#biology #cells #animalcells #igcse

Pg:- 48,49,50

Ch:- 3

An animal cell is the basic building block of animal life. All living organisms, including animals, are made up of cells, and each cell is like a tiny, organized factory where various activities happen to keep the organism alive and functioning. Animal cells belong to a category called eukaryotic cells, which means they have a defined nucleus and other specialized structures called organelles.

Parts of cell:

Cell Membrane

The cell membrane is a thin, flexible layer that surrounds the cell. Its primary role is to protect the cell’s internal components and regulate what enters and exits the cell. Think of it as the cell's "security gate."

• It’s selectively permeable, meaning only specific molecules can pass through it.

• It controls the movement of nutrients, water, oxygen, and waste products in and out of the cell.

Cytoplasm

The cytoplasm is a jelly-like substance that fills the cell and holds all the organelles in place. It’s composed mainly of water, salts, and proteins, and it helps transport materials within the cell.

• Cytoplasm provides a medium for chemical reactions to occur.

• It helps in the movement of organelles within the cell, providing some "cushioning" as well.

Nucleus

The nucleus is often considered the "control center" of the cell because it contains the cell's genetic material (DNA). DNA holds instructions that tell the cell how to build proteins and carry out other critical functions.

• The nucleus is enclosed by a double membrane called the nuclear envelope.

• Inside the nucleus, there’s a structure called the nucleolus, which produces ribosomes (explained below).

Mitochondria

The mitochondria are known as the “powerhouses” of the cell. They are responsible for producing energy in the form of a molecule called ATP (adenosine triphosphate) through a process called cellular respiration.

• Mitochondria break down glucose (sugar) and oxygen to release energy.

• They have their own DNA and can even replicate within the cell.

Ribosomes

Ribosomes are tiny, round structures that make proteins, which are essential for almost all cell functions. They can either float freely in the cytoplasm or attach to another organelle called the endoplasmic reticulum.

Endoplasmic Reticulum (ER)

The endoplasmic reticulum (ER) is a network of membrane-bound tubes and sacs that transport materials within the cell. There are two types of ER:

• Rough ER: Has ribosomes attached to it, giving it a “rough” appearance. It’s involved in protein production and transport.

• Smooth ER: Does not have ribosomes and is involved in producing lipids (fats) and detoxifying chemicals.

Golgi Apparatus

The Golgi apparatus (or Golgi body) is like the cell’s packaging and distribution center. It processes and packages proteins and lipids produced by the ER and sends them to their destinations within or outside the cell.

Lysosomes

Lysosomes contain enzymes that digest food particles, old cell parts, and other materials that the cell doesn’t need. They act like the cell's "recycling centers," breaking down waste and other cellular debris.

• Lysosomes are especially important for keeping the cell clean and removing harmful substances.

Vacuoles

In animal cells, vacuoles are small sacs that store water, nutrients, or waste products. Animal cells typically have smaller, temporary vacuoles compared to plant cells.

Cytoskeleton

The cytoskeleton is a network of protein fibers that gives the cell its shape and helps it maintain its structure. It also assists in cell movement and the transport of materials within the cell.

Functions:

• Energy production (mitochondria).

• Protein synthesis (ribosomes, rough ER, and Golgi apparatus).

• Transport of materials within the cell (ER and cytoplasm).

• Waste breakdown and recycling (lysosomes).

• Storage of materials (vacuoles).

• Protection and selective permeability (cell membrane).

Difference between animal and plant cells:

• Cell Wall: Plant cells have a rigid cell wall outside their cell membrane; animal cells do not.

• Chloroplasts: Plant cells contain chloroplasts for photosynthesis, allowing them to produce their own food. Animal cells lack chloroplasts because animals get energy from consuming food.

• Large Central Vacuole: Plant cells typically have a large central vacuole for storage and maintaining cell shape, while animal cells have smaller, more temporary vacuoles.