Understanding Cell Division: AP Biology Mitosis And Meiosis Test

The graph shows the relative DNA content for each cell type. In the G2 phase of the cell cycle, the DNA content is at its highest, as the cell has replicated its DNA in preparation for cell division. Sample II on the graph has the highest DNA content, indicating that it represents an animal cell in the G2 phase of the cell cycle.

Crossing over occurs during meiosis, which is part of sexual reproduction. It involves the exchange of genetic material between homologous chromosomes, leading to increased genetic variation in the resulting gametes. Asexual reproduction, on the other hand, typically does not involve meiosis or crossing over, as it involves the replication of genetic material without the exchange of genetic information. Therefore, this statement is incorrect.

The incorrect statement is that each chromosome contains precisely one gene; in reality, chromosomes house hundreds or thousands of genes. These genes are DNA segments that encode instructions for protein synthesis, essential for various cellular functions. The other statements are accurate: genes are segments of DNA, many contain information for enzyme and protein production, fertilization combines genes from both sperm and ovum, and genetic mutations—changes in the DNA sequence—can lead to genetic variation.

During metaphase, the chromosomes are duplicated and consist of two sister chromatids joined together. Following cytokinesis, the cell divides into two daughter cells. Each daughter cell will receive an equal number of chromosomes as the parent cell. Since there are 20 chromatids in the parent cell, there are 10 chromosomes (20 divided by 2) in each daughter cell.

The somatic cells derived from a single-celled zygote divide by the process of mitosis. Mitosis is a type of cell division where a single cell divides into two identical daughter cells, each with the same number of chromosomes as the parent cell. This process is responsible for growth, repair, and maintenance of the body's tissues and organs. Meiosis, on the other hand, is a type of cell division that occurs in the formation of gametes (sperm and eggs) and leads to genetic variation. Replication refers to the duplication of DNA, while cytokinesis alone is the division of the cytoplasm. Binary fission is a type of cell division that occurs in prokaryotes, not in eukaryotic somatic cells.

This cell is a plant cell undergoing cytokinesis because the cell plate is forming across the middle of the cell, which is a characteristic of cytokinesis in plant cells. Additionally, the nuclei are re-forming at opposite ends of the cell, which is another characteristic of cytokinesis. This process is different from animal cells, as they form a cleavage furrow during cytokinesis instead of a cell plate. Therefore, the correct answer is a plant cell undergoing cytokinesis.

If a cell completed mitosis but not cytokinesis, it means that the cell has undergone nuclear division but not cell division. This would result in two nuclei within a single cell. Cytokinesis is the process of dividing the cytoplasm and creating two separate cells, but if it does not occur, the cell will have multiple nuclei. Therefore, the correct answer is two nuclei.

During mitosis and cytokinesis, the parent cell divides into two daughter cells. At the end of this process, the daughter cells have the same number of chromosomes as the parent cell. This is because the chromosomes are duplicated during the S phase of the cell cycle, and each daughter cell receives an identical set of chromosomes. Additionally, the daughter cells have the same amount of DNA as the parent cell, as the DNA is replicated during the S phase as well. Therefore, the correct answer is that the daughter cells have the same number of chromosomes and the same amount of DNA.

A chromatid is a replicated chromosome. During the S phase of the cell cycle, a chromosome is duplicated and consists of two identical sister chromatids held together by a centromere. Each chromatid contains a copy of the genetic information of the original chromosome. Therefore, the correct answer is a replicated chromosome.

During anaphase I, the pairs of homologous chromosomes separate, and each chromosome moves towards opposite poles of the cell. However, the sister chromatids, which are still attached to each other at the centromere, remain linked. This ensures that each daughter cell receives one complete set of chromosomes, consisting of one maternal and one paternal homologous chromosome. The separation of the sister chromatids occurs during anaphase II.

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During the cell cycle, chromosomes are replicated during the S phase, which is the second phase of the cycle. This is when DNA synthesis occurs, and each chromosome is duplicated to form sister chromatids. Therefore, the number II represents the point in the cell cycle during which the chromosomes are replicated.

