Why is fertilization necessary

An early development in reproduction occurred in the Annelids. These organisms produce sperm and eggs from undifferentiated cells in their coelom and store them in that cavity. When the coelom becomes filled, the cells are released through an excretory opening or by the body splitting open. Reproductive organs evolved with the development of gonads that produce sperm and eggs. These cells went through meiosis, an adaption of mitosis, which reduced the number of chromosomes in each reproductive cell by half, while increasing the number of cells through cell division.

Complete reproductive systems were developed in insects, with separate sexes. Sperm are made in testes and then travel through coiled tubes to the epididymis for storage.

Eggs mature in the ovary. When they are released from the ovary, they travel to the uterine tubes for fertilization. Some insects have a specialized sac, called a spermatheca , which stores sperm for later use, sometimes up to a year. Fertilization can be timed with environmental or food conditions that are optimal for offspring survival. Vertebrates have similar structures, with a few differences. Non-mammals, such as birds and reptiles, have a common body opening, called a cloaca , for the digestive, excretory and reproductive systems.

Coupling between birds usually involves positioning the cloaca openings opposite each other for transfer of sperm. Mammals have separate openings for the systems in the female and a uterus for support of developing offspring. The uterus has two chambers in species that produce large numbers of offspring at a time, while species that produce one offspring, such as primates, have a single uterus.

This can occur either outside the bodies or inside the female. Both methods have advantages and disadvantages. Once fertilized, the eggs can develop inside the female or outside.

Sustaining these high pressures and temperatures requires a huge amount of energy. The short answer is that nitrogen-containing fertilizers help crop plants grow faster and helps to produce more crops.

This allows agricultural land to be used more efficiently because fertilized land produces more food. The crops take it up of course! Unfortunately, that is not the end of the story. So, while fertilizers make crops grow better and faster, half of the fixed nitrogen we add is lost.

The lost nitrogen can end up in the atmosphere or it can be washed out of the soil and end up in waterways, such as groundwater, streams, lakes, rivers, and oceans Figure 2. This lost nitrogen causes a variety of environmental problems [ 2 ]. Some soil microorganisms can transform nitrogen provided in fertilizers into nitrogen-containing gases, which get released into the atmosphere like the greenhouse gas nitrous oxide N 2 O.

Greenhouse gases are one of the main factors accelerating global warming. In waterways, the addition of external nutrients like excess nitrogen is called eutrophication. Eutrophication is an unwanted fertilization of a waterway and it promotes the growth of microorganisms, algae, and plants, just like the fertilization of soil.

However, the fast growth of microorganisms and plants can use up all the oxygen in these waterways and turn them into so-called dead zones, because aquatic animals cannot live without oxygen. Eutrophication can also lead to the growth of algal species that produce toxic chemicals, called harmful algal blooms. While we need nitrogen from fertilizers in our agricultural soils, we do not need or want additional nitrogen in our atmosphere or waterways.

This means we have to balance the positive benefits of nitrogen fertilization more food with the negative consequences of excess fertilizer environmental problems [ 1 , 2 ]. Scientists are currently working to find this balance to improve our current situation. This solution is called improving the nitrogen use efficiency of agricultural environments. Here are a few examples of ongoing fertilizer research:. Microbiologists and soil scientists are working on ways to improve field conditions to promote the growth of naturally occurring soil nitrogen-fixing bacteria.

Once multicellular organisms evolved and developed specialized cells, some also developed tissues and organs with specialized functions. The evolution of reproductive organs arrived with the development of gonads that produced sperm and eggs.

These cells develop through meiosis, an adaption of mitosis, which reduced the number of chromosomes in each reproductive cell by half, while increasing the number of cells through cell division. The development of specialized gonads to produce sperm and egg was a major step in the evolutionary process.

Meiosis : The development of sperm and eggs occurs via the process of meiosis which reduces the number of chromosomes in each cell by half.

Sperm fertilizing an egg : The evolution of sex-specific gonads led to the development of sperm male and eggs female. When fertilized, if the conditions are favorable, the egg may develop into a new organism.

An early development in reproduction occurred in the Annelids. These organisms produce sperm and eggs from undifferentiated cells in their coelom, storing them in that cavity. When the coelom becomes filled, the cells are released through an excretory opening or by the body splitting open.

Further evolution of reproductive systems resulted in the development of reproductive systems that are sex specific. In these more advanced systems, sperm is made in the testes and then travels through coiled tubes to the epididymis for storage. Additionally, in these more advanced systems, eggs are matured in the ovary; when released, they travel to the uterine tubes for fertilization.

These types of reproductive systems developed in insects compared to annelids which have a coelom for storage. Specifically, in the insect reproductive system, a specialized sac developed, called a spermatheca, which is used to store sperm for later use, sometimes up to a year. This was a key development since fertilization in insects can be timed with environmental or food conditions that are optimal for offspring survival.

Vertebrates have similar structures i. Non-mammals, such as birds and reptiles, have a common body opening, called a cloaca, for the digestive, excretory, and reproductive systems. Coupling between birds usually involves positioning the cloaca openings opposite each other for transfer of sperm.

In mammals, there are separate openings for the systems in the female and a uterus for support of developing offspring. Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance.

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