HANDOUT - 3 1st Term (2023-2024)

Name: Class: VIII Roll: Section:

Subject: Biology Teachers: Zabir Ahmed Date:

Cells:
Cells are the structural and functional unit of life. It is also the simplest unit of life, meaning it is a “living”
unit that can live independently and survive on its own. Inside the cells there are thousands of reactions
taking place that allows organisms to live.

Analogy of a cell is that of a factory:

 It takes in raw materials such as sugars and amino acids. ‘Manufactures’ it to produce products
such as ATP or energy, and proteins. The cells can use these molecules themselves or send
elsewhere.

Structure of a cell:
 Cells consist of a mass of living material called protoplasm (protoplasm is cytoplasm and the
organelles suspended in it combined).
*Protoplasm of cells differ based on the type of cells and the functionality of that cell

Cells are made up of independent compartmentalized structures called Organelles.

*compartmentalized- It means that the organelles are enclosed by their own membranes

Organelles: (Animal Cells)

Nucleus:
Nucleus can be considered to be the “brain” of the cell which means it is the control center of the cell/ it
controls all the processes and activities inside the cell.

The nucleus is enclosed by a membrane called the nuclear envelope. It controls the movement of
molecules in and out of the nucleus and acts as a layer of protection.

Inside the nucleus there is a cytoplasm like substance known as the nucleoplasm. It is the site of chemical
reactions.

Inside the nucleus there is a dense thread-like structure called chromatin which is made up of hereditary
materials known as chromosomes/ DNA. DNA/ chromosomes are the genetic code or information that an
organism inherits from their parents. It acts as a guideline as to how a cell/ organism will act and
determines its traits.

It is also responsible for cell reproduction and cell repair.

Cytoplasm:
 It is a jelly-like substance in which all the organelles of a cell is suspended. It is mostly made up of
water (70-90%).
 It is the site in which most chemical reactions take place.
 It acts as a shock absorbent in case of any external damage.

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Mitochondria:
 Mitochondria can be considered as the ‘powerhouse’ of a cell, which means it is the organelle
responsible for production/ generating energy that the cells require/other cells require.

 It is a double-membrane structure, with the inner membrane being folded, to significantly increase
the surface area. The inner membrane is the site where reactions to produce energy takes place, as
it holds the enzymes required for this reaction are present. Thus, a higher surface area means a lot
of this reaction can happen at the same time.

 The reaction to produce energy is known as respiration reaction. It is the reaction where glucose is
broken down using oxygen to produce carbon dioxide and water and energy in the form of ATP.

*ATP can be considered to be the ‘batteries’ of the cells. Meaning, the energy produced by the
mitochondria can be temporarily stored within the bonds present in the ATP and transported from
one part of the cell to another.

Endoplasmic Reticulum (ER):

 Endoplasmic Reticulum is the site of protein synthesis (Ribosomes attached on the membrane) and
is suspended with the nucleus.

 It is a structure consisting of a stack of flattened sacks connected by a fluid filled space. This
shape allows the organelle to have greater surface area.

* Ribosomes are structures that are responsible for the manufacturing of proteins. They may be found
freely moving in the cytoplasm or found attached to the ER membrane.

*Golgi apparatus:
 It is the organelle where the synthesized proteins are ‘packaged’ for proper transport in or out of the
cell.

Vacuole:
 A small temporary empty storage that is used to store water, food

Centriole:
 It is the organelle responsible for cell division, replication.
 Plays a vital role in pulling apart the DNA into two separate parts during cell division/ replication.

Organelles in a Plant Cell:

Cell Wall:
 It is the outer most structure of a plant cell. It is made of a thick fiber known as cellulose.
 The role of the cell wall is to:
- Provide structure and a definite shape of the cell
- Acts as the selectively permeable membrane to control entry and exit of molecules into and out
of the cell.
- Plays a key part in keeping the cell turgid.

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Chloroplast:
 Chloroplasts are specialized organelles that are responsible for generating energy for the cell.
 Chloroplasts contain a special green pigment known as Chlorophyll.
 Chlorophyll traps sunlight to be used for a reaction knows as Photosynthesis.

Photosynthesis is the process by which plants make their own food. Plants take in Carbon Dioxide from the
air and water from the soil, using light they convert them into glucose and oxygen.

Plant Cell vacuole:

 Plant Cell vacuoles are large, central permanent vacuoles that contain a fluid known as cell sap.
 The cell sap contains dissolved food and nutrients suspended in it.
 The plant cell vacuole has Its own membrane known as Tonoplast. The tonoplast plays a vital role
in helping cells hold its turgid shape.

Eukaryotic VS Prokaryotic Cells:

Prokaryotic Cells
- Prokaryotic Cells are considered to be the earliest amongst living cells.
- Prokaryotic cells are made up of cells from the groups of Bacteria and Archaea.
- Basically, Prokaryotic cells do not have membrane bound organelles. Even the nucleus is not
membrane bound and it is found free floating in the cytoplasm.
- Organisms that are prokaryotes are found to be unicellular(single-cell)

Figure: Example of a Prokaryotic Cell

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Eukaryotic Vs. Prokaryotic Cells:

Eukaryotic Cells Prokaryotic Cells

 Has membrane bound organelles  Has no membrane bound organelles
 Has a Nucleus  Has no Nucleus. DNA found free
 Reactions take place in cytosol as floating and as plastids.
well as inside organelles  All Reactions take place in the
 Does not have Flagella cytoplasm
 Some has cell wall made up of  Some Prokaryotic Cells have a flagella
cellulose  Some has cell wall made up of
 Divide by cell replication phospholipids
 Divides, reproduces by binary fission

Plasmid DNA:
- A plasmid is a small, circular piece of DNA that is different than the chromosomal DNA.
- It replicates independently of chromosomal DNA
- Plasmids are mainly found in bacteria, but they can also be found in archaea and multicellular
organisms.
- They have separate genes from the host cell (cells in which they are found) but cannot live on their
own
- They contain genes that enhance the survival of an organism
*Very important tool in Biotechnology and Recombinant DNA technology

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