Biological Reproduction in Plants and Animals Explained

Reproduction in Flowering Plants

The reproduction of flowering plants involves several key steps:

• Pollination: Pollen is transferred from the male stamen to the female stigma. Pollen is carried by insects or the wind.
• Fertilization: When pollen lands on a stigma of the same species, the pollen grain grows a tube to join with the female sex cell (gamete), known as the ovule.
• Seed Dispersal: After fertilization, the flower’s petals fall off and a fruit usually forms from the ovary. The fertilized ovules form seeds, which are dispersed by wind or animals.
• Seed Germination: Seeds begin to grow when temperature, air, and water conditions are optimal.

Sexual Reproduction in Animals

Sexual reproduction requires two individuals of different sexes, each producing a sex cell called a gamete. This process is divided into several phases:

• Gametogenesis: Reproductive cells or gametes are produced in the sexual organs.
• Copulation: The process in which sperm from a male is inserted into the female’s body.
• Fertilization: The fusion of male and female gametes.
• Embryonic Development: The period during which the embryo develops.
• Birth or Hatching: Birth is the process of expelling the new being from the mother’s body, while hatching is the breaking of the egg and the emergence of the new being.

A. Gametogenesis

Depending on the types of gonads present, animals are classified as:

• Unisexual: They possess only female or male gonads.
• Hermaphrodites: They have both female and male gonads. They can act as either male or female, but still require another individual to reproduce.

B. Fertilization

When the ovule and the spermatozoid join, they form the first cell of the living being, called a zygote. There are two types of fertilization:

• External Fertilization: The union of gametes occurs outside the female body (e.g., fish).
• Internal Fertilization: The union of gametes occurs inside the body of the female, involving copulation.

C. Embryonic Development

The zygote grows and becomes an embryo. Depending on where development takes place, animals are classified as:

• Viviparous: The embryo develops inside the female body. A special organ called the placenta feeds the embryo through the umbilical cord (characteristic of mammals).
• Oviparous: The embryo develops inside an egg outside the mother's body (characteristic of birds, fish, and reptiles).
• Ovoviviparous: The embryo develops inside an egg within the mother's body until it hatches (typical of some snakes, sharks, and amphibians).