The Working Cell Figures 5.14 – 5.19 CHAPTER 5 The Working Cell Figures 5.14 – 5.19

Water Balance in Plant Cells Water balance in plant cells is different They have rigid cell walls They are at the mercy of the environment Figure 5.14

Active Transport: the Pumping of Molecules Across Membranes Active transport requires energy to move molecules across a membrane Lower solute concentration Solute Higher solute concentration Figure 5.15

Exocytosis and Endocytosis: Traffic of Large Molecules Secretes substances outside of the cell Outside cell Plasma membrane Cytoplasm (a) Exocytosis Figure 5.16a

Endocytosis Takes material into the cell (b) Endocytosis Figure 5.16b

In phagocytosis (“cellular eating”) a cell engulfs a particle and packages it within a food vacuole In pinocytosis (“cellular drinking”) a cell “gulps” droplets of fluid by forming tiny vesicles Pseudopod of amoeba Food being ingested Figure 5.17

Receptor-mediated endocytosis Is triggered by the binding of external molecules to membrane proteins

The Role of Membranes in Cell Signaling LDL particle Phospholipid coat Protein Receptor protein Cholesterol Plasma membrane Cholesterol processed Liver cell Figure 5.18

Cellular communication Begins with the reception of an extracellular signal The signal transduction pathway Consists of proteins and other molecules that relay the signal

Reception Transduction Response Outside cell Inside cell Reception Transduction Response Receptor protein Hydrolysis of glycogen releases glucose for energy Signal transduction pathway Epinephrine (adrenaline) from adrenal glands Plasma membrane Figure 5.19

EVOLUTION CONNECTION: EVOLVING ENZYMES Organisms use many different enzymes Scientists compare enzymes from different organisms Comparisons show similarities between organisms

The processes of natural selection and directed evolution Both result in the production of new enzymes with new functions

SUMMARY OF KEY CONCEPTS ATP and Cellular Work Energy for cellular work Adenosine Adenosine (Phosphate transferred to other molecules) Adenosine triphosphate Adenosine diphosphate Energy from organic fuel Visual Summary 5.1

Higher water concentration (hypotonic) Passive Transport, Osmosis, and Active Transport Requires no energy Requires energy Passive transport Osmosis Active transport Higher solute concentration Higher water concentration (hypotonic) Higher solute concentration Solute Water Solute Solute Lower water concentration (hypertonic) Lower solute concentration Lower solute concentration Visual Summary 5.2

Exocytosis and Endocytosis: Traffic of Large Molecules Visual Summary 5.3