"AKC SCIENCE CLASSES"
CLASS 09 TH (CBSE AND MP BOARD)
CHAPTER 05
FUNDAMENTAL UNITS OF LIFE
INTEXT QUESTIONS AND ANSWERS
NCERT INTEXT QUESTIONS (PAGE NO. 59)
Q.01:- Who discovered cells, and how?
Ans:- Robert Hooke (1665). He thinly pared a pieces of cork and observed it under his self made primitive microscope. The scientist found that cork possesses a number of small box-like structures which he named cells (cellulae which later abbreviated to cells). His work was published in the form of a book called Micrographia.
Q.02:- Why is cell called structural and functional unit of life?
Ans:- Structural Unit :- A living organism is made up of one or more cells. Therefore, cell is structural unit of life.
Functional Unit :- All life functions of an organism reside in its cells. Cells may also become specialised to perform specific functions like contraction in muscle cell or impulse transmission in nerve cell. Therefore, cells are functional units of life.
NCERT INTEXT QUESTIONS (PAGE NO. 61)
Q.01:- How do substances like CO2 and water move into and out of the cell? Discuss.
Ans:- CO2 moves into and out of cells by diffusion while water does it through osmosis.
Diffusion :- It is movement of particles of various substances from the region of their higher concentration to the region of their lower concentration.
(ⅰ) In a respiring cell, more CO2 is produce internally. As a result its internal concentration rises. As concentration of CO2 is lower in the outside medium, CO2 passes out from cell into external medium.
(ⅱ) In photosynthetic cell, CO2 is being consumed in photosynthesis. Its intracellular concentration is lower than outside medium. Therefore, CO2 diffuses from outside to inside of the cell.
Osmosis :- It is movement of water from the region of its higher concentration (pure water or dilute solution) to the region of its lower concentration (strong solution) when the two are separated by a semipermeable membrane. Plasma membrane functions as a semipermeable membrane. Cell sap functions as strong solution.
Therefore, external water enters the cell (endosmosis) till wall pressure counter-balances this tendency. If the external medium has a very strong solution, water would pass out from the cell into the external medium. The phenomenon is called exosmosis.
Q.02:- Why is the plasma membrane called a selectively permeable membrane?
Ans:- Cell membrane is semipermeable membrane for water. It permits the entry of gases through diffusion. Ions, sugar, amino acids, etc. pass through the plasma membrane by an active process. Plasma membrane is impermeable to certain other materials. Therefore, it is selectively permeable.
NCERT INTEXT QUESTIONS (PAGE NO. 63)
Q.01:- Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
| SL No. | Prokaryotic | Eukaryotic |
|---|---|---|
| 1 | Size. Generally small(1-10 μm). | Size. Generally large (5-100 μm). |
| 2 | Nuclear Region____________and known as ____________. | Nuclear Region. Well defined and surrounded by a nuclear membrane. |
| 3 | Chromosomes. Single | Chromosomes. More than one chromosome. |
| 4 | Membrane Bound Cell Organelles. Absent. | _____________. |
Ans:-
| SL No. | Prokaryotic | Eukaryotic |
|---|---|---|
| 1 | Size. Generally small(1-10 μm). | Size. Generally large (5-100 μm). |
| 2 | Nuclear Region Poorly defined due to absence of nuclear envelope and known as Nucleoid. | Nuclear Region. Well defined and surrounded by a nuclear membrane. |
| 3 | Chromosomes. Single | Chromosomes. More than one chromosome. |
| 4 | Membrane Bound Cell Organelles. Absent. | Membrane bound cell organelles are present. |
NCERT INTEXT QUESTIONS (PAGE NO. 65)
Q.01:- Can you name the two organelles, we have studied that contain their own genetic material?
Ans:- Yes, Mitochondria and plastids.
Q.02:- If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Ans:- Lysosomes will burst to release digestive enzymes will cause breakdown of various cellular components causing destruction of the cell.
Q.03:- Why are lysosomes known as suicide bags?
Ans:- Lysosomes contain digestive enzymes against all types of organic materials. If their covering membrane breaks as it happens during injury of cell, the digestive enzymes will spill over the cell contents and digest the same. As lysosomes are organelles which on bursting can kill the cells possessing them, they are called suicide bags.
Q.04:- Where are proteins synthesized inside the cell?
Ans:- Proteins are synthesized over the ribosomes.
SCIENCE || CLASS 09TH || CHAPTER 05 || BASIC CONCEPTS || CBSE AND MP BOARD CLICK HERE
