Question

Q1: a- where are chromosome located?
b- what are they composed of ?
c- what is chromatin and how does it change just before the cell divides?
d- what is their chemical composition?
e- how Many pair of chromosomes are present in humans?
please give answers in class 9 ncert solution​

Answer 1

Answer:

A.Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA).

B)Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.

C)The DNA + histone = chromatin

As the cell initiates divisions by either meiosis or mitosis. During the interfaces, DNA is combined with the proteins and organized into a structure called chromatin. This chromatin is a thread like structure which condenses to form chromosomes just before the cell division occurs.

D)Chromatin is composed of DNA (30-40%), RNA (1-10%) and proteins (50-60%). These constituents vary in different organisms and even in the different tissues of the same species (Table 8.2). Even in the same call, the proportions of DNA, RNA and proteins vary with the stage of cell cycle.

E)23 pairs

Different organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes--22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosomes, X and Y.

Answer 2

Answer:

a- chromosomes are located in the nucleus of plant and animal cells

b- They are composed of DNA and protein.

c- Chromatin material is entangled mass of thread-like structures. Chromatin material gets organised into chromosomes, just before the cell divides.

d- The major chemical components of the chromosome are DNA, RNA (nucleic acids), and proteins (histones and nonhistones). DNA, RNA and protein all contribute to the chromosomal mass.

e- 23 pairs of chromosomes are present in humans.