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Cell Basics
Vocabulary: axon, ATP, cell, cell membrane, cell theory, cell wall, chloroplast,
circulation, contractile vacuole, coordination, cyton, digestion, dendrite, DNA,
dynamic equilibrium, endoplasmic reticulum, enzymes, eukaryotic, excretion,
food vacuole, homeostasis, hormones, immunity, life processes,
locomotion, mitochondrion, movement, nucleus, neurotransmitter, organ
system, organs, organelles, progesterone, prokaryotic, receptor molecules,
reproduction, respiration, ribosome, synthesis, system, target cell, target
organs, terminal branches, tissue
Living VS. Non-Living
Complex organisms, such as humans, require many systems for their life
processes. Less complex living things may lack the complex systems of more
complex organisms, but they still carry on the basic life activities. While non-living
things may carry on some of these life processes, they do not carry on all of them,
or these activities do not interact in a manner allowing the non-living thing to
reproduce itself.
Living things carry out almost all the life processes or activities. These life processes
include digestion, respiration, circulation, excretion, locomotion, immunity,
coordination, and synthesis. Non-living things are incapable of carrying out at least
one or more of the life processes. The sum of the energy used in all the life
processes represents the metabolism of the organism.
Homeostasis
The ability to carry on the life processes allow a living thing to maintain dynamic
equilibrium or homeostasiswith their surroundings. Homeostasis is a state of
balance or steady state between a living thing and its environment. Homeostasis
in an organism is constantly threatened. Failure to respond effectively to a failure
of homeostasis can result in disease or death.
The components of living things in humans and other organisms, from organ
systems to cell organelles, interact to maintain a balanced internal environment.
This balanced internal environment is called dynamic
equilibrium or homeostasis. To successfully accomplish this, organisms possess
many control mechanisms that detect internal changes and correct them to restore
the internal balance of the organism. If an organism fails to maintain homeostasis,
this may result in disease or death. Non-living things possess few control
mechanisms to maintain homeostasis.
Organizational Levels
Important levels of organization for structure and function of living things include
cells, tissues, organs, organ systems, and whole organisms. The organs and systems
of the body help to provide all the cells with their basic needs to carry on the life
functions. The cells of the body are of different kinds and are grouped in ways that
help their function.
All living things are composed of one or more cells, each capable of carrying out
the life functions. The organelles present in single-celled organisms often act in the
same manner as the tissues and systems found in many celled organisms. Singlecelled organisms perform all of the life processes needed to maintain homeostasis,
by using specialized cell organelles.
Living things have different levels of organization. The simplest level of
organization is that of the cell. A group of cells with a similar function is called
a tissue. Groups of tissues working together to perform a common function are
called organs. An example of this would include the nervous, muscle, and other
tissues which make up the heart. Groups of organs working together to perform a
common function are referred to as a system or organ system. The blood vessels,
blood, and the heart are organs which work together to form the circulatory
system. Many different systems function together to allow a complex organism to
function.
Cell Structure
Cells have particular structures or organelles that perform specific jobs. These
structures perform the life activities within the cell. Just as body systems are
coordinated and work together in complex organisms, the cells making up those
systems must also be coordinated and organized in a cooperative manner so they
can function efficiently together.
Inside the cell a variety of cell organelles, formed from many different molecules,
carry out the transport of materials, energy capture and release, protein building,
waste disposal, and information storage. Each cell is covered by a membrane that
performs a number of important functions for the cell as well.
Cell Theory
All organisms contain one or more cells which are capable of carrying on the life
activities needed by the organism. This idea is often referred to as the cell theory.
Parts of the Cell Theory
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The cell is the unit of structure in all living things.
The cell is the unit of function in all living things.
All cells come from preexisting cells.
A few exceptions to this theory exist. Viruses lack typical cellular structure. There
also is some question as to how the the first cell arose. In general, the cell theory
holds true for most living things, however.
Cell Types
There are two distinct types of cells. Prokaryotic cells lack a nucleus and other
organelles. Two domains of organisms have this type of cell - Archaebacteria and
Eubacteria, the simplist of all organisms. They still perform life functions but all
activities must be accomplished in the cytoplasm. Eukarotic cells are found in
organisms from the domain Eukarya, which includes all protists (Ameoba and
Paramecium are examples), Fungi (yeast and mushrooms are examples), Plants
(mosses, ferns, gymnosperm pines and angiosperm flowering plants are examples),
and Animals (humans are examples).
Cell Organelles
Cells have particular structures that perform specific jobs. These cell structures are
called organelles and perform the actual work of the cell. These organelles are
formed from many different molecules. Some functions carried out by organelles
include the transport of materials, energy capture and release, protein building,
waste disposal, and information storage. Single celled organisms also have
organelles similar to those in more advanced organisms to complete their life
processes. Many enzymes are needed for the chemical reactions involved in cellular
life processes to occur.
