, Highlights of New Content
This section highlights selected new content in Campbell Biology,
Thirteenth Edition.
Unit 3 Genetics
Chapters 13–17 incorporate changes that help students grasp the
Unit 1 The Chemistry of Life more abstract concepts of genetics as well as recognize their cur-
rent relevance. In Chapter 14, the term phenotypic plasticity has
In Unit 1, new content engages students by showing why understand- been added and defined, and the discussion of sickle-cell disease
ing chemistry is relevant and important as a basis for learning biology. (SCD) has been revised to clarify its occurrence wherever malaria
For example, Chapter 3 has information on discoveries of exoplanets is endemic, not just in Africa. Also, new gene therapy-based treat-
as well as a 2024 study on the presence and location of water on Mars, ments for SCD are described. In Chapter 15, the contribution of
including a new photo in Figure 3.10. Building on this, Chapter 4 now Dr. Nettie Stevens to understanding the role of the Y chromosome
includes the search by the Mars Rover for samples to be analyzed for in sex determination has been added, along with FDA-approved
fossils. In Chapter 5, the text has been updated on the breakthroughs gene therapies for Duchenne muscular dystrophy and certain
achieved by use of computational approaches to predict 3D protein hemophilia cases. Coverage of imprinted genes has also been
structure, including the role of artificial intelligence (AI) and the updated with recent research on two male-parent embryos, and
related 2024 Nobel Prize in Chemistry. The definition of bioinformatics the discussion of human “three-parent” babies has been enhanced.
has been revised to include AI. In Chapter 16, a new interactive CheckPoint activity entitled
CheckPoint: Leading and Lagging Strand Synthesis has been
Unit 2 The Cell inserted to aid students with this difficult topic. Chapter 17
now includes a new CheckPoint activity entitled CheckPoint:
Our main goal for this unit was to make the material more exciting to Transcription and Translation. Content has also been added about
students, to show that cell biology research is dynamic and ongoing. a novel use of the CRISPR system in conjunction with a technique
Chapter 6 includes recent changes in thinking on the role of mitochon- called base editing, as well as mention of new forms of Cas proteins
dria: In addition to being the “powerhouse of the cell” and produc- that minimize “off-target” gene editing.
ing ATP, they have many further functions, including biosynthesis, Chapters 18–21 are extensively updated, driven by exciting new
regulation of apoptosis, and extensive engagement in intracellular and discoveries based on gene-editing technology and use of artificial
extracellular signaling. Chapter 7 includes an update on the discovery intelligence (AI). In Chapter 18, updates have been made to the
of a second co-receptor for HIV called CXCR4. Chapter 11 mentions discussions of master regulatory gene function and colon cancer, as
AlphaFold2, an AI system that predicts 3D protein structures, in the well as nuclear architecture and its possible role in neuropsychiatric
context of why it has been challenging to predict the structure of disorders. In Chapter 19, the topic of emerging viral diseases has
G-protein-coupled receptors (GPCRs). Also included is the recent dis- been updated extensively to discuss SARS-CoV-2 and the COVID-19
covery that a defect in a particular voltage-gated ion channel can cause pandemic. Other Chapter 19 updates include information on vaccine
muscle weakness or stiffness, or even temporary paralysis. Chapter 12 programs, the 2025 measles epidemic, new prevention and treatment
includes a new interactive CheckPoint activity entitled CheckPoint: approaches for HIV infection, and the H5N1 avian influenza
Counting Chromosomes, and coverage of the G1 checkpoint has been epidemic. Chapter 20 introduces new subsections on cell and tissue
updated with new research from 2023, concluding that a subset of culture (including a new figure on organoids), small-molecule drugs,
cells may require ongoing signals to continue progressing through S biologic drugs, and biomaterials for drug delivery. Other updates
and G2. This finding has implications for potential cancer treatments. include discussions of the cloning of human/macaque chimeric
embryos and the associated ethical issues, FDA-approved
CRISPR-based gene therapies for sickle-cell disease, and
establishment of the Human Genome Editing Registry. The coverage
of using DNA technology for environmental cleanup now includes
the term bioremediation. Chapter 21 has a new section, “Application
of artificial intelligence and machine learning to bioinformatics,”
which describes multiple examples of how AI is transforming the
field of bioinformatics. Artificial intelligence has been added as a
key term and defined, as well as a new Figure 21.5 (see next page)
featuring the use of AI in medical diagnosis. Other updates include
results of the ENCODE project and the Cancer Genome Atlas Project,
establishment of the Impact of Genomic Variants on Function
program, a massive international study of primate genomes, and
new information on the FOXP2 gene. Discussions of genome
comparisons have been revised to reflect new thinking about the
relationship of Bacteria, Archaea, and Eukarya.
