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Cellular Biology Homework KEY
Honors Biology
Cell Membrane questions
1. Draw the structure of the cell membrane. You must include phospholipids, integral proteins,
peripheral proteins, carbohydrate markers, and cholesterol.
Notes:
Integral proteins pass all the way through
the membrane.
Peripheral proteins are either on the inside
of the outside of the membrane, but above
or below the phospholipid heads.
Cholesterol is only as long as a single
phospholipid.
2. Define hypotonic, hypertonic, and isotonic solutions.
In a pair of solutions, the hypotonic solution has less dissolved material and therefore more
available water for osmosis or diffusion. Hypertonic has more dissolved material, and therefore
less available water for osmosis or diffusion. Isotonic solutions have the same relative amount of
dissolved material, and thus the same amount of water available for diffusion.
3. If you are hospitalized and given an IV, the bag you are hooked up to is often NS or normal
saline. It is never pure water. Why?
Pure water is hypotonic to your cells. Since water osmoses from hypotonic to hypertonic
solutions, water would flow into your cells, eventual causing them to lyse.
4. Describe what would happen if you put a fish evolved to live in fresh water into the ocean.
The ocean water is hypertonic relative to the fish’s cells. Water would flow out of the fish, and
the fish would dehydrate. It would actually die of thirst while underwater.
5. If a patient with type A blood is transfused with type B blood, they will die. Why?
The carbohydrate markers on the B cells would be recognized as foreign by the patient’s immune
system (which only recognize the A marker as self). Immune cells would begin to respond to the
threat, leading to blood clots, tissue damage, and eventually death.
6. What type of molecules will cross a cell membrane without assistance?
Small molecules (usually less than 3 atoms in size) without a charge will pass, as will hydrophobic
molecules.
7. Cells in your thyroid gland can pump iodide (I-) from low concentrations in the blood into a high
concentration of I- inside the cell. How must this material be crossing the membrane?
Because you are moving from low to high concentration (against the concentration gradient),
active transport must be used.
8. What is the difference between osmosis and diffusion?
Osmosis is diffusion across a membrane.
[Diffusion is the movement of molecules from high to low concentration until equilibrium is
reached. Osmosis is the diffusion of molecules (usually water) across a membrane.]
Cell Anatomy questions
9. Identify the labeled structures in this cell diagram.
Cell
Membrane
Centriole
Golgi
B.
Nucleolus
Nucleus (or DNA)
Ribosome
Lysosome
Rough ER
Nuclear Pore
Mitochondria
10. Describe the nuclear membrane. Give two traits that differ from the cell membrane.
What is an example of a molecule that exits the nucleus? What is an example of something that
enters the nucleus?
The nuclear membrane is composed of two phospholipid bilayers, one top of the other. It lacks
carbohydrate markers and transport proteins. Rather, it is studded with huge protein pores to
allow material to enter and exit the nucleus. Material like mRNA—instructions on building
proteins—leave the nucleus, and material like nucleotides and molecules to repair and build DNA
enter the nucleus.
11. Describe the role of a ribosome, where they are found, and what they are made of. How does
the ribosome relate to the nucleolus?
Ribosomes are large molecules that build proteins from the instructions encoded in mRNA. They
are made of proteins and rRNA. The rRNA is a ribozyme, which catalyzes the building of the
protein. Ribosomes are either found in the cytosol or attached to the ER (the rough ER). The
nucleolus is a dense region in the nucleus where the genes that encode ribosomes are found. So
many ribosomes are needed that the genes are constantly being accessed.
12. What is the difference between rough ER and smooth ER? Why is rough ER often found closest
to the nucleus?
The ER is a series of membrane tubes that carry proteins that either leave the cell or be inserted
into the cell membrane. Rough ER is studded with ribosomes; smooth ER is not.
13. What is the role of the Golgi Bodies?
Golgi bodies are a series of membrane sacs that put the final modification on proteins from the
ER before they go into the membrane or are released from the cell.
14. What is the role of the mitochondria? Of the chloroplasts?
Mitochondria are organelles that recharge ATP, the energy molecule from the cell. Mitochondria
recharge ATP by burning glucose, and harvesting the energy. Chloroplasts harvest the energy
from sunlight to recharge ATP; they are also able to create glucose from carbon dioxide.
15. Mitochondria and chloroplasts are amazing structures. According to the endosymbiotic theory,
they were originally bacteria that were swallowed by the cell but not digested. Rather, they
began to live inside the cell and eventually evolved into the organelles. List at least four pieces
of evidence that support this theory.
Mitochondria and chloroplasts have double membranes from their phagocytosis into a food
vacuole. They have circular DNA, similar to bacteria. They have ribosomes structurally different
from the ribosomes in the cytosol—their ribosomes are similar to bacterial ribosomes. Both are
the same size and shape as bacteria. Both are not built by the cell, by rather mitochondria and
chloroplasts divide through binary fission like bacteria.
16. - A muscle cell has many more mitochondria than a liver cell. Why?
Mitochondria provide energy, powering the muscle.
- Endocrine glands—organs that produce hormones—have more ER and Golgi bodies than usual.
Why? Hormones are exported out of cells, which require many of these organelles that
produce exported proteins.
- Red blood cells kill off all of their mitochondria, and thus have none. Why would they do this?
(hint: think about what a red blood cell does, and what mitochondria do.)
Red blood cells carry oxygen; mitochondria use oxygen. Thus, they get rid of organelles
that would use up the oxygen they carry.
- If you were to disrupt the extracellular matrix in a muscle, what would happen?
The organ would break down into individual muscle cells.
17. Animal cells will explode if placed in hypotonic solutions. Why don’t plants?
Cell walls protect against osmotic shock. As their cells begin to fill with water and swell,
the swelling will eventually be stopped when it hits the cell wall.