Escience lab 3 answers

Faculty Contact

Mary Ayuk mary.ayuk@faculty.umuc.edu

Course Description

(Not open to students who have completed BIOL 101 or BIOL 102. For students not majoring in a science. Fulfills the laboratory science requirement.) An introduction to the structure and function of living organisms. The aim is to apply the scientific method and use scientific and quantitative reasoning to make informed decisions about experimental results in the biological sciences. Topics include the chemical foundations of life, cell biology, genetics, evolution, ecosystems, and interdependence of living organisms. Discussion also covers the importance of the scientific method to biological inquiry and the impact of biological knowledge and technology on human societies. Laboratory activities emphasize the scientific method. Students may receive credit for only one of the following: BIOL 101 - BIOL 102, BIOL 103, BIOL 105, or BSCI 105.

Course Introduction

This course is an introductory course in biology, the study of life, in which we will explore unifying themes and concepts, including biodiversity, the principles of evolution that underlie biodiversity, and the criteria that serve to characterize life and living systems. We will also study concepts underlying the organization and interrelationships of living organisms through experiments based on the scientific method. Further discussion will also include how the scientific method and technological advances have led to the significant body of knowledge that now exists in biology as well as in all other scientific disciplines.

Living organisms are built from a very specific set of building blocks-atoms, molecules, and cells. We will begin with a study of these building blocks and their importance to living things. Next, we will examine the ways in which these building blocks interact to provide the energy living things need to develop, grow, move, work, and respond. The power and elegance of DNA and genes will be discussed, as well as their role in inheritance, human diseases, biodiversity, and evolution.

We will look at plants and animals to understand how atoms, molecules, and cells work together in balanced, interrelated systems that are critical to the health and well-being of living organisms. We will also look at the way in which living things interact with one another and with the nonliving parts of their environment. These interactions play a major role in the overall health of populations, ecosystems, and planet Earth.

In the laboratory portion of the course, we will apply the scientific method to scientific experiments, as well as to everyday questions and problems. Upon this foundation, the molecular and cellular processes common to all living organisms will be studied. We will then investigate scientific classification in the context of the importance of DNA to individual living organisms and to species of organisms as a whole. Finally, we will examine the interdependence of living organisms with each other and the environment, especially with respect to the impact of human populations on the environment and other organisms.

Course Outcomes

After completing this course, you should be able to

· recognize and explain how the scientific method is used to solve problems

· make observations and discriminate between scientific and pseudoscientific explanations

· weigh evidence and make decisions based on strengths and limitations of scientific knowledge and the scientific method

· use knowledge of biological principles, the scientific method, and appropriate technologies to ask relevant questions, develop hypotheses, design and conduct experiments, interpret results, and draw conclusions

Course Materials

Click to access your course materials information

Class Guidelines

Contacting your Faculty Member

You can use the Instant Messages feature within the classroom to send a message to your faculty member.

Click the Classroom Walkthrough Videos link below, and then click The Pager link (old term for Instant Message), to view a how-to video on how to use the Pager/Instant Messages function within the classroom:

Classroom Walkthrough Videos Link

Within the Content section of your classroom, view the Start Here section to learn more about contacting your faculty member.

Course Materials

You will use a number of different materials in this class:

· a free online text book: Open Stax Concepts of Biology

· an online lab manual

· a lab kit

· various common items that you will gather from around your home or purchase at a grocery store

· asynchronous discussions

Lab Kit

To complete this course, you are required to purchase a Custom Biology Lab Kit from eScience Labs Inc.

Lab Kit Ordering Method 1:

If you use financial aid for course materials the lab kit must be purchased through MBS Direct, which is UMUC's virtual bookstore (Bio Lab Kit Sku 1589). Important: You will receive a redemption code from MBS Direct by email that must be entered at the eScience Labs' web-site before the lab kit is shipped to you:

1. Create an account: https://esciencelabs.com/user/register

2. After creating an account, or logging back in again with your email and password, click on “Have a code” in the upper right corner, or use this link: http://esciencelabs.com/have/code

3. Under Code enter your redemption code (received by email), click submit and follow the directions.

***Note: If you do not redeem the code, your kit will not be sent.

Lab Kit Ordering Method 2

If you do *not* use financial aid for course materials it is cheaper to order the lab kit directly from the eScience Labs' web-site using the following directions:

