Isotopes: Isotopes are atoms with the same number of protons but differ in number of neutrons; e.g., a carbon atom has six protons but may have more or less than usual six neutrons

Valence Shell: Outer shell of an atom. Atoms with few electrons in their valence shell tend to have more free electrons since these valence electrons are more loosely bound to the nucleus.

Ionic Bonds: Ionic bonds form when electrons are transferred from one atom to another. Losing or gaining electrons, atoms participating in ionic reactions fill outer shells, and are more stable.

Covalent Bonds: Covalent bonds result when two atoms share electrons so each atom has octet of electrons in the outer shell. . Structural formulas represent shared atom as a line between two atoms; e.g., single covalent bond (H-H), double covalent bond (O=O)Three dimensional shape of molecules is not represented by structural formulas but shape is critical in understanding the biological action of molecules: action of insulin, HIV receptors, etc.

Hydrogen Bond forms between…› slightly positive hydrogen atom of one

molecule and slightly negative atom in another or the same molecule.

pH is a measure of…› How acidic or basic a solution is.

Acidic Solution has more H+ ions Basic Solution has more –OH ions

Buffer is› keep pH steady and within normal limits in

living organisms..

Isomer is…› Are molecules or molecular compounds

that are similar in that they have the same molecular formula, however have different arrangements of the atoms or groups of atoms (functional groups) involved.

› Example: Fructose and glucose (C6H12O6) – same molecular formula but different arrangements

› -OH – Hydroxyl› C=O Carbonyl› -COOH Carboxyl

› -NH2 Amino group

› -SH Sulfhydryl group

› -OPO3 Phosphate group

Hydrolysis Reaction› Reaction that breaks down compounds by the addition of H2O

Dehydration synthesis reaction› Reaction in which two compounds are brought together with

H2O released as a product

Endergonic reaction› A reaction that requires the input of energy to occur

A+B+energy C

Exergonic reaction› A reaction that gives off energy as a product

A+BEnergy +C

Redox reaction› A reaction involving the transfer of electrongs

General formula for monosaccharides are CnH2nOn

Example: C6H12O6 (Glucose) Simple Sugar

› Function: Sugar found in Nucleic Acid› Glucose: Sugar for the body› ATP: Cell Energy

Polysaccharides: Carbohydrate containing 3 or more monosaccharides

Storage form of energy Structural material in and around cells Difference between

› Glycogen: Glucose molecules linked together (animal energy storage)

› Starch: Glucose linked together (Plants energy storage)

› Cellulose: composed of glucose molecules –formation of cell walls

› Chitin: Glucose molecules joined together- Arthopods exoskeleton

Structural Components of the following…› Fats: Lipids made by combining glycerol and

three fatty acids. Used as long-term energy stores in cells

› Phospholipids: is a lipid formed by combining a glycerol molecule with two fatty acids and a phosphate group; bilayered structure – component in cell membrane

› Steroids: are lipids composed of four carbon rings that look like chicken wire. Examples: Cholesterol, sex hormones

Cholesterol

Testosterone

Protein Chains:› Primary Structure: Sequence of amino acids to

form a polypeptide chain (protein)› Secondary Structure: 3-D arrangement of a

protein caused by hydrogen bonding at regular intervals along the polypeptide backbone

› Tertiary Structure: 3-D arrangement of protein caused by interactions among the various R groups of the amino acids involved.

› Quaternary structure: The arrangement of separate polypeptide “subunits” into a single protein

Enzymes are proteins that act as organic catalyst (speed up reaction by lowering the energy (activation energy) needed for the reaction to take place but are not used up in the reaction.

Induced-fit model: of enzyme-substrate interaction describes the active site of an enzyme as specific for a particular substrate that fits its shape.

Allosteric enzyme: An allosteric enzyme is an enzyme that contains a region to which small, regulatory molecules ("effectors") may bind in addition to and separate from the substrate binding site and thereby affect the catalytic activity. On binding the effector, the catalytic activity of the enzyme towards the substrate may be enhanced, in which case the effector is an activator, or reduced, in which case it is a de-activator or inhibitor

Four ways enzymes can be affected:› Temperature› pH› Concentration of the substrate› Concentration of the enzyme involved

Prokaryotic: Simple cell › No nucleus

Nucleoid : Genetic material

› No membrane bond organelles Eukaryotic is more complex

› Nucleus› Membrane bound organelles

Ribosomes: protein synthesis Smooth ER: lipids synthesis, detoxification, and

carbohydrate metabolism Rough ER: Ribosome are attached – proteins are

produced Golgi apparatus: proteins, lipids, and other

macromolecules sent to the Golgi to be modified by the addition of sugars and other molecules to form glycoproteins – products form vesicles

Mitochondria: powerhouse—ATP is made here Lysosome: Digestion center Nucleus: Control center, contains DNA (genetic

material) Vacuole: Storage (Plants have a larger structure) Chloroplast: Plants only – site for photosynthesis

Fluid Mosaic Model: the membrane consist of a phospholipid bilayer with proteins of various lengths and sizes interspersed with cholesterol among the phospholipids.

