SCHOLASTICA

WHY DO PLANTS TRANSPIRATE ?

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During Transpiration process, plants release water (that has been absorbed from the earth through their roots) into the atmosphere through stomata in the form of water vapour. Water constantly evaporates from the surface of leaves through stomata. Transpiration can be taken as analogous to perspiration (sweating) in animals that serves to cool the body but in fact it serves many other purposes for plants and tree. The process of transpiration helps to maintain the turgidity of the plant, keeps the parts of plant cool and helps opening and closing of stomata that are used for exchange of gases such as Carbon Dioxide and Oxygen for Photosynthesis and Respiration. If excessive water is lost through transpiration, the plant starts wilting. Transpiration is an essential process in Water Cycle.

Do you know that about 10 percent of the earth's atmospheric moisture can be attributed to plant transpiration? Plants lose about 90% of absorbed water through transpiration and use only 10% water for biological activities.

The plants growing in deserts such as Cactus (xerophytes) where water is scarce have either very small leaves or no leaves at all for preserving water. Leaves often turn into thorns. These plants respire and photosynthesize through stomata present on their green stems.

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NCERT Book page 123, class 7 (Transport system)

Arteries carry Oxygenated (full of Oxygen) blood to all parts of the body and Veins carry de-oxygenated blood (blood with Carbon Dioxide) to all parts of body BUT with exceptions of Pulmonary Artery and Pulmonary Vein. PULMONARY ARTERY carries blood from the heart to lungs but this blood carries Carbon Dioxide which is taken to lungs for releasing it into the atmosphere through them. Blood then returns from lungs with oxygen through PULMONARY VEIN which in this case carries blood full of Oxygen.

Arteries and Veins are joined together through Capillaries which are extremely small. Do you know that the extensive network of capillaries in an average human body is about 100000 Kms?

2013-09-15T21:03:00.001-07:00

TRANSPORT IN PLANTS

Plants get water and minerals from the soil and prepare their own food in the leaves. See the arrows going upward in the picture below. These arrows show Xylem tissue which transports water and minerals to all parts of the tree. The arrows going downward show the Phloem tissue which carries food from the leaves to all parts of the tree. The innermost brown portion is heartwood which gives mechanical support to the tree.

Some trees have been reported to be as high as 125 meters, and sometimes more. Do you know the highest tree in the world is a Redwood tree in California, US? Its name is Hyperion. Imagine how tough it is for these trees to send water and minerals from roots to the top.

2013-09-15T07:44:00.000-07:00

Class VII TRANSPORT

SOME INTERESTING BLOOD FACTS

Blood makes up around 7% of the weight of a human body.

Blood contains red blood cells, white blood cells and platelets. These blood cells float in a yellow liquid called blood plasma.

Blood plasma is made up of 90% water and also contains various nutrients, electrolytes, gases, proteins, glucose and hormones.

Blood plasma can be separated from the cells by spinning blood in a device known as a centrifuge until the cells collect at the bottom of the tube. Red blood cells have the important job of carrying oxygen around the body.

They also contain a protein called hemoglobin. Hemoglobin contains iron which combines with oxygen to give hemoglobin and our blood, a red color. Red blood cells develop in bone marrow and circulate in the body for around 120 days. White blood cells are an important part of the body’s immune system. They defend against certain bacteria, viruses, cancer cells, infectious diseases and other unwanted materials.

Platelets help blood clot in order to limit bleeding when your skin is cut. Blood clots can occasionally have negative effects, if they form in blood vessels going to the brain they can cause a stroke while clotting in a blood vessel going to the heart can lead to a heart attack.As well as delivering important substances to our cells, blood also helps take away unwanted waste products.