Reproduction

Question 1

What is reproduction?

Answer 1

Reproduction is the replication and passing on of genes in the creation of new individuals of a species to replace those that die.

Question 2

What is asexual reproduction?

Answer 2

Asexual reproduction involves only one parent.

Question 3

How does asexual reproduction take place?

Answer 3

The parent organism simply produces new cells through mitosis, which then grow into a new organism that is identical to the parent.

Question 4

How do amoeba reproduce?

Answer 4

Amoeba reproduce asexually, through binary fission. Just like in cells other organisms that undergo mitosis when they get too large and the surface are to volume ratio becomes too small. With amoeba, in good conditions, division can take place every 2-3 days.

Question 5

What are two ways plants can reproduce asexually?

Answer 5

Two ways plants can reproduce asexually are, vegetative propagation and spore formations

Question 6

What is sexual reproduction?

Answer 6

Sexual reproduction involves the fertilization of a female egg by a male sperm.

Question 7

What are sex cells called?

Answer 7

Sex cells are called gametes

Question 8

When two gametes fuse, what is it called?

Answer 8

When two gametes fuse it’s called fertilization.

Question 9

What is the fertilized gametes called?

Answer 9

The fertilized gametes are called a zygote.

Question 10

What are chromosomes?

Answer 10

Chromosomes are strands of genetic information that are contained within the nucleus of every cell.

Question 11

How many chromosomes do humans have?

Answer 11

Humans have 46 chromosomes.

Question 12

How are gametes different from ordinary cells?

Answer 12

Gametes are different from ordinary cells because they contain half the number of chromosomes as regular cells (23).

Question 13

Why do gametes have half the number of chromosomes?

Answer 13

Gametes have half the number of chromosomes, so that when they fuse they can contain the correct number of chromosomes as a normal cell.

Question 14

What happens if there is more or less chromosomes than the regular amount?

Answer 14

It can lead to mutation if there is more or less chromosomes than the regular amount.

Question 15

How are gametes made?

Answer 15

Gametes are made through a process known as gametogenesis. This involves ordinary cells dividing (e.g) human sperm are made when cells in the testis divide. Because gametes must have half the number of chromosomes, mitosis will not be enough. During gametogenesis, cells divide in a different way, known as meiosis.

Question 16

What is a cell with a full number of chromosomes called ?

Answer 16

A cell with the full number of chromosomes is called a diploid cell.

Question 17

The gametes are called haploid, why?

Answer 17

The gametes are called haploid, because they only have half the number of chromosomes.

Question 18

The female reproduction organs

Answer 18

-The female gametes called eggs or ova, are made in the two ovaries.

• Leading away from the ovaries are the oviducts, they’re also called Fallopian tubes.

They don’t directly connect to the ovaries, but have a funnel shape near the ovaries to catch the released ova.

-The two oviducts lead to the womb , known as the uterus.

Made of muscle that forms thick walls; its relatively small, about the size of your fist, but it can expand enormously when the woman is pregnant. At the base of the uterus there is a narrow opening, guarded by muscles

• This is called the neck of the womb or cervix.

-The cervix leads to the vagina, which opens to the outside

-The opening from the bladder, the urethra, runs in front of the vagina, while the rectum is behind it

The 3 tubes open very much separately to the outide of the body.

Question 19

The male reproductive organs

Answer 19

-The male gametes called spermatozoa or sperm are made in two testes.

• These are found outside of the body in two sacs called the scrotum.

-The sperm are carried away from each testis in a tube called the sperm duct also called the vas deferens.

• The vasa deferentia (plural) join up with the urethra just below the bladder.
• The urethra continues downwards and opens at the tip of the penis.

The urethra is capable of carrying both urine and sperm at different times.

-Where the vasa deferentia joins to the urethra, there is a gland called the prostate gland.

This serves to produce a fluid in which the sperm swim.

-Just behind the prostate gland are the seminal vesicles, which also secrete a fluid.

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Question 20

How does the sperm get to the egg?

Answer 20

Mating introduces sperm into the vagina, the sperm must then travel, using their tails, up through the cervix, uterus and into the oviduct where it can then enter the egg (i.e) fertilize it. The sperm can only travel at a rate of about 4mm per minute, so it takes a while and many will not reach, because chemicals in the uterus dissolve the sperm. Before the sperm can reach though, the egg that has left the ovary and entered the oviduct is being wafted towards the entrance of the oviduct by cilia which line the oviduct. The cilia rhythmically beat to sweep the egg along. This is very slow process and so muscles in the funnel also push it along by peristalsis.

If the egg isn’t fertlizied by a sperm within 8-24 hours after ovulation, it dies. By this time, it would have only travelled a short distance in the oviduct. So a sperm as to reach almost near the top of the oviduct for successful fertilization to occur. When a man is sexually excited, blood is pumped into spaces inside the penis, that makes it erect. To bring the sperm as close as possible to the egg, the man’s penis is placed inside the vagina of the woman. This is known as sexual intercourse. Sperm are pushed out of the penis into vagina by muscles in the walls of the tubes containing sperm contract rhythmically. The wave of contractions begin in the testes, travels along the vasa deferentia and into the penis. The sperm are squeezed along and out through the urethra into the vagina. A process called ejaculation. The fluid produced by the prostate gland and seminal vesicles with the sperm is called semen. The ejaculation deposits millions of sperm to the top of the vagina near the cervix, so there is a good chance that some will reach the egg. However only one sperm can enter the egg. Only the head of the sperm goes in; the tail is left outside. The nucleus of the sperm then fuses with the nucleus of the egg (fertilization). As soon as one sperm enters the egg cell, the membrane of the egg becomes impenetrable, so no other sperm can enter. All the unsuccessful sperm will die.

