Comparison of Gymnosperms and Angiosperms

Plant kingdom is rich with a large number of species. At every stage of evolutionary development there are interesting examples of new structures coming up to give better tools of survival to the plant
The natural habitat of algae is water, so they can be compared to aquatic animals. As life started in the aquatic environment so algae are the most primitive group of plants. Moreover, their structure is simple with no special organs for special functions.
The way amphibian animals are like a linking point between aquatic and terrestrial life, bryophytes show the same characteristic. Bryophytes need water to facilitate reproduction although they live on soil. In bryophytes we witness some development of leaf-like structures and root like structures. Antheridiopore and Archegoniopore can be compared to flowers of angiosperms
When we analyze Pteridophytes we can see development of vascular tissues for transport of substances. Pteridophytes show true roots as well. While the dominant phase is gametophyte in bryophytes it is sporophyte in Pteridophytes. This is another indication of evolution Gymnosperm look more like a common plant, with well defined roots and stem. Appearance of seeds is another indicator of development. Seeds gave the ability to survive longer durations of adverse conditions. This is a sort of guarantee to continue progeny even after a long spell of adverse environmental conditions.
Angiosperms are more advanced because of many factors. The seed is covered, which means more protection to the embryo. Appearance of flowers was a means to facilitate cross pollination for more variations. Angiosperms can modify almost any part for special purpose. For example, certain plants store excess food in modified leaves or stems or roots.
This essay is an interesting description of how from simple thalloid algae plants have developed into more complicated angiosperms. While algae have a simple thallus to carry out all biological functions, angiosperms have dedicated tissue systems for various functions.

Features of Plant Kingdom:
1.Plants are autotrophic, except some carnivorous plants. They trap photo energy from sunlight and convert it to chemical energy through photosynthesis. Because of this plants are the main channel for supplying energy in the food chain on earth.
2. Reproduction in plants can be by any of the following modes: Vegetative or Asexual, and Sexual Reproduction.
3. Plant cell is unique because of presence of cell wall and large vacuoles. Green parts of plant contain chlorophyll, which helps them in trapping the photo energy.
4.Sizes of plants can vary from microscopic to a very large tree. Plants are mainly divided into Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms

5.Lower plants, like algae and bryophytes have thalloid structure, while higher plants, like gymnosperms and angiosperms, have clearly defined roots and stems.
6.In higher plants root gives a means to anchor in the soil and helps the plant in taking minerals and water from the soil. Green leaves on the stem help them in photosynthesis.
7.Most of the plant grow as a result of photosynthesis. After photosynthesis extra food is utilized to facilitate growth.
8.Usually in higher plants growth is unlimited and some taller trees can live a life of more than 1000 years.
9.Being the main carbon fixation agents, plants are very important for the whole ecology.
10.The whole food basket for humans is being filled by the plant kingdom. Even animal products, like milk and poultry, are indirect results of plant's carbon fixation.
11.Plants supply raw materials for a majority of economic activities. Wood for furniture and building materials come from plants. The whole paper industry is dependent on plant kingdom. Think of a life if there. was no paper and you may understand the larger impact on human civilization.
12.Angiosperms have special organs, called flower, to bear sexual parts. Flowers are helpful tool in facilitating variations and further evolution of the plant kingdom.

