Biology Basics: Characteristics of Life

The study of living organisms.
Life is defined by scientists as a "self-sustaining chemical system," according to NASA.

Living organisms are classified into three domains:
- Archaea: single-celled organisms that thrive in extreme environments.
- Bacteria: single-celled organisms that are diverse and abundant.
- Eukarya: organisms whose cells have a nucleus.
Within the Eukarya domain, there are five kingdoms:
- Animalia: multicellular organisms that obtain food by eating other organisms.
- Plantae: multicellular organisms that make their own food through photosynthesis.
- Fungi: organisms that absorb nutrients from their surroundings.
- Protista: mostly single-celled organisms that are diverse and often difficult to classify.
- Monera: single-celled organisms that lack a nucleus (prokaryotes).

The basic unit of life.
Every cell originates from another cell (Omnis cellula a cellula).
Cells contain a membrane, cytoplasm, and genetic material.
Two types of cells exist:
- Prokaryotic: Lack a nucleus (example: bacteria).
- Eukaryotic: Have a nucleus (example: plants, animals).
Animal and plant cells share some characteristics:
- Both have a nucleus, membrane, and mitochondria.
Plant cells have additional features:
- Cell wall: Provides structural support.
- Chloroplasts: Perform photosynthesis.
- Large vacuole: Stores water and other molecules.
Unicellular organisms, like bacteria and amoeba, consist of one cell.
Multicellular organisms, like humans and plants, are made up of many cells.
Nutrition in organisms:
- Autotrophic: Produce their own food through photosynthesis (e.g., plants).
- Heterotrophic: Obtain food by ingesting other organisms (e.g., animals).

Nucleus: Contains DNA, the genetic material of the cell.
Mitochondria: Sites of energy (ATP) production.
Ribosomes: Involved in protein synthesis.
Chloroplasts: Found in plant cells and carry out photosynthesis.
Cell Membrane: Regulates the entry and exit of substances from the cell.
Specialized Cells: Different cells perform different functions (division of labor) such as muscle cells and red blood cells.

Last Universal Common Ancestor: The earliest known organism from which all living organisms on Earth are descended.

Organisms are categorized into Domains and Kingdoms:
- Domains: Archaea, Bacteria, Eukarya.
- Kingdoms: Animalia, Plantae, Fungi, Protista, Monera.
Organisms are classified based on visible and non-visible characteristics.
Taxonomists ask questions to classify organisms, such as:
- Does it have a nucleus?
- Can it reproduce?

Cells are the basic unit of life.
Cell Theory:
- All living organisms are made of cells.
- All cells come from pre-existing cells (Omnis cellula a cellula).

All cells share basic characteristics:
- Cell membrane: A boundary that controls what enters and exits the cell.
- Cytoplasm: The gel-like substance within the cell.
- Genetic material: DNA (in the nucleus for eukaryotic cells).

There are two major types of cells:
- Prokaryotic: Lack a nucleus (e.g., bacteria).
- Eukaryotic: Have a nucleus (e.g., plants, animals).

Both animal and plant cells have:
- A nucleus.
- A cell membrane.
- Mitochondria (energy production).
Plant cells have additional structures:
- A cell wall for support.
- Chloroplasts for photosynthesis.
- A large vacuole for storage.

Organisms obtain nutrients in different ways:
- Autotrophic: Make their own food through photosynthesis (e.g., plants).
- Heterotrophic: Obtain food by ingesting other organisms (e.g., animals).