Thursday 20 October 2011

Class 9 Science Board (SA-1) Questions and Answers (Set 1)

Q1: State the reason of introducing Italian Bee variety in bee farms.

Answer: An Italian bee variety, A. mellifera, has been brought in India to increase yield of
honey. The Italian bees have high honey collection capacity. They sting somewhat less. They stay
in a given beehive for long periods, and breed very well. They have good resistance to diseases.

Q2: State the meaning of uniform circular motion.
Answer: When an object moves in a circular path with uniform speed, its motion is called uniform circular motion.

Q3:Can an object have uniform speed but not constant velocity?
Answer: Yes when an object moves in uniform circular motion. It has uniform speed (as well as the magnitude of velocity is same) but the direction changes every instant. (Note: velocity is a vector quantity).

Q4: Justify the statement "the wool being knitted into a sweater is a physical change".
Answer: Although the wool has gone into many physical changes since it is on Sheep, still it remains the same substance (no change in its chemical/molecular structure). The change has occured in terms of volume, size and physical appearance.

Q5: What makes skin the colour it is? 
Answer: Deep in the epidermis, cells called melanocytes release melanin – a brown pigment that colours your skin. Melanin also filters out harmful ultraviolet radiation in sunlight that can damage skin cells. We all have the same number of melanocytes but they produce more melanin in people with darker skin.

Q6: Why is a haircut painless?
Answer: Hairs, nails, and the upper layer of the epidermis all have something in common: Although they are produced by living cells, they consist mostly of dead cells packed with a strong and waterproof protein called keratin. The shaft of the hair is made of dead cells, so having your hair cut doesn’t hurt. Trimming your nails is
also painless for the same reason.

Q7: How do muscles work?
Skeletal muscle contracts when your brain tells it to. Signals are carried from the brain by neurons or nerve cells, the ends of which form junctions with muscle fibres. The arrival of a nerve signal makes filaments inside the myofibrils slide over each other so that their muscle fibres and, therefore, the muscle get shorter and “pull” on a part of your body so that you move.

Q8: How are muscles attached to bones?
Answer: At each end of a muscle, a cord or sheet called a tendon fixes it firmly to a bone. Each tendon is reinforced with parallel bundles of tough collagen fibres. This makes it incredibly strong so that, when a muscle contracts to pull a bone, its tendon does not tear. A tendon extends from a muscle, through the periosteum, and into the bone’s outer layer where it is firmly anchored.

Q9: How do joints move smoothly?
Answer: Most of your body’s 400 joints are free-moving synovial joints. All share the basic structure you can see here. The ends of the bone are coated with slippery cartilage and are separated by oily synovial
fluid, released by the synovial membrane. The combination of cartilage and fluid allows the joint to move smoothly, without the bone ends rubbing together.

Q10: Give divisions of biomolecules.
Answer: carbohydrates, proteins, lipids and nucleic acids.

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