Chapter 1. Chapter 2: Chemistry and Molecules of Life

1.1 Introduction

Welcome to the Interactive Study Guide for Chapter 2: Chemistry and Molecules of Life! This Study Guide will help you master your understanding of the chapter's Driving Questions, using interactive Infographics and activities, as well as targeted assessment questions. Click "Next" to get started, or select a Driving Question from the drop-down menu to the right.

DRIVING QUESTIONS

• How is matter organized into molecules of living organisms?
• What is the definition of life, and how could Martian life be recognized?
• What is the basic structural unit of life?
• Why is water so important for life and living organisms?

1.2 Driving Question 1

Why should you care?

We literally are what we eat—matter can not be created or destroyed, so every atom of every element in us was once part of some other living organism or the atmosphere or the earth. The atoms of most elements never change because the particles in them do not change. There’s a good chance that right now you may be breathing an oxygen molecule that was once breathed by Julius Caesar. You could have carbon atoms in you that were once part of a Tyrannosaurus.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Understand where the subatomic particles in an atom are and what their characteristics are.
2. Explain why carbon is an essential chemical component of living organisms.
3. Determine whether a molecule is organic or inorganic.
4. Differentiate between the four classes of molecules of life and when pertinent, the subunits that comprise them.

Infographic Focus

The infographics most pertinent to the Driving Question are 2.3, 2.4, and Up Close: Molecules of Life.

Understand where subatomic particles in an atom are and what their characteristics are.

Question 1.1

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• Use different shapes or colors for each kind of particle, so that you can tell them apart.
• Make sure to put the particles in the proper region of the atom.
• Add the symbols +, −, or Ø to each particle to indicate which are positively charged, negatively charged, or neutral.

1.3 Driving Question 2

Why should you care?

What is life? At first, the question of what is alive and what is not seems so elementary that it should not need asking. But, when it gets down to the details of what defines life, the question starts seeming a lot more profound. This chapter ponders the possibility of extraterrestrial life and how we can recognize and find it. Will it fall under the definition of life as we know it? Here on Earth, it is important to understand the nature of life, because it means understanding who we are and how we and all other life forms work.

What should you know?

To fully answer this Driving Question, you should be able to:

1. List and describe 5 characteristics inherent to all living things.
2. Defend an argument about whether a virus is or is not alive and how this may relate to life on Mars.

Infographic Focus

The infographics most pertinent to the Driving Question are 2.1 and 2.10.

List and describe 5 characteristics inherent to all living things.

Question 1.12

What defines life? Refer to Infographic 2.1 in your textbook if necessary.

• Growth

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Unicellular organisms grow by increasing their cell size, while multicellular organisms grow by increasing their number of cells.

Question 1.13

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The ability to grow suggests that an organism is able to take in energy from the environment and use it for processes that include growing larger and proper cell function.

Question 1.14

• Reproduction

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If organisms did not reproduce, there would be no consistent life on the planet. A species must reproduce both to pass on genetic traits that will help their offspring survive and reproduce to maintain the species.

Question 1.15

• Homeostasis

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Temperature, water level, oxygen level, salt level, sleep, eating, nutrient levels, energy levels, etc.

Question 1.16

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Homeostasis is an important characteristic of living things because there is a baseline internal environment that must be maintained to function properly. If homeostasis is disrupted for some reason, for example, you get dehydrated, your body cannot function properly and eventually organ systems begin to shut down.

Question 1.17

• Sense and Respond to Stimuli:

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To see/hear/touch/taste/smell something in your environment and respond to it. For example, if you smell fresh baked bread coming out of the oven your mouth may begin to ‘water’.

Question 1.18

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• See a bright light in a dark cave = move towards it

Question 1.19

• Obtain and Use Energy

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Organisms can gain energy either through sunlight or by eating other organisms.

Question 1.20

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Without the ability to use energy, organisms would not be able to grow, reproduce, maintain homeostasis, sense and respond to stimuli, basically, live.

Question 1.21

The following entities are not considered alive, although they may exhibit some of the characteristics of life. For each item, explain which characteristics of life they exhibit and which ones they lack:

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Exhibit: none. Lack: all.

Question 1.22

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Exhibit: growth (can buy more parts for it), homeostasis (needs to maintain temperature, for example), sense and respond to stimuli (you hit a key, the computer does a function), obtain and use energy (converts electrical energy to processes that preform functions)
Lack: Reproduction

Question 1.23

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Exhibit: reproduction (spreads from computer to computer), sense and respond to stimuli (some computer viruses will only preform their function if the right program is running)
Lack: growth, homeostasis, obtain and use energy

Question 1.24

The following organisms are considered alive, so they meet the five characteristics of living things. It may not be readily apparent, however, how they meet all five characteristics. For each organism below, explain why it isn't readily apparent that they are alive:

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Reproduction (might not be readily apparent or may not happen if another plant is not available)

Question 1.25

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Sense and Respond to Stimuli (most mushrooms don’t respond to touch and make no discernable movements towards the sun)

Question 1.26

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Homeostasis (does not discernably show homeostasis by wilting like a plant would, for example)

1.4 Driving Question 3

Why should you care?

All life on earth is made of cells, and all cells have cell membranes to hold in their contents. Cell membranes serve as boundaries, gatekeepers, and communicators. You wouldn’t be able to think, move, or generally function without proper cell membranes.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Describe the basic structural unit of life.
2. Identify the different parts of the cell membrane.
3. Explain the importance of the cell membrane.

Infographic Focus

The infographics most pertinent to the Driving Question are 2.5 and 2.10.

Identify the parts of the cell membrane.

Question 1.39

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The basic components of a cellular membrane are phospholipids and proteins.

Question 1.40

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1.5 Driving Question 4

Why should you care?

You might rightly say that a sixth characteristic of living things is the presence of water in them. Your body contains around 60% water by weight. All living and actively growing things are made of cells containing mostly water. How did water get to be so important to life? It has several unique characteristics that make it a special molecule.

Because it is a polar molecule (with unevenly distributed charges across it), water is a good solvent for charged or polar substances. Water can break ionic bonds in solutes like salt, so that its component ions are released into the solution as charged particles. The movement of ions in water solution is essential for your brain and muscles to work. Nearly all of the complex chemical interactions that go on every moment of your life—and that enable you to think, live, and breathe—happen in water. The polarity of water molecules is also important in the formation of hydrogen bonds with each other and with other polar biomolecules; this in turn helps keep your DNA together in your cells and your proteins in their proper shapes. Furthermore, you can’t taste or smell organic molecules like sugar or the scent of lemons until they dissolve in water.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Diagram a water molecule and label its components.
2. Explain why water is a polar molecule and why this makes it a good solvent for charged or polar substances.
3. Explain what hydrogen bonding is and its implications for the properties of water.
4. Explain why water is important for life.

Infographic Focus

The infographics most pertinent to the Driving Question are 2.5, 2.6, 2.7, 2.8 and 2.9.

Diagram a water molecule and label its components.

Question 1.45

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