science ppt for class ix cbse

The fundamental unit of life

Made by- Abhishek

Class- 1x

Robert HookeCells were first discovered by Robert Hooke in 1665

Compound Microscope

Unicellular organismsOrganisms having only a single cell are called unicellular organisms.

Multicellular organismsOrganisms having

more than one cell are called multicellular organisms.

Structure of the cellThe cell is made up of Plasma membrane, nucleus, and cytoplasm.

Plasma membrane or cell membraneThis is the outermost covering of the cell that

separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other material. The cell membrane, therefore, is also called a selectively permeable membrane.

Cell wallPlant cells, in addition to the plasma

membrane, have another rigid outer covering called the cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose. Cellulose is complex substance and provides structural strength to plants.

NucleusNucleus is the largest cell structure.

It is a spherical or oval prominent structure, usually located in the centre of the cell. Nucleus has the following important parts- nuclear membrane, nucleoplasm, chromatin material, nucleolus.

Functions of nucleus The nucleus controls all metabolic activities

of the cell.It regulates the cell cycle.It is concentrated with the transmission of

hereditary traits from the parent to off springs.

Prokaryotes Prokaryotic cells are less complex.They are unicellular.Do not have a cell wall surrounding the cell

membrane and a single, looped chromosomes (genetic material) in the cytoplasm.

Include bacteria and blue- green bacteria.Found in the kingdom monera.

Prokaryotic cell

Eukaryotes More complex cells. Includes both unicellular and multicellular organisms. Do have a true nucleus and membrane bound organelles. Organelles are internal structures in cell’s that perform specific

functions. Organelles are surrounded by a single or doubled membrane. Entire eukaryotic cell surrounded by a thin cell membrane that

controls what enters and leaves the cell. Nucleus is located in the centre of the cell. The nucleus contains the genetic material(DNA) and controls the

cell’s activities. Eukaryotes include plant cell, animal cell, fungi, algae, and

protists. Prokaryotes or bacteria lack a nucleus.

Eukaryotic cell

CytoplasmThe protoplasmic mass of the cell inner to plasma membrane and excluding nucleus is called cytoplasm.

Cell organellesThey are sub- cellular structures which have

characteristics form, structure and function where certain processes are localised in eukaryotes. They are the same throughout the living world. Cell organelles continue to survive and perform their functions even outside the cell if they are provided with environment similar to that of cytoplasm. On the basis of membranous covering, cell organelles are of three types- double membrane bound(mitochondria, plastids) single membrane bound( endoplasmic reticulum, Golgi apparatus, lysosomes vacuoles) and membrane less (ribosome).

Endoplasmic reticulum( ER)The endoplasmic reticulum(ER) is a large

network of membrane-bound tubes and sheets. It looks like tubules or round or oblong bags (vesicles). The ER membrane is similar in structure to the plasma membrane. There are two types of ER-rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum(SER).

Golgi apparatusThe Golgi was first described by Camillo

Golgi, consist of a system o 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 potion of a complex cellular membrane system.

Lysosomes Lysosomes are a kind of waste disposal

system of the cell. Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles.

Mitochondria Mitochondria are known as power houses of

the cell. The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP(Adenosine triphopshate) molecules.

Plastids Plastids are present only in plant cells. There

are two types of plastids – chromoplasts( coloured plastids) and leucoplast(white or colourless plastids ). Plastids containing the pigment chlorophyll are known as chloroplasts.

Vacuoles Vacuoles are storage sacs for solid or liquid

contents. Vacuoles are small sized in animal cells white plant cells have very large vacuoles. The central vacuole of some plant cells may occupy 50-90% of the cell volume.

Animal cell

Plant cell