Class 7 Science

Transportation in Organisms

Transportation in Unicellular Organisms: In unicellular organisms, transportation of substances happens through diffusion and osmosis. Gases move in and out of the cell by diffusion. Other substances move by osmosis.

DIFFUSION: Random motion of particles in order to attain equilibrium of concentration is called diffusion. Diffusion can be observed in many aspects of day to day life. The aroma of food comes from the kitchen because of diffusion. A pleasant smell of flowers comes because of diffusion. Bad odour of garbage comes because of diffusion.

OSMOSIS: Movement of water through a semi-permeable membrane from high water concentration to low water concentration is called osmosis. Osmosis is a type of diffusion. Cell membrane is a semi-permeable membrane. Substances move across the cell membrane because of osmosis. Seeds swell up; when soaked in water; because of osmosis.

Review Questions

What is diffusion?

Answer: Random movement of particles in order to attain equilibrium of concentration is called diffusion.

What is osmosis?

Answer: Movement of water through semi-permeable membrane from high water concentration to low water concentration is called osmosis.


CIRCULATORY SYSTEM IN HUMANS

Diffusion and osmosis can result in transportation of substances to short distances only. For bigger and complex organisms, there is a need of a more complex system for transportation of substances.

The circulatory system in humans is composed of three main components, viz. heart, blood vessels and blood.

BLOOD

Blood is a type of tissue which is responsible for transportation of substances. Blood works as the carrier of various substances. Following are the main components of blood.

Blood Cells, Platelets and Plasma

PLASMA: Plasma makes the liquid part of the blood. It makes the largest part of the blood. Plasma is pale in colour.

BLOOD CELLS: There are two main kinds of blood cells in the human blood, viz. Red Blood Cells and White Blood Cells.

Red Blood Cells or Red Blood Corpuscles (RBC): These are in the shape of discs. They contain a pigment; called haemoglobin. Haemobglobin binds with oxygen and thus is mainly responsible for transportation of oxygen in the body. Haemoglobin also transports some amount of carbon dioxide.

White Blood Cells or White Blood Corpuscles (WBC): These are present in various shapes. WBCs engulf foreign particles and harmful microbes. Thus, WBCs help in fighting the diseases. WBCs make the immune system of the body.

PLATELETS: Platelets are responsible for clotting or coagulation of blood. In case of an injury, the blood clots after some time. This prevents excess loss of blood. Clotting of blood is a defense mechanism in the body.



BLOOD VESSELS:

Blood vessels are of three main types, viz. arteries, veins and capillaries.

ARTERIES: Arteries are made of thicker walls. Arteries carry oxygenated blood from the heart to different organs. Pulmonary artery is an exception, because it carries deoxygenated blood from the heart to the lungs.

VEINS: Veins are made of thinner walls. Veins carry deoxygenated blood from different organs to the heart. Pulmonary vein is an exception, because it carries oxygenated blood from the lungs to the heart.

CAPILLARIES: These are fine branches of arteries and veins.

Review Questions

What is blood?

Answer: Blood is a type of tissue which is responsible for transportation of substances.

What is the role of RBCs?

Answer: Transportation of oxygen.



HEART

structure of human heart

The heart is a small muscular organ which is responsible for pumping the blood. The human heart has four chambers, viz. the right auricle, the right ventricle, the left auricle and the left ventricle. The upper chambers are called auricle or atrium. The lower chambers are called ventricle. The following flow chart shows the movement of blood through the heart (the blue colour shows deoxygenated blood and the red colour shows oxygenated blood):

From the body → Right Auricle → Right Ventricle → Pulmonary Artery → Lungs → Pulmonary Vein → Left Auricle → Left Ventricle → To the body

HEART BEAT: While pumping the blood, different chambers of the heart contract and relax in turns. The contraction and relaxation of different chambers produces a thumping sound. This sound can be heard as heart beat. One heart beat indicates one cycle of pumping action by all the four chambers. The heart of a normal human beats for 72 times in a minute. The heart pumps about 70 mL blood in one beat. This means that heart pumps a whopping 5 liter blood in a minute.

PULSE: At certain locations in the body, a pulse; similar to heart beat; can be felt. This happens because of blood rushing in with every heart beat. The pulse rate is same as the heart rate. Pulse can be felt near the wrist, neck, ankle, etc.

STETHOSCOPE: This is a device which is used by doctors to listen to the heart beat and pulse. Stethoscope is composed of a long rubber tube, two ear pieces and a diaphragm.

Review Questions

Which organ in the human body is responsible for pumping of blood?

Answer: heart

Which type of blood is carried by arteries?

Answer: Oxygenated Blood