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Biology Midterm Exam Topic Guide
Unit 1
▪ Chapter One-The Study of Life
o Biological Levels of Organization
▪ Molecules-Organelles-Cells-Tissues-Organs-Organ
Systems-Organism-Population-Community-Ecosystem-Biosphere
o Characteristics Shared by all Living things
▪ Seven main ones:
● Are organized-organized in a hierarchy (cell, tissue, etc)
● Acquire materials and energy-use to carryout everyday activities and
functions
● Reproduce-presence of genes, asexually or sexually
● Respond to stimuli-constitutes behavior, move toward or away from the
stimulus
● Are homeostatic-internal environment stays relatively constant
● Grow and develop-chance in size and structure/shape
● Have the capacity to adapt to their environment-include adaptations that
make them better suited for constantly changing environment
o Feedback systems of regulation
▪ Negative feedback-ATP feeds back to turn off the steps of cellular respiration
▪ Stimulus causes an output to keep an ideal amount of something in the body
▪ Helps our bodies stay balanced
▪ Also seen in feedback inhibition in enzymes
o Basics of evolution and classification (scientific naming) of organisms
▪ Classified based on similarities and relationships to each other (systematics)
● Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (Did King
Phillip come over for giant spaghetti?)
● Get more exclusive as you go down the list
▪ Scientific naming-taxonomy
● Both words are in italics, but only the first is capitalized
● In Latin
● Genus can be abbreviated to single letter (Ex: ​P
...
precision
▪ Accuracy-close to right answer
▪ Precise-repetitions are close together
o Percent change/error
▪ Percent change=(new-old)/old or (final-initial)/initial
▪ Percent error=(​|​experimental-actual​|​)/actual
o Mean
▪ Average
o Standard Deviation
▪ On formula sheet
▪ Tells you how far away from the average that a group is
▪ 68% of population is +/- 1 SD from average
▪ 95% of population will be +/- 2 SD from average
o Standard error
▪ Tells you that as n (population size) increases, error decreases
▪ On formula sheet
o Chi square testing
▪ On formula sheet
▪ Make sure to square top values!!!
▪ Used a lot in genetics
▪ If value is less than the chart, you accept the null hypothesis
▪ If value is greater than the chart, you accept the null hypothesis
3) Chapters 2 and 3
o Inorganic chemistry
▪ Chemistry basics
● Atomic structure
o Positive protons, negative electrons, neutral neutrons
● Bonding
o Covalent-share electrons
o Ionic-transfer electrons
o Try to satisfy octet rule (8 electrons in outer shell)
● Polarity
o Nonpolar-electrons are shared equally
o Polar-electrons are drawn more to one side than the other
o Electronegativity-an atom’s attraction in the covalent bond
▪ Water
● Properties
o high heat capacity-resist rapid temperature change
o high heat of vaporization-surface cooling
o universal solvent-due to its polarity; hydrophobic and hydrophilic
o Cohesion and adhesion-functional for circulatory systems

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High surface tension-water will flow
Solid is less dense than liquid-essential for aquatic life

Solutions
● Mix of multiple substances
▪ Acid/base chemistry
● Acids dissociate in water and increase H+ concentration
● Bases take up H+ or dissociate OH-, decreasing H+ concentration
● pH scale- on log scale; ten fold
● Buffers- resist changes in pH, seen in human blood
Organic chemistry
▪ Major biological molecules
● Carbohydrates
o Short term energy storage
o Can be structural in smaller organisms
o Cell identification (blood type)
o Seen as rings of C & O
o Monosaccharides (simple sugars) and Disaccharides (2
monosaccharides joined by dehydration synthesis)
o Storage polysaccharides: starch for plants and glycogen for
animals
o Structural polysaccharides: cellulose in plant cell wall and chitin in
animal exoskeleton
● Lipids
o Fats
o Major energy storage
o Will not dissolve in water
o Made up of glycerol backbone and fatty acid chains: 3 fatty acids
called triglyceride
o Fatty acids are hydrocarbon chains
o Saturated fatty acids-no covalent double bonds between carbons,
saturated with H’s, solid at room temperature, animals fats
o Unsaturated fatty acids-covalent double bonding, liquid are room
temperature, plant and fish oils
o Hydrogenation means adding hydrogens to saturate an
unsaturated fat
o Emulsifiers can interact with lipid and water
o Phospholipids-found in membranes, amphipathic (both
hydrophobic and hydrophilic)
o Includes steroids and cholesterol
o Atherosclerosis-plaque buildup within walls of blood vessels
● Proteins
o Many types: structural, transport, motive, hormones, immunity,
etc

