notes for class 9

Overview of Cells

The cell is the basic structural and functional unit of life. The cell was discovered by Robert Hooke.Tissues and organs can be created by a combination of cells.

Cellular Respiration

The mechanism through which the meal releases energy in the mitochondria is known as cellular respiration. Glucose is absorbed by cells from meals and burned by cells to provide energy.

Cell Structure and Organization

Eukaryotic cells and prokaryotic cells

Prokaryotic and eukaryotic cells are the two types of cells. Prokaryotic cells lack a distinct nucleus and are primitive in nature. The nucleus of eukaryotic cells is well defined and they are more evolved

The composition of eukaryotic cells

The structure of eukaryotic cells is the most distinct. These cells feature a well-defined nucleus, a cell membrane, and organelles that are bound to the cell membrane. Nuclear membrane refers to the membrane that surrounds the nucleus.

Cell Membrane

The outside of a cell is called the cell membrane.

It is a membrane with phospholipid bilayers.

Its nature makes it selectively permeable.

The fluid mosaic model provides the most accurate description of a cell membrane’s structure.


Molecules diffuse when they migrate from an area of high concentration to one of low concentration.Diffusion is utilised, for instance, to move oxygen and carbon dioxide through cell membranes.

Osmosis in a membrane with a certain permeability

Water moves through a semipermeable membrane using osmosis. Osmosis is a selective process since not all molecules can pass through the membrane. Typically, the only free-flowing molecule through this membrane is water.

Solutions that are isotonic, hypotonic, or hypertonic.

  • Isotonic solutions are ones that contain the same solute and pH level as the cytoplasm or surrounding bodily fluid.
  • When a cell receives an excessive amount of water, hypotonic solutions, which have lower solute concentrations than the surrounding fluid, might cause the cell to burst.
  • Hypertonic solutions shrink cells by forcing water out of the cell because they have a higher concentration of solute than the surrounding fluid.and reduce the size of the cell by forcing water out.

Plant cells have walls.

The presence of a cell wall distinguishes plant cells from animal cells. The cellulose cell wall gives the plant cell its hard structure. It gives plants structural support. Animal cells are less adaptable to environmental changes than plant, fungal, and bacterial cells because they lack cell walls. For instance, a cell’s cell wall allows it to resist a hypotonic solution without bursting.

Organelles of a cell

A variety of membrane-bound organelles, such as the nucleus, endoplasmic reticulum, golgi apparatus, lysosomes, etc., are found in eukaryotic cells, which perform a variety of cellular tasks.


The cell membrane is invaded during endocytosis, and then it is pinched off to form a vesicle that is bound to the membrane. Amoeba frequently exhibits this.


The processing center of the cell is the nucleus. The genetic material for inheritance is contained in a double membrane-bound organelle. Materials can go from the nucleus to the cytoplasm through pores in the nuclear membrane. The nucleus is the cell’s brain because it regulates a variety of processes like cell division, reproduction, inheritance, etc. DNA-containing chromosomes, which make up genetic material, are found in the nucleus. DNA carries information that parents can pass on to their children. The genetic material is located in an area known as the nucleoid in prokaryotes, which lack a clearly defined nucleus.


The genetic material found in the nucleus is called chromosomes. It has linked proteins and DNA. They are found as chromatin strands. The chromatin condenses into a much thicker structure known as a chromosome during the cell’s growth phase. There are 23 pairs of chromosomes in human cells (46).


The genetic material found inside the cell nucleus is a structure called chromatin that resembles a thread. Protein and DNA molecules make up its structure. The genetic material required for an organism’s construction and function is found in its DNA.


The liquid found inside a cell is called cytoplasm. It provides the cell with structure and contains various organelles.


Organelles are structures that aid the cell’s cytoplasm in carrying out a variety of tasks.

In the endoplasmic reticulum

A membrane-bound cell organelle called the endoplasmic reticulum is crucial in the interpretation of the genetic data found in the nucleus.

Rough ER

The ER that include ribosomes are the rough ER. Proteins and nucleic acids make up the ribosome. They are where protein synthesis takes place. The modification and folding of proteins both involve the Rough ER.

Smooth ER

Smooth ERs are not engaged in protein synthesis because they lack ribosomes. However, they participate in lipid metabolism and the detoxification of harmful chemicals.

The Golgi apparatus

The Golgi apparatus is often known as the cell’s post office. They encapsulate and move the proteins throughout the cytoplasm.


Because they contain strong enzymes that can disintegrate a cell, they are sometimes known as suicide bags of the cell. A foreign object is attacked by lysosomes, which also aid in defense.


The powerhouse of a cell is another name for the mitochondria. They use the electron transport chain to produce ATP. They also include mtDNA, which gives them some degree of autonomy. They can produce their own proteins, mitochondria.


Based on the pigment they contain, different cells have different types of plastids. The chloroplast, which contains chlorophyll, is the plastid where photosynthesis takes place. Leucoplast and chromoplast are a couple of the other plastids. Granules of protein, carbohydrates, and oil are kept in leucoplasts. Thylakoids, membranes found in chloroplasts, are embedded in the stroma. Additionally, plasmids have their own ribosomes and DNA.


Large vesicles called vacuoles provide the cell its structural stiffness and can contain either air or water. Plant cells frequently include vacuoles. Animals either have no vacuoles or very few of them.

Comparing animal and plant cells

Animal cells and plant cells differ structurally. Animal cells lack chloroplasts and cell walls, which are present in plant cells. Animal cells either contain very small vacuoles or none at all, whereas plants have huge vacuoles. Animal cells have the nucleus in the middle, while plant cells have it on the outside.

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