Fertilization outside the body

The process of sexual reproduction begins with the union of a sperm and an egg, which is known as fertilisation. This can happen either inside (internal fertilisation) or outside (external fertilisation) the female’s body. Human reproduction exemplifies the former, while seahorse reproduction exemplifies the latter. External fertilisation is a procedure that happens outside of an organism’s body and often requires a body of water for successful fertilisation. For example, sperms and eggs are discharged into the environment. External fertilisation occurs when the female body releases the egg and the male body releases the sperm in the same environment during spawning. Let’s take a deeper look at the issue, its characteristics, advantages and disadvantages.

What exactly is fertilisation?

In numerous species, fertilisation happens outside the female’s body. In these animals, fertilisation occurs in the water. During the spring and rainy seasons, frogs and toads move to ponds and sluggish streams. When the male and female meet in water, the female produces hundreds of eggs. Unlike a hen’s egg, a frog’s egg is not protected by a cell and is hence incredibly fragile. The eggs are bound together by a jelly covering that also protects them. As the eggs are laid, male sperm is put on top of them. Each sperm floats about in the water at random due to its long tail. The sperm and eggs come into contact.

External Fertilization

External Fertilization occurs outside the body. External fertilisation is most commonly found in aquatic environments, where both eggs and sperm are released into the water. Fertilization can occur after the sperm reaches the egg. 

The majority of external fertilisation occurs during the spawning process, when one or more females release their eggs and the male(s) release sperm in the same area at the same time. The length of daylight or the temperature of the water may cause the release of reproductive material. 

Crustaceans (such as crabs and shrimp), mollusks (such as oysters), squid, and echinoderms all spawn (such as sea urchins and sea cucumbers). Courtship behaviour can be observed in pairs of fish that are not broadcast spawners. 

This enables the female to choose a specific male.The egg and sperm release trigger (spawning) causes the egg and sperm to be concentrated in a small area, increasing the possibility of fertilisation.

External fertilisation keeps the eggs from drying out in an aquatic environment. Broadcast spawning can result in a more diverse mix of genes within a group, resulting in greater genetic diversity and a better chance of species survival in a hostile environment. Broadcast spawning is the only mechanism for sessile aquatic organisms like sponges to fertilise and colonise new environments. 

The presence of fertilised eggs and developing young in the water creates predation opportunities, resulting in offspring loss. Individuals must therefore produce millions of eggs. The offspring created by this method must mature quickly. Eggs produced by broadcast spawning have a low survival rate.

Human Fertilization via External Fertilization

Normally, a woman’s egg and sperm are fertilised within her body. After the fertilised egg connects to the uterine lining and grows for around 9 months, a baby is born. This is known as the natural process in humans. Because a tiny fraction of females have trouble conceiving naturally, humans employ external fertilisation, which entails keeping the male’s sperm and the female’s eggs in a Petri dish for a few days. After a few days, the egg is ejected from the female’s body.

Advantages and Disadvantages of External Fertilization

Advantages

• Producing gametes takes a little amount of energy.
• The gametes have the ability to travel long distances.
• Young ones can swiftly occupy vast water regions.
• Females have a far greater success rate since they lay hundreds of eggs.

Disadvantages

• Some gametes do not meet zygotes because of the aquatic environment and kind of water.
• Different animals normally devour the zygote, or it dies from natural reasons.
• Predators do not safeguard the children.

Internal Fertilization

Internal fertilisation is most common in land-based animals, though some aquatic animals use it as well. Following internal fertilisation, offspring are produced in three ways: oviparity, ovoviparity, and viviparity.

In oviparity, fertilised eggs are laid outside the female’s body and develop there, receiving nourishment from the egg’s yolk. Most bony fish, many reptiles, some cartilaginous fish, most amphibians, two mammals, and all birds exhibit this behaviour. Reptiles and insects lay leathery eggs, whereas birds and turtles lay eggs with high calcium carbonate concentrations in the shell, making them hard. These animals are known as oviparous.

In ovoviparity, fertilised eggs are retained in the female, but the embryo is fed by the yolk of the egg; the young are fully developed when they hatch. Some bony fish (such as the guppy, Lebistes reticulatus), sharks, lizards, snakes (such as the garter snake, Thamnophis sirtalis), vipers, and invertebrates exhibit this behaviour (such as the Madagascar hissing cockroach, Gromphadorhina portentosa).

The young develop within the female in viviparity, receiving nourishment from the mother’s blood via a placenta. The offspring develops and is born alive in the female. Most mammals, some cartilaginous fish, and a few reptiles are viviparous as a result of this.

Internal fertilization has the advantage of protecting the fertilized egg from dehydration when it is exposed to the elements on land. Because the embryo is isolated within the female, predation on the young is reduced. Internal fertilisation also improves egg fertilisation by a specific male. Even though this method produces fewer offspring, their survival rate is higher than that of external fertilisation.

Conclusion 

The process of sexual reproduction begins with the union of a sperm and an egg, which is known as fertilisation. External fertilisation occurs when the female body releases the egg and the male body releases the sperm in the same environment during spawning. When the male and female meet in water, the female produces hundreds of eggs. External fertilisation is most commonly found in aquatic environments, where both eggs and sperm are released into the water. The majority of external fertilisation occurs during the spawning process, when one or more females release their eggs and the male release sperm in the same area at the same time.