Differentiate between the following : (a) Polarity and Symmetry (b) Prions and Viroids (c) Rust and Smut diseases (d) Eusporangiate and Leptosporangiate ferns (e) Downy mildews and Powdery mildews.

(a) Polarity and Symmetry

Polarity refers to the inherent physiological differentiation of plant organs, particularly in relation to the direction of growth. It’s evident in the apical-basal axis of a plant, where the apex (shoot) and base (root) exhibit distinct developmental patterns. This is largely governed by auxin transport. Symmetry, on the other hand, describes the arrangement of similar parts around a central axis.

Polarity	Symmetry
Directional growth; apical-basal axis.	Arrangement of parts around an axis.
Physiological differentiation.	Morphological arrangement.
Example: Apical dominance.	Example: Radial symmetry in a flower.

(b) Prions and Viroids

Both prions and viroids are infectious agents, but they differ significantly in their composition. Prions are misfolded proteins that can induce normal proteins to adopt the same misfolded shape, leading to disease. They lack nucleic acid. Viroids are small, circular RNA molecules that do not encode proteins but can replicate within plant cells, causing disease.

Prions	Viroids
Composed of misfolded proteins.	Composed of small, circular RNA.
Affect animals (e.g., Mad Cow Disease).	Affect plants (e.g., Potato Spindle Tuber Disease).
Lack nucleic acid.	Contain RNA, but do not encode proteins.

(c) Rust and Smut Diseases

Both rust and smut are fungal diseases that affect plants, but they differ in their symptoms and the fungal structures they produce. Rust diseases are characterized by reddish-brown pustules on leaves and stems, containing urediniospores and teliospores. Smut diseases, conversely, cause black, powdery masses of spores (smut) that replace plant tissues, particularly in grains.

Rust Diseases	Smut Diseases
Reddish-brown pustules.	Black, powdery masses (smut).
Urediniospores and teliospores present.	Smut spores replace plant tissues.
Example: Wheat stem rust.	Example: Corn smut.

(d) Eusporangiate and Leptosporangiate Ferns

Ferns are classified based on their sporangium development. Eusporangiate ferns have large, thick-walled sporangia that develop from several initial cells, often with a substantial stalk. They are generally considered more primitive. Leptosporangiate ferns have smaller, thin-walled sporangia that develop from a single initial cell, typically with a delicate stalk. They represent the majority of modern ferns.

Eusporangiate Ferns	Leptosporangiate Ferns
Large, thick-walled sporangia.	Small, thin-walled sporangia.
Develop from multiple initial cells.	Develop from a single initial cell.
More primitive.	More advanced; majority of modern ferns.
Example: Equisetum (horsetails).	Example: Dryopteris (wood fern).

(e) Downy Mildews and Powdery Mildews

Both downy and powdery mildews are fungal diseases affecting plants, but they differ in their appearance and the location of fungal growth. Downy mildews appear as yellowish spots on the upper leaf surface, with a downy growth of fungal spores on the underside. Powdery mildews appear as a white, powdery coating on the surface of leaves, stems, and flowers.

Downy Mildews	Powdery Mildews
Yellowish spots on upper leaf surface.	White, powdery coating on plant surfaces.
Downy growth on underside of leaves.	Fungal growth remains on the surface.
Often caused by oomycetes (water molds).	Caused by ascomycete fungi.
Example: Grape downy mildew.	Example: Rose powdery mildew.