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October 8, 2014
Biology I
CSI Worksheet 6 Key
1. What are the three types of cell junctions?

Tight junctions: Specialized proteins in the plasma membrane line up and bind to one another.
This is matched in the nearby cell. The proteins bind to each other and create a water tight seal
between the two cells. This won’t allow solutions or any harmful object to pass through.

Desmosomes: It is a connection that forms bridges between anchoring proteins inside adjacent
cells. Intermediate filaments are involved and connect to the anchoring protein inside the cell.
They help support the connection and diffuse energy and forces placed onto the cell. This is gap
junction is the reason why if one cell is compressed or pulled they don’t all fall apart.

Gap junctions: They are made up of membrane proteins that line up to form a channel between
the cytoplasms. This is how cells can communicate between each other by sharing their
cytoplasm. This allows for diffusion across many cells and for communication to occur between
distant cells.
2. List the four components of cellular respiration, where it occurs in the cell, and list major products
consumed and produced in each step.
a. Glycolysis: Requires 2 ATP to “get started”, produced 4 ATP and NADH, the glucose is turned
into 2 pyruvate atoms for every glucose atom. Glycolysis occurs in the cytoplasm of eukaryotes
and prokaryotes.
b. Pyruvate processing: Pyruvate is processed to release one molecule of carbon dioxide, and the
remaining two carbons are used to form the compound acetyl CoA, NADH if also produced.
Occurs in the matric of the mitochondria or the cytoplasm of prokaryotes.
c. Citric acid cycle: Acetyl CoA is oxidized to two molecules of carbon dioxide, 3 NADH, an ATP and
FADH2 is produced, the cycle runs twice for each glucose molecule oxidized. Occurs in the
matrix of the mitochondria or the cytoplasm of prokaryotes.
d. Electron transport and oxidative phosphorylation: Electrons from NADH and FADH 2 move
through a series of proteins called the electron transport chain (ETC). The energy released in
this reaction is used to create a proton gradient across a membrane; there become a positive
charge in the inner membrane of the mitochondria. This chemical potential energy is changed
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into kinetic energy in the ATP synthase protein this is called oxidative phosphorylation. Oxygen
is used and water is produced.
3. Label the fermentation diagram
Fermentation occurs when there is no
oxygen available to produce ATP. There is
less ATP production and instead of carbon
dioxide being a waste product lactate is
which forms lactic acid.
4. What happens in Photosystem II?
Excited electrons from the antenna complex resonance energy to the reaction center. From there
pheophytin is reduced by electrons in photosystem II. Plastoquinone (PQ) receives electrons from
photosystem II and carries them across the lumen side of the thylakoid and delivers them to more
electronegative molecules in the cytochrome complex. Hydrogen is stripped from the molecules on the
stroma side and dropped off to the lumen side to create a high chemical potential energy. This
potential energy of the hydrogen concentration is used in the ATP synthase molecule to form ATP. Very
similar to the ETC in cellular respiration.
5. What happens in Photosystem I?
Pigments in the antenna complex absorb photons and pass the energy to the photosystem I reaction
center. Electrons are excited from the energy, the reaction center pigments are oxidized. The highenergy electrons are passed through a series of carriers inside the photosystem, then to a molecule
called ferredoxin, and then to the enzyme NADP+ reductase. NADP+ reductase transfers two electrons
to NADP+ to form NADPH. This has a similar function as NADH and FADH2 produced by the citric acid
cycle. NADPH allows cells to reduce carbon dioxide to carbohydrates in the Calvin cycle.
6. Define the Z-scheme.
It is a model for how photosystems I and II interact.
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7. What is the C4 pathway?
The C4 pathway is in mesophyll cells that contain PEP carboxylase. A three carbon compound is fixed to
PEP carboxylase to create a four carbon organic acid. The C4 pathway increases the carbon dioxide
concentration. This helps improve the efficiency of the Calvin cycle.
8. What are CAM plants and what happens inside of them?
CAM occurs in plants that regularly keep their stoma closed on hot, dry days and open them on cool
nights. Much like the C4 pathway the CAM pathway creates higher concentrations of carbon dioxide.
The difference is that carbon dioxide is stored at night and used during the day.
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