Two types of proteins in the cell membrane:› Integral proteins: implanted within the bilayer

and can extend partway or all the way across the membrane

› Peripheral proteins: such as receptor proteins, which are not implanted in the bilayer and are often attached to integral proteins of the membrane

Difference between…› Diffusion: movement of molecules down their

concentration gradient with the use of energy (area of higher concentration to lower concentration)

› Osmosis: movement of water down its concentration gradient (passive diffusion). Going from a higher water concentration to area of lower water concentration

› Active Transport: is the movement of a particle across a selectively permeable membrane against the concentration gradient (Going from low to high concentration)

Hyperosmotic (Hypertonic): moving of water from a high solute in the environment to area of low solute concentration to environment. The water will move out of the cell

60% water40% solute

40% water60% solute

Hypoosmotic (hypotonic): Is when the solute concentration is more in the cell than outside the cell. The water will move in of the cell

40% Water 60% Solute

60% water40% solute

Isosmotic (Isotonic): The solute and water is on the same on both sides

50% solute50% water

50% solute50% water

Phases of Mitosis:› Prophase: Nuclear envelope disappears,

chromatids appear, centrioles moves to poles

› Metaphase: chromosomes move toward the center –Spindle are attached to the centromere

› Anaphase: Chromatids separate and move toward the poles

› Telophase: Chromatids move toward each poles, nuclear envelope reappears, cytokinesis begins

Mitosis: is the dividing of body cells› Daughter cells will have the exact number

chromosomes as the parent cells

Meiosis : is the dividing of sex cells› Daughter cells will have half the number of

chromosomes as the parent cells

Cell cycle includes:› Interphase: the stage that prepares the

cell for the cell division› Mitosis: is the division of the nucleus› Cytokinesis: division of the cytoplasm

This is the way in which the cell has a type of check and balance system that ensures the cell is correct› Checkpoints› Density-dependent inhibition› Growth Factors› Cyclin and Protein kinases

You may want to go back and look over this information

Mitosis MeiosisNumber of cells 2 diploid cells 4 haploid cells

Crossing over No Yes-Prophase I

Number of phases 1 (IPMATC) 2 (IPMATC & PMATC)No Interphase in the second phase

Types of cells Body (Somatic) Cells Sex (Gamete) Cells

Number of chromosomes

Same number of chromosomes as the parent cellDiploid

Different number of chromosomes as the parent cellHaploid

Genetics Genetically Identical to the parent cell

Genetically different to the parent cell

The difference between meiosis I and meiosis II is that the cell does not go through interphase (Chromsome replication) during meiosis II. This will allow the cells to have half the number of chromsomes (haploid).

Crossing over is when the homologous chromosomes match up during prophase I of meiosis, complementary pieces from the two homologous chromosomes wrap around each other and are exchanged between the chromosomes.

Three parts to a nucleotide are…5 carbon sugar, phosphate, and nitrogen base› Serves as a puzzle piece to the nucleic acid

strand (RNA or DNA) Adenine and guanine are purines Cytosine and Thymine are pyrimidine Base pairing states that Adenine will pair

up with thymine and Cytosine will pair up with Guanine (Apple=Tart and Go=Cart)

DNA replication occurs during the S-phase (interphase), semiconservative (which the one strands serves a template)

Built in the 5’ to 3’ direction DNA helicase will unzip the strand by

breaking the hydrogen bonds producing a replication fork

Specific regions along DNA strand serve as primer sites that signal where replication should originate

DNA polymerase – enzyme superstar binds to the primer site and adds nucleotides to the growing DNA chain (will only add to the 3’ end)

The DNA polymerase only being used on the 3’ creates a problem which only allows the one strand to add nucleotides this is known as the leading strand.

