Short Answer TypeList any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family?
(a)Give the evidence that the birds have evolved from reptiles.
(b) Insects, octopus, planaria and vertebrates possess eyes. Can we group these animals together on the basis of the eyes that they possess? Justify your answer giving a reason?
A cross was made between pure breeding pea plants one with round and green seeds and the other with wrinkled and yellow seeds.
(a) Write the phenotype of F1 progeny. Give reason for your answer.
(b) Write the different types of F2 progeny obtained along with their ration when F1 progeny was selfed.
A spherical mirror produces an image of magnification −1 on a screen placed at a distance of 50 cm from the mirror.
(a) Write the type of mirror.
(b) Find the distance of the image from the object.
(c) What is the focal length of the mirror?
(d) Draw the ray diagram to show the image formation in this case.
State the laws of refraction of light. If the speed of light in vacuum is 3 × 108 ms−1, find the speed of light in a medium of absolute refractive index 1.5.
Explain giving reason why the sky appears blue to an observer from the surface of the earth? What will the colour of the sky be for an astronaut staying in the international space station orbiting the earth? Justify your answer giving reason.
Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues. State the reason to explain how and why it happens?
A large number of pesticides and chemicals are used to protect our crops from pests and diseases. Some of these chemicals are washed down into the soil, while some enter in the water bodies. From the soil, they are absorbed by plants along with water and minerals; and from water bodies, they are taken up by aquatic plants and animals. This is how these chemicals enter the food chain. Because these chemicals cannot decompose, they accumulate progressively at each trophic level and their concentration increases. This increase in the concentration of harmful chemicals with each step of the food chain is called biomagnification. That is why food grains, such as wheat and rice, vegetables, fruits and even meat are found to contain pesticide residue.
State the reason why carbon can neither form C4+ cations nor anions but forms a covalent compound. Also, state the reason to explain why covalent compounds:
i) are bad conductors of electricity.
ii) have low melting and boiling point.
(a) Give one example each of a unisexual and a bisexual flower.
(b) Mention the changes a flower undergoes after fertilization.
c) How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Name the respective part of human female reproductive system:
(i) that produces eggs,
ii) where the fusion of eggs and sperm takes place, and
iii) where zygote gets implanted.
b) Describe in brief what happens to the zygote after it gets implanted.
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