Chap 5 class 9 the fundamental unit of life

 Introduction:-

Cell is the building block of all living organisms

Discovery of cell:- 

• Robert Hooke (1665) discovered cell.
• He discovered cell by self designed microscope.
• On viewing thin cutting of cork , he discovered empty spaces containing walls.
• Cells resembled honey comb like structure.

Evolution of cell Theory:- 

• Robert Hooke discovered cell.
• Robert Brown discovered nucleus in a cell 
• Schleiden and Schwann proposed cell theory.

Cell Theory:- 

• Cells are structural and functional unit of life.
• All Organisms are made up of cells .
• All cells arises from pre existing cells only.
• Nucleic acid is the genetic material in all cells.
• Cells interact with each other which results in organisms function.
• Basic chemical composition is more or less similar in all cells.

Cell type:-

Based on internal complexity in cell structure ; two types

Prokaryotic cell :-

• Membrane bound cell organelles are absent.
• Seen in Bacteria.
• No distinct nucleus.
• No definite nuclear membrane.
• Compartmentalization is not seen
• Chromosome single.
• Size :- generally small (1-10micro meter) 1 micro meter  = 10^-6m

Eukaryotic cell:- 

• Membrane bound organelles are present .
• Seen in plants , animals and fungi .
• Distinct nucleus present
• Well defined nucleus ( true nucleus)
• Compartmentalization is seen in eukaryotic cells.
• More than one chromosome
• Size : generally large (5- 100 micro meter)

Size of cells:- 

Cells exist in a variety of shapes and size.

Shapes of cells:- 

Shape of cell vary with functions they perform.

Based on number of cells present in body:- 

Unicellular Organism:-

• One cell constitute the organism 
• Single cell perform the basic functions that are characteristic of Organisms.
• Example:- Amoeba , Chlamydomonas, Paramecium , bacteria etc.

Multicellular organisms:-

• Many cells constitute the organism.
• There is a division of labour in multicellular organisms.

Eukaryotic cells:- characteristics :-

• Membrane bound organelles are present .
• Seen in plants , animals and fungi .
• Compartmentalization is seen in eukaryotic cells.
• Membrane bound nucleus is present.
•  Genetic material is well organised.

Cell organelles:- 

• A cell is made up of components called cell organelles.
• A cell is able to live and perform all its function because of these organelles.
• A cell have more or less same organelles , irrespective of their functions and Organism they found in.

Organelles:- 

Nucleus , Cell membrane,Ribosome , vacuole, SER ,RER , Mitochondria , Golgi bodies , lysosomes etc.

Are all eukaryotic cells identical?

No .

Difference between plant cell and animal cell:-

Plant cell:- 

• Cell wall is present 
• Vacuoles are big and lesser in number.
• Plastids are present
• Single Golgi apparatus called dictyosome present.
• Centriole absent

Animal cells:- 

• Cell wall is absent 
• Vacuoles are small and greater in number.
• Plastids are absent (except Euglena)
• Single complex prominent Golgi body present (dictyosome)
• Centriole present.

Plasma membrane :- 

• Also called cell membrane or selectively permeable membrane.
• It is thin , delicate , outermost , Living covering of the cell.
• It ensure protection.

Active transport :- 

• Movement of molecules across the membrane require energy.
• Movement occur against the concentration gradient.
• ATP provide the energy input from cell.

Passive transport:-

•  Movement of molecule across plasma membrane require no energy from cell .
• Movement occur along concentration gradient by diffusion or osmosis

Osmosis:- Movement of water from region of higher concentration to a region of lower concentration .

Example:- unicellular freshwater organism and most plant cells tend to gain water through osmosis. 

Absorption of water by plant roots is an example of osmosis.

Diffusion:- movement of gases from region of higher concentration to a region of lower concentration.

Behaviour with different Solution:- 

Hypotonic Solution:- Solution in which water concentration is higher than that inside the cell

Cell swell .

Animal cell may also burst

Hypertonic Solution:- Solution in which water concentration is less than that inside the cell

Cell shrink.

Plant cell undergoes plasmolysis.

Isotonic Solution :-  Solution in which water concentration in solution is same as that inside the cell

Structure of Plasma membrane:- 

• It is made up of lipids and proteins .
• Structure seen only through electron microscope.
• Lipid bilayers structure

Function of plasma membrane:- 

• It provides protection to cell.
• It allow movement of substances in and out of cell.
• Flexibility enable cells to engulf food and other materials from surrounding . Example:- Endocytosis in Amoeba.

Cell wall :-  

• It rigid , non living , Fully permeable outermost covering of plant cells and some.fungi.
• It is composed of cellulose.
• Plasmodesmata:- tiny holes through cell wall and middle lamella.

