Flashcards in Chapter 4: Biology of the Cell Deck (310):
What are the functions of Rough ER?
Production of proteins
Formation of transport vehicles
Storage of proteins to be exported from the cell
Which of the following describe the general functions of the cell. Choose all that apply.
Dispose of wastes
Maintain shape of the cell
Sodium diffusion into the cells occurs _____ to the loss of K+.
Cells usually die by one of the two mechanisms: chemical/mechanical damage or _____.
The two types of organelles found in cells are _____ and _______.
Both Na+ and K+ are pumped by the Na/K pumps _______ their concentration gradients in maintaining the resting membrane potential.
Old or worn out organelles in a cell are removed by what organelle?
_____ junctions allow small solutes to travel between adjacent cells.
Where might you find tight junctions in the body?
The replication of the DNA molecule during Interphase occurs during the ______ phase.
Peroxisomes break down harmful substances including:
fatty acid molecules
Also called intracellular fluid
It contains many solutes, proteins and carbohydrates.
Cytosol has a high ____ content.
A codon can code for:
an anticodon of mRNA
True or False:
Peroxisomes are usually smaller in diameter than lysosomes.
Bulk transport refers to the movement of macromolecules across a selectively permeable membrane are two categories of bulk transport mechanisms, _____ and ______.
DNA double helix wound around a cluster of histones
finely filamented mass of DNA and protein
become visible only when the cell is dividing
Internally, cilia and flagella contain cytoplasym and ______. They are enclosed in the plasma membrane.
the study of cells
the use of a microscope to view small-scale structures
produces a two dimensional image by passing visible light through the specimen.
light microscope (LM)
a beam of electrons to "illuminate" the specimen - high resolution
electron microscope (EM)
directs and electron beam through a thin-cut section of the specimen resulting in a 2 dimensional image focused onto a screen for viewing or onto photographic film.
TEM or transmission electron microscope
For detailed three-dimensional study of a specimen's surface
scanning electron microscope (SEM)
the electron beam is moved across the surface of the specimen, and reflected electrons generate a surface-topography image captured on a television screen.
scanning electron microscope (SEM)
Most cells are microscopic in size, but some are large enough to be seen with the _____.
the shape of red blood cells
A relationship exists between the size and shape of a cell and its _____ in the body.
teh cell membrane that forms the outer, limiting barrier separating the internal contents of the cell from the external environment.
Modified extensions of the plasma membrane include ____, _____, and _____.
the largest structure within the cell and is enclosed by a nuclear envelope.
much of the internal content of the nucleus is the _______, ______.
genetic material, deoxribonucleic acid (DNA)
the fluid of the nucleus
all cellular contents located between the plasma membrane and the nucleus
The three primary components of the cytoplasm are the ____, ______, and _____.
Also called the intracellular fluid (ICF)
Is the viscous, syruplike fluid of the cytoplasm.
means little organs
complex, organized structures within cells that have unique characteristics shapes and functions
Two categories of organelles
The cytosol of some cells temporarily stores _____.
are not considered organelles, but are rater aggregates (clusters) of a single type of molecule
The general functions of the cell.
maintain integrity and shape of a cell obtain nutrients and form chemical building blocks
dispose of wastes
The plasma membrane contains several different types of lipids including ______, _____, _______.
Most of the plasma membrane lipids are _____.
The basic structure of the plasma membrane frame work is called the _______.
The phospholipid bilayer ensures that _____ remains inside the cell, and interstitial fluid remains ______.
Scattered within the hydrophobic regions of the phospholipid bilayer.
Cholesterol ______ the membrane and stabilizes it at ______ extremes.
Lipids with attached carbohydrate groups that are located only on the outer phospholipid layer of the membrane, exposed to interstitial fluid.
the carbohydrate portion of the glycolipid molecules and the glycoprotein molecules help to form the _____.
Only ____ and _____ substances can readily penetrate the plasma membrane.
small and nonpolar
Cholesterol is a component of plasma membranes found only in _____ cells, not in plant cells.
Lipids form the main component of the plasma membrane, the proteins dispersed within the lipids make up about ______ of the plasma membrane by weight.
2 types of membrane proteins
integral or peripheral
_________ are embedded within, and extend across, the phospholipid bilayer.
Many integral membrane proteins are ______ that are carbohydrates exposed to the interstitial fluid.