viii
, Highlights of New Content ix
taxonomy to reflect recent changes, largely based on phylogenomic
Figure 21.5 Example of use of artificial intelligence (AI) in research. The title of Chapter 28 has been updated from “Protists”
medical diagnosis.
to “Origin and Diversification of Eukaryotes” to better reflect its
focus. Chapter 27 discusses current hypotheses of archaeal phylog-
eny, including the possible origin of eukaryotes within the Asgard
archaea. In Chapter 28, a new section on reproductive diversity of
eukaryotes in Concept 28.1 reviews the three types of life cycles
found in sexually reproducing eukaryotes. The phylogenetic tree of
major groups of eukaryotes was updated to indicate that excavates
are likely not a monophyletic group, and to update the placement
of cryptophytes and haptophytes. Concept 28.5 discusses recent dis-
coveries in phylogenomic research and describes some of the latest
eukaryotic supergroups to be described. In Chapter 32 and 33, the
phylogenetic tree of animal was updated to present the ctenophores,
sponges, and other animals as a polytomy while resolving some
of the polytomies that were shown in the previous edition. A new
figure (Figure 33.4) and text in Concept 33.1 describe ctenophores.
Chapter 34 was updated with new information about phylogenetic
Unit 4 Mechanisms of Evolution relationships between various groups of hominins, and a new Figure
34.47 presents a phylogenetic tree of hominins.
In Chapter 23, the presentation of the Hardy-Weinberg model and
Hardy-Weinberg equilibrium was revised to illustrate that, in a simpli- Figure 33.4 Anatomy of a sea gooseberry (Pleurobrachia spp.),
fied situation, an allele does not increase or decrease in frequency on a ctenophore.
its own. Two new figures help students visualize how the equation
projects the next generation. By starting with the fundamental con-
cept of allele frequency, we aim to assist students in bridging the gap
between individual- and population-level thinking. The assumptions
of the Hardy-Weinberg model are then discussed as mechanisms of
change that may operate alone or together in a natural population.
The Scientific Skills Exercise and Concept Check 21.2 Question 3 have
been revised to compare frequencies across generations.
Unit 5 The Evolutionary History Unit 6 Plant Form and Function
of Biological Diversity In Chapter 35, the term “prop root” has been replaced with the
more precise term “brace root,” and vascular rays are now more
In Chapter 26, Concepts 26.2 and 26.3 have been reorganized to accurately portrayed. Also, an additional benefit of compound
emphasize the distinction between inferring (that is, determining) a leaves, namely better light penetration through the canopy, is
phylogeny from reading/interpreting a phylogeny—namely, clarify- now mentioned as a possible advantage of compound leaf forms.
ing that we do not both infer a tree’s topology and interpret patterns In Chapter 37, the Scientific Skills Exercise includes a new pho-
of trait evolution based on the same data. Phylogenies are inferred tograph of raspberry plants that better shows the characteristics
from one type of data (for example, molecular genetic sequences) of iron deficiency. Figure 37.15 has been updated to include new
and then used to understand the evolution of other traits (for exam- research indicating that staghorn ferns can grow as colonial
ple, vertebral column, amnion, and hair), as discussed in the section assemblages (“superorganisms”). In Chapter 38, a new interac-
now titled “Mapping Characters on a Phylogeny.” The discussion in tive CheckPoint activity, CheckPoint: Critical Night Length, helps
Concept 26.6 has been updated to reflect current hypotheses about students work through common confusion around the concept of
early branching of the tree of life and the concept of domains. Other critical night length in flowering plants and its related terminol-
revisions throughout Unit 5 including updating phylogeny and ogy (short-day/long-day plants).
