6. LIFE PROCESSES
Human circulatory system: Blood, Heart & Blood vessels.
- In men: 14 to 17 g/ 100 ml.
- In women: 12 to 15 g/ 100 ml.
- In children: 11 to 16 g/ 100 ml.
Our pump – the heart
Pumping process of heart:
- Oxygenated blood from the lungs → left atrium relaxes → blood enters left atrium → left atrium contracts & left ventricle relaxes → blood enters left ventricle → left ventricle contracts → blood is pumped out to the body.
- Deoxygenated blood from the body → right atrium relaxes → blood enters right atrium → right atrium contracts & right ventricle dilates → blood transfers to right ventricle → right ventricle contracts → blood is pumped into the lungs for oxygenation.
Since ventricles have to pump blood into various organs, they have thicker muscular walls than that of atria.
Heart has valves to prevent the backflow of blood when the atria or ventricles contract.
Schematic representation of transport and exchange of oxygen and CO2
Oxygen enters the blood in the lungs
The separation of right side and left side of the heart prevents mixing of oxygenated and deoxygenated blood. This allows a highly efficient supply of oxygen to the body. It is useful in animals that need high energy (birds & mammals) to maintain body temperature.
Animals like amphibians & many reptiles do not use energy to maintain temperature. They depend on the temperature in the environment. Such animals have 3-chambered heart, and tolerate some mixing of the oxygenated and deoxygenated blood.
Fishes have only 2-chambered heart. Here, circulation occurs as follows:
Deoxygenated blood enters the heart → pumped to gills → blood is oxygenated in gills → blood to rest of the body.
Thus, blood goes only once through the heart during one cycle of passage through the body.
In other vertebrates, blood goes through the heart twice during each cycle. This is called double circulation.
The tubes – blood vessels
It includes arteries, veins and capillaries.
Maintenance by platelets
Leakage or loss of blood due to injury leads to reduction in pressure and efficiency of circulatory system.
To avoid this, the platelet cells plug these leaks to clot the blood at the points of injury.
Lymph (Tissue fluid):
Through the pores in the capillary walls, some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form lymph.
It is similar to blood plasma but colourless and contains less protein.
From intercellular spaces, lymph drains into lymphatic capillaries, which join to large lymph vessels that finally open into larger veins.
Lymph carries digested fat from intestine and drains excess fluid from extracellular space back into the blood.
- Xylem: It moves water & minerals from the soil.
- Phloem: It transports products of photosynthesis (energy stores) from leaves to other parts.
Transport of water
In xylem tissue, vessels & tracheids of the roots, stems and leaves are interconnected to form water-conducting channels reaching all parts.
- Take two small same sized pots with same amount of soil. One should have a plant in it. In other pot, place a stick of the same height as the plant.
- Cover the soil in both pots with a plastic sheet so that moisture cannot escape by evaporation.
- Cover both sets with plastic sheets and place in bright sunlight for half an hour.
- In pot with plant, water droplets are found in plastic sheet. It is due to condensation of water vapour released by transpiration. In other pot, water droplets are not formed.
Transport of food & other substances
Transport of soluble products of photosynthesis (food) from leaves to other parts is called translocation.