CBSE Class 7 Science Blood, Heart, Excretion and Transport in Plants Assignment Set 05

Answer: (a) valves. Valves in veins open one way and prevent backflow of blood.

Teacher's Note:
1. Blood in veins is under low pressure.
2. The valves keep it moving towards the heart.

Answer: (a) nephridia. Earthworms have tube-like organs called nephridia that remove waste.

Teacher's Note:
1. Nephridia filter the body fluid of the worm.
2. Insects use Malpighian tubules and vertebrates use kidneys.

Answer: (d) xylem. Xylem carries water and minerals from the roots to the leaves.

Teacher's Note:
1. Phloem carries prepared food instead.
2. Root hairs only absorb water.

Answer: Red blood cells (RBC), white blood cells (WBC) and platelets.

Teacher's Note:
1. They float in the liquid part called plasma.
2. Each has a different job.

Answer: The pericardium is a double-layered membrane that covers and protects the heart.

Teacher's Note:
1. It protects the heart from shocks.
2. A fluid between the layers reduces friction as the heart beats.

Answer: Sphygmomanometer.

Teacher's Note:
1. Blood pressure is written as two numbers, for example 120/80 mm Hg.
2. The first is the pressure when the heart contracts.

Answer: Ascent of sap is the upward movement of water and minerals from the roots to the leaves through the xylem.
Importance of transpiration: 1. it creates the suction pull for ascent of sap; 2. it cools the plant; 3. it helps absorption of water and minerals.

Teacher's Note:
1. Transpiration is loss of water as vapour through the stomata.
2. It acts like a pump for the plant.

Answer: Food made in the leaves is carried as soluble sugars to all parts of the plant through the phloem. It moves upward and downward as needed and the process needs energy.

Teacher's Note:
1. This is different from the movement of water in xylem.
2. Stored food is also moved to parts that grow.

Answer: The heart is a muscular organ about the size of a fist, lying slightly to the left in the chest and covered by the pericardium. It has four chambers: two upper atria and two lower ventricles. The septum separates the right and left sides. Valves between atria and ventricles keep blood flowing one way. Veins bring blood in and arteries carry it out.

Teacher's Note:
1. Right side handles deoxygenated blood and the left side oxygenated blood.
2. The walls of the ventricles are thicker because they pump blood further.

Answer: 1. RBCs contain haemoglobin and are red; WBCs have no haemoglobin and are colourless.
2. RBCs are far more numerous than WBCs.
3. RBCs carry oxygen; WBCs fight germs and protect the body.
4. RBCs have no nucleus (in humans); WBCs have a nucleus.

Teacher's Note:
1. Haemoglobin binds oxygen.
2. WBCs are the defence cells of the body.

Answer: The excretory system has two kidneys, two ureters, a urinary bladder and a urethra.
The kidneys filter the blood. They remove urea, extra water and salts, and the filtered waste forms urine. The urine flows through the ureters to the bladder, where it is stored, and is passed out through the urethra. The cleaned blood leaves through the renal vein.

Teacher's Note:
1. The kidneys are bean-shaped organs near the back.
2. Their filtering units are called nephrons.

Answer: 1. Arteries carry blood away from the heart; veins carry blood towards the heart.
2. Arteries have thick, elastic walls; veins have thinner walls and valves.
3. Arteries mostly carry oxygenated blood; veins mostly carry deoxygenated blood.

Teacher's Note:
1. The pulmonary artery and vein are the exceptions.
2. Blood pressure is higher in arteries.

Answer: Xylem carries water and minerals from the roots to the leaves, in one direction (upward). Phloem carries prepared food from the leaves to other parts, in both directions.

Teacher's Note:
1. Together they form the transport system of plants.
2. Both run in bundles from root to leaf.

Answer: 1. It transports oxygen, food and waste.
2. It protects the body from germs and forms clots to stop bleeding.

Teacher's Note:
1. Blood also helps maintain body temperature.
2. It is called a fluid connective tissue.

Answer: Plasma is the pale yellow liquid part of blood. It carries blood cells, dissolved food, hormones and waste.

Teacher's Note:
1. About half of blood is plasma.
2. It is mostly water and carries substances around the body.

Answer: The pulse is the rhythmic expansion of an artery with each heartbeat. It is easily felt at the wrist.

Teacher's Note:
1. The pulse rate equals the heart rate.
2. A healthy adult has about 72 beats per minute at rest.