Botany – Cells “All living organisms begin life as a single cell… (that) divides repeatedly until it develops into an organism consisting of billions of cells.” I. Cell History A. Remember that cells are microscopic – they can’t be seen with the naked eye 1. We haven’t always known that living organisms were made of cells 2. It took time for us to develop the technology to see microscopically

B. 1665—______________________________________________, an English physicist, examined cork cells C. 1667—______________________________________________ observes “animalcules”- bacteria & protozoans. D. 1809—Jean Baptist de Lamarck concluded that all animal plant tissues are composed of cells E. 1831—English botanist ___________________________________________ discovers the nucleus F. 1838-1839—Cell Theory developed by two scientists… 1. German Botanist ___________________________________________

2. German zoologist __________________________________________ 3. Cell Theory states that ______________________________________ ___________________________________________________________ ___________________________________________________________

G. Refuting Spontaneous Generation – the wrong idea that organisms can arise from nonliving matter. 1. 1668—_______________________________________ demonstrates that maggots

don’t spontaneously originate from rotting meat. a. This seemed to disprove spontaneous generation. b. A HUGE controversy (that would last more than _______ years) soon ensued.

1. 1858—Rudolph Virchow argued that every cell comes from a preexisting cell. 2. 1860—Paris Academy of Sciences offers a prize for experimentally proving or disproving spontaneous generation.

3. 1862—______________________________________________ proved that sterile media remained so if microorganisms in the air were excluded.

II. How big are cells?

A. They are microscopic 1. Most plant cells can’t be seen with the unaided eye 2. Plant cells are usually 10-100 micrometers in length 3. 500 average sized cells could be stretched end-to-end across 1 inch (2.54cm) 4. 30 cells could be easily placed in a pin head B. Why are cells so small? 1. In a spherical cell…

a. The increase in surface area = the square of its diameter increase b. However the increase in volume = the cube of its increase in diameter c. If a cell increased its diameter by 10X, its surface area would increase by 100X, but its volume would increase by 1,000X !

2. Big cells are at a disadvantage a. All substances enter or leave the cell at its surface, small cells have larger surface area to volume ratios. b. The nucleus regulates all aspects of the cell’s activity, small cells have more efficient communication. III. Cell Terminology A. _________________________: cells that don’t have nuclei (e.g. bacteria) – “Pro” means before, “Karyo” means the nucleus

B. __________________________: cells that have nuclei (most plant & animal cells) – “Eu” means true or good C. __________________________: All the living components of a cell D. ____________________________________: The outer boundary of the protoplasm of a cell E. __________________________: All cellular components between the plasma membrane & the nucleus (protoplasm minus the nucleus) – “Cyto” means cell F. __________________________: The soup-like fluid in the cytoplasm, mainly water (cytoplasm minus the organelles) G. __________________________: “Little organs” of the cell. Membrane- bound structures within a cell that have specific functions H. __________________________: The relatively rigid outer boundary of plant cells

IV. Parts of the Cell **Be sure to review the diagrams of the cell and organelles in your textbook!**

A. The Cell Wall 1. Why is the cell wall so critical?

a. Large Trees support branches and leaves that weigh tons, without a skeleton!

b. Cell walls provide rigid walls to support this weight and protect the delicate cell contents within c. In places they are semirigid to allow flexibility d. Cell walls are the primary food source grazing animals e. Cell walls provide us with clothing, shelter, furniture, paper, and fuel 2. What are cell walls made of? a. ______________________________________________ is the main structural component 1) The most abundant polymer on Earth 2) 100 to 15,000 glucose monomers in a long chain b. Typically, cell walls contain: 1) Hemicellulose: a glue-like matrix that holds cellulose fibrils together 2) ___________________________________________: the organic material that gives stiffness to fruit jellies 3) Glycoproteins: proteins that have sugars associated with

their molecules 3. Structure of Cell Walls a. Middle Lamella: _____________________________________

____________________________________________________ ____________________________

1) Usually shared by adjacent cells, it is very thin b. ______________________________________________: A flexible wall laid down on either side of the middle lamella

1) A fine network of cellulose, hemicellulose, pectin, and glycoproteins

c. ______________________________________________: produced inside the primary cell walls; derived from primary cell walls by continued thickening and inclusion of lignin (a complex polymer)

1) Cellulose microfibrils become embedded in the lignin. The lignin causes the cell wall to “set up” – become semi-rigid