Functions of cell wall:- 

• Provide structural strength to plants 
• Prevent bursting of cells in hypotonic solution.
• Helps to connect neighbouring cells.provide protection against injury and infections

Plasmolysis :- when a living plant cell loses water through osmosis, there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is called plasmolysis

Nucleus:-

•  It is a spherical / oval structure near centre of a cell.
• It is present in both plants and animal cells 

Structure of nucleus:- 

Nuclear membrane :-

•  Double layered covering of nucleus.
• Space between two membranes is called perinuclear space .
• Seperates materials inside nucleus from cytoplasm

Nuclear pore:- 

• Pores on nuclear membrane which allow transfer of material from nucleus  to outside
• Formed by fusion of two membranes

Nucleoplasm/ nuclear matrix/ karyolymph- 

• Fluid enclosed by nuclear membrane.
• Support chromosomes and nucleolus 
• Acts as a site for RNA and DNA synthesis.

Nucleolus:-

•  Structure embedded in nucleoplasm
• Composed of proteins and RNA
• ribosomes formation takes place.

Chromatin :-

•  Thin , thread like structure embedded in nucleoplasm .
• contains RNA, DNA and proteins.

Chromosomes:- 

• Rod shaped structure 
• Formed when chromatin condensed together when the cell is about to divide.
• It contain information for inheritance of characters from parents to next generation in the form of DNA (Deoxyribonucleic acid)
• Functional segment of DNA is called gene

Function of nucleus :-  

• Control centre of the cell
• Help in movement of ribosome proteins and RNA through nuclear pores between nucleolus and cytoplasm.
• Help in cellular respiration.
• Genes present inside chromosomes decide the heredity characters.
• Chromosomes contained in nucleus play a crucial role during cell division.

Cytosol:- Fluid present inside the cell.

Cytoplasm:-

•  The fluid content inside the plasma membrane.
• Fluid + cell Organelles
•  It contains dissolved nutrients and waste products 
• It controls the shape of cell to an extent.
• Organelles present inside the cytoplasm perform specific functions without which cell cannot function as a whole.
• Helps in cellular respiration

Protoplasm:- Cytoplasm+ nucleus

Cell Organelles:- 

•  Every cell has a membrane around it to keep its own contents separate from the external environment.
• Large and complex cells, including cells from multicellular organisms need a lot of chemical activities to support their complicated structures and function
• To keep these activities ofdifferent kinds seperate from each other, these cells use membrane bound little structures within themselves.
• We will discuss about  Endoplasmic reticulum, Golgi bodies, Lysosomes, mitochondria, Plastids and vacuoles

Endoplasmic reticulum:- 

• It is a large network of membrane bound tubes and sheets.
• It looks like long tubules or round or oblong bags (vesicles).

Types:- Two types

• Smooth endoplasmic reticulum [SER]
• Rough endoplasmic reticulum [RER]

Rough endoplasmic reticulum:- 

• Ribosome attached to its surface so it is rough.
• Proteins manufactured in ribosomes transported other parts through ER.

Smooth Endoplasmic reticulum:- 

• Fat molecules and lipids are manufactured here.
• Help in detoxification of chemicals.

Functions of ER:-

• It helps in membrane biogenesis because protein is formed by RER and lipid is formed by SER.
•  ER acts as chemical to transport material to different parts of cell.
• Detoxifying poisons and drugs.
• ER works as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.

Golgi apparatus:- 

• Named after Camille Golgi who first described it 
• It is a network of membrane bound vesicles arranged parallel to each other in stack called cisterns.
• These membranes often have connections with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.
• Located near nucleus in animal.
• Freely distributed in plant cells and is called Dictyosomes

Functions of Golgi apparatus:

• Material manufactured in ER is dispatched to various parts inside or outside the cell through Golgi bodies.
• It stores cell secretion. 
• It stores , modify and pack products in vesicles 
• It forms lysosomes.
• It formd pectin.

Lysosomes:-

• It is a membrane bound vesicles containing variety of digestive enzymes.
• It is formed by golgi bodies.
• Enzymes are formed by RER.

Functions:-

• Digest waste materials/worn out organelles.
• Defense against bacterial and viral infection.
• Waste disposal system of cell.
• During cell damage, lysosomes burst and the enzymes digest their own wall.
• Termed as"Suicidal bags of cell."

Mitochondria:-

• Also called plastosome , plastochondria and power house of the cell.
• Energy is released in the form of ATP molecules.
• It can synthesis their own protein as they have their own DNA and ribosomes. That's why it is called semi-autonomous bodies/ strange organelle.

 Structure of mitochondria:-

Outer membrane:- 

• Smooth and porous
• Continuous limiting boundary of mitochondria

Inner membrane:- 

• Deeply folded 
• Folds provide greater surface area to generate ATP

Cristae:- 

• Inner membrane is compartmentalized into various cristae.

Matrix :-

•  Ground substance/space enclosed by inner membrane.

Plastids:-

• Organelle present in plant cells only
• It bear specific colour imparting pigments.
• Two types:- two types

1.  Chromoplasts(coloured plastids) and
2.  Leucoplast( white or colourless plastids)

Chromoplasts which contains chlorophyll pigments is called chloroplast . It provides green colour to cells. 

