Biology: Chapter 3

Question 1

Fertilization

Answer 1

-Fertilization occurs in the widest part of the fallopian tube, the ampulla
-The first sperm to come into direct contact with the secondary oocyte’s cell membrane forms a tube-like structure known as the acrosomal apparatus, which extends to and penetrates the cell membrane
-After this penetration, the cortical reaction occurs which is a release of calcium ions. The calcium ions depolarize the membrane of the ovum. Depolarization prevents fertilization of the ovum by multiple sperm cells and the increased calcium concentration increases the metabolic rate of the newly formed diploid zygote

Question 2

Dizygotic (fraternal) twins

Answer 2

-form from fertilization of two different eggs released during one ovulatory cycle by two different sperm
-Each zygote will implant in the uterine wall, and each develops its own placenta, chorion, and amnion
-No more genetically similar than any other pair of siblings

Question 3

Monozygotic (identical) twins

Answer 3

-from when a single zygote splits into two
-offspring is identical
-If division is incomplete, conjoined twins may result
-Monochorionic/monoamniotic share same amnion and chorion
-Monochrionic/diamniotic each have their own amnion but share chorion
-Dichorionic/diamniotic twins each have their own amnions and chorions

Question 4

Cleavage (development)

Answer 4

-After fertilization, zygote travels to uterus for implantation. If it arrives too late, there will no longer be an endometrium capable of supporting the embryo
-After it moves to the uterus, the zygote undergoes rapid mitotic cell divisions in a process called cleavage
-First cleavage creates an embryo

Question 5

Indeterminate cleavage

Answer 5

results in cells that can still develop into complete organisms

Question 6

Determinate cleavage

Answer 6

results in cells with fates that are already determined. These cells are committed to differentiating into a certain type of cell

Question 7

Blastulation

Answer 7

-Several divisions later, the embryo becomes a solid mass of cells known as a morula
-Once a morula is formed, it undergoes blastulation, which forms the blastula, a hollow ball of cells with a fluid-filled inner cavity known as a blastocoel
-The trophoblast cells surround the blastocoel and give rise to the chorion and later the placenta
-The inner cell mass protrudes into the blastocoel and gives rise to the organism itself

Question 8

Implantation

Answer 8

-The blastula moves through the fallopian tubes to the uterus, where it burrows into the endometrium
-The chorion develops into the placenta
-Chorionic villi support maternal-fetal gas exchange
-Embryo is connected to the placenta by the umbilical cord, which consists of two arteries and one vein.. The vein carries freshly oxygenated blood rich with nutrients from placenta to embryo. The arteries carry deoxygenated blood and waste to the placenta for exchange
-Until the placenta is functional, the embryo is supported by the yolk sac, which also the site of early blood cell development
-The allantois is involved in early fluid exchange between the embryo and the yolk sac
-The amnion surrounds the allantois and is a membrane filled with amniotic fluid which serves as a shock absorber

Question 9

Gastrulation

Answer 9

Once the cell mass implants, it can begin gastrulation which is the generation of three distinct cell layers

Question 10

Ectoderm (primary germ layer)

Answer 10

-outermost layer
-Gives rise to the integument, including the epidermis, hair, nails, and the epithelia of the nose, mouth, and lower anal canal
-The lens of the eye, nervous system, and inner ear as well
-adrenal medulla derives from here

Question 11

Mesoderm (primary germ layer)

Answer 11

-middle layer
-Develops into musculoskeletal, circulatory, and most of the excretory systems
-Also gives rise to the gonads as well as muscular and connective tissue layers of digestive and respiratory systems
-adrenal cortex derives from here

Question 12

Endoderm (primary germ layer)

Answer 12

-innermost layer
-Forms the epithelial linings of the digestive and respiratory tracts, including the lungs
-The pancreas, thyroid, bladder, and distal urinary tracts, and part of the liver are derived from endoderm

Question 13

Selective transcription of the genome (differentiation)

Answer 13

-only the genes needed for that particular cell type are transcribed
-In pancreatic islet cells the genes to produce specific hormones are turned on, while these same genes are turned off in other cell types

Question 14

Neurulation

Answer 14

-Once the three germ layers are formed, neurulation, or the development of the nervous system can begin
-A rod of mesodermal cells called the notochord forms along the long axis of the organism like a primitive spine
-The notochord induces a group of overlying ectodermal cells to slide inward to form neural folds, which surrounds a neural groove
-The neural folds grow towards one another until they fuse into a neural tube, which gives rise to the central nervous system
-At the tip of each neural fold are neural crest cells, which migrate outward to form the peripheral nervous system and specific cell types in other tissues

