Aswajith

A cell is the smallest living unit of a living thing, able to work, grow, and reproduce on its own.

FUNCTION

• A cell is the smallest living unit that keeps life going.

• It takes in food and oxygen, and turns them into energy to stay alive.

• It builds new molecules, like proteins, to grow and repair itself.

• It removes waste so toxic things don’t build up inside.

• It responds to signals from the outside world so it can protect itself and work with other cells.

• It divides to make new cells, helping the body grow and heal.

STRUCTURE

1) Cell wall - plant

• The cell wall is the hard outer shell around plant cells.

• It is made of cellulose fibers, which are strong like tiny wooden threads.

• It gives the cell shape, strength, and protection so the plant can stand tall.

• It stops the cell from bursting when it fills with water, acting like a strong shield.

• Only plants, fungi, and some bacteria have a cell wall — animals do not because they need soft bodies to move.

2)Chloroplast - plant

• Chloroplast is the green food-making factory inside plant cells.

• It has a green pigment called chlorophyll that catches sunlight like a solar panel.

• It uses sunlight, water, and carbon dioxide to make sugar (glucose) for the plant — this is photosynthesis.

• Inside the chloroplast are stacked discs (grana) where sunlight energy is trapped and turned into chemical energy.

• The sugar made is used by the plant for energy and growth, and animals get this energy when they eat plants.

3 ) Mitochondria

• Mitochondria are the tiny power factories of the cell.

• They take sugar and oxygen and turn them into energy sparks called ATP.

• Inside them are folded inner walls (cristae) that give more space to make energy faster.

• They have their own DNA, which means they can grow and divide on their own inside the cell.

• Cells that need a lot of energy (like muscle and brain cells) have many mitochondria.

4)Nucleus

• The nucleus is the big control center of the cell.

• It holds DNA, the instruction book that tells the cell how to live, grow, and make proteins.

• It is surrounded by a nuclear membrane that keeps the DNA safe inside.

• It sends out messages (mRNA) that tell ribosomes what proteins to make.

• It controls cell division, cell repair, and cell activities like a brain of the cell.

5) Vacuole

• A vacuole is a big water storage bag inside the cell.

• It holds water, nutrients, minerals, and waste to keep the cell balanced.

• In plant cells, the vacuole is very large and keeps the cell swollen and firm, helping the plant stand straight.

• In animal cells, vacuoles are small and many, mainly for storing and moving materia

6)Cytoplasm

• Cytoplasm is the thick jelly liquid inside the cell.

• It is mostly water, but filled with salts, sugars, and proteins that keep the cell working.

• All the tiny parts of the cell (organelles) float and move inside it.

• It is the place where thousands of chemical reactions happen every second to keep the cell alive.

• It helps move things from one part of the cell to another like a busy traffic road.

7 )Endoplasmic Reticulum

• The ER is a big folded tunnel system inside the cell that moves materials from one place to another.

• It is attached to the nucleus, so messages and products travel quickly.

• It works like a factory conveyor belt where things are built and sent to other parts of the cell.

There are two types:

• Rough ER has ribosomes stuck on it, so it makes and folds proteins, then sends them to the Golgi body.

• Smooth ER has no ribosomes, so it makes fats (lipids), stores calcium, and cleans poisons and chemicals from the cell.

8)Cell membrane

• The cell membrane is the soft skin around the cell.

• It is made of two layers of fat molecules (phospholipids) that act like a waterproof wall.

• It has proteins that work as gates, pumps, and sensors.

• It chooses what can enter and what must stay out, keeping the inside safe.

• It lets food, water, and oxygen in, and sends waste out.

• It also helps the cell talk to other cells using chemical signals.

9)Nuclear pore

• The nuclear pore is a tiny doorway on the surface of the nucleus.

• It is made of a protein ring that opens and closes like a gate.

• It controls traffic between the nucleus and the cytoplasm.

• mRNA and ribosome parts go out, proteins and materials needed for DNA go in.

• It protects the DNA by allowing only the correct molecules to pass.

10) Ribosome

• A ribosome is a molecular machine made of RNA and proteins.

• It reads the genetic message from mRNA like reading a recipe.

• It joins amino acids one by one to build a protein chain in the correct order.

• As the chain grows, it folds into a working protein (like enzymes, hormones, muscle fibers).

• Without ribosomes, a cell cannot make any proteins, so life cannot exist.

CELL-DIVISION

1) Mitosis

• Mitosis is when one cell makes an exact copy of itself and splits into two identical cells.

• First, the cell copies its DNA, making two complete sets of chromosomes.

• Then the chromosomes line up, pull apart, and move to opposite sides of the cell.

• The cell finally splits in the middle, giving each new cell one full set of DNA.

• Mitosis is how the body grows, heals wounds, and replaces old or damaged cells.

2)Meiosis

• Meiosis is when one cell divides to make four new cells, each with half the amount of DNA.

• First, the DNA is copied once, but the cell splits twice, so the DNA becomes divided.

• Chromosomes mix and swap pieces — this makes every sperm and every egg genetically different.

• The final four cells are not identical and each has only one set of chromosomes, ready for fertilization.

• Meiosis makes sperm in males and eggs in females, leading to new life.

3) Binary fission

• Binary fission is when a single-celled organism (like bacteria(prokaryotic cells (no nucleus))) makes a copy of its DNA and then splits into two new cells.

• First, the DNA duplicates, so there are two matching copies.

• Then the cell grows longer, pulling the DNA copies to opposite sides.

• Finally, the cell pinches in the middle and becomes two separate cells.

• The two new cells are genetically identical, just like twins.

4) Budding

• Budding is when a small bump (bud) grows on the parent’s body and slowly becomes a new baby organism.

• The parent copies its DNA and sends the copy into the growing bud.

• The bud becomes bigger and develops organs or cell parts like the parent.

• When it is ready, it breaks off and lives on its own, or sometimes stays attached to form a group (colony).

• The new organism is genetically identical to the parent, like a clone.

5) Fragmentation

• Fragmentation is when an organism breaks into pieces, and each piece grows into a whole new organism.

• Every fragment already has cells with the full set of DNA, so it knows how to rebuild the missing body parts.

• It happens in organisms with very simple body structures, like starfish, sponges, planaria, and some worms.

• It is a type of asexual reproduction, so no partner is needed.

• The new organisms are genetically identical to the original one.

ENERGY

• Every cell needs energy to live, grow, move, and repair itself.

• The cell gets energy from food molecules like glucose.

• Inside the cell, the mitochondria break glucose using oxygen and make energy.

• The energy is packed into a tiny chemical called ATP (Adenosine Triphosphate).

• ATP is like a battery — the cell spends it to do work and makes more when needed.

• Without ATP, the cell becomes weak and dies, because nothing can run.

CELL DIFFERENTIATION

• Every baby begins as one simple cell with all the DNA instructions for the whole body.

• That cell keeps dividing and makes many new cells, all with the same DNA.

• But soon some cells read only certain parts of the DNA, not all of it.

• This makes the cells change shape and job — some become brain cells, some muscle cells, some blood cells, etc.

• Once a cell gets its special job, it usually keeps that job forever and stops turning into other types.

• Differentiation builds a whole body with many different cell types working together.