________ are not embedded within the lipid bilayer and are attached loosely either to the external or internal surfaces of the membrane and are often "anchored" to the exposed parts of an integral protein.
Membrane proteins are also categorized functionally based upon the ______ they serve.
Provide a means of regulating the movement of substances across the plasma membrane.
What are the different types of transport proteins?
__________ bind specific molecules that are called ligands.
cell surface receptors
molecules that bind to macromolecules.
An example of a cell surface receptor is a ligand is a ________ released form a nerve cell that binds to the cell surface receptor of a muscle cell to initiate contraction.
_____ communicate to other cells that they belong to the body.
Cells of the immune system use identity markers to distinguish _____, healthy cells from foreign, _____, or infected cells that are to be destroyed.
_______ may be attached either to the internal or external surface of a cell for catalyzing chemical reactions.
________ secure the cytoskeleton (the internal, protein support of a cell) to the plasma membrane.
_____________ are for cell-to-cell attachments in which proteins form membrane junctions perform a number of functions including binding cells to one another.
The __________ serves as the physical barrier between a cell and the fluid that surrounds it call the interstitial fluid.
The plasma membrane regulates movement of materials into and out of a cell through __________, establishes and maintains electrochemical gradients across the plasma membrane, functions in cell communication.
Obtaining and eliminating substances across the plasma membrane occur through several different processes that are collectively called _________.
Membrane transport is divided into 2 major categories based upon the requirement for expending cellular energy.
This form of transport does not require cellular energy and depends upon the kinetic energy inherent within a substance as it moves down its concentration gradient.
__________ differ because they require cells to expend energy that involves either a substance being pumped up its concentration gradient or the release of a membrane-bound vesicle.
The 2 major energy requiring processes of transport.
The net movement of a substance from where it is more concentrated to where it is less concentrated is called ____.
Diffusion, if unopposed, occurs until the substance reaches _______.
The rate that substances diffuse is not constant, but is dependent upon environmental condition including _______ and _______.
the "steepness" of it concentration gradient
Steepness of a concentration gradient is a measure of the difference in concentration of a substance between _____. A faster rate of diffusion occurs with a _______ concentration gradient.
When the ____ is higher, there is a greater random movement of the molecules and ions composing a substance, resulting in a faster rate of diffusion.
Solutes that are ____ and _____ move into or out of a cell down their concentration gradient by simple diffusion.
The molecules that are transported through simple diffusion do not require a _______.
What moves through simple diffusion
small nonpolar fatty acids
Small solutes that are charged or nonpolar are effectively blocked from passing through the plasma membrane by the nonpolar phopholipid bilayer and must be transported by plasma membrane proteins.
transport via facilitated diffusion
2 types of facilitated diffusion
channel mediated diffusion
carrier mediated diffusion
the movement of small ions across the plasma membrane through water filled protein channels.
Each channel is typically specific for one type of ion. there are 2
leak and gated channels
a continuously open channel mediated diffusion
a channel that is closed, opens only in response to a stimulus and then stays open for just a fraction of a second before it closes.
Channel mediated diffusion is important in the normal function of both ______ and ____ cells.
muscle and nerve
The movement of small polar molecules, such as simple sugars or amino acids that are assisted across the plasma membrane by a carrier protein.
carrier mediated diffusion
_______ transport substances such as glucose across the plasma membrane.
A carrier protein moves a substance _____ its gradient.
A carrier protein that transports only one substance.
glucose carriers are uniporters
The number of channels and carriers in a plasma membrane determines the maximum rate at which a substance can be ______.
A cell can alter the transport rate of a given substance down its concentration gradient by changing the number of __________ in the plasma membrane.
channel or carrier proteins
Osmosis is unlike the other types of passive membrane transport, because it involves _____ movement and does not involve the movement of solutes.
Osmosis is a _______ movement of water through a _____ membrane.
The plasma membrane is a selectively permeable membrane that allows the passage of water, but is phospholipid bilayer ______ the movement of most solutes.
Water molecules cross the plasma membrane in one of two ways:
They either "slip between" the molecules of the phospholipid bilayer or they move through integral protein water channels
water molecules that cross the plasma membrane through integral protein water channels called ______ during osmosis.
Cells can alter the amount of water that crosses the plasma membrane by changing the number of ______.
