Table of Contents Link

Mr K’s

AP Biology

Unit 2: Cells

Student Notes

Notes adapted from A+ College Ready AP Biology Curriculum

Unit 2 Student Notes Page 1

Table of Contents Link

Unit 2 Student Notes

Table of Contents

A. Basic Cell Structure—Pages 3-7

B. Endosymbiotic Hypothesis—Pages 3-4

C. Membrane Structure—Pages 8-10

D. Eukaryotic Cell Components—Pages 11-15

E. Endomembrane System—Page 12

F. Cellular Transport—Pages 16-21

G. Diffusion—Page 16

H. Osmosis—Pages 16-18

I. Water Potential—Pages 17-18

J. Facilitated Diffusion—Page 18

K. Active Transport—Pages 18-21

L. Cotransport—Pages 19-20

M.Bulk Transport—Pages 20-21

th

Important figures and Illustrations in your Campbell’s 8edition Biology Textbook

Unit 2: Cell Structure & Function, Cell transport 2-3 weeks

Chapter 6 Figures: 6, 8, 9, 10, 12, 13, 14, 16, 17, 18, Table 6.1, 22, 23, 25, 27, 30, 32

Chapter 7 Figures: 2, 3, 4, 5, 7, 8, 9, 10, 11-13, 15-20

Chapter 36 pgs 768-771 Water potential

You should use these notes and the links within along with the figures in your textbook to

prep or to review each days material.

Unit 2 Student Notes Page 2

Table of Contents Link

AP Biology

Basic Cell Structure

Harvard Cell Video:

Inner Life Of A Cell - Full Version.mkv

Cells

Cells are considered to be the basic units of life.

●

The cell is an example of Emergent Properties. The organelles alone can do nothing, but if all of them are put

●

together inside a cell membrane, “life” can emerge.

Cytology is the study of cells; Cytologist – a person who works with cells.

Cell Types

Prokaryotic cells

●

o These organisms (eubacteria and archae) evolved before the evolution of the nuclear membrane and

nucleus. These cells also lack membrane bound organelles. They are extremely small when compared to

eukaryotic cells.

o It is believed that the first prokaryotic cells came into existence about 3. 5 Billion Years Ago (BYA).

o The oldest prokaryotic fossils are found on stromatalites (bacterial mounds) in Shark Bay, Australia.

Eukaryotic cells (“Eu” means “true”)

These cells evolved after the evolution of the nucleus. All organisms on Earth, other than eubacteria and archae

●

are composed of eukaryotic cells. Eukaryotic cells have a membrane bound nucleus and membrane bound

organelles.

Endosymbiotic Hypothesis

The Endosymbiotic Hypothesis, proposed by Lynn Margulis in the 1960s, hypothesized that some prokaryotes

●

begin to live together in symbiotic relationships with the smaller prokaryotes living inside larger ones. This gave

the symbionts a survival advantage over other prokaryotes and eventually they evolved into Eukaryotic cells.

o Smaller organisms gained protection.

o Larger organisms gained energy production or faster motility.

o Over time DNA segments were “swapped” to create a more permanent existence. This “swapping” is

referred to as genetic annealing.

o The smaller prokaryotes eventually became the organelles within the larger prokaryotes.

o Evidence for this hypothesis are found in mitochondria and chloroplasts.

Mitochondria and chloroplasts have their own single circular chromosome like

▪

Bacteria.

Mitochondria and chloroplasts have ribosomes that are similar to those found in

▪

Bacteria.

Mitochondria and chloroplasts are able to independently reproduce within the larger

●

eukaryotic cells. They use a process similar to binary fission. Mitochondria and

chloroplasts have a double phospholipid bilayer cell membrane.

Unit 2 Student Notes Page 3

Table of Contents Link

Endosymbiosis from Learn Genetics: The Evolution of the Cell

The Surface Area- to- Volume Ratio is of GREAT Importance for all cells.

●

As cells grow, the surface area to volume ratio for the cell decreases. Think of the surface area as the cell membrane and

the volume as the internal contents of the cell. As the cell gets larger, it gets harder for cells to transport in and out the

required materials. This is one of the main reasons that cells must always be very small. Smaller cells have a higher surface

area to volume ratio and are better able to transport materials through the cell membrane.

