Reproduction

Question 1

Differences between Sexual and Asexual Reproduction

Answer 1

Fusion of genetic material from two parents
Singler parent produces offspring

Genetically different offspring
Genetically identical to parent offspring

Increased variation and faster evolution
Rapid reproduction and no need to search for mates

Requires two individuals and few organisms are produced
Less variation and slower evolution

Question 2

Signifcance of Meiosis for Reproduction

Answer 2

Breaks up parental combinations of alleles, with homologous chromosomes undergoing crossing over and independent assortment creating new combinations (recombinants)

Produces four genetically unique gametes with each gamete receiving a unique combination of alleles

Question 3

Significance of Gamete Fusion (Fertilization) for Reproduction

Answer 3

Creates a zygote, combines genetic material from both parents and introduces new combinations of alleles with the zygote having a unique genetic makeup different from parents.

Question 4

Differencces between Male and Female in Reproduction

Answer 4

Sperm
Egg

Small
Large

Motile
Sessile

Millions per ejaculation
One or two eggs per month

Minimal cytoplasm and reserves
Significant cytoplasm and reserves

The large number of sperm maximize fertilization chances
Invest resources in fewer eggs for offspring development

Question 5

Anatomy of the Female Reproductive System

Answer 5

Ovary: Site of production where the egg matures, along with site that produces estrogen and progesterone

Oviduct: Site of fertilization, provides a pathway for the egg to travel to the uterus by sweeping it by cilia on its walls

Uterus: Site of implantation of the fertilized egg

Cervix: Muscular tissue that separates the vagina from the uterus, secretes mucus to help sperm swim

Vagina: Organ used in intercourse, folded to allow expansion during birth, and secretes mucus to allow movement of male organ during intercourse and as a primary line of defense

Question 6

Anatomy of Male Reproductive System

Answer 6

Testes: Produces sperm and testosterone

Scrotum: Sac which contains testicles (nutsack)

Sperm Ducts: Two muscular tubes each connected to a testes. Carry sperm rom testes to urethra during ejaculation

Prostate Gland: Secretes alkaline fluid to neutralize the acidic conditions of the urethra and vagina

Seminal vesicle: Secretes mucus to help swimming and fructose to provide energy for sperm

Urethra: Tube inside the penis which is the pathway of semen and urine out of the body

Penis: Male sex organ which ejaculates semen into vagina during intercourse

Epididymis: Coiled tubes where sperm is stored and matures

Question 7

Hormones involved in Menstrual Cycle

Answer 7

Anterior Pituitary: FSH and LH
Ovaries: Estrogen and Progesterone

Estrogen gets produced by the follicle cells
Progesterone gets produced by corpus luteum / yellow cells

Question 8

The Main Hormonal Changes in a Menstrual Cycle

Answer 8

A menstrual cycle is usually 28 days, and the first day is day 1

FSH is secreted by the pituitary gland causing its levels to rise, which simulates the follicles to develop. This allows for the egg inside the follicle to mature and allow the follicle cells to secrete estrogen

Estrogen causes the follicle cells to make more FSH receptors so that they can respond more strongly to the FSH. This increases secretion of FSH which is a positive feedback loop and causes estrogen levels to rise which simulates the thickening of the endometrium

When estrogen levels reach its peak it simulates secretion of LH from the pituitary gland, and when LH reaches its peak it causes ovulation

Once ovulation occurred, LH stimulates the follicle cells to develop into corpus luteum, which starts to reduce estrogen secretion and secrete high amounts of progesterone to prepare for endometrium implantation

The high levels of estrogen and progesterone inhibit FSH and LH making it a negative feedback loop which prevents further follicle development or ovulation

If no fertilization takes place, the corpus luteum degenerates and causes a fall in levels of estrogen and progesterone which stimulates menstruation.

When the levels of estrogen and progesterone are low enough FSH and LH start to be secreted again and a new menstrual cycle beings

Question 9

Feedback Loops in Menstruation Cycle

Answer 9

Positive Feedback:

Rising estrogen levels from developing follicles stimulate the release of GnRH which leads to more FSH production, creating a positive feedback loop that promotes follicle growth

Negative Feedback:

As estrogen levels peak, they supress GnRH and FSH release which limits follicle growth and allows for LH to surge

If pregnancy doesn’t occur, the degenerating corpus luteum leads to a decline in progesterone levels which triggers menstruation and prepares for the cycle to repeat again

Question 10

Function of Anterior Pituitary Hormones in Menstrual Cycle

Answer 10

FSH:

Stimulates development of follicles

Stimulates maturation of oocyte inside the follicle

Stimulates secretion of estrogen from the follicle

LH:

Causes ovulation

Stimulates the development of the corpus luteum after ovulation

Stimulates the follicle cells to secrete less estrogen

Question 11

Function of Ovary Hormones in Menstrual Cycle

Answer 11

Estrogen:

