, some of the “traditionally intermediate” level concepts ... PP3.pdf · 2. Plant cells are...

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© Stephanie Elkowitz1

• Cell Theory

• Unicellular vs. Multicellular

• Prokaryotes & Eukaryotes

• Animal Cells

• Plant Cells

• Bacteria

• Protists

• Cell Membrane Structure & Function

• Cell Receptors & Communication

• Cell Transport (Passive & Active)

• Osmosis

• Tonicity

• Endocytosis & Exocytosis



• A cell is the basic

structural, functional

and biological unit of all

living things.

• A cell is tiny - it cannot

be seen with the naked

eye. It can only be seen

with a microscope.

What is a cell?

Cells


• Cells were discovered by

scientist Robert Hooke

in 1665.

• He called them cells

because they resembled

the cells lived in by

Christian monks in a

monastery.

Cells


• The Cell Theory is scientific theory that describes the

properties of ALL cells.

• There are three tenets to the Cell Theory:

1. All living things are made of cells. Some living things,

such as bacteria, are made of one cell. Other living

things, such as plants and animals, are made of many

cells.

2. The cell is the basic unit of life. A cell is the most basic

unit of structure and function in all living things.

3. Cells arise from pre-existing cells. Cells divide to make

copies of themselves. Cells do NOT arise spontaneous

or from nonliving things.

Cells


• A living thing can be made of one or more cells.

• Unicellular organisms are organisms made of one cell.

• Multicellular organisms are organisms made of many cells.

• Bacteria and protists are unicellular organisms.

• Plants, animals and fungi are multicellular organisms.

Cells


• Unicellular organisms perform life functions using

organelles. Organelles are structures inside of a cell.

– Unicellular organisms use the cell membrane to take in nutrients and

gases, such as oxygen and to excrete waste.

– Unicellular organisms digest nutrients in organelles known as food

vacuole.

– Unicellular organisms use cytoplasm (the jelly substance inside a

cell) to transport substances throughout them.

– Unicellular organisms can use hair-like projections on the outside of

the cell (cilia) or a tail-like structure (flagellum) that extends out of

one side the cell to help them move in the environment.

Cells


• Multicellular organisms are more complex than unicellular

organisms. Their cells work together. Cell that work together

form tissues. Tissues form organs and organs form organ

systems. Organ systems perform important life functions.

– Multicellular organisms take in and digest nutrients using the

digestive system.

– Multicellular organisms take in oxygen using the respiratory system.

– Multicellular organisms use a circulatory system to transport

substances throughout their bodies.

– Multicellular organisms use an excretory to rid their bodies of waste.

– Multicellular organisms use a skeletal and muscular system to help

them move throughout the environment.

Cells


• There are two major types of cells:

1. Prokaryotes

2. Eukaryotes

• Organisms made of prokaryotic cells are called prokaryotes.

• Organisms made of eukaryotic cells are called eukaryotes.

Cells


• Prokaryotes and eukaryotes are different for two MAJOR

reasons:

1. Eukaryotes have a nucleus. Prokaryotes do not.

2. Eukaryotes have membrane-bound organelles.

Prokaryotes do not.

Cells


• Prokaryotes (or prokaryotic cells) do NOT contain a nucleus.

• Prokaryotic DNA is found clumped together in the cytoplasm

in a region known as the nucleoid.

• Prokaryotes do NOT have membrane-bound organelles.

• Prokaryotes DO have ribosomes (important to making

proteins).

• Prokaryotes have a cell membrane and cytoplasm.

• Most prokaryotes have a cell wall.

• Some prokaryotes have a capsule.

• Prokaryotes are very tiny, unicellular organisms.

• Examples: Bacteria, Archaebacteria

Cells


• Eukaryotes (or eukaryotic cells) contain a nucleus.

• Eukaryotic DNA is found inside the nucleus.

• Eukaryotes have membrane bound organelles, such as

mitochondria.

