Notes of class 9 : Structure of Cell

Generalised cell :- Different kinds of cells show some basic structural plan which may be expressed in the term of generalised cell.

In a generalised cell there are three basic parts :-

1. Cell membrane/ Plasma membrane/ Plasma lemma
2. Nucleus
3. Cytoplasm

Organelles :- As organs are functioning in the body of organism for its survival and normal life, the cells also need help of many small structures present inside it for its proper functioning. These small structures inside cell are called the cell organelles.

In the diagram above animal cell and plant cell are compared by considering their generalised form and cell organelles present in it.

Some cell organelles are present only in animal cell some are present only in plant cell and some cell organelles are present in animal as well as in plant both.

Cell wall :-

• Cell wall is present in plant cells only. It is outer most covering of plant cell.
• Cell wall is made up of cellulose ( A kind of complex carbohydrate ; Polysaccharide ). The cellulose is nonliving material so cell wall is also nonliving part of cell.
• Cell wall surrounds the cell membrane in the plant cell.
• Cell wall provide shape and rigidity to the plant cell.
• The cell wall is freely permeable i.e. it allows solvent and solute to pass trough it according to concentration gradient.
• Cell walls of two adjacent plant cells are attached with the help of "middle lamillae".

Plasmodesmata :- 

• The plasmodesmata are minute openings between cell walls of adjacent cells.
• Cytoplasm of one plant cell is continue with adjacent plant cell through plasmodesmata.
• Through plasmodesmata one plant cell can communicate with adjacent plant cell.

Cell membrane :- 

• The cell membrane is outer most covering of animal cell and it is present in the plant cell just below cell wall.
• Cell membrane is made up of lipid ( Fat ) and protein. The cell membrane is living component of a cell.
• Cell membrane is selective permeable i.e. it allows material to pass through them in case of requirement.

 

Notes of class ix 

Topic : Cell

• Meaning of term cell is the small compartment. Robert Hooke observed bee hives like small compartments in the thin slice of cork with the help of self invented microscope. These small chambers were considered as "cell".
• Antony van Leeuwenhoek was credited to observe the first living cell in pond water, sputum, blood  etc.
• The branch of science which deals with study of cell is called "Cytology".

The cell is a microscopic structure so for better understanding of a cell, at first we should have some idea about evolution of microscope which is very first requirement of cytology.

• Antony Van Leeuwenhoek designed first simple microscope having power of magnification 200 times. There was single biconvex lens in this microscope.
• Robert Hooke developed the microscope by using two lenses. It was compound microscope having power of magnification 2000 times.
• Knoll and Ruska designed electron microscope which is having power of magnification 200,000 times.

Cell Theory :- Cell theory was proposed by J.M. Schleiden and Theodor Schwann in 1838/39. Later on in 1858 Rudolf Virchow added one more point in the cell theory.

1. J.M.Schleiden a botanist in 1838 proposed that "Every plant is made up of large number of cells and each cell performs various life processes".
2. Theodor Schwann a zoologist in 1839 proposed that "All animals and plants are composed of cells which serves as a unit of structure and function".
3. Rudolf Virchow said - "Omnis cellula e cellula" that is all cells originate from preexisting cells.

Some important points about cell :-

• Bacterial cell and RBC of human body is considered as smallest cell.
• Nerve cells ( Neuron ) is the longest cell of the body.
• Ostrich egg is the largest cell.
• Small size of cell is facilitating better diffusion of materials through it, so efficiency increases.

__________________________________________________________________________

That's all for this session. We will meet in our next session with the notes on topic "Structure of Cell".

Notes of class 7

Sclerenchyma tissue :- 

• Sclerenchyma is made up of dead cellls.
• Cells of sclerenchyma become dead due to excess deposition of material around the cells.
• Sclerenchyma cells provide mechanical strength to the plant parts.

Complex permanent tissue :- The complex permanent tissue is represented by conducting tissue xylem and phloem. Xylem is responsible for transportation of water and minerals in the plant and phloem is responsible for translocation of prepared food from the leaf to all parts of plants.

Xylem :- 

• Xylem is made up of four types of cells - (i) Xylem tracheids (ii) Xylem vessels (iii) Xylem fibres (iv) Xylem Parenchyma.
• Cells of xylem are thick walled, tubular.
• All cells of xylem are dead except xylem parenchyma.
• Xylem vessels are long tubular cells joint end to end and form a long tubular pipe for transportation of water and mineral in the plant.
• Xylem tracheids are responsible for transverse transportation of water and mineral.
• Xylem fibres are helpful in joining all other cells of xylem tissue together.

   Phloem :- 

• Phloem is made up of four types of cells - (i) Sieve tubes (ii) Companion cells (iii) Phloem Parenchyma (iv) Phloem fibres.
• All cells of phloem are living except phloem fibres.
• Sieve tubes joint end to end and form a long tube through which soluble food move from leaves to other parts of plants.
• At the junction of sieve tube perforated ( with small holes ) cell wall is present which make the sieve plates. It slow down gravitational movement of soluble food.
• Phloem parenchyma cells store the food.
• Phloem fibres join other components (cell ) of phloem tissue.