Adaptions for increasing the surface area without increasing the volume

Surface area to volume ratio can also be used to explain the

●

shape of many cells / cellular surfaces. For example the

folds inside the mitochondria or the flat pancake like

structures inside chloroplasts provide a greater surface area

on which specific reactions can occur. The folds in the lining

of our stomachs or the tiny cellular, finger-like projections

that protrude from the wall of the small intestine (villi and

microvilli) all act to increase the surface area without

increasing the overall size or volume of the organ.

Video explaining above (4 min) IB Biology 2.1.6 Surface area to volume ratio in cells

Size of Cells: Cell Size and Scale

Unit 2 Student Notes Page 4

Table of Contents Link

Basic Prokaryotic Cell (Bacteria and Archae) Structure

●

All prokaryotes are unicellular.

●

Prokaryotic cells possess a single circular chromosome not

enclosed in a nuclear membrane), ribosomes (for making

proteins), and cytoplasm.

●

The cells do not possess membrane-bound organelles like

mitochondria or chloroplasts.

Three basic shapes of prokaryotes exist:

1. Cocci (Means “round”)

2. Bacilli (Means “rod”)

3. Helical or Spiro (Means “spiral”)

●

Most prokaryotes will have a cell wall. (This is NOT the same as a plant’s cell wall.)

o This structure is primarily for protection of the underlying cell membrane.

o It also helps prevent the prokaryotes from bursting in an aquatic environment.

o In eubacteria, the cell wall is mainly composed of a protein and sugar substance known as peptidoglycan.

Unit 2 Student Notes Page 5

Table of Contents Link

●

Scientists/doctors perform Gram stains to identify bacteria as either Gram positive or Gram negative. Different antibiotics

work against each group.

o Gram positive bacteria stain blue. These bacteria possess a THICK peptidoglycan layer.

o Gram negative bacteria stain red. These bacteria possess a THIN peptidoglycan layer BETWEEN phospholipid

layers.

o Some bacteria produce a Capsule that covers the cell wall. The capsule is a sticky substance for adherence to surfaces. The

capsule can protect the bacteria from a host cell’s immune response.

o Although we think of bacteria as germs that make us sick, most bacteria are beneficial. Bacteria are important in the process of

decomposition/mineral recycling. Other bacteria fix nitrogen, do photosynthesis, and help us manufacture certain foods and

chemicals.

o Biofilms are millions of different species of bacteria living in a symbiotic relationship where often the waste products of

one species nourishes other species. Plaque on your teeth are an example. Scientists are now aware that biofilms are

the cause of many chronic infections as they are notoriously difficult to eradicate. Check out this 6 minute video on

biofilms What Are Bacterial Biofilms? A Six Minute Montage

Unit 2 Student Notes Page 6

Table of Contents Link

Basic Structure of Eukaryotic Cells

1. Interactive Cell Models: Interactive Eukaryotic Cell Model

2. Plasma “cell” membrane: This holds the cell together. The eukaryotic cell membrane is very similar to

the prokaryotic cell membrane. The membrane is important for transporting substances into and out of

the cell.

3. Nucleus: This structure controls the activities of a cell by holding the DNA. The DNA serves as the

instructions for building proteins. The DNA of eukaryotes is enclosed within a membrane called the

nuclear membrane or envelope.

Prokaryotic DNA floats in the cytoplasm and is sometimes referred to as nucleoid (nucleus-like).

4. Cytoplasm or cytosol: This fluid filled space contains the nucleus and the other organelles. This area

makes up most of the volume of the cell.

5. Membrane-bound organelles: These enclosed structures specialize to carry out specific jobs within the

cell. Examples include: the nucleus, mitochondria, chloroplasts, the endoplasmic reticulum, and the

Golgi apparatus.

Unit 2 Student Notes Page 7

Table of Contents Link

Membrane Structure and Transport of Molecules

Selectively Permeable

The cell membrane (plasma membrane) is referred to as selectively permeable or semipermeable.

In this class, SPM = Selectively Permeable Membrane

This means that the cell allows or actively transports certain materials into or out of the cell while not allowing

other materials to enter or exit the cell. Typically, small and nonpolar substances can enter the cell

easily, while large and/or polar/charged substances either cannot enter or have to be brought

into the cell via some type of protein channel.

