Simply CBSE

Transportation of Materials — Class 7 Science

Quick revision notes for exam preparation.

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📌 Key Points

  • The circulatory system consists of the heart, blood vessels (arteries, veins, capillaries), and blood.
  • The human heart has four chambers: left atrium, right atrium, left ventricle, and right ventricle.
  • Arteries carry blood away from the heart (thick walls, no valves); veins carry blood towards the heart (thin walls, have valves).
  • Capillaries are very thin-walled blood vessels that allow exchange of nutrients, gases, and waste between blood and tissues.
  • Blood is made up of plasma (90% water), RBCs (carry oxygen using haemoglobin), WBCs (fight diseases), and platelets (help in clotting).
  • Haemoglobin in RBCs binds with oxygen in the lungs to form oxyhaemoglobin and transports it to all body parts.
  • Normal heartbeat rate is 70-80 beats per minute in adults. Pulse rate equals heartbeat rate.
  • Blood group O is the universal donor; blood group AB is the universal recipient.
  • Xylem transports water and minerals upward from roots to leaves. Xylem cells are dead and thick-walled.
  • Phloem transports food (sugars) from leaves to all parts of the plant. Phloem cells are living and thin-walled. This process is called translocation.
  • Roots absorb water from soil through osmosis (movement of water from higher to lower concentration through a semipermeable membrane).
  • Transpiration is the loss of water vapour from leaves through stomata. It creates a suction pull (transpiration pull) for upward water movement.
  • The human excretory system consists of kidneys, ureters, urinary bladder, and urethra.
  • Kidneys contain millions of nephrons that filter blood and form urine. Dialysis replaces kidney function artificially.
  • Plants excrete waste by reusing gases (CO2 and O2), storing waste as resin/gum/latex, and through leaf fall.

📘 Important Definitions

Circulatory System
The organ system consisting of the heart, blood vessels, and blood that transports oxygen, nutrients, and waste products throughout the body.
Haemoglobin
A red pigment present in Red Blood Cells that combines with oxygen to form oxyhaemoglobin and transports oxygen from the lungs to all body parts.
Osmosis
The movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.
Transpiration
The loss of water in the form of water vapour from the aerial parts (mainly leaves) of a plant through tiny pores called stomata.
Translocation
The transport of food (sugars) prepared during photosynthesis from leaves to other parts of the plant through the phloem tissue.
Excretion
The biological process of removing metabolic waste products (such as urea, CO2, and excess salts) from the body.
Nephron
The microscopic filtering unit inside the kidney that filters blood and removes waste to form urine. Each kidney has millions of nephrons.
Dialysis
An artificial process of filtering blood using a machine with a semipermeable membrane, used when kidneys fail to function properly.

⚠️ Common Mistakes

✗ Wrong: All arteries carry oxygenated blood and all veins carry deoxygenated blood.

✓ Correct: Pulmonary artery carries deoxygenated blood (heart to lungs) and pulmonary vein carries oxygenated blood (lungs to heart). These are the two exceptions.

✗ Wrong: Xylem transports food and phloem transports water.

✓ Correct: Xylem transports water and minerals (upward, dead cells). Phloem transports food (both directions, living cells).

✗ Wrong: Atria pump blood out of the heart.

✓ Correct: Atria (upper chambers) receive blood into the heart. Ventricles (lower chambers) pump blood out of the heart. The left ventricle has the thickest wall.

✗ Wrong: Plants do not excrete waste products.

✓ Correct: Plants do excrete, but they lack special excretory organs. They reuse CO2 and O2, store waste as resin, gum, or latex, and remove waste through leaf fall.

✗ Wrong: Excretion and egestion are the same process.

✓ Correct: Excretion is the removal of metabolic waste (urea, CO2). Egestion is the removal of undigested food (faeces) through the anus. They are different processes.

✗ Wrong: Pulse rate is different from heartbeat rate.

✓ Correct: Pulse rate equals heartbeat rate. Each heartbeat (ventricular contraction) creates one pulse wave in the arteries.

📝 Exam Focus

These questions are frequently asked in CBSE exams:

Differentiate between arteries and veins (any 4 points).
3m★★★
Differentiate between xylem and phloem.
3m★★★
Describe the components of blood and their functions.
5m★★★
Explain double circulation in the human heart.
5m★★★
What is transpiration? State its significance.
3m★★★
Describe the human excretory system and the path of urine.
3m★★
What is dialysis? When is it needed?
2m★★
Define osmosis. How do roots absorb water?
2m★★
Why does the left ventricle have a thicker wall than the right ventricle?
2m★★
How does excretion occur in plants?
3m★★

Diagram to practice: Practice drawing: (1) Structure of the human heart with four chambers labelled, (2) Human excretory system showing kidneys, ureters, bladder, and urethra, (3) Cross-section of a plant stem showing xylem and phloem, (4) Table comparing arteries, veins, and capillaries.

🎯 Last-Minute Recall

Close your eyes and try to recall: Key definitions, formulas, and 3 common mistakes. If you can recall 80% without looking, you're exam-ready!