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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology

Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

BIG IDEA II Biological systems utilize free energy and molecular building blocks

to grow, to reproduce and to maintain dynamic homeostasis.

Enduring Understanding 2.D Growth and dynamic homeostasis of a biological system

are influenced by changes in the system’s environment.

Essential Knowledge 2.D.1 All biological systems from cells and organisms to populations,

communities and ecosystems are affected by complex biotic and abiotic

interactions involving exchange of matter and free energy.


Essential Knowledge 2.D.1: All biological systems from cells and

organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.

• Learning Objectives:

– (2.22) The student is able to refine scientific models and

questions about the effect of complex biotic and abiotic

interactions on all biological systems, from cells and organisms to

populations, communities and ecosystems.

– (2.23) The student is able to design a plan for collecting data to

show that all biological systems (cells, organisms, populations,

communities and ecosystems) are affected by complex biotic and

abiotic interactions.

– (2.24) The student is able to analyze data to identify possible

patterns and relationships between a biotic or abiotic factor and

a biological system (cells, organisms, populations, communities

and ecosystems).


Cell activities are affected by interactions with biotic and abiotic factors.

• Illustrative examples of biotic factors include:

– Cell density

– Biofilms

• Illustrative examples of abiotic factors include:

– Temperature

– Water availability

– Sunlight


Cell Density

• In addition to many internal chemical factors, studies

using animal cells in culture have led to the

identification of many external factors, both chemical

and physical, that can influence cell division and

therefore control cell density.

• Contact cell cycle control mechanisms include density-

dependent inhibition and anchorage dependence.

– In density-dependent inhibition, crowded cells stop dividing.

– Anchorage dependence is a phenomenon in which cells must

be attached to a substratum (i.e. extracellular matrix of a tissue) in

order to divide.

Fig. 12-19

Anchorage dependence

Density-dependent inhibition

Density-dependent inhibition

(a) Normal mammalian cells (b) Cancer cells

25 µm 25 µm


Biofilms

• Metabolic cooperation between different

prokaryotic species often occurs in surface-

coating colonies known as biofilms.

– Cells in a biofilm secrete signaling molecules that

recruit nearby cells, causing the colonies to grow.

– The cells also produce proteins that stick the cells

to the substrate and to one another.

– Channels in the biofilm allow nutrients to reach

cells in the interior and wastes to be expelled.

Fig. 11-3

Individual rod- shaped cells

Spore-forming structure (fruiting body)

Aggregation in process

Fruiting bodies

0.5 mm

1

3

2


Organism activities are affected by interactions with biotic and abiotic factors.


– Symbiosis

– Predator-prey relationships


– Water/nutrient availability

– Temperature

– Salinity

– pH


Symbiosis

• Symbiosis is a relationship where two or more

species live in direct and intimate contact with one

another.

– Parasitism

– Mutualism

– Commensalism

Fig. 54-UN2


Predator-Prey Relationships

Predation is a type of density-dependent population control whereby there

is a biological interaction where a predator (an animal that is hunting)

feeds on its prey (the animal that is attacked).


Fig. 53-19

Wolves Moose

2,500

2,000

1,500

1,000

500

Nu

mb

er

of

mo

os

e

0

Nu

mb

er

of

wo

lve

s

50

40

30

20

10

0 1955 1965 1975 1985 1995 2005

Year


The stability of populations, communities and ecosystems is affected by interactions with biotic and abiotic factors.


– Food chains & food webs

– Species diversity

– Population density

– Algal blooms


– Water & nutrient availability


Food Chains & Food Webs

• Trophic structure is the feeding relationships

between organisms in a community – it is a key

factor in community dynamics.

– Food chains link trophic levels from producers

to top carnivores.

– A food web is a branching food chain with

complex trophic interactions.

