Chapter 15 - Production Of Sex Cells

Question 1

What are Gametes? What are Gonads? What is a Zygote? What are primary sex organs? What are secondary sex organs?

Answer 1

Gametes adds sex cells produced in specialised sex organs. Sperm and Ovum for humans

Gonads are the specialised sex organs in charge of the production of sex cells. In humans are the testes and ovary.

A zygote is the fused male and female gamete cells at fertilisation resulting in a single cell.

Primary sex organs are what produced the sex cells; the gonads.

Secondary sex organs are other organs which are essential for reproduction; they store the Gametes, bring them together for fertilisation and support the developing baby

Question 2

Explain the features found in the male reproductive system.

Answer 2

1. Testicles
   The male gonads consists of two testes or testicles.
   - Produces the male Gametes sperm or SPERMATOZOA
   - oval shaped, 4.5cm long, 2.5 cm wide and 3cm thick
   - internally divided into between 200 and 300 LOBULES of compartments filled with fine tubules called SEMINIFEROUS TUBULES; lined with cells that produce the male gamete called GERM CELLS.
   - seminiferous tubules in each compartment of the testis join together to form short, straight tubule. they eventually join into ducts which leave the testis and enter a structure called epididymis.
   - Between the seminiferous tubules are cluster of INTERSTITIAL CELLS that secrete THE MALE HORMONE TESTOSTEONE
2. Scrotum
   - the testes are supported in a skin covered pouch called the scrotum
   - appears as a single pouch of skin, but internally is divided into 2 sacks each containing a testis.
   - production and development of the sperm requires temperature that
   is about 2°C lower than the normal body temperature
   - therefore to allow sperm production to take place, the testes lie outside the body cavity in the scrotum
   - with exposure to the cold, contraction of smooth muscle fibres in the wall of the scrotum moves testes closer to the body where the temperature is higher.
   - if necessary the same muscles react moving the testes away from the body to keep them cooler
3. EPIDIDYMIS
   - highly folded tubule that fits against the rear surface of each testis; if unravelled 5-6m long
   - spermatozoa from testis enter the tubule of the epididymis
   - sperm are stored here for up to a month, during which time they mature
4. VAS DEFERENS
   - tubule of epididymis continues to become the VAS DEFERENS
   - sperm duct which carries sperm away from the Testis
   - it extends upwards from the testis, passes into abdominal cavity and crosses the upper surface of the bladder, it turns downwards looping behind bladder.
   - under the bladder the two vas deferentia join the tube that leaves the bladder
5. Urethra
   - runs although the penis and is a duct for transporting both urine and semen to exterior
6. Seminal vesicles
   - pair of pouch like organs, 5cm in length, located behind the urinary bladder
   - secretes a thick fluid that is rich in sugars and makes up 60% of semen volume
7. Prostate gland
   - is where the 2 vas deferentia join urethra, found under bladder surrounded by urethra
   - single doughnut shaped gland
   - secretes thin, milky alkaline fluid that also becomes part of semen
8. Bulbo-urethral gland (Cowpers gland)
   - 2 small yellow glands each the size of pea and located beneath the prostate either side of urethra
   - secretes clear mucus which acts a LUBRICANT and much of it precedes the emission of the seminal fluid with only a small amount in semen; is carried to urethra by a duct in each gland
9. Penis
   - contains connective tissue that has very Rich blood supply called ERECTILE TISSUE
   - has a large number of sponge-like spaces which fill with blood during sexual arousal
   - causes penis to enlarge, stiffen and become erect.
   - only when penis is erect that it can be successfully introduced to vagina

Question 3

What is semen?

Answer 3

The liquid in which millions of sperm is carried in to reach the egg for fertilisation.

Semen or seminal fluid nourishes and aids the transport of sperm

It is a mixture of secretions from three glands - seminal vesicles. Prostate gland. And bulbo urethral gland

Question 4

What does male reproductive system do during reproduction.