The other strand is known as the lagging strand

The lagging strand consist of tiny pieces called Okazaki fragments, which are later connected by an enzyme called DNA ligase to produce the completed double stranded DNA molecule

RNA primer allows for the RNA strand to bind to the DNA strand (this occurs during replication)

DNA can only stay in the nucleus so it must send its instructions out to the cell. This is done by the second nucleic acid (RNA).

Because DNA and RNA have very similar language it allows it to be accomplished.

Transcription: is the process of taking DNA to a RNA strand (Occurs in the nucleus)› This is done by three steps:

Initiation: When RNA polymerase attaches to the promoter region of a DNA strand

Elongation: a promoter region recognition site that shows the polymerase where transcription will begin. Once RNA polymerase works by adding the appropriate RNA nucleotide to the 3’ of the growing strand

Termination: tells the polymerase should conclude

Translation: process by which the mRNA specified sequence of amino acids is lined up on a ribosome for protein synthesis (mRNA DNA)

Each amino acid carries a specific nucleotides/codes (codon)› Start Codon: AUG› Stop Codon: UAA, UAG, UGA

Anticodon is the complementary to the codon (tRNA) that has been incorporated into the growing protein

Define the following:› Promoter: a base sequence that signals the start

site of genes transcription; this is where RNA polymerase binds to the begin the process

› Operator: a short sequence near the promoter that assists in transcription by interacting with regulatory proteins

› Operon: promoter/operator pair that services multiple genes Well known example is the lac operon

› Repressor: protein that prevents the binding of RNA polymerase to the promoter site

› Enhancer: DNA region also known as “regulator” that is located thousands of bases away frm the promoter

› Inducer: a molecule that binds to and inactivates a repressor

Structural Gene: one that specifies the amino acid sequence of a polypeptide chain

Energy is…› The ability to do work

Entropy is the measure of amount of energy that is not available for work

ATP power cellular work the energy currency of cells (adenosine triphosphate)

Functions:1. CHEMICAL WORK - Supplies energy needed to make macromolecules that make up the cell (and organism)2. TRANSPORT WORK - Supplies energy needed to pump substances across the cell membrane3. MECHANICAL WORK - supplies energy needed to make muscles contract and other cellular parts to move (flagella)

Glycolysis› a) a ten-step process that occurs in the

cytoplasmb) converts each molecule of glucose to two molecules of pyruvic acid (a 3-carbon molecule)c) an anaerobic process - proceeds whether or not O2 is present ; O2 is not requiredd) net yield of 2 ATP per glucose moleculee) net yield of 2 NADH per glucose (NADH is nicotine adenine dinucleotide, a co-enzyme that serves as a carrier for H+ ions liberated as glucose is oxidized.)

Kreb Cycle –occurs in the mitochondria› a) occurs in the inner mitochondrial matrix

b) the acetyl group detaches from the co-enzyme A and enters the reaction cyclec) an aerobic process; will proceed only in the presence of O2d) net yield of 2 ATP per glucose molecule (per 2 acetyl CoA)e) net yield of 6 NADH and 2 FADH2 (FAD serves the same purpose as NAD)f) in this stage of cellular respiration, the oxidation of glucose to CO2 is completed

› GO BACK AND LOOK AT YOUR CYCLE

Electron Transport System – occurs in the mitochondria› a) consists of a series of enzymes on the inner

mitochondrial membraneb) electrons are released from NADH and from FADH2 and as they are passed along the series of enzymes, they give up energy which is used to fuel a process called chemiosmosis by which H+ ions are actively transported across the inner mitochondrial membrane into the outer mitochondrial compartment. The H+ ions then flow back through special pores in the membrane, a process that is thought to drive the process of ATP synthesis.c) net yield of 34 ATP per glucose moleculed) 6 H2O are formed when the electrons unite with O2* at the end of electron transport chain. [* Note: This is the function of oxygen in living organisms!]

Glycolysis occurs in the cytoplasm Kreb Cycle occurs in the mitochondria Electron Transport Chain occurs in the

mitochondria

Chemosismosis: electrons are released from NADH and from FADH2 and as they are passed along the series of enzymes, they give up energy which is used to fuel a process called chemiosmosis by which H+ ions are actively transported across the inner mitochondrial membrane into the outer mitochondrial compartment.