, x Highlights of New Content
Unit 7 Animal Form and Function autoimmune disease, nervous system diseases, and cardiovascular
disease, and providing updated statistics regarding global hunger,
The major focus of this revision in Unit 7 was to help students use infectious diseases (Figure 43.25), sexually transmitted infections,
basic scientific principles to understand the many aspects of ani- infertility, and opioid use.
mal form and function. In particular, we refined our explanation We have also augmented our coverage of non-human
of homeostasis as an underlying theme. A new figure (Figure 40.9) physiology, including adding information about the circulatory
provides an overview of negative and positive feedback in relation system of sea spiders (Chapter 42), refining our explanation of
to stimuli and responses, and another new figure (Figure 40.8B) avian ventilation (Chapter 42), and updating and expanding the
completes the picture by incorporating the concepts of set points, coverage of digestive function in avians, ruminants, and non-
sensors, control centers, and effectors. ruminant herbivores (Chapter 41). In Chapter 45, we removed the
description of calcitonin actions in humans and instead discuss the
evolution of the calcitonin gene family.
Figure 40.9 Overview of negative and positive feedback.
Unit 8 Ecology
The two major goals of the Unit 8 revision were to clarify and accu-
rately represent all types of environments (terrestrial, freshwater,
and marine); and provide new examples while incorporating ele-
ments of conservation biology throughout the unit. Revisions in
Chapter 52 include a new figure (Figure 52.8) and corresponding
text that highlights the ways in which various abiotic factors can
limit range shifts, as well as two new figures and a better descrip-
tion of the processes that bring nutrients to the photic zone in
Narrative explanations and figures presenting homeostatic aquatic environments. In Chapter 53, a new figure (Figure 53.9) and
systems throughout the unit have been revised so that students can annotations clarify the difference between the realized per capita
more readily apply the basic principle to develop mechanistic population growth rate (rrealized) and maximum per capita popula-
explanations for physiological situations. These changes are tion growth rate (rmax). Another new figure (Figure 53.24) illustrates
particularly evident in Chapter 40 (thermoregulation), 41 (blood the concept of the ecological footprint. Chapter 54 features a newly
glucose), 42 (blood pressure, blood gas levels), and 44 (blood pressure, revised figure (54.21) illustrating how the abundance of organisms
volume, and osmolarity). We also apply these principles to the at different trophic levels can be affected by bottom-up or top-down
discussion of hormone feedback loops in Chapters 45 and 46. control, a new figure (Figure 54.25) on contrasting models of suc-
Numerous learning tools have been designed to address common cession, and updates on emerging diseases, with COVID-19 as one
misconceptions and help students apply the concept of homeostasis. example. Revisions to some figures in Chapter 55 provide clearer
For instance, Chapter 40 features a new CheckPoint interactive activity descriptions of nutrient cycling in aquatic ecosystems. Chapter 56
to diagnose and remediate common student misunderstandings about opens with a photo of the colorful Union Island gecko, with a figure
regulators and conformers, and students are given multiple legend that highlights the role that local communities can play in
opportunities to work with feedback loops (for example, the Study Tip conservation success. This chapter includes new text and figures
in Chapter 40, Draw It Question in Figure 40.8, and Test your (Figures 56.25 and 56.26) in Concept 56.4 on the growing problem of
Understanding Question 8 in the Chapter 42 Review). The scientific plastic and microplastic waste in aquatic and terrestrial ecosystems.
principle of flow down gradients also receives greater emphasis in the Concept 56.4 has updated data on atmospheric CO2 concentrations,
Thirteenth Edition. Gradients are introduced in the context of heat global temperatures, and consequences of climate change on eco-
flow (Chapter 40), and subsequently provide the basis for explaining systems. Throughout the unit, we added new examples and photo-
water and solute flow (Chapter 44) and electrical signaling (Chapter graphs of diverse species, such as species on the verge of extinction
48). New interactive CheckPoint activities encourage students to use and introduced species in a range of habitats.
gradients to understand Ventilation and Respiration (Chapter 42) and
the Membrane Potential (Chapter 48). Figure 53.9 Population growth predicted by the exponential and
The Unit 7 revision also introduces new material and updates. logistic models.
For instance, Chapter 43 provides information about the COVID-19
pandemic and a new figure (Figure 43.18) explaining how mRNA
vaccines interact with the immune system, and updates coverage
of relevant topics (sepsis, cytokines, interferons, monoclonal
antibody treatments). Chapter 50 now introduces newly identified
receptors for touch and sour tastants. We also updated our
coverage of malnourishment to include both overnourishment and
undernourishment (Chapter 41), and refined our explanation of
stress to highlight that stress is a physiological response to mental
or physical challenges (Chapter 45). The clinical information has
been updated throughout the Unit, such as describing new
treatments for diabetes mellitus, overnourishment, cancer,
This section highlights selected new content in Campbell Biology,
Thirteenth Edition.
