Write Pteridophyta Classification.

Question:

Write Pteridophyta Classification.

Answer:

Pteridophyta is classified into four main classes:

Psilopsida

• They are the most primitive.
• The stem is photosynthetic and dichotomously branched.
• Rhizoids are present.
• Leaves are mostly absent.
• The sporophyte is homosporous synangium.
• Examples- Psilotum and Tmesipteris.

Lycopsida

• They are commonly known as club moss.
• Well-differentiated plant body with adventitious root, stem, rhizophores and leaves.
• The sporophyte is homosporous or heterosporous.
• Examples- Selaginella, Lycopodium.

Sphenopsida

• Commonly known as horsetail.
• Well-differentiated plant body with roots arising from nodes of the underground rhizome, stem and scaly leaves.
• Homosporous, sporangia are borne on strobili.
• Examples- Equisetum.

Pteropsida

• Commonly known as a fern.
• Well-differentiated plant body with roots, stem and leaves.
• The sporophyte is homosporous or heterosporous.
• Antherozoids are multiflagellate.
• Examples- Pteris, Dryopteris, Adiantum

 

Write Factors of Modern Synthetic Theory of Evolution.

Question: 

Write Factors of Modern Synthetic Theory of Evolution.

Answer:

There are some factors describing the modern theory of synthetic evolution which are as explained below-

In addition to these reactions, the other factors affecting the working of the process are the migration of the individuals from one form of the population to other, hybridization between the races of species increases the genetic variability of the popu­lation.

Recombination or Variation

Recombination of the new genotypes from the existing genes. The gene combinations having same indi­viduals with two kinds of alleles, mixing of the chromosomes during sexual reproduc­tion of two parents produce new individuals, an exchange of the chromosomal pairs of alleles during the meiosis which is called crossing overproduce the new form of gene combinations. Chromosomal mutations like deletion, inversion, duplication, translocation, polyploidy result in the recombination.

Mutation

The changes that occur in the gene due to phenotypic effect differential as the mutation. This produces a variety of changes that may be harmful. Many of the mutant forms of genes are recessive to the normal genes in a homozygous condition. These mutations cause variations in off springs.

Heredity

The transmission occurring in the variations from the parents to their off springs is a primary mechanism in the evolution. The organisms which possess hereditary properties are favored in the struggle for the existence. By this, the off springs benefit from the characteristics of parents.

Natural selection

Natural selection produces a change in the frequency of the genes from one generation to the other favouring the differential form of the reproduction. The natural selection process creates an adaptive relation between the environment and the population through various combinations of genes.

Isolation

It is one of the significant factors responsible for the synthetic theory of evolution. The isolation helps in preventing the interbreeding of related organisms which is a reproductive form of isolation.

What is plant tissue culture? also write procedure, type and uses of plant tissue culture.

Question:

What is plant tissue culture? also write procedure, type and uses of plant tissue culture.

Answer:

Plant tissue culture was a new addition to the methods of plant breeding that developed around the 1950s. Since the conventional breeding techniques could not fulfil the required demand of crops, tissue culture came around as a grand leap in breeding practices. It makes use of parts of a plant to generate multiple copies of the plant in a very short duration. The technique exploits the property of totipotency of plant cell which means that any cell from any part of the plant can be used to generate a whole new plant.

Types of Plant tissue culture

1. Seed Culture
2. Embryo Culture
3. Callus Culture
4. Organ Culture
5. Protoplast Culture
6. Anther Culture

Procedure of Plant tissue culture

The part(s) of the plant used for culturing is known as explants. The explants are cultured in-vitro on a nutrient medium that caters to fulfil its nutritional requirements. The nutrient medium must provide the following:-

1. Macronutrients – This includes elements like nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S) which is required for proper growth and morphogenesis.
2. Micronutrients – Elements like iron (Fe), manganese (Mn), zinc (Zn) etc., which are also crucial to the growth of tissues.
3. Carbon or Energy source – This is one of the most crucial ingredients of the nutrient media. Sucrose is the most widely used carbon source among other carbohydrates that serve to provide C, H, and O.
4. Vitamins, amino acids, and other inorganic salts.