Answer 4

During ejaculation the urethra carries spermatozoa and semen through penis to a slit like opening at the tip.

In reproduction the penis is used to transfer sperm from the male to the into female vagina.

Question 5

Explain the features found in the female reproductive system

Answer 5

1. Ovaries
   - primary sex organ and the gonads which makes the female gamete Ova or eggs
   - almond shaped gland
   - 3cm in length
   - located within the body; each side of abdominal cavity supported by ligaments
   - composed of a mass connective tissue STROMA
   - stroma surrounds a layer of cells containing GERM cells
   - germ cell is enclosed in a FOLLICLE in various stages
2. UTERINE TUBE/FALLOPIAN TUBE
   - funnel like opening (oviducts)
   - 2x which carries the egg from ovary to uterus
   - oviduct is fringed with finger like projects (FRIMBRIAE) which touch surface of ovary
   - FRIMBRIAE helps guide egg to oviduct
   - epithelilium with beating cilia lines tube and helps carry it to uterus
   - contraction of smooth muscle of the wall of uterine tube also aids egg
3. Uterus
   - single, hollow, pear shaped organ situated behind urinary bladder and infront of rectum
   - in pelvic cavity held by broad ligaments;ligaments not tight, has limited movement allowing position to slightly vary; changes if rectum or bladder full
   - made up of SMOOTH MSULCE with soft MUCOUS MEMBRANE lining called ENDOMETRIUM
   - role is protecting and nourishes foetus/embryo during pregnancy
4. CERVIX
   - at the end/neck of uterus
   - protrudes into vagina
5. Vagina
   - canal leading to the outside of the body
   - muscular structure lined with mucous membranes
   - can stretch
   - 10cm length and revived penis in sexual intercourse
   - in childbirth becomes enlarged to form BIRTH CANAL
   - HYMEN is folded tissue covering external opening and broken and torn during sex or other means
6. VULVA
   - vagina opens up to this exterior region
   - made up of external genitalia organs; labia majora, labia Minora and clitoris
7. Labia majora
   - 2 fleshy folds of skin
   - made up of fat and fibrous tissue
   - contains large number of glands which produce an oily secretion
   - outer surfaces =pigmented after puberty with pubic hair
   - inner smooth, lack hair and moist from oil sec.
8. Labia minora
   - beneath and between majora
   - pinkish, without fat or hair
   - surrounds space into which the urethra and vagina open
9. CLITORIS
   - labia minora surround
   - structure = penis
   - contains erectile tissue, blood vessels and nerves.
   - sensitive to touch, becoming engorged when stimulated

Question 6

Difference between Diploid and Haploid

Answer 6

Diploid - the number of chromosomes present in body (or somatic cells) - 2n
In humans 2n = 46 Chr

Haploid - the number of chromosomes present in Gametes -n
In humans n =23 chr

Question 7

What is mieosis. Definition.

Answer 7

Meiosis is a type of cell division in reproducing organisms in the production of gametes.

• involves two rounds of division
• result in four daughter cells
• only one copy of each chromosome. (23 chr - haploid)
• occurs in sex organs/ gonads

Can be referred to as REDUCTION division

INVOLVES 2 NUCLEAR DIVISIONS BUT CHROMOSOMES DUPLICATE ONCE ONLY.

Question 8

Why have meiosis than mitosis

Answer 8

At fertilisation the fusion of egg and sperm results in the doubling of chromosomes number so mitosis is the division process to maintain 64 chromosomes in body cells of an individual.

If mitosis occurs
Eg. 64 +64 from parents = 92
Then 92 + 92 from that individual and sexual partner = 184 chr
10 generations from 64 = 23 552

Question 9

What is the process of gamete development which includes meiosis called. And what different types are they?

