[Biology Class Notes] on Senescence Pdf for Exam

The senescent phase is the period after the reproductive phase, when a cell loses its ability to reproduce. Here, the cell may age and stops dividing, but it does not die. Termed as cell ageing, in this process such cells stay within the body and may cause various illnesses. 

 

Over time, a significant amount of such cells may accumulate in tissues, remain active and release harmful substances. These substances may cause inflammation and damage to the healthy cells near them. They can even give birth to fatal diseases like cancer.

 

Definition of Senescence

In simpler words, senescence is biological ageing. In biology, it refers to the state where cells can no longer divide; however, they remain active and alive. Moreover, it is inevitable in every multicellular organism, be it a human, or animal or a plant. 

 

Therefore, it pertains to the biological ageing of every living thing and involves a gradual decline of morphological features and for the purpose of a cell or the whole organism.

 

Furthermore, the senescent phase entails detriments and benefits for organisms in which such cells live. Even though cellular senescence was first associated with ageing and tumour suppression, recent researches show more results. Current research has found that this phase also plays a part in tissue repair, but promotes cancer. 

 

Moreover, several features distinguish these cells from others. Apart from their inability to divide, they are also bigger than healthy cells. Additionally, they secrete specific molecules, which healthy cells do not. 

 

After reading the senescence definition, one might what causes cell senescence? Read on to know more.

 

Reasons behind Cellular Senescence

There are several reasons behind cellular senescence, some of the primary ones are discussed below –

 

1. Telomere Erosion

It is one of the most common reasons for cellular senescence. Telomeres are a sequence of DNA, which is found at the end of each chromosome. It consists of DNA structures of repeated nucleotides.

 

For instance, repeated nucleotides in human telomeres are TTAGGG. This repetition saves chromosomes from losing crucial information while replicating, and from blending with nearest ones.

 

Moreover, with each replication, the telomeres lose a small part of its DNA as the enzymes responsible for this cannot reach the end of chromosomes. Therefore, chromosomes are shortened after each replication, and after a period, they miss crucial genetic information.

 

Moreover, the cell now goes through DNA damage response (DDR). Thus, they cannot divide anymore and are considered senescent. 

 

2. Other Variation of DNA Damage

Along with telomere erosion, other types of DNA damage can also cause cellular senescence. One of the most common causes here is DNA double-strand breaking. It also brings DDR and subsequently results in the senescent phase of a cell.

 

3. Other Reasons

Apart from any DNA damage, senescence inducers, which act independently of DNA damage, can cause this situation. The reasons includes –

• Presence of signalling molecules, which modifies cellular functions like cellular stress.

• Abnormal expression of several proteins like tumour suppressors.

• Changes in DNA associated proteins like chromatin.

 

Effects of Senescent Phase

The effects of this phase are attributed to the age of individuals. In the case of younger people, it controls the growth of a tumour; it induces the same in the case of older people as well.

 

Moreover, the effects of cellular senescence include secreting molecules that help in tissue repair. 

 

Senescence in Plants

Similar to human beings, senescence in plants is the second last stage of their development. Hormones like ethylene and abscisic acids are some of the typical hormones, which promotes senescence.

 

Moreover, senescence is essential for the fitness and survival of plants.

 

The senescent phase is a vital process in the life-cycle of every living organism. Additionally, students can access study material and join our live classes via the official app and website to learn more about Biology. 

 

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Relevance of Senescence

Senescence is a biological process in which any cell stops dividing. However, it does not die.  The cells that have completely aged stop dividing in the body and then accumulate in the form of tissues. They need to be checked properly so that the harmful substances that they release do not harm the body. They accumulate as a build-up of tissues and may cause diseases like cancer in humans.  They need to be studied properly by all students who need to perform well in their exams. All those students who wish to take up Biology in their later years need to know about Senescence in depth.

How to Study for Senescence before an Exam

• Read up Senescence on

• Go through the entire page and then write all the important concepts down in your own words

• Highlight all the key areas

• Use drawings to understand the topics and subtopics well

• Re-read those sections that have not been properly understood

• Solve questions and solve mock papers on your own

• Revise from everything prior to an exam