Characteristics of Living Things & Cell Theory

Study Notes

Characteristics of Living Things

Living things exhibit movement in some form.
Respiration is a cellular chemical reaction using nutrients to produce energy. The word equation is: Glucose + Oxygen → Carbon Dioxide + Water + Energy
Living things detect and respond to environmental changes (sensitivity).
Growth involves an increase in size, even for single-celled organisms.
Reproduction is the ability to create offspring, genetically identical (asexual) or with combined parental genetic information (sexual).
Excretion is the removal of waste products different from digested material (e.g., CO2).
Living things take in and utilize nutrients for energy, growth, and development.
Plants perform photosynthesis—a chemical reaction—to create glucose using energy from the sun. The word equation is: Solar Energy + Carbon Dioxide + Water → Glucose + Oxygen

Cell Theory

All living things are composed of one or more cells and their products.
The cell is the basic unit of life—it can carry out life processes.
All cells come from pre-existing cells.

Prokaryotes

Prokaryotes are a type of organism.
They are very simple and small single-celled organisms.
They lack a nucleus and membrane-bound organelles. They do have cell membranes, ribosomes, and cytoplasm.
Examples include bacteria and archaea.

Eukaryotes

Eukaryotic cells are more complex.
They have membrane-bound organelles with specialized functions.
They can be single-celled (protists) or multicellular (fungi, plants, animals).
Eukaryotic cells are larger than prokaryotic cells due to their complexity.

Differences Between Plant and Animal Cells

Feature	Plant Cell	Animal Cell
Vacuoles	One large central vacuole	Many small vacuoles
Cell Wall	Present (rigid, provides structure)	Absent (flexible, irregular shape)
Chloroplasts	Present (photosynthesis)	Absent
Lysosomes	Usually absent or very few	Present (breaks down waste)
Centrioles	Absent	Present (involved in cell division)

Organelles Found in Both Plant and Animal Cells

Cytoplasm: Jelly-like substance filling the cell, holding organelles, allowing cellular reactions.
Cell Membrane: Double-layered; semi-permeable, allowing specific substances in and out.
Nucleus: Control center; contains DNA/chromatin; has a semi-permeable membrane.
Nucleolus: Site of ribosome production.
Mitochondria: Makes energy (ATP) through cellular respiration.
Endoplasmic Reticulum (ER): Transport system between nuclear and cell membranes; rough ER has ribosomes, involved in protein and lipid synthesis.
Golgi Bodies: Process and transport materials (e.g., waste, mucus, fats).
Ribosomes: Non-membrane bound organelles where proteins are assembled.
Vacuoles: Single-layered membrane holding fluid; stores food, waste, or water; maintains cell pressure.

Organelles Found Only in Plant Cells

Cell Wall: Provides support and protection to the cell.
Chloroplasts: Contains chlorophyll, absorbs light for photosynthesis.

Organelles Found Only in Animal Cells

Centrioles: Involved in cell division; create spindle fibers.
Lysosomes: Contain digestive enzymes; break down materials and waste, and participate in cell self-destruction (apoptosis).

Cell Cycle (Animal Cells)

Interphase: Normal cell activities; includes G1, S (DNA replication), G2 (preparation for mitosis). G0 is a resting phase, not all cells enter mitosis.
Mitosis: Division of the nucleus; includes Prophase, Metaphase, Anaphase, Telophase.
Cytokinesis: Cytoplasm division, creating two separate cells.

Mitosis Phases

Prophase: Nuclear membrane dissolves; chromatin condenses into chromosomes; centrioles move to opposite poles; spindle fibers form.
Metaphase: Chromosomes line up in the middle of the cell; spindle fibers attach to chromosomes.
Anaphase: Sister chromatids separate and move to opposite poles.
Telophase: Nuclear membrane reforms; chromosomes decondense; cell begins to pinch in the middle.

Cell Division (Why?)

Growth: Cells divide to increase the size of an organism. The surface-area-to-volume ratio becomes limiting for large cells; division enables efficient diffusion and osmosis.
Repair: Damaged or old cells are replaced.
Reproduction (asexual): Single-celled organisms reproduce by simple cell division. (Sexual reproduction is not covered in this section.)

Description

Explore the fundamental characteristics that define living beings, including movement, respiration, and reproduction. Understand the basics of cell theory and the crucial role that cells play in the structure of all living organisms. This quiz covers essential biological concepts for your learning and comprehension.