CBSE Class 7 Science Circulation, Excretion and Transport in Plants Worksheet Set 09

Answer: Haemophilia is an inherited disorder in which the blood does not clot properly, so even a small cut may bleed for a long time.

Teacher's Note:
1. Clotting needs special proteins and platelets.
2. In this disease some of these factors are missing.

Answer: Blood will clot slowly or not at all, so bleeding from a wound will continue for a long time and the person may lose a lot of blood.

Teacher's Note:
1. Platelets gather at the injury and form a clot.
2. Without them the wound is not sealed.

Answer: Thrombocytes.

Teacher's Note:
1. They are tiny colourless cell fragments made in the bone marrow.
2. They help in blood clotting.

Answer: (a) Nephridia. (b) Malpighian tubules. (c) Kidneys. Amoeba and Hydra remove waste by diffusion through the body surface.

Teacher's Note:
1. Simple organisms need no special organs.
2. Larger animals need organs because diffusion alone is too slow.

Answer: Waste products formed in cells are harmful if they collect in the body. Excretion removes them and keeps the body healthy.

Teacher's Note:
1. Wastes such as urea are toxic in large amounts.
2. Removing them also helps maintain water balance.

Answer: Urea (a nitrogenous waste), which is removed in urine dissolved in water.

Teacher's Note:
1. Urea is formed from the breakdown of proteins in the liver.
2. The kidneys separate it from the blood.

Answer: Water evaporates from the leaves through stomata (transpiration). This creates a suction pull that draws water up from the roots through the xylem vessels, even to great heights.

Teacher's Note:
1. The pull is similar to sucking a drink through a straw.
2. Water moves up as a continuous column.

Answer: Xylem vessels.

Teacher's Note:
1. Xylem runs from the roots through the stem to the leaves.
2. Phloem carries food instead.

Answer: The upward movement of water and dissolved minerals from the roots to the leaves through the xylem is called ascent of sap.

Teacher's Note:
1. Transpiration is the main force behind it.
2. It continues all day while the stomata are open.

Answer: It cools the plant, because evaporation of water from the leaves takes away heat.

Teacher's Note:
1. This is similar to sweating in animals.
2. It is most useful on hot days.

Answer: Deoxygenated blood (blood low in oxygen and rich in carbon dioxide).

Teacher's Note:
1. The right side receives blood from the body and sends it to the lungs.
2. The left side handles oxygenated blood.

Answer: The pulmonary vein, which brings blood from the lungs to the left atrium of the heart.

Teacher's Note:
1. Most veins carry deoxygenated blood, so this is the exception.
2. Pulmonary arteries are the opposite exception.

Answer: The bicuspid valve lies between the left atrium and left ventricle. The tricuspid valve lies between the right atrium and right ventricle. Both let blood flow from atrium to ventricle only and prevent it flowing back.

Teacher's Note:
1. Valves open one way like a door.
2. They keep blood moving in the right direction.

Answer: Four chambers: the right atrium, right ventricle, left atrium and left ventricle.

Teacher's Note:
1. The atria are the upper chambers that receive blood.
2. The ventricles are the lower chambers that pump it out.

Answer: It stores urine until it is passed out of the body through the urethra.

Teacher's Note:
1. Urine reaches it from the kidneys through the ureters.
2. It is a muscular, expandable bag.

Answer: Oxygenated blood carrying waste such as urea, which is taken to the kidneys for filtering.

Teacher's Note:
1. The kidneys filter this blood.
2. The cleaned blood leaves through the renal vein.

Answer: It removes waste such as urea and extra water and salts from the body in the form of urine, and helps maintain the water balance of the body.

Teacher's Note:
1. The main organs are the kidneys, ureters, bladder and urethra.
2. The kidneys do the filtering.

Answer: (a) Both A and R are true and R is the correct explanation of A. Root hairs greatly increase absorption surface, which is exactly why they are present.

Teacher's Note:
1. Each root hair is a tiny outgrowth of a root cell.
2. Together they absorb water rapidly.

Answer: (c) A is true but R is false. The septum separates the two sides so that oxygenated and deoxygenated blood do not mix. Flow from atrium to ventricle happens through the valve, so R is false.

Teacher's Note:
1. A is true because the septum is a wall between the two halves.
2. R wrongly gives the septum the job of a valve.