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o Amino acids
o Primary, secondary , tertiary, and quaternary
o Protein denaturation: break bonds, change shape, lose function
● Nucleic acids
o Store, transmit, and help express hereditary information
o Found as long chains of nucleotides
o ATP=chief energy carrier for cells
4) Chapter 6, Sections 4 and 5
o Enzyme function: increase the rate of a reaction by lowering the activation energy
o Enzymatic rate
▪ Increase temperature to increase rate, but too high could denature
▪ Rate increases as you move closer toward optimum pH
▪ Increasing concentration of substrates (or enzymes) increases rate
o Enzyme activation
▪ Gene activation
▪ Activated by another enzyme (like kinase adding phosphate
▪ Binds with assisting compound
● Cofactors (inorganic)
● Coenzymes (organic)
o Enzyme inhibition
▪ Compound binds to active site (or other) and blocks or “motivates” substrate
▪ Competitive inhibitors-bind in the active site and mimic substrate
▪ Noncompetitive inhibitors-bind elsewhere on allosteric site (any site but active)
▪ Cooperativity-allosteric binding that can increase enzyme activity

Unit 2
▪ 5) Chapter 4
o Types of cells
▪ Prokaryote
● Bacteria and Archaea
● Generally smaller
● DNA not found in nucleus (in nucleoid region)
● Circular double-stranded DNA
● No membrane-bound organelles
● No nucleolus
● Have ribosomes
● Usually have a cell wall
▪ Eukaryote
● Have ribosomes
● DNA in nucleus
● Has nucleolus (and nucleus)
● Linear DNA
● Membrane-bound organelles

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Generally larger
Animal, plant, fungi, protists
Multicellular organisms

Cell Parts
▪ The structure helps its function
▪ Nucleus-brain, contains DNA, in eukaryotes, has nuclear envelope
▪ Ribosomes-make proteins, in cytosol or bound or the rough ER
▪ Nucleolus-inside nucleus, makes ribosomes
▪ Cytoplasm (cytosol)
● Cytosol-fluid-like, throughout cell, organelles in it
● Cytoplasm-all space between cell membrane and nuclear membrane
▪ Golgi apparatus-Ships and receives stuff from ER, makes lysosomes
▪ Centrioles-organizes microtubules that make up mitotic spindle, made of
microtubules
▪ Microfilaments-actin-proteins, seen in cytoskeleton
▪ Endoplasmic reticulum-extension of the nuclear envelope, assist production and
packaging
● Smooth ER-lacks ribosomes, makes lipids, breaks down carbohydrates,
stores calcium
● Rough ER▪ Mitochondria-aerobic respiration, form ATP, two membranes, all eukaryotes have
some form of them
▪ Chloroplasts-makes cells green, photosynthesis (converts solar energy to form
sugar), double membrane
▪ Cell wall-in plant cells and prokaryotes and fungi, protective, provide shape and
support, on the very outside
▪ Cytoskeleton-structural support, made of microtubules
▪ Microtubules-in eukaryotic cells, hollow rods of tubulin, cellular motility, support
cell, make up mitotic spindle
▪ Chromatin-complex made of DNA and protein, basic genetic holding structure,
condense into chromosomes at cell division
▪ Peroxisomes-produces hydrogen peroxide, neutralize toxins, common in
breakdown of fats
▪ Endomembrane system-connected set of membranes; nuclear envelope, ER,
Golgi, and vesicles
▪ Plastids-group of vesicular organelles
▪ Lysosomes-intracellular digestion, phagocytic cells (cells that ingest things) have a
lot of them
▪ Cilia and flagella-microtubule-based appendages used for motility
● Cilia-multiple, used to move cell or moe stuff at cell surface
● Flagella-usually singular, cell swimming, more common in prokaryotes
▪ Plasma (cell) membrane-border of cell, in all cells, protection, selective
permeability

