Cell Theory and Characteristics of Life

• The cell theory has 3 tenets.
• All living organisms consist of cells.
• The cell is the basic unit of structure and function in organisms.
• All cells arise from pre-existing cells.
• Cells have diverse shapes and sizes.
• The human body contains over 100 trillion cells.
• Cells are microscopic; 10,000 could fit on a pinhead.
• Cells in the body undergo 500 quadrillion chemical reactions per second.
• Cells are not yet fully understood by science.

Characteristics of Living Things

• Living things grow, reproduce, and require energy.
• The 7 characteristics of living things can be remembered as MR. GREEN.
• M: Movement
• R: Reproduction
• G: Growth
• R: Response
• E: Excretion (waste removal)
• E: Exchange of gases (e.g., breathing)
• N: Nutrition

Cell Types: Prokaryotes vs. Eukaryotes

• Prokaryotes: Unicellular organisms (e.g., bacteria, Euglena, paramecium).
• Eukaryotes: Multicellular organisms (e.g., humans, animals, plants).
• Eukaryotes are larger than prokaryotes; Eukaryotes are 10-100 micrometers, while prokaryotes are 0.1-10 micrometers.

Prokaryotic Movement

• Flagella: Whip-like tails propel the organism forward.
• Cilia: Eyelash-like structures move the organism.
• Pseudopods: "False feet" propel the organism.

Prokaryotes

• Lack a nucleus.
• Act as decomposers.
• The term "prokaryote" means "before nucleus."
• Bacteria are prokaryotes that can cause mass killings.
• Bacteria are used in cheese and yogurt production.
• They aid in food digestion in the stomach.

Eukaryotes

• Possess a nucleus.
• The term "eukaryote" means "true nucleus."
• They are complex cells with a nucleus and organelles.
• Animal, plant, and human cells are eukaryotes.

Cell Membrane

• Controls material flow in and out of the cell.
• Permeable membranes allow all particles to pass through (e.g., coffee filter, sand).
• Impermeable membranes do not allow anything to pass through (e.g., metal, rubber).
• Selectively permeable membranes allow certain substances to pass through (e.g., fabric, T-shirt, water filter).

Diffusion

• Movement from an area of high concentration to low concentration.
• Applies to solids, liquids, or gases.
• Example: Cake smell spreading in a room.

Osmosis

• Diffusion of water or liquids.
• Water molecules move to achieve equilibrium inside and outside the cell.

Unicellular Organisms

• Obtain nutrients by consuming other organisms.
• Exchange gases via diffusion across the cell membrane.
• Oxygen diffuses into the cell, and carbon dioxide diffuses out.
• They sense their surroundings, with bacteria detecting chemicals and photosynthetic protists detecting light.

Multicellular Organisms

• Plants make their own food through photosynthesis.
• Animals and humans consume living things or their products.
• Food is broken down into nutrients for cellular energy.
• Small organisms use diffusion for oxygen.
• Land animals use lungs for gas exchange.
• Oxygen is absorbed, and carbon dioxide is removed.
• They react to the environment using senses.
• Muscles and bones enable movement.

Cell Parts

• Cell Wall: Provides support and protection (plant cells only).
• Cell Membrane: Protects the cell and controls nutrient and waste movement.
• Nucleus: Controls the cell, stores DNA, and directs cell activity.
• Mitochondria: Produces energy for the cell (powerhouse).
• Chloroplast: Site of photosynthesis (plants only), contains chlorophyll.
• Vacuole: Stores food and water, larger in plant cells.
• Cytoplasm: Gel-like material that holds organelles in place.
• Endoplasmic Reticulum: Includes smooth ER (no ribosomes) and rough ER (with ribosomes).
• Ribosomes: Synthesize proteins.
• Golgi Body: Transports lipids and proteins.

Amoeba

• From the Greek word for "change" due to its changing shape.
• It is a eukaryote with a soft membrane and cytoplasm.
• Found in water-based environments, wet soil, and sometimes in humans.
• Most species are harmless, but some can cause disease.
• Has two vacuoles: one for food and water storage, one for water expulsion.
• Can be omnivorous, carnivorous, or herbivorous.
• It is a predator, preying on algae and bacteria.
• Moves using pseudopods ("fake feet").
• Zacharias Jansen invented the first compound microscope.
• Anton van Leeuwenhoek discovered bacteria, calling them "animalcules".
• Robert Hooke coined the term "cells" after observing cork compartments.
• Matthias Schleiden concluded that all plants are made of cells.
• Theodor Schwann concluded that all animals are made of cells.
• Matthias Schleiden and Theodor Schwann were the first two scientists to contribute to the cell theory.
• Rudolph Virchow confirmed that cells reproduce by division.

The cell theory states all living things are made of cells. Living things grow, reproduce, and need energy. Prokaryotic and eukaryotic cells differ in structure and size, with eukaryotes being larger.