MCAT Biology : Cellular Processes and Functions

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #16 : Mitosis And Meiosis

Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).

Meiosis is a form of __________ reproduction and mitosis is a form of __________ reproduction.

Possible Answers:

sexual . . . asexual

asexual . . . sexual

asexual . . . asexual

sexual . . . sexual

Correct answer:

sexual . . . asexual

Explanation:

The key difference between sexual and asexual reproduction is recombination. If a process involves shuffling of genetic material between chromosomes (recombination), then it is sexual reproduction. Recall that crossing over, a type of genetic recombination, occurs during prophase I of meiosis. This leads to the production of daughter cells that are distinct from the parents; therefore, meiosis is a form of sexual reproduction.

In mitosis there is no genetic recombination and the daughter cells are identical to the parent cells; therefore, mitosis is a form of asexual reproduction.

Example Question #17 : Mitosis And Meiosis

Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).

Which of the following is not a characteristic of meiosis?

Possible Answers:

It functions to grow and repair the human body

It produces four haploid daughter cells

It is preceded by the G2 phase

It produces egg and sperm cells with no homologous chromosomes

Correct answer:

It functions to grow and repair the human body

Explanation:

Meiosis is the process by which a diploid cell divides into four haploid daughter cells. The daughter cells produced are called gametes (sperm in males and egg in females). By definition, a haploid cell contains only one set of chromosomes; therefore, the egg and sperm cells will not contain any homologous chromosomes.

Recall that mitosis is part of the cell cycle and that it is preceded by three phases: G1 phase, S phase, and G2 phase. Meiosis is immediately followed by the G2 phase. The main function of meiosis is to produce haploid gametes that can be used for sexual reproduction. Growth and repair of tissues in the human body is accomplished by mitosis, not meiosis.

Example Question #18 : Mitosis And Meiosis

Which of the following occurs in mitosis, but does not occur in meiosis?

Possible Answers:

Separation of homologous chromosomes

None of these answers

Nuclear envelope breakdown

Separation of sister chromatids

Correct answer:

None of these answers

Explanation:

The main differences between meiosis and mitosis are that, during meiosis I, there is recombination between homologous chromosomes and the separation of homologous chromosomes. During mitosis, homologous chromosomes are not separated, only the sister chromatids. Both processes involve the breakdown of the nuclear envelope, allowing DNA to enter the cytoplasm and align at the equatorial plate and both processes involve separation of sister chromatids.

Only meiosis involves separation of homologous chromosomes. Since the question asks for an event exclusive to mitosis, none of these answers are suitable.

Example Question #19 : Mitosis And Meiosis

Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).

Which of the following is true regarding mitosis and meiosis?

I. Meiosis I produces twice as many daughter cells as mitosis

II. Crossing over only occurs during prophase I of meiosis

III. The daughter cells of meiosis I have the same amount of DNA as the daughter cells of mitosis

Possible Answers:

II and III

I and II

II only

I only

Correct answer:

II and III

Explanation:

Meiosis contains two different cellular divisions: meiosis I and meiosis II. Meiosis I produces two haploid daughter cells with chromosomes composed of two sister chromatids, whereas meiosis II produces four haploid daughter cells with singular sister chromatids (single-chromatid chromosomes). Mitosis only has one cellular division and produces two diploid daughter cells.

Statement I is false because meiosis I and mitosis produce the same number of daughter cells. Both divisions result in two daughter cells. Meiosis II divisions will result in four daughter cells.

Crossing over is a type of genetic recombination that exclusively occurs during prophase I of meiosis; therefore, statement II is true. This occurs because crossing over requires the formation of tetrads of homologous chromosomes.

The daughter cells of mitosis contain one sister chromatid from each homologous chromosome and the daughter cells of meiosis I contain one homologous chromosome from each pair. Although their types of chromosomes are different, both daughter cells from each division contain the same amount of DNA. The only difference is that the daughter cells of mitosis contain DNA in the form of sister chromatids, whereas daughter cells of meiosis I contain DNA in the form of the homologous chromosome. Statement III is true. The best answer is II and III. Remember that sister chromatids and homologous chromosomes code for the same genes, but contain different alleles.

Example Question #11 : Mitosis And Meiosis

Meiosis is a form of cell division that occurs in special types of cells called germ cells. It is different from mitosis because it takes a diploid cell and splits it into four, nonidentical haploid cells. In males, these haploid cells are called sperm and in females they are called eggs or ova. Meiosis has two steps: meiosis I and meiosis II. Both steps have their corresponding prophase, metaphase, anaphase, and telophase. Meiosis I phases are similar to mitotic phases, with a few key differences. Meiosis II phases are exactly identical to the mitotic phases. 