Fig. 54-11

Carnivore

Carnivore

Carnivore

Herbivore

Plant

A terrestrial food chain

Quaternary consumers

Tertiary consumers

Secondary consumers

Primary consumers

Primary producers

A marine food chain

Phytoplankton

Zooplankton

Carnivore

Carnivore

Carnivore

Fig. 54-12

Humans

Smaller toothed whales

Baleen whales

Sperm whales

Elephant seals

Leopard seals

Crab-eater seals

Birds Fishes Squids

Carnivorous plankton

Copepods Euphausids (krill)

Phyto- plankton


Limits on Food Chain Length

• Each food chain in a food web is usually only a

few links long

• Two hypotheses attempt to explain food chain

length: the energetic hypothesis and the dynamic

stability hypothesis

– The energetic hypothesis suggests that length is

limited by inefficient energy transfer

– The dynamic stability hypothesis proposes that long

food chains are less stable than short ones

– Most data support the energetic hypothesis


Limits on Food Chain Length: Energetic Hypothesis


Limits on Food Chain Length: Dynamic Stability Hypothesis


Species Diversity

• Species diversity of a community is the variety of organisms that make up the community

• It has two components: species richness and relative abundance

– Species richness is the total number of different species in the community

– Relative abundance is the proportion each species represents of the total individuals in the community


Fig. 54-9

Community 1 A: 25% B: 25% C: 25% D: 25%

Community 2 A: 80% B: 5% C: 5% D: 10%

A B C D


Species Diversity & Ecosystem Stability

• There is growing evidence that the functioning of ecosystems is linked

to biodiversity. Species play essential roles in ecosystems, so local

and global species losses could threaten the stability of the ecosystem.

• There is currently great concern about the stability of both natural and

human-managed ecosystems, particularly given the myriad global

changes already occurring.

• Stability can be defined in several ways, but the most intuitive definition

of a stable system is one having low variability (i.e., little deviation from

its average state) despite shifting environmental conditions.

• Resilience is a somewhat different aspect of stability indicating the

ability of an ecosystem to return to its original state following a

disturbance or other perturbation.

• Diverse ecosystems are more likely to return to a state of stability

following a disturbance than less diverse systems.


Population Density


Algal Blooms

//upload.wikimedia.org/wikipedia/commons/7/74/River_algae_Sichuan.jpg



Biology

Eighth Edition





Enduring Understanding 2.D

Growth and dynamic homeostasis of a biological system


Essential Knowledge 2.D.2

Homeostatic mechanisms reflect both common ancestry and

divergence due to adaptation in different environments.


Essential Knowledge 2.D.2: Homeostatic mechanisms reflect both

common ancestry and divergence due to adaptation in different environments.


– (2.25) The student can construct explanations based on

scientific evidence that homeostatic mechanisms reflect

continuity due to common ancestry and/or divergence due to

adaptation in different environments.

– (2.26) The student is able to analyze data to identify

phylogenetic patterns or relationships, showing that

homeostatic mechanisms reflect both continuity due to

common ancestry and change due to evolution in different

environments.

– (2.27) The student is able to connect differences in the

environment with the evolution of homeostatic mechanisms.


Continuity of homeostatic mechanisms reflects common ancestry, while changes may occur in response to different environmental conditions.

• Structural and functional evidence supports the

relatedness of all domains and the evolution of all

organisms. This evidence can be seen in the following

mechanisms:

– Organisms have various mechanisms for obtaining

nutrients and eliminating wastes (divergence).

– Homeostatic control systems in species of microbes,

plants and animals support common ancestry

(relatedness).


Organisms have various mechanisms for obtaining nutrients and eliminating wastes.

• Illustrative examples include:

– Gas exchange in aquatic and terrestrial plants.

– Digestive mechanisms in animals such as food

vacuoles, gastrovascular cavities, one-way

digestive systems.

– Respiratory systems of aquatic and terrestrial

animals.

– Nitrogenous waste production and elimination

in aquatic and terrestrial animals.


Gas Exchange in Aquatic v. Terrestrial Plants

In aquatic plants, diffusion of O2 &

CO2 occurs across thin membranes

in leaves of aquatic plants.

