Characteristics of Living Things & Cell Theory

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

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.)