THE LIVING WORLD

 Characteristics of Living Organisms:

1. Cellular Structure
2. Metabolism
3. Growth
4. Reproduction
5. Consciousness

Other characteristics of living beings include:

- Adaptation
- Lifespan
- Homeostasis
- Healing and repair
- Movement and variation

Q. What is a defining feature?

A. A feature is said to be defining if it fulfills two criteria:


a) If it is unexceptionally present in all organisms.
b) It should not be part of non-living objects.


1. Cellular Structure: It is the structural and functional unit of life. Cells are present in all living objects. Cells are not present in non-living objects. Therefore, it can be said that cellular structure is a defining feature.

2. Metabolism: (Gk: metabole = change / conversion)

All the organisms are made of chemicals -- these chemicals are constantly being made. These changes are called chemical reactions. All chemical reactions occurring inside our body constitute metabolism.

Metabolism comprises of two events: Anabolism and Catabolism


 

=> These metabolic reactions can occur in vivo or in vitro.

- Metabolism is a characteristic feature of all living organisms and it is absent in non-living objects. It can, therefore, be said that metabolism is a defining feature.

3. Growth:

Growth is defined as an irreversible increase in mass or overall size of our cell / organ or the whole organism. In other words, growth is an increase in body mass.

Growth occurs due to net results of two components of metabolism:

If anabolism > catabolism --- It leads to growth

If anabolism = catabolism --- no growth will occur

If anabolism < catabolism --- it leads to negative growth

Q. Compare plants and animals + growth in living and non-living with respect to growth?





 


 => Since growth is a characteristic of both living and nonliving objects. Growth is, therefore, a non-defining feature.

4. Reproduction:

It is a process of formation / production of offspring having features more or less similar to parents.


Asexual Reproduction: It involves single parent, it is therefore, uniparental. Besides, it does not involve fertilization of gametes.
Types of asexual reproduction:

Fish -- Fission (eg: binary fission in bacteria)

Fry -- Fragmentation (eg: in filamentous algae)

Really -- Regeneration (eg: Planaria)

Very -- Vegetative reproduction

Spicy: sporulation (eg: algae, fungi, bacteria)

Buddy -- Budding (eg: yeast, unicellular fungi, hydra)


Sexual reproduction: It involves two parents = biparental. Besides, it involves the formation of gametes and their fusion.

=> In unicellular organisms, growth and reproduction are synonymous. For instance in bacteria and amoeba -- increase in cell number is associated with the growth. On the other hand, in higher plants and animals, growth and reproduction are mutually exclusive events. A Mutually Exclusive term is used to describe a situation where the occurrence of one event is not influenced or caused by another. Mutually exclusive events never occur at the same time.

- Reproduction is not present universally. For instance Mule (a cross between male donkey [Jack] and female horse [Mare]) and worker bee. Both mule and worker bees are sterile.

=> Since reproduction is somewhere associated with growth in unicellular organisms and since reproduction is not present universally -- it can be considered as a non-defining feature.

5. Consciousness:

It is the ability to sense stimulus / environment and response to it. External stimulus can be physical, chemical or biological. It is unexceptionally shown by all living organisms. It can, therefore, be considered as a defining feature.











































What is Amitosis and Where Does it Occur?

Amitosis is a method of asexual reproduction, which occurs in acellular organisms such as bacteria, protozoans, diseased cells, old cells, mammalian cartilage cells and in fetal membranes, yeast budding, etc. It was first discovered by the scientist, REMAK.



Mechanisms:

-- Nucleus of the cell elongates.
-- Constriction appears in the nucleus, which gradually deepens and divides the nucleus into two daughter nuclei.
-- A constriction appears in the cytoplasm, which divides the cytoplasm and the nuclei into two daughter cells each with a nucleus.
-- In direct division, no spindle formation and no direct chromosome formation occurs.


Q. What is the minimum number of meiotic divisions required to produce 100 wheat grains?

a) 100         b) 125         c) 150         d) 200


Ans (b)

Explanation: Usually, one meiotic division forms 4 pollen grains
                                   One meiotic division forms 1 egg cells
So, to produce 100 wheat grains, we need 100 pollen grains and 100 eggs
To produce 100 pollen, only 25 meiotic divisions are required and to produce 100 eggs, 100 meiotic divisions are required. Therefore, a total of 125 meiotic divisions are required to produce 100 wheat grains.