In terrestrial plants, guard cells

control the opening and closing of

stomata in terrestrial plants.


Osmoregulation and Excretion

• Osmoregulation is the process by which animals

control solute concentrations and balance water

gain and loss.

– It is based largely on controlled movement of solutes

between internal fluids and the external environment.

• Excretion gets rid of metabolic wastes.

– Most metabolic wastes must be excreted from the

body. One of the most important types is nitrogenous

wastes from the breakdown of proteins and nucleic

acids.


Proteins Nucleic acids

Amino acids Nitrogenous bases

–NH2

Amino groups

Most aquatic

animals, including

most bony fishes

Mammals, most

amphibians, sharks,

some bony fishes

Many reptiles

(including

birds), insects,

land snails

Ammonia Urea Uric acid

NH3 NH2

NH2 O C

C

C N

C O N

H H

C O

N C

HN

O H

Nitrogenous Waste Production & Elimination in Aquatic v. Terrestrial Animals

• An animal’s nitrogenous wastes

reflect its phylogeny and habitat.

• The type and quantity of an

animal’s waste products may

have a large impact on its water

balance.

• Among the most important

wastes are the nitrogenous

breakdown products of proteins

and nucleic acids.

Figure 44.8


Forms of Nitrogenous Wastes

• Animals that excrete nitrogenous wastes as ammonia need

access to lots of water:

– Ammonia is released across the whole body surface or through

the gills.

• The liver of mammals and most adult amphibians converts

ammonia to less toxic urea which is carried to the kidneys

in a concentrated form:

– Urea is excreted with a minimal loss of water.

• Insects, land snails, and many reptiles, including birds

excrete uric acid as their major nitrogenous waste:

– Uric acid is largely insoluble in water and can be secreted as a

paste with little water loss.


Homeostatic control systems in species of microbes, plants and animals support common ancestry.

• Illustrative examples include:

– Excretory systems in flatworms, earthworms and

vertebrates.

– Osmoregulation in bacteria, fish and protists.

– Osmoregulation in aquatic and terrestrial plants.

– Circulatory systems in fish, amphibians and mammals.

– Thermoregulation in aquatic and terrestrial animals

(countercurrent exchange mechanisms).


Excretory Systems in Flatworms, Earthworms and Vertebrates


Nucleus

of cap cell

Cilia

Interstitial fluid

filters through

membrane where

cap cell and tubule

cell interdigitate

(interlock)

Tubule cell

Flame

bulb

Nephridiopore

in body wall

Tubule

Protonephridia

(tubules)

Protonephridia: Flame-Bulb Systems in Flatworms

• The protonephridia of flatworms form a network of dead-end tubules connected to external openings. These tubules branch throughout the body.

• Specialized cells called flame bulbs containing cilia cap the branches of each protonephridium.

• During filtration, beating of the cilia draws water and solutes from the interstitial fluid through the flame bulb, releasing filtrate into the tubule network.

• The urine excreted by freshwater flatworms has a low solute concentration, helping to balance osmotic uptake of water from the environment.

Figure 44.10


Metanephridia in Earthworms

• Most annelids have metanephridia,

excretory organs that open internally

to the coelom and are enveloped by a

capillary network.

• As the cilia beat, fluid is drawn into a

collecting tubule, which includes a

storage bladder that opens to the outside.

• The metanephridia of an earthworm have

both excretory and osmoregulatory

functions.

• Earthworms inhabit damp soil and

usually experience a net uptake of

water by osmosis through their skin.

• Their metanephridia balance the water

influx by producing urine that is dilute

(hypoosmotic to body fluids).

Figure 44.11

Nephrostome Metanephridia

Nephridio-

pore

Collecting

tubule

Bladder

Capillary

network

Coelom


Vertebrate Kidneys

• Kidneys are the excretory organs of vertebrates –

they function in both excretion and

osmoregulation.

• Nephrons and associated blood vessels are the

functional unit of the mammalian kidney.

