Unit 2: Cellular Structure and Function

Biology in Focus | Campbell

What is life’s basic unit of structure and function?

the cell

What occurs as a cell increases in volume?

its surface area-to-volume ratio decreases, causing the exchange of materials to become less efficient

How can the concept of surface-area-to-volume ratio be applied to organisms?

as organisms increase in size, their surface-area-to-volume ratio will decrease, affecting the organism’s properties

What is an example of how surface-area-to-volume ratio affects the properties of organisms?

small organisms lose heat at much higher rates than larger organisms as a result of their efficient exchange of heat

What are light microscopes used to study?

stained or living cells

What are electron microscopes used to study?

detailed structures of a cell that cannot be easily seen or observed by light microscopy

What summarizes how prokaryotic and eukaryotic cells differ?

prokaryotic cells are smaller and simpler while eukaryotic cells are bigger and more complex

What are the two distinct types of cells?

prokaryotic and eukaryotic

What are examples of prokaryotes?

bacteria and archaea

What is cytoplasm?

the substance the fills the inside of a cell

What are the characteristics of the genetic material in a prokaryote?

it is one continuous circular DNA molecule that is found free in the in the nucleoid

What structures are found in both prokaryotic and eukaryotic cells?

plasma membrane, cytoplasm, ribosomes, and DNA

What structures are only found in eukaryotic cells?

the nucleus, endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes, and mitochondria

What structures are only found in prokaryotic cells?

nucleoids, plasmids, and capsules

What are flagella?

structures found in some bacteria that are used for motility and might have a thick capsule outside their cell wall for extra protection

True or false: Prokaryotes have membrane-bound organelles

false

What are examples of eukaryotes?

fungi, protists, plants, and animals

What are organelles?

smaller structures within cells

What is the plasma membrane?

the outer envelope of the cell

What is the plasma membrane made up of?

mostly phospholipids and proteins

Why is the plasma membrane important?

it regulates the movement of substances into and out of the cell

What does it mean for the plasma membrane to be semipermeable?

it allows certain substances to pass through it and blocks others

What are peripheral proteins?

proteins loosely associated with the lipid bilayer of the plasma membrane

What are amphipathic/integral proteins?

proteins firmly bound to the plasma membrane

What is the fluid-mosaic model?

the model that describes the cell membrane as mosaic of components that gives the membrane a fluid character

What type of proteins form junctions between adjacent cells?

adhesion

What is the function of receptor proteins?

to serve as docking sites for arrivals at the cell

What do transport proteins form?

pumps that use ATP to actively transport solutes across the membrane

What do channel proteins form?

channels that selectively allow the passage of certain ions of molecules

What are cell surface markers?

proteins or carbohydrates exposed on the extracellular surface that play a role in cell recognition and adhesion

Where are carbohydrate side chains found?

only on the outer surface of the plasma membrane

What is usually the largest organelle in the cell?

the nucleus

What is the function of the nucleus?

to direct what goes in on the cell and be responsible for the cell’s ability to reproduce

What is the nucleus the home of?

the cell’s hereditary information (DNA)

What are chromosomes?

large structures that a cell’s DNA is organized into

What is the most visible structure within the nucleus?

the nucleolus

What is the function of the nucleolus?

to serve as the location where rRNA is made and ribosomes are assembled

What are ribosomes the site for?

protein synthesis

What is the function of ribosomes?

to manufacture all the proteins required or secreted by the cell

What are the physical characteristics of ribosomes?

• round structures composed of two subunits, the large subunit and the small subunit, both of which are composed of rRNA and proteins

• can either be free floating in the cell or attached to the endoplasmic reticulum (ER)

What is the endoplasmic reticulum (ER)?

a continuous channel that extends into many regions of the cytoplasm

What is the function of the endoplasmic reticulum (ER)?

to provide mechanical support and transportation and compartmentalize the cell

How do the smooth and rough ER differ in terms of structure?

the rough ER has ribosomes on its surface while the smooth ER doesn’t

How do the smooth and rough ER differ in terms of function?

the smooth ER makes lipids, carbs and enzymes and detoxifies drugs and poisons, while the rough ER makes proteins and membranes

What is the post office of the cell?

the Golgi apparatus

What is the function of the Golgi apparatus?

to modify, process, and sort the products after the rough ER synthesizes proteins

What are vesicles?

