A TOUR OF THE CELL ALL ORGANISMS ARE MADE OF CELLS

A TOUR OF THE CELLALL ORGANISMS ARE MADE OF

CELLS

ALL ORGANISMS ARE MADE OF CELLS

• The Cell Theory– The invention of the microscope opened a world

of cells to scientists.– Light microscopes were first developed and

used in the early 1600s.• In light microscopes, visible light passes through an

object, what you are looking at, and glass lenses then enlarge the image and project it into the human eye.

– In 1665, Robert Hooke saw compartments in cork using a light microscope.

ROBERT HOOKE AND CORK


• Each compartment he saw, he named cells, even though he was observing the walls of dead plants.

– Around 1700, Anton van Leewenhoek developed his own microscope with which he observed tiny organisms in pond water.• He called these animalcules to his colleagues,

including Hooke.

– In the mid 19th century, after reviewing cells in every organism, scientists formulated the cell theory.


– The cell theory tells us that all living things are composed of cells, and that cells are the basic unit of structure and function in living things.

– All cells come from preexisting cells.• Microscopes as Windows to Cells

– Light microscopes (LM) magnify up to 1000 times the actual size.

– Bacteria or larger are good to view using this microscope.


– Since most of the structures in the cell are smaller than bacteria, it wasn’t until the mid-20th century when the electron microscope was invented that scientists were able to see these structures.• Electron microscopes use electron beams instead of

light to view objects.• Some electron microscopes cam magnify objects

one million times (1000 times a light microscope) to reveal the details of the structures within the cell.

LIGHT v. ELECTRON MICROSCOPE

LIGHT v. ELECTRON MICROSCOPE


• The scanning electron microscope (SEM) is used to study the surface structures of cells.

• The transmission electron microscope (TEM) is used to study the interior of cells.

• The specimens that are viewed by electron microscopes must be killed and preserved while living cells are observed using the light microscope.

– A micrograph is a photograph of the view through a microscope.

SCANNING v. TRANSMISSION


• An Overview of Animal and Plant Cells– Each part of the cell that has a specific job to do

is called an organelle.– There are similarities between animal and plant

cells:• They both have a plasma membrane.

– This defines the boundary of the cell and regulates the passage of chemicals between the cell and the surroundings.

• Each cell has a nucleus where the cell’s genetic material resides in the form of DNA.

ANIMAL CELL

PLANT CELL

ANIMAL v. PLANT CELL


• Anything between the nucleus and the plasma membrane is called the cytoplasm.

• This consists of organelles suspended in a fluid.• Most organelles have their own membrane, which

maintains the chemical environment inside the organelle that are different from the environment of the rest of the cell.

– There are differences between animal and plant cells.• Chloroplasts are present in some plant cells but not

in animal cells.


– Photosynthesis takes place in the chloroplast organelle.– Photosynthesis converts light energy to the chemical

energy stored in molecules of sugars and other organic compounds.

• Plant cells have a cell wall in addition to the plasma membrane.

– This protects the plant cell and maintains the shape.– There are no cell walls in animal cells.

• Two Major Classes of Cells– There are basically two kinds of cells.

• A prokaryotic cell is one that lacks a nucleus and most organelles.


• Bacteria and another organism called archaea are prokaryotes.

• These organisms appear earliest in Earth’s fossil record.

– Eukaryotic cells have nuclei surrounded by its own membrane, and has internal organelles surrounded by their own membranes.• Protists, fungi, plants, and animals consist of

eukaryotic cells which have appeared later than prokaryotes in Earth’s history.

EUKARYOTE v. PROKARYOTE (TEM)

EUKARYOTE v. PROKARYOTE (TEM)


• In eukaryotes, the nucleus is the largest organelle, as can be seen in the preceding pictures.

• Prokaryotes have no nucleus and few organelles and are much simpler than eukaryotes.

• In the prokaryotic cell, the DNA is concentrated in an area called the nucleoid region that is not separated from the rest of the cell by a membrane.

• Size of the prokaryote is considerably smaller than the eukaryote.

– Bacteria are 1 to 10 micrometers in diameter.– Eukaryotes are 10 to 100 micrometers in diameter.

PROKARYOTIC CELL

REVIEW: CONCEPT CHECK 6.1, page 1141. What evidence led to the development of

the cell theory?

