CELLS

Chapter 3

1

Learning Objectives 2

Describe what a cell is and the two general types of cells.

Describe the structure and functions of cell membranes.

Describe several ways in which molecules move across membranes.

Describe how cells are connected and how they communicate with each other.

Describe nine important landmarks in eukaryotic cells.

ALL ORGANISMS ARE MADE OF CELLS

3

What is a Cell?

cell: smallest unit of life that

can function independently

and perform all the

necessary functions of life,

including reproducing itself

4

Cell

A cell is a three-dimensional structure, like a fluid-

filled balloon, in which many of the essential chemical

reactions of life take place.

Nearly all cells contain DNA (deoxyribonucleic acid).

5

Cell 6

Although most cells are too small to see with the

naked eye, there are a few exceptions, including hens’

eggs from the supermarket, each of which is an

individual cell.

The ostrich egg, weighing about three pounds, is

the largest of all cells.

Early Cell Biologists

Van Leeuwenhoek

Hooke

Schleiden

Schwann

Virchow

7

Anton Van Leeuwenhoek

first to microscopically

observe microorganisms

in water

first to see bacteria

8

Robert Hooke

discovered cell in 1655

examined (under a coarse, compound microscope) very thin slices of cork and saw a multitude of tiny pores that he remarked looked like the walled compartments a monk would live in

did not know the real structure or function of a cell

9

What Hooke saw… 10

Illustration from Robert Hooke's

Micrographia, in which he

proposed that living things were

composed of minute structures

called "cells."

Cell Theory

Matthias Schleiden

German botanist

Theodor Schwann

German physiologist

Rudolf Virchow

German pathologist

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Cell Theory

All living things or organisms are made of cells and their products.

Cells are the basic building units of life.

New cells are created by old cells dividing into two.

Schleiden & Schwann

1839

Virchow

1858

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Landmarks in Cell Biology

1595: Jansen (Holland) - 1st compound microscope (>1

lens)

1626: Redi - argue against spontaneous generation

1655: Hooke - ―cells‖ in cork

1674: Leeuwenhoek - protozoans

1833: Brown - cell nucleus

1839: Cell Theory (S & S)

1840: von Roelliker - sperm/egg are also cells

1857: Kolliker - mitochondria

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Landmarks in Cell Biology

1858: Virchow – cells from pre-existing cells

1869: Miescher – DNA

1879: Flemming – chromosome behavior during

mitosis

1898: Golgi – golgi apparatus

1939: 1st TEM

1953: Watson, Crick, Wilkins – DNA double helix

1965: 1st commercial SEM

14

PROKARYOTIC CELLS ARE STRUCTURALLY SIMPLE, BUT THERE ARE MANY TYPES OF

THEM

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Every cell on earth is either…

a eukaryotic cell (from the Greek for

―true nucleus‖)

central control structure called a nucleus

(contains cell’s DNA

organisms composed of eukaryotic cells

are called eukaryotes

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…OR a prokaryote

no nucleus; its DNA simply resides in the middle of the cell

smaller, evolutionarily older, structurally more simple, unicelllular

metabolically diverse. some fuel activities in presence/absence of

oxygen using almost any energy source on earth sulfur in deep sea hydrothermal vents hydrogen sun

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18

Typical Prokaryotes 19

EUKARYOTIC CELLS HAVE COMPARTMENTS WITH

SPECIALIZED FUNCTIONS.

20

Eukaryotes… 21

Eukaryotes…

1.5 billion years after prokaryotes

not all eukaryotes are Protista: nearly all are single-celled

organisms visible only with a microscope

22

Eukaryotic cells have organelles. 23

24

Which feature below is only found in eukaryotic cells?

1. Ribosomes

2. DNA

3. Cell membrane

4. Mitochondria

25

Endosymbiosis Theory

explains presence of two organelles in eukaryotes

chloroplasts (plants/algae)

mitochondria (plants/animals)

2 different types of prokaryotes close

partnerships w/each other

small prokaryotes capable of performing photosynthesis

may have come to live inside a larger ―host‖ prokaryote

photosynthetic ―boarder‖ may have made some of

energy from photosynthesis available to host

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Endosymbiosis Theory

2 cells become more and more dependent on each other until neither cell could live without the other, and they became a single, more complex organism

eventually, photosynthetic prokaryote chloroplast

similarly, prokaryote unusually efficient @ converting food and oxygen easily usable energy might take up residence in another prokaryote mitochondrion

27

Which evidence below supports the theory that

mitochondria and chloroplasts were originally

bacteria?

