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TOPICS ON BIOLOGY FOR ADMISSION TEST
1. Basic structure and characteristics of the eukaryotic cell (cellular organelles, structure, function).
2. Basic metabolic pathways: glycolysis, biological oxidation, photosynthesis (the biological role and basic
characteristics of enzymes).
3. The DNA and its role in heredity: the structure of DNA, the genetic code, the replication of the genetic
material.
4. Cell division I.: Chromatin, chromosomes. The behaviour of chromosomes during mitosis.
5. Cell division II.: Meiosis. The role of meiosis in sexually reproducing organisms.
6. Genetics I.: Genotype, phenotype, genes, alleles. Monohybrid cross, dominant-recessive type of
inheritance, co-dominance. The first Mendelian law of inheritance.
7. Genetics II.: X-linked inheritance. Dihybrid cross: the second Mendelian law of inheritance. Genetic
linkage, crossing-over.
8. From DNA to protein: Translation, mRNA, rRNA, tRNA, ribosomes.
9. Basic anatomy and physiology of the human respiratory system.
10. Basic anatomy and physiology of the human circulatory system.
11. Basic anatomy and physiology of the human digestive system.
12. Basic anatomy and physiology of the human excretory(Urinary) system., importamt
13. Homeostasis: the basic structure and function of the human nervous system.
14. Homeostasis: hormones, the human endocrine system.
15. Basic structure and function of skeletal muscle cells, locomotion in humans.
16. The basic defense systems against infections: the humoral and cellular immune response in humans.
Textbook: Sadava, Heller, Orians, Purves, Hillis (ed.): Life. The Science of Biology, 8th. Edition.
Sinauer Associates, INC., VHPS/W.H. Freeman and Co. Gordonsville, VA, U.S.A.
Almost the answer of all of the above questions can be found on the below website:
http://bcs.whfreeman.com/thelifewire8e/default.asp?s=&n=&i=&v=&o=&ns=0&uid=0&rau=0,
The answer of topics no.15: Basic structure and function of skeletal muscle cells,
http://www.shoppingtrolley.net/skeletal%20muscle.shtml,
http://www.shoppingtrolley.net/lesson3-muscles.shtml,
http://en.wikipedia.org/wiki/Cardiac_muscle
In addition you can find some answers below:
Answers
Macromolecules: Giant Polymers
Macromolecules are polymers constructed by the formation of covalent bonds between smaller molecules
called monomers. Macromolecules in living organisms include polysaccharides, proteins, nucleic acids and
lipids.
Proteins: Polymers of Amino Acids
The functions of proteins include support, protection, catalysis, transport, defense, regulation, and movement.
Protein function sometimes requires an attached prosthetic group.
There are 20 amino acids found in proteins. Each amino acid consists of an amino group, a carboxyl group, a
hydrogen, and a side chain bonded to the α carbon atom.
The side chains, or R groups, of amino acids may be charged, polar, or hydrophobic; there are also special
cases, such as the —SH groups of cysteine, which can form disulfide bridges. The side chains give different
properties to each of the amino acids.
Basic structure of amino acid:
COOH
|
H2N-C-H
|
R
Amino acids are covalently bonded together into polypeptide chains by peptide linkages, which form by
condensation reactions between the carboxyl and amino groups.
Polypeptide chains are folded into specific three-dimensional shapes to form functional proteins. Four levels
of protein structure are possible: primary, secondary, tertiary, and quaternary.
The primary structure of a protein is the sequence of amino acids bonded by peptide linkages. This primary
structure determines both the higher levels of structure and protein function.
The two types of secondary structure-α helices and β pleated sheets-are maintained by hydrogen bonds
between atoms of the amino acid residues.
The tertiary structure of a protein is generated by bending and folding of the polypeptide chain.
The quaternary structure of a protein is the arrangement of two or more polypeptides into a single functional
protein consisting of two or more polypeptide subunits.
Carbohydrates: Sugars and Sugar Polymers
All carbohydrates contain carbon bonded to hydrogen atoms and hydroxyl groups.
Hexoses are monosaccharides that contain six carbon atoms. Examples of hexoses include glucose, galactose,
and fructose, which can exist as chains or rings.
The pentoses are five-carbon monosaccharides. Two pentoses, ribose and deoxyribose, are components of the
nucleic acids RNA and DNA, respectively.
Glycosidic linkages may have either α or β orientation in space. They covalently link monosaccharides into
larger units such as disaccharides, oligosaccharides, and polysaccharides.
Cellulose, a very stable glucose polymer, is the principal component of the cell walls of plants. It is formed by
glucose units linked together by β-glycosidic linkages
Lipids: Water-Insoluble Molecules
Fats and oils are triglycerides, composed of three fatty acids covalently bonded to a glycerol molecule by ester
linkages.
Saturated fatty acids have a hydrocarbon chain with no double bonds.
Phospholipids have a hydrophobic hydrocarbon "tail" and a hydrophilic phosphate "head."
In water, the interactions of the hydrophobic tails and hydrophilic heads of phospholipids generate a
phospholipid bilayer that is two molecules thick. The head groups are directed outward, where they interact
with the surrounding water. The tails are packed together in the interior of the bilayer.
Nucleic Acids: Informational Macromolecules
DNA is the hereditary material. Both DNA and RNA play roles in the formation of proteins. Information
flows from DNA to RNA to protein.
Nucleic acids are polymers made up of nucleotides. A nucleotide consists of a phosphate group, a sugar
(ribose in RNA and deoxyribose in DNA), and a nitrogen-containing base. In DNA the bases are adenine,
guanine, cytosine, and thymine, but in RNA uracil substitutes for thymine.
Not to be memorized
In the nucleic acids, the bases extend from a sugar-phosphate backbone. The information content of DNA and
RNA resides in their base sequences. RNA is single-stranded. DNA is a double-stranded helix in which there
is complementary, hydrogen-bonded base pairing between adenine and thymine (A-T) and guanine and
cytosine (G-C). The two strands of the DNA double helix run in opposite directions
The Cell: The Basic Unit of Life
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All cells come from preexisting cells and have certain processes, types of molecules, and structures in
common.
To maintain adequate exchanges with its environment, a cell's surface area must be large compared with
its volume.
Cells can be visualized by various methods using microscopes.
All cells are surrounded by a plasma membrane
Prokaryotic Cells
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All prokaryotic cells have a plasma membrane, a nucleoid region with DNA (no membrane-enclosed
organelles (nucleus, no Mitochondria) and a cytoplasm that contains ribosomes, water, and dissolved
proteins and small molecules.
Prokaryotes doesn’t contain membrane-enclosed organelles (Nucleus, Mitochondria, golgi apparatus…etc
Some prokaryotes have additional protective structures: cell wall, outer membrane, and capsule.
