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ScienceClass 8CBSE

After fertilisation, the resulting cell which gives rise to a new individual is the (a) embryo (b) ovum (c) foetus zygote

Soln: Answer is (d) zygote Explanation: Zygote is the beginning of formation of a new individual. All the multicellular organisms start their life from single celled zygote.

ScienceClass 8CBSE

Aquatic animals in which fertilisation occurs in water are said to be: (a) viviparous without fertilisation. (b) oviparous with external fertilisation. (c) viviparous with internal fertilisation. (d) oviparous with internal fertilisation.

Soln: Answer is (b) oviparous with external fertilisation. Explanation: Aquatic animals lay eggs and release sperms into water for fertilization to take place. Young one is formed outside the body hence it is called external fertilization.

ScienceClass 8CBSE

In human beings, after fertilisation, the structure which gets embedded in the wall of uterus is (a) ovum (b) embryo (c) foetus zygote

Soln: Answer is zygote Explanation: Egg fuses with sperm to form the zygote which will divide to form a clump of hundreds of cells which form the embryo. The process of moving down embryo from oviduct into uterus is call as implantation.

ScienceClass 8CBSE

Which of the following statements about reproduction in humans is correct? (a) Fertilisation takes place externally. (b) Fertilisation takes place in the testes. (c) During fertilisation egg moves towards the sperm. (d) Fertilisation takes place in the human female.

oln: (d) Fertilisation takes place in the human female. Explanation: Male gametes are introduced into female’s body through vagina. Sperm reach uterus through oviduct. At uterus egg gets fertilized by sperm to form a zygote.

ScienceClass 8CBSE

Reproduction by budding takes place in (a) hydra (c) paramecium (b) amoeba (d) bacteria

Answer is (a) hydra Explanation: Paramecium, Amoeba and bacteria reproduce by binary fission. Hydra reproduce by budding where a bud detacthes from the parent which grows into complete organism.

ScienceClass 8CBSE

Animals exhibiting external fertilisation produce a large number of gametes. Pick the appropriate reason from the following. (a) The animals are small in size and want to produce more offsprings. (b) Food is available in plenty in water. (c) To ensure better chance of fertilisation. (d) Water promotes production of large number of gametes.

Soln: Answer is (c) To ensure better chance of fertilization Explanation: Because they release gametes in water chances of getting washed away by water, wind and rain are more. Hence To ensure better chance of fertilisation. Large number of gametes are produced by Animals exhibiting external fertilization.

ScienceClass 8CBSE

In humans, the development of fertilised egg takes place in the (a) ovary (b) testis (c) oviduct uterus

Soln: Answer is (d) uterus Explanation: The development of fertilised egg takes place in the uterus. Embryo gets embeeded in the wall of uterus for development by implantation.

ScienceClass 8CBSE

Sets of reproductive terms are given below. Choose the set that has an incorrect combination. (a) sperm, testis, sperm duct, penis (b) menstruation, egg, oviduct, uterus (c) sperm, oviduct, egg, uterus ovulation, egg, oviduct, uterus

Soln: (c) sperm, oviduct, egg, uterus Explanation: Sperm is male gamete, egg is female gamete, oviduct and uterus are part of female reproductive system. Hence option c) is incorrect combination.

ScienceClass 8CBSE

It is believed that height of a child depends upon the genes inherited from parents. However, it is often seen that tall parents may have short children and vice-versa. Are there factors other than genes, that can cause these variations?

Soln: Height of a person is not just relied on the hereditary character. It depends on the type of food they eat. Physical exercise they do. Secretion levels of various growth hormones. Disease they encounter in their life.

ScienceClass 8CBSE

Our government has legalised the age for marriage in boys and girls. Give reasons as to why one should get married after a certain age.

In India marriage age for girls is 18 years and for boys it is 21. At age 18 girls are not mature enough physical as well as mentally to carry motherhood. Early motherhood will adversely affect on both mother and the child. For boys its 21 as at early age they are not mature enough mentally and they are not stable enough financially.

ScienceClass 8CBSE

Salma had a very soft and smooth skin during her childhood. As she entered adolescence, she developed pimples on her face. The skin specialist advised her to wash her face at regular intervals. Can you explain the reasons for the appearance of pimples on her face and suggest ways to prevent them?

