D3.1 Reproduction SL(only human)

Question 1

What is reproduction?

Answer 1

Reproduction is the way by which organisms pass on their genes to future generations and ensure the continuity of their species.

Question 2

What are the two types of reproduction?

Answer 2

Asexual and sexual reproduction?

Question 3

What is sexual reproduction?

Answer 3

• Sexual reproduction involves two parents and uses gametes (sex cells).
• The cells of the offspring have two sets of chromosomes, one from each parent
• Involves two stages: meiosis and fertilization
• Is a source of genetic variation by combining genes in different combinations in the gametes and by random fusion of gametes
• Involves the random fusion of gametes (any sperm can fertilize any egg)
• May involve external fertilization (many water animals) or internal fertilization (most land animals)
• Some organisms are capable of both sexual and asexual reproduction

Question 4

What is asexual reproduction?

Answer 4

• Asexual reproduction involves only one parent
• The cells of the offspring have two sets of chromosomes identical to those of the parent
• Produced by mitosis
• All offspring are genetically identical to the parent and to each other - clones

Question 5

What are the different types of asexual reproduction?

Answer 5

Asexual reproduction takes place in different ways, including fission, budding, fragmentation and parthenogenesis.

Question 6

What is fission (asexual reproduction)?

Answer 6

A type of asexual reproduction wherein an organism divides into equal halves resulting in two separate organisms.

Question 7

What is budding (asexual reproduction)?

Answer 7

A form of asexual reproduction in which a new individual organism develops as an outgrowth or bud from the parent organism, eventually detaching to become an independent organism.

Question 8

What is fragmentation (asexual reproduction)?

Answer 8

A method of asexual reproduction, where the parent organism breaks into fragments, with each fragment developing into a new organism.

Question 9

What is parthenogenesis (asexual reproduction)?

Answer 9

Reproduction from an ovum without fertilisation.

Question 10

What is meiosis?

Answer 10

A type of cell division that makes haploid gametes with half the number of chromosomes (one set)

Question 11

What is fertilization?

Answer 11

The fusion of a male and a female gamete to form a zygote

Question 12

What are the advantages of asexual reproduction?

Answer 12

*As only one participant is needed, asexual reproduction ensures that a large number of offspring can be produced within a relatively short period of time. This acts as an advantage in a relatively stable environment, as all the organisms are well-adapted to the environment and can colonise a habitat faster.
*Asexual reproduction is less costly in terms of energy and time, and definitely a less complex process.

Question 13

How could a build-up of damaging mutations in a population of genetic clones cause the extinction of the species?

Answer 13

As the same genetic material is duplicated and passed on to the offspring, chances of genetic variation are low. This, in turn, decreases genetic diversity, the raw material for evolution, which may have disastrous consequences when the environment changes. Similarly, harmful mutations in genes could be catastrophic to the existence of asexually reproducing organisms.

Question 14

Explain why sexual reproduction is less likely to produce a population with a lot of damaging mutations.

Question 15

What are the causes of genetic variation in sexual reproduction?

Answer 15

Sexual reproduction involves the fusion of two haploid gametes to form a diploid zygote, which then grows into a new individual. The offspring produced by sexual reproduction are genetically similar, but not identical to the parents. The possibility for genetic variation in sexual reproduction is enormous and can happen during the formation of gametes as well as during fertilisation e.g. meiosis I crossing over, meiosis I separations of members of homologous pairs, gametes used in fertilization.

Question 16

What is the role of meiosis and fusion of gametes in the sexual life cycle?

Answer 16

Meiosis maintains the number of chromosomes of the species by creating haploid gametes that later fuse to form diploid zygotes.
Egg=23 chromosomes + Sperm= 23 chromosomes = Zygote 46 chromosomes

Question 17

What are the adaptations of a sperm cell?

Answer 17

*The sperm must travel up the female reproductive tract to fuse with the egg (or ovum), hence they are smaller and motile. *Their tails (flagella) help them to swim to the egg
*The mitochondria generate energy for flagellar movement.
*Moreover, millions of sperm are produced every day to increase the chances of some of them reaching the mature egg.

Question 18

What are the adaptions of egg cell/ova?