1. Circular DNA is present in both organelles.

2. Both organelles are larger than other

organelles in the cell.

3. Both organelles are surrounded by a single

lipid bilayer.

4. All of the above.

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CELL MEMBRANES ARE GATEKEEPERS

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All cells are bordered by plasma

membranes 30

Plasma Membranes

lipid bilayer - phospholipids head: glycerol linked to a molecule containing phosphorous polar - has an electrical charge (water is also a polar

molecule and for this reason, other polar molecules mix easily with water.)

hydrophilic (―water loving‖) 2 legs are long chains of carbon and hydrogen atoms. no electrical charge non-polar molecules do not mix with water hydrophobic (―water fearing‖)

hydrophilic head region mixes easily with water, whereas their hydrophobic tail region does not mix with water

31

Plasma Membranes

phospholipid bilayer: in a cell’s plasma membrane, 2 of these sheets of phospholipids are arranged so that the hydrophobic tails are all in contact with each other and the hydrophilic heads are in contact with the watery solution outside and inside the cell

32

33

Molecules within the plasma membrane 34

What determines whether a protein resides on

the surface or extends through the bilayer?

all the amino acids that make up each

protein have side chains that differ from

one another chemically some side chains are hydrophilic

some are hydrophobic

as protein is assembled final shape, side

chains can cause parts of protein to be

attracted to hydrophobic or hydrophilic

regions

35

What determines whether a protein resides on

the surface or extends through the bilayer?

transmembrane protein both hydrophobic and hydrophilic regions

peripheral membrane proteins entirely hydrophilic structure

bind only to head regions of phospholipids

can be positioned on either outer or inner side

of membrane

36

There are four primary types of membrane proteins, each

of which performs a different function.

37

Lipids that make up the cell membrane are

hydrophobic. Hydrophilic molecules, like glucose,

cannot cross this barrier. What major component of

the plasma membrane helps glucose get into and

out of the cell?

1. Phospholipids

2. Carbohydrates

3. Nucleic acids

4. Proteins

5. Fatty acids

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The Plasma Membrane – ―Fluid Mosaic‖

In addition to proteins, two other molecules are found

in the plasma membrane:

Short, branched carbohydrate chains

serve as part of a membrane’s fingerprint along with

recognition proteins

Cholesterol

helps the membrane maintain its flexibility, even at low

temps

some cells ~25%, others (bacteria, plants) - none

39

Smallmouth Bass and Yellow Perch are considered warm

water fish, whereas certain species of char are found in the

arctic. Which fish do you think might have the most

cholesterol in the membranes of its cells?

1. Smallmouth Bass

2. Yellow Perch

3. Arctic char

4. Both 1 and 2 are correct.

40

Faulty membranes can cause disease. 41

What is Cystic Fibrosis?

Why do ―beta blockers‖ reduce

anxiety? 42

Membrane surfaces have a

―fingerprint‖ that identifies the cell. 43

Cells with an

improper fingerprint

are recognized as

foreign and are

attacked by your

body’s defenses

(antibodies).

44

Which of the cell membrane functions below is

possible due to the presence of proteins in the plasma

membrane?

1. The cell membrane determines what molecules will

enter or leave the cell.

2. The cell membrane contains proteins that can bind to

messages sent from other cells and relay the message

to the interior of the cell.

3. The cell membrane contains proteins that act as a

fingerprint for distinguishing between self and foreign

cells.

4. Both 1 and 2 are correct.

5. All of the above. 45

MOLECULES MOVE ACROSS MEMBRANES IN

SEVERAL WAYS

46

Passive transport is the spontaneous

diffusion of molecules across a membrane. 47

Two kinds of passive transport

Diffusion

Osmosis

Diffusion and Concentration Gradients 48

Diffusion passive transport (no

energy needed) solvent particle is

dissolved in a gas or liquid (solvent)

moves from an area of high solute concentration to an area of lower concentration

molecules tend to move down their concentration gradient

Simple & Facilitated Diffusion 49

simple diffusion molecules s/a O2, CO2 (small, no charge) pass directly

through lipid bilayer of membrane w/o assistance

facilitated diffusion spontaneous diffusion across a plasma membrane requires a

transport protein

may be electrically charged repelled by hydrophobic

middle region of phospholipid bilayer

OR may be too big to squeeze through the membrane

In either case, there must be a concentration gradient

from one side of the membrane to the other

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Defects in Transport Proteins 51

