• Home
  • Textbooks
  • Essential Cell Biology
  • Cells: The Fundamental Units of Life

Essential Cell Biology

Bruce Alberts, Karen Hopkin, Alexander D. Johnson

Chapter 1

Cells: The Fundamental Units of Life - all with Video Answers

Educators

Chapter Questions

04:35

Problem 1

"Life" is easy to recognize but difficult to define. According to one popular biology text, living things:
1. Are highly organized compared to natural inanimate objects.
2. Display homeostasis, maintaining a relatively constant internal environment.
3. Reproduce themselves.
4. Grow and develop from simple beginnings.
5. Take energy and matter from the environment and transform it.
6. Respond to stimuli.
7. Show adaptation to their environment. Score a person, a vacuum cleaner, and a potato with respect to these characteristics.

Yifan Zhou
Yifan Zhou
Numerade Educator
06:43

Problem 2

Mutations are mistakes in the DNA that change the genetic plan from that of the previous generation. Imagine a shoe factory. Would you expect mistakes (i.e., unintentional changes in copying the shoe design to lead to improvements in the shoes produced? Explain your answer.

Noah Boudrie
Noah Boudrie
Numerade Educator
09:22

Problem 3

You have embarked on an ambitious research project: to create life in a test tube. You boil up a rich mixture of yeast extract and amino acids in a flask, along with a sprinkling of the inorganic salts known to be essential for life. You seal the flask and allow
it to cool. After several months, the liquid is as clear as ever, and there are no signs of life. A friend suggests that excluding the air was a mistake, since most life as we know it requires oxygen. You repeat the experiment, but this time you leave the flask open to the atmosphere. To your great delight, the liquid becomes cloudy after a few days, and, under the microscope, you see beautiful small cells that are clearly growing and dividing. Does this experiment prove that you managed to generate a novel lifeform? How might you redesign your experiment to allow air into the flask, yet eliminate the possibility that contamination by airborne microorganisms is the explanation for the results? (For a readymade answer, look up the classic experiments of Louis Pasteur.)

Sana Riaz
Sana Riaz
Numerade Educator
03:05

Problem 4

A bacterium weighs about $10^{-12} \mathrm{g}$ and can divide every 20 minutes. If a single bacterial cell carried on dividing at this rate, how long would it take before the mass of bacteria would equal that of the Earth $\left(6 \times 10^{24} \mathrm{kg}\right) ?$ Contrast your result with the fact that bacteria originated at least 3.5 billion years ago and have been dividing ever since. Explain the apparent paradox. (The number of cells $N$ in a culture at time $t$ is described by the equation $N=N_{0} \times 2^{t / G},$ where $N_{0}$ is the number of cells at zero time, and $G$ is the population doubling time.

Mary Katherine
Mary Katherine
Numerade Educator
02:22

Problem 5

Suggest a reason why it would be advantageous for eukaryotic cells to evolve elaborate internal membrane systems that allow them to import substances from the outside, as shown in Figure $1-25$

Yifan Zhou
Yifan Zhou
Numerade Educator
05:37

Problem 6

Discuss the relative advantages and disadvantages of light and electron microscopy. How could you best visualize a living skin cell, a yeast mitochondrion, a bacterium, and a microtubule?

Yifan Zhou
Yifan Zhou
Numerade Educator
00:54

Problem 7

Your next-door neighbor has donated $\$ 100$ in support of cancer research and is horrified to learn that her money is being spent on studying brewer's yeast. How could you put her mind at ease?

Aditya Sood
Aditya Sood
Numerade Educator
07:34

Problem 8

By now you should be familiar with the following cell components. Briefly define what they are and what function they provide for cells.
A. cytosol
B. cytoplasm
C. mitochondria
D. nucleus
E. chloroplasts
F. Iysosomes
G. chromosomes
H. Golgi apparatus
I. peroxisomes
J. plasma membrane
K. endoplasmic reticulum
L. cytoskeleton
M. ribosome

Allison Reynolds
Allison Reynolds
Numerade Educator
05:37

Problem 9

Which of the following statements are correct? Explain your
answers.
A. The hereditary information of a cell is passed on by its proteins.
B. Bacterial DNA is found in the cytoplasm.
C. Plants are composed of prokaryotic cells.
D. With the exception of egg and sperm cells, all of the nucleated cells within a single multicellular organism have the same number of chromosomes.
E. The cytosol includes membrane-enclosed organelles such as lysosomes.
F. The nucleus and a mitochondrion are each surrounded by a double membrane.
G. Protozoans are complex organisms with a set of specialized cells that form tissues such as flagella, mouthparts, stinging darts, and leglike appendages.
H. Lysosomes and peroxisomes are the sites of degradation of unwanted materials.

Allison Reynolds
Allison Reynolds
Numerade Educator
01:31

Problem 10

Identify the different organelles indicated with letters in the electron micrograph of a plant cell shown below. Estimate the length of the scale bar in the figure.

