Summary of 03. কোষ ও এর গঠন HSC || Cell & it’s structure HSC | HSC-27 Biology 1st Paper

Summary of Video:

03. কোষ ও এর গঠন HSC || Cell & its structure HSC | HSC-27 Biology 1st Paper

This video is a detailed lecture on the structure and composition of plant cells, focusing primarily on the Plant Cell Wall, Plasma Membrane, Protoplast, and Protoplasm, as well as their formation, chemical composition, fine structure, and functions. The lecture is delivered in Bengali and is aimed at HSC (Higher Secondary Certificate) level biology students.

Main Ideas and Concepts:

1. Structure and Formation of Plant Cell Wall

Plant Cell Wall Components:
- Composed mainly of cellulose (40%), hemicellulose (20%), pectin (30%), and glycoproteins (10%).
Formation Process:
- Begins during cell division:
  - First, the nucleus divides (karyokinesis).
  - Between the two daughter cells, a proteinaceous substance called pragmoplast (protein fibers including microtubules and microfilaments) accumulates.
  - Golgi bodies release vesicles containing pectin-like substances (basic vesicles) which fuse with the pragmoplast.
  - This fusion forms the middle lamella (middle screen), a jelly-like layer made of pectin and calcium/magnesium pectate salts, acting like cement to hold cells together.
- On both sides of the middle lamella, the primary cell wall forms, made of cellulose, hemicellulose, and pectin.
- In permanent cells, a secondary cell wall forms over the primary wall, thicker and composed of cellulose, lignin, and suberin, arranged in three layers (S1, S2, S3).
- Dividing cells only have a primary cell wall; secondary walls are absent.

2. Chemical and Fine Structure of the Cell Wall

Cellulose molecules (beta-glucose chains) combine to form micelles.
Micelles aggregate into microfibrils (small fibers).
Microfibrils combine to form macrofibrils (thicker fibers).
Macrofibrils create the overall cell wall structure.
The smallest structural unit of the cell wall is the micelle.

3. Functions of the Cell Wall

Provides protection against external injury.
Maintains shape of the cell (shape of the cell wall determines cell shape).
Offers mechanical support and rigidity (plants lack skeletal systems, so cell walls provide structural support).
Facilitates cellular connectivity through plasmodesmata (pores connecting adjacent cells).
Helps in transport of water and mineral salts (especially in xylem cells).

4. Protoplast and Protoplasm

Protoplast: The entire living part of the cell excluding the cell wall; includes Plasma Membrane, cytoplasm, and nucleus.
Protoplasm: The living contents inside the Protoplast, excluding non-living stored materials.
Protoplasm consists of:
- Plasma Membrane (cell membrane)
- Cytoplasm (fluid part called cytosol + organelles)
- Nucleus
Non-living substances inside Protoplast include stored materials such as carbohydrates, proteins, lipids (CPL), and other substances remembered by the mnemonic HISPANIC:
- Hormones
- Pigments (e.g., chlorophyll)
- Enzymes
- Nectar
Other non-living substances: latex, resin, tannins, alkaloids (e.g., nicotine, caffeine, morphine), gums.

5. Properties and Importance of Protoplasm

Named by scientist Felix Dujardin.
Called the physical basis of life by Thomas Huxley because all chemical reactions necessary for life occur in Protoplasm.
Contains 70-80% water, termed the fluid of life.
Exhibits characteristics of living things such as requiring oxygen and nutrients.

6. Movement of Protoplasm

Two types of protoplasmic movement observed in cells:
- Unidirectional (one-way) rotation: Protoplasm moves in one direction around the nucleus; seen in hydrophytes like leafy spurge.
- Multidirectional rotation: Protoplasm moves in multiple directions; seen in plants like Tradescantia.

7. Plasma Membrane (Cell Membrane)

Located just inside the cell wall.
Composed of lipids and proteins arranged