CBSE Notes Class 7 Science Chapter 7 - Transportation in Plants and Animals 

All living organisms need food, water and oxygen for their survival. Green plants need carbon dioxide, water and sunlight. These substances need to be carried or transported to various parts of the body. In addition, waste materials produced within the body also need to be removed. In plants, there is a system (vascular-system) of independent channels, while in animals, transportation is brought about by the circulatory system. 

1.0Transportation in Animals 

• In unicellular animals such as Amoeba and Paramecium, no special transport system is required. 
• Every part of the organism gets nutrients and oxygen directly through cell diffusion. 
• In Hydra and sponges water transports food and oxygen to all parts of the body and takes body wastes away from the different organs for excretion. 
• In multicellular organisms, the transportation is done by a specialized system known as the circulatory system. It consists of the heart, arteries, veins and capillaries. 
• 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. 

2.0Circulatory System

• Circulatory system is a transport system moving substances throughout our body with the help of blood. 
• In an adult human body, there is about 5.5 liters of blood, forming the most amazing transportation system in the body. 
• Humans have a very well-developed and efficient circulatory system. It consists of: 
• Blood 
• Blood vessels 
• Heart

1. Blood 

• Blood is a bright red-coloured fluid flowing inside blood vessels. 
• It consists of plasma which is the liquid part of blood and the three types of cells or corpuscles : (i) red blood cells (RBCs), (ii) white blood cells (WBCs), and (iii) platelets.

2. Blood vessels 

• Blood flows through our body in a complex system of tubes called blood vessels. There are three different types of blood vessels in the body. 
• Arteries : Arteries carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls and are deep seated. 
• Veins : Veins are the vessels which carry carbon dioxide-rich blood from all parts of the body back to the heart. The veins have thin walls. There are valves present in veins which allow blood to flow only towards the heart. 
• Capillaries : On reaching the tissues, the arteries divide into very fine thin walled branches called capillaries. The capillaries join up to form veins which empty into the heart. Gasses and nutrients can easily pass through the walls of capillaries. 

3. Heart

• The heart is a muscular organ which is located in the chest cavity between the lungs with its lower tip slightly tilted towards the left and beats continuously to act as a pump for the transport of blood. 
• The adult human heart is about the size of a clenched fist.
• The heart has four chambers. 
• The two upper chambers are called the atria and the two lower chambers are called the ventricles. 
• The partition between the chambers helps to avoid mixing up blood rich in oxygen with the blood rich in carbon dioxide.

Blood circulation

• Blood circulates throughout the body by the pumping action of the heart. 
• The impure blood (deoxygenated blood, rich in carbon dioxide) is collected from different organs of the body through two major veins (vena cava). The two veins empty blood into the right auricle. 
• This blood enters into the right ventricle and is pumped into the pulmonary artery. Through this artery, blood is carried to the lungs. 
• Exchange of gases (between carbon dioxide and oxygen) takes place in the lungs. 
• The pure blood (oxygenated blood) is carried by the pulmonary vein to the left auricle. From here, it enters the left ventricle and is then carried by an artery called aorta to all parts of the body. 

Heart beat and pulse 

• The heart shows regular contraction and relaxation. 
• This rhythmic contraction of muscles followed by expansion constitutes a heartbeat. 
• In a child, the heart beats varies from 90 to 100 times a minute but in an adult, it varies from 70-72 times per minute. 

3.0Transport of Substances in Plants

• Water required for food manufactured by the plants is absorbed from the soil, through the root system and food is synthesized in the leaves. 
• The water absorbed from the soil through the root system has to be moved upwards to other plant parts and the food synthesized in the leaves has to be carried to other plant parts. 
• In plants, there are special tubes called xylem and phloem, which comprise the conducting tissues of vascular tissues.

1. Transport of water and minerals 

• Upward movement of water and minerals occurs through pipe-like structures or channels, called xylem elements, present in roots, stems and leaves of plants. 
• Water is thus carried to the entire plant. 
• Plants absorb water and minerals by the roots. 
• The roots have root hair. 
• These root hairs increase the surface area for absorbing water and minerals. 
• The root hair absorbs water present between the soil particles and from there it reaches the xylem elements.

2. Translocation of food 

• The prepared food material is carried in a soluble form through another channel, constituted by phloem, from the leaves to all other parts of the body.

3. Transpiration 

• Transpiration is the process of loss of water in a vapor form from the leaves in plants. 
• It occurs through stomata present in the leaves by the process of diffusion. 
• Water absorbed through the roots is moved upwards within the plant body. 
• A part of it is used in the process of photosynthesis and some of it is also used to keep the plant erect and stop it from wilting (drooping). 
• The rest is lost as water vapor enters the atmosphere from the leaves. 
• The evaporation of water from leaves produces a suction pull which helps to pull the water upwards to great heights. 

4.0Excretory System in Humans 

• The waste which is present in the blood has to be removed from the body. 
• A mechanism to filter the blood is required. 
• This is done by the blood capillaries in the kidneys. When the blood reaches the two kidneys, it contains both useful and harmful substances. 
• The useful substances are absorbed back into the blood. 
• The wastes dissolved in water are removed as urine. Excretory system consists of the following organs : A pair of kidneys, ureters, Urinary Bladder and Urethra