Maharashtra Board Class 8 Science Chapter 11 Human Body and Organ System PDF Download

11. Human Body And Organ System

1. From what the organs and organ systems are made up of?

2. Which organ systems are present in human body?

In the last class, we have studied some characters of living organisms. All the vital processes which are essential properties of living beings, are collectively called as life processes.

1. Which processes occur in our body during sound sleep?

2. Which life processes occur continuously in our body?

Different organs in our body are working in group so as to smoothly carry out various life processes. These life processes takes place in various steps. Specific organs carry out the specific steps. Group of organs working together to perform a specific function is called as organ system. Various organ systems like digestive, respiratory, circulatory, nervous, excretory, reproductive, skeletal, muscular, etc. are functioning in our body.

Which different organs perform the function of breathing in the body of animals?

Energy is essential to operate all the life processes in human body. Energy production occurs within the cells. Cells need the supply of soluble nutrients and oxygen for this purpose. This supply takes place with the help of respiratory and circulatory systems. Respiration is carried out through following three steps.

1. External Respiration:

A. Inspiration / Inhalation: Air is taken in through nose and sent towards the lungs through trachea (wind pipe).

B. Expiration / Exhalation: Oxygen from the inspired air goes into blood. Blood carries the CO₂ from various parts of body towards lungs. This air is given out by exhalation.

Both of these processes occurring with the help of lungs are collectively called as external respiration.

2. Internal Respiration:

Exchange of gases between cells and tissue fluid is called as internal respiration. Oxygen moves from blood into tissue fluid and carbon dioxide moves from tissue fluid into blood.

3. Cellular Respiration:

Dissolved nutrients like glucose are slowly burnt (oxidized) with the help of oxygen and energy is released in the form of ATP. Waste materials like CO₂ and water vapours are produced during this process. Cellular respiration can be summarized as follows.

\[C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (38ATP)}\]

Along with the heat; sound and light are also produced during burning of fuel. Similarly, whether the sound and light are produced during oxidation of nutrients in cell?

1. Which organs are present in the respiratory system?

2. One should not talk while eating. Why is it so?

How do the organisms like amoeba, earthworm, cockroach, plants, various aquatic animals, birds respire? Prepare a chart.

Teacher's Note

When we breathe in, air enters our nose and goes to the lungs. Like a bus brings passengers to different places, our blood brings oxygen to every part of our body.

Exam Trick

Remember: Respiration = 3 steps. External (nose and lungs), Internal (blood to cells), Cellular (energy in cells). Think of it like a journey: air comes in, oxygen goes to blood, then to cells.

Points to Remember

External respiration means air goes in and out through nose and lungs.
Internal respiration means oxygen moves from blood to cells.
Cellular respiration burns glucose and makes energy called ATP.
Carbon dioxide is waste that our body removes when we breathe out.
The diaphragm is a muscle that helps us breathe by moving up and down.

Respiratory System: Structure And Function

1. Nose:

Respiratory system and respiration begins with nose. Air is filtered with the help of hair and mucus present in the nose.

2. Pharynx:

Food pipe and wind pipe originate in the pharynx. Wind pipe is present in front of the food pipe. There is a lid at the beginning of wind pipe. This lid closes the wind pipe during passing of food into food pipe and thereby normally prevents the entry of food particles into wind pipe. Otherwise, wind pipe remains open. Hence air passes through pharynx into wind pipe.

3. Wind Pipe:

Wind pipe is swollen at the beginning due to sound box. Wind pipe bifurcates in the thorax. One branch enters the right lung and the other into left lung.

4. Lungs:

A lung is present on either sides of heart in thoracic cavity. Maximum area of thoracic cavity is occupied by lungs and they cover the maximum part of heart. Each lung has double layered covering. It is called as pleura. Lungs are elastic like a sponge. Lungs are made up of many small compartments, called as alveoli. Rich network of capillaries is present around each alveolus.

Walls of alveoli and capillaries are extremely thin. Gaseous exchange can easily take place across these thin walls. As large number of alveoli is present in lungs, larger surface is available for gaseous exchange.

Exchange Of Gases In Lungs:

Gaseous exchange occurs continuously while blood is circulating around the alveoli. An iron containing protein- hemoglobin is present in the RBCs of blood. Hemoglobin absorbs the oxygen from air within alveoli. Simultaneously, CO₂ and water vapours move from blood into the alveoli. Thus, oxygen is taken into the blood and CO₂ and water vapours are removed from the blood and given out by exhalation.

5. Diaphragm:

A muscular partition is present at the base of thoracic cage. This partition is called as diaphragm. It is present between the thoracic cavity and abdominal cavity. Simultaneous rising up of ribs and lowering of diaphragm causes the decrease in pressure on lungs. Due to this, air moves into the lungs through nose. When ribs return to their original position and diaphragm rises up, pressure on the lungs increases. Due to this, air moves out from it through nose. Continuous upward and downward movement of diaphragm is necessary to bring about the breathing.

Teacher's Note

Your nose has tiny hairs that act like a filter. When you breathe, these hairs catch dust and stop it from going into your lungs. It is just like a door that keeps bad things out.

Exam Trick

Remember: The diaphragm is the muscle that makes us breathe. When it moves down, air comes in. When it moves up, air goes out. Think of it like an elevator going up and down.

Points to Remember

The nose filters air with hair and mucus.
The pharynx has a lid that stops food from going into the wind pipe.
The wind pipe splits into two branches that go to both lungs.
Alveoli are tiny air sacs where oxygen and carbon dioxide exchange happens.
The diaphragm moves up and down to help us breathe in and out.

Observe the movements in the region below the thoracic cage, occurring during breathing and discuss in the class.

1. What is meant by blood circulation?

2. Which organs are present in blood circulatory system?

Blood Circulatory System

Circulatory system performs the function of transport of various substances like water, hormones, oxygen, soluble nutrients, and waste materials through different organs. An independent system for blood circulation is present in humans and higher animals. It consists of heart, blood vessels and capillaries.

Heart: Structure And Functions

Heart is present almost at centre in thoracic cage. It is present behind the ribs, between two lungs and slightly inclined on left side.

Size of our heart is equal to one's own fist and its weight is about 360 gram. It is covered by a double layered peritoneal membrane. A fluid is present between two membranes due to which heart is protected from friction and mechanical shocks.

Human heart is a muscular organ. It is made up of involuntary cardiac muscles. They contract and relax with a definite rhythm. This is called as beating of heart.

Internally, heart is divided into left and right compartments by a vertical partition. Each of those compartments is again divided into two chambers. Thus, in all, heart consists of four chambers. Upper chambers are called as atria (singular - atrium) and lower chambers as ventricles.

Teacher's Note

Your heart is about the size of your fist. It pumps blood to your whole body every day without you thinking about it. It is like a powerful pump that sends water to all taps in a house.

Exam Trick

Remember: Heart has 4 chambers. Upper two are atria, lower two are ventricles. Think: A comes first in alphabet, so Atria are above. V comes after, so Ventricles are below.

Points to Remember

The heart is a muscular pump located between the two lungs.
The heart has four chambers: two atria and two ventricles.
The heart beats about 72 times per minute in a healthy person.
A healthy heart pumps 75 ml of blood with each beat.
The heart is covered by a membrane that protects it from injury.

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