PISA QUESTIONS CLASS VI-VIII

HUMAN HEART

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The blood circulatory system consists of heart and blood vessels. Heart is a vital organ located in chest cavity. It beats continuously to act as pump for transport of blood. It has four chambers. There are two upper auricles and two lower ventricles make four chambers in the human heart. The rhythmic contraction and expansion of heart is called heart beat. The human heart beats about 70-80 times per minute in an adult person. This is called heart rate. The four chambered heart separates the oxygenated blood from deoxygenated blood. The main artery is aorta. The pulmonary artery carries deoxygenated blood from heart to lungs. The pulmonary vein carries oxygenated blood from lungs to heart.

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JOINTS OF BONES IN HUMANS

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The bones of our skeleton system are hard and cannot bend. But, because of joints we can bend, and rotate our limbs. It is possible due to joints. The place in our body where bones meet each other is called as joint. It helps in walking, running, swimming, skipping etc. like movements. There are different types of joints in our body. But the main four types of joints have been discussed here.

(i) Fixed Joint (ii) Pivotal Joint (iii) Ball and Socket Joint (iv)Hinge Joint

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NITROGEN CYCLE

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The percentage of nitrogen in the atmosphere is 78 %. Nitrogen is very essential for living organisms as it is a constituent of proteins, vitamins, Chlorophylls, nucleic acids like D.N.A and R.N.A. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and Cynobacteria (blue green algae) fix the atmospheric nitrogen in the soil in form of nitrogenous compounds. In factories when chemical fertilizers are prepared and also during lightening, nitrogen is fixed in nitrogenous compounds.

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