A Typical Animal Cell
Some Cell Organelles
Cell Organelle
Function
control center of the cell
nucleus
mitochondrion
contains DNA which directs the synthesis of
proteins by the cell
carries on the process of cell respiration
converting glucose to ATP energy the cell can
use
endoplasmic reticulum transport channels within the cell
ribosome
found on the endoplasmic reticulum and free
within the cell
responsible for the synthesis of proteins for
the cell
cell membrane
selectively regulates the materials moving to
and from the cell
food vacuole
stores and digests food
contractile vacuole
found in many single celled aquatic organisms
pumps out wastes and excess water from the
cell
chloroplast
cell wall
found in plant cells and algae
carries on the process of photosynthesis
surrounds and supports plant cells
Life Functions
Humans and many other organisms require multiple systems for digestion,
respiration, reproduction, circulation, excretion, movement, coordination,
and immunity. The systems collectively perform the life processes.
Once nutrients enter a cell, the cell will use those raw materials for energy or as
building blocks in the synthesis of compounds necessary for life. The energy we
initially obtain must must be changed into a form cells can use. A type of protein
called an enzyme allows for these changes to occur within the cell.
Humans and other complex organisms require many different organ systems to
carry on the activities required for life. These life activities or processes include
digestion, respiration, reproduction, circulation, excretion, movement,
coordination, and immunity.
Life Processes
Digestion
breakdown of food to simpler molecules which can
enter the cells
Circulation
the movement of materials within an organism or
its cells
Movement (locomotion)
change in position by a living thing
Excretion
removal of cellular waste products by an organism
(wastes may include carbon dioxide, water, salt,
and urea and are released during exhalation,
perspiration, and urine formation.)
Respiration
process which converts the energy in food
to ATP(the form of energy which can be used by
the cells)
Reproduction
the making of more organisms of one's own kind -not needed by an individual living thing but is
needed by its species
Immunity
the ability of an organism to resist disease causing
organisms (pathogens) and foreign invaders
Coordination
the control of the various activities of an organism
(mostly involves the nervous system and endocrine
glands in complex animals)
Synthesis
the production of more complex substances by
combining two or more simpler substances
It is important to realize that cell organelles are involved in many of these life
processes, as well as the organ systems of complex organisms.
Cellular Communication
Neurotransmitters and hormones allow communication between nerve cells and
other body cells as well. If nerve or hormone signals are changed, this disrupts
communication between cells and will adversely effect organism
homeostasis. Additionally, the DNA molecule contains the instructions that direct
the cell’s behavior through the synthesis of proteins.
Cell Membrane Receptors
Cell Membrane Receptors
Many cell
membranes
havereceptor
moleculeson their
surface. These
receptor sites play
an important role in
allowing cells and
organs to
communicate with
one another.
Hormonal Regulation
Hormones provide a primary way for cells to communicate with each other.
A hormone is a chemical messenger with a specific shape that travels through the
bloodstream influencing another target cell or target organ. Upon reaching the cell
the hormone is targeted for, the hormone often activates a gene within a cell to
make another necessary compound. One example of this is provided by the
pituitary gland. This gland at the base of the brain makes a hormone called LH
(luteinizing hormone). This hormone travels through the bloodstream and
stimulates the ovary to produce yellow tissue that produces the
hormone progesterone, which maintains the thickness of the uterus lining. The
graphic below illustrates how this kind of hormonal regulation can work in a plant
cell. Animal cell hormonal regulation involves a similar mechanism.
A Hormonal Feedback Mechanism
The diagram at the
right illustrates how
a hormone can
bind to receptors
on a cell membrane
and trigger that cell
to produce a
needed compound.
Nervous Regulation
Nerve cells or neurons also allow cells to communicate with each other. Neuron
communications are one way organism can detect and respond to stimuli at both
the cellular and organism level. This detection and response to stimuli helps to
maintain homeostasis in the cell or organism. Neurons may stimulate other nerve
cells or muscle cells, thus causing the later to contract and produce movement.
Structure and Function of a (Neuron) Nerve Cell
Structures and their Functions
1. dendrite -- neuron branch which detects stimuli (changes
in the environment)
2. cyton -- cell body of the neuron where normal metabolic
activities occur
3. axon -- longest dendrite covered by a myelin sheath
which provides electrical insulation -- carries nerve message
or impulse to the terminal branches
4. terminal branches -- release nerve chemicals
calledneurotransmitters which stimulate adjacent dendrites
on the next neuron or a muscle cell
Any change in nerve or hormone signals will change the communication between
cells and organs in an organism and thus may cause problems for organism’s
stability and ability to maintain homeostasis.
Cell Membrane
The cell membrane or plasma membrane performs a number of important
functions for the cell. These functions include the separation of the cell from its
outside environment, controlling which molecules enter and leave the cell, and
recognition of chemical signals. The cell membrane consists of two layers of
phospholipids with proteins embedded within these layers. The surface of the cell
contains molecules which recognize other molecules which may attach to or enter
the cell.
Cell Membrane Structure
Membrane Processes
The processes of diffusion and active transport are important in the movement of
materials in and out of cells.
Diffusion
Diffusion or passive
transport is the movement of
materials from a region of
higher to a region of lower
substance concentration. The
diagram at the right shows the
movement of molecules from
higher concentration on side
A to a lower concentration on
side B.