In the context of osmosis, solutes are classified into two categories based upon whether their passage across the plasma membrane is prevented by the phospholipid bilayer.
solutes pass through the bilayer
i.e. small and nonpolar solutes
solutes that are prevented from crossing the bilayer.
i.e. charged, polar, or large solutes
When a solute concentration exists, a water concentration _______.
A solution with a greater concentration of solutes contains a lower concentration of ______ .
The net movement of water by osmosis is dependent upon the concentration gradient between the ______ and the solution in which the cell is immersed.
Water moves toward the solution with the lower ______ concentration.
the pressure exerted by the movement of water across a semipermeable membrane due to a difference in solution concentration.
In osmotic pressure, the steeper the gradient, the ____ amount of water moved by osmosis and the higher the osmotic pressure.
the pressure exerted by a fluid on the inside wall of its container
the ability of a solution to change the volume or pressure of the cell by osmosis is called _____.
both the solution and the cytosol have the same relative concentration of solutes.
the solution has a lower concentration of solutes, and there is a higher concentration of water than in the cytosol.
i.e. pure water
if the difference in concentration is large enough the cell can rupture or _____.
the specific term for rupturing erythrocytes
solution has a higher concentration of solutes, and thus a lower concentration of water than in the cytosol.
If the difference in concentration is large, the cell shrinks, a process called _____.
i.e.e this prevents us from being able to replace fluid by drinking seawater.
Active processes of membrane transport are those that require the expenditure of _____.
Active processes are organized into _____ and _____.
The movement of a solute against its concentration gradient (from low to high concentration) across a cellular membrane.
Active processes are responsible for maintaining concentration gradients between the ____ of a cell and _____.
The _____ source of energy for active transport determines whether the movement is called primary active transport or _____ active transport.
_______ transport uses energy derived directly from the breakdown of ATP.
The addition of a phosphate to a protein is called _____.
Cellular protein pumps that move ions across teh membrane are more specifically called _____.
Ion pumps are a major factor in a cell's ability to _____ its internal concentrations of ions.
An _____ pump moves one type of ion into a cell against its concentration gradient, while moving another type of ion out of the cell against its concentration gradient.
The sodium-potassium pump is a type of _____ pump, because it move Na+ out of the cell and K+ into the cell.
___ Na+ ions are pumped out of the cell for every ____ K+ ions that are pumped into the cell.
Secondary active transport is also called _________ or coupled transport.
In secondary active transport a substance moves against its concentration gradient using energy provided by the movement of a ________ substance down its specific concentration gradient.
If two substances are moved in the same direction, these transport proteins are called.
If the two substances are moved in opposite directions, then the transport proteins are called ______.
The Na+ concentration gradient has potential energy that is harnessed as Na+ moves down its concentration gradient in _____ transport.
Vesicular transport is also called ______ transport.
Vesicular transport is organized into processes of ______ and ________.
It involves energy input to transport large substances (or large amounts of a substance) across the plasma membrane by a vesicle.
vesicular transport or
The means by which either large substances or large amounts of substances are secreted from the cell.
The cellular uptake of large substances or large amounts of substances from the external environment into the cell
What are the three types of endocytosis?
How are the different types of endocytosis differentiated?
based upon the specific material being transported and the mechanism involved.
means cellular eating
means false feet
a nonspecific process that occurs when a cell engulfs or captures a large particle external to the cell by forming membrane extensions that are called pseudopodia.
Only a few types of cells are able to perform ______.
known as cellular drinking
process occurs when the cell internalizes droplets of interstitial fluid that contain dissolved solutes.
uses receptors on the plasma membrane to bind molecules within the interstitial fluid and bring the molecules into the cell.
Receptor mediated endocytosis enables the cell to obtain bulk quantities of certain substances, even though those substances may not be very ________ in the interstitial fluid.
The transport of cholesterol from the blood to a cell is an example of ________.
The _______ also functions in establishing and maintaining an electrochemical gradient at the plasma membrane called the _____________.
resting membrane potential (RMP)
Cells have an electrical charge ______ at the plasma membrane.
The electrical charge difference represents ________ and thus is appropriately called the membrane potential.
The membrane potential when a cell is a rest is more specifically called _____.
the resting membrane potential (RMP)
Two conditions for establishing and maintaining a RMP
an unequal distribution of ion and molecules across the plasma membrane
the relative amounts of positive and negative charges are not equally distributed at the plasma membrane
Cell types vary in the specific value of their resting membrane potential, which typically range between -50 millivolts and ____ mV.
