Cellular Organization

Cells, Tissues, Organs, & Organ Systems of Animals Some animals are single-celled (unicellular) Some are made of many cells (multicellular) Everything that an animal does is ultimately happening at the cellular level.

A. Cells – the smallest functional unit of life 1. Eukaryote – organism with a nucleus, membrane-bound organelles, and more than one chromosome. Ex. – anything BUT bacteria Eukaryotic cells have an evolutionary advantage because their different organelles permit them to become specialized for particular functions! 2. Prokaryote – independent, unicellular organism with NO nucleus, NO membrane-bound organelles, and circular-stranded DNA. Ex. – bacteria

3. Origin of Eukaryotes The Endosymbiont Hypothesis: i. the first cells on Earth were most likely very simple prokaryotes. ii. The eukaryotic cell might have evolved when a large ANAEROBIC prokaryote ingested smaller bacteria and stabilized them instead of digesting them. This AEROBIC bacteria developed into mitochondria. Flagella may have arisen through the ingestion of spiral-shaped bacteria called spirochetes. Chloroplasts most likely evolved from the ingestion of prokaryotes that resembled present-day photosynthetic cyanobacteria. Your mitochondria still shows signs of its origin: First, it produces ATP (all living things need energy) Second, they have their own membrane (this means that they must have entered the cell through endocytosis) Lastly, they have their own DNA! Video

Why are most cells so small? As the radius of a cell increases, the volume of the cell increases faster than the surface area. If the volume becomes too large, the intake of nutrients and output of wastes can’t keep up. Video The yolk of an ostrich egg is the largest cell in existence today!

What happens when a cell starts to get too big? IT DIVIDES!!! This is called mitosis. First, the genetic material (DNA) replicates. Second, the organelles duplicate. Finally, the cell membranes and cell walls separate and form two new cells. This is how your body grows, and heals from injury.

II. Cell Membranes A. Structure: Fluid-Mosaic Model – portrays the cell membrane as a thick liquid or gel in which specific proteins float like ice burgs. 1. Phospholipid Bilayer – has one polar end and one nonpolar end. The nonpolar, hydrophobic, tails of each molecule face each other to form the “filling of the sandwich”. The polar, hydrophilic, heads form the “bread”. The heads are phosphate, the tails are lipid. Hence, phospholipid bilayer.

Structure Continued 2. Cholesterol molecules embedded in the bilayer give it more of a rigid structure. 3. Carbohydrates attach to the bilayer itself, forming glycolipids, or to the floating proteins, forming glycoproteins. The combination of glycolipids and glycoproteins is called the glycocalyx. Every cell has its own unique glycocalyx, thus it is termed the cell’s “fingerprint”. This fingerprint allows for coordinating cell behavior and communication between cells.

B. Functions 1. Regulates material moving in or out of the cell. i. selective permeability – lets some things in but keeps others out; essential for maintaining homeostasis. It exchanges gases, absorbs nutrients needed by the cell, and removes wastes!

Functions Continued 2. Provides surface area for chemical reactions to occur. 3. Serve as receptor sites (glycocalyx).

Movement of H2O Across the Cell Membrane - Osmosis Osmosis – movement of water, from a high concentration to a low concentration; requires no energy input 1. isotonic – the solute (salt, sugar, etc) concentration is the same both inside and outside the cell. 2. hypertonic (more H2O) – higher concentration of water inside the cell, so it moves to a lower concentration OUT of the cell 3. hypotonic (less H2O) – low concentration of water inside the cell, so water moves INTO the cell to even it out.

III. Movement Across Membranes A. Simple Diffusion – molecules randomly move from areas of high concentration to low concentration. Requires no energy input. B. Facilitated Diffusion – a molecule diffuses through a protein channel. Still moving from a high to low concentration gradient requiring no energy input.

Movement Across Membranes Cont’d C. Active Transport – moves molecules AGAINST the concentration gradient for LOW to HIGH; requires ATP (energy). In this type of diffusion, the membrane protein actually changes shape to allow the substance into the cell!

Movement Across Membranes Cont’d F. Endocytosis – involves the movement of large or multiple substances into the cell. 1. pinocytosis – the intake of fluid, “cell drinking”; arms of the cell surround the liquid and pull it in. 2. phagocytosis – the intake of solids, “cell eating”; arms of the cell surround the material and bring it in. 3. receptor-mediated endocytosis – involves a specific receptor protein on the cell membrane (glycocalyx) that recognizes the molecule and binds with it, allowing it access into the cell. Then, the arms of the cell surround the material and bring it in.

Receptor-Mediated Endocytosis Cont’d Remember, this is the way your body identifies invaders. The proteins on the surface of the cell membrane (glycocalyx) are a certain shape. If this shape doesn’t fit with the shape of the incoming substance, it won’t let it in!

Movement Across Membranes Cont’d Exocytosis – the movement of materials out of the cell

What is a virus? Are they alive? A virus is a small piece of genetic material that infects a host and causes it harm. It is NOT made of cells. It does NOT use energy. It can reproduce, but ONLY if it is inside a host. For this reason, some scientists argue that viruses are alive.

I. Levels of Specialization Cells Tissues Organs Organ Systems Organism

B. Tissues A group of similar cells specialized for the performance of a common function. 1. Epithelial - skin 2. Connective and Blood 3. Muscle 4. Nervous – transmits nerve impulses to and from the brain

C. Organs Several different types of tissue working together to perform a common function. Ex. – heart, lungs, liver, kidneys, brain, skin

D. Organ System A group of organs working together to perform a specific function Skeletal System – provides protection for internal organs; serves as an attachment site for muscles, tendons, and ligaments. Circulatory System – brings oxygen to all cells of the body and delivers waste to the kidneys. Integumentary System - provides protection against water and heat loss; acts as a barrier between the body and the outside world. Excretory System – gets rid of excess water, waste, and toxins accumulated in the body. Endocrine System – regulates the production of hormones in the body. Digestive System – breaks down food and delivers nutrients to the bloodstream.

E. Organism All the organ systems working together to maintain a complete living thing.

How do I know if something is alive? It must have ALL of the following characteristics: Made of cells Have genetic material (DNA or RNA) Reproduce Maintain Homeostasis Respond to stimulus Use energy (metabolism)