2. How do the various kinds of microscopes differ as tools in the study of cells?

3. Identify two similarities and two differences between plant and animal cells.

4. How is a eukaryotic cell different from a prokaryotic cell?

MEMBRANES ORGANIZE A CELL’S ACTIVITIES

• Membrane Structure– Membranes isolate enzymes within a cell’s

compartments.– Membranes control the movement of

substances across the boundary with only certain substances allowed to pass, controlling the environment within each compartment it surrounds.

– Proteins and a lipid, phospholipid compose the plasma membrane and other membranes of the cell.

PHOSPHOLIPIDS


cell.– The phospholipid molecule has two fatty acids

instead of three.– The tail (two fatty acids) are hydrophobic, and

the head is hydrophilic and includes a phosphate group (PO₄³⁻).

– The tail is pushed away by water and the head is attracted.

– Phospholipids form membranes between two watery environments.

PLASMA MEMBRANE

PLASMA MEMBRANE


– The plasma membrane separates the cell’s aqueous cytoplasm from the watery environment surrounding the cell.• There the phospholipids form a two layer sandwich of

molecules called the phospholipid bilayer.• In this membrane, phosphate ends face the watery

inside, and the watery outside of the cell.

– The hydrophobic tails are inside the membrane, protected from the water.• There they play a key role as a protective barrier.

FUNCTIONS OF THE PLASMA MEMBRANE


• Oxygen and carbon dioxide, non polar molecules can cross without any problem, but polar molecules (sugars) and other ions cannot.

• All of these components, phospholipids, proteins, and other bodies form a dynamic structure.

• The Many Functions of Membrane Proteins– The proteins in the membrane perform most of

the membrane’s specific functions.– Enzyme’s are enclosed in the membrane and

carry out some of the cell’s chemical reactions.


– The membrane also helps the cells, particularly multicellular organisms, communicate and recognize each other.• This is done with the use of chemical signals.

– Transport proteins help to move water and sugars across the membrane.

– Carbon dioxide and oxygen, non polar molecules, pass without assistance across the membrane.

– Some essential molecules need energy through active transport to move across.

REVIEW: CONCEPT CHECK 6.2, page 117

1. Describe how phospholipid molecules are oriented in the plasma membrane of a cell.

2. What is the function of a transport protein?

MEMBRANES REGULATE THE TRAFFIC OF MOLECULES

• Diffusion– Molecules are constantly in motion.– One result of this motion is diffusion which is

the movement of particles in a substance from where they are more concentrated to areas where they are less concentrated.

– If there is a container that has a membrane or barrier in the middle with water on one side and concentrated molecules on the other side, the concentrated molecules will move to the water

DIFFUSION

DIFFUSION

DIFFUSION

DIFFUSION

DIFFUSION


side, assuming the membrane will let them (or is permeable) until the ratio of molecules is equal on both sides of the membrane.

– When this happens, the solutions are said to be in equilibrium or equal concentrations on both sides of the membrane.

• Passive Transport– Some cell membrane can be barriers to the

diffusion of some substances.


– Selectively permeable membranes will allow some substances to pass through and bock other substances.

– In most cells, a few molecules, such as oxygen and carbon dioxide, pass through the membrane with ease.

– Water will pass through the membrane but with protein channels.

– Passive transport allows these molecules to pass through without requiring any energy.

PASSIVE TRANSPORT

PASSIVE TRANSPORT

PASSIVE TRANSPORT


• Only the random motion of the molecules is required to move these substances across the membrane.

• Small molecules pass more easily than large, but still have restricted access.

• For example, sugars won’t pass through the hydrophobic portion of the plasma membrane.

• They can only pass through by way of transport proteins.

– Facilitated transport is the process where transport proteins facilitate a pathway for certain molecules to pass.

FACILITATED DIFFUSION

PASSIVE v. ACTIVE TRANSPORT

FACILITATED TRANSPORT

FACILITATED TRANSPORT


– There are specific proteins that allow the transport of different substances across the plasma membrane.

– This is how some ions, small polar molecules (water and sugars) pass in and out of the cell.

• Osmosis– The passive transport of water across a

selectively permeable membrane is osmosis.• Suppose there are two solutions, one with high

concentrations of sugar and the other with low concentrations of sugar.


• Imagine a membrane between the two solutions.• Water will pass through the membrane from low

concentration to high concentration until equilibrium is obtained.

