Assertion Reason Questions
For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.
Assertion: Photosynthesis takes place in green parts of the plants.
Reason: Photosynthesis always takes place in leaves.
Photosynthesis takes place in green parts of the plant like leaves. In a few cases the stem is green and also takes part in photosynthesis. The green part of the leaves and stem contains cells which contain the green pigment called chlorophyll. Chlorophyll traps solar energy and converts it into chemical energy during photosynthesis.
Assertion: Capillaries are the thinnest blood vessels.
Reason: Capillaries connect the branches of arteries and veins.
Capillaries are the thinnest blood vessels and connect the branches of arteries and veins. Capillaries allow the exchange of materials like nutrients, respiratory gases, hormones, etc. between the blood and body cells through tissue fluid.
Assertion: The plants store some of the waste products in their body parts.
Reason: Raphides are the solid waste products of plants.
The plants store some of the waste products in their body parts. For example some of the waste products are collected in the leaves, bark and fruits of the plants. The plants get rid of these wastes by shedding of leaves, peeling of bark and fruits. Some of the plant wastes get stored in the fruits of the plant in the form of solid bodies called raphides. These are removed when the fruits, get detached from the plant. For example, the ‘Yam’ fruit has needle shaped raphides on its surface.
Assertion: The movement of water and dissolved salts in xylem is always upwards.
Reason: The upward movement of water is due to low pressure created by transpiration.
The plants take in water (containing dissolved minerals) from the soil through their roots. This water, called xylem sap is carried by the xylem vessels to all the parts of the plant. The xylem vessels of the root of the plant are connected to the xylem vessels of its stem. So, the water (containing dissolved minerals) enters from the root xylem vessels into stem xylem vessels. The xylem vessels of the stem branch into the leaves of plants. So, the water and minerals carried by the xylem vessels in the stem reach the leaves through branched xylem vessels. Since the cells of the leaf are losing water by transpiration, so water from the xylem vessels in the leaf will travel to the cells by osmosis to make up this loss of water. Thus, water is constantly being taken away from the top of the xylem vessels in the leaves thus reduces the effective pressure at the top of the xylem vessels. The pressure at the top of the xylem vessels (in the leaves) is lowered whereas the pressure at bottom of the xylem vessels remains high. Due to this water flows up the xylem vessels.
Assertion: The large intestine is the largest part of the alimentary canal.
Reason: Tiger has a shorter small intestine, than herbivores.
The small intestine is the largest part of the alimentary canal. It is about 6.5 metres long in an adult man. Though small intestine is very long, it is called small intestine because it is very narrow. The length of small intestine differs in various animals depending on the type of food they eat. Meat is a food which is easier to digest. So, tiger which is a carnivorous animal has a shorter small intestine than herbivores.
Assertion: Most of the living organisms carry out aerobic respiration.
Reason: Mitochondria is the site of aerobic respiration in the cell.
Most of the living organisms carry out aerobic respiration. For example human, dogs, cats, lions, deer, birds, lizards, grasshopper, etc. and most of the plants carry out aerobic respiration by using oxygen of air. The first step of breakdown of glucose into pyruvic acid occurs in cytoplasm. Aerobic breakdown of pyruvic acid takes place in mitochondria.
Assertion: The Bowman’s capsule and the tubule together make a nephron.
Reason: The function of tubule is to allow the selective reabsorption of substances like glucose, amino acids, urea, salts and water into the blood capillaries.
The function of tubule of nephron is to allow the selective reabsorption of the useful substances like glucose, amino acids, salts and water into the blood capillaries. The waste materials like urea remains behind in the tubule. It does not get reabsorbed into blood capillaries.
Assertion: Pancreatic juice digests starch, proteins and fats.
Reason: Pancreatic juice contains digestive enzymes like pancreatic amylase, trypsin and lipase.
Pancreas secretes pancreatic juice which contains digestive enzymes like pancreatic amylase, trypsin and lipase. The enzyme amylase breaks down the starch, the enzyme trypsin digests the proteins and the enzyme lipase breaks down the emulsified fats.
Assertion: The accumulation of lactic acid in the muscles causes muscle cramps.
Reason: During vigorous physical exercise leg muscles respire anaerobically.
When anaerobic respiration takes place in human muscles, the glucose is converted into lactic acid with release of small amount of energy. The sudden build up of lactic acid in our muscles during vigorous physical activity can cause muscular cramps.
Assertion: Trachea does not collapse, when there is no air in it.
Reason: Trachea is supported by cartilage.
Trachea is a tube which is commonly known as windpipe. The air coming from the nostrils during breathing passes through trachea. Trachea is supported by rings of soft bones called cartilage. Due to this, trachea does not collapse even when there is no air in it.
Assertion: The average number of heart beat of a person at rest is about 80 per minute.
Reason: One contraction and relaxation of the heart constitutes a complete heart beat.
The average number of heart beat of a person at rest is about 70 to 72 per minute but the number of heart beats increases too much after a physical exercise or when a person is excited.
Assertion: Ureters are the tubes which carry urine from kidneys to the bladder. Reason: Urine is stored in the urethra.
Assertion: Ventricles have thicker walls than auricles.
Reason: Ventricles have to pump blood into various organs with great pressure.