Photophosphorylation: ATP a second product made during the light reaction

Fermentation: an anaerobic respiration in which glucose is broken down to pyruvate during glycolysis. There is only a net gain of 2 ATP. There will be no Kreb Cycle or Electron Transport Chain

Two types of Fermentation:› Lactic Acid Fermentation: The production of

lactic acid without oxygen Examples: Milk products and muscles being

oxygen deficient

› Alcohol Fermentation: The production of ethyl alcohol and carbon dioxide Examples: Yeast (Bread and Alcoholic Beverages)

Two parts to photosynthesis are:› Light (light dependent) reaction: Occurs in the

thylakoid membrane(contains chlorophyll) Inputs to the light reactions are water and light Products: ATP, NADPH, and O2

Oxygen produced in the light reactions comes from H2O and not CO2

› Light Independent Reaction (dark reaction): Occurs in the stroma Inputs into the Calvin cycle are NADPH, ATP, and CO2

More ATP is used than NADPH creating a need for cylic photophosphorylation to create enough ATP for reaction

The carbon of the sugar produced in photosynthesis comes from the CO2 of the Calvin Cycle

Transpiration is the process of water evaporating out of the leaves. When the water goes out of the leaves the water the other parts of plants replace the water through the process known as the Cohesion Tension Theory

Most photosynthesis takes place in the mesophyll portion of the leaf

Aneuploidy: The fusing of an abnormal gamete with a normal one can lead to the production of offspring with an abnormal number of chromosomes

Polyploidy: a condition in which an individual has more than the normal number of sets of chromosomes

Structural Alternations of chromosomes are mutations. Chromosomal mutation which include inversion, deletion, duplications, translocation

What is the difference between linked and unlinked genes?› Linked Genes: group of genes on the same

chromosome If genes are close enough then there is a

higher probability of crossing over

› Unlinked Genes: Genes that are not on the same chromosome Only together if the Law of Independent

Assortment (Mendel’s Law)

Restriction Enzyme are enzymes that cut DNA at specific nucleotide sequence.

Gel Electrophoresis is a technique used to separate and examine DNA fragments. This is when restriction enzymes are used and then separated by electrophoresis. The pieces of DNA are separated on the basis of size with the help of an electric charge. This technique can be used to sequence DNA and determine the order in which the nucleotide appear.

Gel Electrophoresis can be used in forensics. This technique require the use of Restriction fragment length polymorphism (RFLP). DNA is specific of each individual and when it is mixed with restriction enzyme, different combination of RFLPs will be obtained from person to person

Polymerase Chain Reaction (PCR) can be used during Gel Electrophoresis but can also be used to sequence DNA › PCR will amplify the gene to be studied› PCR will allow scientist to study genetic

disorders and amplify trace amounts of DNA found at crime scences.

Applications of DNA technology Recombinant DNA: contains two or more different

sources› Cloning: slow process by which a desired sequence

of DNA is copied numerous times Gel Electrophoresis: technique used to

separate DNA according to size (small=faster). DNA moves from: - to +

Polymerase Chain Reaction (PCR): produces large quantities of sequence in short amount of time

Mutations: Genetic Mistakes Three types of muations are:

› Gene Mutation: Substitutes one bases for another This can include insertion, deletion, and point

mutations

› Chromosomal Mutation: The entire chromosome is messed up This includes inversion, duplication, translocation,

deletion

› Frameshift Mutation: either a base is added or deleted which causes a change in the reading frame

Three causes of mutation:› Radiation : X-rays and gamma waves› Viruses› Random: Age is one example– if a woman

pregnant over 40 has a greater chance for Down Syndrome

Difference between Viruses are protein coat, shape (popcorn ball compare to Apollo lunar lander), and Nucleic acid

Viral Reproduction› Lytic cycle = reproduction occurs, cells

burst› Lysogenic cycle = reproduction does not

immediately occur (dormancy)

Hardy-Weinberg Conditions› No mutations› No gene flow (immigration or emigration)› No genetic drift (populations must be kept

large)› No natural selection (All organisms have

the ability to survive and reproduce)› Random Mating

Hardy Weinberg equation p2 + 2 pq + q2 = 1 p2 Homozygous Dominant2pq Heterozygous Dominant q2 Homozygous Recessive

p. 144-145 – you may need to go back how to answer Hardy-Weinberg equation

Prezygotic barriers:› Behavioral Isolation: Different courtship

rituals› Temporal Isolation: Reproduces at different

times› Mechanical Isolation: reproductive structures

that does not allow reproduction› Gametic Mortality: Inability between sperm

and egg › Ecological Isolation: potential mates that can

reproduce but are not in the same area Postzygotic barriers: feterilization takes

place forming a hybrid

Allopatric Speciation: inbreeding ceases because some sort of barrier separates a single population into two (an area with no food, a mountain, etc.). The populations evolve independently, and if they change enough, then even if the barrier is removed, they can not interbreed