During mitosis, several events occur including condensing of chromosomes, uncoupling of chromatids at the centromere, formation of a spindle, and disappearance of the nucleolus. However, synthesis of DNA does not occur during mitosis. DNA replication takes place during the S phase of the cell cycle, which precedes mitosis. In mitosis, the duplicated chromosomes are separated and distributed to two daughter cells, but no new DNA synthesis occurs.

If the cell whose nuclear material is shown above continues toward completion of mitosis, the next event that would occur is the formation of telophase nuclei. Telophase is the final stage of mitosis, where the nuclear material starts to condense and form two separate nuclei. This is followed by cytokinesis, where the cell membrane divides to form two separate daughter cells.

A kinase is an enzyme that attaches a phosphate group to another molecule through a process called phosphorylation. This process is crucial for regulating various cellular functions, including signal transduction, metabolism, and gene expression. Phosphatase, on the other hand, removes phosphate groups from molecules, while phosphorylase is an enzyme involved in glycogen metabolism. Cyclase refers to enzymes that catalyze the formation of cyclic compounds, and ATPase is responsible for hydrolyzing ATP to release energy. Therefore, the correct answer is kinase.

Taxol disrupts microtubule formation by binding to microtubules and accelerating their assembly from the protein precursor, tubulin. The fibers of the mitotic spindle are composed of microtubules and are crucial for the proper alignment and separation of chromosomes during mitosis. Therefore, when taxol affects the fibers of the mitotic spindle, it disrupts the normal process of mitosis, leading to the inhibition of cell division.

During meiosis I, homologous chromosomes pair up and exchange genetic material through crossing over. This process increases genetic diversity in the resulting gametes. Mitosis and meiosis II do not involve the pairing of homologous chromosomes or crossing over.

For a species with a chromosome number of 2n = 16, there are 8 homologous pairs of chromosomes, meaning it is diploid with a total of 16 chromosomes. During the S phase, each of these chromosomes will replicate to form sister chromatids, but they will still be counted as 16 chromosomes rather than as 32 separate entities. Gametes of this species, being haploid, will contain 8 chromosomes.

Meiosis is a type of cell division that occurs in sexually reproducing organisms, including plants. It is responsible for the production of spores, reduction of chromosome number by half, independent assortment of chromosomes, and crossing over and recombination of homologous chromosomes. These processes contribute to genetic variation and the formation of gametes. However, meiosis does not result in the production of identical daughter cells. Instead, it leads to the formation of genetically diverse haploid cells, which eventually develop into gametes. Therefore, the correct answer is "production of identical daughter cells."

The MPF protein complex turns itself off by activating a process that destroys cyclin. Cyclin is a protein that regulates the cell cycle by binding to and activating cyclin-dependent kinases (CDKs). Once cyclin has fulfilled its role in promoting cell division, it needs to be degraded in order to stop the cell cycle progression. The MPF protein complex activates a process, likely involving the ubiquitin-proteasome system, that targets cyclin for degradation, effectively turning off the cell cycle.

Cancer cells are known to exhibit characteristics that differentiate them from normal cells. One of these characteristics is the lack of density-dependent inhibition, meaning they continue to grow and divide even when the surrounding cells are densely packed. Additionally, cancer cells are not subject to the normal cell cycle controls that regulate the division of normal cells. This means that they can stop dividing at any point in the cell cycle, not necessarily at the appropriate checkpoints. Therefore, the correct answer is A, B, and C.

The correct answer is I only. This is because animals typically go through a life cycle that includes birth, growth, reproduction, and death. This life cycle is characterized by distinct stages such as infancy, childhood, adolescence, and adulthood. In contrast, plants and some other organisms have different life cycles that involve stages such as germination, growth, flowering, and seed production. Therefore, the life cycle of animals is unique to them and is represented by option I only.

