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BIOLOGY REVISION
1.1 Introduction to Cells
 Cell Theory = formulated in the mid-nineteenth century, that living organisms are made
up of cells, are the basic structural/organizational unit of all organisms, and that all cells
come from pre-existing cells.
 Unicellular Organisms = Organisms consisting of only one cell carry out all functions of
life in that cell.
The 7 Functions are = Nutrition, Metabolism, Growth, Response, Excretion, Homeostasis,
Reproduction.
 Limitations on cell size = Surface area to volume ration is important in the limitation of
cell size. The rate at which substances cross this membrane depends on its surface area. If
ratio is too small then substances will not enter the cell as quickly as they are supposed to
and waste product is being produced more rapidly, than they can be excreted.
 Multicellular organisms = Organisms made of more than one cell. Have properties that
emerge from the interaction of their cellular components, and they live together in colonies.
 Stem Cells = The capacity of stem cells to divide and differentiate along different
pathways is necessary in embryonic development. It also makes stem cells suitable for
therapeutic uses. IN OTHER WORDS,  Cells from which all other cells with specialized
functions are generated. Stem cells are special human cells that are able to develop into
many different cell types. This can range from muscle cells to brain cells. In some cases, they
can also fix damaged tissues.
Two Types  Embryonic (Research stem cell, donated to science) and Adult Stem Cells (2
types 1)Fully developed tissues, such as brain and skin and 2) type pluripotent stem cell).
1.2 Ultrastructure of Cells
 Prokaryotic cell structure = Prokaryote have a simple cell structure without
compartments, which means it is a unicellular organism that lacks a nucleus. Prokaryotes
are divided into two distinct groups: the bacteria and the archaea, which scientists believe
have unique evolutionary lineages. Most prokaryotes are small, single-celled organisms that
have a relatively simple structure.
 Cell Division in Prokaryotes = They divide by binary fission used for asexual reproduction.
The singular chromosome is replicated, and the two copies quickly move to the end of the
cell. Division of the cytoplasm of the cell quickly follow. Each of the daughter cells contains
one copy of the chromosome so they are genetically identical.
 Eukaryotic cell structure = Eukaryotes have a compartmentalized cell structure, which
means that they are divided up by partitions into compartments. Partitions being single or
double membranes.
Advantages = Enzymes and substrates can be much more concentrated.
Substances are kept inside of the membrane of an organelle.
pH can be maintained at an ideal level.
Organelles can be moved around within the cell.
1.3 Membrane Structure
 Phospholipid bilayers = it’s a thin polar membrane made of two layers of lipid molecules.
two-layered arrangement of phosphate and lipid molecules that form a cell membrane, the
hydrophobic lipid ends facing inward and the hydrophilic phosphate ends facing outward.
Also called lipid bilayer
Substances = Hydrophilic, attracted to water.
Hydrophobic, not attracted to water.
 Membrane proteins = They are diverse in terms of structure position in the membrane
and function, having a wide range of function. Membrane proteins are common proteins
that are part of, or interact with, biological membranes. Membrane proteins fall into several
broad categories depending on their location.
2 Groups =
Integral proteins are hydrophobic
Peripheral proteins are hydrophilic
 Cholesterol in membranes = Cholesterol is a lipid component that moves in our blood
vessels. (Not fat or oil) It belongs to a group of substances called steroids. HYDROPHOBIC
1.4 Membrane Transport
 Endocytosis = Endocytosis is a cellular process in which substances are brought into the
cell. The material to be internalized is surrounded by an area of cell membrane, which then
buds off inside the cell to form a vesicle containing the ingested material. Endocytosis
includes pinocytosis and phagocytosis.
 Vesicle movement in cells = Vesicles move materials within cells.
Cases =
Content of the vesicle needs to be moved.
Proteins are the reason for vesicle movement.