B. Plasma Membranes 1. ______________________________________________ a. Allows some substances to pass freely b. Actively moves some substances either out of or into the cell c. It inhibits the movement of other substances d. It is extremely important in maintaining cellular

______________________________________ 2. It is only 8-millionths of a millimeter thick and is quite flexible, often forming folds

3. Composed of a ____________________________________________ ___________________________________________________________

Carbohydrates are bonded to lipids and proteins at the surface. 4. Osmotic pressures push the plasma membrane against the cell wall

C. The Nucleus (the control center of the cell) 1. DNA in the nucleus provides information needed to make proteins, grow, differentiate, and carry on other activities 2. DNA also stores hereditary information 3. Complex plants usually have one nucleus that is 2-15 micrometers in diameter a. Plant cells often have one or more ______________________ – darkly-staining bodies that produce ribosomes. D. ______________________________________________ (the manufacturing plant of the cell) – a grouping of dictyosomes forms the Golgi Body.

1. A system of interlinked double-membraned channels subdividing the cytoplasm

2. Primary site of membrane synthesis in the cell 3. ER comes in two varieties: rough & smooth

a. Rough ER is rough because it is studded with ________________________________ 1) Ribosomes—__________________________________ ________________________________________________ ________________________________________________

a) Ribosomes have no bounding membranes and therefore aren’t considered to be organelles by

many. 2) Rough ER synthesizes, secretes, and stores __________ 3) Enzymes are complex proteins

b. Smooth ER has few if any ribosomes 1) Smooth ER functions in ________________________

E. ______________________________________________ (the warehouse of the cell) (this structure is known as the Golgi complex in animal cells) 1. Disc-shaped, often branching hollow tubules 2. Modify carbohydrates attached to proteins that are synthesized and packaged in the ER

3. Complex polysaccharides are assembled within the dictyosomes and collect in small ______________________________________________ that are pinched off from the margins

a. Vesicles migrate to the plasma membrane, fuse with it, and secrete their contents outside the cell

F. Chloroplasts – a type of plastid 1. Chloroplasts are the green organelles within plants where _____________________________ takes place.

a. Chloroplasts take the radiant energy from the sun and store it in a form usable to both plants and animals _________________________________ (long chains of simple sugars like glucose) b. Higher plants have 75-125 chloroplasts per cell

2. Double-membraned organelle a. Outer membrane probably is derived

from ER b. Inner membrane probably originated for the cell membrane of a cyanobacterium

3. ______________________________________________: a colorless fluid matrix containing enzymes a. contains a small circular molecule of DNA, ribosomes, 4 or 5 starch grains, oil droplets, and enzymes 4. ______________________________________________: stacks of thylakoids, which are part of an overlapping and continuous membrane system in the stroma

a. Thylakoid membrane contains green chlorophyll and other pigments essential to photosynthesis

G. ______________________________________ (the Powerhouses of the cell) 1. The energy stored in the chloroplasts (through photosynthesis) as carbohydrates is released by the process of _________________________________ 2. Shaped like cucumbers, rods, or balls, they move throughout the cell and accumulate where energy is needed

3. Bounded by 2 membranes, the inner membrane forming platelike folds called ____________________ which increase the surface area for enzymes to work on

H. ______________________________________________ 1. In mature plants, as much as ____________ of the volume may be taken up by 1 or 2 large central vacuoles

a. Vacuoles accumulate ions and other waste substances, recycle certain materials in the cell, and aid in the breakdown and digestion of organelles

2. Vacuoles in newly formed cells are tiny and numerous. They increase in size and unite as the cell matures. 3. Filled with a watery fluid called ________________________________

and bound by vacuolar membranes called _________________________ a. Cell sap helps maintain osmotic pressure within the cell b. Cell sap often contains anthocyanins that give red, blue, and purple colors to flowers and some reddish leaves

Watch this video reviewing cell organelles: http://youtu.be/LP7xAr2FDFU

Complete this cell review: http://www.clarendoncollege.edu/programs/NatSci/Biology/Botany/online%20lecture%20outlines/plant cell organelles review.htm

V. Cellular Reproduction – A cell’s life begins when a parent cell divides into 2 daughter cells, continues as the cell grows and matures, and ends when the cell divides. This is known as the _____________________________________________. Mitosis is the type of cell division that results in two daughter cells that are identical to their parent cell. We want to produce identical cells when we are growing and repairing an injury. If you start with a diploid parent cell, the daughter cells will also be diploid.