1. Create an account: https://esciencelabs.com/user/register

2. After creating an account, or logging back in again with your email and password, click on “Have a code” in the upper right corner, or use this link: http://esciencelabs.com/have/code

3. Under Code enter kit1589, click submit and follow the directions to purchase the Custom Biology lab kit ($79)

***Note: Regardless of the ordering method used, the kits are the same. When using option 1, you pay MBS and then they send a code via email (MBS sends the code). You must then log in to the eScience Labs’ web-site to redeem the code (mailing address will be entered at their site). When using option 2, you go to the eScience Labs website. At the site, you must enter the following custom kit code, kit1589, and you will then pay eScience Labs directly.

The key differences in the ordering options are:

1. Number of steps: the first option requires 2 steps, whereas the second option requires 1 step.

2. Cost: the second option saves money because you avoid the MBS fees.

3. Payment mode: option 1 accepts credit cards/electronic payments and book vouchers, whereas option 2 only accepts credit cards/electronic payments.

4. Delivery time: kits ordered via method 1 may take up to 7 days longer to be delivered.

Processing Timeline:

Please allow up to 3-5 business days to process your order and an additional 3-5 business days for delivery. eScience Labs ships all lab kits through standard UPS Ground. Kits may be expedited for an additional charge if needed. Please call 1-888-ESL-KITS for more information.

Getting Help from eScience Labs:

If you need any further assistance, our Customer Support team can be reached over the phone (888-375-5487) Monday through Friday, 8am – 5pm Mountain Standard Time. For after hours or weekend help, please email info@esciencelabs.com for assistance.

This comprehensive kit contains the majority of the materials needed to complete each lab exercise but please note that some labs do require students to supply a few additional materials. The kit also provides students with access to the eScience Labs’ Student Portal, which contains several online tutorials and learning tools aimed at increasing the understanding of the various concepts. It is important to remember that while these kits are easy to use, the lab activities and the contents of the lab kit are intended for adults enrolled in this course. Thus, use of the kit and the materials are used at your own risk.

Important: When you receive your lab kit from eScience Labs, check it to make sure all components are provided and are in good working order. eScience Labs will replace any damaged items at no cost. Find their contact information at www.esciencelabs.com.

Lab Manual

The Lab Manual is located in the weekly modules under Content. Before you start conducting your labs, please read the Lab Safety section of the laboratory manual and watch the safety video.

For each lab read the introduction and instructions for each exercise/experiment carefully. You can complete lab 1 without the lab kit.

Pictures Required

You are required to take pictures of your results in the experiments in labs 2, 3, 4, 5, 7 and the final applied lab project. Write your name and date on an index card (piece of paper) and include it within the picture. Insert the pictures as directed in the lab answer sheets. If you do not have access to a digital camera/phone please contact the professor to discuss alternatives.

Additional Materials needed for the labs (not included in lab kit)

Lab 2:

Experiment 1: egg white, potato, onion, hot water, fork, knife, hot water bath, tap water

Lab 3:

Experiment 1: scissors, paper towels, tap water.

Experiment 2: four liquid household products to test (for example: lemon juice, shampoo).

Lab 4:

Experiment 1: cutting board, 2 food products, kitchen knife, paper towels, saliva sample, tap water.

Experiment 2: hot water bath, tap water.

Lab 5:

Experiment 3: fresh soft fruit (one of the following: banana, grapes, strawberries), scissors.

Lab 7:

Experiment 1: paper towels, scissors, sunny location, tap water.

Labs 1 and 6 do not require any additional materials

Copy-right Protected Course Materials

All UMUC course materials, including quiz and exam questions, discussion questions, lab and writing assignments are copyright protected and the property of UMUC. Do not share any course materials on the internet. Sharing, or submitting, any materials from this course is a direct violation of U.S. and International Copyright Law. Civil Penalties for Copyright Violation currently range from $750 to $30,000 per violation.

Additionally, posting of quiz or assignment questions to online "answer" or "homework" websites is academic fraud. This type of activity is a direct violation of

· UMUC's code of conduct, Policy 151.00 section III A, and

· UMUC's Policy 150.25 - Academic Dishonesty and Plagiarism.

