Biology Chapter: Cell and Organization Levels

Protoplasm is the substance filling the cell, with water being the most abundant component (60%).
Water distribution: 40% intracellular fluid (ICF), 20% extracellular fluid (ECF), composed of 5% plasma and 15% interstitial fluids.

The cell membrane is the outer layer, characterized by:
- A bilayer of lipids, amphipathic nature with hydrophilic heads and hydrophobic tails.
- Semi-permeability allowing gas passage, specifically oxygen and carbon dioxide.
Cytoplasm acts as the inner environment, housing organelles and separating the nucleus from the membrane.

The nucleus serves as the control center of the cell, containing DNA and surrounded by a nuclear envelope for protection.
The nucleolus is integral for ribosome production.

Mitochondria are known as the powerhouse, generating ATP for energy.
Endoplasmic reticulum is crucial for protein and lipid synthesis:
- Rough ER creates protein vesicles.
- Smooth ER focuses on lipid synthesis and detoxification.
Golgi apparatus modifies and packages proteins from the rough ER.
Lysosomes contain hydrolase enzymes for digesting unwanted substances and damaged cells, instrumental in macrophages and neutrophils.

The cytoskeleton provides structural support.
Cilia facilitate movement over the cell surface, while flagella enable sperm mobility (longer than cilia).
Spindle fibers assist in chromosome separation during cell division, with centrioles being key to microtubule formation.

Mitosis results in two daughter cells with the same chromosome number, essential for growth and tissue repair; somatic cells are diploid.
Meiosis creates four gametes, each with half the chromosome count; vital for sexual reproduction and results in haploid cells.

Exocytosis expels cellular contents; endocytosis ingests materials, including subtypes:
- Phagocytosis for large solid particles (cell eating).
- Pinocytosis for small liquids (cell drinking).
Diffusion (passive transport) allows molecules to move from higher to lower concentration:
- Simple diffusion occurs spontaneously, while facilitated diffusion involves carrier proteins.
Osmosis entails water movement from higher to lower solute concentration.

Active diffusion moves substances against their concentration gradient, requiring energy:
- Primary active transport utilizes ATP directly.
- Secondary active transport derives energy from primary transport.

Dendrites transmit action potentials towards the cell body, while axons relay them away.
The myelin sheath insulates electrical signals, with nodes of Ranvier enhancing conduction speed.
The axon hillock triggers generation of electrical signals.