Shortcut:

No of meiotic divisions required to produce 'n' number of seeds / grains

No. of grains = n + n / 4

= Egg + Pollen
= 100 + 100 /4
= 125


Q. Number of mitotic divisions required for the formation of 100 cells:

a) 100        b) 50        c) 25        d) 99

Ans: (d)

Explanation:
Number of mitotic divisions for the formation of ‘n’ number of cellls = (n - 1)





Multiple Choice Questions on Cell Cycle

Q1. Which of the following choice is incorrect in relation to the interphase stage?

a) Period of great metabolic activity
b) It covers over 95% of the total duration of cell cycle
c) Absence of replication of DNA
d) Also called as preparatory phase


Q2. Duplication of DNA occurs in:

a) G1 phase
b) S phase
c) G2 phase
d) M phase


Q3. If cell division is restricted in G1 phase of a cell cycle, the condition is known as:

a) G1 phase
b) G2 phase
c) G0 phase
d) M phase

Q4. Go-phase of cell denotes:

a) Check point before entering the next phase
b) Death of cell
c) Temporary pause
d) Exit of cell from cell cycle

Q5. The sequence of cell cycle is:

a) S, M, G1 and G2
b) G1, G2, S and M
c) S, M, G2 and G1
d) G1, S, G2 and M

Q6. The synthesis of spindle proteins occur during:

a) G1-phase
b) S-phase
c) G2-phase
d) M-phase


Q7. Histone protein synthesis occurs during:

a) G1 phase
b) G2 phase
c) M phase
d) S phase

Q8. During cell cycle, DNA replicates:

a) Once
b) Twice
c) Many times
d) Not at all

Q9. Which of the following doubles during S phase:

a) Mitochondria
b) Chloroplast
c) Golgi body
d) All of the above

Q10. Which of the following phase of a cell cycle is called invisible phase:

a) G1 phase
b) S phase
c) G2 phase
d) M phase


Q11. If the DNA content in a cell at G1 phase is 2C, what will be the DNA content at S phase?

a) 2C
b) 4C
c) 1C
d) None



Q12. If the DNA content of a cell at G1 phase is 2C what will be the DNA content of its daughter cells after mitotic division?

a) 2C
b) 4C
c) 1C
d) None

Q13. The DNA content of a cell at G1 phase is 2C, what will be the DNA content of its daughter cells after meiosis II?

a) 2C
b) 1C
c) 4C
d) All of the above











Answer Key:

1. c      4. d     7. d     10. b   13. b
2. b      5. b     8. a     11. b
3. c      6. c     9. d     12. a

How the Cell Cycle is Controlled?

Cell cycle is run by a group of special proteins, called Cyclins and Cdks (cyclin dependent kinases). A cell reproduces by performing an orderly set sequences of irreversible events in which it duplicates its contents and then divide into two. These events are collectively called as cell cycle.

Molecular biologists have made a remarkable progress in identifying the biomolecules that control the cell cycle. Scientists working on frog eggs and yeast cell concluded that the activity of enzymes such as cyclin dependent kinases (Cdk‘s) regulate the cell cycle.

Kinase is a type of enzyme that is responsible for removing a phosphate group from ATP and add to another protein. The kinases involved in the cell cycle are called Cdks because they are activated when they combine with the key protein, cyclin.



At some check-point in the cell cycle (G1 à S and G2 à M), a kinase enzyme combines with cyclin and this moves the cell cycle forward. G1 or S-kinase is capable of initiating the replication of DNA once it combines with S-cyclin. After some time, S-cyclin is destroyed and S-kinase is no longer active. M-kinase, on the other hand, is capable of turning on mitosis once it combines with M-cyclin.

G1 to S transition is carried out by G1 or S cyclin + cdc 2 kinase
G2 to M transition is triggered by maturation promoting factor (MPF) formed by mitotic cyclin + cdc 2 kinase

Measures of DNA Content and Chromosome Content

The amount of DNA within a cell change following each of the following events:

  • Fertilization
  • DNA synthesis
  • Mitosis
  • Meiosis

We use ‘C’ to represent DNA content in a cell and ‘N’ to represent the number of complete sets of chromosomes.

