Class 8 General Science Notes: - Unit-3: Variations, Heredity and Cell Division: Solved Exercise (Long Questions and Answers)

(National Book Foundation - New Book/New Syllabus Based on National Curriculum Pakistan 2023-2024 and Onwards)

(Class 8 General Science Notes for 8th Centralized Exam 2023-2024 and onward, FDE, Islamabad)

C. Long Questions 

Q1. What are variations? Give different causes of variations.

Variations: Two individuals produced sexually are never genetically identical. Variations are differences in traits between individuals of the same species.

Causes of Variations: 

In sexually reproducing organisms, Genetic variations are caused by

•  Crossing over
•  Mutations

Environmental factors which cause variations include.

• Diet
• Temperature
• Humidity

Q2. Describe the process of Mitosis in detail.

Mitosis:

It is the type of cell division in which a parent cell divides to produce two identical daughter cells. Both have the same number of chromosomes as in the parent cell. Growth, development, healing of wounds, regeneration, and asexual reproduction take place in the process of Mitosis.

Process of Mitosis:

Before the start of the process of mitosis, the cell replicates its entire DNA, so as to produce an extra copy of each chromosome.

At first, the nucleus divide into two nuclei called Karyokinesis, and then Cytokinesis takes place. 

The division of the nucleus in Karyokinesis takes place in four phases: Prophase, Metaphase, Anaphase, and Telophase

1.  Prophase: 

DNA is coiled up tightly, so chromosomes become visible as DNA is already replicated and each chromosome has two chromatids attached to Centromere.

2. Metaphase: 

In metaphase, all chromosomes are aligned in the centre of the cell. 

3. Anaphase: 

Each Centromere splits. The separated chromatids move to their poles.

4. Telophase: 

Chromosomes uncoil and disappear.

Cytokinesis: It is the division of cytoplasm in which two daughter cells are separated from each other.

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Unit-3: Variations, Heredity, and Cell Division: Solved Short Questions and Answers

Class 8 General Science Notes

Source: General Science Book (National Book Foundation, Pakistan)

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