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๐ฌ Think about it
Feel the bones down your back and around your chest. They hold you up and shield your heart and lungs. How is this framework built, and how does the rib cage move when you breathe? Let us find out.
What is the skeletal system?
- It is a framework of bones that gives strength and protects organs.
- It includes the skull, vertebral column and rib cage.
- The vertebral column (spine) is made of small bones called vertebrae.
- A cartilage disc between vertebrae cushions them and allows bending.
What is the rib cage and how does it move?
- There are 12 pairs of ribs that form the rib cage.
- The rib cage protects the heart and lungs.
- Ribs join the spine at the back and the breast bone in front.
- Flexible cartilage lets the rib cage expand and contract for breathing.
Rib Cage and Breathing
Flexible cartilage joins ribs
↓
Rib cage expands
Space in the chest increases, air moves in.
↓
Rib cage contracts
Space decreases, air moves out.
Important Points
- The skeletal system is the framework of bones.
- It includes the skull, vertebral column and rib cage.
- The rib cage protects the heart and lungs and moves during breathing.
๐ฌ Meet the Scientists
- Sipra Guha Mukherjee worked with S. C. Maheshwari on plant tissue culture.
- They made a breakthrough by growing a complete plant through anther culture.
- They used an artificial nutrient medium under controlled conditions.
- Their work greatly helped crop improvement and modern agriculture.
๐ Bridging Science and Society
- Yoga from ancient Indian texts includes postures, breathing and meditation.
- Research shows it improves flexibility, posture and breathing.
- It reduces stress and helps prevent lifestyle diseases.
- 21st June is observed every year as International Yoga Day.
๐งช Think as a Scientist
- In 1958, F. C. Steward showed single carrot phloem cells can grow into whole plants.
- The cells dedifferentiated into an unspecialised mass, then redifferentiated into a full plant.
- This ability of mature cells to form a whole new plant is called totipotency.
- It is like the way a zygote divides and develops into a whole organism.
Table 3.6 — Effect of light, air and nutrient medium on growth of the cultured plant cells
| Light | Air | Composition of nutrient medium | Increase in fresh weight (mg) from initial weight |
|---|---|---|---|
| Yes | No | Solid medium + nutrients | Reduced |
| Yes | Yes | Liquid medium + nutrients | 20% increased |
| No | Yes | Liquid medium + nutrients | Reduced |
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What do you conclude about the characteristics of phloem cells of carrot?
They are totipotent — even mature phloem cells can divide and grow into a whole new plant. -
In which combination would you get the highest and lowest biomass, and why?
Highest with light, air and liquid medium (best supply of nutrients and oxygen); lowest when air or light is missing, since growth needs both. -
Will you get the same results with animal cells?
No — most mature animal cells are not totipotent and cannot regrow a whole animal this way. -
Mention two commercial applications of this study.
Growing many identical plants by tissue culture, and producing disease-free or improved crop plants.
๐ Bridging Science and Society
- Crown gall disease makes tumour-like swellings on plant stems.
- It is caused by rapid, uncontrolled cell division.
- The bacterium Agrobacterium tumefaciens causes it.
- Scientists now use this bacterium to put useful genes into plants for better crops.
โ Test Yourself
-
What three parts make up the skeletal system?
View Answer
The skull, vertebral column and rib cage. -
What is the vertebral column made of?
View Answer
Small bones called vertebrae, with cartilage discs between them. -
How many pairs of ribs form the rib cage?
View Answer
12 pairs. -
Why must the rib cage be able to move?
View Answer
So it can expand and contract to move air in and out during breathing.
Important Definitions
- Skeletal system — the framework of bones that supports the body and protects organs.
- Vertebral column — the backbone, made of small bones called vertebrae.
- Totipotency — the ability of some mature plant cells to grow into a whole new plant.