During the S phase of the cell cycle, DNA replication occurs, resulting in the duplication of the DNA content. Therefore, at the end of the S phase, each cell would have 16 picograms of DNA. In the G2 phase, the cell undergoes growth and prepares for cell division. Since no further DNA replication occurs during this phase, the amount of DNA remains the same as at the end of the S phase, which is 16 picograms.

Cytoskeletal elements, specifically microtubules, make up the mitotic spindle apparatus, which is responsible for separating sister chromatids during cell division. On the other hand, the contractile ring, which is required for the separation of daughter cells at the end of the mitotic phase, is made of actin microfilaments.

Both synapsis and alignment of tetrads at the metaphase plate occur in meiosis but not in mitosis. Synapsis is the pairing of homologous chromosomes during prophase I of meiosis, while alignment of tetrads at the metaphase plate occurs during metaphase I of meiosis. In mitosis, homologous chromosomes do not pair up and tetrads are not formed, so these processes do not occur. Chromosome replication, production of daughter cells, and alignment of individual chromosomes at the metaphase plate occur in both meiosis and mitosis.

The two members of a pair of homologous chromosomes differ from each other in terms of the precise sequence of the DNA within each of the chromosomes. While they may have the same genes in the same relative positions, the actual sequence of the DNA can vary between the two chromosomes. This variation in DNA sequence can lead to differences in traits and characteristics between individuals.

The correct answer is III only. This is because plants and some algae undergo a life cycle known as alternation of generations, where they have both a haploid (gametophyte) and diploid (sporophyte) stage in their life cycle. This is different from animals, which typically have a diploid dominant life cycle.

Independent assortment of chromosomes is a result of the random and independent way in which each pair of homologous chromosomes lines up at the metaphase plate during meiosis I. This means that during meiosis I, the homologous chromosomes can align in different combinations, leading to the random distribution of genetic material into the daughter cells. This process contributes to genetic diversity as it allows for different combinations of genes to be passed on to the offspring. The other options mentioned, such as the random nature of fertilization and the distribution of sister chromatids, are not directly related to the independent assortment of chromosomes during meiosis I.

Asexual reproduction and sexual reproduction differ in several ways. Asexual reproduction involves a single parent, while sexual reproduction involves two parents. In asexual reproduction, individuals transmit 100% of their genes to their offspring, while in sexual reproduction, only 50% of the genes are transmitted. Asexual reproduction produces genetically identical offspring, whereas sexual reproduction gives rise to genetically distinct offspring. Additionally, asexual reproduction only requires mitosis, while sexual reproduction always involves meiosis. Therefore, the correct answer is "all of the above" as all the statements accurately describe the differences between asexual and sexual reproduction.

All sexual life cycles in eukaryotes have meiosis, fertilization, and gametes in common. Meiosis is the process of cell division that produces gametes with half the number of chromosomes, which are then involved in fertilization. Fertilization is the fusion of gametes to form a zygote, which develops into a new organism. Gametes are specialized reproductive cells, such as sperm and eggs, that are involved in sexual reproduction. Therefore, the correct answer is II, III, and IV.

The graph shows the relative DNA content for each cell type. The sample that represents a sperm cell would have the lowest DNA content because sperm cells are haploid, meaning they only have one set of chromosomes. The graph shows that sample III has the lowest DNA content compared to samples I and II, indicating that it is more likely to represent a sperm cell.

Cyclin-dependent kinase (Cdk) is present throughout the cell cycle, indicating that statement B is true. Additionally, Cdk is an enzyme that attaches phosphate groups to other proteins, confirming that statement C is also true.

MPF (Maturation Promoting Factor) reaches its threshold concentration at the end of III. MPF is a key regulator of the cell cycle that triggers the transition from G2 phase to M phase (mitosis). It accumulates throughout interphase and reaches its peak concentration at the end of G2, signaling the cell to begin mitosis.