• The mammalian excretory system centers on

paired kidneys which are also the principal site of

water balance and salt regulation.


Proximal tubule

Filtrate

H2O

Salts (NaCl and others)

HCO3–

H+

Urea

Glucose; amino acids

Some drugs

Key

Active transport

Passive transport

CORTEX

OUTER

MEDULLA

INNER

MEDULLA

Descending limb

of loop of

Henle

Thick segment

of ascending

limb

Thin segment

of ascending

limb

Collecting

duct

NaCl

NaCl

NaCl

Distal tubule

NaCl Nutrients

Urea

H2O

NaCl

H2O H2O HCO3

K+

H+ NH3

HCO3

K+ H+

H2O

1 4

3 2

3 5

From Blood Filtrate to Urine: A Closer Look

• Filtrate becomes urine as it flows through the mammalian nephron and

collecting duct – there are 5 main steps in the transformation of blood filtrate to

urine.

Figure 44.14


Adaptations of the Vertebrate Kidney to Diverse Environments

• Vertebrate animals occupy a wide variety of habitats, and variations in

nephron structure and function equip the kidneys of different

vertebrates for osmoregulation in their various habitats.

– Desert Mammals: nephron structure allows them to rid the body

of slats and nitrogenous wastes without squandering water

(secrete hyperosmotic/highly concentrated urine).

– Aquatic Mammals: have a much lower ability to concentrate

urine because dehydration is not a challenge.

– Birds & Reptiles: nephrons specialized for conserving water so

urine is generally highly concentrated.

– Freshwater Fishes/Amphibians: secrete large amounts of very

dilute urine to excrete excess water continuously.

– Marine Fishes: filtration rates are low and very little urine is

excreted.


Circulatory Systems in Fish, Amphibians and Mammals

FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillaries Lung and skin capillaries Gill capillaries

Right Left Right Left Right Left

Systemic

circuit Systemic

circuit

Pulmocutaneous

circuit

Pulmonary

circuit Pulmonary

circuit

Systemic

circulation Vein

Atrium (A)

Heart:

ventricle (V)

Artery Gill

circulation

A

V V V V V

A A A A A Left

Systemic

aorta

Right

systemic

aorta

Figure 42.4


Thermoregulation in Aquatic & Terrestrial Animals

• Thermoregulation is the process by which animals

maintain an internal temperature within a tolerable

range.

• Each animal species has an optimal temperature

range, and thermoregulation helps keep body

temperature within that optimal range.

– Endotherms: warmed mostly by heat

generated by metabolism.

– Ectotherms: gain most of their heat from

external sources.


Variation in Body Temperature

• Animals can have either a variable or a constant

body temperature.

– Poikilotherm: an animal whose body

temperature varies with its environment.

– Homeotherm: an animal with a relatively

constant body temperature.

– Note: the terms “cold-blooded” and “warm-

blooded” are misleading and have been

dropped from the scientific vocabulary!


Balancing Heat Loss and Gain


Balancing Heat Loss & Gain

• Integumentary System: skin, hair, and nails all provide

mechanisms to prevent heat loss and/or gain.

• Insulation: reduces flow of heat between animals and

their environment.

• Evaporative Heat Loss: water absorbs considerable

heat when it evaporates; this heat is carried away from

the body surface with the water vapor.

• Behavioral Responses: sun basking, huddling, fanning

wings, etc.


Countercurrent Heat Exchangers


Control of Body Temperature – Negative Feedback



Biology

Eighth Edition









Biological systems are affected by

disruptions to their dynamic homeostasis.


Essential Knowledge 2.D.3: Biological systems are affected by disruptions to their dynamic homeostasis.


– (2.28) The student is able to use representations

or models to analyze quantitatively and

qualitatively the effects of disruptions to dynamic

homeostasis in biological systems.


Disruptions at the molecular and cellular levels affect the health of the organism.

• Illustrative Example: dehydration/desiccation.

