Cells Composite Cells Movements Through Membranes Cell Cycle

Composite Cell Describing a “typical” cell is difficult due to the variation in cells. A composite cell shows many of the typical structures of a cell. Cells have most, but not all of these structures. Nucleus, cytoplasm, and cell membrane are easily seen under a microscope.

Organelles Specialized structures within the cytoplasm. Suspended in cytosol Perform specific functions, divide the “work” of the cell. Nucleus – directs all of the cells activities and houses the genetic material.

Cell Membrane Regulates movement of substances and is the site of much biological activity. Extremely thin, but flexible and elastic Folded for increased surface area Selectively permeable – controls what comes in and out of the cell.

Cytoplasm Contains networks of membranes and organelles suspended in a clear liquid called cytosol. Cell activities occur here: nutrients are received, processed and used. The following slides deal with organelles contained in the cytoplasm.

Endoplasmic Reticulum Called “ER” for short Flattened, elongated canals and bubbles called vesicles. Interconnected and communicate with the cell membrane, nuclear envelope, and other organelles Tubular network that transports molecules to other organelles.

Smooth and Rough ER that contains ribosomes is called “rough” ER ER that doesn’t contain ribosomes is called “smooth” ER Ribosomes – site of protein synthesis in the cell. Composed of protein and RNA molecules

Golgi Apparatus Composed of a stack of about 6 flattened, membranous sacs Refines, packages, and delivers proteins synthesized on ribosomes.

Mitochondria Can move slowly through cytoplasm and reproduce by dividing. Inner layer contains folds called “cristae” Major site of chemical reactions that transform energy into ATP = gives the cell energy.

Lysosomes “garbage” disposals of the cell Contain powerful enzymes that break down nutrient molecules or foreign particles Help body fight disease w/white blood cells Also destroy worn cellular parts

Homeostasis And Transport

Passive Transport Substances can cross through the plasma membrane without using energy from the cell.

Types of Passive Transport Diffusion- movement of molecules from an area of higher concentration to an area of lower concentration. –Difference in concentrations of molecules across a space is called a concentration gradient.

Osmosis The process by which water molecules diffuse across the plasma membrane from an area of higher concentration to an area of lower concentration.

Facilitated Diffusion

Homeostasis Maintaining stable internal conditions in a changing environment. –Example: The cell membrane allows some substances in while keeping other substances out.