A Tour of the Cell

Question 1

A variety of microscopes have

Answer 1

A variety of microscopes have been developed for a clearer view of cells and cellular structure.
In the 1800s, these studies led to cell theory

Question 2

cell theory

Answer 2

which states that
all living things are composed of cells and
all cells come from other cells

Question 3

Cell size must

Answer 3

be large enough to house DNA, proteins, and structures needed to survive and reproduce, but
remain small enough to allow for a surface-to-volume ratio that will allow adequate exchange with the environment.

Question 4

The plasma membrane

Answer 4

The plasma membrane forms a flexible boundary between the living cell and its surroundings.

Question 5

Phospholipids form a

Answer 5

a two-layer sheet called a phospholipid bilayer in which
hydrophilic heads face outward, exposed to water, and
hydrophobic tails point inward, shielded from water.

Question 6

Membrane proteins are either

Answer 6

attached to the membrane surface or

embedded in the phospholipid bilayer.

Question 7

Some proteins form

Answer 7

channels/tunnels that allow ions and other hydrophilic molecules as they pass through the hydrophobic center of the membrane.
Other proteins serve as pumps using energy to actively transport molecules in / out of the cell.

Question 8

prokaryotic

Answer 8

Bacteria and archaea are prokaryotic cells.

Question 9

eukaryotic cells

Answer 9

All other forms of life are composed of eukaryotic cells.

Question 10

Prokaryotic and eukaryotic cells have

Answer 10

a plasma membrane and

one or more chromosomes and ribosomes.

Question 11

Eukaryotic cells have a

Answer 11

membrane-bound nucleus and

number of other organelles.

Question 12

Prokaryotes

Answer 12

have a nucleoid and no true organelles

Question 13

nucleoid

Answer 13

The DNA of prokaryotic cells is coiled into a region called the nucleoid, but no membrane surrounds the DNA.

Question 14

The surface of prokaryotic cells may

Answer 14

be surrounded by a chemically complex cell wall,
have a capsule surrounding the cell wall,
have short projections that help attach to other cells or the substrate, or
have longer projections called flagella that may propel the cell through its liquid environment.

Question 15

The structures and organelles of eukaryotic cells perform four basic functions.

Answer 15

The nucleus is involved in genetic control of the cell.
The endoplasmic reticulum, ribosomes, and Golgi apparatus are involved in the manufacture, distribution, and breakdown of molecules.
Mitochondria in all cells and chloroplasts in plant cells are involved in energy processing.
Structural support, movement, and communication between cells are functions of the cytoskeleton, plasma membrane and cell wall
The internal membranes of eukaryotic cells partition it into compartments.

Question 16

Cellular metabolism

Answer 16

the many chemical activities of cells, occurs within organelles (inside mitochondria or chloroplasts) or out in the cytosol
Almost all of the organelles and other structures of animals cells are present in plant cells.
A few exceptions exist.
Lysosomes and centrioles are not found in plant cells.
Plant but not animal cells have
a rigid cell wall,
chloroplasts, and
a central vacuole.

Question 17

The nucleus

Answer 17

contains most of the cell’s DNA and
controls the cell’s activities by directing protein synthesis by making messenger RNA (mRNA).
DNA is associated with many proteins in structures called chromosomes.

Question 18

The nuclear envelope

Answer 18

is a double membrane and
has pores that allow material to flow in and out of the nucleus.
The nuclear envelope is attached to a network of cellular membranes called the endoplasmic reticulum.

Question 19

The nucleolus

Answer 19

is a prominent structure in the nucleus and

the site of ribosomal RNA (rRNA) synthesis.

Question 20

Ribosomes

Answer 20

are involved in the cell’s protein synthesis.
Ribosomes are synthesized from rRNA produced in the nucleolus.
Cells that must synthesize large amounts of protein have a large number of ribosomes.
Some ribosomes are free ribosomes; others are bound.

Question 21

Free ribosomes are

Answer 21

suspended in the cytoplasm and

typically involved in making proteins that function within the cytoplasm.

Question 22

Bound ribosomes are

Answer 22

attached to the endoplasmic reticulum (ER) associated with the nuclear envelope and
associated with proteins exported from the cell.

Question 23

endomembrane system.

