GRADE SIX SCIENCE
Hello Boys and Girls, Did you have a good week? Have you been working really hard and doing your best? Have you been doing well at all of your tests? Do ensure that you pay great attention to the exercises and activities that you have to do. Remember that the key to greater success lies in your thinking. You need to think, think through everything.
For the last few weeks we have been looking at the skeletal system. We have looked at its parts and its functions. We’ve seen how important this body system is to the entire human body. Now this week we will find out about another body system, the Circulatory System.
From the diagram of the heart below, we can see the chambers. Count them. The walls of the heart are thick and muscular. They contract and relax all the time, pumping the blood. Blood is always entering and leaving the heart.
Can you guess how much the heart weighs? The heart weighs about 300g. Its size is about the size of a clenched fist. (Clench your fist to see the size of your heart.)
Read this poem written specially for you
Blood and Circulation Do you know what moves and travels ‘Round and ‘round in many tiny vessels It never really does stand idle I wonder, does it work with diesel?
Food, oxygen and carbon dioxide Are only some of the things it transports inside It even helps us fight disease A very necessary substance, if you please
The colour of the substance is most times red Life is in it, it is often said Have you guessed the name of it now? Good for you – come on, take a bow!
J.C. Was your answer blood? You are quite right. An average person has about 5 litres of blood – about a bucket full or a bit less. When we look at blood with the naked eye it looks like a simple thick red liquid. However if we were to examine it with a microscope (an instrument used to make objects appear larger so that they are seen more distinctly) we could find out that floating in it are lots of red blood cells and white blood cells.
The red blood cells are more numerous than the white ones. It is really these red blood cells that make the blood look red. The red blood cells and the white blood cells float around in the liquid part of the blood called plasma.
Most blood cells are formed in the marrow of bones. Have you ever seen the marrow of a chicken bone?
Blood Vessels
Blood flows around the body through tubes called blood cells. Can you name one of the blood vessels? There are three types - capillaries - arteries - veins The capillaries are the smallest of the blood vessels. Their walls are very thin, allowing its contents to leak out quite easily. Water, air and dissolved (digested) food can move freely. This network of capillaries usually joins together, forming small veins. Veins and capillaries can be easily seen on persons of fair complexion. Arteries are the largest of the blood vessels and they take blood away from the heart, the artery walls are thick and elastic for they have to withstand the constant and large flow of blood directly from the heart. ♦ Read as much as you can about the heart. ♦ Find out about the differences between the arteries and the veins. ♦ List some functions of the blood.
Until next week, goodbye Boys and Girls, be good!