Notes For All Chapters – General Science Class 8
1. Introduction
- The human body is made of different systems that work together to keep us alive.
- The circulatory system and respiratory system are important for transporting oxygen and nutrients.
- The excretory system helps remove waste from the body.
2. Circulatory System
(A) What is the Circulatory System?
- The circulatory system transports blood, oxygen, nutrients, and waste throughout the body.
- It consists of the heart, blood, and blood vessels (arteries, veins, and capillaries).
(B) Structure of the Heart
The heart is a muscular organ located in the chest.
It has four chambers:
- Right atrium – Receives oxygen-poor blood.
- Right ventricle – Pumps oxygen-poor blood to the lungs.
- Left atrium – Receives oxygen-rich blood from the lungs.
- Left ventricle – Pumps oxygen-rich blood to the body.
(C) Types of Blood Vessels
| Blood Vessel | Function |
|---|---|
| Arteries | Carry oxygen-rich blood from the heart to the body. |
| Veins | Carry oxygen-poor blood back to the heart. |
| Capillaries | Connect arteries and veins, allowing exchange of oxygen and nutrients. |
3. Human Blood
(A) Components of Blood
| Component | Function |
|---|---|
| Plasma | Liquid part of blood that carries nutrients and waste. |
| Red Blood Cells (RBCs) | Transport oxygen to body cells using hemoglobin. |
| White Blood Cells (WBCs) | Protect the body by fighting infections. |
| Platelets | Help in blood clotting to stop bleeding. |
(B) Functions of Blood
- Transports oxygen and nutrients to cells.
- Carries waste products to the kidneys and lungs.
- Fights infections through WBCs.
- Regulates body temperature and helps in blood clotting.
4. Respiratory System
(A) What is the Respiratory System?
- The respiratory system helps in breathing (inhaling oxygen and exhaling carbon dioxide).
- The main organs are the nose, windpipe (trachea), lungs, and diaphragm.
(B) Process of Respiration
- Inhalation (Breathing in) – The diaphragm moves down, and oxygen enters the lungs.
- Exchange of Gases – Oxygen passes from the lungs into the blood, and carbon dioxide moves into the lungs.
- Exhalation (Breathing out) – The diaphragm moves up, pushing carbon dioxide out of the lungs.
(C) Types of Respiration
| Type | Definition |
|---|---|
| External Respiration | Exchange of gases between the lungs and blood. |
| Internal Respiration | Exchange of gases between blood and body cells. |
5. Excretory System
(A) What is the Excretory System?
- The excretory system removes waste from the body.
- The main organ of excretion is the kidney, which filters blood and produces urine.
(B) Organs of the Excretory System
| Organ | Function |
|---|---|
| Kidneys | Filter blood and remove waste as urine. |
| Ureter | Carries urine from kidneys to the bladder. |
| Urinary Bladder | Stores urine until it is removed from the body. |
| Urethra | Releases urine from the body. |
6. Blood Groups and Blood Donation
(A) Blood Groups
- Humans have four main blood groups: A, B, AB, and O.
- Blood groups are based on the presence of antigens (proteins) in red blood cells.
(B) Universal Donor and Recipient
| Blood Group | Can Donate To | Can Receive From |
|---|---|---|
| O-negative | All blood groups (Universal Donor) | Only O-negative |
| AB-positive | Only AB-positive | All blood groups (Universal Recipient) |
(C) Importance of Blood Donation
- Saves lives during accidents, surgeries, and diseases like anemia.
- Hospitals always need fresh blood for emergencies.
- A healthy person can donate blood every 3 months without harm.
(D) Health Parameters for Blood Donation
- Age: 18-65 years
- Weight: Above 50 kg
- Hemoglobin Level: At least 12.5 g/dL
- No recent illness, infections, or chronic diseases
7. Health and Heart Diseases
(A) Hypertension (High Blood Pressure)
- Caused by: Excess salt, stress, lack of exercise, and unhealthy food.
- Effects: Can lead to heart attacks, strokes, and kidney disease.
- Prevention: Eat less salt, exercise regularly, and avoid smoking.
(B) How to Keep the Heart Healthy?
- Eat a balanced diet (less fat and salt).
- Exercise daily for good blood circulation.
- Avoid smoking and alcohol to prevent heart damage.
- Manage stress and get regular checkups.
8. Functional Relation Between Body Systems
| System | Relation with Circulatory System |
|---|---|
| Respiratory System | Provides oxygen to blood and removes carbon dioxide. |
| Digestive System | Provides nutrients that blood carries to body cells. |
| Excretory System | Removes waste materials carried by the blood. |
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