 Exocytosis = Is a form of active and bulk transport in which cell transports molecules out
of the cell. Vesicles can be used to release materials from cells. If a vesicle fuses with the
plasma membrane, the contents are then outside the membrane and therefore outside the
cell. This process is called exocytosis.
 Simple Diffusion = Diffusion that does not require the assistance of membrane proteins
and it is the net movement from a region of higher to lower concentration. It’s the
spreading out of particles in liquids and gases that happens because the particles are in
continuous motion.
 Facilitated Diffusion = It’s the passive movement of substances, such as biological
molecules or ions, across a plasma membrane. Facilitated diffusion is the transport of
substances across a biological membrane from an area of higher concentration to an area of
lower concentration with the help of a transport molecule. Since substances move along the
direction of their concentration gradient, chemical energy is not directly required
 Osmosis = the movement of water molecules from a solution with a high concentration
of water molecules to a solution with a lower concentration of water molecules, through a
cell's partially permeable membrane.
 Active Transport = Active transport is the process of moving molecules across a cellular
membrane using cellular energy. Active transport is used by cells to accumulate needed
molecules such as glucose and amino acids. Active transport powered by adenosine
triphosphate (ATP) is known as primary active transport.
1.5 The Origin of Cells
 1880s = cells can only be produced by division of a pre-existing cell.
 2010 = created the first artificial cell.
 Origin of the First Cells = The first cells must have arisen from non-living material.
 Endosymbiosis = symbiotic relationship where one organism lives inside the other.
1.6 Cell Division
 Mitosis = In cell biology, mitosis is a part of the cell cycle in which replicated
chromosomes are separated into two new nuclei. Cell division gives rise to genetically
identical cells in which the total number of chromosomes is maintained. Therefore, mitosis
is also known as equational division.
 Meiosis = Meiosis is the process in eukaryotic, sexually reproducing animals that reduces
the number of chromosomes in a cell before reproduction. Many organisms package these
cells into gametes, such as egg and sperm. The gametes can then meet, during
reproduction, and fuse to create a new zygote. Because the number of alleles was reduced
during meiosis, the combination of two gametes will yield a zygote with the same number of
alleles as the parents. IIn diploid organisms, this is two copies of each gene.
 Interphase = It’s the portion of the cell cycle that is not accompanied by gross changes
under the microscope, and includes the G1, S and G2 phases. During interphase, the cell
grows, replicates its DNA and prepares for mitosis. A cell in interphase is not simply
quiescent.
 Supercoiling of chromosomes = During mitosis, the two chromatids that make up each
chromosome must be separated to move to opposite poles of the cell. The DNA molecule in
these chromosomes are immensely long. It is essential to package chromosomes into much
shorter structures. This process is known as condensation of chromosomes, and it occurs
during the first stage of mitosis.
 PRO/META/ANA/TELO
coiling.
= Prophase; chromosomes become shorter and fatter by
= Metaphase; separates duplicated genetic material of a
parent cell.
= Anaphase; each centromere divides, so the pairs of sister
chromatids separate.
= Telophase; chromatids and chromosomes move to opposite
ends of the cell; two nuclei are formed.
 Cytokinesis = Cytokinesis is the part of the cell division process during which the
cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division
begins during or after the late stages of nuclear division in mitosis and meiosis.
ANIMAL = The plasma membrane is pulled inward around the equator of the cell to form a
cleavage furrow. This accomplished using a ring contractile protein immediately inside the
plasma membrane at the equator.
PLANT = Cells vesicles are moved to the equator where they fuse to form tubular structures
across the equator. Fusion of more vesicles form two layers of membrane across the whole
of the equator, which develop into plasma membranes of the two daughter cells.
Calculating Magnification
 Magnification =
Image Size
------------------------------Actual size of Specimen
 mm (millimiters of ruler) to μm (micrometers) x 1000  FOR IMAGE SIZE
 17 mm x 1000 = 17000
 M = I/A
A = I/M
I=AxM