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Vacuole-storage organelle, in all eukaryotes, though most prevalent in plant cells
as a central vacuole and stores water; contractile vacuole squeexes out water to
propel cell or modify tonicity
o Endosymbiotic Theory
▪ Eukaryotic cell formed when one cell engulfed another
▪ Mitochondria, chloroplasts, and nucleus can act like their own cells
● Contain their own DNA
● Can make proteins
● Have double membranes
● Have ribosomes
● Divide independently
o Cell size
▪ Surface area: volume ratio
● Want a high ratio
● Want more surface area, and less volume (demand)
6) Chapter 5, Part 1
o Membrane structure and components
▪ Fluid mosaic models: can move and is made of many parts
▪ Made of amphipathic phospholipids arranged in a bilayer
● Constant lateral movement and little flip-flop
● Hydrophilic heads and hydrophobic tails
▪ Integral and peripheral membrane proteins
▪ Glycolipids and glycoproteins-carbohydrates attached for cell-cell recognition
▪ Membrane proteins:
● Channels and carriers
● Stationary enzymes
● Receptors
● Recognition/communication
● Junctions
● Maintenance of cell exterior (protein matrix)
o Rules of Membrane Permeability
▪ Selective permeability
▪ Main function of membrane is to decide what can and cannot enter the cell
▪ Nonpolar dissolve freely
▪ Ions and polar molecules are slowed or stopped and will need a transporter
(charged atoms, glucose, water)
o Passive transport
▪ Simple diffusion-occurs for molecules that easily cross the membrane on their
own
▪ Osmosis-diffusion of water
● Tonicity-ability of a surrounding solution to cause a cell to gain or lose
water

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Hypotonic-concentration of solutes outside of cell is less than that
inside the cell; water rushes into the cell, cell swells and bursts
o Hypertonic-concentration of solutes outside of cell is greater than
that inside cell; water leaves the cell, which shrinks
o Isotonic-concentration of solutes inside and outside of cell is in
equilibrium; normal shape, water entering and leaving
o Solutions have tonicities, NOT CELLS
o Water chases solutes, but still moves down its own gradient
o Plants’ situation
▪ Has rigid wall outside plasma membrane
▪ Beneficial in hypotonic solutions
▪ Cell wall only expands so much before exerting turgor
pressure that resists further water uptake
▪ Turgid cells are considered the healthy state for plants
▪ Indicates they are well-watered and maintains moist
“crispness” we associate with healthy plants
▪ In isotonic solution, plant cells do not have tendency for
water to enter, and cells are said to be flaccid (limp)
▪ In hypertonic solution, a cell wall is a disadvantage
● As water leaves the cell, the plasma membrane
pulls away from the cell wall (plasmolysis), which
can be damaging and deadly
● Water potential
o The physical property that predicts the direction in which water
will flow
o Is the sum of solute potential (-) and pressure potential (+ or -)
o Cell will change until water potential inside the cell equals water
potential outside the cell
o Water is attracted to the more negative water potential
o Water still moves form a region of higher water potential to a
region of lower water potential
▪ Facilitated diffusion
● Requires a protein channel, but still no energy
● Still moves down their concentration gradient
● Help of channel proteins or carrier proteins
● More efficient with this help
Active transport
▪ Pushed across a membrane against their concentration
▪ Requires an input of energy
▪ Performed by carrier proteins
▪ Electrogenic pump
● a transporter that generates a charge difference across a membrane
▪ Helps set up membrane potential

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Electrochemical gradient considers both the solute concentration and the
attraction of charges
Cotransport
● Active transport of one molecule is coupled with a second active transport
mechanism as it moves back down its gradient
● ATP powers the first pump, but the first pump powers the second pump
Bulk Transport
● Exocytosis-transport vesicles from Golgi meet with plasma membrane and
release contents
● Endocytosis-new molecules are taken in by an infolding of the plasma
membrane
o Includes phagocytosis (big) and pinocytosis (small, liquids)