Cell cycle A cell’s life begins when a parent cell divides into 2 daughter cells, continues as the cell grows and matures, and ends when the cell divides. This is known as the cell cycle.

Overview of the events of mitosis:

INTERPHASE – the period between cell division.

When cells are not actively dividing, they are in interphase. A cell may spend up to 95% of its life in interphase. At this time, the DNA is in a loose, soupy form known as chromatin. The chromatin contains the animal’s chromosomes. Chromosomes are long strands of DNA where genes (instructions for specific traits and proteins) are encoded. Interphase can be divided into three periods; the G1 Period, S Period, and G2 Period.

1. During the G1 (Gap 1) Period the cell increases in

size to adult cell size. 2. During the S (Synthesis) Period, DNA replication

takes place. 3. During the G2 (Gap 2) Period, mitochondria and

other cellular organelles replicate. Also, the chromosomes begin to coil and condense.

Parts of a replicated chromosome include… 1. Sister chromatids – the identical strands of DNA 2. Centromere – structure that holds the sister chromatids together 3. Kinetochore – structures that develop on the sides of a centromere during late prophase. The spindle fibers attach at this point of the chromosome.

MITOSIS Mitosis refers to division of the nucleus, normally accompanied by the division of the rest of the cell called cytokinesis. Mitosis is divided into four phases; prophase, metaphase, anaphase, and telophase.

PROPHASE - During prophase, the following events take place:

1. The centrosomes replicate and then migrate to opposite poles of the nucleus. Spindle fibers stretch out between them as they move, forming a football-shaped spindle between the centrosomes.

2. Microtubules radiate outward from the centrosomes to form asters. The asters will push the poles of the cell away from each other during late anaphase and telophase.

3. The nuclear chromatin condenses into visible chromosomes. 4. The nucleolus gradually disappears.

5. The nuclear membrane completely fragments. 6. Some spindle fibers grow from the poles to the center of the cell and attach to the

chromosomes at the kinetochores.

METAPHASE - During metaphase, the following events take place:

1. The spindle fibers pull the chromosomes to the center of the cell. 2. The chromosomes are lined up along an invisible circular plate,

perpendicular to the axis of the spindle, called the equator.

ANAPHASE - During anaphase, the following events take place:

1. The centrosomes begin reeling in their spindle fibers. 2. The centromeres break, allowing the sister chromatids to separate

and be dragged toward opposite poles. 3. The sister chromatids, once separated, are known as daughter

chromosomes. 4. The aster bodies begin pushing the poles of the cell further apart.

TELOPHASE - During telophase, the following events take place:

1. The daughter chromosomes reach opposite poles. 2. The spindle begins to break down. 3. The chromosomes begin to uncoil and become chromatin once

again. 4. Nuclear envelopes form around the two newly formed nuclei. 5. Nucleoli reform 6. A cell plate begins to form

CYTOKINESIS Cytokinesis is the process whereby the cytoplasm of a single eukaryotic cell is divided to form two identical daughter cells. This process begins with the formation of a cell plate across the parent cell’s midline (old metaphase equator).

A. Formation of a Cell Plate

1. Golgi-derived vesicles move along microtubules to the cell’s center. 2. These vesicles become a thin barrier at the spindle equator, the phragmoplast. The phragmoplast serves as a scaffold for cell plate assembly.

3. Vesicles continue to fuse to the phragmoplast, forming a disc-like cell plate in the center of the cell. 4. Primary cell walls and plasma membranes begin to form on both sides of the cell plate.

B. Vesicles fuse around the edge of the cell plate, expanding it laterally until its membranes touch and fuse with the existing parent cell’s plasma membrane. This results in the formation of the middle lamella.

1. When the cell plate reaches the parent cell’s cell walls, the plasma membranes on either side of the cell plate unite with the existing plasma membrane, and two daughter cells are formed. 2. Recall that the middle lamella is the first, flexible boundary

between the two cells. C. Formation of Cell Walls

1. A flexible wall of cellulose, hemicellulose, pectin, and glycoproteins is laid down on either side of the middle lamella. This forms the primary cell wall.

2. The secondary cell wall is produced by continuing thickening of the primary cell wall with the addition of lignin. Lignin causes the cell wall to “set up” (become semi-rigid).

Watch these review videos covering cell life cycles & mitosis: http://iknow.net/cell_div_education.html

Complete this review of cellular mitosis: http://www.clarendoncollege.edu/programs/NatSci/Biology/Botany/online%20lecture%20outlines/plant cell mitosis.htm