Answer 18

*On the other hand, the eggs or ova are larger and immotile.
*They carry food reserves that act as energy sources for the dividing zygote.
*Normally in humans, only one egg is released by the ovary every month.

Question 19

Draw a labelled and annotated diagram of male reproductive system.

Answer 19

Question 20

Draw a labelled and annotated diagram of female reproductive system.

Answer 20

Question 21

What is the function sperm duct?

Answer 21

Tubes through which the sperm travel from the testes to the urethra during ejaculation

Question 22

What is the function of the prostate gland?

Answer 22

Produces fluids that help in the transport and nourishment of the sperm. The sperm together with these fluids are referred to as semen. Semen is a slightly alkaline fluid that keeps the sperm viable.

Question 23

What is the function of the urethra?

Answer 23

A common tube through which both the sperm and urine leave the penis

Question 24

What is the function of the penis?

Answer 24

A muscular, erectile organ that helps in the transfer of the sperm from the male reproductive system to the vagina of the female reproductive system

Question 25

What is the function of the epididymis?

Answer 25

Highly coiled tubes where sperm mature and are stored (till the time of ejaculation)

Question 26

What is the function of the scrotum?

Answer 26

Sacs that hold the testes and maintain them at temperature 2–3 °C lower than the body temperature facilitating sperm production

Question 27

What is the function of the testes?

Answer 27

Produce sperm and testosterone (the male sex hormone)

Question 28

What is the function of the bulbourethral gland?

Answer 28

Produces fluids that help in the transport and nourishment of the sperm. The sperm together with these fluids are referred to as semen. Semen is a slightly alkaline fluid that keeps the sperm viable.

Question 29

What is the function of the seminal vesicles?

Answer 29

Produces fluids that help in the transport and nourishment of the sperm. The sperm together with these fluids are referred to as semen. Semen is a slightly alkaline fluid that keeps the sperm viable.

Question 30

What is the function the erectile tissue?

Answer 30

Spongy erectile tissue can fill with blood when a male is sexually stimulated. This causes the penis to enlarge, lengthen and become rigid, in a condition known as an erection.

Question 31

What is the function of the fallopian tubes?

Answer 31

Tube through which the eggs (ova) travel from the ovaries. Fertilisation occurs here.

Question 32

What is the function of the vagina?

Answer 32

Muscular canal that extends from the outside to the cervix

Question 33

What is the function of the uterus?

Answer 33

Nourishes the developing foetus till birth

Question 34

What is the function of the ovaries?

Answer 34

Produce eggs and the female hormones oestradiol and progesterone

Question 35

What is the function of the cervix?

Answer 35

Lower part of the uterus. Menstrual blood passes from the uterus to the vagina through the cervix. Widens during birth of the baby.

Question 36

What is the menstrual cycle?

Answer 36

The menstrual cycle marks the onset of puberty in human females. Every month, the female body prepares itself for a possible pregnancy. This cycle of recurring changes that results due to variation in the levels of ovarian and pituitary hormones is known as the menstrual cycle.

Question 37

How long does a menstrual cycle typically last? And does two cycles does it comprise of?

Answer 37

Typically, the menstrual cycle lasts for 28 days and comprises the ovarian cycle and the uterine cycle. It is important to note that the changes in both the organs happen simultaneously.

Question 38

What is the ovarian cycle?

Answer 38

The ovarian cycle refers to the cyclic changes seen in the ovaries and can be further subdivided into three phases: the follicular phase, ovulation and the luteal phase.

Question 39

What is the FSH(Follicle Stimulating Hormones)?

Answer 39

Made by the pituitary gland promotes the development of follicles in the ovary.

Question 40

What is LH(Luteinising hormone)?

Answer 40

Made in the pituitary gland promotes ovulation and the formation of the corpus luteum.

Question 41

What is oestrogen?

Answer 41

Made by developing follicle and corpus luteum in the ovary promotes thickening of the uterus lining.

Question 42

What is progesterone?

Answer 42

Made by the corpus luteum maintains the thickest uterus.

Question 43

What is the follicular phase?