Yifan Zhou
Yifan Zhou
Numerade Educator
04:36

Problem 11

There are three major classes of protein filaments that make up the cytoskeleton of a typical animal cell. What are they, and what are the differences in their functions? Which cytoskeletal filaments would be most plentiful in a muscle cell or in an epidermal cell making up the outer layer of the skin? Explain your answers.

Yifan Zhou
Yifan Zhou
Numerade Educator
04:35

Problem 12

Natural selection is such a powerful force in evolution because organisms or cells with even a small reproductive advantage will eventually outnumber their competitors. To illustrate how quickly this process can occur, consider a cell culture that contains 1 million bacterial cells that double every 20 minutes. A single cell in this culture acquires a mutation that allows it to divide faster, with a generation time of only 15 minutes. Assuming that there is an unlimited food supply and no cell death, how long would it take before the progeny of the mutated cell became predominant in the culture? (Before you go through the calculation, make a guess: do you think it would take about a day, a week, a month, or a year?) How many cells of either type are present in the culture at this time? (The number of cells $N$ in the culture at time $t$ is described by the equation $N=N_{0} \times 2^{t / G},$ where $N_{0}$ is the number of cells at zero time and $G$ is the generation time.

Yifan Zhou
Yifan Zhou
Numerade Educator
04:35

Problem 12

Natural selection is such a powerful force in evolution because organisms or cells with even a small reproductive advantage will eventually outnumber their competitors. To illustrate how quickly this process can occur, consider a cell culture that contains 1 million bacterial cells that double every 20 minutes. A single cell in this culture acquires a mutation that allows it to divide faster, with a generation time of only 15 minutes. Assuming that there is an unlimited food supply and no cell death, how long would it take before the progeny of the mutated cell became predominant in the culture? (Before you go through the calculation, make a guess: do you think it would take about a day, a week, a month, or a year?) How many cells of either type are present in the culture at this time? (The number of cells $N$ in the culture at time $t$ is described by the equation $N=N_{0} \times 2^{t / G},$ where $N_{0}$ is the number of cells at zero time and $G$ is the generation time.

Yifan Zhou
Yifan Zhou
Numerade Educator
01:23

Problem 13

When bacteria are cultured under adverse conditions-for example, in the presence of a poison such as an antibioticmost cells grow and divide slowly. But it is not uncommon to find that the rate of proliferation is restored to normal after a few days. Suggest why this may be the case.

Yifan Zhou
Yifan Zhou
Numerade Educator
01:23

Problem 13

When bacteria are cultured under adverse conditions-for example, in the presence of a poison such as an antibioticmost cells grow and divide slowly. But it is not uncommon to find that the rate of proliferation is restored to normal after a few days. Suggest why this may be the case.

Yifan Zhou
Yifan Zhou
Numerade Educator
03:01

Problem 14

Apply the principle of exponential growth of a population of cells in a culture (as described in Question $1-12$ ) to the cells in a multicellular organism, such as yourself. There are about $10^{13}$ cells in your body. Assume that one cell has acquired mutations that allow it to divide in an uncontrolled manner to become a cancer cell. Some cancer cells can proliferate with a generation time of about 24 hours. If none of the cancer cells died, how long would it take before $10^{13}$ cells in your body would be cancer cells? (Use the equation $N=N_{0} \times 2^{t / G},$ with $t$ the time and $G$ the generation time. Hint: $\left.10^{13} \approx 2^{43} .\right)$

Yifan Zhou
Yifan Zhou
Numerade Educator
07:54

Problem 15

"The structure and function of a living cell are dictated by the laws of chemistry, physics, and thermodynamics." Provide examples that support (or refute) this claim.

Noah Boudrie
Noah Boudrie
Numerade Educator
01:34

Problem 16

What, if any, are the advantages in being multicellular?

Aditya Sood
Aditya Sood
Numerade Educator
02:26

Problem 17

Draw to scale the outline of two spherical cells, one a bacterium with a diameter of $1 \mu \mathrm{m}$, the other an animal cell with a diameter of $15 \mu \mathrm{m}$. Calculate the volume, surface area, and surface-to-volume ratio for each cell. How would the latter ratio change if you included the internal membranes of the animal cell in the calculation of surface area (assume internal membranes have 15 times the area of the plasma membrane)? (The volume of a sphere is given by $4 \pi r^{3} / 3$ and its surface by $4 \pi r^{2},$ where $r$ is its radius.) Discuss the following hypothesis: "Internal membranes allowed bigger cells to evolve."

Rabeya Zahid
Rabeya Zahid
Numerade Educator
03:48

Problem 18

What are the arguments that all living cells evolved from a common ancestor cell? Imagine the very "early days" of evolution of life on Earth. Would you assume that the primordial ancestor cell was the first and only cell to form?

Yifan Zhou
Yifan Zhou
Numerade Educator
09:49

Problem 19

Looking at some pond water with a light microscope, you notice an unfamiliar rod-shaped cell about $200 \mu \mathrm{m}$ long. Knowing that some exceptional bacteria can be as big as this or even bigger, you wonder whether your cell is a bacterium or a eukaryote. How will you decide? If it is not a eukaryote, how will you discover whether it is a bacterium or an archaeon?

Sana Riaz
Sana Riaz
Numerade Educator