Unit 3 Genetics
Chapters 13–17 incorporate changes that help students grasp the
Unit 1 The Chemistry of Life more abstract concepts of genetics as well as recognize their cur-
rent relevance. In Chapter 14, the term phenotypic plasticity has
In Unit 1, new content engages students by showing why understand- been added and defined, and the discussion of sickle-cell disease
ing chemistry is relevant and important as a basis for learning biology. (SCD) has been revised to clarify its occurrence wherever malaria
For example, Chapter 3 has information on discoveries of exoplanets is endemic, not just in Africa. Also, new gene therapy-based treat-
as well as a 2024 study on the presence and location of water on Mars, ments for SCD are described. In Chapter 15, the contribution of
including a new photo in Figure 3.10. Building on this, Chapter 4 now Dr. Nettie Stevens to understanding the role of the Y chromosome
includes the search by the Mars Rover for samples to be analyzed for in sex determination has been added, along with FDA-approved
fossils. In Chapter 5, the text has been updated on the breakthroughs gene therapies for Duchenne muscular dystrophy and certain
achieved by use of computational approaches to predict 3D protein hemophilia cases. Coverage of imprinted genes has also been
structure, including the role of artificial intelligence (AI) and the updated with recent research on two male-parent embryos, and
related 2024 Nobel Prize in Chemistry. The definition of bioinformatics the discussion of human “three-parent” babies has been enhanced.
has been revised to include AI. In Chapter 16, a new interactive CheckPoint activity entitled
CheckPoint: Leading and Lagging Strand Synthesis has been
Unit 2 The Cell inserted to aid students with this difficult topic. Chapter 17
now includes a new CheckPoint activity entitled CheckPoint:
Our main goal for this unit was to make the material more exciting to Transcription and Translation. Content has also been added about
students, to show that cell biology research is dynamic and ongoing. a novel use of the CRISPR system in conjunction with a technique
Chapter 6 includes recent changes in thinking on the role of mitochon- called base editing, as well as mention of new forms of Cas proteins
dria: In addition to being the “powerhouse of the cell” and produc- that minimize “off-target” gene editing.
ing ATP, they have many further functions, including biosynthesis, Chapters 18–21 are extensively updated, driven by exciting new
regulation of apoptosis, and extensive engagement in intracellular and discoveries based on gene-editing technology and use of artificial
extracellular signaling. Chapter 7 includes an update on the discovery intelligence (AI). In Chapter 18, updates have been made to the
of a second co-receptor for HIV called CXCR4. Chapter 11 mentions discussions of master regulatory gene function and colon cancer, as
AlphaFold2, an AI system that predicts 3D protein structures, in the well as nuclear architecture and its possible role in neuropsychiatric
context of why it has been challenging to predict the structure of disorders. In Chapter 19, the topic of emerging viral diseases has
G-protein-coupled receptors (GPCRs). Also included is the recent dis- been updated extensively to discuss SARS-CoV-2 and the COVID-19
covery that a defect in a particular voltage-gated ion channel can cause pandemic. Other Chapter 19 updates include information on vaccine
muscle weakness or stiffness, or even temporary paralysis. Chapter 12 programs, the 2025 measles epidemic, new prevention and treatment
includes a new interactive CheckPoint activity entitled CheckPoint: approaches for HIV infection, and the H5N1 avian influenza
Counting Chromosomes, and coverage of the G1 checkpoint has been epidemic. Chapter 20 introduces new subsections on cell and tissue
updated with new research from 2023, concluding that a subset of culture (including a new figure on organoids), small-molecule drugs,
cells may require ongoing signals to continue progressing through S biologic drugs, and biomaterials for drug delivery. Other updates
and G2. This finding has implications for potential cancer treatments. include discussions of the cloning of human/macaque chimeric
embryos and the associated ethical issues, FDA-approved
CRISPR-based gene therapies for sickle-cell disease, and
establishment of the Human Genome Editing Registry. The coverage
of using DNA technology for environmental cleanup now includes
the term bioremediation. Chapter 21 has a new section, “Application
of artificial intelligence and machine learning to bioinformatics,”
which describes multiple examples of how AI is transforming the
field of bioinformatics. Artificial intelligence has been added as a
key term and defined, as well as a new Figure 21.5 (see next page)
featuring the use of AI in medical diagnosis. Other updates include
results of the ENCODE project and the Cancer Genome Atlas Project,
establishment of the Impact of Genomic Variants on Function
program, a massive international study of primate genomes, and
new information on the FOXP2 gene. Discussions of genome
comparisons have been revised to reflect new thinking about the
relationship of Bacteria, Archaea, and Eukarya.