In a gamete -- the amount of DNA is say, 1C
And the number of chromosomes say,    1N

Upon fertilization, both the DNA content and the number of chromosomes doubles to 2C and 2N respectively.

Following DNA synthesis, the DNA content doubles again to 4C, but each pair of sister chromatids is still as a single chromosome, so the number of chromosomes remain unchanged at ‘2N’


What is the Difference Between Mitosis and Meiosis?



What is Cell Cycle? What are the Different Phases of a Cell Cycle?

Complete lifecycle of a cell is called the cell cycle. In other words, it is an orderly series of changes that occurs in a cell by which the cell duplicates its genetic material along with that it duplicates other content; finally, it divides and results in the formation of two daughter cells. An interphase occurs between two phases. During interphase, a cell grows in size and prepares itself for the next division. Interphase is also the most active phase of a cell cycle. During this phase, the metabolism activity of cell increases and a series of changes occur during the same phase. However, these changes are not visible under the microscope. That is why some scientists have termed interphase as a Resting Phase. Howard and Pelc -- two scientists have classified interphase into three sub-stages:




 The time taken by the cell to divide is known as generation time. For yeast, generation time is about 90 minutes.


(I) G1 Phase / Pre-DNA synthesis phase / Post-mitotic phase:
-- Maximum growth of the cell along with an increase in the size of the nucleus is seen.
--  It is the longest duration of the Interphase
-- During this phase, there is synthesis of nucleotides / amino acids / energy-rich molecules (ATP)
-- Polymerisation of nucleotide results in RNA synthesis.
-- RNA polymerase becomes active along with the enzymes for DNA synthesis.an
-- Synthesis of amino acids, which are involved in histone protein synthesis.

(II) S-Phase (DNA Synthesis Phase):

-- DNA duplication / replication takes place.
-- Chromosome consists of two chromatids
-- Centriole duplication occurs in the cytoplasm
-- Amino acids polymerize and form histone proteins
-- Assembly of kinetochore subunits
-- The duplicated chromosomes will not appear during this phase and that's why this phase is known as INVISIBLE PHASE


G2-Phase / Post-DNA synthesis phase / Pre-mitosis phase


-- Known as the second growth phase.
-- Cell size increases
-- Nucleus size increase
-- RNA synthesis takes place
-- Protein synthesis takes place
-- Duplication of most of the cell organelles (along with the division of mitochondria and division of plastids)
-- Biochemicals are formed for the synthesis of spindle fibres.
-- Tubulin protein synthesis takes place.
-- It is also signified by the synthesis of some protein kinases for the regulation of cell division






Where to Take Admission for MBBS Course?

Students preparing for medical entrance tests must be thinking about where to take admission for MBBS course. Well, it's a very genuine question that would strike in every student's mind. I think every student must be aware of two medical entrance tests: the first one is AIPMT (All India Pre-medical Test), which is conducted by CBSE and the other one is AIIMS (All India Institute of Medical Sciences). However, there are other prestigious institutions where students can get admission through an all India entrance test. For instance, JIPMER, MGIMS-Wardha, Manipal-MAHE, COMED-K, AMU and AFMC, to name only a few. These institutions are known for their quality of education and placement.



Getting admission to these prestigious institutions is definitely a tough task, but not an impossible task for sure. It is, therefore, important to work hard in the right direction and pass the test for a better future. AIMPTBIO is always there to help aspiring students in the best possible manner.


List of Private Medical Colleges in India

Dear Students, in the last post, I had mentioned the list of government medical colleges where students can take admission to MBBS first year through an All India Pre-Medical Test. Besides, there are many private medical colleges in India where students can either take admission directly or through an entrance test. Since the list of private medical colleges in India is very large, I have considered only three states (Andhra Pradesh. Bihar, New Delhi)in this post. However, I will add the next three states in my next post.



