Ecology Lecture Notes

Hydrosere (Hydrarch Succession) with PPT


Stages of Hydrosere

Hydrosere
(Hydrarch Succession)

What is Hydrosere or Hydrarch Succession?

A succession originates in a water body (aquatic environment) is called Hydrosere or Hydrarch Succession. Such a succession does not necessarily lead to the development of a land community. If the water body is sufficiently large and with wave action, the succession usually results in the formation of a large aquatic climax community. If the hydrarch succession starts from a comparatively small water body such as a pond, there is always a high probability for the formation of a terrestrial climax community. The important characteristics of hydrosere are given below:

Ø  Hydrosere usually starts from a pond

Ø  Phytoplanktons will be the pioneer community

Ø  A forest or a grassland will be the climax community

Ø  Includes several seral stages of plant and animal communities

Ø  Seral communities of plants are more obvious than animals.

Just like other successions, the hydrosere is also completed through a sequence of several Seral Stages (Seral Communities). The seral stages of a typical Hydrosere succession are as follows:

Seral stages of Hydrosere

(1).  Phyto-planktons stage

(2).  Rooted submerged stage

(3).  Rooted floating stage

(4).  Reed-swamp stage

(5).  Sedge-meadow stage

(6).  Woodland stage

(7).  Forest stage

Process of Hydrosere

(1). Phytoplankton stage:

Ø  Phytoplanktons will be pioneer community in the hydrosere.

Ø  Algal spores are brought into the water in the initial stages of the succession.

Ø  These algal spores germinate and quickly colonize in the water body.

Ø  They multiply and grow for some time. They fix light energy (photosynthesis).

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Ecology Lecture Notes

Different Types of Ecological Succession


Classification of Succession

Types of Ecological Succession
(Classification of Ecological Succession)

In the previous post, we have discussed the Process of Ecological Succession. Here we will discuss the classification of different types of ecological successions. The ecological succession is classified into different types based on different criterions such as the origin of succession, cause, community composition and nature of substratum. An outline of the classification is given below:

(1).  Primary and Secondary Succession (based on the starting of succession)

(2).  Autogenic and Allogenic Succession (based on the cause of succession)

(3).  Autotrophic and Heterotrophic Succession (based on the community composition)

(4).  Hydrosere and Xerosere (based on the nature substratum)

(5).   Microsuccession (succession of microbes)

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Ecology Lecture Notes

Process of Ecological Succession (PPT)


Process of Succession

Stages of Ecological Succession
(Formation of an Ecosystem)

What is Ecological Succession?

Definition: Ecological succession is the gradual and sequential replacement of one community by the other in an area over a period of time. According to E.P. Odum (1971), the ecological succession is an orderly process of community change in a unit area. It is the process of change in species composition in an ecosystem over time. In simpler terms, it is the process of Ecosystem Development in nature.

Population Vs Community

Population: The group of individuals of a particular species occupying in a unit area. Example: population of Aedes aegypti (yellow fever mosquito) in an area.

Community: A community can be defined as a combination of different populations in an ecosystem. For example a pond ecosystem may consist of populations of Spirogyra (algae) Diatoms, Frogs, Fishes and Insects.

The community in an ecosystem is NOT stable. It passes through many developmental stages in definite sequence over a period of time. These developmental stages in most of the cases will be from simple to complex and it is collectively called as community dynamics.

Process of Ecosystem Succession

The ecological succession is a complex process and it may take thousands of years. Frederic Clements in 1916 for the first time proposed the sequential phases of an ecological succession. The process of succession is completed through a series of sequential steps as given below:

(1).      Nudation
(2).      Invasion
(3).      Competition and Co-action
(4).      Reaction
(5).      Stabilization (climax)

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Molecular Biology Tutorials

Tumor Suppressor Gene Rb and its Role in Cell Cycle and Cancer


tumor suppressor gene example

Retinoblastoma Protein (pRb) – A Tumor Suppressor Gene/Protein
(The Importance of pRb in Cell Cycle Regulation and Cancer)

What is Retinoblastoma? What is the cause of Retinoblastoma?

Retinoblastoma or RB is a type of cancer affecting the retina of young individuals. RB occurs in the human population both spontaneously and as a heritable disorder. The genetic reason for the occurrence of RB is associated with a structural aberration of the chromosome. In human, the Rb gene is present on the chromosome 13 at the q-14 region. The loss of this region of due to deletion or mutation causes the retinoblastoma.

The condition of retinoblastoma arises only when both the copies of the Rb gene are lost. In the inherited form of the disease, one parental chromosome carries an alteration in this region. A spontaneous mutation in the retinal cells which results in the inactivation of the other copy of Rb gene can cause the tumor development. Thus, the loss of function of Rb protein due to mutation or deletion is the cause of retinoblastoma.

How Rb acts as a tumor suppressor gene?

A tumor suppressor gene is a gene that prevents the development of cancer. When this gene is mutated and its function is lost forever, there is a very high chance of the cell to enter into a cancerous growth.

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Molecular Biology Tutorials

Extrinsic Pathway of Apoptosis (Apoptosis Molecular Mechanism Part 2)


Receptor Mediated Apoptosis

Extrinsic Pathway of Apoptosis
(The Receptor-Mediated Programmed Cell Death Pathway)

In the extrinsic pathway of apoptosis, the death-inducing signal for the programmed cell death is triggered by an external stimulus. For receiving such an external death-inducing signal, the cell possesses plasma membrane receptors specific to each stimulus and thus the extrinsic signalling of apoptosis is also known as the Receptor Mediated programmed cell death pathway.

The external stimuli for the apoptosis in most of the cases will be a cytokine. The most studied cytokine to induce extrinsic pathway of apoptosis is an extracellular messenger protein called Tumor Necrosis Factor (TNF). TNF is so named because it was first discovered as a protein factor which induces cell death in cancerous cells. The TNF cytokine is produced by the cells of the immune system in response towards the adverse conditions. The adverse conditions that can provoke the immune cells to produce TNF are:

Ø  Exposure to radiation

Ø  Introduction of viral toxins

Ø  Exposure to elevated temperature

Ø  Exposure to other toxic substances

The detailed signaling mechanism of TNF-mediated extrinsic pathway of apoptosis is summarized below:

Ø  TNF first binds to its receptor called TNFR1 (Tumor Necrosis Factor Receptor-1) present on the plasma membrane.

Ø  TNFR1 is a member of death receptor family proteins that turn on the apoptotic cell death process in eukaryotic cells.

Ø  TNFR1 is a trans-membrane receptor with an external ligand binding domain and a cytosolic domain.

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