If you are caught engaging in this type of activity you risk sanction by the university. Possible sanctions include:

· A grade of F on the work in question

· A grade of F in the course

· Suspension from the university for Academic Dishonesty

· Expulsion for Academic Dishonesty

Please do your own work and don't risk these consequences!

Helpful Resources

A. Orientation to Science Courses

The Science Learning Center (SLC). You can enter this site from under Content, Course Resources. The SLC houses a set of instructional and support materials of use across the science curriculum. Currently, the SLC houses two items:

1. The Scientific Method Tutorial - This module provides an excellent description of the Scientific Method. This method is integral to all science, and is important for our course.

2. The Science Studies Tutorial - This piece is designed to provide students with some tips and strategies for taking a science course. Some of the strategies in this unit are generic and apply to students' general study habits for all courses. Other segments of the unit are specific to taking a science course. This unit is short and should not take more than 30-40 minutes to complete. I recommend that you read the unit during the first couple of weeks of the semester. If you have difficulty with science, then the Science Study Skills Unit is a MUST READ.

B. Orientation to College Writing

i. College Writing Essentials

· Majority of content is written in the student’s own words, and directly quoted content is limited to less than 10% of total content

· Introduction previews the main points, and conclusion summarizes main points

· Ideas are presented clearly, follow sound logic, and flow coherently and cohesively

· Content is expressed using standard grammar, punctuation and spelling conventions

· Paragraph content reflects reasonable transitions

· Content reflects synthesis and critical analysis of referenced sources

· Ideas are supported by referenced evidence, and full citations are provided for all reference sources

ii. UMUC Writing Resources ( http://www.umuc.edu/ewc/ ). You can access helpful writing resources through UMUC’s Effective Writing Center (EWC. The EWC provides excellent information for improving your writing skills, writing a paper, incorporating citation formats, and many other writing skills.

iii. The Research Assignment Calculator for Time management of your research papers. https://libapps.umuc.edu/calculator/calculator.shtml

C. Library Guide for the Sciences

The UMUC library has developed resources to aid in research of science related databases, Websites, books, and e-books. The Library Services site also provides information on how to find articles, and 24-hour access to UMUC librarians. The link to the Library Guide can be found at http://libguides.umuc.edu/science.

D. Additional Academic Support

First Online Course? If this is your first time taking a UMUC online course, then please walk through the introductory video orientations before our class begins (Go to LEO Help > Classroom Walkthrough). It will be of significant assistance to you. Get familiar with navigating around LEO by navigating through the various parts of our classroom to see all that is available.

Tips for Success

· Login to LEO one week before the semester begins

·

· Complete the LEO Classroom Walkthrough resources available at http://www.umuc.edu/students/leo/videos.cfm

· View and print syllabus. Mark calendar with important course dates

· Read start-up/orientation materials posted by faculty member

· Begin the course work on time and early (in the first 1-2 days of the semester)

· Start weekly assignments early in the week (Do not wait until 1-2 days before they are due)

· Check the online classroom, classroom News items and Alerts, and your email every 1-2 days for announcements and new information

E. Student Participation Expectations

a. Time Commitment:

Now that you have read the Syllabus, you should recognize that this course requires active student participation. An on-line course requires you to put in at least the same amount of time as an in-classroom course. For an eight-week course, you should expect to spend at least six hours per week participating in class discussions and activities and then about 12-15 hours in study, assigned reading, and preparing assignments outside of class. Active participation is required in all online courses, and you should expect to log in to your online course several times a week.

b. Study and Work Habits:

Summing Up a Successful Online Student. An online course places more responsibility on the student (and subsequently more independence) than a face-to-face course. Therefore, a successful online student must exercise more self-discipline than a face-to-face student. A successful online student is one who:

· reads the Course Schedule's assigned reading material thoroughly before responding in a conference

· prepares personal study notes (like classroom notes) each week from the reading assignment addressing key points, key figures, and defines any bold-faced terms

· considers outlining the course material for personal study

· participates two-to-three times per week in conferences and avoids late week conference comments

· engages the material and others with enthusiasm and courtesy

· schedules adequate time to do the work

· asks for help when needed

· interacts with others in the class

· is self-motivated

· turns in well-drafted, proofed, and properly cited and referenced assignments prior to their due dates

· keeps copies of all work and instructor responses in case of an emergency

Grading Information

This course consists of the following graded items:

Percentage

Academic Integrity Tutorial (Quiz)

0.5%

Discussion Participation (7 @ 2% each)

14%

Laboratory Assignments (7 @ 3.5% each)

24.5%

Quizzes (7 @ 3% each)

21%

Written assignment: Biology and Technology in the Real World

10%

Outline Final Applied Lab Project

1%

Final Applied Lab Project

9%

Final Examination

20%

Total

100%

Late Submission Policy

If you are unable to submit an assignment on time contact your professor before the submission deadline to ask for an extension. This does not guarantee that an extension will be granted and/or the professor may require documentation.