• Eukaryotes have ribosomes.

• Eukaryotes have a cell membrane, cytoplasm & ribosomes.

• Some eukaryotes have a cell wall.

• Eukaryotes do NOT have a capsule.

• Eukaryotes are unicellular or multicellular organisms.

• Eukaryotes are larger and more complex than prokaryotes.

• Examples: Protists, fungi, plants, animals

Cells


• Compare and contrast prokaryotes and eukaryotes.

Cells

Prokaryotes Eukaryotes


• Compare and contrast prokaryotes and eukaryotes.

Cells

Prokaryotes Eukaryotes

• No nucleus

• DNA in a region

called nucleoid

• No membrane-

bound

organelles

• Some have a

capsule

• Unicellular

• Ex: Bacteria,

Archaebacteria

• Nucleus which

contains DNA

• Membrane-bound

organelles

• No capsule

• Unicellular or

multicellular

organisms

• Ex: Plants,

Animals, Fungi,

Protists

• Ribosomes

• Cytoplasm & cell

membrane

• Some have a cell

wall


• When scientists study cells, they often focus on 4 different

types of cells:

1. Bacteria

2. Protists

3. Animal Cells

4. Plant Cells

• Note: There are other types of cells, such as fungal cells.

Fungal cells make up fungi. We will not study fungal cells in

this presentation.

Cells


• There are four features that ALL cells have in common:

1. They are surrounded by a cell membrane.

2. They contain cytoplasm, a jelly-like substance inside

the cell.

3. They contain DNA, which codes for all characteristics of

the cell. Prokaryotes usually have one long strand of

DNA. Eukaryotes have multiple strands of DNA called

chromosomes.

4. They contain ribosomes, structures important to

making proteins.

Cells


• A bacterium is a unicellular

organism.

• Bacteria are prokaryotes.

• Most bacteria have a cell wall (in

addition to a cell membrane).

• Many bacteria have a flagellum (a

tail-like structure that helps them

move).

• Most bacteria have to “eat” food but

some can make their own food.

– Example: Cyanobacteria or blue-green

algae perform photosynthesis.

Cells


• A protist is (usually) a unicellular

organism.

• Protists are eukaryotes.

• Protists do not have a cell wall.

• Many protists have a special structure

called a contractile vacuole. A

contractile vacuole helps remove

excess water in the organism.

• Many protists have cilia (hair-like

projections that help them move).

• Protists can make their own food or

“eat” food.

Cells


• Animals are multicellular

organisms. They are made of

animal cells.

• Animal cells are eukaryotic.

• Animal cells do not have a cell

wall.

• Some animal cells have cilia

or a flagellum.

• Animals cannot make their

own food. They must eat in

order to provide nutrients to

their cells.

Cells

Human blood cells


• Plants are multicellular

organisms. They are made of

plant cells.

• Plant cells are eukaryotes.

• Plant cells have a cell wall.

• Plants cells have structures

known as chloroplasts.

Chloroplasts are organelles that

perform photosynthesis. They

enable plant cells to capture

energy from the sun and make

food.

Cells


• Like all eukaryotic cells, animal

cells contain a nucleus and

organelles. Organelles are

structures found inside a cell.

They perform various functions.

• Let’s study important

organelles found inside an

animal cell.

Cells


• The cell membrane is a

structure that surrounds the

cell. It acts like a barrier. It

allows substances to pass in

and out of the cell and helps

a cell communicate with

other cells.

Cells

Cell Membrane


• Cytoplasm is jelly-like

material located in the cell in

which the organelles are

contained. It is composed of

water and dissolved

nutrients and salts

Cells

Cytoplasm


• The nucleus is often referred

to as the control center of

the cell. It contains DNA and

controls many of the cell’s

functions.

• Within the nucleus is a

structure called the

nucleolus. The nucleolus

produces parts of the

ribosomes.

