Human Body Structure for Class 4 Science

• Human body structure is complex and made of several organ systems.
• All these organ systems perform specific physiological functions.
• Our body is a complex structure which is made of several organ systems.
• All these organ systems perform specific physiological functions.
• Our bodies are made up of cells which is why cell is called structural and functional unit of life. Similar cells group together to form tissues, similar tissues form organs and organs responsible for a particular bodily function make an organ system.
• The organ systems of the body are the respiratory system, excretory system, digestive system of the human body, skeletal system of the human body, nervous system, circulatory system, etc.

• The human body consists of elements like nitrogen, hydrogen, calcium, carbon, phosphorus, etc.
• All these elements are essential as they are the structural component of the body and help in its growth and development.

Cells and Tissues

Question 1:

Why Cell Wall Is Present in Plant Cell Whereas Absent in Animal Cell?

Answers:

• Plants cannot move like animals; instead, they grow and develop in a fixed place.
• For this reason plants cannot protect themselves from harsh weather conditions and other types of physical stress.
• So, plants have an additional layer over their cells called the cell wall. It is a rigid, waxy and hard structure that protects the cells and the other components of the cell.

Question 2:

Why Are Some Plastids Termed Chloroplasts?

Answers:

• Some plastids are termed chloroplasts because of the presence of chlorophyll.
• Chlorophyll is a green pigment that helps in trapping sunlight during photosynthesis.

Question 3:

Which Cellular Component Is Called the ‘Powerhouse of the Cell’?

Answers:

• Mitochondria are called the ‘powerhouse of the cell’ because they are the organs of cellular respiration.
• They produce energy from the food after digestion.

Question 4:

Why Nucleus Is Called the Brain of the Cell?

Answers:

• The nucleus is called the ‘brain’ of the cell because it is the centre of vital cellular activities like cell division.
• It also controls the functioning of cell organelles.
• The nucleus contains genetic materials that determine certain physical characteristics like eye colour, height, skin colour etc.

Human Body Organ System

Question 1:

Why Do Our Heart Muscles Not Work According to Our Will but Other Muscles Like the Ones in Our Hands and Legs Do?

Answers:

• Both our heart muscles and body muscles are made of different muscle tissues.
• The heart constitutes cardiac muscles which are involuntary and cannot be controlled as per our own will, whereas the muscles in limbs are skeletal muscles that can be controlled.

Question 2:

Why Does the Pupil of the Eye Shrink When Exposed to Harsh Light at Night?

Answers:

• The shrinking of the pupil of the eye in front of harsh light at night is a type of reflex action.
• The pupil shrinks to control the amount of light entering the eyes so that it does not harm the sensitive parts of the eye.
• A reflex action is a type of quick action that involves a sudden and instant movement of muscles or organs of the body in response to an external stimulus.

Question 3:

Can We Survive With Only One Kidney?

Answers:

• Yes, we can survive with one kidney.
• The kidney is a vital organ of the excretory system.
• Its primary function is to purify the blood by eliminating waste products through the urine.
• In case one kidney is present in the human body, it needs to perform the function of both kidneys, due to which there are minor changes in the size of the kidney.In case one kidney is present in the human body, it needs to perform the function of both kidneys, due to which there are minor changes in the size of the kidney.

Question 4:

Why Are Blood Vessels Like Veins and Arteries Connected to the Heart? What Is the Major Difference Between Them?

Answers:

• Both arteries and veins are connected to the heart to facilitate blood flow from the heart to various body organs.
• The arteries carry blood away from the heart, whereas the veins carry blood toward the heart

Composition of Human Body

Question 1:

How Do Dairy Products Like Milk and Cheese Help in the Growth and Development of Bones and Teeth?

Answers:

• Milk and cheese are rich in calcium.
• Calcium helps in the calcification of bones. It is a process that makes our bones and teeth stronger by continuous calcium deposition.
• Hence, dairy products like milk and cheese play a vital role in the growth and development of bones and teeth.

Question 2:

What Will Happen if We Do Not Drink Water for a Few Days?

Answers:

• Both arteries and veins are connected to the heart to facilitate blood flow from the heart to various body organs.
• The arteries carry blood away from the heart, whereas the veins carry blood toward the heart

Question 3:

Can a Low Level of Oxygen in the Blood Cause a Brain Stroke?

Answers:

• Yes, a low level of oxygen in the blood can cause a brain stroke.
• Blood carries oxygen to the organs of the human body. It is essential as oxygen is required for energy production in the cells of various organs.
• The brain is a vital organ that helps in coordination, movement and remembering. It is sensitive to the level of oxygen in the blood. The cells of the brain start dying in less than 5 minutes in the absence of a sufficient amount of oxygen. As a result, it leads to brain stroke.s