- Books Name
- Science Made Easy Science Book
- Science Made Easy
- CBSE Class 9
• The cytoplasm is the fluid content inside the plasma membrane.
• It also contains many specialised cell organelles. Each of these organelles performs a specific
function for the cell.
→ Function of Cytoplasm
• It helps in exchange of material between cell organelles.
• It act as store of vital chemicals such as amino acid, glucose, vitamins and iron etc.
• It is the site of certain metabolic pathways such as glycolysis.
Endoplasmic Reticulum (ER)
• The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.
• It looks like long tubules or round or oblong bags (vesicles).
• The ER membrane is similar in structure to the plasma membrane. It is also made up of lipid and
→ Types of Endoplasmic Reticulum
(i) Rough endoplasmic reticulum (RER)
(ii) Smooth endoplasmic reticulum (SER)
→ Functions of Endoplasmic Reticulum
• RER looks rough under a microscope because it has particles called ribosomes attached to its
surface. The ribosomes, which are present in all active cells, are the sites of protein manufacture.
The manufactured proteins are then sent to various places in the cell depending on need, using the
• The SER helps in the manufacture of fat molecules, or lipids, important for cell function.
• Some of these proteins and lipids help in building the cell membrane. This process is known as
• Some other proteins and lipids function as enzymes and hormones.
• Although the ER varies greatly in appearance in different cells, it always forms a network system.
• One function of the ER is to serve as channels for the transport of materials (especially proteins)
between various regions of the cytoplasm or between the cytoplasm and the nucleus.
• The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical
activities of the cell.
• In the liver cells of the group of animals called vertebrates, SER plays a crucial role in detoxifying
many poisons and drugs.
• The Golgi apparatus consists of a system of membrane-bound vesicles arranged approximately
parallel to each other in stacks called cisterns.
• These membranes often have connections with the membranes of ER and therefore constitute
another portion of a complex cellular membrane system.
→ Function of Golgi Body
• The material synthesised near the ER is packaged and dispatched to various targets inside and
outside the cell through the Golgi apparatus.
• Its functions include the storage, modification and packaging of products in vesicles. In some
cases, complex sugars may be made from simple sugars in the Golgi apparatus.
• The Golgi apparatus is also involved in the formation of lysosomes.
• Lysosomes are a kind of waste disposal system of the cell.
• It helps to keep the cell clean by digesting any foreign material as well as worn-out cell organelle
• Lysosomes have membrane-bounded structure whose sacs are filled with digestive enzymes.
→ Functions of Lysosomes
• Lysosomes break foreign materials entering the cell, such as bacteria or food as well as old
organelles into small pieces.
• They contain powerful digestive enzymes which are made in RER which is capable of breaking
down all organic material made in RER.
• During the disturbance in cellular metabolism such as when the cell gets damaged, lysosomes
may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the
‘suicide bags’ of a cell.
• Mitochondria are known as the powerhouses of the cell.
→ Structure of mitochondria
• Mitochondria have two membrane coverings.
• The outer membrane is very porous while the inner membrane is deeply folded.
• These folds create a large surface area for ATP-generating chemical reactions.
→ Functions of mitochondria
• The energy required for various chemical activities needed for life is released by mitochondria in
the form of ATP (Adenosine triphopshate) molecules.
• ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new
chemical compounds and for mechanical work.
• Mitochondria have their own DNA and ribosomes. Therefore, mitochondria are able to make some
of their own proteins.
• Plastids are present only in plant cells.
• There are three types of plastids:
(i) Chromoplasts (coloured plastids).
(ii) Leucoplasts (white or colourless plastids).
(iii) Chloroplasts (contains the pigment chlorophyll).
→ Structure of Plastids
• The internal organisation of the plastids consists of numerous membrane layers embedded in a
material called the stroma.
• Plastids also have their own DNA and ribosomes like mitochondria and similar to its structure.
→ Function of Plastids
• Chloroplasts are important for photosynthesis in plants.
• Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll.
• Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules
• Vacuoles are storage sacs for solid or liquid contents.
• They are small sized in animal cells while plant cells have very large vacuoles.
→ Function of vacuoles
• The central vacuole of some plant cells may occupy 50-90% of the cell volume.
• In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell.
• Many important substance in the life of the plant cell are stored in vacuoles which include amino
acids, sugars, various organic acids and some proteins.
• In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba
• In some unicellular organisms, specialised vacuoles also play important roles in expelling excess