During prophase of mitosis in animal cells, several events occur. The centrioles move toward opposite poles, the nucleolus can no longer be seen, the nuclear envelope disappears, and the spindle is organized. However, chromosomes are not duplicated during prophase. Chromosome duplication occurs during the S phase of interphase, which is prior to mitosis.

A female somatic cell is the correct answer because it is a human cell that contains 22 pairs of autosomes and two X chromosomes. This combination of chromosomes is characteristic of female cells. The other options, such as an unfertilized egg cell, a sperm cell, and a male somatic cell, do not have this specific combination of chromosomes.

The correct answer is B and C only. Dinoflagellates and diatoms are both groups of eukaryotic organisms in which the nuclear envelope remains intact during mitosis. This means that the nucleus remains enclosed within a membrane throughout the process of cell division. Seedless plants, on the other hand, do not have an intact nuclear envelope during mitosis. Therefore, the correct answer is B and C only.

The false statement is:

"At sexual maturity, ovaries and testes produce diploid gametes by meiosis." In fact, during sexual maturity, the ovaries and testes produce haploid gametes through the process of meiosis, not diploid gametes. Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in gametes (sperm and egg cells) with a single set of chromosomes (n), rather than two sets (2n), as seen in diploid cells. These haploid gametes then combine during fertilization, restoring the diploid chromosome number in the resulting zygote.

The decrease in the amount of cyclin at a specific point in the cell cycle is caused by its destruction by a process initiated by the activity of MPF complexes. MPF complexes, also known as M-phase promoting factor, are responsible for regulating the progression of the cell cycle. Once MPF complexes become active, they trigger the degradation of cyclin, leading to its decrease. This allows the cell cycle to proceed to the next phase.

The correct answer is E, prophase. Prophase marks the beginning of mitosis and includes several important changes within the cell that set the stage for successful cell division. In animal cells, the centrioles—which are located near the nucleus—start to separate and move towards opposite poles of the cell, laying the groundwork for the mitotic spindle formation. This migration is crucial, as centrioles are responsible for organizing the microtubules that form the mitotic spindle, the structure that will eventually pull the sister chromatids apart.

Kinases are enzymes that control the activities of other proteins by phosphorylating them. Phosphorylation is the process of adding a phosphate group to a protein, which can change its structure and function. Kinases play a crucial role in many cellular processes, including cell signaling, metabolism, and cell division. They regulate the activity of proteins by adding phosphate groups to specific amino acids, which can activate or deactivate the target protein. Therefore, kinases are the enzymes responsible for controlling protein activities through phosphorylation.

By examining a karyotype, which is a visual representation of an organism's chromosomes, it is possible to determine the sex of an animal and identify whether a plant form is a gametophyte or sporophyte. Karyotypes can reveal the presence of specific sex chromosomes, such as the X and Y chromosomes in humans, which can indicate the sex of an animal. Additionally, the number and structure of chromosomes can vary between gametophytes and sporophytes in plants, allowing for their differentiation. Therefore, the correct answer is A and B only.

During mitosis in both plant and animal cells, the microtubules of the spindle originate from the centrosome. The centrosome is a structure located near the nucleus that contains a pair of centrioles. These centrioles play a crucial role in organizing the microtubules and are responsible for forming the spindle apparatus. The spindle is essential for the proper alignment and separation of chromosomes during cell division. Therefore, the centrosome is the correct answer as it is the origin of the microtubules in the spindle during mitosis.

The correct answer is cyclin. Cyclins are proteins produced at specific times in the cell cycle that bind to cyclin-dependent kinases (Cdks) to form an active complex. This cyclin-Cdk complex regulates the progression of the cell cycle by activating various target proteins involved in cell division.

During anaphase, the chromosomes separate and move towards opposite poles of the cell. This movement is facilitated by the shortening of microtubules, which are responsible for pulling the chromosomes apart. If a drug prevents the shortening of microtubules, it would hinder the movement of chromosomes during anaphase, as they would not be able to separate properly. Therefore, the drug that prevents shortening of microtubules would have the greatest impact on the movement of chromosomes during anaphase.

