Cell division, Genetics, and Molecular Biology

Question 1

Explain why there is a limit to how large a cell can grow

Answer 1

If a cell continued to grow, its plasma membrane would be too small to meet its metabolic needs.

The cell must stop growing once it reaches a certain size. . New growth, therefore must come from addition of new cells.

Question 2

Define the term “cell cycle”

Answer 2

A single cell cycle is defined as the sequence of events from one cell division to the next.

Question 3

Summarize how advances in technology led to the new theories about the origin of cells

Answer 3

Researchers had begun to identify some cell structures many others- including genetic material - appeared transparent under a microscope. These structures were impossible to differentiate, even at high magnifications. Although scientists could observe the division of cells, they could not infer how distinct cellular processes work .

Question 4

What is the central feature of the cell cycle?

Answer 4

the way that genetic material is duplicated and then passed

• from the original cell, called parent cell
• to each new cell, called daughter cell.

This process is made possible by the highly organized arrangement of genetic material within a cell

Question 5

In what structures us the genetic information of a cell contained? Where are these structures located?

Answer 5

DNA “deoxyribonucleic acid” - a molecule of nucleic acid that governs processes of hereditary in the cells of organisms.

DNA is found in each chromosome of a cell. A chromosomes is a length of DNA and its associated proteins.

Question 6

What is a centromere and where would you find it?

Answer 6

Centromere - the constricted ( pinched-in) region in the condensed chromosome is a specialized region

Centromere is located at by forming pairs of identical chromosomes joined.

Question 7

How many chromosomes are there in the somatic cells of humans?

Answer 7

Human somatic cells have 46 chromosomes

Question 8

What are homologous chromosomes?

Answer 8

Homologous chromosomes “similar-looking chromosomes) - organized into 22 pairs; known as autosomes.

Autosomes - two sex chromosomes that may or may not be homologous pair; are numbered 1 through 22.

Question 9

Why are the X and Y chromosomes know as the sex chromosomes?

Answer 9

The sex chromes determine the sex of an individual .

• A human female has two X chromosomes.
• a human male has one X and one Y chromosome.

By convention, the sex chromosomes are counted as a pair even though X and Y are not homologous.

Question 10

Clearly differentiates these terms diploid, haploid, polyploid.

Answer 10

Diploid - A cell that contains pairs of homologous chromosomes is said to be diploid. 46 or 23 pairs

Haploid - A cell that contains unpaired chromosomes is said to be haploid

• Human gametes, or reproductive cells (egg and sperm cells)
• The haploid number of chromosomes in a species is designated as n.

Polypoid - they have sets of more than two homologous chromosomes

Question 11

What is karyotype?

Answer 11

Karyotype - set of chromosomes that an individual possesses called the individual’s karyotype.

Question 12

Describe how the 22 autosomes and the sex chromosomes are distinct from one another.

Answer 12

• Their overall length,
• the location of the centromere,
• their staining properties/banding pattern

Each chromosomes has a distinct pattern of banding when stained.

Three characteristics are the same in homologous chromosomes,

Scientists can use these characteristics to identify individual chromosomes and to match pairs of homologous chromosomes.

Question 13

What are the main phrases of the cell cycle?

Describe each phase.

Answer 13

G1 phase “Growth 1”/”Gap 1” -

• can’t identify any specific activities taking place during phase 1.
• know that important growth processes are occurring; the cell grows quickly

S Phase “Synthesis”

• midway through interphase, the cell’s DNA is copied exactly.
• DNA in the chromatin replicates to create a second identical set of DNA
• two identical chromosomes called sister chromatids, joined at the centromere,
• New genetic material is synthesized during the phase

G2 “Growth 2”/ “Gap 2”

• Cells that have completed the S phase then enter the last segment of interphase
• DNA replication in the S phase has consumed a great deal of energy , so this second growth stage lets the cell rebuild its reserves of energy to prepare for division.
• Cell manufactures proteins and other molecules to make structures required for division of the nucleus and cell.

