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1. Organs and Their Types
What is an Organ?
An organ is a part of the human body that does a certain job.
Types of Organs
- External Organs: These are outside of the body.
Example: The ear’s job is to detect sounds. - Internal Organs: These are inside the body.
Example: Kidney.
2. The Circulatory System
Overview of the Circulatory System
One important body system is the circulatory system, which includes the heart and blood vessels. These organs work together to move blood around the body.
How the Circulatory System Works
The heart pumps the blood, which then moves through tubes called blood vessels. These blood vessels form a network that covers your entire body. Each time your heart beats, it pushes blood through the vessels, and you can feel this movement as a pulse in some body parts.
Interesting Fact: Blood Vessel Length
If you stretched all your blood vessels out, they would be about 100,000 kilometers long—more than twice around the Earth.
The Heart and Its Role in Circulation
Your heart is a strong muscle inside your chest, slightly to the left. It is about the size of your fist and is always beating to pump blood by contracting and relaxing.
How the Heart Works
This pumping process has six stages:
- The heart pumps blood to your lungs, where it picks up oxygen from the air you breathe.
- The oxygen-rich blood travels back to the heart.
- The heart pumps the blood again, sending it to all parts of your body to deliver oxygen.
- The blood, now low in oxygen, returns to the heart.
- The whole process repeats continuously.
Changing Ideas About the Circulatory System
- Galen’s Theory: Long ago, Galen believed the body had two separate, one-way systems for blood: one carried bright red blood from the heart for air, and the other carried blue blood from the liver for food.
- New Contributions: Ibn al-Nafis and Michael Servetus later proposed that blood moved from the heart to the lungs and back, but they did not think it traveled to the rest of the body.
William Harvey’s Discovery
In the 17th century, William Harvey discovered that the heart pumps blood to every part of the body. He asked questions, experimented, measured blood flow, and published his findings. Initially doubted, his ideas eventually became accepted.
What We Know Today
The heart pumps blood through one single system of vessels to the entire body.
Circulation in Vertebrates
Animals with backbones are called vertebrates. Humans are vertebrates. Many vertebrates have circulatory systems similar to humans, but their heart rates differ.
Blood Vessels and Their Role
Blood vessels are tubes that carry blood around your body.
Types of Blood Vessels
- Arteries: Carry blood away from the heart to capillaries.
- Capillaries: Tiny vessels that deliver water, oxygen, and nutrients to cells and remove waste.
- Veins: Carry blood from the capillaries back to the heart.
The Color of Blood: Myths and Facts
All blood in your body is red. Oxygen-rich blood is bright red (in arteries), while oxygen-poor blood is dark red (in veins). Veins look blue under the skin, which is why some people think blood is blue.
3. The Respiratory System
Overview of the Respiratory System
The respiratory system is a group of organs that allow gas exchange between air and your body. In humans, this happens in the lungs and in every cell.
The main parts:
- Tubes that carry air to the lungs
- The lungs
- A muscle called the diaphragm
How Breathing Works
Breathing has two parts:
- Inhaling: Diaphragm contracts and moves down, ribs lift up, chest expands, lungs fill with air. Oxygen passes into blood.
- Exhaling: Diaphragm relaxes and moves up, ribs move in, chest contracts, air goes out, carrying carbon dioxide.
One inhale and one exhale make a complete breath. Breathing rate = number of complete breaths per minute.
Lung Volume
The amount of air your lungs can hold is called lung volume.
4. Microbes and Diseases
Microbes and Where They Live
Microbes are almost everywhere: in air, on food, on our skin, on surfaces, and inside our bodies.
Infection and Disease
If harmful microbes enter the body, the person is infected. A disease happens when infection causes damage to organs or body systems.
Examples of Diseases Caused by Microbes
- Common cold: virus
- Whooping cough: bacteria
- Athlete’s foot: fungus
- Malaria: parasite
How Microbes Spread
This is called transmission. Harmful microbes can spread:
- Through air (coughing, sneezing)
- By touch (hugging, handshakes, objects)
- Through water and food
- By animals
Interesting Facts About Germs
- There are 10,000 to 10 million bacteria on each hand.
- Damp hands spread 1,000 times more germs than dry hands.
- Bacteria on fingertips double after using the toilet.
- One person can spread nearly one million bacteria in a school day.
Preventing the Spread: Handwashing
Handwashing is the best way to stop germs from spreading.
Five steps:
- Wet hands with water.
- Rub with soap.
- Wash for at least 20 seconds.
- Rinse.
- Dry.
(20 seconds = singing “Happy Birthday” twice.)
Airborne Transmission of Diseases
Most diseases spread through the air from coughs or sneezes. Breathing infected air can make you sick.
The Body’s Defence Mechanism
Your body fights microbes by producing mucus to trap them and by making you sneeze or cough to expel them.
Facts About Sneezing and Coughing
- A sneeze can travel up to 160 km/h.
- A sneeze can contain up to 100,000 microbes.
- A cough can spread germs 3 meters if uncovered.
- Bacteria can live for up to 40 minutes on surfaces.
Questions & Answers
Question : What other external organs can you name?
Answer: Eyes, nose, skin, mouth
Question : What is the function of these organs?
Answer:
Eyes – detect light and help us see
Nose – detects smells
Skin – protects body
Mouth – eating and speaking
Question: Match the organ in each body picture with its correct name and function. Write the letter of the picture, the name of the organ and its function.
Answer:
- Brain → controls the body
- Lungs → takes in oxygen
- Heart → pumps blood
- Stomach → breaks down food
- Intestines → extracts (removes) nutrients from food
Question : Do you think all animals have the same heart rate? What are your reasons for your ideas?
Answer: No, different vertebrates have different heart rates
Question : Does the size of an animal make a difference to its heart rate?
Answer: Yes, generally larger animals have slower heart rates.
Question c: Order the animals from the fastest to the slowest heart rate. Explain why you have put them in this order.
Answer: F (shrew) → C (hamster) → E (domestic cat) → B (human) → D (horse) → A (blue whale)
Smaller animals need faster heart rates to maintain their metabolism.
Question 1: What is blood made from?
Answer: Blood is made of cells and plasma that carry oxygen and nutrients.
Question 2: Is blood made in the heart?
Answer: No, the heart pumps blood, it doesn’t make blood.
Question 3: Is the function of the heart to clean blood?
Answer: No, the heart pumps blood. Kidneys clean blood.
Question 4: Do arteries contain clean blood and veins dirty blood?
Answer: No, arteries carry oxygen-rich blood from the heart, veins carry oxygen-poor blood back to the heart. All blood is red.