Notes for class 7

Location of permanent tissue in the plants :- The permanent tissue is present in all parts of plant except meristematic zone.

Permanent tissues are of two types :-

1. Simple permanent tissue :- Simple permanent tissue is called simple because it is made up of only one kind of cells. All the cells of this type of tissue are identical in structure and function. For example :- Epidermis, Cork, Parenchyma, Collenchyma, Sclerenchyma etc.
2. Complex permanent tissue :- In complex permanent tissue more than one kind of cells are present which perform a specific function. For example :- Xylem and Phloem.

Protective simple permanent tissue :-

Epidermis :- 

• Epidermis is present as external protective cover over all parts of plant.
• The epidermis is made up of living cells.
• Epidermis is present as single layer.
• Ex. - Epidermis of leaves secrete a waxy substance called cuticle.

Cork :- 

• Cork is simple permanent tissue which is protective in function.
• Cells of cork are dead.
• Cork is found in woody dicot stem.

 Supportive simple permanent tissue :-

Parenchyma tissue :-

• Cells of parenchyma tissue are living.
• Cell wall is thin and large vacuole is present in the center of cell for storage of materials.
• Cells are oval or polygonal in shape and nucleus ,cytoplasm shifts towards periphery.
• Parenchyma tissue stores food material and help in cell to cell conduction of water in the plant.

Note :- The parenchyma tissue having chloroplast in it, is called Clorenchyma  . The chlorenchyma tissue is involve in photosynthesis. It is found in the leaves.

Collenchyma tissue :-

• Cells of collenchyma is living but its shape is elongated.
• Collenchymatous cells are thick at the corners due to deposition of materials.
• Main function of collenchyma tissue is to provide the mechanical strength and flexibility to aerial parts of plants.

Internal stucture of root :- In T. S. of root given in previous class, root hairs are visible surrounded by soil particles. Just behind epidermis, there is a cortex ( a group of parenchymatous cells ) . Last layer of cortex is called the endodermis. Xylem tissue is present behind endodermis. Water from soil enter to root hair cell by endosmosis process. From here the water move from cell to cell from cortex and reach to  endodermis. The endodermis does not allow water to return back from xylem vessels.

Root pressure :- Pressure created by the water in  xylem vessels by continuous entry of water from root hairs to xylem vessels via cortex of root, is called root pressure.
 Root pressure is important for plants for ascent of sap. It is initial pushing force.

Note :-  Water column is continue, without any air bubbles in the xylem of root, xylem of stem and xylem of leaves.

Transpiration :- Loss of water in the form of water vapour through the aerial parts of plants ( leaf, stem etc. ) is called the transpiration.

Transpiration pull :- Transpiration pull is the force which pull water through xylem vessels of leaf, stem and root. This pull force plays a vital role in the ascent of sap.

Minerals :- Minerals are important for proper growth and development of plants and for proper functioning of its different physiology.
More than 60 elements are found in different plants out of which approx. 17 elements come under category of essential elements and rest all are considered as non-essential elements.

NOTES OF CLASS 8

Structure of root :- 

• Root is underground part of plant.
• Root hairs are unicellular structure of root which absorb the water and dissolved minerals from soil.
• Root hairs originate from epidermal cell.
• Cell membrane and cell wall of root hairs are very thin and concentrated cell sap is filled in root hair cells.
• Root hairs have large surface area so it is an adaptation for absorption of water and minerals.

Active transport :- Transport of molecules and ions against concentration gradient ( from less to more ) by using energy molecule ATP is called active transport.

In plants, minerals are absorbed and transported through active transportation .

Path of water and mineral ( sap ) in the plant :- This diagram will illustrate the path of sap in plants from root to leaves -

Internal structure of root :- 

Draw above diagram and its description will appear in tomorrow's notes.

take care ..... Bye.

FOR CLASS 7 :-
Many students are asking that where to write these notes. So, my dear students you have to write it in your fair biology copy.

Kinds of meristematic tissue :-

1. Apical meristematic tissue ( Apical meristem ) :- This tissue is present in the tip portion of plants like root tip, stem tip and tip of side branches. Main function of apical meristem is to help plant in its primary growth (growth in height of plant).

2. Lateral meristematic tissue ( Lateral meristem or Cambium ):- This meristematic tissue is responsible for increase of thickness of plant (Secondary growth).

3. Intercalary meristematic tissue ( Intercalary meristem ) :- Intercalary meristem is responsible for growth of side branches in the plants.

Permanent tissue :- 

• Cells of permanent tissue do not have power of cell division.
• Nuclear content of these cells are less in comparison to cytoplasmic contents.
• These cells have large vacuoles for storage of different kinds of materials.

__________________________________________________________________________

Draw following diagrams in your fair copy :-

Description of above diagrams will appear in our next session , next week monday & tuesday.

Till then take care bye.....