A student is observing a set of cells under the microscope. He takes notes but forgets to write the mitotic phase for each slide. His notes are as follows.

Cell A: Site of ribosome synthesis disappears

Cell B: The nuclear content spills out into the cytoplasm

Cell C: No sister chromatids are visible

What is the mitotic phase of each cell?

Possible Answers:

Cell A: Metaphase

Cell B: Prophase

Cell C: Metaphase

Cell A: Anaphase

Cell B: Anaphase

Cell C: Metaphase

Cell A: Prophase

Cell B: Anaphase

Cell C: Telophase

Cell A: Prophase

Cell B: Prophase

Cell C: Telophase

Correct answer:

Cell A: Prophase

Cell B: Prophase

Cell C: Telophase

Explanation:

There are four main phases in mitosis: prophase, metaphase, anaphase, and telophase. Prophase involves nuclear membrane breakdown, formation of mitotic spindle, and disappearance of nucleolus. Recall that nucleolus is the site of ribosome synthesis; therefore, cell A is in prophase. The question states that the nuclear contents are spilling out in Cell B. Nuclear membrane holds the contents of nucleus in place. During prophase, this nuclear membrane breaks down, causing the contents of the nucleus (like chromosomes) to spill out into the cytoplasm.

Metaphase involves the alignment of the chromosomes (with sister chromatids) along the equatorial line of the cell. In anaphase, the aligned chromosomes are pulled towards the opposite ends of the cell, causing the sister chromatids to separate. Finally, in telophase two distinct cell start appearing with chromosomes that have no sister chromatids; therefore, cell C must be in telophase.

Mitosis is immediately followed by cytokinesis, during which the cytoplasm is divided equally between the two daughter cells.

Example Question #31 : Cellular Processes And Functions

Meiosis is a form of cell division that occurs in special types of cells called germ cells. It is different from mitosis because it takes a diploid cell and splits it into four, nonidentical haploid cells. In males, these haploid cells are called sperm and in females they are called eggs or ova. Meiosis has two steps: meiosis I and meiosis II. Both steps have their corresponding prophase, metaphase, anaphase, and telophase. Meiosis I phases are similar to mitotic phases, with a few key differences. Meiosis II phases are exactly identical to the mitotic phases. 

In humans, a cell in prophase has __________ chromosomes, in metaphase has __________ chromosomes, and in anaphase has __________ chromosomes.

Possible Answers:

 . . .  . . . 

 . . .  . . . 

 . . .  . . . 

 . . .  . . . 

Correct answer:

 . . .  . . . 

Explanation:

Humans are diploid organisms with a total of 46 chromosomes (2n = 46). They have 23 distinct chromosomes and each chromosome has a homologous chromosome, giving a total of 46 chromosomes. Upon completion of DNA replication in S phase, each chromosome gains an identical sister chromatid that is joined to the original chromosome at the centromere; however, this whole entity is still considered a single chromosome. When a cell enters prophase of mitosis, there are a total of 46 chromosomes, each with a sister chromatid. In metaphase, the cell still has 46 chromosomes and these chromosomes align along the midline of the cell. In anaphase, the sister chromatids get pulled apart to opposite ends; therefore, the sister chromatid separates from the chromosome and becomes its own chromosome. This means that in anaphase there are a total of 92 chromosomes in the cell.

These 92 chromosomes get pulled to opposite ends where 2 new daughter cells (with 46 chromosomes and no sister chromatids) are produced.

Example Question #32 : Cellular Processes And Functions

Meiosis is a form of cell division that occurs in special types of cells called germ cells. It is different from mitosis because it takes a diploid cell and splits it into four, nonidentical haploid cells. In males, these haploid cells are called sperm and in females they are called eggs or ova. Meiosis has two steps: meiosis I and meiosis II. Both steps have their corresponding prophase, metaphase, anaphase, and telophase. Meiosis I phases are similar to mitotic phases, with a few key differences. Meiosis II phases are exactly identical to the mitotic phases. 

Which of the following is true regarding meiosis and mitosis?

I. Prophase I of meiosis and prophase of mitosis both involve recombination

II. In humans, cells in metaphase of mitosis will have twice as many columns of chromosomes as cells in metaphase I

III. The daughter cells of mitosis have similar ploidy number as daughter cells of meiosis I

Possible Answers:

I and II

I only

I and III

II only

Correct answer:

II only

Explanation:

Mitosis and meiosis are both processes that involve cell division. In mitosis, a diploid parent cell divides and gives rise to two identical, diploid daughter cells. In meiosis, a diploid parent cell divides and gives rise to four identical, haploid daughter cells. Meiosis is divided into meiosis I and meiosis II. Meiosis I is unique because its prophase (prophase I) involves exchange of genetic material between chromosomes. This process is called recombination. Meiosis II is similar to mitosis. Note that both meiosis I and II have prophase, metaphase, anaphase, and telophase.