Answer 43

Lasts approx. 14 days (in a 28-day cycle) and begins first day of menstrual flow (bleeding). At this point, the levels of both ovarian and pituitary hormones are low. The anterior pituitary secretes follicle-stimulating hormone (FSH) and luteinising hormone (LH). Inside each ovary are small sac-like fluid-filled structures or the follicles, with each follicle containing one immature egg. FSH stimulates the growth of these ovarian follicles. The growing follicle secretes oestradiol (the primary form of oestrogen in a human female). It is important to note that although many follicles begin to develop simultaneously, usually only one of these follicles matures while the others regress.

Question 44

What is the ovulation phase?

Answer 44

Middle of the cycle (around Day 12), a sharp rise in the level of oestradiol stimulates the anterior pituitary to secrete LH (to a greater extent) and FSH (to a lesser extent). The spurt of LH causes the follicle to rupture, releasing the mature egg. This is known as ovulation and occurs in the middle of the menstrual cycle (around Day 14 of a 28-day cycle). The egg begins its passage to the uterus.

Question 45

What is luteal phase?

Answer 45

Following ovulation, LH and FSH levels drop. Under the influence of LH, the ruptured follicle is converted into the corpus luteum (yellow body) wherein the ruptured follicle is filled with cells. This period is known as the luteal phase. The corpus luteum secretes progesterone and oestradiol. As the levels of oestradiol and progesterone rise, the secretion of FSH and LH is inhibited by a negative feedback mechanism. This stage lasts for about 14 days.

Question 46

What is the uterine cycle?

Answer 46

The uterine cycle refers to the changes that occur in the uterus and can be divided into menstruation, the proliferative phase and the secretory phase. It is important to note that the changes in the ovaries and the uterus happen simultaneously.

Question 47

What is proliferative phase?

Answer 47

The proliferative phase coincides with the follicular phase and continues till ovulation. Oestradiol secreted by the growing follicle causes a thickening of the endometrial lining of the uterus preparing it for a possible pregnancy.

Question 48

What is the secretory phase?

Answer 48

The secretory phase roughly corresponds to the luteal phase of the ovarian cycle. Under the influence of progesterone, the uterine lining thickens further and changes into a secretory layer, in preparation for a potential implantation.

Question 49

What is menstruation?

Answer 49

Towards the end of the luteal phase, the decrease in levels of FSH and LH causes the corpus luteum to break down. The subsequent decrease in the levels of progesterone and oestradiol causes the thickened lining of the uterus to break down. The sloughed off layers, the unfertilised egg and blood are shed from the body through the vagina, resulting in menstrual bleeding.

Question 50

What happens after menstruation?

Answer 50

In response to the low levels of ovarian hormones, the anterior pituitary secretes FSH and LH, a new follicle develops and the next cycle begins.

Question 51

What does menstruation mark? And what is the end of menstruation?

Answer 51

The menstrual cycle marks the onset of puberty and continues until menopause.

Question 52

What are the graphs for different level of hormones in menstrual cycle?

Answer 52

Question 53

What is the negative feedback loop for hormones in the menstrual cycle?

Answer 53

Negative feedback occurs when an increase in the level of one hormone inhibits the secretion of other hormones. For example, as the levels of oestradiol increase in the follicular phase, FSH secretion is inhibited, causing the other follicles to regress.
Soon after ovulation, the follicle is converted to the corpus luteum and secretes both progesterone and oestradiol (to a lesser extent). As the level of progesterone increases, the release of both FSH and LH is inhibited, that is negative feedback sets in.

Question 54

What is the positive feedback loop for hormones in the menstrual cycle?

Answer 54

Eventually, the surge in oestradiol levels in the middle of the cycle causes a rise in the levels of LH and FSH. This is an example of positive feedback, where the rise in the level of one hormone causes an increase in the levels of other hormones.

Question 55

What is necessary for fertilization?

Answer 55

For fertilization to occur both partners must be fertile, which involves producing good quality gametes and, for the male, being able to deliver them to the female. This is not always the case as sometimes one or both of the partners is not fertile.

Question 56

What are the causes of infertility in males?

Answer 56

Question 57

What are the causes of infertility in females?

Answer 57

Question 58

What is fertilisation?