Active Transport
In active transport, molecules move from a
region of lower concentration to a region of
higher concentration. As this process does
not naturally occur, the cell has to use
energy in the form of ATP to make active
transport occur.
Cell Chemistry
Many organic and inorganic substances dissolved in cells allow necessary chemical
reactions to take place in order to maintain life. Large organic food molecules such
as proteins and starches must initially be broken down through the life process
of digestion in order to enter cells.
Organic Molecules and Digestive End Products
Organic Molecule
Digestive End Product(s)
carbohydrates
simple sugars (glucose)
proteins
amino acids
lipids (fats)
fatty acids and glycerol
Asexual Reproduction
Species are maintained in existence through the life spans process
of reproduction. Asexual reproduction produces genetically identical offspring
from a single parent cell. The process of mitosis is associated with asexual
reproduction and the growth and repair of cells in sexually reproducing organisms.
Reproduction and development are necessary for the continuation of any
species. Asexual reproduction is a method of reproduction with all the
genetic information coming from one parent.
Some Methods of Asexual Reproduction
1. binary fission -- involves an
equal division of both the
organism cytoplasm and
nucleus to form two identical
organisms
-- the diagram of the protist at
the right is example of this
2. budding -- involves one
parent dividing its nucleus
(genetic material) equally, but
cytoplasm unequally
-- the diagram of a yeast at the
right is an example of this
3. sporulation (spore
formation) -- is reproduction
involving specialized single
cells coming from one parent
-- the diagram of mold spores
being formed at the right is an
example of this
Asexual reproduction is sometimes called cloning. Cloning is the production
of identical genetic copies. All forms of asexual reproduction are variations of
the cell division process of mitosis. Mitosis is associated with asexual
reproduction, as well as growth and repair in sexually reproducing organisms.
Mitosis
Mitosis is the method used for cell division and reproduction in cells not involved
in sexual reproduction. This process starts with one replication (copying of the
chromosome material) and one division of the chromosome material. This results
in the chromosome numbers in the two cells produced being the same as in the
parent cell. This process is represented in the graphic which follows.
An Overview of the Process of Mitosis
The Cell Cycle
The cell cycle is the lifespan of a cell. It is divided into three parts: Interphase,
Mitosis, and Cytokinesis. Interphase is divided into three parts. G1 - or the first
growth phase, is the stage in a cells life when normal cell functioning is occurring.
A cell will remain in this stage unless it receives a signal to reproduce. Cells can
receive signals from neighboring cells during development of a multi-cellular
organism, or it may receive a signal for repair of neighboring cells or a cell may
receive a signal to divide if the cell becomes too large for intracellular transport to
occur effectively. When a cell receives the signal to divide, it moves into the
second stage of interphase called synthesis. Synthesis is the longest part of the cell
cycle because this is the stage when a cells DNA replicates. DNA
replication involves separating the double helix, complimentary nucleotides finding
their match (Adenine joins with Thymine, Cytosine joins with Guanine) and two
identical strands of DNA forming. Once this is accomplished, and proteins have
confirmed its success, a cell moves into the third phase of interphase called G2, or
the second growth phase. Here, organelles replicate and the cell grows in
anticipation of dividing into two smaller cells.
If everything goes according to plan, a cell is ready to move into the mitotic stage
of the cell cycle. Mitosis is the division of the nucleus stage. It is a choreographed
mechanism to efficiently and accurately divide the two identical copies of DNA
into the newly forming cells and it is done the same way in every living cell. The
four parts of this cycle are prophase, metaphase, anaphase and telophase (PMAT).
In prophase, the DNA which is in long, stringy chromatin form condenses and coils
up into chromosomes. The identical pieces of DNA are joined together with a
centromere. During this phase, the nuclear membrane in eukaryotes begins to
disintegrate. In metaphase, the pairedchromatids line up (chromosomes) single file
down the equator of the cell. In anaphase, the sister chromatids separate and
identical chromatids each move to opposite poles.Telophase is when the
chromosomes begin to uncoil again back into chromatin and new nuclear
membranes begin to form in eukaryotes.
The final stage of the cell cycle begins in telophase when the cells cytoplasm begins
to divide. In animal cells, the cell membrane pinches in during this stage
called cytokinesis. In plant cells, a cell plate forms between the newly forming
nuclei as the cell wall can't pinch in. This continues until two new cells are formed
with identical DNA.
2 Key Results of Mitosis
1. The same chromosome number is retained from generation to generation.
2. Each daughter cell receives an exact copy of the chromosomes of the parent
cell. (clones)
Asexual Heredity
Every organism requires a set of coded instructions for specifying its traits. For
offspring to resemble their parents, there must be a reliable way to transfer
information from one generation to the next. Heredity is the passage of these
instructions from one generation to another. The DNA molecule provides the
mechanism for transferring these instructions.
In asexually reproducing organisms, all the genes come from a single parent. As
asexually produced offspring are produced by the cell division process of mitosis,
all offspring are normally genetically identical to the parent.
CREDIT: http://www.regentsprep.org/regents/biology/2011%20Web%20Pages/Cells%20Cell%20Division.htm