Metaphase in both mitosis and meiosis involves the alignment of the cell’s nuclear material along the midline. In mitosis, sister chromatids line along the midline. This means that in humans there will be a total of 46 columns of chromosomes along the midline (46 chromosomes with their respective sister chromatids). In meiosis I, however, it is slightly different. Recall that prophase I involves tetrad formation. This means that homologous chromosomes (with their respective sister chromatids) pair up along the midline, reducing the amount of columns of chromosomes in metaphase I to half of metaphase in mitosis. This means that in humans there will be only 23 columns of chromosomes in metaphase I.

Ploidy number refers to the amount of homologous chromosomes present. In humans, there are two sets of homologous chromosomes; therefore, humans are diploid. As mentioned mitosis produces two identical, diploid daughter cells (each cell has homologous chromosomes). In meiosis I two identical, haploid daughter cells are produced. These daughter cells have 23 chromosomes with sister chromatids; however, they lack their homologous pair and are, therefore, haploid. These two daughter cells undergo meiosis II and produce the final products of meiosis, which are four haploid daughter cells. Remember that the daughter cells of meiosis II will not have a sister chromatid because the sister chromatids are pulled to opposite poles during anaphase II.

Example Question #33 : Cellular Processes And Functions

Meiosis is a form of cell division that occurs in special types of cells called germ cells. It is different from mitosis because it takes a diploid cell and splits it into four, nonidentical haploid cells. In males, these haploid cells are called sperm and in females they are called eggs or ova. Meiosis has two steps: meiosis I and meiosis II. Both steps have their corresponding prophase, metaphase, anaphase, and telophase. Meiosis I phases are similar to mitotic phases, with a few key differences. Meiosis II phases are exactly identical to the mitotic phases. 

Which of the following eukaryotic process is similar to the bacterial asexual reproduction?

Possible Answers:

Transcription

DNA replication

Meiosis I

Mitosis

Correct answer:

Mitosis

Explanation:

Asexual reproduction is cell division that involves no sexual recombination. Recall that mitosis in eukaryotes produces two identical daughter cells with identical genetic make up. This is because there is no sexual recombination during mitosis.

Meiosis, on the other hand, undergoes sexual recombination during prophase I and is considered a form of sexual reproduction, which increases genetic variation. Meiosis occurs in the gonads, the site of sperm (in testes) and oocyte (in ovaries) production. DNA replication and transcription are not involved in cell division and reproduction.

Example Question #34 : Cellular Processes And Functions

Nuclear transport is a very important concept of study in modern cellular biology. Transport of proteins into the nucleus of an organism requires energy in the form of GTP, which is attached to a protein called Ras-related Nuclear protein (RAN).

RAN is a monomeric G protein found in both the cytosol as well as the nucleus and its phosphorylation state plays an important role in the movement of proteins into and out of the nucleus. Specifically, RAN-GTP and RAN-GDP binds to nuclear import and export receptors and carries them into or out of the nucleus. They also play a role in dropping off cargo that import and export receptors hold onto. RAN's functions are controlled by two other proteins: RAN guanine exchange factor (RAN-GEF) and RAN GTPase activating protein (GAP). RAN-GEF binds a GTP onto RAN, while RAN-GAP hydrolyzes GTP into GDP. As a result, there is a RAN-GTP and RAN-GDP concentration gradient that forms between the cytosol and nucleus.

During prophase, what most likely happens to the RAN-GTP and RAN-GDP concentration gradient? 

Possible Answers:

There is no change in the concentration gradient during prophase

The concentration gradient strengthens because the cell requires more proteins to diffuse into the nucleus during mitosis

The concentration gradient breaks down because the nuclear membrane breaks down

The concentration gradient breaks down because the cell no longer requires protein movement into or out of the nucleus

The concentration gradient strengthens because the nuclear envelope becomes even more impermeable

Correct answer:

The concentration gradient breaks down because the nuclear membrane breaks down

Explanation:

During mitosis, the nuclear envelope breaks down to allow the formation of chromosomes. Since all concentration gradients are dependent upon the impermeability of a membrane, when this envelope breaks down, the concentration gradient weakens and disappears. 

Example Question #1 : Understanding Photosynthesis

Which of the following is not part of the Calvin cycle?

Possible Answers:

ATP production

addition of light

Fixation of carbon dioxide

oxidation of NADPH

Regeneration of RuBP

Correct answer:

ATP production

Explanation:

ATP is produced during the light-dependent reactions of photosynthesis by photosystem II. Carbon dioxide is fixed by combining with RuBP during calvin cycle. NAPDH donates electrons causing it to be oxdized to NADP+.

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