The algae are divided into three main classes

I. Chlorophyceae
Characteristics:
1. They are commonly called green algae.
2. The plant body may be unicellular, colonial or filamentous.
3. They are usually grass green due to the dominance of pigments chlorophyll a and b. The pigments are localized in definite chloroplasts. The chloroplasts may be discoid, plate-like, reticulate, cup shaped, spiral or ribbon-shaped in different species.
4. Most of the members have one or more storage bodies called pyrenoids located in the chloroplasts. Pyrenoids contain protein besides starch. Some algae may store food in the form of oil droplets.
5. Green algae usually have a rigid cell wall made of an inner layer of cellulose and an outer layer of pectose.
Reproduction:
1. Vegetative reproduction usually takes place by fragmentation or by formation of different types of spores.
2. Asexual reproduction is by flagellated zoospores produced in zoosporangia.
3. The sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous, anisogamous or oogamous.
Common Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.
ll. Phaeophyceae
Characteristics:
1.They are also known as brown algae and are found primarily in marine habitats.
2.They range from simple branched, filamentous forms (Ectocarpus) to profusely branched forms as represented by kelps, which may reach a height of 100 metres.
3. They possess chlorophyll a, c, carotenoids and xanthophylls. They vary in colour from olive green to various shades of brown depending upon the amount of the xanthophyll pigment, fucoxanthin present in them.
4. Food is stored as complex carbohydrates, which may be in the form of laminarin or mannitol.
5. The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin. The protoplast contains, in addition to plastids, a centrally located vacuole and nucleus
The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf like photosynthetic organ - the frond.
Reproduction:
1.Vegetative reproduction takes place by fragmentation.
2. Asexual reproduction in most brown algae is by biflagellate zoospores that are pear-shaped and have two unequal laterally attached flagella.
3. Sexual reproduction may be isogamous, anisogamous or oogamous. Union of gametes may take place in water or within the oogonium (oogamous species). The gametes are pyriform (pear shaped) and bear two laterally attached flagella.
Common Examples: Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.
III. Rhodophyceae
Characteristics:
1. They are commonly called red algae because of the predominance of the red pigment, r-phycoerythrin in their body.
2. Majority of the red algae are marine with greater concentrations found in the warmer areas. They Occur in both well-lighted regions close to the surface of water and also at great depths in oceans where relatively little light penetrates.
3. The red thalli of most of the red algae are multicellular. Some of them have complex body organisation.
4. The food is stored as floridean starch which is very similar to amylopectin and glycogen in structure.
Reproduction:
1.The red algae reproduce vegetatively by fragmentation.
2.They reproduce asexually by non-motile spores and sexually by non-motile gametes.
3. Sexual reproduction is oogamous and accompanied by complex post fertilization developments.
Common Examples: Polysiphonia, Porphyra, Gracilaria and Gelidium.

Horticulturists are interested in Ginkgo as it has natural immunity to several plant diseases.
Important features are as follow
i)The plant is a tall tree of upto 30 m height.
ii) Leaves - shaped.
iii) Leaves have furcate venation.
iv) Dwarf shoots of female plant bear distinct megasporangiate structures.
v) Endosperm of roasted seed is edible 
Horticulturists prefer to grow only male plants,as female plant give unpleasant smell.   

Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as microspore and the larger one is known as megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. The male gametophyte releases the male gametes and these reach the female gametophyte to fuse with the egg. The development of the zygote takes place inside the female gametophyte. This retention and germination of the megaspore within the megasporangium ensure proper development of the zygote. The zygote develops into the future sporophyte. The evolution of the seed habit is related to the retention of the megaspore.
Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit.
Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.

Differences between natural and artificial system are

The vascular plants dominate earth and make the planet green everywhere.The features which enable this quality to happen are 
(i) Strong roots capable of penetrating deep into the soil.
(ii) Development of waterproof layer on aerial surfaces especially the leaves to reduce transpiration.
(iii) Presence of strong, woody mechanical tissue to provide mechanical support to aerial parts and allow them to rise to a great height.
(iv) Vascular tissues are present for long distance transport of substances.

Protonemal cell of moss - haploid
Primary endosperm nucleus in dicots - triploid
Leaf cell of moss - haploid
Prothallus cell of ferns - haploid
Gemma cell in Marchantia - haploid
Meristem Cell of monocots - diploid
Ovum of liverworts - haploid
Zygote of ferns - diploid

Zoospores Flagellate spores, under favourable conditions.
Aplanospores  Non-flagellate, thin-walled spores under approaching unfavourable condition.
Hypnospores Thin-walled, resting spores in unfavourable condition.
Akinetes Thin-walled and thick-walled spores formed from whole cells in unfavourable conditions.
Autospores Spores which look exactly parent cell formed under favourable conditions.