Eukaryotic Cells
Like prokaryotic cells, eukaryotic cells have a plasma membrane, cytoplasm, and ribosomes. However,
eukaryotic cells are larger and contain many membrane-enclosed organelles. The membranes that envelop
organelles in the eukaryotic cell are partial barriers, ensuring that the chemical composition of the interior of
the organelle differs from that of the surrounding cytoplasm.
Cell organelles (cell ultra structures)
12345-
The Nucleus
Endoplasmic reticulum
Golgi apparatus
Mitochondria and Chloproplast
Lysosomes
Organelles that Process Information (The nucleus)
The nucleus is usually the largest organelle in a cell. It is surrounded by a double membrane (the nuclear
envelope), which disassembles during cell division. Within the nucleus, the nucleolus is the source of the
ribosomes which is produce their and export to the cytoplasm.
The cell nucleus is a remarkable organelle because it forms the package for our genes and their controlling
factors. It functions to:
Store genes on chromosomes
Organize genes into chromosomes to allow cell division.
Transport regulatory factors & gene products via nuclear pores
Produce messages ( messenger Ribonucleic acid or mRNA) that code for protein synthesis.
Produce ribosomes in the nucleolus
The nucleus contains most of the cell's DNA, which associates with protein to form chromatin. Chromatin is
diffuse throughout the nucleus until just before cell division, when it condenses to form chromosomes.
The Endomembrane System
The endoplasmic reticulum system is made up of a series of interrelated compartment enclosed by
membranes: endoplasmic reticulum (rough and smooth), the Golgi apparatus and lysosomes
 The rough endoplasmic reticulum has attached ribosomes that synthesize proteins. The smooth
endoplasmic reticulum lacks ribosomes and is associated with the synthesis of lipids and detoxification
of poisons and drugs.
Endoplasmic reticulum is a network of tubules, vesicles and sacs that are interconnected. They may serve
specialized functions in the cell including
- protein synthesis,
- Sequestration of calcium
- production of steroids
- Storage and production of glycogen
-Rough endoplasmic reticulum bears the ribosomes during protein synthesis. The newly synthesized proteins
are sequestered in sacs, called cisternae . The system then sends the proteins via small vesicles to the Golgi
Complex , or, in the case of membrane proteins, it inserts them into the membrane. The Ribosomes sit on the
outer surfaces of the sacs (or cisternae). They resemble small beads sitting in rosettes or in a linear pattern
The Golgi Apparatus

The Golgi apparatus consists of a stack of membrane-bounded cisternae located between the
endoplasmic reticulum and the cell surface. A myriad of enzymes (proteins) are present in the Golgi to
perform its various synthetic activities.

The Golgi apparatus receives materials (proteins) from the rough ER by means of vesicles that fuse its cis
region:
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Some of these (proteins) will eventually end up as integral membrane proteins embedded in the
plasma membrane.
Other proteins moving through the Golgi will end up in lysosomes
or be secreted by exocytosis (e.g., digestive enzymes).
The major processing activity is glycosylation: the adding of sugar molecules to form glycoproteins.

Lysosomes contain many digestive enzymes. Lysosomes fuse with the phagosomes produced by
phagocytosis to form secondary lysosomes, in which engulfed materials are digested. Undigested
materials are secreted from the cell when the secondary lysosome fuses with the plasma membrane.
Organelles that Process Energy (Mitochondria and chloroplasts)
 Mitochondria are enclosed by an outer membrane and an inner membrane that folds inward to form
cristae. Mitochondria contain the proteins needed for cellular respiration (electrons transport chain, proton
pumping and ATP synthesis), lipid synthesis and the Kreb’s cycle (Citric acid cycle) Kreb’s cycle takes
place in the matrix.
Mitochondria contain their own DNA and ribosomes and are capable of making some of their own
proteins
Mitochondrial Substructure
Mitochondria contain two membranes, separated by a space. Both are the
typical "unit membrane" (railroad track) in structure. The space which is
enclosed by the inner membrane is the matrix. This appears moderately
dense and one may find strands of DNA, ribosomes, or small granules in
the matrix. The mitochondria are able to code for part of their proteins
with these molecular tools. The above cartoon shows the diagram of the
mitochondrial membranes and the enclosed compartments.
How are mitochondria organized to be powerhouses?
The food we eat is oxidized to produce high-energy electrons that are converted to stored energy. This energy
is stored in high energy phosphate bonds in a molecule called adenosine triphosphate, or ATP. ATP is
converted from adenosine diphosphate by adding the phosphate group with the high-energy bond. Various
reactions in the cell can either use energy (whereby the ATP is converted back to ADP, releasing the high
energy bond) or produce it (whereby the ATP is produced from ADP).
Steps from glycolysis to the electron transport chain. Why are mitochondria
important?
Lets break down each of the steps so you can see how food turns into ATP energy packets and water. The
food we eat must first be converted to basic chemicals that the cell can use. Some of the best energy supplying
foods contain sugars or carbohydrates ...bread, for example. Using this as an example, the sugars are broken
down by enzymes that split them into the simplest form of sugar which is called glucose. Then, glucose
enters the cell by special molecules in the membrane called “glucose transporters”.
Once inside the cell, glucose is broken down to make ATP in two pathways. The first pathway requires no
oxygen and is called anaerobic metabolism. This pathway is called glycolysis and it occurs in the cytoplasm
outside the mitochondria. During glycolysis, glucose is broken down into pyruvate. Other foods like fats can
also be broken down for use as fuel (see following cartoon). Each reaction is designed to produce some
hydrogen ions (electrons) that can be used to make energy packets (ATP). However, only 4 ATP molecules
can be made by one molecule of glucose run through this pathway. That is why mitochondria and oxygen are
so important. We need to continue the breakdown process with the Kreb’s cycle inside the
mitochondria (matrix) in order to get enough ATP (~ 28 ATP/one glucose sugar) to run all the cell
functions
The events that occur inside and outside mitochondria are diagrammed in the above cartoon. Pyruvate is
carried into the mitochondria and there it is converted into Acetyl Co-A which enters the Kreb's cycle. This
first reaction produces carbon dioxide because it involves the removal of one carbon from the pyruvate.
How does the Kreb's cycle work?
The whole idea behind respiration in the mitochondria is to use the Kreb’s cycle (also called the citric acid
cycle) to get as many electrons out of the food we eat as possible. These electrons (in the form of hydrogen
ions) are then used to drive pumps that produce ATP. The energy carried by ATP is then used for all kinds of
cellular functions like movement, transport, entry and exit of products, division, etc. To produce ATP from
pyruvate it is a complicated process in which many factors (like Acetyl CoA , NAD, FAD, enzymes (electron
transport chain which is located int he inner membrane of mitochondria, ATP synthase…), proton gradient
and Oxygen are need. ATP is produced in matrix, also O2 couple to H+ (proton or Hydrogen ion) and
electrons to produce water also this take place in matrix.
why do we need mitochondria?
