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  • The centromere is the point on a chromosome where sister chromatids are linked together.
  • During mitosis, spindle fibers attach to the centromere via the kinetochore.

The chromosomes are morphologically divided in 4 subtypes according to position of centromere on the chromosomes :

Telocentric, and

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Metacentric : The centromere is in the middle of the chromosome so that the two arms of the chromosomes are almost equal.

Submetacentric : If arms' lengths are unequal due to off centre location of centromere, the chromosome is said to be submetacentric.

Telocentric : The centromere is located at the terminal end of the chromosome.

Acrocentric : centromere is towards one end of chromosome so that there is a very short arm, may be so short that it is hard to observe, but still present, and another very long arm.

enter image source here

Centromere is the region where a protein complex called kinetochore appears during cell division . A chromosome can attach to spindle fibres with the help of kinetochore.

Interestingly, DNA at centromere is late duplicating, hence sister chromatids remain attached at this point till metaphase. As the DNA duplication at centromere ends, anaphase and chromatid deparation can begin.

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Radial symmetry is seen in aquatic animals: these are mostly bottom-dwelling as well. Please note that organisms with radial symmetry has oral and aboral sides and a central axis passes through the body.

Body of an animal with radial symmetry could be divided in two equal halves by cutting through any plane passing through central axis. Such an organism has no left/right/ or anterior/posterior distinction. Members of Phylum Cnidaria show radial symmetry, such as a Hydra.



Many cnidarians like sea anemones are biradially symmetrical, i.e. their body could be divided in equal parts by cutting through only two radial planes.

Another group of animals belonging to Phylum Echinodermata show pentaradial symmetry, i.e. their body can be equally divided by cutting through specific five radii.



Meiosis generates genetic diversity through a process called crossing over which allows new combinations of variations to appear in gene pool. Homozygous chromosomes come side by side and they exchange genetic material during prophase of meiosis I.



Consider combined effects of all these to understand the impact of meiosis:

  • Homologous chromosomes may carry two different alleles on same genetic loci, i.e. there could be heterozygous condition for a gene. (for example, allele for antigen A in one and allele for antigen B in another chromosome: both are for ABO blood group determination)
  • There are a number of genes linearly arranged on chromosomes , hence several of them may remain in heterozygous condition. (there could be heterozygosity for ABO blood group, iris colour of eye, and sickele cell anaemia in same individual)
  • Each organism has a number of chromosomes in genome, hence several pairs are undergoing crossing over during one meiosis. (in case of human, 22 autosomal pair among 23 pair of chromosomes are participating in crossing over)
  • Chiasmatal points appear randomly on homologous chromosomes, hence amount of genetic material exchanged in every case/cell could be different. (different recombinations appear after each crossing over, hence diversity increases with more number of meiotic divisions taking place in an organism)

  • In first anaphase, homologous chromosomes with already exchanged parts separate. In second anaphase, chromatid separation takes place. Separation in these two stages will see different chromosomal recombinations to appear in gametes.

Meiosis is the process of formation of gametes. Due to crossing over, there appears huge variety in genetic recombinants. Now these gametes undergo random fertilisation with another set of gametes. This further increases chance of new genetic combinations to appear in progeny.



What Is an enzyme?

Featured 1 month ago


Enzymes are biological catalysts that speed up the rate of a biochemical reaction without changing the thermodynamics of the system.


#color(blue)("Enzymes")# are biological catalysts that speed up the rate of a biochemical reaction without changing the thermodynamics of the system, meaning, enzymes will change how fast a reaction occurs (kinetics) and NOT if a reaction occurs(thermodynamics)


#color(white)(aaaaa)#How exactly do enzymes lower the activation energy?

In order to understand how enzymes catalyze reactions, we must first get through some basic terminology.



The figure above is a #color(blue)("free energy diagram")#. It shows us the reaction progress (x axis) and the change in #color(blue)("Gibbs Free Energy"(DeltaG))# associated with the reaction (y axis).

#(DeltaG)# is just a term scientists used to describe if a reaction is spontaneous or not, or in other words, if the reaction will occur by itself without any added energy.

#color(white)(aaaaaaaa)##color(red)((-)DeltaG ->"exergonic reaction" ("spontaneous")#
#color(white)(aaaaaaaa)##color(red)((+)DeltaG ->"endergonic reaction"("nonspontaneous")#

In the reaction showcased above, the starting point for the reactant, or the #color(blue)("Ground State")#, is at a higher Gibbs free energy level than the product. This means that the product is thermodynamically more stable than the reactant, and thus, the reaction proceeds spontaneously in the forward direction (exergonic reaction). The #(DeltaG)# of the reaction can be calculated as follows:


When an #color(blue)("substrate")# binds to the enzyme's #color(blue)("active site")#, together they form an #color(blue)("enzyme-substrate complex [ES]")# and subsequent catalysis forms products and regenerates the enzyme.

#color(white)(aaaaaaaaaaaa)##color(red)(E + S rightleftharpoons ES -> E + P)#

Before the reaction proceeds, though, it must overcome a certain energy barrier, or #color(blue)("Activation energy")#. Activation energy, is the change in free energy between the #"Ground state"# and the #color(blue)("Transition state"#, the top most energy hill in the diagram.

The #"Transition state"# is a moment in time where bond breakage, bond reformation and the correct orientation for molecules to react occurs. For this to occur, however, sufficient energy is required. So how does an enzyme achieve this?

During enzyme-substrate binding, #color(blue)("weak non-covalent interactions (H bonding, ionic interactions, hydrophobic interactions)")# will form which will not only add to the stability of the #"[ES]"# complex but also release some energy called the #color(blue)("Binding energy")#. Since the energy released by the weak interactions (binding energy) offsets the energy required to reach the transition state, the overall net activation energy is lowered and the reaction can proceed at a faster rate.


The predater/pray interaction must be (and generally is) a zero sum exchange.


So much prey, so many predators.
You increase the prey, the number of predators goes up.
Should predators overkill, they would eventually have to move out of the area for lack of food.

The image below exhibits prey-predator population dynamics in nature:-



There are exceptions to the rule, like rabbits in Australia. But rabbits were artificially introduced in a continent that had no indigenous predators capable if reacting to the extraordinary fertility of rabbits.
This made man the natural rabbit predator by means of culling, trapping, fencing, sterilising... which eventually re-established an acceptable equilibrium.


In plants, it is a single chambered fruit formed from a carpel, containing seeds.


There are different kinds of follicles in the field of biology, such as in the ovaries of human females during the menstrual cycle or hair follicles. Though in specific types of plants (angiosperms) (i.e milkweed) create a single cavernous fruit which releases two or more seeds, this "fruit" is called a follicle.

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