Chapter 9
o Cell Cycle and cell division
▪ Includes Interphase and M (mitotic) phase
▪ Interphase: G1, S, and G2 phases
● S-replication of chromosomes (copying DNA)
● G1 and G2 are growth phases
▪ Mitosis
● Four main steps: prophase, metaphase, anaphase, and telophase
▪ Eukaryotic Cell division results in two genetically identical daughter cells
▪ Prokaryotes undergo binary fission
▪ Somatic (body) cells are 2n and Sex cells are n
o Cell cycle Regulation/control
▪ Checkpoints
● control points in the cell cycle where “stop” or “go ahead” signals will
regulate the cycle; make sure it’s ready for the next part
● Major ones within G1, at the end of G2, and during M phase
● G1=restriction point
● Most cells are in G0 interphase, meaning they aren’t actively dividing
● Go ahead signals are produced by the phosphorylation of particular
proteins (done by kinases)
▪ Cyclins/Cdks
● Cyclin-dependent kinases (Cdks)=specific kinases for the cell cycle, but
they are actually present consistently throughout the cycle
o Dependent upon proteins called cyclins, which fluctuate
throughout the cycle
● If the level of cyclin is high enough to activate Cdks at the checkpoints,
then a “go ahead” signal is produced
● If the cell is not prepared to proceed, cyclin levels will be kept lower and
Cdks will not be activated
● Cyclin-Cdk complexes may activate enzymes
● Changes in cyclin levels are caused by internal and external factors

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Internal and External factors
● Internal factors
o Completion of essential steps (duplication of organelles,
attachment of kinetochores, etc)
● External factors
o Density-dependent inhibition
▪ If a cell is touching cells on all sides, it will lower cyclin
levels to prevent division and overcrowding (exception:
cancer)
o Anchorage dependence
▪ Cells must be attached to a substratum to divide
▪ Need a base to attach to
o Growth factors
▪ Protein released by certain cells that stimulates other cells
to divide
▪ Cells respond differently to specific GF’s and combos of
them

Cancer
▪ Process/formation
● Cancerous cells ignore signals that regulate the cell cycle and go not
require growth factors
● Avoid the normal trigger for apoptosis (cell suicide)
● Cells have a mutation that alter the function of their protein products,
resulting in faulty cell cycle control
● Mass of cells called tumors (non-serious benign and serious malignant)
● Lots of effects (disabled metabolism, loss of cellular function, etc)
● Metastasis-spread of cancer cells to locations distant from the original site
▪ Treatment
● High-energy radiation
o Damage DNA of cancerous cells, so messed up they can’t fix it
o Could potentially cause more cancer
● Chemotherapy-drugs
o Interfere with specific steps of cell cycle
o Target cells actively dividing, so causes hair loss, nausea, etc
● “Personalized” treatment
o Individual targeting
Chapter 5, Part 2
o Cell communication
▪ General signaling
● Three main steps: reception, transduction, and response
o Reception-different types of receptors
▪ Always a ligand (signaling molecule that binds)
o Transduction

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Move signal through the cell
Sequence of phosphorylation
● Done by protein called kinases
● Add a phosphate
▪ Phosphorylation cascade
o Response
▪ Cellular response-changing enzymatic activity
▪ Nuclear response-involves transcription factors and
change in production in the cell
Reception of Cell signals
● G protein-coupled receptors (extracellular)
o Receptor binds to ligand, shape change leads to binding of G
protein, G protein is then turned on by joining with GTP, active G
protein goes to a specific enzyme and activates it to lead to a
cellular response, system is reset
● Receptor Tyrosine Kinases-RTKs (extracellular)
o Set off a lot of signal transduction pathways at once
o Dimerization of receptors causes the kinase portion of the
molecule to add phosphates (from ATP) to its tyrosine amino acids
● Ligand-Gated Ion Channels (extracellular)
o Channel with a closed gate will open when its bound by a
particular ligand, allowing ion influx into the cell
● Intracellular receptors
o Small, hydrophobic ligands can act as messengers that freely cross
the membrane, so some receptors can be found in the cytoplasm
or even nucleus
Transduction of Signals (Signal transduction pathways)
● Signal transduction pathways are like falling dominoes
o Interaction of mostly proteins in sequences acting like “relay
molecules”
● Phosphorylation
o Addition of a phosphate causes a change in shape of a protein
o Generally activates a protein
o Done by protein kinase-enzymes that transfer phosphate groups
from ATP to a protein
● Dephosphorylation
o Taking away of a phosphate
o Generally deactivates a protein
o Done by protein phosphatase-enzymes that remove phosphate
groups, forms ATP, can shut off a communication signal
● Cell communication relies upon a balance of kinases and phosphatases
● Second Messenger systems

