About Lesson
Introduction
All organisms need food, water, and oxygen for survival, which must be transported to various parts of their body. Waste products also need to be transported to excretion sites. The heart and blood vessels function to transport substances and form the circulatory system.
7.1 Circulatory System
Blood
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Blood flows out when you get a cut. It is a fluid that transports substances like digested food, oxygen, and waste materials.
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Blood is composed of plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets.
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RBCs contain hemoglobin, which binds with oxygen and gives blood its red color.
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WBCs fight against germs.
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Platelets help in clotting blood.
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Blood Vessels
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Arteries: Carry oxygen-rich blood from the heart to the body. They have thick elastic walls due to high pressure.
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Veins: Carry carbon dioxide-rich blood back to the heart. They have thin walls and valves to prevent backflow.
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Capillaries: Connect arteries and veins, allowing exchange of substances with tissues.
Heart
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The heart is an organ that pumps blood throughout the body. It has four chambers: two atria and two ventricles.
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The right side of the heart handles deoxygenated blood, while the left side handles oxygenated blood.
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The heart’s rhythmic contraction and relaxation constitute a heartbeat.
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7.2 Excretion in Animals
Excretory System in Humans
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The excretory system removes waste products like urea from the blood.
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Kidneys: Filter blood to produce urine, which travels through ureters to the urinary bladder and is expelled via the urethra.
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Dialysis: Used for patients with kidney failure to filter blood artificially.
Excretion in Other Animals
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Aquatic animals like fish excrete ammonia directly into water.
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Birds, lizards, and insects excrete uric acid.
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7.3 Transport of Substances in Plants
Water and Minerals Transport
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Roots absorb water and minerals, which are transported through xylem vessels to the leaves.
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Transpiration: The process of water evaporation from leaves, which generates a suction pull, helping water rise through xylem vessels.
Food Transport
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The food produced in leaves is transported to other parts of the plant via phloem vessels.
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