Transport of substances

• The process of transport of substances is very important in a living body.
• This ensures that the different organ systems of the living organism work efficiently.
• The following are some of the substances that need to be transported:
• Food to all the cells where it will be broken down/oxidized for the release of energy.
• Oxygen which is required for the oxidation process.
• Water and minerals which are required for proper functioning of the body of an organism.
• Waste products, formed as a result of life activities, which needs to be removed from the cells and the body.

Transport in Animals:

• In unicellular animals such as Amoeba and Paramoecium, no special transport system is required.

Amoeba                     Paramoecium

• Every part of the organism gets nutrients and oxygen directly through cell diffusion.
• In Hydra, water transports food and oxygen to all parts of the body and takes body wastes away from the different organs for excretion.

Hydra

• In multicellular organisms, the transportation is done by a specialized system known as the circulatory system.
• For instance, in human beings, the circulatory system consists of the heart, arteries, veins, and capillaries.  

Human circulatory system

• It forms a broad network which carries blood to all parts of the body.
• Blood is the medium for transport of all the necessary materials to different parts of the body.

Transport in Humans:

• Humans have a very well-developed and efficient circulatory system. It consists of:
• Blood
• Blood vessels— They are of three kinds: arteries, veins, and capillaries
• A thick muscular organ called the heart

Blood:

• Blood is a fluid that flows in the blood vessels.
• It forms a medium through which nutrients, important gases, water, and waste products are transported inside the organism.
• It constitutes about 8% of the body weight.
• Blood consists of several cells floating in straw-coloured liquid called plasma. These cells are:

1. Red blood cells (RBCs)
2. White blood cells (WBCs)
3. Blood platelets

Blood cells in the blood stream

• Red blood cells are flat and disc-like in shape with a depression in the centre.

Red blood cells

• They contain the red pigment called haemoglobin.
• This haemoglobin combines with oxygen to form oxyhaemoglobin which helps in transporting oxygen throughout the body.
• White blood cells are larger than RBCs but do not have haemoglobin.

White blood cells

• They move actively and protect the body against disease-causing micro-organisms by destroying them.
• Whenever you have a cut on your body, blood comes out. It stops bleeding after sometime.

Blood platelets

• It happens due to the presence of blood platelets in the blood.
• Blood platelets are colourless, small, irregularly shaped, and much smaller than the RBCs.

Blood Vessels:

• Blood flows through our body in a complex system of tubes called blood vessels. There are three types of blood vessels:

1. Arteries 
2. Capillaries
3. Veins

• Capillaries are the thinnest of the blood vessels and connect arteries to veins.

• Capillaries are thin-walled blood vessels and form a network of extremely tiny blood vessels between arteries and veins.
• The walls of the capillaries are so thin that diffusion of gases and chemical substances takes place very easily.