ANDHRA PRADESH

1. Alluri Sitaram Raju Academy of Medical Sciences, Eluru (Annual intake: 100)

2. Bhaskar Medical College, Yenkapally (Annual intake: 150)

3. Chalmeda Anand Rao Institute Of Medical Sciences, Karimnagar (Annual intake: 150)

4. Deccan College of Medical Sciences, Hyderabad (Annual intake: 150)

5. Dr. P.S.I. Medical College , Chinoutpalli (Annual intake: 150)

6. Dr. VRK Womens Medical College, Aziznagar (Annual intake: 100)

7. Fathima Instt. of Medical Sciences,Kadapa (Annual intake: 100)

8. Great Eastern Medical School and Hospital,Srikakulam (Annual income: --)

9. GSL Medical College, Rajahmundry (Annual intake: 150)

10. Kamineni Institute of Medical Sciences, Narketpally (Annual intake: 150)

11. Katuri Medical College, Guntur (Annual intake: 150)

12. Konaseema Institute of Medical Sciences & Research Foundation, (Annual intake: 150)

Amalapuram
13. Maharajah Institute of Medical Sciences, Vizianagaram (Annual intake: 100)

14. Mamata Medical College, Khammam (Annual intake: 150)

15. Medicity Institute Of Medical Sciences, Ghanpur (Annual intake: 100)

16. MNR Medical College, Sangareddy (Annual intake: 100)

17. Narayana Medical College, Nellore (Annual intake: 100)

18. NRI Medical College, Guntur (Annual intake: 150)

19. P E S Institute Of Medical Sciences and Research, Kuppam (Annual intake: 150)

20. Prathima Institute Of Medical Sciences, Karimnagar (Annual intake: 150)

21. S V S Medical College, Mehboobnagar (Annual intake: 100)

22. Santhiram Medical College, Nandyal (Annual intake: 100)

23. Shadan Institute of Medical Sciences,
Research Centre and Teaching Hospital, Peerancheru (Annual intake: 150)

BIHAR

1. Katihar Medical College, Katihar (Annual intake: 060)

2. Mata Gujri Memorial Medical College, Kishanganj (Annual intake: 060)

3. Narayan Medical College & Hospital, Sasaram (Annual intake: ---)

DELHI


1. Army College of Medical Sciences, New Delhi (Annual intake: 100)



List of Medical Entrance Exams in India

Dear Students, if you’re reading this post, then you must be aspiring to become a doctor. Well, it is very important to gather information regarding the number of medical entrance exams in India. My aim is to give you the right information regarding the different medical entrance tests that are being conducted on All India basis. In this post, I’m considering government colleges only; however, there are several private medical colleges where students can take admission. In the next post, I’ll surely cover private medical colleges in India.

National Level Medical Entrance Exams

EXAMS INFORMATION

AIPMT -- CBSE (Link: http://aipmt.nic.in)

AIIMS (Link: http://www.aiimsexams.org/)

JIPMER -- Pondicherry (Link: http://www.jipmer.edu.in)

MGIMS -- Wardha (Link: http://www.mgims.ac.in/)

MANIPAL -- CET (Link: http://www.manipal.edu)

CMC -- Ludhiana (Link: http://cmcludhiana.in/)

IPU-CET-- Delhi (Link: http://ipu.ac.in)

AMU--CET-- Aligarh (Link: http://www.amu.ac.in/)

COMEDK -- Karnataka (Link: https://www.comedk.org)


State-level Medical Entrance Exams:

Assam -- CEE (Link: www.ceemedu.org/)

Bihar -- CECE (Link: http://bceceboard.com/)

EAMCET -- A.P (Link: http://www.apeamcet.org)

Goa--CET (Link: www.dtegoa.gov.in)

Gujarat -- CET (Link: http://www.gseb.org)

JK--CET (Link: http://jkgov.com/)

KEA--CET-- Karnataka (Link: http://kea.kar.nic.in)

KEAM -- CEE -- Kerala (Link: www.cee.kerala.gov.in)

MH--CET -- Maharashtra (Link: www.dmer.org/)

UP -- CPMT (Link: http://www.updgme.in/ http://upcpmt.in)


WB--JEE (Link: http://www.wbjeeb.nic.in)

U--PMT -- Uttarakhand (Link: http://hnbumu.ac.in/index.html)

Chhattisgarh
-- PMT (Link: http://www.cgdteraipur.ac.in/)

Jharkhand -- CECE (Link: http://jceceboard.org)