Can reduce or even bring facilitated diffusion to a complete stop

Serious health consequences

Many genetic diseases s/a cystinuria

when structured and functioning properly, this transport protein facilitates the diffusion of some amino acids (including cystine, from which the disease gets its name) out of the kidneys

when proteins are malformed, they cannot facilitate diffusion

amino acids build up in the kidneys, forming painful and dangerous kidney stones

Osmosis is the passive diffusion of water

across a membrane 52

Direction of Osmosis 53

Direction is determined only by a difference in total

concentration of all molecules dissolved in water

doesn’t matter what solutes they are

Which side of the membrane has more ―dissolved

stuff?‖ Water will move in that direction.

For this reason, small increases in the salinity of

lakes can have disastrous consequences for

organisms living there, from fish to bacteria

An amoeba (a single-celled protist) is placed in a

solution. The volume of the cell increases (cell

swells). Which statement below is the correct

interpretation of this result?

1. The amoeba is in a hypertonic solution.

2. Water is moving into the amoeba.

3. The amoeba is in a isotonic solution.

4. Water is moving out of the amoeba.

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In active transport, cells use energy to

move small molecules 55

Molecules can’t always move spontaneously

and effortlessly in/out of cells active transport: when their transport takes energy

necessary if molecules to be moved are very large

or if they are being moved against their

concentration gradient

In all active transport, membrane proteins act

like motorized revolving doors push molecules into cell regardless of concentration

of on either side of membrane

Two distinct types of active transport 56

1. Primary – uses energy directly

from ATP

2. Secondary – ATP is not used

directly

Primary Active Transport 57

To help break down food into more digestible

bits, cells lining stomach create an acidic

environment by pumping large numbers of H+

ions into the stomach contents, against their

concentration gradient.

H+ pumping increases ability to digest food but

comes at a great energy cost (ATP) because

protons would not normally flow into a region

against concentration gradient.

Primary Active Transport 58

A normal cell has a high concentration of potassium on the

inside and a low concentration of potassium on the outside.

Also, a normal cell has a low concentration of sodium on the

inside and a high concentration on the outside. Yet, the net

movement of potassium is into the cell and the net

movement of sodium is out of the cell. What type of

transport is involved?

1. Osmosis

2. Facilitated transport

3. Active transport

4. Simple diffusion

5. Secondary active transport

59

Secondary Active Transport 60

Indirect method many transporter proteins use for

fueling their activities.

Transport protein simultaneously moves one

molecule against its concentration gradient while

letting another flow down its concentration

gradient.

No ATP is used directly.

At some other time/location, energy from ATP was

used to pump one of the types of molecules

involved against itsconcentration gradient.

An intestinal epithelial cell powers the movement of

glucose into the cell against its concentration

gradient by simultaneously transporting sodium

down its concentration gradient. Which transport

mechanism is responsible?

1. Osmosis

2. Facilitated transport

3. Active transport

4. Simple diffusion

5. Secondary active transport

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Endocytosis and exocytosis are used

for bulk transport of particles 62

Many molecules are just too big to get into a

cell by passive or active transport.

membrane protein is only so big

some cells in the immune system must ingest

(and destroy) entire bacterial cells that are

invading your body

Endocytosis: cells engulf large

molecules/bacteria with plasma membrane.

Exocytosis: opposite process; releases materials

from the cell

Endocytosis and exocytosis are used

for bulk transport of particles 63

3 types of endocytosis 64

Phagocytosis – ―cell eating‖

Pinocytosis – ―cell drinking‖

Receptor-mediated endocytosis

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66

Faulty cell membranes are a primary

cause of cardiovascular disease 67

Cholesterol often builds up on artery walls

reduces area available for blood flow

causes artery to harden

too much circulating LDL cholesterol can lead to

cardiovascular disease and death it’s good

to remove as much cholesterol from bloodstream

as quickly as possible

Individuals lucky enough to have large numbers of

LDL receptors on liver cell membranes have a

significantly lower risk of cardiovascular disease

Faulty cell membranes are a primary

cause of cardiovascular disease 68

Those who consume food laden with too much cholesterol

or who have the misfortune of inheriting genes that code

for faulty liver cell membranes that have only a few LDL

receptors, can have a heavy load of circulating blood

cholesterol.