The whole idea behind this process is to get as much ATP out of glucose (or other food products) as possible.
If we have no oxygen, we get only 4 molecules of ATP energy packets for each glucose molecule (in
glycolysis). However, if we have oxygen, then we get to run the Kreb’s cycle to produce many more
hydrogen ions that can run those ATP pumps. From the Kreb’s cycle we get 24-28 ATP molecules out of one
molecule of glucose converted to pyruvate (plus the 4 molecules we got out of glycolysis). So, you can see
how much more energy we can get out of a molecule of glucose if our mitochondria are working and if we
have oxygen.
Plasma Membrane Composition and Structure
Biological membranes consist of lipids, proteins, and carbohydrates. The fluid mosaic model of membrane
structure describes a phospholipid bilayer in which proteins can move about laterally within the membrane.
Integral membrane proteins are at least partially inserted into the phospholipid bilayer. Peripheral membrane
proteins are attached to the surface of the bilayer by ionic bonds. The two surfaces of a membrane may have
different properties because of their different phospholipid composition, exposed domains of integral
membrane proteins, and peripheral membrane proteins.
Carbohydrates attached to proteins or phospholipids project from the external surface of the plasma
membrane and function as recognition signals for interactions between cells.
Membrane components may:
be protective
regulate transport in and out of cell or subcellular domain
allow selective receptivity and signal transduction by providing transmembrane receptors that bind
signaling molecules
allow cell recognition
provide anchoring sites for cytoskeletal filaments or components of the extracellular matrix. This allows the
cell to maintain its shape and perhaps move to distant sites.
provide a stable site for the binding and catalysis of enzymes.
Membrane transport
Passive Membrane Transport
Substances can diffuse passively across a membrane by three processes: simple diffusion through the
phospholipids bilayer, facilitated diffusion through protein channels, or facilitated diffusion by means of a
carrier protein.
A solute diffuses across a membrane from a region with a greater concentration of that solute to a region with
a lesser concentration of that solute. Equilibrium is reached when the concentrations of the solute are identical
on both sides of the membrane.
The rate of simple diffusion of a solute across a membrane is directly proportional to its concentration
gradient across the membrane. An important factor in simple diffusion across a membrane is the lipid
solubility of the solute.
In osmosis, water diffuses from regions of higher water concentration to regions of lower water concentration.
Channel proteins and carrier proteins function in facilitated diffusion.
The rate of carrier-mediated facilitated diffusion reaches a maximum when a solute concentration is reached
that saturates the carrier proteins so that no increase in rate is observed with further increases in solute
concentration.
Active Transport
Active transport requires the use of chemical energy to move substances across a membrane against a
concentration gradient.
Active transport proteins may be uniports, symports, or antiports.
In primary active transport, energy from the hydrolysis of ATP is used to move ions into or out of cells
against their concentration gradients.
Secondary active transport couples the passive movement of one solute with its concentration gradient to the
movement of another solute against its concentration gradient. Energy from ATP is used indirectly to
establish the concentration gradient that results in the movement of the first solute
Endocytosis and Exocytosis
Endocytosis transports macromolecules, large particles, and small cells into eukaryotic cells by means of
engulfment by and vesicle formation from the plasma membrane. Phagocytosis and pinocytosis are both
nonspecific types of endocytosis.
In receptor-mediated endocytosis, a specific membrane receptor protein binds to a particular macromolecule.
In exocytosis, materials in vesicles are secreted from the cell when the vesicles fuse with the plasma
membrane.
The Human
Respiratory System
The Pathway
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the oral pharynx
through the glottis
into the trachea
into the right and left bronchi, which branches and rebranches into
bronchioles, each of which terminates in a cluster of
alveoli
Air enters the nostrils
passes through the
nasopharynx,
Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult
lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80
times the area of our skin!).
Breathing
In mammals, the diaphragm divides the body cavity into the

abdominal cavity, which contains the viscera (e.g., stomach and intestines) and the

thoracic cavity, which contains the heart and lungs.

During inspiration (inhaling),
o The external intercostal muscles contract, lifting the ribs up and out.
o The diaphragm contracts, drawing it down .
During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs
returns them to their normal volume. At rest, we breath 15-18 times a minute exchanging about 500 ml
of air.
In more vigorous expiration,
o The internal intercostal muscles draw the ribs down and inward
o The wall of the abdomen contracts pushing the stomach and liver upward.
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Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each
breath. This is called the vital capacity. Even with maximum expiration, about 1200 ml of residual
air remain.
The table shows what happens to the composition of air when it reaches the alveoli. Some of the oxygen
dissolves in the film of moisture covering the epithelium of the alveoli. From here it diffuses into the blood in
a nearby capillary then it enters a red blood cell and combines with the hemoglobin.
Hemoglobin consist of four globulin (proteins) and heam group which contains Iron ion (Fe+2 ) to which
Oxygen used to bind.(Iron gives the red colour to the blood)
Myoglobin has a high affinity for O2 and serves as an O2 reserve in muscle.
At the same time, some of the carbon dioxide in the blood diffuses into the alveoli from which it can be
exhaled.
Composition of atmospheric air and expired air in a typical subject.
Note that only a fraction of the oxygen inhaled is taken up by the lungs.
Component
N2 (plus inert gases)
Atmospheric Air (%) Expired Air (%)
78.62
74.9
O2
20.85
15.3
CO2
0.03
3.6
H2O
0.5
6.2
100.0%
100.0%
Gas Exchange in Human Lungs
In mammalian lungs, the gas
exchange surface area provided by
the millions of alveoli is enormous,
and the diffusion path length
between the air and perfusing blood
is very short.
Surface tension in the alveoli would
make inflation of the lungs difficult
if the alveoli did not produce
surfactant.
Transport of Respiratory Gases
Oxygen is reversibly bound to
hemoglobin in red blood cells. Each
molecule of hemoglobin can carry a
maximum of four molecules of O2.
Because of positive cooperativity,
the affinity of hemoglobin for O2
depends on the PO2 (concentration
of Oxygen) to which the
hemoglobin is exposed. Therefore,
hemoglobin picks up O2 as it flows
through respiratory exchange
structures and gives up O2 in
metabolically active tissues.
Carbon dioxide (Co2) is transported in the blood principally as bicarbonate ions (dissolved in blood).
