Short Answer TypeExplain the meaning of sexually transmitted diseases (STDs). Give two examples of STDs each, caused due to
(i) bacterial infection and (ii) viral infection. State in brief how the spread of such diseases may be prevented.
State and describe in brief any three main factors responsible for the rise of a new species.
Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason.
A blue color flower plant denoted by BB is crossbred with that of white color flower plant denoted by bb.
(a) State the color of flower you would expect in their F1 generation plants.
(b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.
The image of a candle flame placed at a distance 30 cm from a spherical lens is formed on a screen placed at a distance of 60 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.4 cm, find the height of its image.
State the type of mirror preferred as
(i) Rear view mirror in vehicles, (ii) shaving mirror.
Justify your answer giving two reasons in each case.
A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams for the
(i) defect of vision and also (ii) for its correction
Define the terms pollination and fertilization. Draw a diagram of a pistil showing pollen tube growth into the ovule and label the following:
Pollen grain, male gamete, female gamete, ovary.
Describe in brief the role of (i) testis (ii) seminal vesicle, (iii) vas deferens, (iv) ureter and (v) prostate gland in human male reproductive system.
Long Answer TypeList the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms a three times magnified real image of an object placed 16 cm in front of it.
Sign conventions for spherical mirrors
I. Objects are always placed to the left of the mirror i.e. light must fall on the mirror from left to right.
II. All distances are measured from the pole of the mirror.
III. Distances along the direction of the incident ray (along positive X - axis) are taken as positive, while distances along the direction of the reflected ray (along negative X-axis) are taken as negative.
IV. Heights measured perpendicular to and above the principal axis (along positive Y-axis) are taken as positive.
V. Heights measured perpendicular to and below the principal axis (along negative Y-axis) are taken as negative.
Given,
Magnification, m = −3 (real image is inverted always)
Object distance, u = −16 cm
Now,
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