitosis and meiosis.
Scientists are now able to deliberately transfer genes between organisms, and can
observe how these genes are expressed in the phenotype of organisms at the
cellular level.
Discovery of enzymes allow scientists to understand how cells are able to carry out
metabolism.
2.1.3 State that all unicellular organisms carry out all the functions of life.
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All living organisms, even unicellular ones
o carry out metabolism, which is the sum of all chemical reactions in living
organisms.
o respond to their environment .
o are able to keep internal conditions stable through homeostasis.
o have the capability to grow and reproduce.
o are able to obtain nutrition.
2.1.4 Compare the relative sizes of molecules, cell membrane thickness,
viruses, bacteria, organelles and cells, using the appropriate SI unit.
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Molecules – 1 nm
Membranes – 10 nm
Viruses - 100 nm
Bacteria - 1 µm
Organelles up to 10
µm
Most cells up to 100
µm
1 mm = 1000 µm = 1
000 000 nm
2.1.5 Calculate the linear magnification of drawings and the actual size of
specimens in images of known magnification.
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Magnification can be stated or indicated with a scale bar.
To calculate magnification, divide the measured length of the diagram by the
actual length of the specimen.
o Measure the scale bar on the diagram with a ruler and convert to that
measurement to the units used in the diagram.
o Divide the length you measured and converted by the size the scale bar
represents.
Example calculating magnification: The scale bar shows to be 10mm =50 µm.
o First convert the 10 mm to µm. 10 mm = 10,000 µm.
o Divide the converted length of 10,000 µm by 50 µm (the actual size of the
specimen). This gives you the magnification of 200x.
You can also calculate the length of the specimen by dividing the length of the
drawing by the magnification.
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Try this example 2.1.6 Explain the importance of the surface area to volume ratio as a factor
limiting cell size.
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For cells to function they need to take in required substances, such as O2 or ions,
expel waste products, and exchange heat between the cytoplasm and the
environment.
The rates at which heat is transferred and which these substances enter or leave
the cell depend on its surface area to volume ratio.
The larger the cell the smaller the Surface Area:Volume ratio, making it less and
less and efficient.
Because of this cells cannot grow larger indefinitely, and at some point will have to
stop growing and/or divide.
To calculate the SA:V ratio of a cubeo Measure the length of one side.
o To calculate SA square the length of the side and then multiply it by 6 (the
number of sides)
o To calculate V cube the length of the side.
o Divide SA by V to get SA:V
o Example: a square with the side of 2mm.
 SA of cube: 22 is 4 multiplied by 6 is 24
 V of cube: 23 = 8
 SA/V = 3
2.1.7 State that multicellular organisms show emergent properties
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The idea that the whole is greater than the sum of its parts.
Novel properties emerge as the complexity of the organism grows.
Cells form tissues, tissues form organs, organs form organ systems, and organ
systems form multicellular organisms.
For example, a test tube of stomach cells and other molecules used in digestion
will not digest food. Digestion will only occur when molecules are arranged in the
specific form of a stomach.
2.1.8 Explain that cells in multicellular organisms differentiate to carry out
specialized functions by expressing some of their genes but not others.
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Every cell contains the entire genome of the organism. However not all of the
genes are expressed in all the cells.
For example the gene that produces amylase (digests sugars) is expressed in your
mouth but not in your hair.
Cells develop in different ways allowing them to carry out more specific functions
in multicellular organisms.
The process of cells developing differently because of gene regulation is called
differentiation.
It is more efficient for multicellular organisms to have differentiated cells.
2.1.9 State that stem cells retain the capacity to divide and have the ability
to differentiate along different pathways.
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Certain cells in the body maintain their ability to divide and differentiate into
different types of cells.
Embryos in the early stages are composed of stem cells.
Adults maintain stem cells the tissues that need to be replaced frequently such as
bone marrow and skin.
2.1.10 Outline one therapeutic use of stem cells.
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The mammalian central nervous system cannot fully repair itself when damaged or
diseased. Brain and spinal cord injuries, strokes and disorders that destroy these
neurons such as Alzheimer’s and Parkinson’s disease, have devastating and
irreversible effects.
It was discovered in 1998 that the human adult brain produces new neurons
indicating that there are stem cells there.
Possibly by culturing these neural stem cells and implanting them into individuals
with damaged neurons, that they could be stimulated to grow new functioning
neurons.
In 2005 stem cells were used to restore the insulation tissue of neurons in
laboratory rats resulting in subsequent improvements in their mobility.