This outcome can result in the early onset of

cardiovascular disease.

Familial hypercholesterolemia – no LDL receptors

cholesterol accumulates in the arteries so rapidly that

cardiovascular disease begins to develop even before

puberty and death from heart attacks can occur before

the age of 30

Faulty cell membranes are a primary

cause of cardiovascular disease 69

CELLS ARE CONNECTED AND COMMUNICATE WITH

EACH OTHER

70

Connections between cells hold them in place

and enable them to communicate with each other 71

Involves numerous types of protein

and glycoprotein adhesion molecules

Tight Junctions 72

form continuous, water-tight seals around

cells and also anchor cells in place

particularly important in the small

intestine where digestion occurs

Desmosomes 73

are like spot welds or rivets that fasten cells

together into strong sheets

function like Velcro: they hold cells together but

are not water-tight

found in much of the tissue-lining cavities of

animal bodies

Gap Junctions 74

Pores surrounded by special proteins that form open channels

between two cells

large enough for salts, sugars, amino acids, and electrical

signals to pass through

too small for the passage of organelles or larger molecules

such as proteins and nucleic acids

Important mechanism for cell-to-cell communication

heart: electrical signal telling muscle cells to contract is

passed from cell to cell through gap junctions

also important in allowing a cell to recognize that it has

bumped up against another cell

chemicals flowing from one cell to the next can signal to the

body to stop producing cells of a particular type.

75

Your skin is water proof. What type of cell-cell

junction is most likely involved in creating a water-

tight barrier between the outside and inside of your

body?

1. Tight junctions

2. Desmosomes

3. Gap junctions

76

How can a lack of communication

between cells lead to cancer? 77

Contact inhibition – normal cells generally stop dividing

when they bump up against other cells

no contact inhibition with cancer cells

divide continuously, eventually forming a mass of cells

(tumor)

Cancer cells usually have reduced numbers of gap

junctions

harder for a cell to detect that it has bumped up

against other cells

cell is more likely to continue dividing tumorous mass

of dividing cells

Plasmodesmata 78

Plasmodesmata

most plants have anywhere from 1,000 to

100,000 microscopic tube-like channels

connect cells to each other, enabling

communication and transport between them

NINE IMPORTANT LANDMARKS DISTINGUISH

EUKARYOTIC CELLS

79

1. The Nucleus 80

The nucleus is the largest and most

prominent organelle in most eukaryotic

cells

The nucleus has two primary functions:

genetic control center

storehouse for hereditary information

1. The Nucleus 81

Nucleolus

area near the center of the nucleus where subunits of

the ribosomes are assembled

ribosomes are the site of protein assembly

found in both prokaryotes & eukaryotes

ribosomes are found on endoplasmic reticulum and/or

free-floating in cytoplasm

Chromatin

DNA & surrounding proteins

1. The Nucleus 82

Nuclear membrane (nuclear envelope)

surrounds nucleus, separates it from cytoplasm

2 bilayers on top of each other

covered with tiny pores

made from multiple proteins embedded

within the phospholipid membranes

spans both bilayers

enable large molecules to pass from nucleus

cytoplasm

83

2. Cytoplasm & Cytoskeleton 84

2. Cytoplasm & Cytoskeleton 85

Cytosol:

―soup" within which all other cell organelles

reside

most cellular metabolism occurs here

mostly water but also full of proteins

control cell metabolism

Cytoplasm: collective term for cytosol plus

organelles suspended within cytosol

2. Cytoplasm & Cytoskeleton 86

Cilia

short projections that often occur in large numbers on

a single cell

move fluid along/past a cell

sweeps airways to our lungs clean of debris (such as

dust) from the air that we breathe.