Membrane Structure

o A phospholipid bilayer makes up the majority of the cell membrane and the organelle

membranes.

o Phospholipids are amphipathic molecules. They have both hydrophilic and hydrophobic

components/sides. These molecules form a bilayer because the hydrophilic portions of the

molecule (the phosphate groups) orient themselves toward the water that is located both

inside and outside the cell, while the hydrophobic portions of the molecule (the fatty acid

tails) orient themselves away from the water and toward each other in the center of the

membrane.

Structure of a Phospholipid and Bilayer - cell

Unit 2 Student Notes Page 8

Table of Contents Link

Proteins: Many different types of proteins are embedded into the phospholipid bilayer.

Integral Proteins run completely through the bi-layer from the outside to the inside and function in the transport

●

of molecules across the membrane. They also help to maintain the INTEGRITY of the membrane.

Peripheral Proteins are located on one side of the membrane. They do not extend through the bi-layer.

●

Peripheral proteins can act as receptors for cell signals, as catalysts/enzymes, and as structural components of

the cytoskeleton.

The proteins of the cell membrane can also perform the following functions:

Molecule transport: Each transport protein aids the transport of a specific molecule, ion, etc across the

● …

membrane.

Act as enzymes to catalyze specific reactions.

●

Cell to cell communication and recognition: These proteins can help cells attach to each other and work

●

together and/or communicate with each other.

Signal Receptors: Act to receive hormones or other signaling molecules which circulate in the blood or interstitial

●

fluids.

Attachment points: Some proteins act as attachment points for the cytoskeleton.

●

Cholesterol

This lipid molecule functions to keep the membrane from being too fluid, and too permeable to some small

●

molecules. It also helps to secure the proteins that are embedded in the membrane.

Cholesterol helps to keep the cell membranes of plant cells from freezing solid in very cold temperatures.

●

Cell Membranes DEFINE Compartments! Membranes Organize Cellular Complexity

My Analogy? A one room schoolhouse vs HTHS. In a one room schoolhouse, do you think you could offer all of the

courses and academies we have at HTHS? It would be chaos! But if each course is in a different room, a different

environment, then you could!

Unit 2 Student Notes Page 9

Table of Contents Link

Fluid Mosaic Model of the Cell Membrane

● The current scientific model of the cell membrane is referred to as the Fluid-Mosaic model because it looks like a

moving (Fluid) puzzle (mosaic). The phospholipids compose the fluid portion, while the proteins are embedded

within like a mosaic. All the pieces can move laterally, like students moving from seat to seat. The proteins

moving in this sea of phospholipids are like a teacher moving around the student desks. Imagine the ceiling and

floor are water molecules. The water molecules prevent vertical movement of the cell membrane components.

Professor Dave Explains Cell Membranes! (7 min) Structure Of The Cell Membrane: Active

and Passive Transport

AP Biology

Unit 2 Student Notes Page 10

Table of Contents Link

Eukaryotic Cell Components

There are four main parts to Eukaryotic Cells:

●

Plasma “cell” membrane: This structure holds the cell together and helps to regulate which substances can enter/exit the

cell.

●

Nucleus: This controls the activities of a cell because it contains the DNA which acts as the instruction for building the cell’s

proteins and determining its traits.

●

Cytoplasm or cytosol: This fluid-filled space contains the organelles and makes up most of the volume of the cell.

●

Organelles: These structures specialize to carry specific functions within the cell. By specializing, they divide up the labor

and make the cell more efficient. It is important to note that the number and distribution of organelles differs from cell

type to cell type.

Nucleus

●

This acts as a control center for all activities performed by

the cell.

●

It is the source of the cell’s genetic information or DNA.

Nuclear Envelope

●

It is composed mainly of a double phospholipid bi- layer.

●

It encloses the DNA.

●

It also contains pores (tunnels) composed from proteins

which allow certain specific materials to enter/exit the

nucleus. The messenger RNA must exit the nucleus and go

to the ribosomes where it acts as the directions for making

proteins.

DNA

●

Chromatin phase—During most of the cell’s life cycle, the DNA is loose and spread-out throughout the nucleus. During the

chromatin phase, the DNA looks like a bowl of plain spaghetti noodles. During the phase, the DNA can be transcribed and

used to make proteins. Working form of DNA

●

Chromosome phase—During this phase, the DNA coils around proteins called histones (in eukaryotes and archae). The

coiling helps to organize the DNA so that it can be correctly distributed during the processes of nuclear and cell division

Nucleolus

●

This structure appears as a dark spot within the nucleus.