Chloroplast also contains yellow or orange pigments.

Leucoplast stores starch , oils and proteins.

Plastids are also double layered organelle.

Ground substance is called stroma.

It contains own DNA and ribosome so called semi-autonomous / strange organelle.

Vacuoles:-

• Vacuoles are storage sacs for solid or liquid contents.
• It is small sized in animal cells 
• plant cells have very large vacuoles.
• In plant it occupy 50-90% of the cell volume.
• Membrane of vacuole is called tonoplast.
• It provides turgidity and rigidity to the cell.
• It store amino acids, sugars, various organic acids and some proteins.
• In unicellular organism like Amoeba , specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.

Cell division:- 

The process by which new cells are made is called cell division.

Types:- two types.

1. Meiosis and
2. Mitosis

Meiosis/ Reductional division:-

• It occurs in Germinal cells to form gametes i.e. sperm in male and ovum in female.
• It is called Reductional division because number of chromosome in daughter cells get reduced to half on division.

Mitosis/Equational division:-

• It occurs in somatic cells.
• It is called Equational division because on division number of chromosome remain same in daughter cells.

Page number 59

Question 1. Who discovered cells, and how?

Answer: Robert Hooke discovered cells in 1665 while examining a thin slice of cork through a self-designed microscope. He saw that the cork resembled the structure of a honey comb consisting of many little compartments. These small boxes are called cells.

Question 2. Why the cell is called the structural and Junctional unit of life?

Answer: A cell is capable of independently carrying out all necessary activities of life. So, they are called basic or functional unit of life.

Page number 61

Question 1. How do substances like C02 and water move in and out of the cell? Discuss.

Answer: CO2 moves by diffusion and H2O move by osmosis through cell membrane.

Question 2. Why is the plasma membrane called a selectively permeable membrane?

Answer: It is called selectively permeable membrane because it allows the entry and exit of some substances, not all.

Page number 63:-

Question 1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Answer:

Page number 65

Question 1. Can you name the two organelles we have studied that contain their own genetic material?

Answer: The two organelles which have their own genetic material are:

1. Mitochondria 2. Plastids

Question 2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: The cell will not be able to revive and lysosomes will digest it.

 

Question 3. Why are lysosomes known as suicide hags?

Answer: When the cell gets damaged, lysosomes may burst, and the enzymes digest their own cell. Therefore lysosomes are known as suicide bags.

Question 4. Where are proteins synthesised inside the cell?

Answer: The proteins are synthesised in the ribosomes that are also known as protein factories.

Page number 67

Question 1. Make a comparison and write down ways in which plant cells are also different from animal cells.

Answer:

Question 2. How is prokaryotic cell different from a eukaryotic cell?

Answer: Prokaryotic cell is generally smaller in size (1-10 pm), nuclear region is poorly defined, the cell organelles are not membrane-bound and has a single chromosome.

Eukaryotic cell is generally larger in size (5-100 pm), nuclear region is well defined with nuclear membrane. Membrane-bound cell organelles are present and has more than one chromosome.

 

Question 3. What would happen if the plasma membrane ruptures or breaks down?

Answer: If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out.

Question 4. What would happen to the life of a cell if there was no Golgi apparatus?

Answer: Golgi apparatus has the function of storage, modification and packaging of the products in vesicles. If there were no Golgi bodies, packaging and dispatching of materials synthesised by the cell will be stocked.

Question 5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondria is known as powerhouse of the cell because it releases the energy required for different activities of life.

Question 6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer: Lipids and proteins are synthesised in ER [Endoplasmic Reticulum].

 

Question 7. How does Amoeba obtain it’s food?

Answer: Amoeba take it’s food by the cell membrane which forms the food vacuole.

Question 8. What is osmosis?

Answer: Osmosis is the process of movement of water molecule from a region of higher water concentration through a semi-permeable membrane to a region of lower water concentration.

Question 9. Carry out the following osmosis experiment:

Take four peeled potato halves and scoop each one out to make potato cups, one of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water.

Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C ‘

(d) Put one teaspoon sugar in the boiled potato cup D

Keep these for two hours. Then observe the four potato cups and answer the following:

(i) Explain why water gathers in the hollowed portion of B and C.

(ii) Why is potato A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed out portions of A and D.

Answer:

(i) Water gathers in B and C because in both the situations there is difference in the concentration of water in the trough and water in the cup of Potato. Hence, osmosis takes place as the potato cells act as a semi-permeable membrane.

(ii) Potato A is necessary for this experiment for comparison, it acts as a control.

(iii) Water does not gather in the hollowed out portions of A and D. As cup of A does not have change in the concentration for water to flow. For osmosis to occur one of the concentration should be higher than the other.

In cup D, the cells are dead and hence the semi-permeable membrane does not exists for the flow of water and no osmosis takes place.

Thank you :-)