Cells

Nucleolus

Nucleus


• Ribosomes are small

organelles where protein

synthesis takes place. They

are found floating freely in

cytoplasm or attached to

endoplasmic reticulum.

Cells

Ribosome


• Endoplasmic reticulum (ER) is a

series of interconnected

membranes found outside the

nucleus.

• There are two types of ER:

– Rough ER has ribosomes attached

to it giving it a “rough” appearance.

It transports materials throughout

the cell and produces proteins.

– Smooth ER does not have

ribosomes attached to it. Like

Rough ER, it transports materials

throughout the cell but produces

lipids instead of proteins.

Cells

Rough ERSmooth ER


• The Golgi Bodies (also called

Golgi Apparatus or Golgi

complex) sort and package

materials such as proteins and

carbohydrates into vesicles.

These vesicles are delivered to

certain part of the cell or

exported from the cell.

Cells

Golgi Bodies


• Mitochondria are round or

rod-shaped organelles with

a double membrane.

• A mitochondrion is often

called a “powerhouse of

the cell" because it

produces energy for the

cell. Mitochondria convert

chemical energy in sugar to

usable energy for the cell.

This energy is known as

ATP.

Cells

Mitochondria


• Vacuoles are vesicles in the

cell that store nutrients,

waste or water. Sometimes

we name vacuoles based

on what they contain. For

example, a food vacuole

contains food.

Cells

Vacuoles


• Lysosomes are small,

round vesicles that contain

enzymes that digest cell

nutrients and break down

old cell parts. To digest

food, they merge with food

vacuoles to digest

nutrients.

Cells

Lysosome


• Plant cells are eukaryotic

like animal cells. They have

the following organelles

just like animal cells:

– Cell membrane

– Cytoplasm

– Nucleus

– Nucleolus

– Ribosomes

– Rough and Smooth ER

– Golgi Bodies

– Mitochondria

– Vacuoles

Cells

Nucleus &

NucleolusCytoplasmRough ER

Golgi

Bodies

Smooth ER

Cell Membrane

RibosomeMitochondria

Vacuole


• Plant cells also have

chloroplasts. Chloroplasts

perform photosynthesis.

Photosynthesis is the

process of making food

(sugar) using energy from

the sun.

• Chloroplast contains green

pigment called chlorophyll.

Chlorophyll captures energy

from sun, enabling the cell

to perform photosynthesis.

Cells

Chloroplast


• Plant cells also have a cell

wall. The cell wall is located

just outside the cell

membrane. The cell wall is

rigid and helps provide

structure and protection.

Cells

Cell Wall


• There are three major differences between plant and animal

cells:

1. Plant cells contain chloroplasts. By performing photosynthesis,

plants can make their own food. Animal cells do not contain

chloroplasts and so animals must consume food in order to obtain

nutrients.

2. Plant cells are surrounded by a cell wall. Animal cells are not.

3. Although both plant and animal cells contain vacuoles, plant cells

contain one very large central vacuole whereas animal cells contain

small vacuoles. Plant cells have a large central vacuole filled with

water which helps maintain the shape of the cell. Animal cells

contain multiple small vacuoles, filled with food, water or waste.

Cells


• There are two other minor differences between animal and

plant cells:

1. Some animal cells have cilia or flagella. Cells in the human

respiratory tract have cilia. Cilia “sweep” debris, mucus and dirt out

of the lungs. Sperm (male reproductive cells) have flagella. A

flagellum helps sperm move. Plant cells never have cilia or flagella.

2. Animal cells have structures called centrioles that help animal cells

divide. Plants cells do not have centrioles.

Cells


• A bacterium is a simple,

unicellular, prokaryotic organism.

• A bacterium is very tiny. In fact, a

bacterium is the smallest kind of

cell. The average bacterium is 10

to 100 times smaller than a plant

or animal cell.

• The shape of bacteria varies.

Bacteria can be rod, spherical or

spiral shaped.

• Let’s study important structures

found in a rod-shaped bacterium.