●

The nucleolus functions to make the ribosomal RNA (rRNA) and proteins which make up the cell’s ribosomes.

Ribosomes

These are CELL PARTICLES made of ribosomal RNA (rRNA) and proteins. Ribosomes are not usually considered to

●

be organelles because they are not enclosed within a membrane. All cell types, both prokaryotic and eukaryotic,

have ribosomes.

Ribosomes are the sites of Protein Synthesis. The cell’s normal proteins and enzymes are ALL made here.

●

Two types of ribosomes exist based on location:

●

o Free Ribosomes– These float “freely” in the cytoplasm of a cell. (They are found in ALL TYPES of

cells.) These ribosomes make proteins that will stay and function inside the cell that made them.

o Bound Ribosomes – These ribosomes are attached to the rough endoplasmic reticulum (RER).

(These are ONLY found in Eukaryotes ONLY because only they have the RER.) Bound ribosomes make

proteins that will leave the cell to be used elsewhere. Many of these proteins acts as cellular

communication signals or as antibodies to fight infections.

Unit 2 Student Notes Page 11

Table of Contents Link

Endomembrane system

The endomembrane system (endo = “within”) is a group of membranes and organelles in eukaryotic cells that work

together to modify, package, and transport lipids and proteins. Once the bound ribosomes make their

proteins, the proteins enter the Rough ER and are eventually packaged into phospholipid-based secretory

vesicles. These vesicles transport the proteins to the Golgi apparatus where they will be modified. After

modification, the proteins are once again packaged into a lipid-based vesicle and shipped to the cell

membrane. The proteins are excreted from the cell while the phospholipids that made up the vesicle

become part of the cell membrane. The general pathway is (RER →Secretory vesicle→ Golgi →secretory

→

vesicle Membrane for release. In some cases, the packaged proteins/enzymes become part of a lysosome instead of

being transported out of the cell.

KNOW THIS PATHWAY! For the synthesis of a protein bound for export beginning with transcription

●

Endoplasmic Reticulum (ER)

o It is composed of a network of small tubes called cisternae. (“cisternae” means “tubes”)

o The ER is ALWAYS found just outside and around the nucleus.

o Two types of ER can exist inside EUKARYOTIC cells:

Smooth Endoplasmic Reticulum (SER)

▪

●

This structure helps with the synthesis of lipids, phospholipids, and steroids.

●

It also helps with carbohydrate breakdown.

●

The smooth ER can also aid in the detoxification of the blood. (Liver cells are loaded with SER.)

●

It also helps the storage of Ca++, needed for muscle contraction. (Muscle cells have lots of SER.)

Rough Endoplasmic Reticulum (RER)

▪

●

This structure helps with protein synthesis, modification, and transport.

●

Ribosomes are bound to the outside of the organelle and deposit the newly constructed proteins into

the Rough ER. Inside the structure, the proteins are folded into the specific 3-D structure needed to

function.

Unit 2 Student Notes Page 12

Table of Contents Link

o Golgi Apparatus

o The Golgi Apparatus or Golgi Body modifies proteins by attaching sugars to them. (called Glycoproteins). The Golgi may

act as a warehouse for storage of proteins, but eventually packages the proteins and ships them out in vesicles. The

Golgi apparatus is usually located near the cell membrane.

WATCH THIS 3 MINUTE VIDEO Endomembrane transport animation: The Endomembrane System

o Lysosomes

o These organelles contain powerful hydrolytic enzymes and acids. The lysosomes help to carry out the process of

intracellular digestion. This process helps to breakdown materials within a cell. Once broken down, the components of

some of these materials may be recycled for other purposes.

o Vacuoles and Vesicles: These organelles act as phospholipid-based storage containers for the storage of materials needed by

the cell. Various types such as Food, Contractile, Transport, Secretory and Central exist in different types of cells.

o Mitochondria:

o ARE NOT THE POWERHOUSE OF THE CELL! It is more of an energy CONVERTER. If you EVER say this on

a test or quiz I will automatically give you a ZERO for that question.

o Aerobic Respiration:

o The mitochondria perform the process of aerobic cellular respiration. During this process the energy from food is

transferred to the bonds of ADP and P to create ATP. ATP then serves as the source of energy for most of the cell’s

processes.

o Mitochondria:

o Have their own DNA

o Have their own bacteria-like ribosomes, its own enzymes,

o can reproduce independently via binary fission. Click for a short video

o The inner membrane of the mitochondria are folded into structures known as cristae. The folds increase the surface area

and serve as the sites for the electron transport chain.

o Evolutionary Significance: All evidence shows that Mitochondria have descended from aerobic bacteria that entered into a

symbiotic relationship with larger prokaryotic cells that could provide protection in return for the ATP produced by the

mitochondria. Together they would have an evolutionary advantage over other bacteria. The advantage allowed them to

survive and reproduce and eventually led to the evolution of Eukaryotic cells.