Question 15

Teratogens

Answer 15

substances that interfere with development, causing defects or death of developing embryos

Question 16

Specification (cell specialization)

Answer 16

the cell is reversibly designated as a specific type of cell

Question 17

Determination (cell specialization)

Answer 17

-commitment of a cell to a particular function in the future
-Prior to determination the cell can become any cell type
-After determination the cell is irreversibly committed to a specific lineag

Question 18

Differentiation (cell specialization)

Answer 18

the cell begins to undertake changes such as structure, function, and biochemistry in order to develop into the determined cell type

Question 19

Stem cells

Answer 19

cells that have not yet differentiated or that give rise to other cells that will differentiate

Question 20

Totipotent

Answer 20

-cells with the greatest potency
-Can differentiate into any cell type, either in the fetus or in placental structures

Question 21

Pluripotent

Answer 21

cells can differentiate into any cell type except for those found in the placental structures

Question 22

Multipotent

Answer 22

-cells can differentiate into multiple types of cells within a particular group
-An example would be hematopoietic stem cells which are capable of differentiating into all of the cells found in the blood

Question 23

Autocrine signals

Answer 23

act on the same cell that secreted the signal in the first place

Question 24

Paracrine signals

Answer 24

act on cells in the local area

Question 25

Juxtacrine signals

Answer 25

involve a cell directly stimulating receptors of an adjacent cell

Question 26

Endocrine signals

Answer 26

involve secreted hormones that travel through the bloodstream to a distant target tissue

Question 27

Inducers

Answer 27

-Inducers are often growth factors, which are peptides that promote differentiation and mitosis in certain tissues
-One of the main methods of signaling occurs via the use of gradients. Morphogens, or molecules that cause determination of cells, diffuse throughout the organism. Locations closer to the origin of the morphogen will be exposed to higher concentrations, while areas further away will have less exposure

Question 28

Cell migration

Answer 28

Cells must be able to disconnect from adjacent structures and migrate to their correct location

Question 29

Apoptosis

Answer 29

-programmed cell death
-During the process of apoptosis the cell undergoes changes in morphology and divides into many self-contained protrusions called apoptotic blebs, which can then be broken apart into apoptotic bodies and digested by other cells
-the blebs are contained by a membrane which prevents the release of harmful substances into the extracellular environment

Question 30

Necrosis

Answer 30

-cell dies as a result of injury
-internal substances can be leaked

Question 31

Regenerative capacity

Answer 31

-ability of an organism to regrow certain parts of the body
-When regeneration is required, stem cells can migrate to the appropriate part of the body to initiate regrowth

Question 32

Complete regeneration

Answer 32

lost or damaged tissues are replaced with identical tissues

Question 33

Incomplete regeneration

Answer 33

the newly formed tissue is not identical in structure or function to the tissue that has been injured or lost

Question 34

Senescence

Answer 34

-biological aging
-At the cellular level, senescence results in the failure of cells to divide

Question 35

Foramen ovale

Answer 35

one-way valve that connects the right atrium to the left atrium. This allows blood entering the right atrium from the inferior vena cava to flow into the left atrium instead of the right ventricle. This reroutes blood from the lungs. The right side of the heart is at a higher pressure than the left side until after birth

Question 36

Ductus arteriosus

Answer 36

shunts leftover blood from the pulmonary artery to the aorta. Reroutes blood from the lungs

Question 37

Ductus venosus

Answer 37

shunts blood returning from the placenta via the umbilical vein directly into the inferior vena cava. The liver is bypassed

Question 38

First Trimester

Answer 38

-Major organs begin to develop during the first few weeks
-Heart begins to beat at about 22 days, and soon afterward the eyes, gonads, limbs, and liver start to form
- Cartilaginous skeleton begins to harden into bone by the seventh week
-By the end of eight weeks most of the organs have formed, the brain is fairly developed and the embryo becomes known as a fetus

Question 39

Second Trimester

Answer 39

-Begins to move within the amniotic fluid, its face takes on a human appearance, and its toes and fingers elongate

Question 40

Third Trimester

Answer 40

-Antibodies are transported by highly selective active transport from mother to fetus
-Growth rate slows and the fetus becomes less active, as it has less room to move

Question 41

Parturition (birth)

Answer 41

vaginal childbirth, accomplished by rhythmic contractions of uterine smooth muscle, coordinated by prostaglandins and the peptide hormone oxytocin

Question 42

Water breaking (birth)

Answer 42

-cervix thins out and the amniotic sac ruptures
-Strong uterine contractions then result in the birth of the fetus

Question 43

Afterbirth

Answer 43

the placenta and umbilical cord are expelled