Flagella

much longer than cilia

occur in prokaryotes, single-celled eukaryotes, many

algae/plants

animals – only sperm

2. Cytoplasm & Cytoskeleton 87

3. Mitochondria 88

cell’s all-purpose energy converters present in virtually all eukaryotic cells mitochondria allow us to convert energy contained

within chemical bonds of dietary carbohydrates, fats, and proteins in food CO2, H2O, and ATP (energy source used by all cells use to fuel all functions/activities; more in ch. 4)

energy conversion requires a significant amount of oxygen, organisms’ mitochondria consume most of the oxygen used by each cell

89

3. Mitochondria - Endosymbiosis 90

As learned earlier, mitochondria may very well have

existed as separate single-celled bacteria-like organisms

billions of years ago

similar to bacteria in size and shape

may have originated when symbiotic bacteria took up

permanent residence within other cells

strongest evidence for this is that mitochondria have

their own DNA

Mixed in among the approximately 3,000 proteins in

each mitochondrion, there are anywhere from two to ten

copies of its own little ring-shaped DNA. This DNA carries

the instructions for making 13 important mitochondrial

proteins necessary for metabolism and energy production.

4. Lysosomes 91

―Floating garbage disposal‖

mitochondria wear out after ~10 days of intensive

activity

white blood cells constantly track down and consume

bacterial invaders, which they then have to dispose of

1000s of ongoing reactions of cellular metabolism

produce many waste macromolecules that cells must

digest and recycle

4. Lysosomes 92

4. Lysosomes 93

Round, membrane-enclosed, acid-filled

~ 50 different digestive enzymes and a super-acidic,

corrosive fluid

if a lysosome were to burst, it would almost immediately

kill cell by rapidly digesting all component parts

Some enzymes break down lipids, others carbohydrates,

others proteins, and still others nucleic acids

Frequently a first step when a cell consumes and begins

digesting a particle of food or even an invading bacterium

Most component parts of molecules that are digested (s/a

amino acids) released back into the cell where they can be

re-used by cell as raw materials

4. Lysosomes – Tay-Sachs Disease 94

Result of malfunctioning lysosomes individual inherits an inability to produce a critical

lipid-digesting enzyme

lipids continue to be sent to the lysosome where they

accumulate, undigested

lysosome swells until it bursts and digests the whole cell

or until it chokes the cell to death

process occurs in large numbers of cells and eventually

leads to death

Which cellular component would be responsible for the classic shape of a red blood cell?

1. Nucleus

2. Cytoskeleton

3. Lysosome

4. Mitochondria

95

Endomembrane System 96

production and modification of biological molecules

mass of interrelated membranes spreading out from

& surrounding nucleus

~20% of cell’s volume

forms chambers within cell that contain their own

mixture of chemicals

smooth endoplasmic reticulum

rough endoplasmic reticulum

golgi apparatus

5. Endoplasmic Reticulum 97

cells build proteins and

disarm toxins

5. Endoplasmic Reticulum (Rough) 98

Large series of interconnected, flattened sacs connected

directly to nuclear envelope

rough ER almost completely surrounds the nucleus (usually)

called ―rough‖ because surface is studded w/ribosomes

cells w/high rates of protein production have large numbers of

ribosomes

more on ribosomes in Chapter 5

5. Endoplasmic Reticulum (Rough) 99

Primary function: fold and package proteins that will be

shipped elsewhere

example: poisonous frogs package their poison in rough ER

of the cells in which it is produced before transporting it to

the poison glands on their skin

Proteins that are used within cell are generally produced

on free-floating ribosomes in cytoplasm

5. Endoplasmic Reticulum (Rough) 100

5. Endoplasmic Reticulum (Smooth) 101

no ribosomes bound to it

connected to rough ER but farther from nucleus

w/slightly different appearance

looks like a collection of branched tubes

synthesizes lipids such as fatty acids, phospholipids,

and steroids

exactly which lipids are produced varies throughout the

organism and across plant and animal species

following their production these lipids are packaged in

transport vesicles and are then sent to either other

parts of the cell or to the plasma membrane for export

5. Endoplasmic Reticulum (Smooth) 102

ALSO – smooth ER helps protect us from the

following through the use of detoxifying enzymes

alcohol, antibiotics, barbiturates, amphetamines

toxic metabolic waste products produced in our bodies

Smooth ER proliferates in cells that are exposed to

large amounts of particular drugs

increases the capacity for detoxification, but as the

cells become more and more efficient at detoxification,

our tolerances to the very drugs the smooth ER is trying

to destroy can increase.

