MODULE 1: PLANTS AND ANIMALS: REPRODUCTION, DEVELOPMENT, AND
THEIR FUNCTIONS
Lesson 1: Human Reproduction and Development
Asexual reproduction is the mode of reproduction that does not involve the use of gametes or sex
cells.
Sexual reproduction is the mode of reproduction that involves the use of gametes or sex cells.
Types of Asexual Reproduction
• Fission - Type of asexual reproduction involving the division of body into two or more
equal parts.
• Budding - Type of asexual reproduction where a new individual arises as an outgrowth
(bud) from its parent, develops organs like those of the parent, and then detaches itself.
• Fragmentation - Type of asexual reproduction where the body breaks into two or more
parts, with each fragment capable of becoming a complete individual; in animals,
fragmentation is usually followed by regeneration where the missing parts are produced.
For example, a lost arm of the starfish may be regenerated by mitotic cell divisions.
• Sporulation - Type of asexual reproduction where a new individual forms from an
aggregation of cells surrounded by a resistant capsule or spore, which later germinates.
Types of union of gametes
1. Isogamy - Fusion of similar gametes which are usually motile.
Examples: Chlamydomonas producing gametes or Spirogyra undergoing conjugation.
2. Heterogamy - Fusion of dissimilar gametes. In oogamy, a large immotile gamete, the
egg is fertilized by a small motile gamete, the sperm.
Examples: animal sperm and egg.
Special terms for sexual reproduction
1. Bisexual reproduction - Type of sexual reproduction involving the union of gametes from
two genetically different parents.
Examples: humans, papaya
2. Hermaphrodite - An individual with both male and female reproductive tissues.
Example: worms
Differences between asexual and sexual reproduction
In asexual reproduction, an offspring is genetically identical to the parent, which means the
offspring is a CLONE of the parent. Sexual reproduction, on the other hand, generally produces
variation in the offspring because this results in the recombination of genomes from the parents’
gametes.
Stages of Animal Development
A. Gametogenesis- Stage of development that yields haploid gametes.
Haploid (n) condition- When a cell has only half the chromosome number or only one set
of chromosomes.
Diploid (2n) condition- When a cell has the full chromosome number or two sets of
chromosomes.
B. Fertilization- Stage of development that results in a unicellular diploid zygote.
C. Cleavage- Stage of development involving a series of mitotic divisions to produce a
multicellular blastula from a unicellular zygote.
❖ Totipotent cell- A cell that is capable of differentiating to become any kind of cell.
D. Gastrulation - formation of three germ layers: ectoderm, mesoderm, and endoderm. Each
will give rise to specific tissues and organs.
E. Organogenesis- Stage of development where the different germ layers differentiate into
specific organ systems.
F. Growth- Stage of development characterized by an increase in size of an individual.
Twins
• Monozygotic twins- Also known as identical twins; result from the union of a sperm
and egg to form a single zygote that splits up during the first cleavage stage.
• Dizygotic twins - Also known as fraternal twins; results from the development of two
or more separate fertilization events where the resulting zygotes develop almost
simultaneously.
Human Reproductive System
A. Male Reproductive System
• Testis- Where sperms are produced.
• Epididymis- Where sperms are temporarily stored.
• Scrotal sac/scrotum - Supports the testis and epididymis.
• Vas deferens - Where the sperm passes through from the testis before it joins the urethra.
• Urethra - Serves as passageway of both sperm and urine.
• Seminal vesicle - Secretes fluid that forms part of the semen.
• Prostate gland - Secretes fluid that also provides alkalinity to the semen.
• Bulbourethral glands- produce clear, viscous secretion that helps to lubricate the urethra
for sperm to pass through.
B. Female Reproductive System
• Clitoris- The homologue (equivalent) of the penis in females.
• Vagina- Main entrance to the female reproductive tract.
• Cervix- Projection of the uterus into the vagina; leads to the uterus.
• Uterus- Also known as the womb, where the embryo develops.
• Endometrial lining/endometrium- Innermost lining of the uterus where the embryo
implants and develop.
• Fallopian tubes- where fertilization takes place.
• Ovaries- Female gonads that release the oocytes during ovulation.
Human Development
1. Fertilization
2. Cleavage
3. Morula and Blastocyst
◉ Morula- A human blastula made up of a solid ball of cells.
◉ Blastocyst- A human blastula composed of the inner cell mass, which becomes the
embryo, and the trophectoderm, which becomes the placenta.
4. Implantation- Attachment of blastocyst to endometrium of uterus; start of pregnancy.
5. Gestation- Differentiate embryonic development from fetal development in terms of period
covered during this period.
The Menstrual Cycle
I. Ovarian Cycle
• Follicular phase- the follicles begin to mature.
• Ovulation- the discharge of mature ovum from the ovary
• Luteal phase- prepares the uterus for gestation to house and nourish an embryo.
II. Uterine cycle:
• Menstrual phase- early part of the follicular phase of the ovaries (days 1-5). AKA “the
period”
• Proliferative phase- latter part of the follicular phase of the ovaries (days 8-14)
• Secretory phase- corresponds to the luteal phase of the ovaries.
Contraception and Its Types
• Ovulation-suppressing methods- Oral contraceptives
• Barrier methods- Physical (Condom, Diaphragm, Cervical cap)
• Chemical methods- Spermicidal jelly and foam
• Surgical methods- Vasectomy and Tubal ligation
• Implantation-suppressing methods- IUD and Morning-after pill
• Natural methods: Abstinence, Calendar