Cells


• Bacteria are surrounded

by a cell wall. The cell wall

protects the bacteria and

helps maintain its shape.

• Inside the cell wall is the

cell membrane. The cell

membrane controls what

enters and leaves the cell.

Cells

Cell Wall

Cell Membrane


• Some bacteria have a

capsule. A capsule is an

extra layer that surrounds

the bacteria outside the cell

wall.

• A capsule helps protect the

bacteria from being eaten

and destroyed by other cells.

For example, it helps protect

disease-causing bacteria

from being destroyed by

white blood cells.

Cells

Capsule


• Many bacteria (but not all)

have a flagellum.

• A flagellum is a tail-like

structure that extends out of

the bacterium. It whips

around and propels the

bacterium forward.

Cells

Flagellum


• Bacteria do not have a

nucleus. Their DNA is

located in the cytoplasm and

not in an enclosed structure.

• Often, bacterial DNA is

clumped together in a

region. We call this region

the nucleoid.

Cells

Nucleoid (DNA)


• Many bacteria have an extra

small, circular piece of DNA.

This “accessory DNA” is

called a plasmid.

• A plasmid can be transferred

from one bacterium to

another. A plasmid often

carries genes that increase

the bacteria’s survival such

as antibiotic resistance.

Cells

Plasmid


• Bacteria have ribosomes.

Ribosomes are small,

circular organelles that

perform protein synthesis.

• Cytoplasm is the jelly-like

material that fills the cell of

a bacterium. It is made of

water and dissolved

nutrients and salts.

Cells

Ribsomes

Cytoplasm


• Protists are a diverse group

of mostly unicellular,

eukaryotic organisms.

• There are many different

kinds of protists. Some are

animal-like, some are plant-

like and some are fungus-

like.

• In this presentation, we will

study a paramecium, an

animal-like protist.

Paramecium live in aquatic

environments.Cells


• The cell membrane is a

structure that surrounds

the protist. It acts like a

barrier. It allows

substances to pass in and

out of the cell.

Cells

Cell Membrane


• Cilia are small, hair-like

projections that are attached to

the cell membrane. They help

paramecium move through water.

They also help it eat.

Cells

Cilia


• There is an indentation on

one side of the paramecium

called the oral groove. This

indentation is like a mouth.

• Cilia sweep food into the oral

groove. The food is trapped

in the groove.

• The gullet is the bottom of

the oral groove. Food is

forced into small vacuoles

(called food vacuoles) in the

gullet.

Cells

Oral

Groove

Gullet


• Vacuoles are vesicles in the

cell that store nutrients,

waste or water. Sometimes

we name vacuoles based on

what they contain. For

example, a food vacuole

contains food.

Cells

Vacuoles


• Paramecium have a

special, star-shaped

contractile vacuole.

• Paramecium live in water

and sometimes they take

in excess water. The

contractile vacuole

collects the excess water

and pumps it out the cell.

Without this structure, the

cell would swell with water

and burst.

Cells

Contractile

Vacuole


• Lysosomes are small,

round vesicles that contain

enzymes that digest food.

Lysosomes fuse with food

vacuoles to digest

nutrients inside them.

Cells

Lysosomes


• Paramecium have two

nuclei. They have a large

macronucleus and a small

micronucleus.

• The macronucleus contains

most of the organism’s

genetic information needed

for day-to-day existence.

• The micronucleus contains

an extra copy of the

organism’s genetic

information.

Cells

MacronucleusMicronucleus


• Like other eukaryotic cells, protists also have:

– Mitochondria

– Ribosomes

– Smooth and Rough RE

– Golgi Bodies

– Cytoplasm

• Note: These organelles are not shown in most diagrams of

protists. However, they are found in all protists.

Cells


• Some protists have

chloroplasts. Protists that

have chloroplasts can

perform photosynthesis

and make their own food.

• Most algae are protists.