Repairs the endometrium after menstruation

Stimulates LH secretion

Has positive feedback loop during the first half of the cycle to make more FSH receptors

Has negative feedback loop during the second half of the cycle to inhibit secretion of FSH and LH

Progesterone:

Maintains the lining of the endometrium to prepare it for implantation

Inhibits the secretion of FSH and LH

Question 12

Fertilization Process

Answer 12

Sperm navigates through female reproductive system towards egg using tail

Specific molecules on the sperm’s surface bind to complementary receptors on the zona pellucida which ensures species-specific fertilization

Sperm’s acrosome releases enzymes that digest a path through the zona pellucida which allows the sperm to reach the egg’s plasma membrane

The sperm’s head which contains the genetic material enters the egg’s cytoplasm

The rest of the sperm is degraded and not incorporated into the embryo

The membrane surrounding the sperm and egg nucleus dissolves, which allows for both nucleuses to come fuse forming a zygote, containing combined genetic information from both parents

Question 13

IVF Process

Answer 13

For three weeks, a woman takes a drug to stop her normal menstrual cycle

For 10-12 days, high does of FSH are injected once a day to have many follicles develop in the ovaries

LH and HCG are then injected to promote superovulation. HCG loosens the eggs in the follicles and matures them

A device is inserted through the vagina wall extracts the eggs from the follicles

Sperm is collected from the male individual and they get processed to find the healthiest ones

Many sperm and egg get mixed in a petri dish, and get incubated at 37 degrees

The next day, the dishes are observed to see if fertilization happened, and if it did then two or three of the embryos are chosen to be placed in the uterus through a long plastic tube

A pregnancy test is done a few weeks later to find out if any of the embryos have implanted, and a scan is done a few weeks later to find out if the pregnancy is progressing normally

Question 14

Arguements for and Against IVF

Answer 14

Helps infertile couples to have children
Against God’s will

Embryos that are killed through IVF can not feel pain
Multiple embryos are produced than needed and get denied a chance of life

The cost is worth it
IVF is very expensive

Improving medical technology makes it safe
Risk to the mother of multiple pregnancies

Question 15

Benefits of Superovulation

Answer 15

Having more eggs available for fertilization outside the body improves chances of obtaining viable embryos for implantation

With multiple eggs there’s a higher chance of obtaining a healthy embryo suitable for transfer to the uterus

Question 16

Adaptations of Sperm

Answer 16

Divided into three sections

Head contains nucleus which has parental DNA, acrosome cap which releases enzymes that digest the zona pellucida, and centrioles needed to divide the zygote

Mid-piece contains mitochondria which provides ATP to move the tail

Tail has a microtubule to facilitate movement

Question 17

Adaptations of Egg

Answer 17

Surrounded by two layers:

Zona pellucida which acts as a barrier to sperm entry

Corona radiata which is an external layer of follicular cells that provide support and nourishment to the egg

Additionally, cortical granules release their contents to harden zona pellucida upon fertilization to prevent polyspermy

Large cytoplasm to provide nutrients needed for mitosis of the developing zygote

Question 18

FSH and LH in Puberty for Males and Females

Answer 18

FSH Stimulates follicle growth and maturation in ovaries
LH triggers ovulation from follicle

FSH supports sperm production
LH stimulates testosterone production

Estrogen is produced in the follicles
Testosterone is produced in the testes

Question 19

Secondary Sexual Characteristics During Puberty

Answer 19

Growth of hair in pubic area and under the armpit, and change of behaviour associate with sex drive

Development and enlargement of the testes, scrotum and penis
Maturation of the ovaries and enlargement of vagina and uterus

Increased skeletal muscle development
Development of breasts

Deepening of voice
Widening of pelvis

Continuous production of sperm
Monthly ovulation and menstruation

Question 20

Spermatogenesis

Answer 20

Formation of sperm in males, and takes place in seminiferous tubules

Germinal epithelial cells divide by mitosis to produce spermatogonia (diploid)

Spermatogonia undergo growth and become primary spermatocytes

FSH simulates primary spermatocytes to undergo Meiosis 1 and become secondary spermatocytes

Testosterone simulates secondary spermatocytes to undergo Meiosis 2 to become spermatids (4 spermatids total)

Spermatids move to the center of the seminiferous tubule where they associate with Sertoli cells through the help of testosterone to help them mature into spermatozoan

Sertoli cells provide nourishment to developing sperm and to aid with development, and Leydig cells secrete testosterone

Question 21

Oogenesis

Answer 21

Production of the egg, and takes place in ovaries and begins before birth

Before birth, germinal epithelial cells undergo mitosis to form Oogonia

Oogonia undergo mitosis and develop into primary oocyte, which are surrounded by layers of cells forming a primordial follicle

Primary oocytes begin Meiosis 1 but stop in prophase 1 until puberty

During puberty, primordial follicles develop into primary follicles, growing larger in size

FSH simulates primary follicles to develop into secondary follicles which contains an extra layer of cells

Primary oocyte undergoes Meiosis 1, forming 2 haploid cells which are uneven in size. The larger one which receives most of the cytoplasm is called the secondary oocyte, whereas the smaller one is called the 1st polar body which eventually disintegrates

Just before ovulation, secondary follicle continues to develop which eventually forms the mature follicle which leads to the secondary oocyte beginning Meiosis 2 but stopping at prophase 2.