viii
, Highlights of New Content ix
taxonomy to reflect recent changes, largely based on phylogenomic
Figure 21.5 Example of use of artificial intelligence (AI) in research. The title of Chapter 28 has been updated from “Protists”
medical diagnosis.
to “Origin and Diversification of Eukaryotes” to better reflect its
focus. Chapter 27 discusses current hypotheses of archaeal phylog-
eny, including the possible origin of eukaryotes within the Asgard
archaea. In Chapter 28, a new section on reproductive diversity of
eukaryotes in Concept 28.1 reviews the three types of life cycles
found in sexually reproducing eukaryotes. The phylogenetic tree of
major groups of eukaryotes was updated to indicate that excavates
are likely not a monophyletic group, and to update the placement
of cryptophytes and haptophytes. Concept 28.5 discusses recent dis-
coveries in phylogenomic research and describes some of the latest
eukaryotic supergroups to be described. In Chapter 32 and 33, the
phylogenetic tree of animal was updated to present the ctenophores,
sponges, and other animals as a polytomy while resolving some
of the polytomies that were shown in the previous edition. A new
figure (Figure 33.4) and text in Concept 33.1 describe ctenophores.
Chapter 34 was updated with new information about phylogenetic
Unit 4 Mechanisms of Evolution relationships between various groups of hominins, and a new Figure
34.47 presents a phylogenetic tree of hominins.
In Chapter 23, the presentation of the Hardy-Weinberg model and
Hardy-Weinberg equilibrium was revised to illustrate that, in a simpli- Figure 33.4 Anatomy of a sea gooseberry (Pleurobrachia spp.),
fied situation, an allele does not increase or decrease in frequency on a ctenophore.
its own. Two new figures help students visualize how the equation
projects the next generation. By starting with the fundamental con-
cept of allele frequency, we aim to assist students in bridging the gap
between individual- and population-level thinking. The assumptions
of the Hardy-Weinberg model are then discussed as mechanisms of
change that may operate alone or together in a natural population.
The Scientific Skills Exercise and Concept Check 21.2 Question 3 have
been revised to compare frequencies across generations.
Unit 5 The Evolutionary History Unit 6 Plant Form and Function
of Biological Diversity In Chapter 35, the term “prop root” has been replaced with the
more precise term “brace root,” and vascular rays are now more
In Chapter 26, Concepts 26.2 and 26.3 have been reorganized to accurately portrayed. Also, an additional benefit of compound
emphasize the distinction between inferring (that is, determining) a leaves, namely better light penetration through the canopy, is
phylogeny from reading/interpreting a phylogeny—namely, clarify- now mentioned as a possible advantage of compound leaf forms.
ing that we do not both infer a tree’s topology and interpret patterns In Chapter 37, the Scientific Skills Exercise includes a new pho-
of trait evolution based on the same data. Phylogenies are inferred tograph of raspberry plants that better shows the characteristics
from one type of data (for example, molecular genetic sequences) of iron deficiency. Figure 37.15 has been updated to include new
and then used to understand the evolution of other traits (for exam- research indicating that staghorn ferns can grow as colonial
ple, vertebral column, amnion, and hair), as discussed in the section assemblages (“superorganisms”). In Chapter 38, a new interac-
now titled “Mapping Characters on a Phylogeny.” The discussion in tive CheckPoint activity, CheckPoint: Critical Night Length, helps
Concept 26.6 has been updated to reflect current hypotheses about students work through common confusion around the concept of
early branching of the tree of life and the concept of domains. Other critical night length in flowering plants and its related terminol-
revisions throughout Unit 5 including updating phylogeny and ogy (short-day/long-day plants).