the little sacs that materials sent out of the cell through the plasma membrane are packaged into

What are the power stations of the cell?

mitochondria

What is the function of mitochondria?

to convert energy from organic molecules into useful energy for the cell

What is the most common energy molecule in the cell?

adenosine triphosphate (ATP)

What do mitochondria consist of?

an inner portion and an outer portion

What does the inner mitochondrial membrane do?

form folds known as cristae and separate the innermost area from the intermembrane space

What does the outer mitochondrial membrane do?

separate the intermembrane space from the cytoplasm

What are the garbage collectors of the cell?

lysosomes

What are lysosomes?

sacs of digestive enzymes that break down old, worn-out organelles, debris, or large ingested particles

When are lysosomes made?

when vesicles containing specific enzymes form the trans Golgi fuse with vesicles made during endocytosis

What process are lysosomes essential to?

apoptosis

What are vacuoles?

fluid-filled sacs that store water, food, wastes, salts or pigments

What are peroxisomes?

organelles that detoxify various substances, producing hydrogen peroxide (H₂O₂) as a product and have enzymes that break down hydrogen peroxide into oxygen and water

What is the cytoskeleton?

the network of protein fibers that determine the shape of a cell

What are the most important fibers in the cytoskeleton?

microtubules and microfilaments

What are microtubules made up of?

a protein called tubulin

What is the function of microtubules?

cellular division and movement

What are microfilaments made up of?

a protein called actin

What are microfilaments important for?

movement

How do microfilaments grow and shrink?

actin monomers are joined together and broken apart as needed

What properties do cilia and flagella have in single-celled organisms?

locomotive

What allows the cilia and flagella structure to move?

their beating motion

What structures do plant cells have that animal cells don’t?

cell walls, chloroplasts, and central vacuoles

What structures do animals cells that plant cells don’t?

centrioles

What is a cell wall?

a rigid layer just outside the plasma membrane that provides support for plant cells

What gives plants their characteristic green color?

chlorophyll

What is the function of chloroplasts?

to convert light energy to chemical energy (ATP)

What is the central vacuole?

the large vacuoles that take up the cytoplasm within a plant cell

What is the function of centrioles?

to help move chromosomes

What 2 factors does the ability of molecules to move across the cell membrane depend on?

1. the semipermeability of the plasma membrane

2. the size and charge of particles that want to get through

How do small substances cross the membrane without any resistance?

like dissolves like

Why can only hydrophobic materials pass the central zone of the membrane?

the lipid bilayer is hydrophilic on the outside and hydrophobic on the inside

What occurs if a hydrophilic material attempts to pass through the membrane?

the bilayer won’t let it pass without assistance

What are aquaporins?

water-specific channels

How are glucose and ions transported across the membrane?

via membrane proteins

What can happen to membranes as ions move across them?

they may become polarized

What is diffusion?

the movement of particles from an area of high concentration to an area of low concentration; moving down the concentration gradient

When does simple diffusion occur?

when the molecule that is diffusing is hydrophobic

Why is it called simple diffusion?

because the small nonpolar molecule can just drift right through the membrane without trouble

When does facilitated diffusion occur?

when diffusion requires the help of a channel-type protein

When does passive transport occur?

anytime that a substance is moving by diffusion

Why is it called passive transport?

because there is no outside energy required to power the movement

What is the difference between osmosis and diffusion?

the membrane is usually permeable to solute in diffusion, while in osmosis, it is not

How is the cell wall important to protect it against osmotic changes in plants?

the cell membrane can shrink away from the wall if it loses water and can expand and squeeze tightly against the cell wall if it takes in water

What is tonicity used to describe?

osmotic gradients

What does it mean for an environment to be isotonic to the cell?

the solute concentration is the same inside and outside

When is a solution hypertonic?

when it has more total dissolved solutes than the cell

When is a solution hypotonic?

when it has less total dissolved solutes than the cell

What is water potential?

the measure of potential energy in water

What does water potential describe?

the eagerness of water to flow from an area of high water potential to an area of low water potential

What is water potential affected by?

pressure potential and solute potential

What does adding a solute do to the water potential of a solution?

it lowers the water potential, causing water to be less likely to leave this solution and more likely to flow into it

What is active transport?

the movement of particles from an area of low concentration to an area of high concentration; moving against the concentration gradient

When does primary active transport occur?

when ATP is directly utilized to transport something