Springfield Central High School. What is a cell? What are the key concepts to understand this unit? Where do cells fit into the order of scale studied.

Unit 4 Lesson 2Cell Form

Springfield Central High School

Questions to Ponder from Lesson 1 What is a cell?What are the key concepts to understand this unit?Where do cells fit into the order of scale studied in biology?

How old are the oldest known fossils of cells?

What are organelles?

What are the three points to the cell theory?Who were the scientists involved in the discovery of the cell theory?

Why are the definition of cells and the characteristics of life similar? 

What is the cell membrane and why is it so important to life?

What is the significance of Stanley Miller’s experiment? What are the two types of cells?

What are the key characteristics of a plant cell?

What are the key characteristics of an animal cell?

How do the two types of cells differ?

Massachusetts Frameworks for Cell Form UnitCentral Concepts: Cells have specific structures and functions that make them distinctive. Processes in a cell can be classified broadly as growth, maintenance, and reproduction.

• 2.1   Relate cell parts/organelles (plasma membrane, nuclear envelope, nucleus, nucleolus, cytoplasm, mitochondrion, endoplasmic reticulum, Golgi apparatus, lysosome, ribosome, vacuole, cell wall, chloroplast, cytoskeleton, centriole, cilium, flagellum, pseudopod) to their functions. Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis, facilitated diffusion, active transport).

• 2.2   Compare and contrast, at the cellular level, the general structures and degrees of complexity of prokaryotes and eukaryotes.

• 2.3   Use cellular evidence (e.g., cell structure, cell number, cell reproduction) and modes of nutrition to describe the six kingdoms (Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia).

Cells Defined:Cells are small packages that have all the characteristics of life.  These packages  are surrounded by a special double layer of fat known as a phospholipid bilayer, which separates the outer environment from the cell's inner environment. The separation of the outer environment from the inner environment allows the cell to maintain homeostasis. 

A definition of a biological cell: the smallest unit that can perform all life processes; cells are surrounded by a membrane and contain DNA and cytoplasm.

The Two Types of Cells: Prokaryotes and Eukaryotes

There are two types of cells: Prokaryote and Eukaryote. You should already know that a prokaryote cell does not have a nucleus or any self-contained organelles; while a eukaryote cell does have a nucleus and can have other self-contained organelles. 

A. Types of organisms that are Prokaryotes and Eukaryotes

B. Prokaryote celled organisms:ArchaeaEubacteria

C. Eukaryote celled organisms: Protist  (aka.

protoctista)Fungus Plant Animal

Prokaryotes: Archaea and Eubacteria• Prokaryote cells are always single celled organisms, which do not

contain a nucleus or other membrane bond structures.• There are two types of prokaryote cells.

• Archaea (aka Archaebacteria) • Eubacteria

Let’s look at a labeled drawing and actual photographs of prokaryotes

Some Facts About Prokaryotes

• Some prokaryotes can consume rocks, hydrogen gas, metal even uranium.

• In addition to oxygen, prokaryotes can "breathe" things like carbon dioxide, metals, and salts.

• Prokaryotes can live in some of the most extreme environments on Earth!

• Archaea are the most thermophilic (heat loving) organisms known!• The oldest microbial fossils are about 3.8 billion years old! • Microbes can be found almost everywhere on Earth. • Some places scientists have not yet found bacteria are in magma and in

some places in the Atacama Desert of South America!• There are about 200 species of bacteria in your mouth.• 1,000 bacteria can fit on the tip of a pin. • There are more bacterial cells than human cells in your body. • Your skin contains about 1 trillion bacterial cells. • Bacteria were first discovered in the 1670s by van Leeuwenhoek. • There are more prokaryotes on your hand than there are people on the

planet. Facts from: http://sciences.unlv.edu/desertsurvivors/Pages/episode2.htm

More facts About Prokaryotes• Bacteria and archaea are

prokaryotes, or single-celled microscopic organisms that have no nucleus, unlike your cells.

• Bacterial cells have a cell wall,

cell membrane, cytoplasm, DNA, and ribosomes.

• Bacterial cells can be spherical, rod shaped, or spiral shaped.

