CLASS 9 - Cell - Fundamental Unit of Life - Question Bank CBSE

Cell - Fundamental Unit of Life

Question 1

Differentiate between organ and organelles.

Solution:
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.

Question 2

Define chromatin, chromosome and chromatid.

Solution:
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.

Question 3 

Why is meiosis termed as reductional division?

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

Question 4

What is the significance of crossing over?

Solution:
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.

Question 5

Define centriole, centromere and chiasma.

Solution:
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.

Question 6

Differentiate between haploid and diploid cells.

Solution:

The main difference between haploid and diploid cells is the number of chromosome sets found in the nucleus. Ploidy is the area of biology that refers to the number of chromosomes in a cell. Therefore, cells with two sets are diploid, and those with one set are haploid. In diploid organisms, such as humans, the haploid cells are used only for the sex cells for reproduction, while the rest of the cells are diploid. Another difference between haploid and diploid cells is how they reproduce. Haploid cells are reproduced using meiosis, while diploid cells go through mitosis. Most mammals are diploid organisms, and their somatic cells will typically be diploid and their gamete cells will be haploid.

Question 7

What are gametes?

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

Question 8

Differentiate between identical and fraternal twins.

Solution:
Identical twins are formed when a one 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.

Question 9

What are homologous chromosomes?

Solution:
Homologous Chromosomes are those that remains 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).

Question 10

What is the significance of mitosis?

Solution:
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.

Question 11

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

Solution:
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.

Comment

Question 12

State the relationship between meiosis and fertilization.

Solution:
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.

Question 13

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

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

Question 14

Distinguish between heterochromatin and euchromatin.

Solution:
The difference between heterochromatin and euchromatin are:
 

Heterochromatin	Euchromatin
Chromatin is rich in RNA.	Forms the bulk of chromosomes.
Responsible for nucleic acid metabolism.	Contains active genes.

Question 15

Why is the cell called the structural and functional

 unit of life?

Solution:
Cells constitute various components of plants and animals. A cell is the smallest unit of life and is capable of all living functions. Cells are the building blocks of life. This is the reason why cells are referred to as the basic structural and functional units of life. All cells vary in their shape, size, and activity they perform. In fact, the shape and size of the cell is related to the specific functions they perform.

Question 16

Why is the plasma membrane called a 

selectively permeable membrane?

Solution:
The cell membrane or the plasma membrane is known as a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

THAT'S ALL GUYS ..!!
THESE ARE IMPORTANT QUESTIONS , MUST STUDY BEFORE EXAMS

AND NOTE THESE MOST OF THE QUESTIONS ARE BEING TAKEN FROM GOOGLE ( I MEAN SITES ) BUT ARE EDITED !!

SO STUDY HARD AND GET GOOD MARKS !!

SUMIT BHADRA 

( ACS )