During ovulation, the secondary oocyte bursts out of the follicle, thus leaving the ovary and entering the oviducts. Only if fertilization takes place does the secondary oocyte complete Meiosis 2 producing an ovum.

Question 22

Spermatogenesis VS Oogenesis

Answer 22

Both produce haploid cell
Both include meiosis and mitosis
Both have cell growth before meiosis

Occurs in testes
Occurs in ovaries

Starts during puberty
Starts during embryonic development

Continuous process and goes until death
Discontinuous process and stops at menopause

Cytokinesis splits cytoplasm equally
Cytokinesis splits cytoplasm unequally

Question 23

Mechanisms to Prevent Polyspermy

Answer 23

Sperm’s head contains acrosome, releasing enzymes to digest zona pellucida. When the sperm interacts with the egg’s surface, the acrosome releases the enzymes. The enzymes create a path through the zona pellucida, allowing the sperm to penetrate. Once the sperm enters the egg, the zona pellucida undergoes structural changes to make itself impenetrable to other sperm

As soon as sperm’s membrane fuses with egg’s membrane, a change in egg’s membrane’s electrical potential occurs. This creates a positive charge which repels other positively charged sperm to block them from fusing with the egg. The egg’s cytoplasm undergoes cortical reaction, where calcium ions get released which trigger cortical granules to activate to harden the zona pellucida, forming an impenetrable barrier

Question 24

Role of HCG and Pregnancy Tests

Answer 24

HCG stimulates corpus luteum to continue producing progesterone for maintaining the endometrium to keep pregnancy healthy

A pregnancy test uses monoclonal antibodies specialized to bind specifically to HCG. HCG is present in the mother’s urine, and the test strip is placed in urine. If HCG is present in the urine, it will bind to the monoclonal antibodies which results in a color change, causing a band to appear on the test strip indicating a positive pregnancy test

Question 25

HCG Site of Production and Role

Answer 25

Site of production is embryo (blastocyst) or placenta

Prevents degeneration of corpus luteum
Stimulates corpus luteum to grow and secrete progesterone to maintain endometrium

Question 26

Progesterone & Estrogen Site of Production and Role

Answer 26

Site of production is ovary during early pregnancy and placenta once it has formed (mid pregnancy)

Maintains endometrium in thickened conditions

Question 27

Function of Placenta

Answer 27

Secretes estrogen and progesterone to maintain uterine lining

Facilitates exchange of materials between mother and fetus

Allows antibodies to pass to fetus

Prevents blood mixing

Question 28

Umbilical Cord

Answer 28

Connects placenta to fetus

Umbilical arteries carry CO2 to placenta, while veins carry O2 and more glucose to the fetus

Question 29

Amniotic Sac and Fluid

Answer 29

A bag that forms around the fetus which secretes amniotic fluid and prevents entry of pathogens

Supports and protects fetus from mechanical shock, allows it to move, and provides the fetus a sterile environment

Question 30

Progesterone Production in Pregnancy

Answer 30

After ovulation, the empty follicle in the ovary transforms into corpus luteum, which produces progesterone to maintain healthy endometrium in preparation for blastocyst implantation

As the placenta develops, the placenta takes over progesterone production around the 8th week of pregnancy to ensure a continuous supply of progesterone throughout pregnancy

Question 31

Role of Progesterone in Pregnancy

Answer 31

Maintains healthy endometrium

Keeps the uterus relaxed and prevents premature contractions, and suppresses production of oxytocin to prevent contractions

Suppresses the immune system to prevent mother’s body from rejecting the fetus

Question 32

Transition to Childbirth and Contractions

Answer 32

At the end of pregnancy, progesterone levels drop while estrogen levels rise

The rise in estrogen levels initiates uterine contractions which causes baby’s head to move to the cervix

Contractions stimulate stretch receptors in cervix which then signal the brain to release oxytocin from the posterior pituitary gland

Oxytocin causes uterine contractions which stimulates stretch receptors to cause higher secretion of oxytocin thus creating positive feedback loop

Frequent uterine contractions cause the cervix to relax thus dilating it

Baby’s head gets pushed out of the cervix and vagina along with the rest of the body after that

Umbilical cord is cut and contractions continue to push out placenta