5. Endoplasmic Reticulum (Smooth) 103

Just as cells with high rates of protein production

have large numbers of ribosomes, we find huge

amounts of smooth ER in liver cells because they are

the primary sites of molecular detoxification

Other cells that are packed with ER include plasma

cells in the blood that produce immune system

proteins for export and pancreas cells that secrete

large amounts of digestive enzymes

5. Endoplasmic Reticulum (Smooth) 104

Chronic exposure to many drugs (from antibiotics to heroin)

can induce a proliferation of smooth ER, particularly in the

liver, and the smooth ER’s associated detoxification

enzymes. This proliferation in turn increases tolerance to the

drugs, necessitating higher doses. Moreover, the increased

detoxification capacity of the cells often enables the cell to

better detoxify other compounds, even if the person has

never been exposed to them. This increased detoxification

capacity can lead to problems. An individual who has been

exposed to large amounts of drugs, for example, may end

up responding less well to antibiotics.

Which cells below would have the smoothest endoplasmic reticulum?

1. Kidney cells

2. Kidney cells of an alcoholic

3. Liver cells

4. Liver cells of an alcoholic

105

6. Golgi Apparatus 106

Flattened stack of membranes (each of which is

called a Golgi body) that are not interconnected

Processes molecules synthesized within a cell—

primarily proteins and lipids—and packages those

that are destined for use elsewhere in the body

Also a site of carbohydrate synthesis, including the

complex polysaccharides found in many plasma

membranes

6. Golgi Apparatus 107

Transport vesicles bud from the endoplasmic reticulum move through cytoplasm Golgi apparatus vesicles fuse w/Golgi apparatus, dump contents

Golgi body.

~ 4 successive chambers , molecules get passed from one to the next enzymes make slight modifications to molecule (ex:

phosphates or sugars)

Molecules then bud off from Golgi apparatus in a vesicle, move cytoplasm

108

109

7. Cell Wall 110

Provides additional protection and support for plant cells

Made from polysaccharides, including cellulose

Animal cells do not have cell walls, but some archaea, bacteria, protists, & fungi do, although cell wall chemical composition differs from those found in plants

7. Cell Wall 111

Cell wall ~100 times thicker than plasma membrane, thus giving the plant tremendous structural strength some plants can grow several hundred feet tall also helps increase plants’ water resistance provides protection from insects, etc.

Cell wall does not completely seal off plant cells from one another porous, allowing water, solutes to reach plasma

membrane plasmodesmata: channels connecting adjacent cells,

allowing passage of molecules between cells

8. Vacuoles 112

Stands out in plant cells but also found in protists, fungi, and animals surrounded by a membrane filled w/fluid occupies 50 - 90% of plant cell’s interior space

Plays important role in five different areas of plant life nutrient storage waste management predator deterrence sexual reproduction physical support

8. Vacuoles 113

Nutrient storage: amino acids, sugars, ions, etc.

Waste management: vacuole retains waste products and

degrades them with digestive enzymes (like the lysosome in

animal cells)

Predator deterrence: poisonous, nasty-tasting materials can

accumulate inside vacuoles of some plants

Sexual reproduction: vacuole may contain pigments that give

some flowers their color, enabling them to attract birds and

insects that help the plant reproduce

8. Vacuoles 114

Physical support: high concentrations of dissolved substances

within the vacuole can cause water to rush into the cells via

osmosis

water increases fluid pressure inside vacuole

turgor pressure allows flowers, other plant parts to stand

upright

plant wilting is result of loss of turgor pressure

9. Chloroplast 115

found in all plants and

eukaryotic algae

site of photosynthesis

conversion of light energy

into chemical energy of

food molecules; oxygen is

a by-product (more in

chapter 4)

9. Chloroplast 116

Circular DNA (contains many of the genes essential for photosynthesis)

Dual outer membrane of chloroplast is consistent w/idea that a cell engulfed a photosynthetic bacterium, enveloping it with its plasma membrane in endocytosis.

Endosymbiosis theory chloroplasts might have originally been bacteria that

were engulfed by a predatory cell remained alive, became cell’s meal ticket, providing

food for the cell in exchange for protection

117

Which answer below is not found in a eukaryotic cell?

1. Cell wall

2. DNA without membrane

3. Endoplasmic reticulum

4. Chloroplast

5. Lysosome

118