Unit 3 Section 1 Cellular Replication

What is the difference between a benign tumor and a malignant tumor?

Benign tumors do not metastasize; malignant tumors do.

In the laboratory, cancer cells fail to show density-dependent inhibition of growth in cell culture. What is one explanation that could account for this?

Cancer cells continuously secrete growth factors into the cell culture medium.

During binary fission, each copy of the duplicating chromosome moves to opposite ends of the cell. What does this achieve?

It ensures that each daughter cell receives one copy of the chromosome.

You have two flasks (labeled A and B) that each contain an equal population of normal animal cells. You place flask A in a machine called a shaking incubator, which shakes the flask at 37°C and keeps the cells moving so as to not allow them to adhere to the bottom of the flask. Flask B is allowed to sit in an incubator (without shaking) at 37°C. If you let the cells in each flask grow for a week, which of the following results are you most likely to observe?

The cells in flask B will have grown significantly, but the cells in flask A will have not grown at all.

You and your lab partner are observing a cell under a microscope, but you do not know whether it is a eukaryote or a prokaryote. Which of the following observations regarding the chromosomes would you use to immediately conclude that the cell is a eukaryote?

The chromosomes are housed in a membrane-enclosed nucleus.

During cell division, what role do centrosomes play?

They organize the microtubules.

Eukaryotic cells spend most of their cell cycle in which phase?

interphase

sister chromatids are

joined together at a centromere

During which phase of mitosis do the chromosomes line up on a plane equidistant from the two spindle poles?

metaphase

If scientists studying cancer could understand how to promote cell division in cells that do not ordinarily divide, this might help people who had injuries involving

muscle or nerve cells

Which of the following is probably the main factor responsible for the phenomenon of density-dependent inhibition?

physical contact of cell-surface proteins between adjacent cells

Which of the following features likely accounts for the difference between plant and animal cell cytokinesis?

plant cells have cell walls

The phase of mitosis during which the mitotic spindle begins to form is

prophase

Which of the following helps maintain the structure of chromosomes and control the activity of genes?

proteins

Prior to mitosis and after S phase, each chromosome of a eukaryotic cell consists of a pair of identical structures called

sister chromatids

During which phase of mitosis does the nuclear envelope re-form?

telophase

At the start of mitotic anaphase,

the centromeres of each chromosome come apart.

Looking into your microscope, you spot an unusual cell. Instead of the typical rounded cell shape, the cell has a very narrow middle separating two bulging ends. It sort of looks like the number 8! You realize that this cell is

undergoing cytokinesis

A skin cell of a red fox has 34 chromosomes. You look at the cell under a microscope and see that it has 34 chromosomes and one nucleus. Several hours later, you look at the same cell again and see that it has double the amount of DNA and one nucleus. A little while later, you see that it has 68 chromosomes and two nuclei. What stage of the cell cycle was this cell in when you viewed it at each time point?

First view: G1; second view: G2; third view: telophase

Immune system cells enter a resting phase after undergoing mitosis. When activated—for example, by an infection—they can reenter the sequence of events in the cell cycle that leads to cell division. What would be the correct cell cycle sequence of events for these reactivated cells?

G1, S, G2, M

The genetic material is duplicated during

S phase

You are asked to culture an unidentified sample of animal tissue. You notice that the cells seem to fail to exhibit density-dependent inhibition. The source of this tissue sample is most likely

a cancerous tumor.

The creation of genetically identical offspring by a single parent, without the participation of sperm and egg, is called

asexual reproduction

When animal cells are grown in a petri dish, they typically stop dividing once they have formed a single, unbroken layer on the bottom of the dish. This arrest of division is an example of

density-dependent inhibition

A benign tumor differs from a malignant tumor in that a benign tumor

does not metastasize

Which of the following is a feature of plant cell division that distinguishes it from animal cell division?

formation of a cell plate

Consider the photograph shown below. You can determine this is a plant cell rather than an animal cell because it has __________.

formed a cell plate