Question 21

Implantation of the zygote

Answer 21

The final stage of early embryo development is the implantation of the zygote into the endometrial lining of the uterus

-The zygote breaches the jelly coat that was surrounding it and preventing its attachment to the endometrium

-Digestive enzymes are released which degrade the endometrial lining, while autocrine hormones released from the zygote trigger its implantation into the uterine wall

Only once the zygote is embedded within the uterine wall can the next stage of embryogenesis occur

-The growing embryo will gain oxygen and nutrients from the endometrial tissue fluid, ensuring its continued development

-The entire process (from fertilization to implantation) takes roughly 6 – 8 days

Question 22

Implantation in the Endometrium

Answer 22

When a zygote becomes implanted in the endometrial lining it begins to secrete human chorionic gonadotropin (hCG)

-hCG promotes the maintenance of the corpus luteum within the ovary and prevents its degeneration
As a consequence of this, the corpus luteum survives and continues to produce both oestrogen and progesterone

-Oestrogen inhibits FSH (follicle stimulating hormone) and LH (luteinizing hormone) production by the pituitary gland, preventing the release of more eggs from the ovaries

-Progesterone also functions to maintain the endometrium (which is nourishing the embryo) and thicken the cervix
The levels of hCG are maintained for roughly 8 – 10 weeks while the placenta is being developed

-After this time, the placenta becomes responsible for progesterone secretion and nourishing the embryo

-At this point the corpus luteum is no longer required and begins to degenerate as hCG levels drop

Question 23

What is the placenta

Answer 23

It functions as the life support system for the fetus, serving two key functions.

Question 24

What are the functions of the placenta?

Answer 24

-It facilitates the exchange of materials between the mother and fetus

-It secretes hormones to maintain the pregnancy after the corpus luteum has degenerated

Question 25

Structure of the Placenta

Answer 25

-The placenta is a disc-shaped structure that nourishes the developing fetus -It is formed from the development of the trophoblast upon implantation and eventually invades the uterine wall -Maternal blood pools via open ended arterioles into intervillous spaces within the placenta called lacunae -Chorionic villi extend into these pools of blood and mediate the exchange of materials between the fetus and the mother -Exchanged material is transported from the villi to the fetus via an umbilical cord, which connects the fetus to the placenta -Upon birth, the placenta is expelled from the uterus with the infant – it is then separated from the infant by severing the umbilical cord (the point of separation becomes the belly button)

Question 26

What is gestation?

Answer 26

This is the period of time during which the embryo develops into a fetus and then into a baby.

Question 27

Amniotic sac

Answer 27

The amniotic sac separates the fetus from the mother and hence functions as a barrier against infection -The fetus develops in a fluid-filled space that is encased by an amniotic sac

Question 28

What is amniotic fluid?

Answer 28

The amniotic sac is filled with a protective liquid called amniotic fluid, which serves a number of key roles: -The fluid is largely incompressible and good at absorbing pressure, and so protects the fetus from impacts to the uterus -The fluid also creates buoyancy so that the fetus does not have to support its own weight while a skeletal system develops -Finally, amniotic fluid prevents the dehydration of fetal tissues The amniotic sac ruptures when a woman comes to term during labor – this is known as her ‘waters breaking'

Question 29

Child birth

Answer 29

The process of childbirth is called parturition and occurs via positive feedback under hormonal control -Positive feedback involves a response that reinforces the change detected (it functions to amplify the change) -In the case of childbirth, fetal growth eventually causes stretching of the uterine walls, which is detected by stretch receptors -This triggers the release of hormones (oxytocin) that induce uterine muscles to contract, further reducing space in the womb -This causes more stretching and hence more contraction until the origin stimulus (the fetus) is removed (i.e. birth)

Question 30

The role of positive feedback in the birth process

Answer 30

- Baby pushes against cervix, causing it to stretch - Stretching of cervix causes nerve impulses to be sent to brain - Brain stimulates posterior pituitary to release oxytocin - Oxytocin causes smooth muscle lining the uterus to contract

Question 31

Hormonal Control

Answer 31

The chemical regulators of the birthing process include oxytocin, estrogen, progesterone and prostaglandin

Question 32

The menstrual cycle

Answer 32

- Once per month in an adult woman, one egg is released into the oviduct - Before the egg is released, the uterus becomes thick and spongy, ready to receive a fertilized egg in it’s thickened lining - It becomes full of many tiny blood vessels that would supply the embryo with nutrients and oxygen. - If the egg isn’t fertilized, it dies by the time it reaches the uterus -No implantation occurs and it continues downward into the vagina. - Because the thick spongy layer is no longer required, it beings to break down, gradually disintegrating and slowly excreted out through the vagina - This is called menstration, or the period as it last for about 5 days. After menstration the uterus walls rebuild to be able to receive another fertilized egg. - The entire cycle is controlled by hormones.