Chapter 3 - Kaplan MCAT Biology Review

2025-2026

fertilization

the joining of a sperm and an ovum

fertilization usually occurs in the

ampulla of fallopian tube

ampulla

widest part of fallopian tube

sperm uses _____ to penetrate the corona radiata and zona pellucida

acrosomal enzymes

sperm uses acrosomal enzymes to penetrate the ____ and ___

corona radiata and zona pellucida

once sperm contacts the oocytes plasma membrane, it establishes the ___ and injects its ___

acrosomal apparatus, pronucleus

acrosomal apparatus

tube-like structure that extends and penetrates the cell membrane

when the first sperm penetrates, it causes a release of ____

calcium ions

the release of calcium ions after sperm penetration prevents _____ and increases the ____

-additional sperm from fertilizing the egg

-the metabolic rate of the resulting diploid zygote

cortical reaction

when first sperm penetrates, release of calcium ions, no other sperm can fertilize egg, resulting diploid zygote’s metabolic rate increases

fraternal (dizygotic) twins

fertilization of 2 eggs by 2 different sperm

dizygotic twins

fraternal twins

monozygotic twins

identical twins

identical (monozygotic) twins

the splitting of a zygote into 2

classifications of monozygotic twins

-monochorionic

-monoamniotic

-dichorionic

-diamniotic

monochorionic

share same chorion

monoamniotic

share same amnion

dichorionic

have own chorion

diamniotic

have own amnion

cleavage

-the early division of cells in the embryo

-results in larger number of smaller cells

zygote becomes a _____ after first cleavage

embryo

indeterminate cleavage

results in cells that are capable of becoming any cell in the organism

determinate cleavage

results in cells that are committed to differentiating into a specific cell type

morula

solid mass of cells seen in early development

morula goes through ____ to form blastula

blastulation

blastula is also called

blastocyte

blastula

-has fluid filled center (blastocoel)

-2 dif structures (trophoblast and inner cell mass)

trophoblast

becomes placental structures

inner cell mass

becomes the developing organism

blastula implants in the endometrial lining and forms the ____

placenta

chorion contains

chorionic villi

chorionic villi

-penetrates the endometrium

-creates interface between maternal and fetal blood

before placenta, embryo is supported by

yolk sac

allantois

involved in early fluid exchange between embryo and yolk sac

amnion

-lies in chorion

-produces amniotic fluid

umbelical cord

connects developing organism to placenta

gastrulation

the generation of 3 distinct cell layers

archenteron

-blastopore at end

-grows through blastocoel, contacts opposite side, establishes 3 primary germ layers

3 layers of gastrulation

-ectoderm

-mesoderm

-endoderm

ectoderm

-epidermis

-epithelia of nose, mouth, anal canal, nervous system, adrenal medula, lens of eye

mesoderm

-much of muscleoskeletal, circulatory, and excretory systems

-gonads, muscular and connective tissue layers of the digestive & respiratory systems, adrenal cortex

endoderm

-much of the epithelial linings of respiratory and digestive tracts

-parts of pancreas, thyroid, bladder, and digestive urinary tracts

neurulation

-development of nervous system

-begins after formation of 3 germ layers

notochord induces a group of overlying ectodermal cells to form ____ surrounding a ____

-neural folds

-neural groove

neural folds

fuse and form neural tube, which becomes CNS

tip of each neural fold contains

neural crest cells

neural crest cells

become the peripheral nervous system &specific cell types in other tissues

teratogens

substances that interfere with development, causing defects or death

if mother has diabetes

increased fetal size, hypoglycemia

if mother has folic acid deficiency

neural tube defects

cell specialization

each cell must perform a specialized function

specification

cell is reversibly designated as a specific cell type

determination

-the commitment to a specific cell lineage

-may be accomplished by uneven segregation of cellular material during mitosis or w morphogens

morphogens

cause determination of cells

to respond to a certain morphogen, a cell must have __

competency

differentiation

the changes a cell undergoes due to selective transcription

selective transcription changes a cell in order to

take on characteristics appropriate to its cell line

stem cells

capable of developing into various cell types

types of stem cells

-totipotent

-pluripotent

-multipotent

totipotent cells

able to differentiate into all cell types

pluripotent cells

able to differentiate into all 3 germ layers and their derivatives

multipotent cells

able to differentiate into only a specific subset of cell types

cells communicate through

signaling methods

inducer

releases factors to promote the differentiation of a competent responder

autocrine signals

act on the same cell that released the signal

paracrine signals

act on local cells

juxtacrine cells

act through direct stimulation of adjacent cells

endocrine signals

act on distant tissues after traveling through bloodstream

growth factors

peptides that promote differentiation and mitosis in certain tissues

reciprocal induction

if 2 tissues both induce further differentiation in each other

signaling often occurs via

gradients

cells may need to ____ to arrive at correct location

migrate

apoptosis

programmed cell death via formation of apoptotic blebs

apoptotic blebs can subsequently be ____ and _____ by other cells

absorbed and digested

apoptosis can also be used for

sculpting certain structures

regenerative capacity

the ability of an organism to regrow certain parts of the body

liver has ____ regenerative capacity

high

heart has ____ regenerative capacity

low

senescence

the result of multiple molecular and metabolic processes, like shortening of telomeres during cell division

nutrient, gas, and waste exchange w fetus occurs at the

placenta

for a fetus, oxygen and CO2 are passively exchanged due to

concentration gradients

fetal hemoglobin (HbF) has a ___ affinity for oxygen than adult hemoglobin (HbA)

higher

HbF

fetal hemoglobin

placental barrier also serves as

immune protection

placenta’s endocrine functions

secretes estrogen, progesterone, and human chorionic gonadotropin

hCG

human chorionic gonadotropin

umbelical arteries

carry deoxegenated blood from the fetus to the placenta

umbelical vein

carries oxygenated blood from placenta to fetus

fetal circulatory system’s 3 shunts

-foramen ovale

-ductus arteriosus

-ductus venosis

foramen ovale

connects right atrium to left atrium, bypassing lungs

ductus arteriosus

connects pulmonary artery to aorta, bypassing lungs

ductus venosis

connects umbelical vein to inferior vena cava, bypassing liver

first trimester

-organogenesis occurs

-development of heart, eyes, gonads, limbs, liver, brain

second trimester

-tremendous growth occurs

-movement begins

-face becomes distinctly human

-digits elongate

third trimester

-rapid growth and brain development continue

-transfer of antibodies to the fetus

birth

-cervix thins out

-amniotic sac ruptures

-uterine contractions coordinated by prostaglandins and oxytocin

-birth of fetus

-placenta and umbelical cord expelled