Neurons have a RMP of _____.
The net movement of each of these (Na+ and K+) is dependent upon both the number of its ____ channels and the ____ gradient, which is the combination of the electrical gradient at the plasma membrane.
_______ diffusion is the most important factor in establishing the specific value of the resting membrane potential.
Movement of K+ is dependent upon its __________.
Potassium ions exit the cell through K+ leak channels moving down their relatively _____ chemical concentration gradient from the cytosol into the interstitial fluid.
The movement of K+ to the outside of a cell, however, opposed by the ______.
Sodium diffusion into cells occurs ______ the loss of K+, and is also dependent upon its electrochemical gradient.
Sodium ions enter the cell through Na+ leak channels moving _____ their chemical concentration gradient from the interstitial fluid into the cytosol.
The _____ pumps are significant in maintaining the gradients of both K+ and Na+ following their diffusion.
_____ or _____ contact between two cells is important in the normal functioning of some cells, especially those of the immune system.
Physical or direct contact
An example of _____ contact between cells is the contact that occurs between _____ and ____ during the process of fertilization.
sperm and oocyte
Direct contact is also critical in the process of development and in _________ following injury.
Programmed cell death occurs both to promote proper development and to remove harmful _____.
Cells of our immune system promote programmed cell death in some virus-infected cells to reduce further spread of ______.
Cells die by one of two mechanisms
1. they are killed by harmful agents or mechanical damage
2. they are induced to commit suicide, a process of programmed cell death
Chromosomes appear due to coiling of chromatin.
Nucleolus breaks down
Spindle fibers begin to form from centrioles.
Centrioles move toward opposing cell poles
Nuclear envelope breaks down at the end of this stage.
Chromosomes uncoil to form chromatin.
A nucleolus reforms within each nucleus.
Spindle fibers break up and disappear.
New nuclear envelope forms around each set of chromosomes.
Cytokinesis continues as cleavage furrow deepens.
Spindle fibers attach to the centromeres of the chromosomes extending from the centrioles.
Chromosomes are aligned at the equatorial plate of the cell by spindle fibers.
Sister chromatids are separated by spindle fibers and moved toward opposite ends of the cell.
During this process centromeres that held sister chromatids together seperate; each sister chromatid is now a chromosome with its own centromere.
Centriole replication is completed and enzymes and other structures needed for cell division are synthesized.
(the second gap phase)
_______ of the cell cycle cells grow and produce new organelles, and other structures needed for DNA replication.
Replication of the centrioles to produce two centriole pairs is also initiated in this phase.
(the first gap stage)
The 46 double helix strands of DNA are replicated.
Forming DNA requires large numbers of deoxyribonucleotides and the enzyme DNA polymerase. All of these components are located in the nuceloplasm within the nucleus.
The cell cycle depicts the steps in the replication of a _________.
The cell cycle consists of all the changes the cell undergoes as it divides into two identical cells called ___________.
The two major phases in the cell cycle are ________ and _______ phase.
On average, the cell is in interphase for approximatel ____ hours, and going through the mitotic phase for ____ hours.
_______ are all of the cells in the body other than the sex cells.
Mitosis occurs in ____, when cells divide their nucleus.
Meiosis occurs in ______, when cells divide their nucleus.
Sex cells either form _____ or ______ .
sperm or oocytes
A _______ is a structure containing a pair of perpendicularly oriented cylindrical centrioles located in close proximity to the nucleus.
Body cells communicate to our immune cells that they both belong to the body and are healthy through direct contact that involves the _________.
The glycocalyx is the coating of ______ on the external surface of a cell.
The immune system is able to distinguish normal, healthy cells from unwanted cells by making direct contact with a cell to determine if it exhibits the same pattern of sugars of the ________ as the body's cells.
Most communication between cells occurs through ____
Ligands involved in communication include ________ from nerve cells and ________ from endocrine cells.
The cell that receives the information has a receptor that can bind the ligands which initiates mechanisms for controlling the ______, _________, and other ______ of individual cells.
growth, reproduction, and other cellular processes
Three types of receptors that bind ligands
Channel linked receptors
G protein-coupled receptors
receptor that permits ion passage either into or out of a cell in response to ligand binding
receptor that function as protein kinase enzymes are activated to directly phosphorylate other enzymes within the cell
receptors that involve protein kinase activation
G protein-coupled receptors
Membrane-bound organelles within the cytoplasm are surround by a membrane that separates the organelle's contents from ____.