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Small, non-protein molecules that can easily diffuse throughout
the cell and also can play a role in transduction
o Water-soluble, may be ions
o Cyclic AMP
▪ Extracellular signal binds to G protein-coupled receptor,
causing an enzyme called adenylyl cyclase to convert ATP
to CAMP
▪ Activates protein kinase A, which phosphorylates other
proteins
▪ Converted to AMP by phosphodiesterase
o Ca2+ ion and IP3 (found especially in muscles)
▪ G protein-coupled receptor binds ligand, phospholipase C
is activated, phospholipid PIP2 is split
Response to signals
● Regulation of transcription (in nucleus)
o Forming RNA from a DNA template
o Can cause more or less protein production
o Signal might go to transcription factors, which can help turn on a
gene-leading to making of more proteins
● Cytoplasmic responses
o Changes in protein activity
o Ex: directional growth, activation of cell division, activation of an
internal enzyme, etc
● Fine-tuning signals
o Signal amplification: one step leads to activation of many in the
next step
o Specificity: cells can respond differently or not at all to the same
signal
o Scaffolding proteins: efficiency of signal transduction can be
increased by attaching relay proteins to one another
o Signal termination: signal pathway must eventually be shut down;
includes releasing ligands, inactivating G proteins, etc
Apoptosis
● Purposeful, programmed cell death
● Protects neighboring cells form damage
● DNA and organelles are chopped up, parts are packaged in vesicles, cell
undergoes blebbing, and scavenger cells clean up
● Signaling molecule activates a phosphorylation cascade that leads to
activation of proteases called caspases
o Protease-enzyme that cuts up proteins
o Caspases-suicide enzymes, specific type of protease
● External death signal
o From neighboring cells

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o Is a ligand that binds a cell-surface receptor
Internal nuclear-ER signals
o Nucleus signals excessive DNA damage
o ER signals excessive protein misfolding (being made incorrectly)
Parkinson’s and Alzheimer’s
o Excessive cell death
o Nervous system disorders
Cancer
o Lack of apoptosis

Unit 3
9) Chapter 6, Sections 1, 2, and 3
● Energy basics
o The capacity to cause change; ability to rearrange a collection of matter
o Potential energy-matter possesses because of its location or structure
▪ Chemical energy-available for release in a chemical reaction
o Kinetic energy-associated with the relative motion of objects
▪ Thermal energy-associated with the random movement of atoms or molecules
● Heat-thermal energy in transfer form one object to another
o Most energy is lost by a system as heat
● Law of Thermodynamics
o First: Energy can be transferred and transformed, but it cannot be created or destroyed
o Second: Every energy transfer or transformation increases the entropy (disorder) of the
universe
▪ For a process to occur spontaneously, it must increase the entropy of the universe
● Energy considerations in reactions
o Endergonic reaction-a reaction that absorbs free energy from its surroundings; positive
delta G; nonspontaneous
o Exergonic reaction-proceeds with a net release of free energy; delta g is negative;
spontaneous
● Oxidation/Reduction
o Oxidation loses electrons, becoming more positive
o Reduction gains electrons, becoming more negative (reducing charge)
10) Chapter 7
● Metabolism
o Are all of the chemical reactions in our bodies
o Catabolism=break it down; cellular respiration
o Anabolism=build it up; photosynthesis
o ATP is the energy source
● Cellular respiration
o Systematic series of catabolic reactions that break down organic molecules into simpler
products, and release chemical free energy for cells to use
o Consumes oxygen and organic compounds; Produces CO2, H2O, energy

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Uses NADH and FADH2
Makes ATP
Two types
▪ Aerobic respiration (with oxygen)
● Glycolysis-breaks glucose into two pyruvates; makes 2 ATP
● Krebs Cycle-completes the breakdown of glucose into CO2 while making
ATP and NADH/FADH2
o Generates 2 ATP, 8 NADH, and 2 FADH2 for each glucose molecule
● Electron Transport Chain-series of proteins found embedded in the inner
mitochondrial membrane
o Passes the electrons along
o Final electron acceptor: oxygen
o Regenerates NAD+ and FAD
o Electrons, hydrogen, and oxygen combine to form water as a
byproduct
o Four complexes
o Oxidative phosphorylation (chemiosmosis)
▪ H+ are pumped against their gradient from matrix into
intermembrane space, then passively moved through ATP
synthase to make ATP
▪ Affects pH
● 32-38 ATP total
● Substrate-level phosphorylation
o ATP that is made in glycolysis and Krebs Cycle as enzymes transfer
a phosphate to local ADP
o Phosphate must be removed from a substrate and need
somewhere to go
▪ Anaerobic Respiration (no oxygen)
● Glycolysis
o Same as in aerobic
o Makes two ATP
● Fermentation
o Makes no ATP
o Regenerates electron carriers so they can go through glycolysis
again
o Alcohol
▪ Generates ethanol
▪ Makes CO2
▪ Occurs in yeast
o Lactic acid
▪ Generates lactic acid
▪ Occurs in mammals
▪ In muscle cells