Human circulatory system
The circulatory system is a complex arrangement of tubes that transport blood as well as waste products
throughout the entire body.
The heart is the main pump. The heart is divided into four chambers. The top two chambers are the atriums
and the bottom two chambers are the ventricles. The atriums both contract at the same time as do the two
ventricles. Blood enters the heart via the superior and the inferior vena cava. These are the two largest veins in
the body. The right atrium receives the blood first. The right atrium contracts and forces the blood into the
right ventricle.
When the right ventricle contracts the blood is pumped into both lungs via the pulmonary artery. This portion
of the circulatory system is sometimes referred to as pulmonary circulation or lesser circulation. The
pulmonary artery is the only artery in the body that carries deoxygenated blood. Blood is returned from the
lungs via the pulmonary veins. These are the only veins in the body that carry oxygenated blood. The
oxygenated blood is returned to the left atrium. When the atrium contracts the blood is forced into the left
ventricle. The left ventricle is the strongest and most muscular portion of a healthy heart.
This is due to the fact that the left ventricle works the hardest. It must force blood throughout the body. When
the left ventricle contracts, blood is forced into the aorta. The aorta is the main artery leaving the heart.
The oxygenated blood is now forced throughout the body through a series of arteries that gradually become
smaller and smaller. Blood flows from arteries into arterioles. From arterioles into capillaries. At this point the
blood is able to make close contact with individual cells. Here is were waste products are picked up and
oxygen is delivered.
The blood now starts its return trip to the heart. From the capillaries the blood flows into venules. These are
very small veins. (About the same size as capillaries) From the venules the blood is forced into veins These
veins all return blood either into the superior or the inferior vena cava. As stated earlier, the inferior and the
superior vena cava return the deoxygenated blood to the right atrium of the heart.
The Human Heart: Two Pumps in One
The human heart has four chambers. Valves in the heart prevent the backflow of blood.
The cardiac cycle has two phases: systole, in which the ventricles contract; and diastole, in which the
ventricles relax. The sequential heart sounds ("lub-dub") are made by the closing of the heart valves.
Blood pressure can be measured using a sphygmomanometer and a stethoscope.
The autonomic nervous system controls heart rate: Sympathetic activity increases heart rate, and
parasympathetic activity decreases it.
Action Potential
Resting Membrane Potential
When a neuron is not sending a signal, it is "at rest."
When a neuron is at rest, the inside of the neuron is
negative relative to the outside. Although the
concentrations of the different ions attempt to balance
out on both sides of the membrane, they cannot because
the cell membrane allows only some ions to pass
through channels (ion channels). At rest, potassium ions
(K+) can cross
through the membrane easily. Also at rest, chloride ions
+
(Cl )and sodium ions (Na ) have a more difficult time crossing. The negatively charged protein molecules (A-)
inside the neuron cannot cross the membrane. In addition to these selective ion channels, there is a pump that
uses energy to move three sodium ions out of the neuron for every two potassium ions it puts in. Finally,
when all these forces balance out, and the difference in the voltage between the inside and outside of the
neuron is measured, you have the resting potential. The resting membrane potential of a neuron is about -70
mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside. At rest, there are
relatively more sodium ions outside the neuron and more potassium ions inside that neuron.
An action potential is caused by positive ions moving in and then out of the neuron at a certain spot on the
neuron membrane.
An action potential is initiated by a stimulus above a certain intensity or threshold. Not all stimuli initiate an
action potential. The stimulus could be a pin prick, light, heat, sound or an electrical disturbance in another
part of the neuron. An action potential occurs when a neuron sends information down an axon, away from the
cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential. The
action potential is an explosion of electrical activity that is created by a depolarizing current. This means that
some event (a stimulus) causes the resting potential to move toward 0 mV. When the depolarization reaches
about -55 mV a neuron will fire an action potential. This is the threshold
action potential
Depolarization
A stimulus causes a gate in the Na+ Channel to open. Since there is a high concentration of Na+ outside, Na+
diffuses into the neuron. The electrical potential changes to ~ +40 mV.
Repolarization
Depolarization causes the K+ Channel gate to immediately open. K+ diffuses out of the neuron. This
reestablishes the initial electrical potential of ~ -70 mV.
Refractory Period
During this time (~ 1 msec), the Na+ and K+ Channels cannot be opened by a stimulus.
The Na+/K+ Pump actively pumps Na+ out of the neuron and K+ into the neuron. This reestablishes the
initial ion distribution of the resting neuron.
This single action potential acts as a stimulus to neighbouring proteins and initiates an action potential in
another part of the neuron. Ultimately a wave of action potentials travel from the dendrites all the way to the
axon terminals. At the axon terminal, the electrical impulse is converted to a chemical signal
Blood component: A Fluid Tissue
Blood can be divided into:
1- A plasma portion (water, salts, gases, ions, nutrient molecules, and proteins) Plasma is the
liquid portion of the blood - protein-salt solution in which red and white blood cells and platelets
are suspended. Plasma, which is 90 percent water, constitutes about 55 percent of blood volume.
Plasma contains albumin (the chief protein constituent), fibrinogen (responsible, in part, for the
clotting of blood), globulins (including antibodies), and other clotting proteins. Plasma serves a
variety of functions:
- Maintaining a satisfactory blood pressure and volume to supplying critical proteins for blood
clotting and immunity.
- It also serves as the medium of exchange for vital minerals such as sodium and potassium, thus
helping maintain a proper balance in the body, which is critical to cell function.
2- A cellular portion (red blood cells, white blood cells, and platelets). All of the cellular
components are produced from stem cells in the bone marrow:
Red blood cells transport respiratory gases. Red blood cells contain hemoglobin, a complex iron-containing
protein that carries oxygen throughout the body and gives blood its red color. The percentage of blood volume
composed of red blood cells is called the “hematocrit.” The average hematocrit in an adult male is 47 percent.
Their production in the bone marrow is stimulated by erythropoietin, which is produced in response to
hypoxia in the tissues. They live for approximately 120 days in the circulatory system and are eventually
removed by the spleen
White blood cells are responsible for protecting the body from invasion by foreign substances such as
bacteria, fungi, and viruses. The majority of white blood cells are produced in the bone marrow, where they
outnumber red blood cells by two to one. However, in the blood stream, there are about 600 red blood cells
for every white blood cell. There are several types of white blood cells; Granulocytes and macrophages
protect against infection by surrounding and destroying invading bacteria and viruses, and lymphocytes aid in
immune defense.
Platelets, along with circulating proteins, are involved in blood clotting. Platelets are made in the bone
marrow and survive in the circulatory system for an average of 9–10 days before being removed from the
body by the spleen.
