Water balance between cells and their surroundings is crucial to organisms. Cells shrink

Membranes are fluid mosaics of lipids and proteins with many functions. The proteins embedded in a membranes phospholipid bilayer perform various functions.

Membranes form spontaneously, a critical step in the origin of life.

Passive transport is diffusion across a membrane with no energy investment. Solutes diffuse across membranes down their concentration gradients.

Osmosis is the diffusion of water across a membrane.

Water balance between cells and their surroundings is crucial to organisms. Cells shrink in a hypertonic solution and swell in a hypotonic solution. In isotonic solutions, animal cells are normal, but plant cells are flaccid.

Transport proteins can facilitate diffusion across membranes.

Research on another membrane protein led to the discovery of aquaporins. Aquaporins are water channels in cells with high water transport needs.

Cells expend energy in the active transport of a solute.

Exocytosis and endocytosis transport large molecules across membranes. A vesicle may fuse with the membrane and expel its contents (exocytosis), or the membrane may fold inward, enclosing material from the outside (endocytosis).

Cells transform energy as they perform work. Kinetic energy is the energy of motion. Potential energy is energy stored in the location or structure of matter. Chemical energy is potential energy available for release in a chemical reaction. According to the laws of thermodynamics, energy can change form but cannot be created or destroyed, and energy transformations increase disorder, or entropy, with some energy being lost as heat.

Chemical reactions either release or store energy. Exergonic reactions release energy. Endergonic reactions require energy and yield products rich in potential energy. Metabolism encompasses all of a cells chemical reactions.

ATP drives cellular work by coupling exergonic and endergonic reactions. The transfer of a phosphate group from ATP is involved in chemical, mechanical, and transport work.

Enzymes speed up the cells chemical reactions by lowering energy barriers. Enzymes are protein catalysts that decrease the activation energy (EA) needed to begin a reaction.

A specific enzyme catalyzes each cellular reaction. An enzymes substrate binds specifically to its active site.

Enzyme inhibitors can regulate enzyme activity in a cell. A competitive inhibitor competes with the substrate for the active site. A noncompetitive inhibitor alters an enzymes function by changing its shape. Feedback inhibition helps regulate metabolism.

Many drugs, pesticides, and poisons are enzyme inhibitors.

Fill in the following concept map to review the processes by which molecules move across membranes.

Label the parts of the following diagram illustrating the catalytic cycle of an enzyme.

Which best describes the structure of a cell membrane? a. proteins between two bilayers of phospholipids b. proteins embedded in a bilayer of phospholipids c. a bilayer of protein coating a layer of phospholipids d. phospholipids between two layers of protein e. cholesterol embedded in a bilayer of phospholipids

Consider the following: chemical bonds in the gasoline in a cars gas tank and the movement of the car along the road; a biker at the top of a hill and the ride he took to get there. The first parts of these situations illustrate ______, and the second parts illustrate ______. a. the first law of thermodynamics ... the second law b. kinetic energy ... potential energy c. an exergonic reaction ... an endergonic reaction d. potential energy ... kinetic energy e. the second law of thermodynamics ... the first law

A plant cell placed in distilled water will ______; an animal cell placed in distilled water will ______. a. burst ... burst b. become flaccid ... shrivel c. become flaccid ... be normal in shape d. become turgid ... be normal in shape e. become turgid ... burst

The sodium concentration in a cell is 10 times less than the concentration in the surrounding fluid. How can the cell move sodium out of the cell? (Explain.) a. passive transport d. osmosis b. diffusion e. any of these processes c. active transport

The synthesis of ATP from ADP and a. is an exergonic process. b. involves the hydrolysis of a phosphate bond. c. transfers a phosphate, priming a protein to do work. d. stores energy in a form that can drive cellular work. e. releases energy.

Facilitated diffusion across a membrane requires ______ and moves a solute ______ its concentration gradient. a. transport proteins ... up (against) b. transport proteins ... down c. energy ... up d. energy and transport proteins ... up e. energy and transport proteins ... down

What are aquaporins? Where would you expect to find them? 1

How do the two laws of thermodynamics apply to living organisms? 1

What are the main types of cellular work? How does ATP provide the energy for this work? 1

Why is the barrier of the activation energy beneficial for organic molecules? Explain how enzymes lower EA. 1

How do the components and structure of cell membranes relate to the functions of membranes? 1

Sometimes inhibitors can be harmful to a cell; often they are beneficial. Explain. P 1

Explain how each of the following food preservation methods would interfere with a microbes enzyme activity and ability to break down food: canning (heating), freezing, pickling (soaking in acetic acid), salting. 1

A biologist performed two series of experiments on lactase, the enzyme that hydrolyzes lactose to glucose and galactose. First, she made up 10% lactose solutions containing different concentrations of enzyme and measured the rate at which galactose was produced (grams of galactose per minute). Results of these experiments are shown in Table A below. In the second series of experiments (Table B), she prepared 2% enzyme solutions containing different concentrations of lactose and again measured the rate of galactose production. A lysosome, a digestive organelle in a cell, has an internal pH of around 4.

Draw a curve on the graph that you would predict for a lysosomal enzyme, labeling its optimal pH. 1

Organophosphates (organic compounds containing phosphate groups) are commonly used as insecticides to improve crop yield. Organophosphates typically interfere with nerve signal transmission by inhibiting the enzymes that degrade transmitter molecules. They affect humans and other vertebrates as well as insects. Thus, the use of organophosphate pesticides poses some health risks. On the other hand, these molecules break down rapidly upon exposure to air and sunlight. As a consumer, what level of risk are you willing to accept in exchange for an abundant and affordable food supply?