Answer 9

The process of gamete development which includes meiosis is called GAMETEOGENESIS

The 2 types

1. SPERMATOGENESIS; formation of sperm or spermatozoa in testes
2. OOGENESIS; formation of ova in ovary

Question 10

What are HOMOLOGOUS CHROMOSOMES?

Answer 10

HOMOLOGOUS CHROMOSOMES - each pair of chromosomes which are identical in size and shape.

• each pair carries genetic information that influenced the same characteristics

Question 11

What happens prior to undergoing meiosis?

Answer 11

Cell goes through interphase stage during with it grows and DNA is replicated via mitosis.

Question 12

What happens in the First Meiotic Stage? REDUCTION IN CHROMOSOME

Answer 12

1. Similar to mitosis however
   - chromosomes become visible as long threads
   - each has duplicated DNA and consists a pair of chromatids; appears as four strands frequently twisted
2. gradually move so chromosomes pair off into HOMOLOGOUS chromosomes
   - then SHRINK AND THICKEN DNA - tightly coiled
3. spindle fibres form, stretching between poles of the cell
   - pairs chromosomes move towards the spindle fibres until Metaphase.
4. Metaphase; arranged on the spindle fibre across equator of cell
5. Anaphase; the pairs of homologous chromosomes seperate from centromere (centromere does not separate)and members of the each chromatid pair moves to opposing poles
   = 23 chromosomes moving to each pole
   Thus assembling in each pair is half of O.G
6. During telophase the cytoplasm May split and divide into 2 parts

Question 13

How is 1st meiotic division different from mitosis?

Answer 13

First mitotic division of meiosis; the number of chromosomes assembling at each pole of cell is half of original cell.

In mitosis the centromeres divide so that each chromatid becomes a chromosome. Forty six then migrated to pole of cell.

Question 14

What occurs during the second division Of MEIOSIS? SEPARATION OF CHROMATIDS

Answer 14

1. At the beginning the 2 cells are haploid - contains half of parental chromosomes
2. Each daughter cell with 23 chromosomes undergo same sequence of events in which the chromatids separate and migrate to either end of cell.
   Results in 4 haploid cells being formed.
3. During second phase of PROPHASE; new spindle fibre forms at each end of O.G spindle fibre; usually at right angles to original.
4. Chromosomes in each cell gradually move towards the equator so at METAPHASE they are arranged on new spindle fibre.
5. CENTROMERE divides, so each chromatid is now separate from chromosome
6. Anaphase; new chromosomes migrate to opposite poles
7. Telophase; nuclear membrane begins to form and cytoplasm stars to divide.
8. At the end = 4 new cells formed, each with half the number of chromosomes of original cell.

Question 15

What are the differences between mitosis and meiosis?

Answer 15

Differences reflect roles in human body and involves processes of DNA replication to produce doubling of the number chromosomes prior to their respective cell division process.

Mitosis

1. One duplication of chromosomes and One nuclear division
2. Produces 2 diploid cells
3. Homologous chromosomes do nor pair
4. Chromatids separate so each cell gets a complete set of exact daughter chromosomes
5. Chromosomes do not change genetic makeup materials
6. Produces new cells for growth and repair

Meiosis
1. One duplication of chromosomes and two nuclear divisions
2. Produces 4 haploid cells
3. Homologous chromosomes pair off
4. At 1st meiotic division; members of homologous pairs separate so that new cells get a haploid set of chromosomes.
At 2nd set of meiotic division; chromatids separate giving 4 haploid cells
5. Genetic makeup of chromosomes can be changed via CROSSING OVER
6. Produces haploid Gametes for sexual reproduction

Question 16

What is Crossing over?

Answer 16

Important feature in meiosis which occurs during prophase of 1st meiotic division.

When homologous chromosomes are paired, the chromatids may break and exchange segments = Crossing over

• creates new combinations of genes so that the chromosomes passed on to offspring are not the same as those inherited from parents.

Question 17

Why is production of sperm and eggs cells via meiosis important for fertilisation?