ABO Blood Types
The most well known and medically important blood types are in the ABO group. They were discovered in
1900 and 1901 at the University of Vienna by Karl Landsteiner in the process of trying to learn why blood
transfusions sometimes cause death and at other times save a patient. In 1930, he belatedly received the
Nobel Prize for this discovery.
All humans and many other primates can be typed for the ABO blood group. There are four types: A, B, AB,
and O. There are two antigens and two antibodies that are mostly responsible for the ABO types. The
specific combination of these four components determines an individual's type in most cases. The table below
shows the possible permutations of antigens and antibodies with the corresponding ABO type ("yes" indicates
the presence of a component and "no" indicates its absence in the blood of an individual).
ABO
Blood Type
A
B
O
AB
Antigen
A
Antigen
B
Antibody Antibody
anti-A
Anti-B
yes
no
no
yes
No
Yes
No
Yes
no
yes
yes
no
yes
no
yes
no
For example, people with type A blood will have the A antigen on the surface of their red cells (as shown in
the table below). As a result, anti-A antibodies will not be produced by them because they would cause the
destruction of their own blood. However, if B type blood is injected into their systems, anti-B antibodies in
their plasma will recognize it as alien and burst or agglutinate the introduced red cells in order to cleanse the
blood of alien protein.
Please learn the following two expressions:
Phenotype: Appearance of an organism, resulting from the interaction of its genotype and its environment
Genotype: Genetic constitution of an individual
Blood
Group
Antigens
on RBCs
Antibodies in
Serum
Genotypes
A
A
Anti-B
AA or AO
B
B
Anti-A
BB or BO
AB
A and B
Neither
AB
O
Neither Anti-A and anti-B
OO
Blood with phenotype A has AA or AO genetypes
Blood with phenotype B has BB or BO genotypes
Blood with pheotype O has OO genotype
Blood with phenotype AB has AB genotype
Individuals with type O blood do not produce ABO antigens. Therefore, their blood normally will not be
rejected when it is given to others with different ABO types. As a result, type O people are universal donors
for transfusions, but they can receive only type O blood themselves. Those who have type AB blood do not
make any ABO antibodies. Their blood does not discriminate against any other ABO type. Consequently,
they are universal receivers for transfusions, but there blood will be agglutinated when given to people with
every other type because they produce both kinds of antigens.
Enzymes: Biological Catalysts
Enzymes are biological catalysts, proteins that are highly specific for their substrates. Substrates bind to the
active site, where catalysis takes place, forming an enzyme-substrate complex.
At the active site, a substrate can be oriented correctly, chemically modified, or strained. As a result, the
substrate readily forms its transition state, and the reaction proceeds.
The active site where substrate binds determines the specificity of an enzyme. Upon binding to substrate,
some enzymes change shape, facilitating catalysis
Some enzymes require cofactors to carry out catalysis. Prosthetic groups are permanently bound to the
enzyme. Coenzymes are not usually bound to the enzyme. They can be considered substrates, as they are
changed by the reaction and then released from the enzyme.
Metabolism is organized into pathways in which the product of one reaction is a reactant for the next reaction.
Each reaction in the pathway is catalyzed by an enzyme.
Enzymes are sensitive to their environment.Both pH and temperature affect enzyme activity.
Human endocrine system
Endocrine cells secrete chemical messages called hormones, which bind to receptors on or in target cells.
Most hormones are peptides, proteins, steroids, or amines. Peptide and protein hormones and some amines are
water-soluble; steroids and some amines are lipid-soluble.
The receptors for water-soluble hormones are on the cell surface. The receptors for lipid-soluble hormones are
inside the cell.
Some hormones diffuse to targets near the site of secretion. Autocrine hormones influence the cell that
secretes them; paracrine hormones influence nearby cells.
Most hormones are distributed throughout the body by the circulatory system.
Hormones cause different responses in different target cells.
Vertebrate Endocrine Systems
Humans have eight major endocrine glands that secrete many hormones
1- The pituitary gland is divided into two parts. The anterior pituitary and the posterior pituitary
The posterior pituitary secretes two neurohormones, antidiuretic hormone and oxytocin.
The anterior pituitary secretes tropic hormones (thyrotropin, adrenocorticotropin, luteinizing
hormone, and follicle- stimulating hormone), as well as growth hormone, prolactin, melanocytestimulating hormone.
2- The anterior pituitary is controlled by neurohormones produced by cells in the hypothalamus and
transported through portal blood vessels to the anterior pituitary.
3, 4- The thyroid gland is controlled by thyrotropin and secretes thyroxine, which controls cell
metabolism. The level of calcium in the blood is regulated by three hormones. Calcitonin
(produced by Parathyroid gland) lowers blood calcium by promoting bone deposition. Parathyroid
hormone (produced by Parathyroid gland) raises blood calcium by promoting bone turnover and
decreased calcium excretion.
5- The pancreas secretes three hormones. Insulin stimulates glucose uptake by cells and lowers
blood glucose, glucagon raises blood glucose, and somatostatin slows the rate of nutrient
absorption from the gut.
6- The adrenal gland has two portions, one within the other. The hormones of the adrenal medulla,
epinephrine and norepinephrine, stimulate the liver to supply glucose to the blood, as well as other
fight-or-flight reactions. The adrenal cortex produce three classes of corticosteroids:
glucocorticoids , mineralocorticoids, and small amounts of sex steroids. Aldosterone is a
mineralocorticoid that stimulates the kidney to conserve sodium and to excrete potassium.
Cortisol is a glucocorticoid that decreases glucose utilization by most cells.
7- Sex hormones (androgens in males, estrogens and progesterone in females) are produced by the
gonads in response to tropic hormones. Sex hormones control sexual development, secondary
sexual characteristics, and reproductive functions.
8- The pineal hormone produce melatonin is involved in controlling biological rhythms and photoperiodism.
Human Excretory System
Our kidneys are located on
either side of the spine, just
up under the bottom ribs.
They are well supplied
with blood via the renal
artery and renal vein.
Urine made in the kidney
collects in the renal pelvis
within the kidney, then
flows down the ureter to
the bladder where it is
stored until voided. From
the bladder, the urine flows Front view of urinary tract
to the outside via the
urethra, (which in the
male also serves as part of
the reproductory tract).
The kidney is composed of
an outer layer, the cortex,
and an inner core, the
medulla. The kidney
consists of repeating units
(tubules) called nephrons.