Algae are unicellular or

multicellular organisms

found in aquatic

environments.

Multicellular algae is

commonly called seaweed.

Cells


• All cells have a cell membrane.

• A cell membrane is the structure that separates the interior

of a cell from the external environment.

Cells


• A cell membrane has 3 important functions:

1. It protects the contents of the cell - it acts as a barrier

that keeps foreign substances outside of the cell

2. It controls what enters and leaves the cell. The

membrane is selectively permeable; it selects what can

pass or permeate into or out of a cell

3. It is important to cell signaling or communication.

Substances outside the cell can bind to receptors on the

cell membrane. These substances signal the cell to

perform an action such as to synthesize a substance or

export a substance.

Cells


• The cell membrane is made of

phospholipids. A phospholipid

is a molecule made of a

phosphate group (the “head”)

and lipid (the “tail”).

• There are two layers of

phospholipids in a cell

membrane. For this reason,

the cell membrane is also

called the phospholipids

bilayer.

Cells

Hydrophilic Head

Hydrophobic Tail


• There are 2 parts to a phospholipid: the head and tail

– The head is hydrophilic (water loving) and faces outwards (to the

external environment) and inward (towards the inside of the cell).

– The tail is hydrophobic (water fearing) and makes up the “inside” of

the cell membrane. The tails from each layer face towards each

other.

Cells

Hydrophilic Head

Hydrophobic TailPhospholipid

OUTSIDE CELL

INSIDE CELL


• There are different types of molecules embedded in the

phospholipid bilayer. These molecules are important to the

structure and function of the cell membrane.

Cells


• Transmembrane proteins span across the entire membrane.

Transmembrane proteins form channels, pumps or

receptors.

Cells


• Peripheral proteins are found only in the outer or inner layer

of the cell membrane. These proteins help with cell signaling

or catalyzing reactions in a cell.

Cells


• Glycoproteins are proteins with a sugar molecule attached.

• Glycoproteins often act as antigens. An antigen is like an

identification card. It signals to other cells what that cell is

and whether the cell is foreign or belongs to the organism.

Cells


• Cholesterol is a type of lipid.

• Cholesterol is dispersed throughout the phospholipid bilayer

and help the membrane stay fluid, or flexible. Cholesterol

also helps stabilize the phospholipid bilayer.

Cells


• Transmembrane proteins

are the most important

to cell communication.

They allow a cell to

respond to external

environmental changes

and factors.

• Transmembrane proteins

that are important to cell

communication are

called membrane

receptors.

Cells


• Membrane receptors bind

signaling molecules called

ligands.

• A ligand can be a hormone,

neurotransmitter or protein.

• Ligands cause the function

of a cell to change.

• Example: When the square

ligand binds the receptor,

substances enter the cell

through the channel

protein.

Cells


• Ligands have a specific

shape and can only fit

into membrane

receptors that

complement their shape.

• Likewise, a membrane

receptor has a specific

shape. It has a specific

shape and can bind only

one signaling molecule

or ligand.

Cells


• A ligand binds to the cell membrane receptor on the

extracellular side of the cell membrane. When it binds, it

causes a change on the intracellular side of the membrane

receptor protein. This change could:

– Open channels in the cell membrane. When the channels open, ions

or other substances can enter and exit the cell.

– Activate enzymes. These enzymes catalyze reactions in the cell.

– Cause muscle contractions, nerve impulses or cell growth.

Cells


• Membrane receptors are also found on the surface of

organelles in a cell.

• When a ligand binds to the receptor on an organelle, it

causes a change in the organelle.

• Example: Receptors found on the nucleus are called nuclear

receptors. When a ligand binds to a nuclear receptor, it can

cause genes to turn on or off.

Cells


• Substances move across the membrane. The movement of

substances in and out of is called cell transport.

• There are two kinds of cell transport:

1. Passive transport 2. Active transport

Cells


• Passive transport is the movement of a substance down a

concentration gradient. In other words, a substance moves

from high concentration to low concentration.

