Hierarchy of structure (Aristotle): Organism >
Organ-system > Organ > Tissue > Cell
Cell: Smallest unit of life.
Xavier Bichat (1771-1802): Tissues → Organ
Purkinje (1835): Fertilized hen’s egg → embryo in
28 days
19th c. botanists: plant tissues; many types of cells
Cell Theory (Matthias Schleiden, 1838 & Theodor
Schwann, 1839)
1. All organisms are composed of one or
more cells
2. Cells are the basic unit of structure and
organization of all organisms
3. Cells arise only from pre-existing cells.
1590s
1665
1674
1838
1839
1855
Invention of the lens
First compound microscope
Robert Hooke
• Observed a thin slice of cork
• Coined the term “cells”
• “Cells”
=
“chamber-like”
structures
Anton van Leeuwenhoek
• First to observe living cells
• Animalcules = protists
Matthias Schleiden
• “Plants are composed of cells”
Theodor Schwann
• Animals are composed of cells
Rudolf Virchow
• “All cells are produced from
pre-existing cells.” (Dead cells
can’t reproduce.)
Organismal Theory: Theory that states a multicellular organism has a structured plan. (Reichert)
Omnis cellula e cellula: All cells come from pre-existing cells (Remark & Virchow 1858)
Plasmodesmata: Cytoplasmic bridges. Connect cells.
Homeostasis: Cells communicate with one another. They are coordinated in their actions. (Sherrington &
Pavlov)
Tissue culture: Cells can be cultured away from a body
Unicellular, multicellular, & acellular organisms
• Unicellular: One cell. Carry out life functions. All components. No heredity.
• Multicellular: Billions of cells.
• Acellular: No cellular compartments.
Eukaryotic & prokaryotic
• Eukaryotic: Have organelles, have chromosomes, multicellular, specialized. Ex: plant & animal cells
• Prokaryotic: No organelles, filamentous, unicellular. Ex: Bacteria, E. coli.
Cell modification: Re-acquired by the cell after cell division that helps the cell in different beneficial ways.
Two surfaces:
1. Apical: Upper edge. Facing the external environment
2. Basal: Bottom edge.
Apical modification: Found on the apical surface of the cell. Cilia & flagella help with movement. Villi and
microvilli increase surface area for more efficient absorption.
• Cilia: Short, hair-like structures that move in waves. Ex: amoeba
o Non-motile cilia: Eyelashes and nose hair.
• Flagella: Long, whiplike structures formed from microtubules. Ex: sperm cell
• Villi: Finger-like projections that arise from the epithelial layer in some organs.
• Microvilli: Smaller projections that arise from the cell’s surface
• Pseudopods: Small limbs for mobility. Temporary, irregular lobes formed by amoebas and some other
eukaryotic cells. Bulge outward to move the cell or engulf prey.
• Extra Cellular Matrix (ECM): Large network of proteins. Ex: cell wall.
o Glycoprotein: Main ingredient of ECM. Collagen.
Basal modification: Found on the basal surface of the cell.
• Desmosomes/Hemidesmosomes: Anchoring junction of the basal
surface of the cell. Rivet-like links between cytoskeleton and extracellular
matrix components such as the basal lamina that underlie epithelia.
Primarily composed of keratin, integrins and cadherins. Connect two
cells
Lateral modification: Found on the basal surface of the cell. Serves as a barrier.
• Tight junction: Act as barriers that regulate the movement of water and
solutes between epithelial layers. Prevent leakage of ECF.
• Adhering junction: Anchoring junction. Fasten cells to one another.
• Gap junction: Communicating junctions. Closable channels that connect
the cytoplasm of adjoining animal cells. Allow direct exchange of
chemical between the cytoplasm of two cells.
Specialized Cells
Roots: Absorb water and dissolve nutrients. Anchor plants to the ground. Helps
the plant grow. Cells divide at the root tip or root cap.
• Apical meristems: Where the plant grows from. Growth regions. Not
completely specialized.
• Meristem tissue: The only place where mitosis takes place in plants
Stems: Three functions: (1) Produce leaves, branches and flowers. (2) Hold
leaves up to the sunlight. (3) Transport substances between roots and leaves.
• Xylem and phloem: Transport systems of the plant
• Xylem: Transports water upward from the roots
• Phloem: Transports carbohydrates and nutrients produced by
photosynthesis
Leaves: Absorb light and carry out the process of photosynthesis
• Cuticle: A waxy covering that prevents water loss.
• Epidermis: Layer under the cuticle
• Mesophyll: Under the epidermis. Where photosynthesis takes place.
• Xylem and phloem: Under the epidermis as well.
• Stoma/stomata: Little openings on the underside of leaves. Where
oxygen leaves.
• Guard cells: Cells that close the stomata.
Blood
•
Red blood cells: Carry oxygen to all parts of the body, CO2 back to the
lungs. No nucleus, few mitochondria, not much ATP.
Muscle
• Skeletal muscles: For movement. Attached to bones. Voluntary. Lots of
mitochondria, lots of ATP.
• Smooth muscles: Stomach, blood vessels, intestines. Not voluntary. Lots
of mitochondria, lots of ATP.
• Cardiac muscles: Only in the heart. Never stops. Not voluntary. Lots of
mitochondria, lots of ATP.
Epithelium or Epithelial cells: Skin cells. Cover the glands and tissues that cover
the interior and exterior body surfaces. Not much mitochondria, not much ATP.
Nerve cells or neurons: Carry electrical impulses from the body to the brain. Do
not regenerate.
• Synapse: Where impulses travel between neurons.
• Axons: Long tails. Major branching fiber.
• Dendrites: Little extensions on the main cells.