The “tops” of the nephrons
make up or are in the
cortex, while their long
tubule portions make up
the medulla. To the right is
a diagram of an individual
nephron. Each nephron has a closely associated blood supply. Blood comes in at the glomerulus and transfers
water and solutes to the nephron at Bowman’s capsule. In the proximal tubule, water and some “good”
molecules are absorbed back into the body, while a few other, unwanted molecules/ions are added to the
urine. Then, the filtrate goes down the loop of Henle (in the medulla) where more water is removed (back
into the bloodstream) on the way “down”, but the “up” side is impervious to water. In the distal tubule, more
water and some “good” solutes are removed from the urine, while some more unwanted molecules are put in.
From there, the urine flows down a collecting duct which gathers urine from several nephrons. As the
collecting duct goes back through the medulla, more water is removed from the urine. The collecting ducts
eventually end up at the renal pelvis which collects the urine from all of them. The area where the collecting
ducts enter the renal pelvis is a common area for formation of kidney stones, often giving them a “staghorn”
shape.
As you can see above: The glomeruli and the proximal and distal convoluted tubules are located in the cortex
of the kidney. Certain molecules are actively resorbed from the glomerular filtrate by the tubule cells, and
other molecules are actively secreted. Straight sections of
renal tubules called loops of Henle and collecting ducts are arranged in parallel in the medulla of the kidney.
.
Regulation of Kidney Functions
Kidney function in mammals is controlled by autoregulatory mechanisms that maintain a constant high
glomerular filtration rate even if blood pressure varies.
An important autoregulatory mechanism is the release of renin by the kidney when blood pressure falls.
Chromosomes, the Cell Cycle, and Cell Division
Cell division must be initiated by a reproductive signal. Cell division consists of three steps: replication of the
genetic material (DNA), segregation of the two DNA molecules to separate portions of the cell, and
cytokinesis, or division of the cytoplasm.
In prokaryotes, cellular DNA is a single molecule, or chromosome. Prokaryotes reproduce by cell fission.
In eukaryotes, cells divide by either mitosis or meiosis.
Interphase and the Control of Cell Division
The mitotic cell cycle has two main phases: interphase (during which cells are not dividing) and mitosis
(when cells are dividing).
During most of the cell cycle, the cell is in interphase, which is divided into three subphases: S, G1, and G2.
DNA is replicated during the S phase.
Eukaryotic Chromosomes
A eukaryotic chromosome contains a DNA molecule bound to proteins in a complex called chromatin. At
mitosis, the replicated chromatids are held together at the centromere. Each chromatid consists of one doublestranded DNA molecule.
During interphase, the DNA in chromatin is wound around cores of histones (protein) to form nucleosomes.
DNA folds over and over again, packing itself within the nucleus. During mitosis or meiosis, it folds even
more.
Mitosis: Distributing Exact Copies of Genetic Information
After DNA is replicated during the S phase, the first sign of mitosis is the separation of the replicated
centrosomes, which initiate microtubule formation for the spindle.
Mitosis can be divided into several phases, called prophase, prometaphase, metaphase, anaphase, and
telophase.
During prophase, the chromosomes condense and appear as paired chromatids, and the spindle forms.
During prometaphase, the chromosomes move toward the middle of the spindle. In metaphase, they gather at
the middle of the cell with their centromeres on the equatorial plate. At the end of metaphase, the centromeres
holding the sister chromatids together separate, and during anaphase, each chromatid, now called the daughter
chromosome, migrates to its pole along the microtubule track.
During anaphase sister chromatids are separate.
During telophase, the chromosomes become less condensed. The nuclear envelopes and nucleoli re-form, thus
producing two nuclei whose chromosomes are identical to each other and to those of the cell that began the
cycle.
Cytokinesis: The Division of the Cytoplasm
Nuclear division is usually followed by cytokinesis. Animal cell cytoplasm usually divides by a furrowing of
the plasma membrane, caused by the contraction of cytoplasmic microfilaments
Reproduction: Asexual and Sexual
The cell cycle can repeat itself many times, forming a clone of genetically identical cells.
Asexual reproduction produces a new organism that is genetically identical to the parent. Any genetic variety
is the result of mutations.
In sexual reproduction, two haploid gametes—one from each parent—unite in fertilization to form a
genetically unique, diploid zygote.
In sexually reproducing organisms, certain cells in the adult (testes and ovary) undergo meiosis, a process by
which a diploid cell (cell with 46 chromosomes) produces haploid gametes (23 chromosomes).
Each gamete contains a random selection of one of each pair of homologous chromosomes(one from mother
and one from father) as it comes to gether it forms diploid cell (46 chromosomes) the zygote which grows to
form embryo.
Meiosis: A Pair of Nuclear Divisions
Meiosis reduces the chromosome number from diploid to haploid, ensures that each haploid cell contains one
member of each chromosome pair, and results in genetically diverse products. It consists of two nuclear
divisions.
During prophase I of the first meiotic division, homologous chromosomes pair up with each other, and
material may be exchanged between the two homologs by crossing over. In metaphase I, the paired homologs
line up at the equatorial plate.
In anaphase I, entire chromosomes, each with two chromatids, migrate to the poles. By the end of meiosis I,
there are two nuclei, each with the haploid number of chromosomes.
In meiosis II, the sister chromatids separate. No DNA replication precedes this division, which in other
aspects is similar to mitosis. The result of meiosis is four cells, each with a haploid chromosome content.
The Genetic Code
The genetic code consists of triplets of nucleotide bases (codons). There are four bases, so there are 64
possible codons.
One mRNA codon indicates the starting point of translation and codes for methionine. Three stop codons
indicate the end of translation. The other 60 codons code only for particular amino acids.
Because there are only 20 different amino acids, the genetic code is redundant; that is, there is more than one
codon for certain amino acids. But the code is not ambiguous: A single codon does not encode more than one
amino acid.
6.3 What are enzymes?
The rate of a chemical reaction is independent of ΔG, but is determined by the energy barrier.
Enzymes are protein catalysts that affect the rates of biological reactions by lowering the energy
barrier, supplying the activation energy needed to initiate a reaction.
Substrates bind to the enzyme's active site—the site of catalysis—forming an enzyme–substrate
complex. Enzymes are highly specific for their substrates.
6.4 How do enzymes work?
Binding substrate causes many enzymes to change shape, exposing their active site(s) and allowing
catalysis. The change in enzyme shape caused by substrate binding is known as induced fit. Some
enzymes require other substances, known as cofactors, to carry out catalysis. Prosthetic groups are
permanently bound to the enzyme; coenzymes are not. Coenzymes can be considered substrates, as
they are changed by the reaction and then released from the enzyme.
44.1 What cells are unique to the nervous systems?
Nervous systems include neurons and glial cells. Neurons are organized in circuits with sensory
inputs, integration, and outputs to effectors. Glial cells serve support functions.
In vertebrates, the brain and spinal cord form the central nervous system, which communicates with
the rest of the body via the peripheral nervous system. The CNS increases in complexity from
invertebrates to vertebrates and from fish to mammals.