Cells

High concentration

Low concentration

“Even”

concentration• Passive transport occurs

spontaneously. It does NOT

require energy.

• Passive transport stops

once the concentration of

the substance “evens out”

between the inside and

outside of cell.


• There are two kinds of passive transport:

– Diffusion

– Facilitated Diffusion

Cells


• With diffusion, substances pass directly across the

phospholipid bilayer.

• Only small substances can diffuse in and out of the cell.

• This is how oxygen and carbon dioxide enter and exit cells.

Cells


• With facilitated diffusion, substances use a channel or

carrier protein to diffuse across a membrane.

• Both proteins create channels across the membrane.

– A channel protein often allows ions (charged particles) to enter and

exit a cell.

– A carrier protein is more selective than a channel protein. It often

helps larger substances, such as simple sugars, diffuse across a

membrane.

Cells

Channel protein Carrier protein


• Active transport is the

movement of a

substance against a

concentration gradient.

It is the movement from

low concentration to

high concentration.

• Active transport does not

occur spontaneously. It

requires energy (ATP).

Cells

Low concentration

High concentration


• Active transport occurs with

the help of transmembrane

proteins. The proteins act as

pumps.

• The pumps use ATP to

transport substance from

low concentration to high

concentration. They break

ATP down into ADP, releasing

energy which is used to move

the substance across the

membrane.

Cells


• Active transport is important to all forms of life.

• For example:

– Plants have pumps in the cells of their roots that help extract salts

and minerals for the soil. Salts and minerals exist in very dilute

solutions in the soil. Without active transport pumps, plants would

not be able to obtain these vital nutrients.

– Human cells have active transport pumps that maintain fluid

balance and volume of cells. They also rely on active transport to

help conduct nerve signals.

Cells


• Osmosis is a special type

of passive transport. It is

the diffusion of water.

Specifically, it is facilitated

diffusion of water with a

channel protein.

• Osmosis is the movement

of water from a high

concentration of water to

low concentration of

water.

Cells

Water

High water

concentration

Low water

concentration


• We don’t refer to the concentration of water in a solution. We

refer to the concentration of the solute in a solution.

Cells

High water concentration

Low solute concentration

Low water concentration

High solute concentration


• Osmosis occurs across

cell membranes when the

solute concentration is

different inside and

outside a cell.

• When the concentration of

solute is lower outside a

cell, the concentration of

water is higher. Therefore,

water moves from outside

the cell to inside the cell.

Cells


• When the concentration of

solute is higher outside a

cell, the concentration of

water is lower. Therefore,

water moves from inside

the cell to outside the cell.

Cells


• If the solute concentration

is the same inside the cell

and outside the cell, water

does not diffuse across

the membrane.

Cells


• Tonicity is a measure to compare the concentration of water

in two different solutions. It compares concentration in

terms of the solute, not the solvent (water).

• There are three classifications of tonicity that one solution

can have relative to another:

1. Isotonic

2. Hypertonic

3. Hypotonic

Cells


• A solution that contains the same concentration as another

solution is called isotonic. In other words, an isotonic

solution has the same concentration as another solution.

• A solution that contains more solute than another solution is

called hypertonic. In other words, a hypertonic solution is

more concentrated compared to another solution.

• A solution that contains less solute than another solution is

called hypotonic. In other words, a hypotonic solution is less

concentrated compared to another solution.

Cells


• Animal cells and plant cells change shape and size due to

osmosis.

• There are three scenarios where osmosis could change the

shape and size of the cells:

1. The cell is placed in a hypertonic solution.

2. The cell is placed in a hypotonic solution.

3. The cell is placed in an isotonic solution

Cells


• When a cell is placed in an

isotonic solution, the

container has the same

solute concentration

compared to inside the cell.

Therefore, water does not

enter or leave the cell.

• The cells remain their normal

size and shape.