Each organelle differs in is shape, _____ and associated enzymes.
Membrane bound organelles (5)
The ___ typically extends from the nuclear envelope to the plasma membrane and composes about one-half of the membrane within a cell.
The extensive ER ______ surface serves as a point of attachment for ______.
The ribosomes of rough ER produce _____ that will be released from the cell, incorporated into the plasma membrane, and serve as digestive enzymes of lysosomes.
Transport from the ER occurs when small, enclosed membrane sacs pinch off from the ER.
Transport vesicles shuttle proteins from the rough ER lumen to the _______ for further modicfication.
The amount of rough ER is greater in cells producing large amounts of ____ for secretion, such as a cell in the pancreas that releases insulin to control blood glucose.
The ER also helps form ____.
Smooth ER functions include _____, ______, and _____.
storage of different types of lipids
This organelle is responsible for carbohydrate metabolism and detoxification of drugs and poisons.
Abundant amounts of smooth ER occur within the cells in the liver to ______ alcohol
The ______ is typically composed of several elongated, flattened saclike membranous structures called cisernae.
The golgi body has two poles called the ____ and ____.
cis-face and trans-face
The cis-face is closer in proximity to the ____ and the diameter of its flattened sac is larger compared to the trans-face.
One of the primary functions of the golgi apparatus is to _____, ______, and ______ that are made by the rough ER.
modify, package, and sort proteins
Transport vesicles arrive from the ER and fuse with the _____ of the Golgi apparatus.
The ______ is referred to as the "warehouse" center.
At the ____, in the Golgi apparatus, secretory vesicles form and carry both the modified and newly formed molecules away.
Molecule arrive at the receiving region, ____, are modified and packaged within the lumen, are then shipped out at the shipping region, _____.
The small organelle which are membranous sacs that contain digestive enzymes, which are immersed in acidic fluid.
Within a healthy cell,_____ digest the contents of endocytosed vesicles.
Lysosomes also digest molecular structures of _______ organelles which is called _____.
When a cell is damaged or dies, ______ from its lysosomes are eventually released into the cytosol.
The _____ is called the "garbagemen" because of their cleanup activities and "suicide packet" because of their function in autolysis.
Organelles that are membrane enclosed sacs that contain over 50 different enzymes that vary by cell type.
______ are usually smaller in diameter than lysosomes.
Peroxisomes are initially formed by _____ first pinching off from the rough ER.
Bound ribosomes are used to ______ proteins destined for export out of the cell, to become an integral part of the plasma membrane, or to serve as enzymes within lysosomes.
Non-membrane bound organelles are composed of either protein alone or protein and ____.
Peroxisomes engage in _____ synthesis.
Peroxisomes were first named based on their role in _____ digestion, which involves removal of hydrogen from a molecule with the accompanying production of hydrogen peroxide.
Peroxisomes function in both ____ and ____ of molecules
digestion and synthesis
An extensive array of membrane-bound structures that includes (5)
*All of these structures are either directly attached to one another or connected through vesicles that move between them
The plasma membrane and _______ are also considered part of this membrane system.
_______, are the only membrane-bound organelles that are not components of the endomembrane system.
Oblong shaped organelles with a double membrane with the folds of the inner membrane called cristae.
The matrix, which is the inner region of a mitochondrion, contains a small, unique circular fragment of _____ that has genes for producing mitochondrial proteins.
Mitochondria engage in ______ respiration to complete the digestion of glucose and other fuel molecules, such as fatty acids.
Mitochondria numbers within cells increase with greater demands for ______.
Free ribosomes are suspended within the ____.
In general, all other proteins that function within the cell are _______ by free ribosomes.
The cytoskeleton has a central role in numerous cellular activities that include intracellular _______ and ________ organelles, ______, and movement of materials.
structural support and organization of organelles, cell division, and movement of materials
The cytoskeleton is formed by a framework of ______.
diverse fibrous proteins
The cytoskeleton extends throughout the interior of a cell and ____ proteins in the plasma membrane.
The three separate types of protein molecules that form the cytoskeleton.