Question 14

Name the three important functions of mitosis and cytokinesis.

Answer 14

1. Growth: they enable organisms to grow from a single-celled zygote into a mature organism that may contain hundreds of trillion of cells
2. Maintenance: They produce new cells to replace worn out or dead cells.
3. Repair: They can regenerate damaged tissues.

Question 15

Why must each daughter cell have the correct genetic information?

Answer 15

-Each daughter cell must have the correct genetic information.

• The genetic material of the parent cell must be replicated
• The replicated chromatin must be condensed and organized as chromosomes in the nucleus
• One complete set of chromosomes must be divided into each of two new nuclei.
• The cell cytoplasm must divide to produce two complete and functional daughter cells.

Question 16

What are the four phases of mitosis?

Answer 16

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 17

List the key events that happens to chromosomes in each phase.

Answer 17

Prophase

• DNA chromatin condenses into tightly packaged visible chromosomes
• Nucleolus disappears & nuclear envelope breaks down releasing chromosomes into cytoplasm
• Centrioles move to opposite poles & radiate spindle fibres which attach to centromere of chromosomes
• Spindle Fibers (made of microtubule subunits) guide chromosomes during cell division)
• Homologus Chromosomes DO NOT pair up.

Metaphase (Middle)

• Spindle fibres guide chromosomes to middle equator
• Thick, coiled chromosomes are lined up in the centre of the cell in the metaphase plate. Spindle Fibres are attachment to the chromosomes.

Anaphase (Apart)

• The chromosomes have separated and are moving toward the poles
• Spindle fibers shorten (removal of microtubule subunits) splitting centromeres apart & sister chromatids separate to opposite poles
• At same time, other spindle fibres lengthen forcing poles away from each other elongating the cell

Telophase (Two Cells)

• Two masses of chromosomes unwind into 2 less visible chromatin masses
• Spindle fibers dissolve, nucleolus & nuclear envelope reforms around each mass of chromatin
• Telophase followed by actual division of cytoplasm called cytokinesis
• Animal cells form an indentation along cell equator & eventually pinches into two new daughter cell
• Plant cells from rigid cell plate between 2 chromatin masses that becomes the cell wall.

Question 18

How do mitosis and cytokinesis differ in plant cells and animal cells?

Answer 18

• Plant cells do not have centrioles, but they do form a spindle apparatus
• The rigid cell of wall of a plant cell is much stronger than the membrane of an animal cell. The cell wall does not furrow and pinch in during cytokenesis
• Instead, a membrane called a cell plate forms between the two daughters nuclei.
• The cell plate extends across the diameter of the cell, and it is then reinforced by the addition of cellulose and proteins to create a new cell wall.

Question 19

Describe the two key outcomes of meiosis.

Answer 19

-Reduction division: Meiosis is sometimes referral to as a reduction division because it is a form of cell division that produces daughter cells with fewer chromosomes than the parent cells.

Recombination: The products of meiosis have different combinations of genes. Genetic recombination gives rise to offspring that are genetically distinct from one another and their parents.

Question 20

In what ways does meiosis serve a different function than mitosis?

Answer 20

• Mitosis produces two diploid (2n) somatic cells that are genetically identical to each other and the original parent cell,
• Meiosis produces four haploid (n) gametes that are genetically unique from each other and the original parent (germ) cell

Question 21

Where does meiosis take place?

Answer 21

Meiosis or reduction division occurs during gametogenesis in the formation of gametes (sperm and ova). Meiosis occurs in the testes and ovaries of males and females, respectively, in the primordial germ cells.

Question 22

Describe the phases of meiosis 1 and meiosis 2.

Answer 22

• Meiosis I begins with one diploid parent cell and ends with two haploid daughter cells, halving the number of chromosomes in each cell.
• Meiosis II starts with two haploid parent cells and ends with four haploid daughter cells, maintaining the number of chromosomes in each cell.