Answer 17

Male and female productive system is specialised in the production of Gametes.

At fertilisation the different types of Gametes fuse to form a single cell called a zygote.

From a zygote a multi celled organism develops.

Thus offspring produced sexually originates from cells of parents making it a cellular event.

Therefore these cells must only contain half the amount of chromosomes of body cells - produced by meiosis

Question 18

Explain the process of SPERMATOGENESIS.

Answer 18

Entire process takes 72 days and is continuous process after puberty - with 200 mil/per day

1. The seminiferous tubules of the testes are lined with immature cells called SPERMATOGONIA or sperm mother cells which contain a DIPLOID number of chromosomes.
   * nourished by Sertoli cells
2. At PUBERTY, the spermatogonia begin dividing by mitosis and so provides a continuous source of new cells for the production of SPERMATOZOA.
3. Some daughter cells of from the spermatogonia are PUSHED INWARDS towards the centre of the tubule, where they undergo a period of growth. Theses enlarged spermatozoa are called PRIMARY SPERMATOCYTES
4. Primary spermatocytes are like spermatogonia, are diploid and undergoes the first stage of meiosis to produce SECONDARY SPERMATOCYTES which are HAPLOID.
5. The second meiotic division divides each secondary SPERMATOCYTES into two SPERMATIDS. Thus 4 HAPLOID spermatids are formed by meiosis from one diploid spermatogonium.
6. Final stage of SPERMATOGENESIS occurs when the spermatids mature into SPERMATOZOA.
   - During this time much of the cell’s CYTOPLASM IS LOST and TAIL containing Contractile material forms.
   - maturing of sperm is nourished during this stage by special cells that extend from the outer portion of the seminiferous tubules into the centre.

Question 19

Structure of SPERM

Answer 19

• is microscopic; 0.06mm long
• has head, neck, middle piece and tail

Tail = flagella capable of violent swimming motions to propel the cell forward

Head = nuclear material with fluid filled vesicle at its tip; enzymes important if sperm reaches egg; to break down layer of cells surrounding the egg so fertilisation can occur.

Middle piece = contains mitochondria, where respiration takes place to provide energy for movement of the cell.
- around mitochondria is a thin layer of cytoplasm; so little cytoplasm makes sperm have short survival Period and receive nourishment from semen which they are suspended in

Question 20

Explain what occurs during OOGENEIS.

Answer 20

1. Before female baby is born; millions of egg mother cells or OOGONIA develops in ovaries
   - are DIPLOID and divide by mitosis to produce the cells that will eventually develop into ova.
2. By the time of Birth; each ovary contains 400 000 oogonia which have undergone a growth phase to become PRIMARY OOCYTES.
   - begins prophase of 1st meiotic division but the process STOPS at this point.
   - Each primary oocyte is surrounded by a single layer of cells forming a PRIMARY FOLLICLE
3. At puberty; process of follicle and maturation of eggs begin.
   - as follicle matures the primary oocyte contained within it completes the 1st meiotic division stages producing two HAPLOID CELLS
4. These cells are unequal in size.
   - larger one receives half of chromosomes but nearly all of cytoplasm and is called the SECONDARY OOCYTE
   - the smaller cell Receives other half of the chromosomes and little cytoplasm = 1st POLAR BODY
5. The secondary oocyte immediately commences 2nd meiotic division but stops at METAPHASE.
6. At the stage OVULATION OCCURS;follicle ruptures, expelling secondary oocyte along with polar body.
7. In uterine tube if PENETRATED BY SPERM, meiosis is quickly completed; producing two unequal cells both haploid.
   - larger one = OVUM/ mature egg
   - smaller cell is the 2nd POLAR BODY
8. 1st polar body may also undergo 2nd meiotic division producing 2 additional polar bodies.
   - all polar bodies disintegrate

Thus female oogenesis produces one OVUM from primary oocyte while male spermatogenesis produces 4 sperm from each primary follicle.