Cellular Transport Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. The diffusion of water across a selectively permeable membrane is called osmosis. The structure most responsible for maintaining cell homeostasis is the plasma membrane. If a cell is placed in salt water, water leaves the cell by osmosis.

Hypotonic In a hypotonic solution, the concentration of dissolved substances is lower in the solution outside the cell than the concentration inside the cell. Water enters(moves) into a cell placed in a hypotonic solution.

Hypertonic In a hypertonic solution, the concentration of dissolved substances outside the cell is higher than the concentration inside the cell. Water moves out of a cell if the cell is placed in a hypertonic solution. If cells are placed in a strong sugar solution, water will pass from the cells to the sugar solution. If it is not watered, a tulip plant wilts because it loses turgor pressure. Plasmolysis—loss of water from a cell resulting in a drop of turgor pressure.

Passive Transport 3 Types Facilitated diffusion Diffusion Osmosis Compare and contrast the structure and function of channel proteins and carrier proteins.

Active Transport A cell can move particles from a region of lesser(lower) concentration to a region of greater(higher) concentration. Dynamic equilibrium-continuous movement of particles but no overall change in concentration. Endocytosis Exocytosis

Cell Growth and Reproduction Figure 8.9 KNOW As a cell’s size increases, its volume increases much faster than its surface area. Dark-stained structures that carry the genetic material are the chromosomes. The cell cycle is the sequence of growth and division of a cell. G1 S stage G2 Mitosis The majority of a cell’s life is spent in the growth period in known as interphase. G1, S Stage, and G2 are all Interphase

Mitosis A cell enters its period of nuclear division called mitosis. Interphase Prophase The two halves of the doubled structure are called sister chromatids Sister chromatids are held together by a structure called a centromere. By the end of prophase The chromosomes have coiled tighter The nuclear envelope has broken down The nucleolus has disappeared Centrioles present—only in animals not plants The spindle is a football-shaped, cagelike structure consisting of thin fibers made of microtubules. Metaphase

Mitosis cont. Anaphase Telophase Cytokinesis Fig 8.15 KNOW The centromeres split and the sister chromatids are pulled apart to opposite poles of the cell. Telophase Cytokinesis Fig 8.15 KNOW

Control of the Cell Cycle A series of enzymes monitors a cell’s progress from phase to phase during the cell cycle. Cancer-uncontrolled cell division A gene is a segment of DNA that controls the production of a protein. When people move from one country to another, cancer rates appear to follow the pattern of the country in which they are currently living, not their county of origin. Causes of cancer: Environmental Influences UV Radiation Viruses