Neurons generally receive information via their dendrites, of which there can be many, and transmit
information via their single axons, which end in axon terminals. Review Figure 44.3
Where neurons and their target cells meet, information is transmitted across specialized junctions called
synapses.
44.2 How do neurons generate and conduct signals?
See Web/CD Tutorial 44.1
Neurons have an electric charge difference across their plasma membranes, the membrane potential.
The membrane potential is created by ion pumps and ion channels. When a neuron is not active, its
membrane potential is a resting potential.
The sodium-potassium pump concentrates K+ on the inside of a neuron and Na + on the outside.
Potassium channels allow K+ to diffuse out of the neuron, leaving behind unbalanced negative charges.
The resting potential is perturbed when ion channels open or close, changing the permeability of the
plasma membrane to charged ions. Through this mechanism, the plasma membrane can become
depolarized or hyperpolarized. Review Figure 44.9
An action potential is a rapid reversal in charge across a portion of the plasma membrane resulting
from the sequential opening and closing of voltage-gated Na+ and K+ channels. These changes in
voltage-gated channels occur when the plasma membrane depolarizes to a threshold level.
Action potentials are all-or-none, self-regenerating events. They are conducted down axons because
local current flow depolarizes adjacent regions of membrane and brings them to threshold.
In myelinated axons, action potentials appear to jump between nodes of Ranvier,
44.3 How do neurons communicate with other cells?
Neurons communicate with each other and with other cells by transmitting information over chemical
synapses (with neurotransmitters) or electrical synapses.
The neuromuscular junction is a well-studied chemical synapse between a motor neuron and a
skeletal muscle cell. Its neurotransmitter is ACh, which causes a depolarization of the postsynaptic
membrane when it binds to its receptor.
When an action potential reaches an axon terminal, it causes the release of neurotransmitters, which
diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
Ionotropic receptors are ion channels or directly influence ion channels. Metabotropic receptors are
G protein-linked receptors that influence the postsynaptic cell through various signal transduction
pathways and result in the opening or closing of ion channels. The actions of ionotropic synapses are
generally faster than those of metabotropic synapses
50.1 What do animals require from food?
Animals are heterotrophs that derive their energy and molecular building blocks, directly or indirectly,
from autotrophs.
Carbohydrates, fats, and proteins in food supply animals with metabolic energy. A measure of the
energy content of food is the kilocalorie. Excess caloric intake is
Humans require eight essential amino acids in the diet. Different animals need mineral elements in
different amounts. Macronutrients are needed in large quantities. Micronutrients are needed in small
amounts. Review Figure 50.5 and
Vitamins are organic molecules that must be obtained in food. Review Table 50.2 (Part 1), 50.2
(Part 2),
Fat Soluble Vitamins
Fat-soluble vitamins are absorbed, together with fat from the intestine, into the circulation. Once absorbed
into the circulation these vitamins are carried to the liver where they are stored.
Vitamins A, D, E and K make up the fat soluble vitamins. Vitamins A, D and K are stored in the liver and
vitamin E is distributed throughout the body's fatty tissues.
Water Soluble Vitamins
Water-soluble vitamins, such as Vitamin C and the B vitamins are stored in the body for only a brief period of
time and are then excreted by the kidneys. The one exception to this is vitamin B12, which is stored in the
liver. Water-soluble vitamins need to be taken daily.
Vitamin sources, uses and deficiency problems
Vitamin A (fat-soluble)



Sources: Dairy products, eggs, liver. Can be converted by the body from the beta-carotene found in
green vegetables, carrots and liver.
Uses: Maintains the health of the epithelium and acts on the retina's dark adaptation mechanism.
Deficiency leads to night blindness
Vitamin B1 (thiamine) (water-soluble)



Sources: Yeast, egg yolk, liver, wheatgerm, nuts, red meat and cereals
Uses: Carbohydrate metabolism
Deficiency leads to: Fatigue, irritability, loss of appetite; severe deficiency can lead to beri-beri
Vitamin B2 (riboflavin) (water-soluble)



Sources: Dairy products, liver, vegetables, eggs, cereals, fruit, yeast
Uses: Intracellular metabolism
Deficiency leads to: Painful tongue and fissures
Vitamin B12 (water-soluble)



Sources: Liver, red meat, dairy products and fish
Uses: Essential for manufacturing of genetic material in cells. Involved in the production of
erythrocytes
Deficiency leads to: pernicious anaemia
Vitamin C (ascorbic acid) (water-soluble)



Sources: Green vegetables and fruit
Uses: Essential for the maintenance of bones, teeth and gums, ligaments and blood vessels. It is also
necessary for ensuring a normal immune response to infection
Deficiency leads to: Scurvy
Vitamin D (fat-soluble)



Sources: Fish liver oils, dairy produce. Vitamin D is formed in the skin when it is exposed to sunlight
Uses: Has a role in the absorption of calcium, which is essential for the maintenance of healthy bones
Deficiency leads to: Rickets
Vitamin E (fat-soluble)



Sources: Pure vegetable oils; wheatgerm, wholemeal bread and cereals, egg yoke, nuts sunflower
seeds
Uses: Protects tissues against damage; promotes normal growth and development; helps in normal red
blood cell formation
Deficiency leads to: May cause muscular dystrophy
Vitamin K (fat-soluble)



Sources: Green vegetables
Uses: Used by the liver for the formation of prothrombin
Deficiency leads to: Bleeding due to delayed clotting times caused by lack of clotting factors.
5.2 How do animals ingest and digest food?
Digestion involves the breakdown of complex food molecules into monomers that can be absorbed and
utilized by cells. In most animals, digestion takes place in a tubular gut. Review Figure 50.8
Absorptive areas of the gut are characterized by a large surface area produced by extensive folding and
numerous villi and microvilli. Review Figure 50.9
Hydrolytic enzymes break down proteins, carbohydrates, and fats into their monomeric units. To prevent
the organism itself from being digested, many of these enzymes are released as inactive zymogens,
which become activated when secreted into the gut.
50.3 How does the vertebrate gastrointestinal system function?
The vertebrate gut can be divided into several compartments with different functions. Review Figure
50.10, Web/CD Activity 50.4
The cells and tissues of the vertebrate gut are organized in the same way throughout its length. The
innermost tissue layer, the mucosa, is the secretory and absorptive surface. The submucosa contains
blood and lymph vessels, and a nerve plexus. External to the submucosa are two smooth muscle
layers. Between the two muscle layers is another nerve plexus that controls the movements of the gut.
