Cell Membrane (Plasma Membrane):

Structure: A flexible phospholipid bilayer with embedded proteins (often described by the fluid mosaic model). It's selectively permeable, meaning it controls what enters and leaves the cell.
Function: Regulates the passage of substances; maintains the cell's integrity; involved in cell communication.

Cytoplasm:

Structure: The jelly-like substance filling the cell, consisting of the cytosol (the fluid portion) and the organelles suspended within it.
Function: It's the site of many metabolic reactions and provides support for the organelles.

Nucleus:

Structure: A large, usually spherical organelle enclosed by a double membrane called the nuclear envelope, which has nuclear pores. It contains chromatin (DNA combined with proteins) and a denser region called the nucleolus.
Function: The control center of the cell; it controls cell activities by regulating gene expression and stores the genetic material (DNA). The nucleolus is where ribosomes are synthesized.

Mitochondria:

Structure: Often bean-shaped, with a double membrane. The inner membrane is folded into structures called cristae, increasing its surface area. They contain their own DNA and ribosomes.
Function: The "powerhouse of the cell"; they are the primary site of cellular respiration, where glucose is broken down to produce ATP (adenosine triphosphate), the main energy currency of the cell.

Ribosomes:

Structure: Small, granular structures made of ribosomal RNA (rRNA) and protein. They can be found freely in the cytoplasm or attached to the Endoplasmic Reticulum.
Function: The site of protein synthesis (translation), where genetic information from mRNA is used to build proteins.

Endoplasmic Reticulum (ER):

A network of interconnected membranes forming sacs and tubules.
- Rough ER (RER): Covered with ribosomes, giving it a "rough" appearance.
- Function: Involved in the synthesis, folding, modification, and transport of proteins destined for secretion or insertion into membranes.
- Smooth ER (SER): Lacks ribosomes, giving it a "smooth" appearance.
- Function: Involved in the synthesis of lipids (like steroids and phospholipids), detoxification of drugs and poisons, and storage of calcium ions.

Golgi Apparatus (Golgi Complex/Body):

Structure: A stack of flattened, membrane-bound sacs called cisternae.
Function: Receives proteins and lipids from the ER, modifies them, sorts them, and packages them into vesicles for secretion out of the cell or delivery to other organelles. It's often called the cell's "post office."

Lysosomes (primarily in animal cells, rare in plant cells):

Structure: Small, spherical, membrane-bound sacs that contain powerful hydrolytic (digestive) enzymes.
Function: Break down waste materials, cellular debris, worn-out organelles, and foreign invaders (like bacteria). They are also involved in programmed cell death (apoptosis).

Vacuoles (small and temporary in animal cells):

Structure: Membrane-bound sacs.
Function: Primarily for storage of water, nutrients, and waste products. In animal cells, they are typically small and involved in temporary storage or transport.

Plant-Specific Organelles:

• Cell Wall:
• Structure: A rigid outer layer found outside the cell membrane, primarily composed of cellulose in plants. It is fully permeable.
• Function: Provides structural support, protection, and maintains the cell's fixed shape. It also prevents excessive water uptake.
• Chloroplasts:
• Structure: Double-membraned organelles that contain stacks of flattened sacs called thylakoids (stacked into grana) surrounded by a fluid-filled space called the stroma. They also contain their own DNA and ribosomes.
• Function: The site of photosynthesis, the process where light energy is converted into chemical energy (sugars). They contain the green pigment chlorophyll.
• Central Vacuole:
• Structure: A single, very large, membrane-bound sac that can occupy up to 80-90% of the plant cell's volume.
• Function: Stores water, nutrients, pigments, and waste products. Crucially, it maintains turgor pressure against the cell wall, which is essential for supporting the plant and preventing wilting.