All living organisms need essential substances like food, water, and oxygen for their survival. They also need to remove waste products generated within their bodies. These substances need to be moved to and from different parts of the organism. This movement of substances within an organism is called **transportation**.

In animals, a specialised system is responsible for transporting substances. This system includes the heart and blood vessels and is called the **circulatory system**.

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Circulatory System

The circulatory system is responsible for transporting vital substances throughout the body and collecting waste materials for removal.

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Blood

**Blood** is the fluid medium that flows within the blood vessels of animals. It is the primary transport substance in the circulatory system.

Blood performs several crucial transport functions:

• Transports **digested food** from the small intestine to all other parts of the body.
• Carries **oxygen** from the lungs to the cells throughout the body.
• Transports **waste products**, including carbon dioxide and other metabolic wastes, from the body's cells to the organs responsible for their removal (like lungs and kidneys).

Blood is composed of a liquid part called **plasma**, in which various types of cells are suspended:

• **Red Blood Cells (RBCs):** These cells contain a red pigment called **haemoglobin**. Haemoglobin binds with oxygen and is responsible for transporting oxygen to all the cells of the body. The presence of haemoglobin gives blood its red colour. Efficient oxygen delivery would be difficult without haemoglobin.
• **White Blood Cells (WBCs):** These cells are part of the body's immune system and help **fight against germs and infections** that enter the body.
• **Platelets:** These are small, irregular-shaped cell fragments that play a vital role in the **clotting of blood**. When there is a cut or injury, platelets help in forming a blood clot, which plugs the wound and stops bleeding.

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Blood Vessels

**Blood vessels** are a network of tube-like structures through which blood flows throughout the body. There are different types of blood vessels with specific functions:

• **Arteries:** These blood vessels carry blood **away from the heart** to all other parts of the body. Arteries generally carry **oxygen-rich blood** (oxygenated blood) from the heart, except for the pulmonary artery. Since blood flows rapidly and under high pressure in arteries, they have **thick, elastic walls** to withstand this pressure.

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Activity 11.1

Feeling the pulse on the inner side of the wrist (or other pulse points) allows you to detect the rhythmic **throbbing** movement in the arteries. This throbbing, called the **pulse**, is caused by the flow of blood being pumped by the heart through the arteries. The number of pulse beats per minute is the **pulse rate**. A healthy adult at rest typically has a pulse rate between 72 and 80 beats per minute. The pulse rate indicates the rate at which the heart is beating.

Table 11.1: Recording Pulse Rate (Example Structure):

S. No.	Name	Pulse per minute
1.	Self	...
2.	Friend 1	...
...	...

• **Veins:** These blood vessels carry blood **back towards the heart** from all parts of the body. Veins generally carry **carbon dioxide-rich blood** (deoxygenated blood), except for the pulmonary vein. Veins have **thin walls** compared to arteries. Veins contain **valves** that ensure blood flows only in one direction, towards the heart, and prevent backflow.

Arteries branch into smaller vessels called **arterioles**, which further divide into extremely thin tubes called **capillaries** within the tissues. It is at the capillaries that the exchange of substances (oxygen, nutrients, waste products) between the blood and the body cells occurs. Capillaries then join together to form small veins (venules), which merge into larger veins that lead back to the heart.

Special Case: Pulmonary Vessels: The **pulmonary artery** is an exception; it carries carbon dioxide-rich blood from the heart to the lungs. The **pulmonary vein** is also an exception; it carries oxygen-rich blood from the lungs back to the heart.

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Heart

The **heart** is a muscular organ that acts as a central **pump** for the circulatory system. It continuously pumps blood throughout the body, ensuring the transport of substances. The human heart is located in the chest cavity, slightly tilted towards the left, and is roughly the size of a person's fist.

To prevent the mixing of oxygen-rich blood and carbon dioxide-rich blood, the human heart has **four chambers**: two upper chambers called **atria** (singular: atrium) and two lower chambers called **ventricles**. A muscular partition completely separates the right and left sides of the heart, keeping oxygenated and deoxygenated blood separate.

The circulatory pathway involves blood flowing from the heart to the lungs (for oxygenation), back to the heart, and then pumped to the rest of the body. Deoxygenated blood from the body returns to the heart, and is then sent to the lungs.

Discovery of Blood Circulation: The English physician **William Harvey** is credited with discovering the circulation of blood in the 17th century, revolutionizing understanding of the body's transport system.

Blood Donation: Donating blood is a safe and voluntary act that saves lives by providing blood for surgeries, injuries, or conditions where the body cannot produce enough blood. Donated blood is stored in **Blood Banks**.

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Heartbeat

The walls of the heart chambers are made of muscles that contract and relax rhythmically. This rhythmic **contraction followed by relaxation** constitutes a **heartbeat**. The heart beats continuously throughout life.

The sound of the heartbeat can be felt on the chest or heard using a medical instrument called a **stethoscope**. A stethoscope amplifies the sounds of the heart, allowing doctors to listen and assess heart health.