– Dehydration is the excessive loss of body water, with an accompanying disruption

of metabolic processes. Extreme dehydration, or desiccation, is fatal for most

animals.

– Symptoms may include headaches, decreased blood pressure, and dizziness or

fainting when standing up due to orthostatic hypotension. Untreated dehydration

generally results in delirium, unconsciousness, swelling of the tongue and, in

extreme cases, death.

– The symptoms become increasingly severe with greater water loss. One's heart

and respiration rates begin to increase to compensate for decreased plasma

volume and blood pressure, while body temperature may rise because of

decreased sweating.

– At around 5% to 6% water loss, one may become groggy or sleepy, experience

headaches or nausea, and may feel tingling in one's limbs.

– With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and

wrinkle (decreased skin turgor), vision may dim, urination will be greatly reduced

and may become painful, and delirium may begin. Losses greater than 15% are

usually fatal.


Disruptions to ecosystems impact the dynamic homeostasis or balance of the ecosystem.

• Illustrative Example: invasive species.


Disruptions to ecosystems impact the dynamic homeostasis or balance of the ecosystem.

• Illustrative Example: human impact.

– As the human population has grown, our activities

have disrupted the trophic structure, energy flow, and

chemical cycling of many ecosystems.

– In addition to transporting nutrients from one location

to another, humans have added new materials, some

of them toxins, to ecosystems.

– Disruptions that deplete nutrients in one area and

increase them in other areas can be detrimental to

ecosystem dynamics.


Fig. 55-17: Agriculture & Nitrogen Cycling


Fig. 55-18 – Contamination of Aquatic Ecosystems

Winter Summer


Acid Precipitation


Toxins in the Environment

• Humans release many toxic chemicals, including synthetics previously unknown to nature

• In some cases, harmful substances persist for long periods in an ecosystem

• One reason toxins are harmful is that they become more concentrated in successive trophic levels

• Biological magnification concentrates toxins at higher trophic levels, where biomass is lower

Fig. 55-20

Lake trout 4.83 ppm

Herring gull eggs 124 ppm

Smelt 1.04 ppm

Phytoplankton 0.025 ppm

Zooplankton 0.123 ppm


Greenhouse Gases and Global Warming

Ozo

ne layer

thic

kn

ess (

Do

bso

ns)

Fig. 55-23

Year

’05 2000 ’95 ’90 ’85 ’80 ’75 ’70 ’65 ’60 1955 0

100

250

200

300

350

Fig. 55-24

O2

Sunlight

Cl2O2

Chlorine

Chlorine atom

O3

O2

ClO

ClO

Fig. 55-25

(a) September 1979 (b) September 2006



Biology

Eighth Edition









Plants and animals have a variety of chemical defenses

against infections that affect dynamic homeostasis.


Essential Knowledge 2.D.4: Plants and animals have a variety

of chemical defenses against infections that affect dynamic homeostasis.


– (2.29) The student can create representations

and models to describe immune responses.

– (2.30) The student can create representations or

models to describe nonspecific immune defenses

in plants and animals.


Plants, invertebrates and vertebrates have multiple, nonspecific immune responses.

• A nonspecific immune response is a nonspecific

prevention of the entrance of invaders to the body.

– Plant defenses against pathogens include molecular

recognition systems with systemic responses; infection

triggers chemical responses that destroy infected and adjacent

cells, thus localizing the effects.

– Invertebrate immune systems have nonspecific response

mechanisms, but the lack pathogen-specific defense responses.

– Vertebrate immune systems have nonspecific and

nonheritable defense mechanisms against pathogens, but they

also have specific immune responses.


Chemical Defenses in Plants

• Plants have a variety of chemical defenses against infections

that affect dynamic homeostasis – these are examples of

nonspecific immune responses.

– Plant defenses against pathogens include molecular recognition

systems with systemic responses;

– Infection triggers chemical responses that destroy infected and

adjacent cells, thus localizing the effects.

• Chemical defenses in plant cells are an illustration of how cells

communicate with each other through direct contact with other

cells (via plasmodesmata).

