HL Bio - Unit #4.3: Reproduction

Asexual Reproduction: 

Reproduction from one parent where the offsprings are genetically identical 

• Reproduction through: Mitosis and Binary fission 

• Advantages

  • Good for organisms that can’t find partners 

  • Much quicker process, so it’s good for organism that need to be very abundant  

• Disadvantages: 

  • Organism that reproduce asexually can’t evolve since it’s genetically identical products

Sexual Reproduction

Reproduction from two parents where the offsprings are genetically different from both

• Reproduction through: Meiosis once per generation

• Advantages: 

  • New combinations each generation

  • Genetic variation is made 

  • Allows for evolution (better at adapting)

• Disadvantages:

  • Requires two parents (if another parent isn’t found reproduction can’t occur)

  • Reproduction sexually takes much longer

Meiosis

the process where the cells divide twice using mitosis until it’s DNA has halved (creates 4 gametes with 23 chromosomes each)

Male Sperm Cell

1. Smaller

2. Can swim using their tail 

3. Millions are constantly produced after puberty 

4. Contains 23 haploids

5. Food Store: Sugar in the seminal fluid

Female Egg Cell

1. Much larger

2. Do not move - Pushed along the oviduct 

3. Once a month an egg matures, starting at puberty until menopause

4. Food Store: Protein and fat within the cytoplasm

Male: Vas Deferens/ Sperm Duct

Carries sperm to the penis during ejaculation

Male: Prostate Gland

Adds alkaline fluids to the semen to neutralise the acidity of a vagina

Male: Seminal Vesicle

Provides sperm with nutrients like fructose sugar for respiration

• Also adds mucus on the sperm to protect it

Male: Urethra

Delivers semen during ejaculation and urine during excretion

• The sperm duct closes when not erect and when erect it opens and ureter closes

Male: Penis/Erectile Muscles

Muscles that become erect to penetrate the vagina

Male: Epididymis

Where sperm mature and gain their mobility

• Sperm is stored here waiting to be ejaculated

Male: Testis/Testes/Testicles

Produces sperm and testosterone

• Composed of the seminiferous tubules

Male: Scrotum

Protects and contains the testes outside of the body

• It’s outside so it can have a lower temperature for sperm production

Female: Uterus/Myometrium

Provides protection, nutrients, waste removal for a developing fetus

• It’s muscular walls will contract to aid with childbirth

Female: Fallopian Tube/ Oviduct

Connect the ovary to the uterus

• Where fertilisation occurs

Female: Ovary

Where eggs are stored to be fully matured every once a month

• Also produces estrogen and progesterone

Female: Endometrium/ Uterus Lining

Develops each month in preparation of a fertilised egg

• Implants into the lining and then becomes the placenta

Female: Cervix

A muscular opening to the uterus

• Closes to protect the developing fetus and opens to form the birth canal

Female: Vagina

Has the penis enter during sexual intercourse and is where sperm is received

• ALso forms the birth canal

Female: Vulva

Protects the internal parts of the female reproductive system

Menstrual Cycle

Occurs from puberty till menopause (Stopping during pregnancy and ill-health)

Ovarian Cycle

Controls production and release of eggs

2 phases of the ovarian cycle

1. Follicular Phase:

   • Group of follicles develop in the ovary where an ovary (in each one) is stimulated to grow

   • The most developed follicle breaks open and releases the egg into the oviduct (others will degenerate)

2. Luteal Phase

   • The fully developed follicle with the egg develops into a cyst called the “Corpus Luteum”

   • Releases hormones to support pregnancy 

   • If fertilisation doesn’t occur corpus luteum breaks down and the cycle repeats

What day does ovulation occur

Ovulation normally occurs on day 14 of the cycle

Uterine Cycle

Preparation and maintenance of the endometrium to receive and embryo

Phases of the uterine Cycle

1. Follicular Phase: 

   • Endometrium thickens and is more richly supplied with blood

2. Luteal Phase:

   • Phase where the fertilisation of the egg is awaited 

   • If this doesn’t occur then the endometrium will start breaking down

3. Menstruation/Period:

   • A week where the lining is being shed and the ovaries return to the follicular phase 

   • Once this phase is over the endometrium begins to build up once more

Hormones Released During the Cycle:

1. Follicle Stimulating Hormone (FSH):

2. Oestradiol/ Estrogen: 

3. Luteinizing Hormone (LH)

4. Progesterone

Follicle Stimulating Hormone (FSH):

• Produced in the anterior pituitary gland

• Stimulates follicular growth within the ovaries

• Stimulates oestrogen secretion 

Oestradiol/ Estrogen:

• Produced in the ovaries

• Thickens the endometrium

• Increases FSH receptors that make follicles more receptive to FSH continuously increases estrogen → Positive feedback

  • Then when it gets too high it stops FSH production → Negative feedback

• Stimulates FSH and LH release pre-ovulation (Spike)

  • Then prevents FSH and LH for the rest of the cycl

Luteinizing Hormone (LH)

• Produced in the anterior pituitary gland

• A hormone sent out in a surge causing ovulation

• Result in the formation of the corpus luteum cyst

  • Stimulates the completion of meiosis in the oocyte

Progesterone

• Produced in the ovaries

• Thickens the endometrium 

• Prevents FSH and LH → Negative feeback

Fertilisation

1. Sperm has a chemical receptor that detects chemicals that the eggs releases 

2. Sperm swims

3. Sperm secretes an enzyme from its acrosome (head) to digest through the eggs Zona Pellucida 

4. First sperm to make it through the zona pellucida will bind to the eggs plasma membrane

5. Sperms nucleus/ DNA will enter the egg and binds with the eggs nucleus to form the zygote → This is fertilisation 

6. Right after fertilisation the egg will rebuild glycoproteins layers to stop other sperms from entering 

Zona Pellucida

An outer coat of the egg made up of glycoproteins

Vitro Fertilisation (IVF):

1. Stopping the the women's pituitary gland from secreting FSH/LH which will subsequently stop oestrogen and progesterone production

   • For 2 weeks a nasal spray containing a drug is used to stop the pituitary gland 

2. They are then given FSH/LH for 10 days to stimulate follicles

3. Follicles are forced to mature using Human Chorionic Gonadotropin (hCG)

4. Egg that has been ovulated will be taken out ~34 hours after the hCG injection and then mixed with sperm to fertilise 

5. When fertilised it’s implanted back into the uterus 

   • Extra progesterone is given as a tablet placed in the vagina