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Differentiate between organ and organelles.

Organ is any distinct part of an organism that is specialized to perform one or a number of functions. Eg: ear, eyes, leaves, roots. Organelles are parts of a cell having definite structure and function. Eg: nucleus, mitochondria.


Define chromatin, chromosome and chromatid.

The material in the nucleus of a cell that forms the chromosomes during cell division is called chromatin.

Chromosomes appear as definitely shaped structures in the nucleus of a cell and are the carriers of hereditary characters from parents to offspring.

The arms of the chromosomes are known as chromatids.


Why is meiosis termed as reductional division?

Meiosis is termed as reductional division as it yields cells that have half the number of chromosomes after completing the process of cell division.


What is the significance of crossing over?

During meiosis, homologous chromosomes pair up and the chromatids of maternal and paternal chromosomes exchange segments or genes. The resultant chromosome is thus different from the parental chromosomes and has the characters of both the parents. Such crossing over and chromatid exchange leads to variability in the gene combinations in gametes.


Define centriole, centromere and chiasma.

Centrioles are paired cylindrical structures found in the cytoplasm of a cell near the nuclear membrane and produce spindle fibres.

Centromere is the region in the chromosome where the chromatids are attached.

Chiasma is the point at which the chromatids of maternal and paternal chromosomes exchange segments during meiosis.


Differentiate between haploid and diploid cells.

Haploid cells are those that have half the number of chromosomes in their nucleus.

Diploid cells are those that have double the number of chromosomes or a complete set in their nucleus.


What are gametes?

Gametes are cells with half the number of chromosomes formed as a result of meiosis.


Differentiate between identical and fraternal twins.

Identical twins are formed when a single fertilized ovum, separates into two embryos by mitosis. They show no variability in their traits and belong to the same sex. Fraternal twins are the result of simultaneous fertilization of two separate ova by two separate sperms. The two zygotes formed have different sets of chromosomes and are genetically different, but grow together in the same uterus.


What are homologous chromosomes?

Homologous chromosomes are those that exist in pairs in a diploid cell, each of which is contributed by the male or the female parent. They are usually similar in shape and size and contain identical sets of loci (position of genes).


What is the significance of mitosis?

The significance of mitosis is as follows:

1. In unicellular organisms, it is a mode of reproduction.

2. In multicellular organisms, it leads to growth and development.

3. It maintains chromosome number in the body cells of an individual.

4. It repairs the worn out tissues of the body and helps in healing wounds.


" All organisms have even number of chromosomes." Why?

All organisms have even number of chromosomes because all organisms have chromosomes in homologous pairs where one member of the pair is contributed from each of the parent.


State the relationship between meiosis and fertilization.

During meiosis gametes that have the same number of chromosomes are formed. But during fertilization the gametes of male and female unite to form a zygote in which the number of chromosome characteristics of the species is restored.


Which type of cell division is responsible for regeneration of tail in a lizard?

Mitosis is essential for regeneration of tail in a lizard. The growth and development of every organism depends on mitosis.


Distinguish between heterochromatin and euchromatin.

The difference between heterochromatin and euchromatin are:



Chromatin is rich in RNA.

Forms the bulk of chromosomes.

Responsible for nucleic acid metabolism.

Contains active genes.



Draw a diagram of mitochondria and label its parts.



Write the phases of cell cycle.

The cell cycle consists of interphase and cell dividing phase. Three stages of cell cycle are called G1 phase, S phase and G2 phase. The resting phase or stage between two mitotic divisions is called interphase. There is no division in interphase but the volume of nuclear and cytoplasmic substances increases. G1 phase is post mitotic gap period. S phase is synthetic phase. G2 phase is called premitotic gap phase.


Draw and label the parts of a plant cell.




What is cell theory? Who formulated it?

The cell theory was formulated by Mathias Jacob Schleiden and Theodar Schwann. The cell theory states that, all living things are composed of cells and cell products. Cells are the structural and functional units of all living things. All metabolic reactions in living things take place within the cell.


Draw the diagram of nuclear envelope.


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