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Only about 34% of the potential chemical energy in glucose is transferred to heat, and the
rest is lost from the system as heat
o Carbohydrates are best because they start at the beginning of the process and can
therefore generate more ATP
o Overall payoffs: 34 from ETC, 2 from glycolysis, 2 from Krebs Cycle, none from
fermentation (just estimates)
o Regulation of processes
▪ Basic supply and demand
▪ Feedback inhibition (negative feedback control) from citrate and ATP
● Will send products back and stop the process
▪ Positive feedback from AMP (indicates lack of ATP) and will activate enzymes
11) Chapter 8
● Heterotrophs vs Autotrophs
o Heterotrophs-consumers; don’t make their own “food”
o Autotrophs-producers; plants, algae, and cyanobacteria that can generate their own “food”
● Chloroplast structure and function and Basics of light function
o Chloroplasts
▪ Present in all green parts of the plant
▪ Found in mesophyll cells-interior tissue of the leaf
▪ Double-membrane envelope surrounding a dense fluid stroma
▪ Thylakoids-membranous sacs (third levels of membranes) enclosed in the chloroplast
● Stacks called grana
● Chlorophyll (green pigment) resides in the thylakoid membranes
o Light function
▪ Provide energy for photosynthesis
▪ Chlorophyll a, Chlorophyll b, and carotenoids help light absorption
▪ Chlorophylls absorb all light other than yellow/green, which it reflects
● Photosynthesis
o Production of carbohydrates from sunlight and CO2
▪ The Light Reactions
● Production of NADPH through electron excitation
● Production of ATP through chemiosmosis/photophosphorylation
o Pumping of H+ across protein chain between photosystems
o Photophosphorylation=phosphorylation powered by light
● Splitting of H2O to harvest electrons-production of O2
● Converting solar energy into chemical energy in the form of ATP and NADPH
● Does not involve making carbohydrates or using CO2
● Chlorophylls do the majority of light absorption, while carotenoids are
involved in photoprotection-absorption of excessive light energy
● Photosystems consist of Reaction center and light-harvesting complex
o PSII-comes first, contains P680
o PSI-comes second, contains P700

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Both involved in using light energy to power the synthesis of ATP and
NADPH, via the passing of electrons along the thylakoid membrane
● Ferredoxin passes electrons to NADP+ to form NADPH
● The energy from sunlight pushes electrons from water, to PSII, down a protein
chain, to PSI, and then to NADPH, forming ATP on the side
● Generates NADPH, ATP, and oxygen gas
▪ The Dark Reactions
● Occurs in the stroma
● Series of anabolic reactions that make sugars from carbon dioxide
● Three main phases
o Carbon fixation
▪ Changes carbon from gaseous form as CO2 to solid form in 2
PGAs
o Reduction
▪ Each PGA undergoes a reaction with ATP, then NADPH, to
form G3Ps, while changing ATP to ADP and NADPH to NADP+
o Regeneration
▪ Five of the six G3Ps must be used to regenerate RuBP so that
the cycle can continue
● Production of carbohydrates from Co2, using NADPH and ATP from the light
reactions
● Regenerates ADP and NADP+ for the light reactions
All of the atmospheric oxygen we breathe is the result of photosynthesis