The smallest components of the cytoskeleton with a diameter of about 7 nanometers.
Microfilaments are composed of ____ protein monomers that are organized into two thin, intertwined protein filaments similar to two twisted pearl strands.
Microfilaments help maintain ______, form internal support of microvilli, separate the two cells formed during cytokinesis, facilitate cytoplasmic streaming, and participate in ____.
Hollow cylinders that are approximately 25 nanometers in diameter composed of long chains of a globular protein called tubulin.
More rigid than microfilaments and support cells structurally and stabilize junctions between them. i.e. Keratin
A structure typically in close proximity to the nucleus and contains a pair of perpendicularly oriented cylindrical centrioles surround by protein that is amorphous.
The primary function of centrosome is _______ microtubules within the cytoskeleton.
Large barrel shaped protein complexes that are major protein digesting organelles located within both the cytosol and nucleus of cells.
The garbage disposal for unwanted protein.
_____ and _____ flagella are extensions of the plasma membrane involved in movement.
Cilia and flagella
______ are structures that increase the surface area of the plasma membrane.
Cilia contain both ______ and supportive _____ proteins.
cytoplasm and microtubule
Flagella are ____ than cilia but have the same basic shape.
The only example of a human cell with flagellum is ____.
The movement of both cilia and flagella occurs through the _______ within their core.
Thin, microscopic membrane extensions from the surface of the plasma membrane.
Microvilli provide a more extensive plasma membrane surface are for more efficient _______.
Membrane junctions ____ and ____ cells.
connect and support
Three major types of membrane junctions
Composed of plasma membrane proteins that form strands or rows of proteins.
______ junctions function to seal off the intercellular space and prevent substances from passing between the cells.
Tight junction requires all materials to move _____ rather than between the cells.
This type of membrane junction is composed of several different proteins that bind neighboring cells.
The nucleus is enclosed within a double membrane that is called the ____.
The nuclear envelope separates the cytoplasm from the ____.
This boundary controls the movement of materials between the nucleus and the surrounding cytoplasm. Each of the two layers of the nuclear envelope is a phospholipid bilayer and is continuous with the rough ER.
open passageways formed by proteins that extend through fused regions of the nuclear envelope.
A nucleolus is not membrane bound and is composed of _____ and ____ and is responsible for producing the large and small subunits of ribosomes.
protein and RNA
Steps of transcriptions
1 DNA is unwound and RNA polymerase attaches to the promoter of the gene
2 RNA polymerase forms an RNA copy of the gene
3 The RNA strand is released from the DNA strand
_____ is the cell division that takes place in somatic cells.
Chromatins are composed of ____ and _____.
DNA and proteins
One of the main factors that influences membrane permeability is ____.
Are microscopic projections of the plasma membrane and function to increase the surface area of the plasma membrane.
move chromosomes during cell division
The ____ is a general term for all cellular contents between the plasma membrane and the nucleus.
_______ form a nucleic acid biomolecule is formed by repeating monomers
DNA is specifically composed of ______.
deoxyribonucleotides, which includes five-carbon sugar deoxyribose, a phosphate, and one of four nitrogenous bases
The four nitrogenous bases
Nucleotide monomers are linked through the phosphate groups by ____ to form a polymer strand.
Adenine only pairs with ___, which is a complementary base pairing.
Cytosine pairs only with ____, which is a complementary base pairing.
Adenine is only found in ____.
Uracil is only found in ____.
DNA serves as the template to form an ____ molecule that is complementary to the sequence of the nucleotides in the gene.
Forming RNA during transcription requires both large number of ____ and the enzyme ______.
Process of transcription
Initiation - DNA is unwound
Elongation- Hydrogen bond forms between bases of DNA and the newly forming RNA molecule
Termination - RNA polymerase reaches the terminal region of the gene; newly formed RNA strand is released from the DNA strand
The synthesis of a new protein and takes place at ribosomes within the cytosol.
Pre mRNA includes ____, which are noncoding regions.
Translation requires ribosomes, ____, ____ and large numbers of free amino acids.
Three functional types of RNA are required for protein synthesis
The ____ gradient is dependent on the combination of the ____ gradient and the chemical concentration gradient.
What are the common cell shapes?
The cytosol close to the plasma membrane contains relatively more ____ than does the interstitial fluid that is close to the plasma membrane.
The synthesis of steroid hormones occurs in the ____.