Unit 2 Student Notes Page 13

Table of Contents Link

Chloroplasts

These organelles are the sites of

Photosynthesis in plants and algae.

Chloroplasts are a type of Plastid or

pigment container.

Like mitochondria, chloroplasts have

their own DNA, ribosomes, and

enzymes! They can also reproduce

independently via binary fission too!

The interior of a chloroplast is

composed of stacks of sack-like

structures known as thylakoids. This

stack-like arrangement increases the

surface area needed to carry out the light-dependent stages of photosynthesis.

The stroma is mostly a watery space in between the thylakoids and outer membrane. The stroma serves as the site of the Calvin

Cycle (the metabolic pathway in which sugar is made).

Evolutionary Significance: Evidence shows that Chloroplasts evolved from blue-green bacteria (cyanobacteria) that entered into a

symbiotic relationship with other bacteria.

Endosymbiont Hypothesis uses all of the available evidence to scientifically explain the symbiotic relationships that led to the

evolution of eukaryotic cells from prokaryotic cells. (See earlier in the notes for details)

Cytoskeleton

●

These structures help to support and protect the cell.

●

The cytoskeleton also helps to keep inner organelles organized. The spindle fibers that help to move the chromosomes

during mitosis and meiosis are composed of elements of the cytoskeleton.

●

The cytoskeleton also helps to make up structures such as flagella and cilia which aid in cell motility or cell organelle

movement. (Much like your skeleton helps you move.)

●

The cytoskeleton is composed of various sized protein fibers known as either microtubules, microfilaments, or

intermediate filaments. (Your skeleton has different sized structures too. Largest – bones, middle – Ligament and

tendons, smallest- muscle fibers.)

Unit 2 Student Notes Page 14

Table of Contents Link

●

Protective or weight bearing structures for cells:

o Cell Wall of Plant Cells--It is composed primarily of the carbohydrate cellulose. It functions to provide support and

protection to the plant. It may also protect the cells from bursting if they are exposed to hypotonic conditions.

o Cell Walls of Fungus--Composed of the carbohydrate called Chitin. The functions of the fungal cell wall are similar to

those of the plant cell wall.

●

Extra Cellular Matrix (ECM) See diagram below of ECM Extracellular matrix | Structure of a cell | Biology | Khan Academy

(Khan Academy)

o The extracellular matrix consists of molecules that are secreted by a cell into the space out the cell’s membrane. The

extracellular matrix can form cell walls, bone, cartilage, etc… The ECM can function to provide support, to segregate

different tissues from one another, and to regulate intercellular communication.

A CELL IS THE MORE THAN THE SUM OF ITS PARTS! Only when all the parts come together and work together can “LIFE” happen.

This is known as Emergent Properties 1.1 Emergent Properties

With Increasing Complexity Novel Properties Emerge

Unit 2 Student Notes Page 15

Table of Contents Link

AP Biology

Cellular Transport Mechanisms

●

Material Transport

o COand O(both gases) can diffuse across the wet phospholipid bi-layer because they are neutrally charged and

2 2

small particles.

o Ions, polar molecules, and large molecules move through the membrane with the help of either channel or carrier

proteins.

●

Passive Transport NO ENERGY REQUIRED! The process is powered by energy from the environment – NOT from the cell.)

Diffusion

●

Diffusion operates upon an established concentration [ ] gradient or difference in concentration.

o Materials flow from high concentration to low concentration until equilibrium is achieved.

Once equilibrium is reached, the particles still move, but net diffusion ceases.

▪

o This is how the majority of materials are transported in cells. (Because it requires no Energy (E) expenditure by the

cell…which saves E for maintaining homeostasis, repair, and reproduction.)

