Biology 101 Medgar Evers College Fall 2017 Movement across the cell membrane, Photosynthesis, and Cell Division Biology 101 Medgar Evers College Fall 2017

Overview: Life at the Edge The plasma membrane is the boundary that separates the living cell from its surroundings. The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Fluid Mosaic Model Singer and Nicholson: Phospholipid bilayer Figure 7.3 The fluid mosaic model for membranes Hydrophobic regions of protein Hydrophilic regions of protein

Passive Transport The movement of material from high concentration to low concentration Osmosis is the diffusion of water across a selectively permeable membrane. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Water Balance of Cells Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane. Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water. Cell shrinks. Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Osmosis: Three Types of Solutions Hypotonic solution Isotonic solution Hypertonic solution H2O H2O H2O H2O (a) Animal cell Normal Shriveled Lysed H2O H2O H2O H2O Figure 7.13 The water balance of living cells (b) Plant cell Turgid (normal) Flaccid Plasmolyzed

Facilitated Diffusion: Passive Transport Aided by Proteins In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane. Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane. Channel proteins include Aquaporins, for facilitated diffusion of water Ion channels that open or close in response to a stimulus (gated channels). For the Cell Biology Video Water Movement through an Aquaporin, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Solute Channel protein Carrier protein Carrier proteins undergo a subtle change in shape that translocates the solute-binding site across the membrane EXTRACELLULAR FLUID Solute Channel protein CYTOPLASM A channel protein Figure 7.15 Two types of transport proteins that carry out facilitated diffusion Solute Carrier protein A carrier protein: shape change

Active transport uses cell energy to move solutes against their gradients The movement of material from low concentration to high concentration Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Need for Energy in Active Transport Active transport moves substances against their concentration gradient / uphill. Active transport requires energy, usually in the form of ATP Active transport is performed by specific membrane carrier proteins that use ATP energy to change shape, thereby pumping the solute across the membrane. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Review: Passive transport Active transport Diffusion ATP Diffusion Facilitated diffusion Figure 7.17 Review: passive and active transport

Photosynthesis Organisms like plants and algae are known as producers! They undergo photosynthesis to make sugars, release oxygen and water! Photosynthesis occurs in specialized organelles called chloroplast. Two reactions; light reaction and dark reaction

Chloroplast

Reactions of photosynthesis Light reaction occurs in the grana Dark reaction occurs in the stroma In the light reaction, water is split into oxygen, and hydrogens, and some ATP is made. In the dark reaction, the hydrogens are combined with carbon dioxide to form sugars such as glucose. Plants store excess sugars in the form of starch

Mitosis Cell division in plant and animal cells that results in two new cells. Organisms must undergo cell division in order to grow, regenerate damage cells and replicate. Mitosis results in two genetically identical cells! Mitosis produces cells with the full set of chromosomes known as diploid cells. Mitosis takes place all over the body.

Cell cycle

Stages of Mitosis Prophase Metaphase Anaphase Telophase

Meiosis A special form of cell division that takes place in the gonads resulting in cells that have half the number of chromosomes. These are haploid cells.

Differences between Meiosis and Mitosis

Differences between mitosis and meiosis # of divisions # of daughter cells Types of cells produced Location where it occurs Genetic variation Y/N