After adolescence sweat glands and sebaceous glands increase their secretion. As Salma entered adolescence her sweat gland and sebaceous glands increased their secretion which resulted in the pimples on her face. Regular face wash can keep the face clean and dry which will help Salma to get rid of pimples.

ScienceClass 8CBSE

John and Radha were classmates since childhood. When Radha became eleven years old, she developed a little swelling on her neck. She visited the doctor who started medication for her. After a few years, John also developed a slight protrusion on his throat. He got worried and went to the doctor. But, the doctor assured him that it was a normal feature in boys while they are growing up. Can you think of any reasons for the difference in diagnoses?

Goitre may be reason behind swelling of Radha’s neck Goitre is the condition of the thyroid gland during which the gland produces insufficient quantity of thyroxine. In case of JOHN’s swelling of neck may be because of Adam’s apple which is the result of growth of voice box in adolescent boys.

ScienceClass 8CBSE

In human females, each time during maturation and release of egg the inner wall of uterus thickens. Is this thickening permanent? Give reasons.

Thickening of uterus wall is not permanent. Upon fertilization zygote starts developing and gets embedded in the uterus wall. This results in pregnancy. During pregnancy no more ore eggs are released thickened uterine lining is released after the delivery of the baby.

ScienceClass 8CBSE

Name the hormone which would be released during the following situations: (a) a frightened person. (b) growth of a child to adult. (c) development of caterpillar to moth. (d) development of tadpole to frog.

Adrenaline the hormone which would be released when a person is frightened Growth hormone is responsible for growth of a child to Insect hormones are responsible for development of caterpillar to Thyroxine is responsible for the development of tadpole to

ScienceClass 8CBSE

Given below are certain food items required for proper nourishment of adolescents. Name the nutrients present in the food items and write their functions. S. No. Food items Major nutrients Functions 1 Pulses and nuts 2 Oranges and Amla 3 Sugar, Roti 4 Oils 5 Vegetables

Soln: S. No. Food items Major nutrients Functions 1 Pulses and nuts Proteins Growth, repair of body cells 2 Oranges and Amla Iron And Vitamins Formation of blood keeps the body healthy 3 Sugar, Roti Cabohydrates Provide energy 4 Oils Fats Provide energy 5 Vegetables Vitamins and minerals Keeps the body healthy and disease free

ScienceClass 8CBSE

During adolescence, the body of boys and girls undergoes certain changes. Given below are a few of those changes. (a) Broad shoulders (b) Wider chests (c) Wider region below waist (d) Development of muscles (e) Development of mammary glands (f) Growth of facial hair (g) Acne and pimples on face (h) Development of sex organs (i) High-pitched voice (j) Growth of pubic hair. Categorise these changes into those that occur in boys and those that occur in girls and fill in the table given below.

Body Changes Boys Girls Broad shoulders Wider region below waist Wider chests Development of mammary glands Growth of muscles Acne and pimples on face Growth of facial hair Development of sex organs Acne and pimples on face High-pitched voice Development of sex organs Development of pubic hair Development of pubic hair

ScienceClass 8CBSE

A few of Paheli’s classmates eat potato chips and burgers regularly during the recess at school. Are they healthy eating habits? Give reasons.

As Potato chips and burgers have very little nutritional value they are not the good foods.

ScienceClass 8CBSE

We should avoid taking medicines/drugs unless prescribed by a doctor. Give reasons.

We should not take medicines/drugs unless prescribed by a doctor because some medicines have side effects and adverse effects. One can get addicted to drugs which ruin our health and happiness.

ScienceClass 8CBSE

Mention any two features each that are seen in boys and girls each to distinguish them from each other at puberty.

Two features seen in boys at puberty are: Growth of facial hairs Voice becomes Two features seen in girls at puberty are: Breast development Region below the waist becomes

ScienceClass 8CBSE

Lila always eats only dal and rice in every meal. She often falls ill and has become prone to diseases. Can you suggest changes in her diet which can make her healthy and free from disease?

Food Lila takes everyday consists of only carbohydrates and proteins. To be free from disease Lila should eat food with vitamins and minerals. She should eat more vegetables and fruits.

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