Apart from these, the culture media also serves as a medium for supplying phytohormones or plant growth regulators to the issues which bring about their morphogenesis as per requirement. The tissues of the explants first lose their specificity to form a hard brown lump known as callus. The callus then splits to develop a plant organ or a whole new plant depending upon the quantity and composition of phytohormones supplied. The entire process requires strict aseptic conditions to be maintained at all times as a single contamination can ruin an entire batch of plants.

Uses of Plant tissue culture

Tissue culture is used to develop thousands of genetically identical plants from one single parent plant known as somaclones, and this process is known as micropropagation. The method offers an advantage over other methods as it can be used to develop disease free plants from disease-rode plants by using their meristems (apical and axillary) as explants.

Since this method produces new plantlets by the score of thousands, it has been used extensively for the production of commercially important plants including food plants like tomato, banana, apple etc. The most notable example of the application of micropropagation was observed in the farming of orchids as it rose exponentially due to the availability of millions of plantlets due to tissue culture methods.

For a more detailed understanding of plant tissue 

What is Ecological Succession? also write examples and type of ecological succession.

Question: 

What is Ecological Succession? also write examples and type of ecological succession.

Answer:

Ecological succession is the steady and gradual change in a species of a given area with respect to the changing environment. It is a predictable change and is an inevitable process of nature as all the biotic components have to keep up with the changes in our environment.

The ultimate aim of this process is to reach equilibrium in the ecosystem. The community that achieves this aim is called a climax community. In an attempt to reach this equilibrium, some species increase in number while some other decrease.

In an area, the sequence of communities that undergo changes is called sere. Thus, each community that changes is called a seral stage or seral community.

All the communities that we observe today around us have undergone succession over a period of time since their existence. Thus, we can say that evolution is a process that has taken place simultaneously along with that of ecological succession. Also, the initiation of life on earth can be considered to be a result of this succession process.

If we consider an area where life starts from scratch by the process of succession, it is known as primary succession. However, if life starts at a place after the area has lost all the life forms existing there, the process is called secondary succession.

It is obvious that primary succession is a rather slow process as life has to start from nothing whereas secondary succession is faster because it starts at a place which had already supported life before. Moreover, the first species that comes into existence during primary succession is known as pioneer species.

Types of Ecological Succession

These are the following types of ecological succession:

Primary Succession

Primary succession is the succession that starts in lifeless areas such as the regions devoid of soil or the areas where the soil is unable to sustain life.

When the planet was first formed there was no soil on earth. The earth was only made up of rocks. These rocks were broken down by microorganisms and eroded to form soil. The soil then becomes the foundation of plant life. These plants help in the survival of different animals and progress from primary succession to the climax community.

If this primary ecosystem is destroyed, secondary succession takes place.

Secondary Succession

Secondary succession occurs when the primary ecosystem gets destroyed. For eg., a climax community gets destroyed by fire. It gets recolonized after the destruction. This is known as secondary ecological succession. Small plants emerge first, followed by larger plants. The tall trees block the sunlight and change the structure of the organisms below the canopy. Finally, the climax community arrives.

Cyclic Succession

This is only the change in the structure of an ecosystem on a cyclic basis. Some plants remain dormant for the rest of the year and emerge all at once. This drastically changes the structure of an ecosystem.

Seral Community

“A seral community is an intermediate stage of ecological succession advancing towards the climax community.”

A seral community is replaced by the subsequent community. It consists of simple food webs and food chains. It exhibits a very low degree of diversity. The individuals are less in number and the nutrients are also less.

There are seven different types of series:

Examples of Ecological Succession

Following are the important examples of ecological succession:

Acadia National Park

This national park suffered a huge wildfire. Restoration of the forest was left to nature. In the initial years, only small plants grew on the burnt soil. After several years, the forest showed diversity in tree species. However, the trees before the fire were mostly evergreen, while the trees that grew after the fire were deciduous in nature.