Sympatric speciation: Interbreeding ceases even though no physical barrier prevents it.› Two several forms

Polyploidy: a conditions in which an individual has more than the normal number of sets of chromosomes

Balanced polymorphism: this condition can lead to speciation if two variants diverge enough to no longer be able to interbreed

Microevolution: Evolution on a species level

Macroevolution: Evolution on a large scale

Genetic Drift: 1. Genetic drift refers to changes in

allele frequencies of a gene pool due to chance, more often in small populations2. Genetic drift occurs when founders start a new population, or after a genetic bottleneck with interbreeding.

Gene Flow:1. Gene flow (gene migration) is the movement of alleles among populations by migration of breeding individuals.2. Gene flow can increase variation within a population by introducing novel alleles 3. Continued gene flow decreases diversity among populations, causing gene pools to become similar.4. Gene flow among populations can prevent speciation from occurring.

Fitness: Describe the ability of an organism to survive and reproduce (produce fertile offspring)

Natural Selection: The ability of the organisms to survive and reproduce› Three conditions of natural selection

Variation: a population must exhibit phenotypic variance –difference between individuals

Heritability: if a trait cannot be inherited, it cannot be selected for or against

Differential reproductive success: measure how many offspring you produce that survive relative to how many the other individuals in your population produce

Protist is a eukaryotic Autotrophic or heterotrophic Multicellular or unicellular Mostly asexual Mostly aquatic Motile or nonmotile

Ex: Euglena, Amoeba, Paramecium, Algae, Slime Molds

The domain is larger than the kingdom on the hierarchical level of classification.

Domain is based on molecular classification› Three domain system:

Archae– no nucleus (prokaryote), cell wall without peptioglycan, lives in extreme environment

Bacteria- No nucleus (prokaryote), cell wall with peptioglycan, all other bacteria

Eukarya- Nucleus (eukaryote), some with cell wall, motile/nonmotile

Six Kingdoms› Protista: Heterotrophic or Autotrophic

Unicellular or Multicellular Mostly aquatic Mostly asexual Motile or Nonmotile The endosymbiosis theory explains how organisms

developed organelles

Fungi› Heterotrophic › Unicellular or Multicellular › Mostly terrestrial › Asexual or sexual › Nonmotile › Important decomposers in the environment › Ex: Mushrooms, molds, yeasts

Plantae› Multicellular › Autotrophic › Mostly terrestrial › Asexual or Sexual › Nonmotile

Animal› Multicellular › Heterotrophic › Terrestrial and Aquatic › Sexual (a few are asexual) › Motile (a few are nonmotile--sessile)

Archaebacteria› Prokaryotic› Lives in Extreme Environments› Cell wall made up of without peptioglycan

Eubacteria› Prokarytic› Cell wall made up of peptioglycan› Normal Bacteria

Photoautotroph: An organism capable of synthesizing its own food from inorganic substances using light as an energy source.

Chemoautotroph: An organism (typically a bacterium or a protozoan ) that obtains energy through chemical process, which is by the oxidation of electron donating molecules from the environment, rather than by photosynthesis.

Chemoheterotroph: An organism deriving energy by ingesting intermediates or building blocks that it is incapable of creating on its own.

Photoheterotroph: An organism that depends on light for most of its energy and principally on organic compounds for its carbon.

Eumetazoa: tissues and organs present; nervous system with neurons

Acoelomate: no body cavity; body double-walled sac surrounding digestive cavity; single opening to outside; characteristic of flatworms

Pseudocoelomate:no body cavity; body double-walled sac surrounding digestive cavity; single opening to outside; characteristic of flatworms

Coelomates: have body cavity Protostomes: Mouth develops first Deuterostomes: Anus develops first

Protostome – mouth develops firstDeuterostome – anus develops first

Ectoderm – outside layer, skinMesoderm – middle layer, musclesEndoderm – inside layer, gut

Coelom – body cavityPseudocoelom - partial body cavity

Radial Symmetry - Body parts arranged in a wheelBilateral Symmetry – right and left sides

Three parts to a plant include› Roots› Shoots› Leaves

Three basic tissue include› Ground tissue: that makes up most of the body

of the plant, is found between the dermal and vascular tissue. It can be divided into three cell types: collenchyma, parenchyma, an dsclerenchyma

› Vascular tissue: Xylem: support structure that strengthens the

plant and functions as a passageway for the transport water and minerals from the soil

Phloem: Function as the highway for plants in the assisting of sugars from one place to another.