• In plants, cells communicate over short distances by using local

regulators (chemicals) that target cells in the vicinity of the

emitting cell.


Defense Response Against Pathogen in Plants


Plant Defenses Against Herbivores


Innate/Nonspecific Immunity of Invertebrates

• In insects, an exoskeleton made of chitin forms

the first barrier to pathogens.

• The digestive system is protected by low pH

and lysozyme, an enzyme that digests

microbial cell walls.

• Hemocytes (special cells) circulate within

hemolymph (insect blood-like substance) and

carry out phagocytosis, the ingestion and

digestion of foreign substances including

bacteria.


Phagocytosis by an Invertebrate Hemocytic Cell


Mammals use specific immune responses triggered by natural or artificial agents that disrupt homeostasis.

• Animals are constantly under attack by pathogens,

infectious agents that cause disease.

• Dedicated immune cells patrol the body fluids,

searching out and destroying foreign cells. These

defenses make up an immune system.

• Most animal immune systems use receptors that

specifically bind molecules from foreign cells or

viruses (cellular communication).

• There are two general strategies for such molecular

recognition: innate immunity and acquired

immunity.

Fig. 43-2

INNATE IMMUNITY

Recognition of traits shared by broad ranges of pathogens, using a small set of receptors

•

• Rapid response

• Recognition of traits specific to particular pathogens, using a vast array of receptors

• Slower response

ACQUIRED IMMUNITY

Pathogens (microorganisms

and viruses)

Barrier defenses: Skin Mucous membranes Secretions

Internal defenses: Phagocytic cells Antimicrobial proteins Inflammatory response Natural killer cells

Humoral response: Antibodies defend against infection in body fluids.

Cell-mediated response: Cytotoxic lymphocytes defend against infection in body cells.


Innate/Nonspecific Immunity: Barrier Defenses

• Barrier defenses include the skin and mucous

membranes of the respiratory, urinary, and

reproductive tracts:

– Mucus traps and allows for the removal of

microbes.

– Many body fluids including saliva, mucus, and

tears are hostile to microbes because they

contain lysozyme.

– The low pH of skin and the digestive system

prevents growth of microbes.


Cellular Innate Defenses

• Cellular innate defenses combat pathogens that get through the skin.

They include phagocytic white blood cells and antimicrobial proteins.

– The nonspecific cellular defense of vertebrates is headed up by cells

called phagocytes. Macrophages and neutrophils roam the body in

search of bacteria and dead cells to engulf and clear away.

– Phagocytic WBCs recognize microbes using toll-like receptors (TLRs).

– They recognize fragments of molecules characteristic of a particular type

of pathogen…this helps to increase the efficiency of phagocytosis.


Cellular Innate Defenses & Phagocytosis

• Phagocytic cells get some assistance in recognizing

foreign invaders by a protein molecule called

complement.

• About 30 proteins make up the complement system.

• These proteins makes sure that molecules to be cleared

have some sort of identification displaying the need for

phagocyte assistance.

• Complement coats these cells, stimulating phagocytes to

ingest them.

• This is a part of the non-specific immune defense because

the phagocytes are no seeking particular invaders.


Antimicrobial Peptides and Proteins

• Peptides and proteins function in innate defense by attacking microbes directly

or impeding their reproduction.

• For example, interferon proteins provide innate defense against viruses and

help activate macrophages. It does so by causing cells adjacent to an infected

cell to produce substances that inhibit viral replication.


Fig. 43-8-3

Pathogen Splinter

Macrophage

Mast cell

Chemical signals

Capillary

Phagocytic cell Red blood cells

Fluid

Phagocytosis

In local inflammation, histamine and other chemicals released from

injured cells promote changes in blood vessels that allow more fluid, more

phagocytes, and antimicrobial proteins to enter the tissues.

Inflammatory Responses http://www.sumanasinc.com/webcontent/animations/content/inflammatory.html

http://www.sumanasinc.com/webcontent/animations/content/inflammatory.html


Natural Killer Cells & MHC

• Ever wonder how phagocytes and other cells of the immune system avoid

killing all cells?