Osmosis: The diffusion of Water

●

Osmosis is a type of diffusion. This means that water moves from areas of high water concentration to areas of low water

concentration. Osmosis is also often defined in terms of the solutes that are dissolved in the water. In terms of solutes,

water moves from areas of low solute concentration (high water concentration) to areas of high solute concentration (low

water concentration).

●

Osmosis is also often defined in terms of the words hypotonic and hypertonic. Water ALWAYS flows from Hypotonic (low

solute concentration/high water concentration) to Hypertonic (high solute concentration/low water concentration).

o Osmosis often happens when a membrane is impermeable to a solute that is present in different concentrations on

each side of the membrane. Water moves to even out the solute concentrations.

Plants, fungi, and bacteria have cell walls that may affect water movement, see below.

▪

Most water movement into or out of the cell occurs through proteins called aquaporins. These proteins

▪

act as tunnels for only water movement.

●

Osmosis is crucial for all cells to control.

Osmoregulation—the process of regulating the solute and water concentrations of the cell or body. This is one of the main

functions of the urinary system.

Turgid – This refers to a condition when there is lots of water in a cell that possesses a cell wall, so the cells are rigid and stiff.

Flaccid – This refers to a condition when there is not very much water in a cell that possesses a cell wall, so the cells are limp and

wilted.

Plasmolysis – This is when the cell membrane shrivels away from the cell wall. This happens when a cell is placed into a hypertonic

environment. Water leaves the cell and it shrivels up. This is why salty environments kill plants.

Diffusion and Osmosis - Passive Transport: https://www.youtube.com/watch?v=PRi6uHDKeW4 4 min video

Unit 2 Student Notes Page 16

Table of Contents Link

Assume that the membrane is impermeable to the solute in each of the two diagrams included below.

Osmosis in Animal Cells

Water Potential (Represented by the Greek letter psi: Ψ…after Poseidon’s Trident.)

● Water Potential is a measure of the relative tendency of water to

move from one area to another. Water potential takes into

account both the effects of solute concentration and pressure.

Such calculations are important when trying to determine the

effects of osmosis on cells that possess a cell wall.

● Ψ Ψ

Water always flows from High to Low . The total water potential

of pure water in an open container is 0.

Ψ

o Pressure Potential (Represented by .)

P

Pushing is positive pressure being exerted on the

▪

(+Ψ

cell. P)

(-Ψ

Pulling away from is negative pressure P) being

▪

exerted on a cell. (Important when you consider a

plant is having water pulled out of it by transpiration

at the stomata and pushed into the xylem vascular

Unit 2 Student Notes Page 17

Table of Contents Link

cylinder in the root.

Solute Potential (Represented by the symbol Ψ) = -iCRT

Ψ

o

S

S

i = is the ionization constant. The ionization constant is essentially the number of ions that are formed

▪

when a substance dissolves.

●

The ionization for sugars is always 1. Sugars don’t ionize when they dissolve.

-

●

The ionization constant for NaCl is 2 because it ionizes into 1Na+ and 1Clion when it dissolves.

+2 -

●

The ionization constant for CaClis 3 because the salt dissolves into 1 Caand 2Clions.

2

●

Don’t forget to include the leading negative sign from the formula.

C = the molar concentration or molarity measured in moles of solute/Liter of solution.

▪

R = the pressure constant. (R= 0.0831liter-bars/mole-K)

▪

⁰C=K) You must use the Kelvin temperature in these calculations.

T = the temperature in Kelvin. (273+

▪

Total Water Potential (Represented by Ψ) =

Ψ Ψ+Ψ

T

o T S P

Water Potential is important during the process of transpiration. The water potential is highest in the soil (value is

closer to 0) and lowest in the air (value is farther away from 0 in negative direction). Water thus moves

from the soil into the roots, from the roots to the stem, and the stem to the leaves, and from the leaves

out the stomata into the air.

Facilitated Diffusion

●

Facilitated diffusion (a type of passive transport) transports

materials from high concentration to low concentration. This

type of transport requires the help of channel or transport

proteins because the materials that are being transported are

either polar/ionic/large.

●

Aquaporins- Channel proteins which help move water (because

it is a polar molecule) across a membrane via facilitated

diffusion.

●

Gated-ion channels move sodium and potassium ions in and

out of neurons are also examples of channel proteins which aid

in the process of facilitated diffusion.

