Download Grade IX Science Ch-5 CW Notes

ATHENA GLOBAL SCHOOL
Grade-IX
Sub: Science
Ch 5-The Fundamental Unit of Life
Define cell.
The cell is the basic structural and functional unit of life.
Why cell is called a fundamental unit?
Cell is called a fundamental unit of life because it contains DNA in which chromosomes are present and
helps in inheritance of the character.
Define prokaryote with example
Cells having nucleus without nuclear membrane is called prokaryote. e.g., paramecium,
Define Eukaryote with example .
Cells having nucleus with well organized nuclear membrane are called Eukaryote. e.g., cells of plants and
animals
Define unicellular organism.
Organisms made up of single cell are called unicellular organisms (Uni -one; cellular-cell)
Define multi cellular organism.
Organisms made up of more than one cell are called multi cellular organisms (multi-many; cellular-cell)
Parts of cell:
i) Plasma membrane
ii) Nucleus
iii) Cytoplasm
Define plasma membrane.
The outer most covering of cell that separates contents of the cell from natural environment.
Functions of plasma membrane:
It allows or permits the entry and exit of some materials .It also prevents the movement of other material
present inside the cell body.
Movement or exchange:
Some substances like carbon dioxide and oxygen can move across the cell membranes by the process
called diffusion.
The movement of water molecules through plasma membrane is carried out by the process called
osmosis.
What will happen in the cells by adding salt or sugar solution?
The following three steps could happen:
i)
ii)
iii)
If the surrounding medium has higher water concentration than the cell(hypotonic solution)
,then the cell will gain water and swell up.
If the surrounding medium and cell contains same level of water (isotonic solution), there
will be no movement of water molecules .
If the surrounding medium has lower water concentration than the cell (Hypertonic solution),
then the cell will shrink .
Endocytosis:
The flexibility of cell membrane also enables the cell to engulf the food and other materials from external
environment.This process is called as endocytosis. Amoeba acquires its food through this type of process.
13) Cell wall:
It is non living and and protects the cell. It lies outside of the plasma membrane and mainly composed of
cellulose (carbohydrates)
14) Uses of cellulose:
It is a complex substance and it provides structural strength to the plants.
15) Plasmolysis:
When a living plant cell looses water through osmosis, it results in contraction of contents of the cell
away from cell wall. The cells which are in the condition of plasmolysis are called flaccid cells.
16) Structure of nucleus:
i) Nucleus contains double layer covering called as nuclear membrane which has pores (small
holes)which allows the transfer of materials between cytoplasm and nucleoplasm .
ii) The nucleus contains thread like structure and it is called as chromatin material, whenever the cell
undergoes cell division the chromatin material gets organized into chromosomes.
iii) Chromosomes contains information for inheritance of characters from parents to next generation.
iv) Chromosomes is composed of DNA and proteins.
v) DNA molecules contains the information necessary for constructing and organizing cells.
vi) The functional segments of DNA are called genes.
vii) In some organisms like bacteria the nuclear region is not clear due to absence of nuclear membrane.
This undefined nuclear region is called as nucleoid.
Endoplasmic reticulum:
Endoplasmic reticulum is a large network of membrane bound by tubes and sheets.There are two types of
endoplasmic reticulum(i) Rough endoplasmic reticulum ,(ii)smooth endoplasmic reticulum.The RER
looks rough under microscope because ribosomes are attached to its surface.These Ribosomes are the
sites of protein manufacture.The manufactured proteins are sent to various places inside the cell
depending on its need.The SER helps in manufacture of fat molecules or lipids which is important for
cell function and building the cell membrane.This process is known as membrane biogenesis.
FUNCTIONS OF ER:
1) Serves as channels for transporting materials.
2) Increasing surface area for biochemical activities.
3) Detoxifying many poisons and drugs.
GOLGI APPARATUS:
(I)It is a system of membrane bound vesicles arranged approximately parallel to each other in stacks
called cisterns.
(ii)The materials synthesized near the ER is packaged and dispatched to various places inside and outside
through this Golgi apparatus .
(iii) It was first described by Camillo Golgi. The Golgi apparatus is involved in the synthesis of cell wall,
plasma membrane and lysosomes.
LYSOSOMES:
It is a tiny bag like structure and distributed evenly in cytoplasm. Lysosomes helps to keep the cell clean
by digesting any foreign materials as well as worn out cells.
Lysosomes are called the suicide bags of cell
MITOCHONDRIA:
(i)
(ii)
(iii)
Mitochondria are known as power house of the cell. It varies in structure and
Mitochondria have two membrane , the outer membrane is porous while the inner
membrane is deeply folded .These folded structures creates a large surface area for ATP
generating chemical reactions.
The energy required for various chemical activities is released by mitochondria in the
form of ATP (Adenosine tri phosphate) molecules. So ATP is known as energy currency
of the cell.
Mitochondria have their own DNA and Ribosomes .
PLASTIDS:
(i)
(ii)
(iii)
(iv)
(v)
(vi)
Plastids are present in plant cell. There are three types of plastids: chromoplasts
,chloroplasts, leucoplasts.
Plastids containing the pigment chlorophyll are known as chloroplasts.
Chloroplasts are important for photosynthesis in plants. It helps to trap the solar energy .
Chromoplasts impart colours to the flower which helps for pollination of flowers.
Leucoplasts contains materials such as starch, fat, protein granules for storage.
Plastids have their own DNA and Ribosomes.
VACUOLE:
Vacuoles are referred as storage unit of solid and liquid particles. It is smaller in size in case of
animal cells whereas in plant cells it has very large vacuoles. The central part of vacuole in plant cells
may occupy 90% of the cell volume. In plant cells vacuoles are full of cell sap (watery particles made
up of sugar, amino acid etc.,) and provides turgidity to the cell