Why does menstruation occur?
Menstruation occurs at the time of puberty in females. Menstruation occurs to prevent the pregnancy phase. It releases the tissues which supports the foetus to grow during the pregnancy. Menstruation is the bleeding phase, where an egg released by female does not get fertilized or attached to the uterine wall then uterine lining dies due to deficiency of hormone (progesterone), and the lining of fallopian tube breaks down and then the blood oozes out from the ruptured vessels through the vaginal opening.
When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Outline a project which aims to find the dominant coat colour in dogs.
Draw the structure for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
How is the sex of the child determined in human beings?
(a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Calculate the number of electrons constituting one coulomb of charge.
What is an homologous series? Explain with an example.
Why is variation beneficial to the species but not necessarily for the individual?
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
What are the differences between autotrophic nutrition and heterotrophic nutrition?
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
Why should we conserve forests and wildlife?
Why are some substances biodegradable and some non-biodegradable?
Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Define the principal focus of a concave mirror.
How are the areas of study – evolution and classification – interlinked?
How are the modes for reproduction different in unicellular and multicellular organisms?