Review Figure 50.11
Swallowing is a reflex that pushes the bolus of food into the esophagus. Peristalsis and other
movements of the gut move the bolus down the esophagus and through the entire length of the gut.
Sphincters block the gut at certain locations, but they relax as a wave of peristalsis approaches.
Review Figure 50.12
Digestion begins in the mouth, where amylase is secreted with the saliva. Digestion of protein begins in
the stomach, where parietal cells secrete HCl and chief cells secrete pepsinogen, a zymogen that
becomes pepsin when activated by low pH and autocatalysis. The mucosa also secretes mucus,
which protects the tissues of the gut. Review Figure 50.13
In the duodenum, pancreatic enzymes carry out most of the digestion of food. Bile from the liver and
gallbladder emulsify fats into micelles. Bicarbonate ions from the pancreas neutralize the pH of the
chyme entering from the stomach to produce an environment conducive to the actions of pancreatic
enzymes such as trypsin. Review Figure 50.15 and Table 50.3 (Part 1), 50.3 (Part 2)
Final enzymatic cleavage of polypeptides and disaccharides occurs among the microvilli of the intestinal
mucosa. Amino acids, monosaccharides, and inorganic ions are absorbed by the microvilli. Specific
transporter proteins are sometimes involved. Sodium co-transport often powers the active transport of
nutrients.
Fats broken down by lipases are absorbed mostly as monoglycerides and fatty acids and are
resynthesized into triglycerides within cells. The triglycerides are combined with cholesterol and
phospholipids and coated with protein to form chylomicrons, which pass out of the mucosal cells and
into lymphatic vessels in the submucosa. Review Figure 50.16, Web/CD Tutorial 50.1
Water and ions are absorbed in the large intestine as waste matter is consolidated into feces, which is
periodically eliminated.
50.4 How is the flow of nutrients controlled and regulated?
Autonomic reflexes coordinate activity of the digestive tract, which has an intrinsic nervous system that
can act independently of the CNS.
The actions of the stomach and small intestine are largely controlled by the hormones gastrin,
secretin, and cholecystokinin. Review Figure 50.18
The liver plays a central role in directing the traffic of fuel molecules. During the absorptive period, the
liver takes up and stores fats and carbohydrates, converting monosaccharides to glycogen or fats. The
liver also takes up amino acids and uses them to produce blood plasma proteins, and can engage in
gluconeogenesis.
Fat and cholesterol are shipped out of the liver as low-density lipoproteins. High-density
lipoproteins act as acceptors of cholesterol and are believed to bring fat and cholesterol back to the
liver.
Insulin largely controls fuel metabolism during the absorptive period and promotes glucose uptake as
well as glycogen and fat synthesis. During the postabsorptive period, lack of insulin blocks the uptake
and utilization of glucose by most cells of the body except neurons. If blood glucose levels fall,
glucagon secretion increases, stimulating the liver to break down glycogen and release glucose to the
blood. Review Figure 50.19, Web/CD Tutorial 50.2
Food intake is governed by sensations of hunger and satiety, which are determined by brain
mechanisms. Review Figure 50.20
18.1 What are the major defense systems of animals?
Animal defenses against pathogens are based on the body's ability to distinguish between self and
nonself.
Nonspecific (innate) defenses are inherited mechanisms that protect the body from many kinds of
pathogens and typically act rapidly.
Specific defenses are adaptive mechanisms that respond to a specific pathogen. They develop slowly
but are long-lasting.
Many defenses are implemented by cells and proteins carried in the blood plasma and lymph. Review
Figure 18.1, Web/CD Activity 18.1
White blood cells fall into two broad groups. Phagocytes include macrophages that engulf
pathogens by phagocytosis. Lymphocytes, which include B cells and T cells, participate in specific
responses. Review Figure 18.2, Web/CD Tutorial 18.1
18.2 What are the characteristics of the nonspecific defenses?
Humoral and cellular immune response in humans.
An animal's nonspecific defenses include physical barriers such as the skin and competing resident
microorganisms known as normal flora. Review Table 18.1 Part 1, 18.1 Part 2
Circulating defensive cells, such as phagocytes and natural killer cells, eliminate invaders.
The inflammation response calls on several cells and proteins that act against invading pathogens.
Mast cells release histamines, which cause blood vessels to dilate and become "leaky." Review
Figure 18.4, Web/CD Activity 18.2
A cell signaling pathway involving the toll receptor stimulates the body's defenses.
18.3 How does specific immunity develop?
See Web/CD Tutorial 18.2
The specific immune response is characterized by recognition of specific antigens, mechanisms for
developing a response to an enormous diversity of antigenic determinants, the ability to distinguish
self from nonself, and immunological memory of the antigens it has encountered.
Each antibody and each T cell is specific for a single antigenic determinant. T cell receptors bind to
antigens on the surface of virus-infected cells.
The humoral immune response is directed against pathogens in the blood, lymph, and tissue fluids.
The cellular immune response is directed against an antigen established within a host cell. Both
responses are mediated by antigenic fragments being presented on a cell surface along the proteins of
the major histocompatibility complex.
Clonal selection accounts for the specificity and diversity of the immune response as well as
immunological memory and tolerance to self. Review Figure 18.6
An activated lymphocyte produces effector cells that carry out an attack on the antigen and memory
cells that retain the ability to divide to produce more effector and memory cells. Effector B cells are
called plasma cells.
18.4 What is the humoral immune response?
See Web/CD Tutorial 18.3
B cells are the basis of the humoral immune response. Activated B cells, stimulated by signals from
helper T cells with the same specificity, form plasma cells, which synthesize and secrete specific
antibodies.
The basic unit of an antibody, or immunoglobulin, is a tetramer of four polypeptides: two identical
light chains and two identical heavy chains, each consisting of a constant region and a variable
region. Review Figure 18.9, Web/CD Activity 18.3
18.5 What is the cellular immune response?
See Web/CD Tutorial 18.4
T cells are the effectors of the cellular immune response. T cell receptors are similar in structure to the
immunologlobulins, having variable and constant regions. Review Figure 18.12
There are two types of T cells. Cytotoxic T cells recognize and kill virus-infected cells or mutated cells.
Helper T cells direct both the cellular and humoral immune responses.
The genes of the major histocompatibility complex (MHC) encode membrane proteins that bind antigenic
fragments and present them to T cells. Review Figure 18.13
18.6 How do animals make so many different antibodies?
See Web/CD Tutorial 18.5
B cell genomes undergo changes as the cell develops so that each cell can produce a specific antibody
protein. The immunoglobulin chains derive from "supergenes" that are constructed from one each of
numerous V, D, J, and C genes. This DNA rearrangement and rejoining yields a unique immunoglobulin
chain. Review Figures 18.16 and 18.17