After telophase I of meiosis, the chromosomal makeup of each daughter cell is haploid, meaning they contain half the number of chromosomes as the original cell. Additionally, the chromosomes are composed of two chromatids, which are the replicated copies of the original chromosome. This is because during meiosis I, homologous chromosomes separate, resulting in the formation of two daughter cells with a haploid number of chromosomes, each consisting of two chromatids.

The correct answer is II only because most fungi and some protists have a life cycle that involves alternating between a haploid and a diploid stage. This is known as the alternation of generations, where the haploid stage produces gametes that fuse to form a diploid zygote, which then undergoes meiosis to produce haploid spores. This cycle allows for genetic diversity and adaptation in these organisms.

In the provided graph, stage IV represents mitosis because it shows a rapid decrease in DNA amount, indicating the division of replicated chromosomes into two daughter nuclei during the M phase of the cell cycle.

Golgi-derived vesicles are primarily responsible for cytokinesis in plant cells. During cytokinesis, these vesicles fuse together at the equatorial plane of the cell, forming a cell plate. The cell plate then expands and fuses with the existing cell wall, dividing the cytoplasm into two daughter cells. This process is unique to plant cells and is different from animal cell cytokinesis, which involves the formation of a cleavage furrow. Kinetochores, actin and myosin, centrioles and basal bodies, and cyclin-dependent kinases are not directly involved in cytokinesis in plant cells.

The M phase of the cell cycle consists of several stages, including prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. These stages occur in a specific order. During prophase, the chromatin condenses into chromosomes, the nuclear envelope breaks down, and the mitotic spindle begins to form. Prometaphase follows, during which the nuclear envelope completely disintegrates and the spindle fibers attach to the centromeres of the chromosomes. Metaphase is the next stage, where the chromosomes align along the equator of the cell. Anaphase then occurs, where the sister chromatids separate and move towards opposite poles of the cell. Telophase follows, during which the chromosomes reach the poles of the cell and decondense, and the nuclear envelope reforms. Finally, cytokinesis takes place, where the cytoplasm divides, resulting in the formation of two daughter cells. Therefore, the correct sequence of steps in the M phase of the cell cycle is prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.

The bacterial chromosome consists of a single, circular DNA molecule. DNA replication begins at the origin of replication. It is highly folded within the cell and has genes that control binary fission. However, the statement that its centromeres uncouple during metaphase of mitosis is false. Bacteria do not have centromeres like eukaryotic cells do, and they undergo a different process called binary fission for cell division, not mitosis.

Density-dependent inhibition refers to the phenomenon where cells stop dividing and growing when they become too crowded. This is because as cells become more numerous, the amount of required growth factors and nutrients per cell becomes insufficient to support their growth. This limitation in resources prevents cells from continuing to divide and grow, leading to the inhibition of cell growth.

The correct answer is:

"A diploid plant (sporophyte) produces, by meiosis, a spore that gives rise to a multicellular, haploid pollen grain (gametophyte)."

This is an example of the alternation of generations, a reproductive cycle seen in plants and some algae. In this cycle, two distinct multicellular stages alternate: a diploid sporophyte stage and a haploid gametophyte stage. Here, the diploid sporophyte produces haploid spores via meiosis. These spores develop into the multicellular gametophyte, which, in turn, produces gametes by mitosis. When gametes fuse during fertilization, they form a new diploid zygote, starting the cycle again with the sporophyte generation. None of the other options describe this distinct alternation between multicellular haploid and diploid stages.

The synaptonemal complex disappears during late prophase of meiosis I. This is the stage where homologous chromosomes pair up and undergo crossing over, which is the exchange of genetic material between them. The synaptonemal complex is a protein structure that holds the homologous chromosomes together during this process. Once crossing over is complete, the synaptonemal complex disassembles, allowing the homologous chromosomes to separate and proceed to the next stage of meiosis.