For assignments submitted late without a pre-approved extension:

· A penalty of 10% per week will be applied to lab assignments, writing assignments and quizzes

· Late participation in discussion topics will result in zero points

· Late submission of the final applied lab project and the final exam will not be accepted and result in zero points.

Extra Credit and Make-up Work Policy

· No opportunities for extra credit will be offered in this course

· No make-up work will be assigned in this course

Academic Integrity Tutorial

Please visit UMUC's Academic Integrity Tutorial (https://www.umuc.edu/writingcenter/plagiarism/index.cfm)

After completing the tutorial, take the quiz (at the end of tutorial) and submit the certificate in the assignment folder. You can either do a screenshot of the certificate (submit as a jpg file), or you can follow the instructions for "how to email your certificate", use your own email address and then submit the received pdf document in the assignment folder. You will only receive a certificate when you score 90% or more, but you will be able to retake the quiz as many times as needed to get that score.

Quizzes

Each of the 7 weekly quizzes consist of 20 multiple choice or multiple select questions. You will have 2 hours to complete each quiz once you start. Make sure you have 2 hours of uninterrupted time before starting a quiz because you can NOT save a quiz and come back to finish it later. Optional:You can submit a second attempt at each quiz. If you do, the highest score of the two attempts will count towards your course grade.

Final Examination

The final examination will be a timed, unproctored final exam. You will have five (05) hours to complete the final exam. Your Final Exam **will not be accepted** if submitted after the submission deadline. The final exam may consist of multiple choice, fill-in-the-blank, matching, short answer, and essay questions.

Final Applied Lab Project

Demonstration of your knowledge of basic laboratory skills, experimental design, and/or data evaluation will be assessed by the submission of an applied final lab project. See Project Descriptions below for more details on this final project. Note the earlier deadline for the outline.

Discussion Participation

By registering for a Web-based course, you have made a commitment to participate in your online course discussions as well as other online activities. Please plan to participate regularly. Participation for this course is defined as proactive involvement in weekly discussion conferences and/or answering discussion questions. This may require you to actively reflect on weekly reading assignments and to develop original ideas in your responses. You are expected to demonstrate critical thinking and your understanding of the content in the assigned readings as they relate to the issues identified in the discussion. You are expected to make your own contribution in a main topic as well as respond with value-added comments to at least two of your classmates. You are encouraged to respond to other students as well as to your instructor. You will note in the grading policy that your online discussion participation counts significantly toward your final grade.

You are expected to adhere to the general rules of online etiquette. It’s important to follow the guidelines of proper online etiquette to ensure good communication between you, your classmates and your instructors. Keep the five online etiquette tips below in mind during your online course:

1. Respect. Whether the class is online or on-site, respect is essential. It allows all involved parties to focus on the objective and prevents distracting disagreements. Be sure to use a polite tone, read before responding and be constructive with your criticism. It’s important to treat all online interactions the same as face-to-face interactions.

2. Use Proper Formatting, Punctuation and Grammar. The same rules of English apply in the online classroom setting. Capitalize letters when necessary, use appropriate punctuation and avoid using slang and abbreviations. You’ll not only make your posts easier to read; you’ll demonstrate your professionalism and personal value.

3. Be Careful. Because tone is difficult to convey online, sarcasm or humor can easily be misinterpreted. Though you may be tempted to joke around with your classmates, something written for a laugh may offend others. If you are unsure whether your message will be misconstrued, consider using an emoticon to lighten the tone.

4. Go to Your Instructor First. If you have a disagreement or issue with a fellow classmate, go to your instructor before the situation escalates. It’s best to make your instructor aware of the situation before it affects the classroom dynamics or the way you engage with your peers.

