The main difference between anatropous ovule and orthotropous ovule is that the anatropous ovules are inverted, with the micropyle located near the base, whereas the orthotropous ovules are straight, with the micropyle located at the top.
Ovules are female reproductive structures in flowering plants. They are located within the ovary of the flower. Ovules play a crucial role in the sexual reproduction of plants. Anatropous and orthotropous are two types of ovules in flowering plants.
Key Areas Covered
1. What is an Anatropous Ovule
– Definition, Orientation, Structure
2. What is an Orthotropous Ovule
– Definition, Orientation, Structure
3. Similarities Between Anatropous and Orthotropous Ovule
– Outline of Common Features
4. Difference Between Anatropous and Orthotropous Ovuley
– Comparison of Key Differences
Key Terms
Anatropous Ovule, Orthotropous Ovule
What is an Anatropous Ovule
An anatropous ovule is a completely inverted ovule turned back 180 degrees on its stalk. The micropyle is located near the base of the ovule rather than on the top. There are three parts of the anatropous ovule. They are the integument, nucellus, and embryo sac. The integument is the outermost layer, while the nucellus is located in the center, containing the female gametophyte or the embryo sac. Moreover, in anatropous ovules, the ovule body fuses with the funiculus.
This ovule develops into a seed, which forms as a result of the fertilization between the male gamete and the female gamete. Anatropous ovules play a major role in the fertilization process. The inversion of the nucellus in the anatropous ovule protects the developing embryo. This inversion also helps in the more efficient transport of nutrients from the parent plant to the embryo. Generally, the cells of the micropyle at the base of the ovule make it easier for the pollen tube to enter the ovule and deliver the male gamete to the egg cell.
Anatropous ovules are the most common type of ovule in angiosperms. They are also present in some gymnosperms. Moreover, anatropous ovules are usually located on the surface of the female cone and are not enclosed within an ovary in gymnosperms.
What is an Orthotropous Ovule
An orthotropous ovule is characterized by a straight, upright orientation in which the nucellus is aligned with the micropile. They are found particularly in non-flowering plants. Orthotropous ovules are common in the plant families Polygonaceae and Piperaceae. However, orthotropous ovules are less common than anatropous ovules.
There are three parts in the ovule, namely the integument, the nucellus, and the embryo sac. The orthotropous ovule is straight and upright. The nucellus is located at the base of the ovule, while the micropile is located at the top. The micropyle and the hilum lie directly in the same line. Furthermore, this orientation facilitates the pollen tube to enter the ovule and reach the egg cell easily. In addition, orthologous ovules do not exhibit the fusion of the ovule body with the funiculus.
Similarities Between Anatropous and Orthotropous Ovule
- They contain the same basic structures, such as the integuments, nucellus, and embryo sac.
- Moreover, the pollen grain can fertilize both types of ovules to form a zygote.
- Anatropous and orthotropous ovules have the potential to develop into seeds once fertilization occurs.
Difference Between Anatropous and Orthotropous Ovule
Definition
Anatropous ovules are a type of ovule found in flowering plants where the ovule is inverted, with the micropyle located near the base. On the other hand, orthotropous ovules are a type of ovule that is straight with the micropyle located at the top.
Ovule Orientation
Anatropous ovules are inverted 180 degrees completely, while orthotropous ovules are straight.
Micropyle
In an anatropous ovule, the micropyle is located at the bottom, whereas in an orthotropous ovule, the micropyle is located at the apex.
Fusion
In anatropous ovules, the ovule body fuses with the funiculus, while in orthotropous ovules, there is no such fusion of the ovule with the funiculus.
Type of Plants
Anatropous ovules are common in angiosperms and also found in some gymnosperms, whereas orthotropous ovules are common in gymnosperms, particularly in Polygonaceae and Piperaceae families.
Conclusion
In brief, ovules are female reproductive structures present in flowering plants. Anatropous ovules and orthotropous ovules are two forms of ovules in plants. The main difference between anatropous ovule and orthotropous ovule is that the anatropous ovules are inverted, with the micropyle located near the base, whereas the orthotropous ovules are straight, with the micropyle located at the top.
Reference:
1. “Ovule – An Overview.” Science Direct.
Image Courtesy:
1. “Ovules in flower” – The original uploader was Tameeria at English Wikipedia. – Transferred from en. Wikipedia to Commons. (CC BY-SA 3.0) via Commons Wikimedia
2. “Image from page 88 of “Botany of the southern states. In two parts” (1866)” By Internet Archive Book Images (Public Domain) via Flickr
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