Unit 4
12) Chapter 10
▪ Key inheritance terminology
o Genes-hereditary units; segments of DNA
o Haploid-single set of chromosomes; n; sex cells
o Diploid-double set of chromosomes; 2n; somatic cells
o Locus-a gene’s specific location along the length of a chromosome
o Gametes-the vehicles for transmission of genes to offspring; sperms and eggs; have 23
chromosomes
o Somatic cells-body cells; have 46 chromosomes
o Sex cells-sperms and eggs
▪ Karyotype
o Ordered display of chromosomes arranged in pairs
o Pairs Homologous chromosomes-same length, same centromere position, same staining
pattern, code for the same traits
o Can help show mutations
▪ Sexual life cycles
o Animals
▪ Germ cells generate haploid gamete through meiosis

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▪ Fertilization of egg develops into a diploid zygote
▪ Mitosis leads to a diploid multicellular organism
▪ Haploid cell, diploid organism
Plants/algae
▪ Alternation of generations
▪ Has both diploid (sporophyte) and haploid (gametophyte) multicellular stages
▪ Haploid and diploid organisms
Fungi/protists
▪ Only diploid stage is a single-celled zygote, so no multicellular diploid
▪ Diploid cell, haploid organism

Meiosis
o Cuts the number of chromosomes from diploid to haploid
o Two division stages-meiosis I and II
o Meiosis I:
▪ Prophase I:
● Synapsis occurs when paired homologous chromosomes are connected
along their lengths
o Genetic recombination, crossing over, occurs-exchange of
corresponding segments of DNA from non-sister chromatids;
region called chiasma
▪ Metaphase I:
● Chromosomes at midline, but two-by two in homologous pairs
▪ Anaphase I:
● Each homologous chromosome goes its own way
● Split homologs, not chromatids
▪ Telophase I and Cytokinesis
● Occur simultaneously
● Two haploid daughter cells, but DNA is still just duplicated
o Meiosis II:
▪ Just like mitosis
▪ We finish with haploid cells that are not genetically identical
o Events unique to meiosis (not in mitosis)
▪ Synapsis and crossing over
▪ Homologous pairs at metaphase plate
▪ Separation of homologues, rather than sister chromatids
o Comparing to mitosis
▪ Meiosis-two division steps, generates four haploid genetically different daughter
cells, includes crossing over, produces gametes
▪ Mitosis-one division step, generates two diploid genetically identical cells, does
not include crossing over, produces cells for growth and other things
Genetic variation
o Mutation naturally occur
o Three main mechanisms:

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Independent assortment of chromosomes
● When homologous pairs line up at the metaphase plate, they can line up
in different way
▪ Genetic recombination
● Crossing over that occurs during synapsis
▪ Random fertilization
● Random joining of a particular egg and sperm
● Each gametes if one of 8
...
99% of the population is homozygous
recessive
● Huntington’s-degenerative disorder of the nervous system with no
phenotypic symptoms until middle age
▪ X-linked disorders
● Generally recessive, so seen almost exclusively in men
● Colorblindness
● Duchenne muscular dystrophy-weakening of muscles and loss of
coordination
● Hemophilia-absence of proteins from the clotting cascade
o Chromosomal disorders/mutations
▪ Can be the result of abnormal chromosome number or alterations of chromosome
structure
▪ Abnormal chromosome number
● Nondisjunction
o Homologous chromosomes do not separate during meiosis I, or
sister chromatids do no separate during meiosis II
o Causes aneuploidy
▪ Monosomic=2n-1; missing chromosome

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Trisomic-2n+1; extra chromosome
● Example: down syndrome
o Three copies of chromosome 21
o Short stature, mental retardation, heart
defects
o Risk increases with age of mother
▪ Sex chromosome aneuploidies
● Trisomic:
o XXY-Klinefelter syndrome; still male, some
female characteristics, low intelligence
o XYY
o XXX-Trisomy X
● Monosomic
o Monosomy X
o Sterile, potentially lowered intelligence
o Causes polyploidy
▪ Cell has more than two complete sets
▪ Triploidy (3n) and tetraploidy (4n) are common in plants,
but lethal in humans
Alterations in structure
● Not losing of gaining an entire chromosome
● Four main types:
o Deletion-removes a segment
▪ Cri du chat
● Chromosome five
● Brain/head malformation
o Duplication-repeats a segment
o Inversion-reverse a segment
o Translocation-moves a segment from one chromosome to a
nonhomologous chromosomes
▪ In many cancers
▪ Chronic Myelogenous Leukemia (CML)
● Translocation in mitosis on chromosomes 9 and 22
● Makes shorter chromosome 22-Philadelphia
chromosome



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