Four types of tissue: Connective, epithelial, muscle, and nervous
Animal cell
• Cell membrane: A double layer that supports and protects the cell. Allows
materials in and out
• Lysosome: Contains digestive enzymes that destroy damaged organelles
and invaders
• Cytoplasm: Jelly-like fluid that surrounds and protects the organelles.
• Nucleus: The control center of the cell. Contains the DNA
• Nuclear membrane: Surrounds the nucleus.
• Nucleolus: A round structure in the nucleus that makes ribosomes
• Vacuole: Stores food and water.
• Golgi body: Processes and packages materials for the cell
• Mitochondria: The “Powerhouse”. Breaks down food to produce energy
in the form of ATP.
• Rough ER: Builds and transports substances through the cell. Has
ribosomes on it.
• Smooth ER: Builds and transports substances through the cell. Does not
have ribosomes.
• Ribosome: Helps make protein for the cell.
Plant cell
• Cell membrane: A double layer that supports and protects the cell. Allows
materials in and out
• Cytoplasm: Jelly-like fluid that surrounds and protects the organelles.
• Nucleus: The control center of the cell. Contains the DNA
• Nuclear membrane: Surrounds the nucleus.
• Nucleolus: A round structure in the nucleus that makes ribosomes
• Vacuole: Stores food and water.
• Golgi body: Processes and packages materials for the cell
• Mitochondria: The “Powerhouse”. Breaks down food to produce energy
in the form of ATP.
• Rough ER: Builds and transports substances through the cell. Has
ribosomes on it.
• Smooth ER: Builds and transports substances through the cell. Does not
have ribosomes.
• Ribosome: Helps make protein for the cell.
• Cell Wall: Gives shape and protection to plant cells.
• Chloroplast: Changes sunlight into sugar for plant cells. Contains a green
pigment called chlorophyll.
•
•
•
•
•
•
•
•
•
•
•
•
Chromosomes: Structures of the tightly
packaged DNA
Chromatin: Builds up chromosomes.
Packaged on the chromosome.
Chromatid: Half a chromosome. Sister
chromatids = 1 chromosome.
Centromere: Links the pair of chromatids.
Spindle fiber: Fibrous structure from the
cytoplasm which forms to the centriole
Diploid: 2n; A cell with two of each kind of
chromosomes
Haploid: n; A cell with one of each kind of
chromosome. Also called gametes.
Gametes: Sperm or egg cells
Homologous
chromosomes:
Paired
chromosomes with genes for the same
trait arranged in the same order. May have
different alleles.
Allele: Gene form for each variation of a
trait of an organism.
Zygote: Fertilized egg which has a diploid
number of chromosomes.
Tetrad: 2 homologous chromosomes come
together and the 4 chromatids overlap.
The Cell Cycle – the sequence of growth and
division of a cell
Two periods:
• Interphase: Cells grow. Organelles double.
93% of cell’s life
1. Growth 1: Organelles double.
2. Synthesis: DNA is replicated.
3. Growth 2: Proteins needed for mitosis
are produced.
• Cell division: Mitosis and meiosis
Mitosis: Cell nucleus divides into two identical cell nuclei. Body cells.
1. Prophase: “Prepare”; Chromosomes turn into chromatids. Spindle fibers form. Centrioles move to
opposite sides of the cell. Nuclear membrane breaks down.
2. Metaphase: “Middle”; Centromeres of the chromatid pairs line up in the middle of the cell. Each
chromatid attach to spindle fibers.
o Metaphase plate: location where the centromeres line up in the center of the cell.
3. Anaphase: “Apart”; Spindle fibers pull the chromatids apart. Chromatids move to opposite sides of the
cell. No more chromosome, only broken pairs of chromatids.
4. Telophase: Chromosomes reach opposite sides of cell. Spindle fibers break up. Nuclear membrane
forms.
Cytokinesis: The two cells completely divide. Cell membrane is completely formed.
Meiosis: Number of chromosomes are halved. Enables sexual reproduction and zygote formation. Sex cells.
1. Interphase: Chromosomes replicate. Each chromosome consists of 2 identical sister chromatids.
Resting phase.
2. Prophase 1: Each pair of homologous chromosomes come together to form a tetrad. Tetrads are so
tight that non-sister chromatids from the homologous pair undergo crossing over.
o Crossing over: The exchange of genetic material by non-sister chromatids. Results in a new
combination of alleles.
3. Metaphase 1: Homologous chromosomes line up together in pairs. Note in mitosis, homologous
chromosomes line up in the middle independently of each other.
4. Anaphase 1: Spindle fibers attach to the centromeres of each pair. Homologous chromosomes
separate and move to opposite ends of the cell. Centromeres do not split like they do in mitosis. Each
cell will get one chromosome from each homologous pair.
5. Telophase 1: Spindle fibers break down. Chromosomes uncoil. Cytoplasm divides. Two new haploid
cells form.
6. Interphase 2 (optional): Another cell division is needed because the number of chromosomes has not
been reduced. After telophase 1, there may be a short interphase, but not always. If a cell does have
a second interphase, there is no replication of chromosomes.
Meiosis II: Remember, the chromosomes did not duplicate in interphase 2.
7. Prophase 2: Chromosomes line up in the middle of the cell. Spindle fibers begin to form.
8. Metaphase 2: Chromosomes line up on the metaphase plate.
9. Anaphase 2: Centromeres split. Sister chromatids separate and move to opposite sides of the cell.
10. Telophase 2: Nuclei re-form. Spindle fibers appear. Cytoplasm divides into two.
Mitosis
Meiosis
Involves
•Two rounds of
•Creates 2 daughter
divisions
PMAT
cells
•Creates 4 daughter
•Creates an exact copy
cells
Way for
•Creates body cells
•Creates sex cells
cells to
•Creates a cell with 2n divide
•Creates a cell with n
(diploid)
(haploid)