Answer 23

Many of the membranes within a eukaryotic cell are part of the endomembrane system.
Some of these membranes are physically connected and some are related by the transfer of membrane segments by tiny vesicles (sacs made of membrane).
Many of these organelles work together in the synthesis, storage, and
export of molecules.
The endomembrane system includes
the nuclear envelope,
endoplasmic reticulum (ER),
Golgi apparatus,
lysosomes,
vacuoles, and
the plasma membrane.

Question 24

Smooth Endoplasmic reticulum

Answer 24

lacks attached ribosomes
is involved in a variety of diverse metabolic processes.
Smooth ER contains enzymes important in the synthesis of lipids, oils, phospholipids, and steroids.
Other enzymes help process (detoxify) drugs, alcohol, and other potentially harmful substances.
Some smooth ER helps store calcium ions.

Question 25

Rough Endoplasmic reticulum

Answer 25

lines and is attached to the outer surface of the nuclear membranes (is continuous with the nuclear membrane) and is studded with ribosomes.
additional membrane for itself and proteins destined for secretions.

Question 26

The Golgi apparatus

Answer 26

serves as a molecular warehouse and finishing factory for products manufactured by the ER.
Products travel in transport vesicles from the ER to the Golgi apparatus.
One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock.
Products are modified / processed as they move through the Golgi

Question 27

A lysosome

Answer 27

is a membranous sac containing digestive enzymes.
The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing.
The membrane serves to safely isolate these potent enzymes from the rest of the cell.

Question 28

Lysosomes help digest food particles engulfed by a cell.

Answer 28

A food vacuole binds with a lysosome.
The enzymes in the lysosome digest the food.
The nutrients are then released into the cell.

Question 29

Lysosomes also help remove or recycle damaged parts of a cell.

Answer 29

The damaged organelle is first enclosed in a membrane vesicle.
Then a lysosome
fuses with the vesicle,
dismantles its contents, and
breaks down the damaged organelle.

Question 30

Vacuoles

Answer 30

are large vesicles that have a variety of functions.
Some protists have contractile vacuoles that help to eliminate water from the protist.
In plants, vacuoles may have digestive functions, contain pigments or contain poisons that protect the plant.

Question 31

Mitochondria

Answer 31

are organelles that carry out cellular respiration in nearly all eukaryotic cells.
Cellular respiration converts the chemical energy in foods to chemical energy in ATP (adenosine triphosphate).

Question 32

Chloroplasts

Answer 32

are the photosynthesizing organelles of all plants.

Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar molecules.

Question 33

Mitochondria and chloroplasts have

Answer 33

DNA and ribosomes.

The structure of this DNA and these ribosomes is very similar to that found in prokaryotic cells.

Question 34

The endosymbiont theory

Answer 34

proposes that
mitochondria and chloroplasts were formerly small prokaryotes and
they began living within larger cells.

Question 35

cytoskeleton

Answer 35

Cells contain a network of protein fibers, called the cytoskeleton, which functions in structural support and motility.
Scientists believe that motility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins.

Question 36

The cytoskeleton is composed of three kinds of fibers

Answer 36

Microfilaments
Intermediate filaments
Microtubules

Question 37

Microfilaments

Answer 37

(actin filaments) support the cell’s shape and are involved in motility.

Question 38

Intermediate filaments

Answer 38

reinforce cell shape & anchor organelles.

Question 39

Microtubules

Answer 39

(made of tubulin) give the cell rigidity and act as tracks for organelle movement.

Question 40

flagella and cilia

Answer 40

While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons.
Cells that sweep mucus out of our lungs have cilia.
Animal sperm are flagellated.
Flagella (longer than cilia) propel a cell by an undulating, whiplike motion.
Cilia work more like the oars of a crew boat.
Although differences exist, flagella and cilia have a common structure and mechanism of movement.
Both flagella and cilia are made of microtubules wrapped in an extension of the plasma membrane.
Cilia and flagella move by bending motor proteins called dynein feet.

Question 41

rigid cell wall

Answer 41

A plant cell, but not an animal cell, has a rigid cell wall that
protects and provides skeletal support that helps keep the plant upright against gravity and
is primarily composed of cellulose.