Biology Chapter 4: Tour of the Cell- Guided Reading Activities

How many sources of DNA does a typical plant cell contain?

3

The nuclear envelope has passages for substances moving into and out of the nucleus. These passages are called nuclear pores and they are made by proteins that are inserted into the plasma membrane that makes up the nuclear envelope. These proteins are assembled by which of the following?

Bound ribosomes

10. In biology, the relationship between form and function is critical. Briefly explain how this is apparent at the level of the cell. Your answer should include a specific example of how form follows function in a cell.

Cellular organelles have structures (form) that allow them to perform their function(s) effi- ciently. For example, lysosomes and peroxisomes are membranous sacs that allow for the com- partmentalization of their toxic contents.

List the four basic functional groupings of eukaryotic organelles and structures and give an example within each group.

(1) Genetic control of the cell: nucleus, (2) manufacture and distribution of molecules within the cell: Golgi apparatus, (3) energy processing: mitochondria, (4) structure: plasma membrane

Briefly describe the relationship between the nucleus and ribosomes. Your answer should include the following key terms: mRNA, rRNA, and protein synthesis.

The nucleus contains the DNA that is copied into an mRNA copy. The rRNA is made within the nucleolus, which is a structure within the nucleus. The rRNA becomes part of a ribosome. The ribosome then uses the mRNA copy to perform protein synthesis.

7. True or false: A protein that is destined to be inserted into the plasma membrane as opposed to being secreted still travels through the Golgi stacks. If false, make it a correct statement.

True

6. You are an evolutionary biologist working for the Smithsonian. On a fossil dig in the Eastern Montana Badlands, you discover fossil evidence that shows early eukaryotic cells containing only free ribosomes. Briefly state what conclusion(s) could be drawn from this evidence.

You might infer that early eukaryotic cells mostly made proteins that functioned within the cytosol.

6. What other organelle of the endomembrane system would you expect to find in great abun- dance? Briefly explain your answer.

You would also expect the pancreas to have an extensive network of Golgi, which would be neces- sary to ship the enzymes out of the cells of the pancreas.

Which type of ER would you expect the cells of the pancreas to have in greater abundance than other cells? Briefly explain your answer.

You would expect the cells of the pancreas to have a large amount of rough endoplasmic reticulum because it would be making a large amount of proteins for excretion.

Neurons are very long cells that require the movement of substances from one end of the cell to the other. Which type of cytoskeletal fiber would you expect to find participating in this process?

You would expect them to have a network of microtubles for this transport.

8. Place the following steps in the order in which they occur: a. Proteins are modified as they pass through the Golgi apparatus. b. A vesicle from the rough ER fuses with the Golgi membrane. c. A vesicle buds off from a Golgi stack. d. A vesicle containing a secretory protein fuses with the cell's plasma membrane.

b,a,c,d

b. Rigid structure that helps maintain bacterial cell shape: ____________

cell wall

a. The organelle responsible for performing photosynthesis: ____________

chloroplast

DNA and its associated proteins are referred to as ____________.

chromatin

e. Carry genes: ____________

chromosomes

The ____________ refers to a collection of protein fibers that provides structural support to the cell in addition to movement.

cytoskeleton

c. Thick fluid inside cells: ____________

cytosol

Which of the following is the correct sequence of structures for a mitochondrion, from outside to inside? a. Cristae b. Outer membrane c. Intermembrane space d. Matrix

d,a,c,b

a. Used for movement by certain cells: ____________

flagella

b. A stack of interconnected sacs: ____________

granum

A(n) _______________ uses a beam of light to illuminate the specimen.

light microscope

____________ are organelles involved in the metabolism of fatty acids.

peroxisomes

_________are connections between plant cells that allow for the passage of water and nutrients.

plasmodesmata

4. Smooth endoplasmic reticulum (SER) lacks ____________, which gives it a "smooth" appearance.

ribosomes

d. Structures within cells that assemble proteins: ____________

ribosomes

c. Thick fluid found within the inner membrane: ____________

stroma

d. Contain chlorophyll molecules embedded into a membrane: ____________

thylakoid

Which of the following spans a cell's membrane and allows for signaling between the ECM and cytoskeleton?

Integrins

_________________ are a distinguishing characteristic of eukaryotic cells.

Internal membranes

4. Place the following discoveries/technological advances in order: visualization using an electron microscope, isolation of actin and myosin from muscle cells, immunofluorescence, use of a video camera to observe events in real time, molecular cytochemistry, and microscopy used to establish how actin and myosin interact.

Isolation of actin and myosin, microscopy used to establish how actin and myosin interact, vi- sualization using an electron microscope, immunofluorescence, molecular cytochemistry, and use of a video camera in real time

5. A cell's plasma membrane acts as both a boundary and barrier for the cell. Briefly explain how the walls and roof of a home are a good analogy for the plasma membrane.

It is a good analogy because the walls and roof of your home define the boundary of your home (inside versus outside). They also act as a barrier: They keep what's outside out and what's inside in

3. The literal translation of endoplasmic reticulum is "within the cytoplasm" and "little net." Briefly explain why endoplasmic reticulum was a good choice of words for naming that organelle. Use Figure 4.5 on page 58 of your textbook to help formulate your answer.

It was a good choice because the endoplasmic reticulum (ER) covers the nucleus like an extensively folded net. The ER is positioned well to receive genetic information coming from the nucleus.

11. Internal compartmentalization is crucial to the proper function of a cell. List two organelles where this is important and briefly explain why you chose them.

Lysosomes because they compartmentalize acids and destructive enzymes; peroxisomes because they make hydrogen peroxide (a toxic substance) as a by-product of their metabolism

Beginning students usually confuse magnification and resolution. Briefly compare magnifica- tion with resolution.

Magnification is the apparent increase in size of an object, whereas resolution is the ability to distinguish between two points.

____________are responsible for converting the energy within food to molecules of ATP.

Mitichondria

2. Which of the following cellular components is not part of the endomembrane system?

Mitochondria

List three pieces of evidence that suggest mitochondria and chloroplasts evolved from pro- karyotic cells.

Mitochondria and chloroplasts have a singular circular chromosome similar to prokaryotes, they have ribosomes that are similar to prokaryotes, and they reproduce themselves similar to prokaryotes.

3. Which of the following associations is incorrect?

SEM; detailed structure of a nucleus

4. Your small intestine absorbs nutrients from the food you eat. Are you able to draw any conclu- sions about the surface area-to-volume ratios of the cells that line the small intestine? If so, briefly explain your answer.

The cells that line the small intestine have a high surface area-to-volume ratio. This allows them to maximize absorption of nutrients.

True or false: A mitochondrion has three separate phospholipid bilayers. If false, make it a correct statement.

False, it has two separate plasma membranes.

8. True or false: Gap junctions prevent substances from leaking through cell layers. If false, make it a correct statement.

False, tight junctions prevent substances from leaking through cell layers.

Briefly explain how the plasma membrane is supported both internally by elements of the cytoskeleton and externally by the ECM.

Fibrous proteins help to provide structure intracellularly and extracellularly. For example, collagen forms a large portion of the ECM, which helps to protect the cell and holds cells together.