Biology: Reproduction Methods

Asexual Reproduction

• Asexual reproduction produces genetically identical offspring from a single parent.
• Bacteria reproduce through binary fission, where one bacterium divides into two identical cells.
• Generation time is the time taken for a cell to divide.
• Advantages include speed and maintaining desirable characteristics.
• Disadvantages include lack of genetic diversity, making offspring susceptible to the same diseases and environmental changes.

Sexual Reproduction

• Sexual reproduction involves the fusion of two gametes (sex cells) to create a zygote, resulting in genetically unique offspring.
• Fertilization is the fusion of gamete nuclei.
• Gametes are haploid (half a set of chromosomes).
• Zygotes are diploid (full set of chromosomes).
• Advantages include genetic diversity, allowing quick adaptation to environmental changes.
• Disadvantages include time and energy involved as offspring are not identical to their parents, and the need to find a mate.

Flowering Plants - Reproduction

• Flowers are the reproductive organs of flowering plants.
• They usually contain both male and female reproductive parts.
• The structures of insect-pollinated and wind-pollinated flowers differ.
• Insect-pollinated flowers are often brightly colored and scented, with nectar and large pollen.
• Wind-pollinated flowers are often small, dull-colored, with a large volume of light pollen.

Functions of Parts of a Flower

• Sepals protect the flower bud.
• Petals attract pollinators.
• Anthers produce pollen grains (containing male gametes).
• Stigma is a platform for pollen to land.
• Ovary contains ovules that develop into seeds.

Pollination

• Pollination is the transfer of pollen from the anther to the stigma.
• Agents of pollination include insects, birds, mammals, water, and wind.

Self-Pollination vs. Cross-Pollination

• Self-pollination: pollen transferred to the same flower or another flower on the same plant.
• Cross-pollination: pollen transferred to a flower on a different plant of the same species.
• Advantages and disadvantages of each method are listed.

Fertilization in Plants

• Pollen tube grows and releases enzymes.
• Pollen tube reaches and then grows into the ovary.
• The pollen nucleus travels down the pollen tube to the ovule.
• Fertilisation occurs when the pollen nucleus fuses with the female nucleus.
• A zygote is formed and develops into a seed.

Germination

• Germination is the process controlled by enzymes.
• Water activates enzymes to convert insoluble food stores into soluble form.
• Oxygen is necessary for aerobic respiration.
• The required temperature ensures enzymes work optimally.

Sexual Reproduction in Humans - Male

• Testes produce sperm and testosterone.
• Scrotum holds testicles.
• Sperm duct carries sperm to the urethra.
• Prostate gland produces seminal fluid.
• Urethra carries semen to the tip of the penis.
• Penis is the male sex organ for transferring semen to the female.

Sexual Reproduction in Humans - Female

• Ovaries produce ova (eggs), progesterone, and estrogen.
• Oviduct (fallopian tube) carries the ovum to the uterus.
• Uterus is the site for fetal development.
• Cervix is the neck of the uterus with a small opening.
• Vagina receives the penis and is the birth canal.

Fertilisation and Early Development

• One sperm penetrates the ovum.
• The zygote forms, which divides, and grows.
• The zygote implants itself in the uterus wall.
• The fetus develops with the umbilical cord and placenta.
• The placenta facilitates exchange of nutrients and waste between the mother and fetus.

Adaptive Features of Gametes

• Sperm: small, elongated, streamlined, contains energy storage (mitochondria), and millions in number to have high chance of fertilizing the ovum.
• Ovum: larger, spherical with protective layer (jelly coat).

Sexual Hormones in Humans

• Hormones regulate secondary sexual characteristics during puberty.
• Primary sexual characteristics are present during development in the uterus.
• Secondary sexual characteristics include changes during puberty.
• Testosterone and estrogen play crucial roles in development and regulation of secondary sexual characteristics.
• The menstrual cycle involves the interplay of hormones (FSH, LH, estrogen, progesterone) in the ovaries and the uterus.
• The cycle has phases: menstruation, follicle maturing, ovulation, and the corpus luteum formation.