• The solution with higher concentration of solute is said to be hypertonic.

• The solution with lower concentration of solute is said to be hypotonic.

• When equilibrium is obtained or the solutes are equal on both sides of the membrane, the solutions are said to be isotonic.

OSMOSIS

OSMOSIS

HYPOTONIC vs. HYPERTONIC

OSMOSIS

OSMOSIS


– Water Balance in Animal Cells• In animal cells, in hypotonic solutions, water is

gained, the cell swells, and can pop.• In hypertonic solutions, the cells lose water and

shrivel and die.• Fish constantly undergo hypotonic changes, with its

gills and kidneys preventing the buildup of water.

– Water Balance in Plant Cells• Plants have strong cell walls.• Their cells are healthiest in hypotonic environments.

OSMOSIS


• When water flows inward, the cell wall firms up and applies pressure to prevent the cell from absorbing too much water and bursting as an animal cell might.

• Plant cells in isotonic environments become limp because there is no movement of water.

• Most house plants, or non-woody plants then wilt.• In a hypertonic environment, the plant cell loses

water, shrivels, the plasma membrane pulls away from the cell wall, and the cell dies.

• Active Transport– Energy is required sometimes for cells to move


some molecules or ions across membranes.– This process is called active transport, and

utilizes transport proteins that pump solutes across the membrane, usually in an opposite direction to the way it travels in diffusion.• The energy is supplied by mitochondria as chemical

energy.• In animal cells, active transport is utilized in the

Na⁺/K⁺ pump.– The cell has a higher concentration of K⁺ ions, and the fluid

surrounding the cell has a higher concentration of Na⁺ ions.

SODIUM-POTASSIUM PUMP

SODIUM POTASSIUM PUMP


– The plasma membrane pumps K⁺ ions into the cell and Na⁺ out of the cell to help maintain these differences.

• Transport of Large Molecules– Large particles move in and out of the cell

packaged in vesicles, or small membrane sacs that specialize in this process.

– Proteins leaving the cell leave in a vesicle that fuses with the plasma membrane and empties outside the cell in a process called exocytosis.


– Endocytosis takes material into the cell within vesicles the at bud inward from the plasma membrane.

LARGE MOLECULE TRANSPORT

ENDOCYTOSIS

EXOCYTOSIS AND ENDOCYTOSIS


1. What is diffusion?

2. What role does a cellular membrane play in passive transport?

3. Distinguish between hypertonic, hypotonic, and isotonic solutions, and give an example of how each affects an animal cell.

4. What role does active transport play in cell function?

5. How do vesicles transport large molecules out of a cell?

THE CELL BUILDS A DIVERSITY OF PRODUCTS

• Structure and Function of the Nucleus– DNA is contained in the nucleus attached to

protein fibers called chromatin.– The nuclear envelope surrounds the nucleus.

• Substances can move in and out of the nucleus through pores in the envelope.

– The nucleolus is contained in the nucleus.• Its function is to make ribosomes.

CELL NUCLEUS

NUCELUS


• Ribosomes– These are made up of proteins and nucleic

acids.– They are bound to the rough endoplasmic

reticulum in the cytoplasm.– Nuclear DNA contains the instructions for

making proteins.– The proteins are constructed by the ribosomes.

RIBOSOME


– Proteins that make up the membranes are made by the ribosomes.

– Some of the proteins are exported by the cell.– Some ribosomes are suspended in the

cytoplasm and make enzymes and other proteins that stay within the cell.

• The Endoplasmic Reticulum– These are membranes found within the

cytoplasm of the cell.

ENDOPLASMIC RETICULUM



– An analogy of its function would be as a manufacturing and transportation facility.

– Rough Endoplasmic Reticulum• The ribosomes position themselves on this to

produce the proteins that remain in the cell or are exported by the vesicles.

– Salivary glands, that secrete large amounts of digestive enzymes, have large amounts of rough ER.

– Smooth Endoplasmic Reticulum• This is connected to the rough ER but lacks the

ribosomes.



• The Golgi Apparatus– After leaving the endoplasmic reticulum the

protein made there moves through the cell in a vesicle to the Golgi apparatus where it is modified, stored, or sent out of the cell to make other chemical products.

– The enzymes of the Golgi apparatus assist in this refining and modifying of the product.