• All cells in the body (except red blood cells) have a class 1 MHC protein

on their surface.

• MHC molecules are normal cell-surface proteins that are encoded by a family

of genes called the major histocompatibility complex.

• These are a group of genes that slightly differ from one individual to another –

A MAJOR COMPONENT OF “SELF-RECOGNITION”.

• The immune system accepts as “friendly” any cell that has the identical match

for this molecule. Anything with a different MHC is “foreign”.

– Cancerous or infected cells no longer express this protein; and natural killer (NK)

cells attack these damaged cells:

– NKC’s often trigger apoptosis in the cells they attack.

– Apoptosis is programmed cell death brought about by signals that trigger the

activation of a cascade of “suicide” proteins in the cells destined to die.


Mammals use specific immune responses triggered by natural or artificial agents that disrupt dynamic homeostasis.

• The mammalian immune system includes two

types of specific responses: cell mediated and

humoral.

– In the cell-mediated response, cytotoxic T

cells, a type of lymphocytic white blood cell,

“target” intracellular pathogens when antigens

are displayed on the outside of the cells.

– In the humoral response, B cells, a type of

lymphocytic white blood cell, produce

antibodies against specific extracellular

antigens.


B cells and T cells provide pathogen-specific recognition in adaptive immunity.

• Vertebrates have two types of lymphocytes: B

cells (proliferate in bone marrow) and T cells

(mature in the thymus).

• These circulate through the blood and both

recognize particular antigens.

– Antigens are foreign molecules that elicit a response

by lymphocytes. B and T cells recognize them by

specific receptors embedded on their plasma

membranes.

– Antibodies are proteins secreted by B cells during an

immune response.


Antigens and Antibodies

• Antibodies are proteins produced by B cells, and

each antibody is specific to a particular antigen.

• Antigens in the body are recognized by antibodies to

the antigen.


Activation of B and T Cells

• B or T cell activation occurs when an antigen

binds to a B or T cell:

– B cell activation is enhanced by cytokines. When

activated, B cells form 2 types of clones: effector cells

(combat the antigen) and memory cells (recognize

antigen in subsequent infections).

– B cell receptors bind to INTACT antigens.

– T cell receptors bind to antigens that are displayed by

antigen-presenting cells on their MHCs.

– Each B or T cell responds to only ONE antigen.


B Cell Receptors for Antigens

• B cell receptors bind to specific, intact antigens – whether

that antigen is free or on the surface of a pathogen.


T Cell Receptors for Antigens

V V

C C

• T cells bind to small fragments of antigens presented on

the surface of macrophages.


The TWO Branches of Acquired Immunity

• HUMORAL IMMUNE RESPONSE: involves the

activation and cloning of effector B cells, which

produce antibodies that circulate in the blood.

• CELL-MEDIATED IMMUNE RESPONSE: involves

the activation and clonal selection of cytotoxic T

cells, which identify and destroy infected cells.

• NOTE: Helper T cells aid in BOTH responses –

when activated with the Class II MHC molecules of

an antigen-presenting cell, they secrete cytokines

that stimulate and activate both B cells and

cytotoxic T cells.


Class I and Class II MHC Molecules are Different


Antigen Presentation by Cells

Participants in the Acquired Immune Response http://bcs.whfreeman.com/thelifewire/content/chp18/1802004.html (humoral response)

http://bcs.whfreeman.com/thelifewire/content/chp18/1802003.html (cell-mediated response)

Figure 43.14

Humoral immune response Cell-mediated immune response

First exposure to antigen

Intact antigens Antigens engulfed and

displayed by dendritic cells

Antigens displayed

by infected cells

Activate Activate Activate

Gives rise to Gives rise to Gives rise to

B cell Helper

T cell Cytotoxic

T cell

Plasma

cells

Memory

B cells

Active and

memory

helper

T cells

Memory

cytotoxic

T cells

Active

cytotoxic

T cells

Secrete antibodies that defend against

pathogens and toxins in extracellular fluid

Defend against infected cells, cancer

cells, and transplanted tissues

Secreted

cytokines

activate


Helper T Cells: A Response to Nearly All Antigens

Figure 43.15

After a dendritic cell engulfs and degrades a bacterium, it displays

bacterial antigen fragments along with a class II MHC molecule on the cell’s surface. A specific helper T cell binds

to the displayed complex. This interaction promotes secretion of cytokines by the dendritic cell.