During the G2 phase of interphase, the cell prepares for mitosis by synthesizing proteins and duplicating its organelles. At the start of mitosis, during the prophase, the chromosomes condense and become visible under a microscope. Each chromosome consists of two identical sister chromatids, which are held together by a structure called the centromere. The chromatids remain attached until they separate during the anaphase. Therefore, from the G2 phase of interphase through metaphase, the chromosomes are composed of two chromatids.

When cells in the process of dividing are subjected to colchicine, a drug that interferes with the functioning of the spindle apparatus, mitosis will be arrested at the metaphase stage. The spindle apparatus is responsible for separating the duplicated chromosomes, and in metaphase, the chromosomes align in the middle of the cell. If the spindle apparatus is not functioning properly due to the interference of colchicine, the chromosomes will not be able to separate and the cell division process will be halted.

The drawing that best represents a stage where independent assortment could occur (if more chromosome pairs were shown) is V.

Here's why:

Independent Assortment: This principle states that during meiosis, homologous chromosomes (and the alleles they carry) are distributed to daughter cells independently of each other. This means different chromosome pairs can be arranged in various combinations, leading to a vast array of possible gametes.

Metaphase I: Independent assortment happens specifically in metaphase I of meiosis. In this stage, homologous pairs line up randomly at the metaphase plate.

Diagram V likely depicts metaphase I (or possibly prometaphase) where chromosomes are aligning at the metaphase plate. If there were multiple chromosome pairs present, they could line up in different orientations, leading to independent assortment.

The description states that two centrosomes are arranged at opposite poles of the cell. The phase of mitosis where this arrangement occurs is prometaphase. In prometaphase, the nuclear envelope breaks down, allowing the centrosomes to move to opposite ends of the cell and form the spindle apparatus. Therefore, the correct answer is C, prometaphase. The lowercase "c" is likely a typographical error and can be ignored.

Based on the graph, it can be observed that sample III has the lowest relative DNA content compared to samples I and II. In plants, gametophyte cells are haploid, meaning they have half the number of chromosomes as the diploid sporophyte cells. Therefore, the sample with the lowest DNA content (III) is likely to represent a gametophyte cell, as it would contain half the amount of DNA compared to the diploid sporophyte cells represented by samples I and II.

Before division, sister chromatids are attached at centromeres. After separation, each chromatid becomes a daughter chromosome. During anaphase, if 20 centromeres are observed, the dividing cell has 20 chromosomes. Each pole receives 10 chromatids, making each a chromosome in the daughter cell. Thus, after cytokinesis, each daughter cell has 10 chromosomes, each consisting of a single chromatid. Therefore, the answer is '10 chromosomes.'

The nucleus with 6 picograms of DNA is in the G2 stage of the cell cycle. This is because the G2 stage follows the S stage, during which DNA replication occurs. In the G2 stage, the cell prepares for cell division by synthesizing proteins and organelles necessary for cell division. Since the measured DNA levels range from 3 to 6 picograms per nucleus, the nucleus with 6 picograms of DNA is likely in the G2 stage where DNA replication has already occurred.

This graph shows the relative amounts of DNA in different stages of a cell's life cycle. Here's how it relates to meiosis:

I: Represents a normal diploid cell in the G1 phase. This is the starting point before DNA replication.

II: Represents a cell after DNA replication (in the G2 phase or prophase). The DNA content has doubled.

III: Represents a haploid cell after meiosis I and II. The DNA content is half of the original diploid cell.

Therefore, during meiosis, cells go from I to II to III.

Here's a breakdown:

I to II: The cell replicates its DNA in the S phase of interphase, increasing the DNA content.

II to III: Meiosis I reduces the chromosome number by half, but each chromosome still has two chromatids. Meiosis II then separates the sister chromatids, resulting in haploid cells with half the original DNA content.

During metaphase of mitosis, the chromosomes align in the middle of the cell, forming a single line called the metaphase plate. This is the stage at which chromosomes are photographed in the preparation of a karyotype, a visual representation of an individual's chromosomes arranged in pairs. In metaphase, the chromosomes are condensed and visible, making it easier to capture their structure and count them accurately.