Answer 58

Fertilisation is the union of the sperm with the egg resulting in a diploid zygote. The egg released from the follicle travels down the oviduct. At this point, if the egg encounters a sperm, then fertilisation may take place. Thus, fertilisation takes place in the oviduct.

Question 59

What is the egg/ovum structure prior to fertilisation?

Answer 59

The egg that is released from the follicle has not yet completed meiosis II and is referred to as the secondary oocyte. The cytoplasm contains cortical granules filled with enzymes. Outer to the plasma membrane are two layers: the zona pellucida and the corona radiata. The zona pellucida is a jelly-like, non-cellular layer composed of glycoproteins that prevents the entry of sperm. Outer to the zona pellucida is the corona radiata, which consists of follicular cells that provide nourishment to the egg.

Question 60

What is the sperm structure prior to fertilisation?

Answer 60

The sperm consists of a head, midpiece and tail. The head contains the haploid nucleus, a cap-like acrosome which contains hydrolytic enzymes and paired centrioles. The midpiece carries the mitochondria that power the movement of the sperm. The tail is a flagellum that helps in movement.

Question 61

What is capacitation?

Answer 61

The sperm that enter the female reproductive tract move towards the oocyte. The sperm undergo physiological changes in the female reproductive system that lead to their activation.

Question 62

Why are some many sperms released during in vivo(in body through intercourse) fertilisation?

Answer 62

Of the millions of sperm that enter the female reproductive tract, only a few reach the oocyte and still fewer start to traverse through the zona pellucida

Question 63

What is the role of the complementary receptors present in the sperms?

Answer 63

The complementary receptors present on the head of the first sperm that reaches the cell membrane bind to the proteins on the oocyte plasma membrane. As a result, both the cell membranes fuse together.

Question 64

What does the binding of the sperm and ovum cause?

Answer 64

The binding of the sperm activates the oocyte in a step called egg activation.

Question 65

What happens during egg activation?

Answer 65

This results in a series of changes, like the rise of intracellular calcium levels, completion of meiosis II and the cortical reaction. The resulting changes in the plasma membrane of the egg and the zona pellucida prevent other sperm from fusing with the fertilised egg.

Question 66

What happens to the sperm once it bind to the ovum?

Answer 66

When the fertilising sperm binds to the oocyte, the head of the sperm enters the cytoplasm of the egg, while the midpiece and tail are destroyed. The sperm nucleus undergoes a series of changes to form the male pronucleus. The male pronucleus and the female pronucleus both have a haploid genome. The nuclear membranes of the male and female pronuclei dissolve, chromatin from both nuclei condense to form chromosomes resulting in a single-celled diploid organism. The diploid zygote now undergoes mitotic division.

Question 67

What does in vitro mean?

Answer 67

‘In vitro’ means outside the body

Question 68

What is the solution to infertility?

Answer 68

Today, IVF is a common and effective form of assisted reproductive technology, used as a treatment for infertility or to overcome genetic problems. Unlike natural conception, in IVF, the fertilisation of the egg and the sperm take place in a laboratory.

Question 69

What are the series of steps for IVF?

Answer 69

1. The normal menstrual cycle is suppressed using medicines. This treatment takes about 2 weeks and helps the healthcare worker to control the timing of ovulation.
2. The person undergoing treatment is given fertility drugs. These drugs contain FSH which stimulates follicles, resulting in superovulation or the production of multiple eggs (against the normal of one egg per month). Increasing the number of eggs produced increases the chances of successful fertilisation.
3. The person undergoing treatment is then injected with the hormone human chorionic gonadotropin (hCG), which causes the follicles to mature. Before the follicles rupture, the eggs are collected by a technique called follicular aspiration.
4. The eggs are put into a petri dish and the sperm from the donor is transferred to the dish. After 16–18 hours, the sample is assessed to see whether fertilisation has occurred.
5. If fertilisation has occurred, the fertilised eggs are allowed to grow in a specially formulated culture medium in the laboratory.
6. Healthy embryos are selected and transferred to the uterus. This can happen on Day 3 or Day 5. This is known as implantation. Often, multiple embryos are transferred to improve chances of implantation and this may lead to multiple births.
7. A pregnancy test approximately 2 weeks after implantation determines whether the process was successful or not.