› Dermal Tissue: provides the protective outer covering for plants. Skin of the plant is its epidermis

Within the epidermis is guard cells which control the opening and closing of gaps called stomata –which is vital to photosynthesis.

Alternation of generation: Plant life cycle, so named because during the cycle, plants sometimes exist as a diploid organism and at other times as a haploid organisms.

Primary Growth: Occurs in the apical meristem which is the region that lengthens the plants.

Secondary Growth: Occurs in the lateral meristem which causes the plant to increase in width

Transpiration: Is the process of moving water through the plant. The water is removed from the plant through evaporation out of the leaves. Transpiration creates a negative pressure in the leaves and xylem tissue due to the evaporative loss of water. Water molecules display molecular attraction (cohesion) and other water molecules, in effect creating a single united water molecule that runs the length of the plant.

Translocation: the transport of carbohydrates through the phloem. The movement of the sugar into the phloem creates a driving force because it establishes a concentration gradient. The gradient leads to the passive diffusion of water into the phloem, causing an increase in the pressure of these cells.

Xylem: support structure that strengthens the plant and functions as a passageway for the transport water and minerals from the soil

Phloem: Function as the highway for plants in the assisting of sugars from one place to another.

Abscisic acid: “babysitter hormone” It makes sure that seeds do not germinate too early, inhibits cell growth, and stimulates the closing of the stomata to make sure the plant maintains enough water.

Auxin: (Important AP Biology exam hormone selection) – elongation of stems, and plants a role in phototropism and gravitropism

Cytokinins: promotes cell division and leaf enlargement. Supermarkets use this to keep veggies of fresh. Fountain of youth hormone

Ethylene: Initiates fruit ripening and causes flowers and leaves to drop from trees

Gibberellins: Stem elongation. Think Grow when comes to this hormone. It is also thought to induce the growth of dormant seeds, buds, and flowers

Phototropism: plant’s growth response to light. Auxin is the hormone in charge of stem elongation here. The stem elongation occurs at the apical meristem

Photoperiodism: the response by a plant to change in the length of the day.

Short-day plants: Exposure to a night longer than a certain number of hours. › Flowering: end of the summer to end of the

winter Example: Poinsettas

Long-day plants: exposure to a night shorter than a certain number of hours› Flowering: Late spring to early summer

Example: Spinach

Four major tissue in animals include:› Epithelial: is made of closely-packed cells

arranged in flat sheets. Epithelia form the surface of the skin, line the various cavities and tubes of the body, and cover the internal organs.

Muscle: Three kinds of muscle are found in vertebrates: › Skeletal muscle is made of long fibers whose

contraction provides the force of locomotion and other voluntary body movements.

› Smooth muscle lines the walls of the hollow structures of the body, such as the intestine, urinary bladder, uterus, and blood vessels. Its contraction, which is involuntary, reduces the size of these hollow organs.

› The heart is made of cardiac muscle.

Connective Tissue› The cells of connective tissue are embedded in a

great amount of extracellular material. This matrix is secreted by the cells. It consists of protein fibers embedded in an amorphous mixture of protein-polysaccharide ("proteoglycan") molecules.

› This includes: Cartilage, bone, ligaments, tendons, adipose tissue

Nerve: Nerve tissue is composed of nerve cells called neurons and glial cells.› Neurons are specialized for the conduction of

nerve impulses. A typical neuron consists of a cell body which contains the nucleus; a number of short fibers — dendrites — extending from the cell body a single long fiber, the axon.

Ectoderm: Tissue that covers the body coverings.› Forms the central nervous system, the lens of

the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands

Mesoderm:layer forms in the embryos of triploblastic animals. During gastrulation, some of the cells migrating inward contribute to the mesoderm, an additional layer between the endoderm and the ectoderm.

The formation of a mesoderm led to the development of a coelom. Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks› Forms the skeletal muscle, the skeleton, the

dermis of skin, connective tissue, the urogenital system, the heart, blood (lymph cells), and the spleen

Endoderm: is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula› Forms into the stomach, the colon, the liver,

the pancreas, the urinary bladder, the lining of the urethra, the epithelial parts of trachea, the lungs, the pharynx, the thyroid, the parathyroid, and the intestines.