Transportation in Animals and Plants: Class 7 Science NCERT Guide

The Human Circulatory System: Our Body's Highway

In humans and other animals, the job of transportation is handled by the circulatory system. Think of it as a complex network of roads (blood vessels) with a central pump (the heart) that keeps traffic (blood) moving. This system has three main parts:

1. Blood: This red fluid is the actual transport medium. It carries oxygen from the lungs to all body cells, picks up carbon dioxide waste to be exhaled, delivers nutrients from our food, and helps fight infections.
2. Blood Vessels: These are the tubes or pipes through which blood flows. There are three types: Arteries carry oxygen-rich blood away from the heart to the body. Veins bring oxygen-poor blood back to the heart. Capillaries are tiny, thin vessels that connect arteries and veins, allowing the exchange of substances between the blood and body cells.
3. Heart: This muscular organ acts as a tireless pump. It contracts and relaxes rhythmically to push blood throughout the body. Without the heart's pumping action, blood would not be able to reach all the places it needs to go.

The Journey of Blood Through the Heart

1. Step 1: Deoxygenated Blood Enters the Heart — Veins from all over the body collect blood that has delivered its oxygen and is now rich in carbon dioxide. This deoxygenated (blue) blood enters the right atrium (upper right chamber) of the heart.
2. Step 2: Pumping to the Lungs — From the right atrium, the blood moves to the right ventricle (lower right chamber). The heart then pumps this blood through the pulmonary artery to the lungs.
3. Step 3: Gas Exchange in the Lungs — In the lungs, the blood releases its carbon dioxide (which we breathe out) and picks up fresh oxygen (which we breathe in). The blood is now oxygenated (red).
4. Step 4: Oxygenated Blood Returns to the Heart — This fresh, oxygen-rich blood travels from the lungs through the pulmonary vein and enters the left atrium (upper left chamber) of the heart.
5. Step 5: Pumping to the Body — The blood moves to the left ventricle (lower left chamber), the strongest part of the heart. With a powerful pump, the heart sends this oxygenated blood through the aorta (the main artery) to the rest of the body, starting the cycle all over again.

Transportation in Plants: The Vascular Tissues

Xylem

This is a plant tissue that forms a network of continuous tubes from the roots to the leaves. Its main function is to transport water and dissolved minerals absorbed by the roots upwards to the rest of the plant. This upward movement is driven by a process called transpiration.

Phloem

This is another plant tissue that transports food (glucose), prepared in the leaves during photosynthesis, to all other parts of the plant, including the stem, roots, and fruits. This process of transporting food is called translocation.

Transpiration

This is the evaporation of water from the surfaces of leaves, mainly through tiny pores called stomata. This water loss creates a suction pull, like sipping a drink through a straw, which helps pull water up from the roots through the xylem.

Key Differences to Remember

• Arteries vs. Veins: Arteries carry blood Away from the heart and have thick, elastic walls to handle high pressure. Veins carry blood Towards the heart and have thinner walls and valves to prevent the backflow of blood.
• Xylem vs. Phloem: Xylem transports water and minerals upwards only (unidirectional flow). Phloem transports food in both upward and downward directions (bidirectional flow), wherever it is needed.
• Blood Components: Remember the roles! Red Blood Cells (RBCs) carry oxygen. White Blood Cells (WBCs) fight infection. Platelets help in blood clotting.
• Excretion vs. Egestion: Excretion is the removal of metabolic waste from the body (like urea in urine). Egestion is the removal of undigested food (faeces). The circulatory system is key for excretion, carrying waste to the kidneys.

Practice Questions with Solutions

• Q: Name the three main components of the circulatory system in humans and briefly state their functions. A: Step 1: Identify the three main components. Step 2: Describe the function of each component. Final answer: The three main components are: 1. Heart: Pumps blood throughout the body. 2. Blood vessels (arteries, veins, capillaries): Carry blood to and from the heart and to all body parts. 3. Blood: Transports oxygen, nutrients, hormones, and waste products.
• Q: Differentiate between xylem and phloem based on their function and the substances they transport. A: Step 1: Define xylem and its function. Step 2: Define phloem and its function. Final answer: Xylem transports water and minerals from the roots to other parts of the plant. Phloem transports food (sugars) prepared in the leaves to all other parts of the plant.
• Q: What are the four main components of blood? Which component is responsible for carrying oxygen? A: Step 1: List the four main components of blood. Step 2: Identify the component responsible for oxygen transport. Final answer: The four main components of blood are plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets. Red blood cells (RBCs) are responsible for carrying oxygen.
• Q: Explain the process of transpiration in plants and its importance. A: Step 1: Define transpiration. Step 2: Explain its importance. Final answer: Transpiration is the process by which plants release excess water vapor into the atmosphere through small pores (stomata) on their leaves. Its importance includes creating a suction pull that helps absorb water and minerals from the soil, and cooling the plant.

Frequently Asked Questions