Chapter 4

Question 1

The history of eukaryotes

Answer 1

• the first eukaryotic cells appeared 2 to 3 billion years ago
• bacteria, archaea, and eukarya all evolved from the Last common ancestor
• first primitive eukaryotes were likely single-called and independent
• over time cells aggregated, forming colonies
• cells within colonies became specialized to perform a specific function
• complex multicellular organisms evolved as individual cells lost the ability to survive separately from the intact colony

Question 2

Flagella and cilia

Answer 2

• projections used for locomotion or moving substances along the cell surface
  Flagella - long projections; few in number
  Cilia - short projections; numerous

Question 3

The glycocalyx

Answer 3

• an outermost layer that comes into direct contact with the environment
• composed of polysaccharides
• appears as: a network of fibers, a slime layer, and a capsule
• contributes to protection, adherence, and signal reception

Question 4

Boundary structure: The cell wall

Answer 4

• most animals lack cell walls
• Protozoa and helminths do not have cell walls
  Cell walls of fungi:
• rigid and provide structural support and shape
• different in chemical composition from bacterial and archaeal cell walls
• thick inner layer of polysaccharide fibers composed of chitin or cellulose
• thin outer layer of mixed glycans

Question 5

Boundary structures: the cell membrane

Answer 5

typical bilayer of phospholipids in which protein molecules are embedded
- contain sterols of various kinds: relative rigidity gives stability to the membrane, important in cells that do not have a cell wall
The cytoplasmic membranes of eukaryotes have a similar function as those in bacteria and archaea, serving as selectively permeable Barriers

Question 6

Internal structures: the nucleus

Answer 6

Most prominent organelle of eukaryotic cells; separated from the cell cytoplasm by an external boundary called the nuclear envelope
- composed of two parallel membranes (lipid-bilayers) separated by a narrow space
- perforated with small, regularly spaced pores, formed at sites where the membranes unite
- macromolecules migrate through the pores to the cytoplasm and vice versa

Question 7

Internal structures: endoplasmic reticulum

Answer 7

A series of membrane tunnels used in transport and storage
Rough endoplasmic reticulum:
- allows transport materials from the nucleus to the cytoplasm and to the cell’s exterior
- ribosomes attaches to its membrane surface
Smooth endoplasmic reticulum:
- closed tubular network without ribosomes
- functions in nutrient processing and synthesis and storage or non protein macromolecules such as lipids

Question 8

Internal structures: Golgi apparatus

Answer 8

The site in the cell in which proteins are modified and then sent to their final destination
Consists of several flattened, disc-shaped sacs called cisternae
Always closely associated with the endoplasmic reticulum:
- transitional vesicles from the endoplasmic reticulum are picked up at the face of the Golgi apparatus
- proteins are modified within the cisternae by the addition of polysaccharides and lipids
- condensing vesicles pinch off of the Golgi apparatus and are then conveyed to lysosomes or transported outside the cell

Question 9

Natures assembly line

Answer 9

Nucleus, endoplasmic reticulum, and Golgi apparatus
- a segment of DNA containing the instructions for producing a protein is copied into RNA, and this RNA transcript is passed out through the nucleus pores directly to the ribosomes on the endoplasmic reticulum
- specific proteins on the RER are deposited in the lumen and transported to the Golgi apparatus
- proteins in the Golgi apparatus are chemically modified and packaged into vesicles to be used by cell

Question 10

The transport process

Answer 10

Lysosomes:
- bud off the Golgi apparatus as a vesicle
- contain a variety of enzymes involved in the intracellular digestion of food particles and protection against invading microorganisms
- participate in the removal of cell debris in damaged tissues
Vacuoles:
- membrane-bound sacs containing fluids or solid particles to be digested, excreted, or stored
- found in phagocytic cells in response to food and other substances that have been engulfed
- contents of a food vacuole are digested through a merger or a vacuole with a lysosome

Question 11

Mitochondria

Answer 11

generate energy fro the cell
Composed of a smooth, continuous outer membrane with an inner folded membrane
Folds on the inner membrane are called cristae:
- hold the enzymes and electron carriers of aerobic respiration
- extracts chemical energy contained in nutrient molecules and stores it in the form of high-energy molecules, or ATP
Unique organelles
- divide independently of the cell
- contain circular strands of DNA
- have bacteria-sized 70S ribosomes

Question 12

Cytoplasm

Answer 12

Cytoplasm: substance inside the plasma and outside the nucleus
Cytosol: fluid portion of cytoplasm
Cytoskeleton: made of microfilaments and intermediate filaments; gives shape and support
Cytoplasmic streaming: movement of the cytoplasm throughout a cell