Ecological Succession of Coral Reefs

Small coral polyps colonize the rocks. These polyps grow and divide to form coral colonies. The shape of the coral reefs attracts small fish and crustaceans that are food for the larger fish. Thus, a fully functional coral reef exists.

Write Dicotyledonous and Monocotyledonous Leaves.

Question: 

Write Dicotyledonous and Monocotyledonous Leaves.

Answer:

Dicotyledonous and Monocotyledonous Leaves

Dicot Leaf

Dicotyledonous leaf shows reticulate venation.

• Lamina consists of epidermis, mesophyll and vascular system.
• The epidermis is covered by cuticle and stomata; abaxial epidermis (lower surface) possesses more stomata than adaxial epidermis (upper surface). Sometimes adaxial epidermis lack stomata.
• Mesophyll, (parenchymatous cells) composed of the palisade and spongy parenchyma is present in between the adaxial epidermis and abaxial epidermis.
• The chloroplasts present in mesophyll perform photosynthesis in leaves.
• Vascular bundles are surrounded by bundle sheath cells and form the veins and midrib.

Monocot Leaf

Monocotyledonous leaves are characterized by parallel venation. The anatomy of a monocot leaf includes:

• Both adaxial epidermis and abaxial epidermis bear stomata.
• There is no differentiated palisade and spongy parenchyma of the mesophyll.
• Bulliform cells are present, which is developed from adaxial epidermal cells and the veins.
• Bulliform cells are large, void cells which are responsible for the curling of leaves for minimal loss of water.

Write Dicotyledonous and Monocotyledonous Roots.

Question:

Write Dicotyledonous and Monocotyledonous Roots.

Answer:

Dicot Root

• Dicot plants have the taproot system.
• The outermost layer is called the epidermis. The epidermal cells sometimes project out which appear as the root hairs.
• The epidermis is followed by the multi-layered cortex, loosely made of the parenchyma cells with intercellular spaces.
• The inner layer of the cortex is called endodermis, which is tightly packed by the barrel shaped-cells.
• Endodermis is followed by pericycle, which are a few layers of thick-walled parenchyma cells.
• In dicots, the central pith is not distinct.
• There are two to four xylem and phloem.
• The xylem and phloem are remarked by a layer of parenchymatous cells known as conjunctive tissue.

During secondary growth, the cambium separates the xylem and phloem. Pericycle, vascular bundles and pith fuse to form stele in dicots.

Monocot Root

Monocot roots do not show much difference in the anatomy from that of the dicot roots.

• Monocot plants possess an adventitious root system.
• As in the dicots, the epidermis forms the outermost layer, followed by cortex, pericycle, endodermis, vascular bundles (xylem and phloem) and pith (random order).
• Pith is conspicuous and large.
• The number of xylem in a monocot is six or more.
• Secondary growth is not seen in the monocot plants.

Write Dicotyledonous and Monocotyledonous Stem.

Question: 

Write Dicotyledonous and Monocotyledonous Stem.

Answer

Dicot Stem

The dicotyledonous stem is usually solid. The transverse section of a typical young dicotyledonous stem consists of the following parts:

• The epidermis is the outermost protective layer, which is covered with a thin layer of cuticle.
• Epidermis possesses trichomes and a few stomata.
• Cortex is multi-layered cells sandwiched between epidermis and pericycle.
• The outer layer, hypodermis (collenchymatous cells), the cortical layers (parenchymatous cells) and the inner layer, endodermis together make up the three subzones of the cortex.
• Next to endodermis is the pericycle, which is constituted of semi-lunar patches of sclerenchyma.
• ‘Circled’/ ‘ring’ arrangement of vascular bundles is present only in dicot stem.
• The Vascular bundle is conjoint, open and with endarch protoxylem.
• Pith is evident and is made of parenchymatous cells.

Monocot Stem

Monocot stem is usually hollow with no secondary growth. The anatomy of monocot and dicot stem are similar, however, some notable differences are as follows:

• The hypodermis of the cortex in monocots is made of sclerenchymatous cells.
• Vascular bundles are numerous, but scattered, conjoint and closed, surrounded by the ground tissue.
• Phloem parenchyma is absent.