5. Stay on Topic, and Keep it Brief. Online classes require a lot of reading, and when responding, it may be difficult to decide where to start. Focus your comments into short topics to keep the conversation flowing. Avoid being too wordy, and instead say what you need to say without veering off topic.

To increase the possibility of you earning full credit for weekly participation, you must:

· Participate individually with meaningful and original comments in the dialogue of the posted discussion questions. (See Academic Policies for information about plagiarism.)

· Make a minimum of 3 posts per week . Your original post and 2 comments on any other clasmates posts which will reflect the content of the discussion.

· Ensure your posted content is written in your own words. Repetitive (redundant) answers, copied articles or portions of articles from Web sites, books, magazines and so on will not count towards participation

· Cite properly and consistently and include all sources used for your responses

The due date for weekly discussion(s) is listed in the course schedule.

Do not put off your class work until the end of the week. The deadline for online classroom discussion participation is 11:59pm ET on the due date unless stated otherwise. You must participate in the classroom discussions before the stated deadline to receive credit.

What is "good" participation?

For discussion participation, what matters here is the quality of your responses, not quantity.

Here are some examples of good responses:

"Mary - you mention in your answer that human cloning is currently being investigated. In your research did you see any companies that were actually doing human cloning? I did not think that human cloning even a possibility in our lifetime. I think the government should regulate cloning practices of all animals to make sure that the science is not being used in a harmful or unethical way." Another example:

"Joe, I really enjoyed reading your paper. I like the way that you formatted it, using pictures and tables to support your facts. The table you included about the increase in Flu deaths was very interesting - I did not realize that so many people die in other countries from something as simple as the flu!" Your responses may include an observation, a counterexample, a suggestion, a statement of respectful disagreement, a solution, a question about the material or the process, an insight, an admission, an assent, an example, an idea, a corroboration, or a speculation. Remember to include your sources of information (if applicable)! Here are some examples of inadequate responses/participation: "Good job, I liked your answers!" or, "Joe - I liked your paper very much!" or, "I agree!"

Any response that is intimidating, disrespectful, belittling and/or or demeaning will not be tolerated and may be deleted.

Project Descriptions

Laboratory Assignments

Addresses course outcomes 1-4:

· recognize and explain how the scientific method is used to solve problems

· make observations and discriminate between scientific and pseudoscientific explanations

· weigh evidence and make decisions based on strengths and limitations of scientific knowledge and the scientific method

· use knowledge of biological principles, the scientific method, and appropriate technologies to ask relevant questions, develop hypotheses, design and conduct experiments, interpret results, and draw conclusions

You are required to submit the following 7 lab assignments:

Lab 1: Introduction to Science

Lab 2 : Chemistry of Life

Lab 3: Osmosis

Lab 4: Enzymes

Lab 5: Transcription and Translation

Lab 6: Taxonomy

Lab 7: Ecological Interactions

Preliminary **required** activities

When you receive your lab kit from Escience Labs, check it to make sure all components are provided and are in good working order. Escience Labs will replace any damaged items at no cost. Find their contact information in the UMUC Biology Lab Manual and at www.esciencelabs.com.

Before you start conducting your labs, please read the Lab Safety section of the UMUC Biology Lab Manual and watch the safety video.

Photos Required!

You are required to take pictures of your results in the experiments in labs 2, 3, 4, 5, 7 and the final applied lab project. Write your name and date on an index card (piece of paper) and include it within the picture. Insert the pictures as directed in the lab answer sheets. If you do not have access to a digital camera/phone please contact the professor to discuss alternatives. You will receive 0 points if a lab assignment or final applied lab project is submitted without pictures of your results (a note with your name and the date must be included in the picture). Labs and final projects without pictures will earn a zero grade even if all other sections of the lab have been completed.

************

It is highly recommended that you adopt the following approach for each lab:

1. One or two weeks before the due date for a given lab, check the materials list for the lab and begin to gather the items that you will need. This practice will ensure that you will indeed have all the materials you need when you are ready to start the lab activity. Some labs require access to a stove or refrigerator (this will be indicated in the materials list).

2. Also, one or two weeks before the due date for a given lab, check the time necessary to complete the activity so that you can schedule your time accordingly. For example, some labs may be spread out over a couple of days or require two hours of work-these labs cannot be started an hour before they are due and successfully completed.