Question 13

Chloroplasts

Answer 13

• found in algae and plant cells
• capable of converting energy from sunlight into chemical energy through photosynthesis
• produce oxygen gas as a by-product of photosynthesis
• resemble mitochondria but are larger, contain special pigments, and are more varied in shape

Question 14

Ribosomes

Answer 14

Distributed throughout the cell:
- scattered freely in the cytoplasm and cytoskeleton
- attached to the rough endoplasmic reticulum
- appear inside the mitochondria and chloroplasts
Multiple ribosomes are often found arranged in short chains called poly ribosomes (polysomes)
Size and structure:
- large and small subunits of ribonucleoprotein
- eukaryotic ribosome is 80S, a combination of 60S and 40S subunits

Question 15

The cytoskeleton

Answer 15

Functions:
- anchoring organelles
- moving RNA and vesicles
- Permitting shape and changes and movement
Three main types of cytoskeleton elements:
- actin filaments: long, thin protein strands
- Intermediate filaments: ropelike structures
- microtubules: long, hollow tubes

Question 16

Fungal cells

Answer 16

Yeasts:
- round to oval shape
- asexual reproduction, budding
Hyphae: long, threadlike cells found in the bodies of filamentous fungi
Pseudohyphia: chain of yeast cells
- some fungal cells are considered dimorphic and can take either form, depending on growth conditions

Question 17

Fungi and human disease

Answer 17

Nearly 300 species of fungi can cause human disease
Three types of fungal diseases in humans:
- community-acquired infections caused by environmental pathogens
- hospital-associated infections caused by fungal pathogens in clinical settings
- opportunistic infections caused by low-virulence species infecting already-weakened individuals

Question 18

Fungi and human disease:
Fungus

Answer 18

• harmless spores can cause opportunistic infections in AIDS patients
• fungal cell walls give off chemical substances that can trigger allergies
• toxins produced by poisonous mushrooms can induce neurological disturbances and even death
• aspergillus flavus synthesizes a poison called aflotaxin, potentially lethal to animals who eat contaminated grain

Question 19

Agricultural impact of fungi

Answer 19

A number of species are pathogenic to corn and grains:
- reduces corn production
- can cause disease in domestic animals consuming contaminated feed crops
Fungi rot fresh produce during shipping and storage:
- 40% of yearly crop is consumed by fungi

Question 20

The transport process

Answer 20

• DNA turns into RNA then leaves the nucleus
• it then goes to the transitional vesicles which then take it all to the smooth and rough endoplasmic reticulum
• then it can go to the condensing vesicles which carry it out of the cell
• this is how viruses can be packed up, put into a vesicles, sent outside of the cell, then used to help with creation of more virus particles

Question 21

fungal nutrition

Answer 21

heterotrophic: acquire nutrients from a wide variety of organic substrates
saprobic: these substrates from the remnants of dead plants and animals in soil or aquatic habitats
parasitic: grow on bodies of living animals or plants, although very few require a living host
- fungi penetrate the substrate and secrete enzymes that reduces it to small molecules that can be absorbed by the cells
- fungi are often found in nutritionally poor or adverse environments, and those with high salt or sugar content

Question 22

morphology of fungi

Answer 22

• cells of most microscopic fungi grow in loose associations or colonies
• colonies of yeasts are much like bacteria: they have a soft, uniform texture and appearance
• colonies of filamentous fungi are noted for the striking cottony, hairy, or velvety texture

Question 23

morphology of fungi: definitions

Answer 23

mycelium: the woven, intertwining mass of hyphae that makes up the body or colony of a mold
septa: the nature of the septa varies from solid partitions with no communication between the compartments to partial walls with small pores that allow the flow of organelles and nutrients between adjacent compartments:
- nonseptate hyphae consist of one, long, continuous cell
vegetative hyphae are responsible for the visible mass of growth that appears on a substrate
- reproductive, or fertile, hyphae produce spores

Question 24

reproductive strategies and spore formation

Answer 24

most can propagate by the outward growth of existing hyphae or by fragmentation
Spores:
- primary reproductive mode of fungi
- can be disposed through the environment by air, water, and living things
- will germinate upon finding a favorable substrate and produce a new fungus colony in a short time

Question 25

sporangiospores

Answer 25

- formed by successive cleavages within a saclike head called a sporangium, which is attached to a stalk, the sporangiophore

Question 26

conidiospores or conidia:

Answer 26

- free spores not enclosed by a spore-bearing sac

Question 27

the protozoa

Answer 27

- name comes from the Greek for "first animals" - about 12,000 species of single-celled creatures - most are harmless, free-living inhabitants of water and soil - a few species are pathogens responsible for hundreds or millions of infections each year

Question 28

protozoan form and function: 1

Answer 28

single cells containing all of the major eukaryotic organelles cytoplasm divided into two parts: - ectoplasm: clear outer layer involved in locomotion, feeding, and protection - endoplasm: granular inner region housing the nucleus, mitochondria, and food and contractile vacuoles

Question 29

protozoan form and function: 2

Answer 29

- some organelles act as a primitive nervous system to coordinate movement - can move through fluids by means of pseudopods ("false feet") - cell membrane regulates food, wastes, and secretions - cell shape can remain constant (as in most ciliates), or change constantly (as in amoebas) - size of most protozoans range from 3 to 300 microns: - giant amoebas and ciliates range from 3 to 4

Question 30

nutritional and habitat range

Answer 30

- heterotrophic, require food in a complex organic form - free-living species scavenge dead plant or animal debris or graze on bacteria and algae - some have special feeding structures, such as oral grooves - some absorb food directly through the cell membrane - pathogenic species may live on the fluid of their host, such as plasma and digestive juices, or actively feed on tissues - main limiting factor is availability of moisture - can survive in extremes of temperature and pH

Question 31

life cycle

Answer 31

- trophozoite: motile feeding stage requiring ample food and moisture to stay active Cyst: - dormant, resting stage when conditions in the environment became unfavorable - resistant to heat, drying, and chemicals - important factor in the spread of diseases

Question 32

life cycles and transitions

Answer 32

- some protozoan groups exist only in trophozoite phase - many alternate between the trophozoite and cyst stage, depending on the habitat - Trichomonas vaginalis, a common STD, does not form cysts and must be transmitted by intimate contact - entamoeba histolytica and giardia lamblia form cysts and are readily transmitted in contaminated water and foods

Question 33

reproduction

Answer 33

all protozoa reproduce by relatively simple, asexual mitotic cell division or multiple fission sexual reproduction also occurs in most protozoa: - ciliates participate in conjugation in which two cells fuse and exchange micronuclei - this results in new and different genetic combinations that can be advantageous in evolution

Question 34

the helminths

Answer 34

- include tapeworms, flukes, and roundworms - adult specimens are usually large enough to be seen with the naked eye - not all flatworms and roundworms are parasites; many live free in soil and water - disease-causing helminths spread part of their lived in the gastrointestinal tract

Question 35

flatworms and roundworms

Answer 35

flatworms (phylum Platyhelminthes): - very thin, often segmented body plan - divided into cestodes (tapeworms) and trematodes (flukes) roundworms (phylum Aschelminthes): - also called nematodes - elongated, cylindrical, unsegmented body

Question 36

general worm morphology

Answer 36

- multicellular animals that are equipped to some degree with organs and organ systems - in pathogenic heminths, the most developed organ is the reproductive tract - therefore, there is a reduction in the digestive, excretory, nervous, and muscular systems

Question 37

life cycles and reproduction: 1

Answer 37

- complete life cycle includes the fertilized egg, larval, and adult stages - adults derive nutrients and reproduce sexually in a host's body - nematodes: sexes are separate and different in appearance - trematodes: sexes can be separate or hermaphroditic - cestodes: generally hermaphroditic

Question 38

life cycles and reproduction: 2

Answer 38

Helminth life cycle: - must transmit an infective form (egg or larva) to the body of another host - the host in which the larva develops is known as the intermediate (secondary) host - adulthood and matin occur in the definitive (final) host - transport host is an intermediate that experiences no parasitic development -> sources for human infection are contaminated food, soil, and water or infected animals

Question 39

egg laying

Answer 39

fertilized eggs: - released to the environment - provided with a protective shell and extra food to air their development into larvae - vulnerable to heat, cold, drying, and predators -> certain helminths can lay from 200,000 to 25 million eggs a day to assure successful completion of their life cycle

Question 40

a helminth cycle: the pinworm

Answer 40

enterobius vermicularis: - pinworm to seatworm - common infestation of the large intestine - range from 2 to 12 mm long with a tapered, curved cylindrical shape

Question 41

How can you tell if a eukaryote is unicellular or multicellular?

Answer 41

It is unicellular if the organisms is made up of one cell that carries out all functions It is multicellular if the organism is made up of many difference cells

Question 42

The main types of eukaryotic microorganisms

Answer 42

Protozoans Algae Fungi Plants Animals