The M phase checkpoint is responsible for ensuring that all chromosomes are properly aligned before the cell enters anaphase. If a cell no longer produces a normal protein kinase for this checkpoint, it would likely result in the cell prematurely entering anaphase without proper chromosome alignment. However, the answer states that the cell would undergo normal mitosis, indicating that the mutation does not affect the overall progression of mitosis. Instead, it would fail to enter the next G1 phase, suggesting that the mutation disrupts the cell cycle control mechanisms that regulate progression from M phase to G1 phase.

During metaphase, chromosomes line up at the center of the cell. Each chromosome consists of two identical sister chromatids. In anaphase, these sister chromatids separate and move towards opposite poles of the cell. Since the cell started with 8 chromosomes, and each chromosome has 2 chromatids, there will be a total of 16 chromatids (now considered individual chromosomes) during anaphase.

Cells at the completion of meiosis have half the number of chromosomes compared to cells that have replicated their DNA and are about to begin meiosis. Additionally, they have one-fourth the amount of DNA. This is because during meiosis, the number of chromosomes is reduced by half through two rounds of cell division, resulting in the formation of gametes with a haploid number of chromosomes. The amount of DNA is also reduced because the DNA is replicated only once during the S phase of interphase, but is divided equally between the resulting cells during meiosis.

The graph shows the relative DNA content for each cell type. In a nerve cell arrested in G0 of the cell cycle, the DNA content would be at a constant level, as the cell is not actively dividing. Sample I on the graph shows a constant DNA content, indicating that it could be from a nerve cell arrested in G0. Sample II and III show fluctuations in DNA content, suggesting that they are from cells that are actively dividing.

In the given life cycle progression, the missing step is mitosis. After the spore, the next step should be mitosis, which is the process of cell division that results in the growth and development of the gametophyte. This is followed by the formation of gametes, fertilization, and the formation of a zygote. Meiosis is already mentioned in the progression, so it is not the missing step. Synapsis and karyotype are not relevant to the progression of the life cycle.

During the cell cycle, cyclin E forms a complex with Cdk 2 to regulate the progression of the cell from G1 to S phase. The amount of cyclin E is highest during G1, indicating its importance in initiating DNA replication and entry into the S phase. This is because cyclin E is synthesized during G1 and accumulates until it reaches its peak level, after which it is degraded. Therefore, the correct statement is that the amount of cyclin E is highest during G1.

During mitosis, a diploid cell's DNA content changes as represented on the graph by going from level II to level I. This reflects the process where the cell first duplicates its DNA (increasing the amount, shown as II), then divides, resulting in two daughter cells each with the original amount of DNA (returning to level I).

The correct answer is PDGF. Fibroblasts, which are cells involved in wound healing, have receptors on their membranes for PDGF (Platelet-Derived Growth Factor). PDGF binds to these receptors and activates a signaling pathway that promotes cell growth, division, and tissue repair, aiding in the healing process by attracting fibroblasts to the injury site.

Each cell division doubles the number of cells. Starting with one cell (the fertilized egg), the first division produces 2 cells, the second division produces 4 cells, the third division produces 8 cells, the fourth division produces 16 cells, and the fifth division produces 32 cells. Therefore, after five cell divisions, the early embryo would have 32 cells. 

In plants, the gametophyte is the haploid (n) phase of the life cycle that produces gametes. Gametes are formed through mitosis, a type of cell division that results in two identical daughter cells with the same number of chromosomes as the parent cell. Therefore, gametophyte mitosis is the process that directly leads to the formation of gametes in plants.

Mitotic spindles are not present in prokaryotic cells. Prokaryotic cells undergo a process called binary fission, which does not involve the formation of mitotic spindles. Therefore, the statement that the mitotic spindles in prokaryotic cells are composed of microtubules is not true.