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Activity 11.2

Constructing a simple model of a stethoscope (using a funnel, rubber tube, and rubber sheet/balloon) allows one to listen to their own heartbeat sound. Placing the funnel's covered mouth on the chest near the heart amplifies the sound. Counting the heartbeats per minute (heart rate) and comparing it with the pulse rate (measured in Activity 11.1) at rest and after exercise shows that they are typically the same, as each heartbeat generates one pulse in the arteries. Exercise increases both heart rate and pulse rate.

Table 11.2: Recording Heartbeat and Pulse Rate (Example Structure):

Name of student	While resting	After running (4–5 minutes)
	Heartbeat (beats/min)	Pulse rate (beats/min)	Heartbeat (beats/min)	Pulse rate (beats/min)
Self	...	...	...	...
Student 1	...	...	...	...
...	...	...	...	...

The rhythmic beating of the heart ensures continuous circulation and transport of substances.

Simple organisms like sponges and Hydra do not have a circulatory system. They obtain food and oxygen and remove waste directly from the water they live in, as water flows through their bodies.

Excretion In Animals

**Excretion** is the process of removing **waste products** produced in the cells of living organisms. These wastes are often toxic and need to be eliminated from the body.

Besides the removal of carbon dioxide (through lungs during exhalation) and undigested food (through egestion), animals generate other waste materials from cellular functions.

The organs involved in excretion form the **excretory system**.

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Excretory System In Humans

The human excretory system filters waste materials from the blood and removes them from the body.

It consists of:

• Two **Kidneys**: These are the primary filtering organs. Blood containing both useful and harmful substances reaches the kidneys. The useful substances are reabsorbed back into the blood, while waste products, dissolved in water, are filtered out to form **urine**.
• Two **Ureters**: Tubes that carry urine from the kidneys down to the urinary bladder.
• A **Urinary bladder**: A muscular sac that stores urine temporarily.
• A **Urethra**: A muscular tube at the end of the bladder through which urine is passed out of the body via the urinary opening.

The major waste product in human urine is **urea**. Urine also contains water and other waste products. An adult human typically produces 1–1.8 litres of urine in 24 hours.

Sometimes, kidneys may fail to work due to infection or injury. In such cases, waste products accumulate in the blood. A process called **dialysis** is used to filter the blood periodically through an artificial kidney, enabling the person to survive.

Another way the body excretes waste is through **sweating**. Sweat, produced by sweat glands, contains water and salts. Evaporation of sweat from the skin surface also helps to cool the body, similar to how water evaporating from an earthen pot (matka) keeps the water inside cool.

Excretion in other animals: The main excretory product varies among different animals depending on water availability:

• Aquatic animals (like fish) often excrete waste as **ammonia**, which directly dissolves in water.
• Some land animals (birds, lizards, snakes) excrete a semi-solid white compound called **uric acid**.

Transport Of Substances In Plants

Like animals, plants also need to transport substances. Water and mineral nutrients are absorbed from the soil and transported upwards to the leaves, where food is synthesised through photosynthesis. This food then needs to be transported to all other parts of the plant, including those that cannot photosynthesise (like roots).

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Transport Of Water And Minerals

Plants absorb water and mineral nutrients from the soil primarily through their **roots**. The surface area for absorption is significantly increased by **root hair**, which are fine extensions of root cells that are in close contact with the water in the soil particles.

Water and minerals absorbed by the roots are transported upwards throughout the plant via a specialised transport system.

Plants have pipe-like **vessels** made of special cells, forming **vascular tissue**. The vascular tissue responsible for transporting water and mineral nutrients from the roots to the leaves and other aerial parts is called **xylem**.

The xylem forms a continuous network of channels connecting the roots, stem, branches, and leaves, ensuring water supply to all parts of the plant.

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Activity 11.3

Placing a herb with its stem base cut into coloured water demonstrates the upward transport of water through the stem. The coloured water rises up the stem and becomes visible in the stem's cross-section and potentially in the veins of the leaves the next day. This visually shows that the stem conducts water upwards. Along with water, dissolved minerals are also transported upwards through the xylem vessels within the stem.

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Transpiration:

Plants absorb a large amount of water from the soil, but not all of it is used for photosynthesis or other metabolic processes. A significant amount of the absorbed water is released into the atmosphere as water vapour through a process called **transpiration**. This evaporation of water occurs mainly through the **stomata** (tiny pores) present on the surface of the leaves (as learned in Chapters 1 and 14).

Transpiration is important for two main reasons:

1. It generates a **suction pull** or transpiration pull. As water evaporates from the leaves, it creates a 'pulling' force that helps to draw water up from the roots through the xylem vessels to the leaves, even to great heights in tall trees. This is similar to how you suck liquid up through a straw.
2. It helps in **cooling the plant** as water evaporates from the leaf surface.

While xylem transports water and minerals upwards, food prepared by the leaves (during photosynthesis) needs to be transported to all other parts of the plant, including the roots, fruits, and storage organs. This downward and lateral transport of food is carried out by another type of vascular tissue called **phloem**. Thus, xylem and phloem together constitute the plant's vascular transport system.

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