Rods = bacilli (singular form is bacillus) Spirals = spirilla (singular form is spirillum)Spheres = cocci (singlular form is coccus)

Archaea• Archaea are single celled organisms that have similar structure as the

Eubacteria.• However, the Archaea are genetically and biochemically quite

different from the Eubacteria.• Archaea produce proteins and replicate their DNA differently

than do the eubacteria. • Archaea like eukaryotes use the DNA code for the amino acid

methionine as a start codon. • Archaea are extremophiles, which means that they love extreme

environmemts.• Archaea are believed to be closely related to the early cells from

billions of years ago, when all earth environments were extreme.• Many scientists see the evolutionary link between prokaryotes and

eukaryotes to be made from the archaea

Eubacteria• Eubacteria aka bacteria aka germs.• Eubacteria are the common single celled organisms that lack a

nucleus and membrane bound structures.• We usually associate bacteria with the pathogens that cause many

illnesses.• However, most Eubacteria exist as ditritivores or symbionts and not

pathogens.

Different Forms

DifferentFunctions

Eukaryote Cells

• Eukaryote cells are cells that contain a phospholipid bilayer membrane bound nucleus and other phospholipid membrane bound structures (known as organelles).

• Eukaryote cells have membrane bound compartments in them.• These compartments can have a separate chemical

environment than the rest of the cell.• This allows for a wider variety of chemistry within

the cell and therefore a more complex form of life

Let’s have a look at an example of a eukaryote cell: an animal cell

Organelles of Eukaryotes

Refer to this Web pagehttp://biology.clc.uc.edu/courses/bio104/cells.htm

• One of the distinguishing characteristics of eukaryotic cells is that they have small membrane enclosed structures called organelles.

• Organelle means “little organ”, so organelles are like the organs of a cell.

• Organelles have various forms and perform various functions. • The presence of a certain organelle will allow a cell to perform the

organelles function; this allows for some of the diversity between different cell types.

Plant Cell vs Animal Cell

Animal cells are eukarotic; they have a nucleus.

Animal cells have other organelles; make special note that animal cell vacuoles are small. Animal cells lack chloroplasts.

Animal cells have a cell membrane; they do not have a cell wall.

Plant cells are eukaryotic; they have a nucleus.

Plant cells have other organelles; make special note that plant cell vacuoles are large. Plant cells have chloroplasts.

Plant cells have a cell membrane, and they have a cell wall made of the polysaccharide cellulose.

Plant Cell• Plant cells are distinguished by

having a nucleus, a cellulose cell wall, chloroplasts, and a large vacuole.

• Since plant cells are eukaryotes, plant cells must have a membrane bound nucleus to store the cell’s DNA

• A cell wall made from the sugar cellulose if found around the plant cells.

• Most plant cells contain the organelle for photosynthesis known as chloroplast.

• Plant cells have sap filled large vacuoles.

• Plant cells have other organelles found in eukaryote cells such as: endoplasmic reticulum, golgi body, mitochondria, and nucleolus.

Animal Cell• Animal cells are distinguished by

their lack of any cell wall; animal cells have an undefined shape; animal cells are surrounded by a phospholipid bilayer membrane; animal cells have a centrosome to help with cell division. Naturally animal cells have nuclei.

• Animal cells have no definite shape because animal cells have no cell wall.

• Animal cells can take different forms to allow them to perform different functions.

• Animal cells have other organelles found in eukaryote cells such as: endoplasmic reticulum, golgi body, mitochondria, nucleolus, lysosome, and small vacuole.

Diversity of Cells = Diversity of Life

Different Forms

DifferentFunctions

• The diversity of cells allows for the diversity of life.

• Evolution has selected for this diversity of life stategies and forms of cells.

• Some cells survive as single celled organisms: such as both types of prokaryotes and some eukaryotic protist.

• Other cells work independently within a multicelled organism: such as blood cells

• While other cells that have similar functions are organized into tissues which in turn can form the organs that make up complex living things like you and me.

Questions to Ponder from Lesson 2 What is a cell?What are the two major types of cells?What organisms have the two types of cells ?

Are there more human cells or bacteria cells in your body?

What are organelles?Scientists now feel that the archaea or the eubacteria are more closely related to eukaryotes?

What is a phospholipid bilayer?

Similar cells can be organized into what layer of scale in biology?

What structure are found in prokaryote cells? What are the shapes that bacteria can be found taking?

What are the key characteristics of a plant cell?

What are the key characteristics of an animal cell?

How do the two types of cells differ?