GOLGI APPARATUS

GOLGI APPARATUS


• Vacuoles– Theses are large membrane bound sacs in the

cytoplasm.– Their function is to store undigested nutrients.– Some plants have a large central vacuole that

stores salts and absorbs water causing the cells to expand.• In flowering plants, the central vacuole in the petals

contain colorful pigments and helps to attract pollinating insects.

VACUOLES

VACUOLES

VACUOLES


• In leaf plants, the central vacuole can contain poisons that protect the plant against predators such as leaf-eating animals.

• Lysosomes– These are also membrane-bound sacs that

contain digestive enzymes that break down macromolecules such as proteins, nucleic acids, and polysaccharides.• A function is to fuse with incoming food vacuoles and

expose the nutrients to enzymes that digest them to nourish the food.

LYSOSOMES

LYSOSOMES


• They also help to destroy harmful bacteria.• They are recycling centers for damaged organelles.

• Membranes Pathways in a Cell– This is the process of exocytosis and

endocytosis, the refining of products in the Golgi apparatus, the breakdown of products in the lysosomes.

– Vesicle formation in one organelle takes place and the product can exit the cell without ever crossing a membrane.

MEMBRANE PATHWAYS

MEMBRANE PATHWAYS

MEMBRANE PATHWAYS


1. In what way does the nucleus direct the activities of a cell?

2. Trace the path of a protein from the time it is produced by a ribosome on the ER until it reaches its destination.

3. How are undigested nutrients in a vacuole made available to a cell?

CHLOROPLASTS AND MITOCHONDRIA ENERGIZE CELLS

• Chloroplasts– Chloroplasts are where the process of

photosynthesis takes place.• This is the process where plants and algae use light

energy to make sugars and other organic compounds or chemical energy.

– Two membranes enclose the chloroplast with the internal membrane dividing it into compartments.

CHLOROPLASTS

CHLOROPLASTS


• Mitochondria– Most organisms get their energy through a

process called cellular respiration.– In eukaryotic cells, this process takes place in

the mitochondria.– Energy is released from the sugars and other

organic molecules, then using this energy to form ATP (adenosine triphosphate), the main energy source that cells use for most of their work.


– Chloroplasts are found only in plants whereas mitochondria are found in all eukaryotic cells.

– Its structure is related to its function.• The inner membrane has numerous folds into which

the enzymes that function in cellular respiration are built.

• These folds increase the surface area allowing for more cellular respiration to take place.

MITOCHONDRIA

MITOCHONDRIA


1. How are the function of chloroplasts and mitochondria similar?

2. How does a cell use the energy produced by mitochondria?

3. In what way is energy changed by reactions in a chloroplast?

4. How is membrane structure important to the functions of mitochondria and chloroplast?

An Internal Skeleton Supports the Cell and Enables Movement

• The Cytoskeleton– The cytoskeleton is a network of protein fibers

that extend throughout the cytoplasm giving support and movement to the cell and its organelles.• It is made up of microtubules, straight hollow tubes

giving the cell rigidity, shape, and organization.– Protein subunits can be added or subtracted to lengthen or

shorten it.– These also provide tracks on which the organelles can

move.

CYTOSKELETON

CYTOSKELETON


• Microfilaments are thinner and more solid and enable the cell to move or change shape.

• Flagella and Cilia– Some cells move as a result of the action of

structures projecting from the cell.– Flagella are long, thin whip-like structures, with

a core of microtubules, causing the movement of the cell.

– Cilia are shorter and more numerous, are also composed of microtubules, and move in a back and forth motion.


• Some cells can be stationary but have flagella and cilia to move fluid over its surface.

• An example is the tracheal lining where foreign particles are removed by the sweeping action of the cilia.

• The Cell as a Coordinated Unit– White cells prevent infection by engulfing

bacteria.


– Extension of protein from the cytoskeleton move the WBC toward the bacteria.

– The bacteria is destroyed by the lysosomes made by the ER and Golgi apparatus.

– Ribosomes make the protein of the cytoskeleton and enzymes of the lysosomes.

– The proteins are made under the direction of the DNA in the nucleus.

– The energy for these processes is produced in the mitochondria.

COORDINATED ACTIONS OF THE CELL

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A TOUR OF THE CELL ALL ORGANISMS ARE MADE OF CELLS