CBSE Pathshala

Q.1. What is heredity? Ans:- Heredity refers to the transmission of characters or traits from the parents to their offspring. Q.2. Name the plant on which Mendel performed his experiments? Ans:- Garden Pea ( Pisum sativum .) Q.3. Define variation? Ans:-Variation refers to the differences in the characters or traits about the individuals of a species. Q.4. Define a gene? Ans:- Gene is a small segment of DNA on a chromosome occupying specific position in which is a hereditary determinant or unit of a biological function. Q.5.Write the expanded form of DNA? Ans:- DNA - Deoxyribonucleic Acid. Q.6. What are the components of chromosome? Ans:- Each chromosome is double or replicated and consists of two thread like structures called chromatids attached to each other at centromere. .Each chromatid has a number of dense areas arranged linearly which are known as chromomeres. They represent the areas of active genes. .Internally each chromosome has two spirally coiled

8 th Science: Chapter:  Reproduction and Reaching of adolescence 1. How are human twins produced? Ans: There are two way twins are formed. (a) Twins occur when a single egg is fertilized to form one zygote which then divides into two separate embryos.(b) Twins occur when two separate eggs  are fertilized by two separate sperm. 2. Whose sex chromosomes is responsible for sex of unborn baby, either father’s or mother’s sex hormones. Ans: The sex chromosomes of the father determine the sex of an unborn baby. 3. Why ace and pimple appear in adolescent age of human being? Ans: This is because during puberty the secretion of sweat glands and sebaceous glands (oil glands) increases in the skin. 4. What is Adam’s apple? At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as bump in the throat called Adam’s apple. 5. Why does reproductive age of women starts from menarche and end at menopause? Women start producing eggs whe

1. What are pathogens?[1] Ans. Disease-causing organisms are called pathogens 2. List any two human activities that lead to an increase in the carbon dioxide content of air.[1] Ans: a. Combustion of wood. b. Deforestation. c. Respiration 3. (a) Name any two green house gases. (b) What causes global warming?[2] Ans:  (a) Carbon dioxide (CO2), methane (CH4), ozone (O3) and water vapour (H2O) green house gases. (b) The greenhouse gases do not allow heat rays to escape from the earth resulting in an increase of temperature of the earth. Hence, green house gases cause global warming. 4. Give two examples each of biodegradable and non-biodegradable pollutants.[2] Ans: Biodegradable pollutants-cow dung and paper Non-biodegradable pollutants-polythene, plastic and DDT 5. Write two points of difference between gymnosperms and angiosperms.[2] Ans:   Gymnosperms    (i) The seeds are naked. (ii) The microspores and megaspores are produced by male and female cones. Angiosperms (i) T