The Fundamental Unit of Life (NCERT - Class 9)

What is a cell?

Cell is the structural and functional unit of life. It forms the basic structure of an organism.

Why is the cell a structural unit of life?

Because the body of an organism is made by the cell.

Why is the cell the fundamental/functional unit of life?

Because all functions of the body are carried out by the cell.

What does 'cell' mean in Latin?

A little room.

Where are cells found?

In multicellular and unicellular organisms.

Why is there a difference between the shape and size of a cell?

Different cells perform different functions, the shape and size of the cells are related to the function they perform.

Define organelle.

Certain specific components that perform specific functions inside the cell are known as organelles.

Each cell has the capacity to?

Perform basic functions.

Types of shapes of cells?

Fixed and changing.

What did Robert Hooke discover and when?

Discovered the cork cell has a honeycomb structure with a primitive microscope in 1665

What did Leeuwenhoek discover and when?

Discovered the living cell in 1674.

What did Robert Brown discover and when?

Discovered the nucleus in 1831.

What did Purkinje do and when?

Coined the term protoplasm in 1839.

What is the cell theory?

Schleiden (1838) and Schwann (1839):
Cell is the structural and fundamental unit of life.
All cell organelles are made up of cells.
Virchow (1855):
A cell arises from a pre-existing cell.

What constitutes the basic unit of a cell?

Organelles.

Do all cells have the same organelles?

Yes.

What is the basic structure of a cell?

Plasma membrane
Cell wall

Cytoplasm
Protoplasm

Nucleus

Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Mitochondria
Plastids
Vacuoles

Diffusion

The movement of gaseous molecules across the cell from their higher concentration to their lower concentration.

Osmosis

The movement of water molecules from its higher concentration to its lower concentration through a semi permeable membrane. It is a special case of diffusion.

Give examples of diffusion.

1. When freshwater unicellular organisms and plants gain water.
2. Absorption of water by roots.
3. When nutrients are obtained by the cell.

Endocytosis

The process in which the cell takes in material and food from its external environment using energy.

Function of plasma membrane

1. Protects the cell
2. Separates the external environment from the cells' internal environment

Which organelle's structure can be observed only with an electron microscope?

Plasma membrane

Characteristics of the plasma membrane

Living
Made up of lipids and proteins
Flexible
Outermost covering of the cell
Semi permeable

What are the processes that take place in the plasma membrane

Diffusion
Osmosis
Endocytosis

Types of solution

Hypotonic
Hypertonic
Isotonic

Define hypotonic solution

Water more than solute
Less concentrated
Endosmosis
Cell will swell

Define hypertonic solution

Solute more than water
More concentrated
Exosmosis
Plasmolysis
Cell will shrink

Define isotonic solution

Water is equal to solute
Same concentration
No net movement of water
No change in the shape of cells

Define endosmosis

Osmosis toward the inside of a cell

Define exosmosis

Osmosis away from the inside of a cell

Define plasmolysis

Process in which cells lose water in a hypertonic solution, contraction of contents away from the cell wall

Functions of cell wall

Protective layer
Permits the cell to withstand hypotonic external media by exerting a pressure equal to the pressure that the swollen cell is exerting

Characteristics of cell wall

Absent in animal cells
Made up of cellulose
Freely permeable
Rigid and non living layer

Function of nucleus

Directs all the activities of a cell and determines the way a cell will develop and what form it will exhibit at maturity
Plays an important role in cell division

Characteristics of nucleus

Double layered membrane with pores in it which allow the transfer of material from inside the nucleus to the cytoplasm called the nuclear membrane
Contains protoplasm
Contains DNA

What are chromosomes

Rod like structures made up of DNA and protein

What are genes

Functional segments of DNA

What is chromatin

Entangled thread that contains DNA that untangles when the cell is about to divide

Differentiate between prokaryotic and eukaryotic cells. (4 pts)

1. P.C.- generally small (1-10 micro units)
E.C.- generally large (5-100 micro units)
2. P.C.- nuclear region: undefined, containing only nucleic acids and known and nucleoid
E.C.- well defined and surrounded by a nuclear membrane
3. P.C.- a single chromosome
E.C.- more than one chromosome
4. P.C.- membrane bound cell organelles are absent
E.C.- membrane bound cell organelles are present.

Define DNA

deoxyribonucleic acid contains the information necessary for constructing and organising cells

I micro unit=

10-6 m

Characteristics of cytoplasm

Fluid content inside the plasma membrane
Contains cell organelles

Why are viruses considered non-living?

They lack membranes and do not show characteristics of life until they enter a living body and use its cell machinery to multiply

Two types of ER and their differences

1. RER- rough endoplasmic reticulum
SER- smooth endoplasmic reticulum
2. RER- protein synthesis
SER- lipid synthesis

What is the function of SER (3 pts)

Detoxification of many poisons and drugs in the liver cells of vertebrae
Other proteins and lipids function as enzymes and hormones in the SER
Membrane biogenesis

What is membrane biogenesis

When some proteins and lipids help in the building of the cell membrane

What is the structure of ER

Large network of membrane bound tubes and sheets that always forms a network system

Which cell organelle varies greatly in appearance in different cells

ER

Function of ER (2 pts)

Serves as channels for transportation of materials between various regions of the cytoplasm and nucleus
Cytoplasmic framework that provides a surface for some bio chemical activities

What did Camilo Golgi do

Describe the Golgi apparatus
'black reaction'

Structure of the Golgi apparatus

System of membrane bound vesicles arranged approximately parallel to each other in sacks called cisterns

What is the connection between ER and Golgi apparatus

Membranes of the ER are connected with the membranes of the Golgi apparatus that forms a complex membrane system

function of golgi apparatus (3 pts)

Modifies, sorts, and packages proteins in vesicles
Complex sugars can be made from simple sugars
Involved in the formation of lysosomes

function of lysosomes (2)

waste removal; digests foreign material
During the disturbance in cellular metabolism/when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell (because they contain powerful enzymes capable of breaking down all organic matter)

What is the structure of lysosomes

Membrane bound sacs filled with digestive enzymes made by the RER

functions of mitochondria + why is it different from other organelles

Energy for chemical activities is released in the mitochondria as ATP (adenosine triphosphate)
Contains their own DNA and ribosomes to produce their own enzymes

What is the structure of the mitochondria

Double membraned structure where the inner membrane is highly folded to increase inner surface area and the outer membrane is very porous

How is ATP made?

ADP+P+energy

Types of plastids and their function

Chloroplasts: contains various pigments and chlorophyll (chlorophyll)
Chromoplasts: (colourful)
Leucoplasts: materials stored here (colourless)

What is the structure of plastids

Internal structure: consists of membrane layers embedded in stoma
External structure: similar to mitochondria, have their own DNA and ribosomes

What is the function of plastids (3)

carry out photosynthesis
Manufacture and store food
contain pigments used in photosynthesis, types of pigments in a plastid determine the cell's colour

Function of vacuoles in plant and animal cells + unicellular organisms

In plant cells: provide rigidity and turgidity to the cell
Full of cell sap
Occupy 50-90% of cell volume
Amino acids, sugars and various organic acids and proteins are stored in vacuoles
In animal cell: small sized
In unicellular organisms: contains food items
Sometimes remove excess water and wastes

Differentiate between plant and animal cells

1. P.C.- larger
A.C.- smaller
2. P.C.- have a fixed shape
A.C.- do not have a fixed shape
3. P.C.- have cell wall
A.C.- don't have cell wall
4. P.C.- have large central vacuole
A.C.- have no/small vacuoles
5. P.C.- plastids are present
A.C.- plastids are absent