Main Difference – Fertilization vs Germination

Fertilization and germination are two events of sexual reproduction in plants. The main difference between fertilization and germination is that fertilization is the fusion of gametes, which forms the zygote whereas germination is the development of a plant from seed or spore under favorable conditions. Fertilization occurs after the pollination in flowering plants. The zygote is the result of fertilization that develops into the embryo. The embryo of the seed plants is contained inside the seed. Under favorable conditions, the seed absorbs water, and the root grows through the seed coat. Fertilization occurs in all types of organisms that produce gametes while germination only occurs in fungi and plants.  

Key Areas Covered

1. What is Fertilization
     – Definition, Fertilization in Plants, Fertilization in Animals, Mechanism
2. What is Germination
     – Definition, Germination of Seeds, Germination of Spores, Mechanism
3. What are the Similarities Between Fertilization and Germination
     – Outline of Common Features
4. What is the Difference Between Fertilization and Germination
     – Comparison of Key Differences

Key Terms: Embryo, Epigeal Germination, Fertilization, Germination, Hypogeal Germination, Plants, Seed, Sexual Reproduction, Spore, Zygote

What is Fertilization

Fertilization is the fusion of male and female gametes in plants, animals, and other organisms. The fusion of gametes is also called syngamy.

Fertilization in Plants

In flowering plants, fertilization follows pollination. During pollination, pollen grains land on the stigma of a flower in the same species. A pollen consists of a tube cell and a generative cell. Tube cell produces the pollen tube. Generative cell develops two sperm cells. The pollen tube grows down the style until it finds the ovary. Once the pollen tube penetrates the ovule using a tiny hole in the ovule called micropyle, it bursts, releasing the two sperm cells into the embryo sac.

Double Fertilization

Double fertilization occurs in flowering plants (angiosperms); one sperm fertilizes the egg cell situated at the bottom of the female gametophyte, forming the diploid zygote. Female gametophyte is also called the embryo sac. The other sperm cell is fused with the central cell. The central cell contains two haploid polar nuclei. Hence, the resulting cells are triploid, which are divided by mitosis, forming the endosperm. Endosperm is a nutrient-rich tissue, found inside the seed. Different stages of double fertilization in flowering plants are shown in figure 1.

Figure 1: Double Fertilization

The ovary of an angiosperm is developed into a fruit after the fertilization. Some plants like avocados contain a single ovule in the ovary per a flower. These plants develop a single seed per fruit. Some plants like kiwi fruit contain several ovules in the ovary of a flower. They produce multiple seeds per fruit. In fruits with multi-seeds, multiple pollen grains are involved in the fertilization of several ovules.

Fertilization in Animals

The two types of fertilizations in animals are internal fertilization and external fertilization. Internal fertilization shows high survival rates of the embryo than the external fertilization. 

Internal Fertilization

Internal fertilization takes place inside the female organism. Oviparity, viviparity, and ovoviparity are the three methods of internal fertilization. Internal fertilization occurs in mammals, reptiles, some birds, and some fish.

External Fertilization

External fertilization takes place in damp environments outside the female organism. The eggs and sperms are called spawn in the external fertilization. Both male and female gametes should be released to the environment at the same time. However, the gametes as well as the embryo should be protected from dehydration as they exist on the outside of the female organism. External fertilization occurs in frog, fish, echinoderms, mollusks, and crustaceans. 

What is Germination

Germination refers to the development of a plant from a seed or spore under favorable conditions. The plants that produce seeds are called seed plants. Spores are produced by both lower plants as well as fungi.

Germination of Seeds

Some seeds are dormant and the others non-dormant. Non-dormant seeds start germination with proper humidity and temperature. Imbibition is the uptake of water by the seed. Upon imbibition, seeds expand, and enzymes become activated, and food inside the seed become hydrated. The activated enzymes start the metabolic processes, enabling the growth of the embryo. The radical or the root first emerge from the seed coat. Eventually, the shoot emerges from the seed.

The two types of germination of seed plants are epigeal germination and hypogeal germination, which are shown in figure 2.

Figure 2: Types of Germination

During epigeal germination, the cotyledons of the seed are brought above the ground due to the elongation of the embryonic stem or the hypocotyl. In hypogeal germination, the cotyledons remain in the soil due to the elongation of the epicotyl. The epigeal germination of the mung beans is shown in video 1.

Video 1: Epigeal Germination of Mung Beans

Germination of Spores

Bacteria, fungi, algae, and lower plants such as bryophytes and ferns produce spores. As most of the spores are dormant, they have to undergo maturation prior to germination. Upon germination, the dormant spores decrease heat resistance and refractility, release of dipicolinic acid, and increase in permeability.

Imbibition is the first step of germination of spores as well. The breakdown of the wall of the spore allows the release of the thallus. During the outgrowth of the thallus, DNA replication, gene transcription, and protein synthesis take place in an orderly manner. The functional genes in DNA replication, transcription, protein synthesis, transport, and regulation are activated. Then, cell division, cell membrane and cell wall expansion take place, aiding the further growth of the thallus.

Similarities Between Fertilization and Germination

• Both fertilization and germination are two events of the sexual reproduction in plants.
• Both fertilization germination occurs in other organisms as well.

Difference Between Fertilization and Germination

Definition

Fertilization: Fertilization refers to the fusion of male and female gametes in plants, animals, and other organisms.

Germination: Germination refers to the development of a plant from a seed or spore under favorable conditions.

Significance

Fertilization: Fertilization is the fusion of gametes to form the zygote.

Germination: Germination is the formation of a new plant from the seed.

Followed by

Fertilization: Pollination is followed by fertilization in flowering plants.

Germination: Germination takes place when the spread seeds or spores meet favorable conditions.

Conditions

Fertilization: Fertilization takes place in damp environments in lower plants.

Germination: Germination takes place under proper temperature and humidity.

Examples

Fertilization: Fertilization occurs in all gamete-producing organisms.

Germination: Germination occurs in seed-producing plants and fungi.

Conclusion

Fertilization and germination are two events of the farthest events of the sexual reproduction of plants. During fertilization, the fusion of two gametes takes place, producing the zygote that eventually becomes the embryo. Germination is the development of a new plant from the seed. Both fertilization and germination also occur in animals and fungi respectively. The main difference between fertilization and germination is the mechanism of each event during reproduction.

Reference:

1.Monroy, Alberto. “Fertilization.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 22 Nov. 2017, Available here.
2.“Seed germination.” Plants In Motion, Available here.
3.“Plant Science 4 U.” Types of Seed Germination – Epigeal vs Hypogeal, Available here.
4.Setlow, P. “Spore germination.” Current opinion in microbiology., U.S. National Library of Medicine, Dec. 2003, Available here.

Image Courtesy:

1. “Double Fertilization” By The original uploader was Triploid at English Wikipedia (CC-BY 3.0) via Commons Wikimedia
2. “Germination-en” By Germination.svg: *Germinacion.png: Kat1992derivative work: Begoonderivative work: Begoon – This file was derived from Germination.svg (CC BY-SA 3.0) via Commons Wikimedia

ncG1vNJzZmiolZm2oq2NnKamZ5Ses6ex0Z6lnJ1dl7K1w8SepWaelafBqrjIs5itoZ%2BjeqK6w2aenqqdnruiwMiopWg%3D