Biology Cells Overview

Cells serve as the fundamental building blocks of all living organisms.
Contain protoplasm, consisting of the cell surface membrane, cytoplasm, and nucleus.

Cell Surface Membrane:
- Selectively permeable, regulates substance movement in/out.
- Acts as receptor sites for external stimuli.
- Composed of proteins and phospholipids; defines cell boundary.
Cytoplasm:
- Aqueous medium housing various organelles.
Nucleus:
- Houses hereditary material (DNA) organized as chromatin and chromosomes.
- Surrounded by a nuclear membrane with pores for selective transport.
- Controls cell activities including growth and division.
Cell Wall (Plant Cells Only):
- Rigid structure made of cellulose; provides support and protection.
- Can undergo lignification and is fully permeable.

Rough Endoplasmic Reticulum (RER):
- Studded with ribosomes; specializes in protein synthesis and transport.
Smooth Endoplasmic Reticulum (SER):
- Lacks ribosomes; involved in lipid and hormone synthesis, detoxification.
Golgi Apparatus/Body:
- Stack of membrane-bound sacs; modifies, stores, and packages proteins for secretion.
Ribosomes:
- Composed of ribosomal RNA; synthesizes proteins either as secretory or intra-cellular.
Mitochondria:
- Double-membrane organelle; produces ATP, essential for energy metabolism.
- Abundant in energy-demanding cells; can contain thousands in highly active cells.
Chloroplasts (Plant Cells Only):
- Double-membrane organelle containing thylakoids with chlorophyll for photosynthesis.
- Converts sunlight into glucose and stores starch.
Vacuoles:
- Fluid-filled organelles; provide structural support to plant cells and store waste and nutrients.

Differentiation:
- Process where cells develop specialized structures for specific functions.
Tissues:
- Composed of similar cells; Simple tissues consist of the same cell type (e.g., muscular tissue).
- Complex tissues, like blood, include multiple cell types.
Organs:
- Consist of various tissues that work collaboratively for specific functions (e.g., stomach integrates gland, muscle, and nerve tissues).