Unit 2 Student Notes Page 18

Table of Contents Link

Active Transport: https://www.youtube.com/watch?v=PRi6uHDK

eW4

Active Transport (This process uses ENERGY This energy is often provided by ATP Hydrolysis.)

● …it will require energy.)

This process moves materials against the concentration gradient. (Like pushing a car up a hill

●

Materials are being moved from areas of low concentration to areas of high concentration.

o The Na+/K+ Pump of the nervous system, is an example.

o Energy from ATP by Phosphorylation (Attaching a phosphate ion to a structure to make it work.) activates the

protein to grab and move molecules.

Mr. Anderson explains how ATP can power cellular processes (9 min): ATP: Adenosine Triphosphate

Electrogenic Pump (A.K.A. Proton [H+] Pump)

●

This is the most important active transport protein for all life forms. Proton pumps are important in processes involved in

the electron transport chain of photosynthesis and cellular respiration.

o Hydrogen ions (protons), H+, move out of the cell to create a gradient. (Outside is + and inside is -.) Diffusion can

now occur based on charges into and out of cell. The gradient serves as a source of energy for producing ATP.

Co-transport

●

Co-transport is a process in which two substances are simultaneously transported across a membrane by one protein, or

protein complex which does not have ATPase activity.

●

Co-transport is a type of active transport. Usually one of the substances moves with the concentration gradient (from high

to low concentration). The movement of this substance provides the energy to transport the other substances against the

concentration gradient (from low to high concentration).

o Symport: When transport protein moves both substances in the same direction.

o Antiport: When transport protein moves the two substances in opposite directions

●

An example of co-transport is the absorption of glucose by epithelial cells in the gut. In the gut, glucose is co-transported

with sodium ions. The concentration of Sodium ions is higher outside the gut cells than it is inside them. The

sodium/potassium pump establishes and helps to maintain the sodium concentration gradient. This is called primary active

transport. Sodium then moves into the cells (through a transport protein (symport) down its concentration gradient. The

concentration of glucose is higher inside the cells that it is outside the cells. The energy from the movement of the sodium

ions powers the secondary active transport of glucose into the cells by the same transport protein or symport.

Unit 2 Student Notes Page 19

Table of Contents Link

Large Molecule Transport or Bulk Transport

The movement of molecules that are TOO big for proteins to transport. All forms of bulk transport require the cell to expend energy

and thus can be classified as forms of active transport.

Unit 2 Student Notes Page 20

Table of Contents Link

Exocytosis – This is the process of moving large materials out of a cell. Exocytosis is often referred to as secretion. An example of this

process would be Pancreatic cells releasing the hormone Insulin into the blood stream to help regulate blood glucose

levels. Typically, this involves vesicles from Golgi Apparatus fusing with the cell membrane and secreting the proteins

they contained into the interstitial fluids.

Endocytosis – This is the process of moving large materials into a cell. (“Endo” means “in”)

Phagocytosis – This process is transports large, solid particles into the cell. It usually involves the surrounding of the particles with

the cell membrane, the engulfing of the particles, and the surrounding of the particles with a vesicle. A

white blood cell taking in a bacterial cell is a good example of phagocytosis. Phagocytosis is often followed

by the process of intracellular digestion.

Pinocytosis – Pinocytosis is a mode of endocytosis in which small particles suspended in extracellular fluid are brought into the cell

through an invagination of the cell membrane, resulting in a suspension of the particles within a small

vesicle inside the cell. These pinocytotic vesicles subsequently fuse with lysosomes to hydrolyze (break

down) the particles.

Receptor-Mediated Endocytosis

Receptor mediated endocytosis is an endocytic mechanism in which specific molecules are transported into the cell. The specificity

results from a receptor-ligand interaction. In this case, the ligand is the substance that is being transported

into the cell. The ligand binds to a receptor (on the cell membrane) that is specific to that particular ligand.

This triggers an endocytotic process and the ligand is ingested. The transport of cholesterol into cells is a

good example. LDL cholesterol normally binds to receptors on the cell membrane and is then transported

into cells. Individuals with the genetic condition familial hypercholesterolemia don’t have receptors for LDL

cholesterol. The LDL can’t be transported into the cells, stays in the bloodstream, and causes clogging of the

arteries.

Transport Vesicles shown in video microscopy Directing Traffic: How Vesicles Transport Cargo

Unit 2 Student Notes Page 21