3. Before you begin a lab activity, download the lab manual and lab questions documents to your computer or portable device or print the lab activity from the online lab manual. This is important, because you will perform many of the lab activities away from the online environment, and you will want to have the detailed instructions and the lab questions in front of you as you perform the lab activity.

4. Read the corresponding sections of the text book and course modules, the introduction and all the directions for the entire lab assignment before you begin. It is especially important that you read the directions to the activity before you actually perform the activity. In some cases, you may need to reuse materials in subsequent experiments. It is also a good idea to familiarize yourself with the questions that accompany each activity ahead of time so that you know what to look for and take note of while performing the activity.

5. Perform the lab activity, and while doing so, take thorough notes so that you will be able to answer the questions that accompany each activity. Remember to take a picture of your results. Optimally, you should answer lab experiment questions as you work your way through each component of the experiment.

6. Answer the questions that accompany each lab activity. You will be expected to submit your answers to your instructor as instructed.

IMPORTANT: To conduct your laboratory exercises, use the Laboratory Manual that is available in the LEO classroom.

************

Submission Format:

For each lab assignment follow the instructions in the Lab Manual provided in under the Content tab. You will find one answer sheet for each lab (same questions as those in the lab manual). Type your answers directly in these documents. Once your lab is completed, save your document as “lastname lab #.doc” (example”Smith lab1.doc”), and submit your assignment document in the corresponding Assignment Folder.

Your collected data should be presented as specified in the laboratory manual and may be in the form of tables, graphs, diagrams, or narratives. You should be prepared to provide the images of graphs, diagrams, or sketches in the lab documents or as separate files. You can photograph or scan any images and embed them into your lab document. If you have any issues with graphics created within software packages, you can capture screen images. On the Macintosh use Command-Shift-4 to capture a portion of the screen; the image will be saved to the desktop. On IBM-PC clones (the PC), use CTRL-ALT-PrstScrn to capture an image into the memory and then paste it into the lab document.

Each laboratory assignment must be submitted no later than 11.59 PM ET on the due date listed in the Course Schedule.

Addresses course outcomes 1-4:

· recognize and explain how the scientific method is used to solve problems

· make observations and discriminate between scientific and pseudoscientific explanations

· weigh evidence and make decisions based on strengths and limitations of scientific knowledge and the scientific method

· use knowledge of biological principles, the scientific method, and appropriate technologies to ask relevant questions, develop hypotheses, design and conduct experiments, interpret results, and draw conclusions

Lab 1: Introduction to Science

The scientific method will be introduced using problems that can be related to everyday life. Students will work through laboratory exercises in order to gain an understanding of the process of scientific inquiry. Complete both activities.

Time: 1 hour

Concepts to explore: Testable observations, Hypothesis, Null hypothesis, Experimental approach, Variables, Controls

Experiments: This lab includes several critical thinking exercises that test student knowledge of the scientific method.

Exercise 1: Data Interpretation

Exercise 2: Experimental Variables

Exercise 3: Testable Observations

Exercise 4: Conversion

No lab kit materials are required. You do not have to wait for the lab kit to complete this lab.

Lab 2: Chemistry of Life

Basic properties of the chemistry that underlies biology are explored in this lab. Students will determine the presence of biological macromolecules such as proteins and carbohydrates using reagents that change color in their presence.

Time: 2 1/2 hours

Additional materials needed:

· Experiment 1: egg white, potato, onion, hot water, fork, knife, hot water bath, tap water

Concepts to explore: Atoms, Elements, Compounds, Chemical bonds, Molecules/Macromolecules, Energy and metabolism, Proteins, Carbohydrates, Lipids.

Experiments:

Experiment 1: Testing for Biomolecules

· Students use the Biuret reagent to test for the presence of protein in egg white, gelatin, a glucose solution and water. Biuret reagent is normally blue but changes to pink when short peptides are present and to violet when longer polypeptides are present.

· Students use Benedict’s Reagent to test for reducing sugars such as glucose. When glucose reacts with copper present in the Benedict’s reagent an orange or red colored precipitate is formed.

· Students use IKI to test for starch. When starch reacts with IKI a dark purple precipitate is formed.

Pictures required for all tests in Experiment 1. Please include an index card with name and date within the picture frames.

Lab 3: Osmosis

The structure and function of cells will be investigated. The properties of cellular membranes will also be studied, paying special attention to the selective passage of molecules in and out of living cells.