Cells

Animal cell

Plant cell

Animal cell

Plant cell


• When a cell is placed in a

hypertonic solution, there is a

higher solute concentration in

the container compared to

inside the cell. Therefore,

water leaves the cell.

• Animal cells shrink and

shrivel.

• With plant cells, the cell wall

remains rigid but the cell

membrane pulls away and the

“inside of the cell” shrinks.

Cells

Water

leaves

the cell

Water

leaves

the cell


• When a cell is placed in a

hypotonic solution, there is a

lower solute concentration in the

container compared to inside the

cell, so water enters the cell.

• Animal cells swell and burst.

• The cell wall in plant cells

prevents the cell from bursting.

The pressure inside the cell

increases due to some water

entering the cell. This pressure is

called turgor pressure.

Cells

Water enters

the cell

Water

enters

the cell

Animal cell

Plant cell


• The images below are actual pictures of red blood cells in a

hypertonic, hypotonic and isotonic solution. Which image

shows an example of red blood cells in a hypertonic

solution? What about a hypotonic and isotonic solution?

Cells

© Stephanie Elkowitz87Cells

Hypertonic solution

Red blood cells shrink

Isotonic solution Hypotonic solution

Red blood cells swell

© Stephanie Elkowitz88Cells

• IV or intravenous therapy is the

direct infusion of medication or

liquid substances into a

person’s bloodstream.

• When a person receives IV

therapy, it’s imperative that the

solute concentration of the

infused liquid is isotonic to the

concentration of blood. If not,

blood cells can shrivel or swell.

This can be deadly to a patient.


• Some cells perform a

special type of active

transport called

endocytosis and

exocytosis.

• In endocytosis, cells

engulf substances.

• In exocytosis, cells

expel substances.

Cells


• In endocytosis, cells consume or absorb substances by

engulfing them.

• Endocytosis allows cells to absorb large molecules that

cannot pass across the cell membrane or through channels

in the membrane.

• There are three major types of endocytosis:

1. Phagocytosis

2. Pinocytosis

3. Receptor-Mediated Endocytosis

Cells


• Phagocytosis is the process by which

a cell engulfs a solid particle.

• In phagocytosis, the cell membrane

extends around the particle.

• Phagocytosis is used by bacteria and

protists to “eat.” For this reason,

phagocytosis is also called “cell

eating.”

• Phagocytosis is also used by white

blood cells in the human body to

engulf pathogens and cell debris.

Cells


• Pinocytosis is a non-specific process

by which a cell brings particles into

the cell.

• The cell membrane invaginates or

pinches around the particle.

• This process is often used to take in

extracellular fluid. For this reason,

pinocytosis is also called “cell

drinking.”

Cells


• Receptor-mediated endocytosis is a

specific form of endocytosis.

• In receptor-mediated endocytosis,

substances bind to receptors on the

membrane. This causes the membrane

to invaginate. The cell internalizes the

substances bound to the receptors.

• This form of endocytosis is often used

for cell communication. These

receptors often bind hormones. When

the hormones enter the cell, they signal

a reaction in the cell.

Cells


• Exocytosis is a process that

expels substances out of a

cell.

• Exocytosis is important to

expelling wastes from a cell.

It is also important to

releasing proteins made by

the cell. This is the most

common way cells release

hormones or enzymes.

Cells


• Exocytosis occurs in three

steps:

1. Golgi bodies package

substances to be expelled

from the cell into vesicles.

2. The vesicles travel to the

cell membrane.

3. The vesicles fuse with the

cell membrane and the

contents inside the

vesicle are expelled out of

the cell.

Cells

Step 1

Step 2

Step 3


• Images obtained from commons.wikimedia.org courtesy:

Roger Moreno, NIAID, NEON_ja, Fleliaer, Calleamanecer,

Zephyris, harmid

• Other images obtained from the Public Domain

• Clipart by Stephanie Elkowitz

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