Tuesday, December 23, 2008

THE FUNDAMENTAL UNIT OF LIFE -Part 1

THE FUNDAMENTAL UNIT OF LIFE Lesson 1

Question and Answers

1. Who discovered cells, and how?
Robert Hooke discovered cells when he observed a thin slice of cork under a microscope.

2. Why is the cell called the structural and functional unit of life?
The cell is the structural unit of life because they are the basic building blocks of the body and that all organisms are made up of cells. It is the functional unit of life because it performs different functions.

1. How do substances like CO2 and water move in and out of cell. Discuss.
Carbon dioxide moves across the cell membrane by the process of diffusion. Water obeys the law of diffusion and its movement through the cell membrane is called osmosis.

2. Why is the plasma membrane called a selectively permeable membrane?
The cell membrane is called a selectively permeable membrane because it only allows the entry and exit of some substances into and outside the cell.

Cell Membrane or Plasma Membrane




Differences between prokaryotic and eukaryotic cells


Prokaryotic cell

Eukaryotic cell

1. A cell wall formed of amino sugars is present.

A cell wall formed of cellulose is present in plant cells.

2. Membrane bound organelles such as endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, vacuoles etc are absent.

Membrane bound organelles such as endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, vacuoles etc are present.

3. Chromosome is single and strand of DNA is present in the cytoplasm.

Chromosomes are multiple and formed of DNA which are present in the nuclear membrane.

4. Nucleoid is not enclosed in the nuclear membrane.

Nuclear material is enclosed in the nuclear membrane.

5. Nucleoli and microtic apparatus are absent.

Nucleoli and microtic apparatus are present.

6. They lack 9+2 axial filament structure.

They possess 9+2 aial filament structure.

7. Small sized (1-10 micrometer).

Big sized (5-100 micrometer).

8. Cell dividies only by budding or by fission. Mitosis does not occur.

Cell divides by mitosis and meiosis cell division.

9. Ribosomes are of 70S type.

Ribosomes are of 80S type.


 

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