, x Highlights of New Content
Unit 7 Animal Form and Function autoimmune disease, nervous system diseases, and cardiovascular
disease, and providing updated statistics regarding global hunger,
The major focus of this revision in Unit 7 was to help students use infectious diseases (Figure 43.25), sexually transmitted infections,
basic scientific principles to understand the many aspects of ani- infertility, and opioid use.
mal form and function. In particular, we refined our explanation We have also augmented our coverage of non-human
of homeostasis as an underlying theme. A new figure (Figure 40.9) physiology, including adding information about the circulatory
provides an overview of negative and positive feedback in relation system of sea spiders (Chapter 42), refining our explanation of
to stimuli and responses, and another new figure (Figure 40.8B) avian ventilation (Chapter 42), and updating and expanding the
completes the picture by incorporating the concepts of set points, coverage of digestive function in avians, ruminants, and non-
sensors, control centers, and effectors. ruminant herbivores (Chapter 41). In Chapter 45, we removed the
description of calcitonin actions in humans and instead discuss the
evolution of the calcitonin gene family.
Figure 40.9 Overview of negative and positive feedback.
Unit 8 Ecology
The two major goals of the Unit 8 revision were to clarify and accu-
rately represent all types of environments (terrestrial, freshwater,
and marine); and provide new examples while incorporating ele-
ments of conservation biology throughout the unit. Revisions in
Chapter 52 include a new figure (Figure 52.8) and corresponding
text that highlights the ways in which various abiotic factors can
limit range shifts, as well as two new figures and a better descrip-
tion of the processes that bring nutrients to the photic zone in
Narrative explanations and figures presenting homeostatic aquatic environments. In Chapter 53, a new figure (Figure 53.9) and
systems throughout the unit have been revised so that students can annotations clarify the difference between the realized per capita
more readily apply the basic principle to develop mechanistic population growth rate (rrealized) and maximum per capita popula-
explanations for physiological situations. These changes are tion growth rate (rmax). Another new figure (Figure 53.24) illustrates
particularly evident in Chapter 40 (thermoregulation), 41 (blood the concept of the ecological footprint. Chapter 54 features a newly
glucose), 42 (blood pressure, blood gas levels), and 44 (blood pressure, revised figure (54.21) illustrating how the abundance of organisms
volume, and osmolarity). We also apply these principles to the at different trophic levels can be affected by bottom-up or top-down
discussion of hormone feedback loops in Chapters 45 and 46. control, a new figure (Figure 54.25) on contrasting models of suc-
Numerous learning tools have been designed to address common cession, and updates on emerging diseases, with COVID-19 as one
misconceptions and help students apply the concept of homeostasis. example. Revisions to some figures in Chapter 55 provide clearer
For instance, Chapter 40 features a new CheckPoint interactive activity descriptions of nutrient cycling in aquatic ecosystems. Chapter 56
to diagnose and remediate common student misunderstandings about opens with a photo of the colorful Union Island gecko, with a figure
regulators and conformers, and students are given multiple legend that highlights the role that local communities can play in
opportunities to work with feedback loops (for example, the Study Tip conservation success. This chapter includes new text and figures
in Chapter 40, Draw It Question in Figure 40.8, and Test your (Figures 56.25 and 56.26) in Concept 56.4 on the growing problem of
Understanding Question 8 in the Chapter 42 Review). The scientific plastic and microplastic waste in aquatic and terrestrial ecosystems.
principle of flow down gradients also receives greater emphasis in the Concept 56.4 has updated data on atmospheric CO2 concentrations,
Thirteenth Edition. Gradients are introduced in the context of heat global temperatures, and consequences of climate change on eco-
flow (Chapter 40), and subsequently provide the basis for explaining systems. Throughout the unit, we added new examples and photo-
water and solute flow (Chapter 44) and electrical signaling (Chapter graphs of diverse species, such as species on the verge of extinction
48). New interactive CheckPoint activities encourage students to use and introduced species in a range of habitats.
gradients to understand Ventilation and Respiration (Chapter 42) and
the Membrane Potential (Chapter 48). Figure 53.9 Population growth predicted by the exponential and
The Unit 7 revision also introduces new material and updates. logistic models.
For instance, Chapter 43 provides information about the COVID-19
pandemic and a new figure (Figure 43.18) explaining how mRNA
vaccines interact with the immune system, and updates coverage
of relevant topics (sepsis, cytokines, interferons, monoclonal
antibody treatments). Chapter 50 now introduces newly identified
receptors for touch and sour tastants. We also updated our
coverage of malnourishment to include both overnourishment and
undernourishment (Chapter 41), and refined our explanation of
stress to highlight that stress is a physiological response to mental
or physical challenges (Chapter 45). The clinical information has
been updated throughout the Unit, such as describing new
treatments for diabetes mellitus, overnourishment, cancer,
