Transportation in Animals and Plants - Class 7 Science (CBSE)
Based on the 2025-26 NCERT syllabus for Class 7 Science. This chapter explains how materials are transported within living organisms through specialised systems.
1. Why this chapter matters
Every living organism needs to transport nutrients, gases, and waste products within its body. Understanding these transport systems is essential for understanding how our body works. In CBSE exams, this chapter contributes 8-10 marks with diagram-based questions.
2. The circulatory system in humans
The circulatory system consists of the heart, blood vessels, and blood. It transports oxygen, nutrients, hormones, and waste products.
3. The heart
The heart is a muscular organ that pumps blood throughout the body. It is located in the chest cavity, slightly tilted to the left.
Structure
The heart has four chambers:
- Two upper chambers: Left atrium and right atrium.
- Two lower chambers: Left ventricle and right ventricle.
Heartbeat
The heart beats continuously (about 72 times per minute in an adult). Each heartbeat has two phases:
- Contraction (systole): Heart pumps blood out.
- Relaxation (diastole): Heart fills with blood.
4. Blood vessels
Arteries
Thick-walled blood vessels that carry blood AWAY from the heart. They carry oxygen-rich blood (except the pulmonary artery).
- Have thick, elastic walls.
- Pulse can be felt in arteries.
- Branch into smaller vessels called arterioles.
Veins
Thin-walled blood vessels that carry blood TOWARDS the heart. They carry carbon dioxide-rich blood (except the pulmonary vein).
- Have thinner walls and valves to prevent backflow.
- Superficial veins are visible under the skin.
Capillaries
Extremely thin-walled vessels that connect arteries and veins. They are the site of exchange of gases, nutrients, and wastes.
5. Comparison of blood vessels
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Direction | Away from heart | Towards heart | Connect arteries and veins |
| Wall thickness | Thick | Thin | One cell thick |
| Valves | No | Yes | No |
| Blood pressure | High | Low | Very low |
| Oxygen level | Usually high | Usually low | Variable |
6. Blood and its components
Blood is a connective tissue that circulates throughout the body.
Components
| Component | Percentage | Function |
|---|---|---|
| Plasma | 55% | Liquid part; carries nutrients, hormones, waste |
| Red blood cells (RBCs) | 44% | Carry oxygen (contain haemoglobin) |
| White blood cells (WBCs) | Less than 1% | Fight infections (part of immune system) |
| Platelets | Less than 1% | Help in blood clotting |
Haemoglobin
Haemoglobin is a red pigment in RBCs that binds with oxygen. It gives blood its red colour. Oxygenated blood is bright red; deoxygenated blood is dark red.
7. The excretory system
The excretory system removes waste products from the body, especially nitrogenous wastes like urea.
Organs of the excretory system
- Kidneys (two bean-shaped organs)
- Ureters (tubes connecting kidneys to urinary bladder)
- Urinary bladder (stores urine)
- Urethra (tube through which urine exits)
How kidneys work
- Each kidney contains millions of filtering units called nephrons.
- Nephrons filter blood, removing urea and excess water and salts.
- The filtered waste forms urine.
- Cleaned blood returns to circulation.
Other excretory organs
- Skin: Removes water and salts through sweat.
- Lungs: Remove carbon dioxide and water vapour.
- Liver: Breaks down haemoglobin and produces bile.
8. Transport in plants
Plants do not have a heart or blood. Instead, they have two types of vascular tissues.
Xylem
Xylem transports water and minerals from roots to leaves.
- Movement is one-directional (upward only).
- Dead cells form continuous tubes (tracheids and vessels).
- Water moves due to root pressure and transpiration pull.
Phloem
Phloem transports food (sugars) from leaves to other parts of the plant.
- Movement is multi-directional (up and down).
- Living cells (sieve tubes) form the conducting channels.
- Food is transported to roots, stems, fruits, and storage organs.
9. Transpiration
Transpiration is the loss of water vapour from plant leaves through stomata.
Importance of transpiration
- Creates transpiration pull that draws water up through xylem.
- Helps in cooling the plant.
- Helps in the absorption of minerals from soil.
Factors affecting transpiration
- Temperature: Higher temperature increases transpiration.
- Humidity: Higher humidity decreases transpiration.
- Wind speed: Higher wind increases transpiration.
- Light: More light increases transpiration.
10. Worked examples
Example 1: Why do arteries have thick walls?
Arteries carry blood at high pressure from the heart. Thick, elastic walls allow them to withstand this pressure.
Example 2: What would happen if there were no valves in veins?
Blood in veins flows against gravity (upward). Without valves, blood would pool in the lower parts of the body and not return to the heart effectively.
Example 3: How does water move from roots to the top of a tall tree?
Water enters roots through osmosis, creating root pressure. More importantly, transpiration from leaves creates a continuous suction (transpiration pull) that draws water up the xylem vessels.
11. Common mistakes and how to fix them
| Mistake | Fix |
|---|---|
| Thinking all arteries carry oxygen-rich blood | Pulmonary artery carries deoxygenated blood to lungs |
| Confusing xylem and phloem functions | Xylem: water upward. Phloem: food everywhere |
| Believing veins have no pulse | Veins do not have a pulse; arteries do |
| Saying the heart has three chambers | The human heart has FOUR chambers |
| Forgetting that transpiration helps transport | Transpiration pull is the main force moving water up |
12. CBSE exam focus
| Question type | Marks | Frequency |
|---|---|---|
| Heart structure and function | 2-3 marks | 1 question |
| Blood components (table) | 2 marks | 1 question |
| Types of blood vessels | 2 marks | 1 question |
| Excretory system diagram | 3 marks | 1 question |
| Xylem and phloem transport | 2-3 marks | 1 question |
13. Self-test
- List the components of blood and their functions.
- What is the function of haemoglobin?
- Draw a labelled diagram showing the human excretory system.
- Distinguish between xylem and phloem.
- What is transpiration? Why is it important for plants?
- Why is it necessary to excrete waste from the body?
14. Answer key
- Plasma (carries nutrients), RBCs (carry oxygen), WBCs (fight infection), Platelets (clotting).
- Haemoglobin in RBCs binds with oxygen and transports it to all body cells.
- Diagram should include: kidneys, ureters, urinary bladder, urethra.
- Xylem: dead cells, transports water upward. Phloem: living cells, transports food in all directions.
- Transpiration is water loss from leaves through stomata. It creates suction (transpiration pull) that draws water up from roots.
- Waste products are toxic. If not removed, they accumulate and damage cells and organs.
15. Quick revision
- Heart: 4-chambered pump (atria + ventricles).
- Arteries carry blood away; veins carry blood to heart.
- Blood: plasma, RBCs (oxygen), WBCs (immunity), platelets (clotting).
- Excretory system: kidneys remove urea as urine.
- Xylem: water and minerals upward from roots.
- Phloem: food from leaves to all parts.
- Transpiration: water loss from leaves, creates pull for water transport.
- Nephrons are the filtering units in kidneys.