Proliferation of the T cell, stimulated

by cytokines from both the dendritic

cell and the T cell itself, gives rise to

a clone of activated helper T cells

(not shown), all with receptors for the

same MHC–antigen complex.

The cells in this clone

secrete other cytokines

that help activate B cells

and cytotoxic T cells.

Cell-mediated

immunity

(attack on

infected cells)

Humoral

immunity

(secretion of

antibodies by

plasma cells)

Dendritic

cell

Dendritic

cell

Bacterium

Peptide antigen

Class II MHC

molecule

TCR

CD4

Helper T cell

Cytokines

Cytotoxic T cell

B cell

1

2 3

1

2 3

B Cells: A Response to Extracellular Pathogens

2

1 3

B cell

Bacterium

Peptide

antigen

Class II

MHC

molecule

TCR

Helper T cell

CD4

Activated

helper T cell Clone of memory

B cells

Cytokines

Clone of plasma cells Secreted antibody

molecules

Endoplasmic

reticulum of

plasma cell

Macrophage

After a macrophage engulfs and degrades

a bacterium, it displays a peptide antigen

complexed with a class II MHC molecule.

A helper T cell that recognizes the displayed

complex is activated with the aid of cytokines

secreted from the macrophage, forming a

clone of activated helper T cells (not shown).

1 A B cell that has taken up and degraded the

same bacterium displays class II MHC–peptide

antigen complexes. An activated helper T cell

bearing receptors specific for the displayed

antigen binds to the B cell. This interaction,

with the aid of cytokines from the T cell,

activates the B cell.

2 The activated B cell proliferates

and differentiates into memory

B cells and antibody-secreting

plasma cells. The secreted

antibodies are specific for the

same bacterial antigen that

initiated the response.

3

Figure 43.17


Cytotoxic T cell

Perforin

Granzymes

CD8 TCR

Class I MHC

molecule

Target

cell Peptide

antigen

Pore

Released

cytotoxic

T cell

Apoptotic

target cell

Cancer

cell

Cytotoxic

T cell

A specific cytotoxic T cell binds to a

class I MHC–antigen complex on a

Target cell. This interaction, along with

cytokines from helper T cells, leads to

the activation of the cytotoxic cell.

1 The activated T cell releases perforin

molecules, which form pores in the

target cell membrane, and other enzymes),

which enter the target cell by endocytosis.

2 The granzymes initiate apoptosis within the

target cells, leading to fragmentation of the

nucleus, release of small apoptotic bodies,

and eventual cell death. The released

cytotoxic T cell can attack other target cells.

3

1

2

3

Figure 43.16

Cytotoxic T Cells: A Response to Infected Cells and Cancer Cells


Primary and Secondary Immune Response http://www.professorcrista.com/files/animations/posted_animations/humoral_secondary.html

Antibody c

oncentr

ation

(arb

itra

ry u

nits)

104

103

102

101

100

0 7 14 21 28 35 42 49 56

Time (days) Figure 43.13

Antibodies

to A Antibodies

to B

Primary

response to

antigen A

produces anti-

bodies to A

2 Day 1: First

exposure to

antigen A

1 Day 28:

Second exposure

to antigen A; first

exposure to

antigen B

3 Secondary response to anti-

gen A produces antibodies

to A; primary response to anti-

gen B produces antibodies to B

4

http://www.professorcrista.com/files/animations/posted_animations/humoral_secondary.html

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