Question 23

How is the outcome of meiosis different from the outcome of mitosis?

Answer 23

Cells divide and reproduce in two ways, mitosis and meiosis.

• Mitosis results in two identical daughter cells.
• Meiosis results in four sex cells.

Question 24

Distinguish independent assortment from crossing over.

Answer 24

Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.

Chiasmata formation between non-sister chromatids can result in an exchange of alleles.

Crossing over is the exchange of DNA material between non-sister homologous chromatids.

Question 25

Describe nondisjunction, and outline the difference between monosomy and trisomy

Answer 25

Nondisjunction is the failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of chromosomes.

Trisomies and monosomies are two types of chromosomal abnormalities.

• Trisomy is when a person has three of a particular chromosome, instead of the usual two.
• Monosomy is when they just have one chromosome instead of the usual two.

Question 26

Identify key similarities and differences between spermatogenesis and oogenesis.

Answer 26

Spermatogenesis and oogenesis are the processes of formation of male and female gametes.

• Spermatogenesis leads to the formation of sperms
• Oogenesis helps in the formation of ova.

Question 27

How does the process of asymmetrical cytokinesis help to ensure a healthy zygote?

Answer 27

About three months after conception, two million primary oocytes can be found in the ovaries. They are arrested in prophase 1 and remain that way until puberty. Every month after puberty, one primary oocyte undergoes meiosis. In contrast to spermatogenesis, however, oogenesis involves an unequal division of cytoplasm.

Question 28

How does the timing of spermatogenesis differ from the timing of oogenesis? In what way is the timing of these processes suited to their functions?

Answer 28

• The spermatogenesis undergoes mitosis to produce diploid primary spermatocyte and secondary spermatocyte undergoes meiosis 2 producing 4 viable haploid spermatids, which form mature sperm at epididymis.
• While the Oocyte undergoes meiosis 1 producing 1 larger haploid secondary Oocyte & 1 smaller first polar body ( unequal cytoplasmic division. Both secondary Oocyte & First polar body undergoes meiosis, 2 producing 1 larger viable ovum and 3 unviable secondary polar bodies that are reabsorbed by ovary.

Males produce 4 viable spermatids with even cytoplasmic division but often arrested in Oogenesis or not completed if the egg isn’t fertilized.

Question 29

Explain how the development of fraternal twins is different from the development of identical twins.

Answer 29

A single secondary oocyte at each ovulation, occasionally more than one secondary oocyte may be released. If both of these oocytes are fertilized and successful implant in the uterus - Fraternal Twins are Born

A single zygote or Blastocyst divides into two separate bodies in the first few days of embryonic development, identical twins maybe born

Question 30

Distinguish asexual reproduction from sexual reproduction.

Answer 30

Asexual reproduction is the reproductive process in which a parent organism produces genetically identical offspring.

Sexual Reproduction involves the production of gametes by meiosis, followed by fertilization between genetically distinct parental gametes to produce genetically distinct offspring.

Question 31

In what ways does the asexual reproduction of prokaryotic cells differ from mitosis?

Answer 31

• Mitosis is cell division that results in two identical daughter cells and is primarily used for growth of an organism.
• Binary fission is different from mitosis because prokaryotic cells do not have a true nucleus like eukaryotes. Also, there is no mitotic spindle formation in the nucleus during binary fission.

Question 32

In what way does conjugation differ from sexual reproduction?

Answer 32

Conjugation involves the transfer of genetic material from one cell to another by cell-to-cell contact through a bridging structure called a pilus while sexual reproduction involves the production of gametes by meiosis.

Question 33

Describe two ways that plants can reproduce asexually.

Answer 33

Budding - a form of asexual reproduction in which a complete nut miniature version of the parents grows out from the parent’s body.

• The new organism then separates to become an independent organism
• For example: Vegetative Reproduction - take place in many plants.

Fragmentation - a form of asexual reproduction involves the creation of new plants from a fragment (portion) of a parent plant.

• For example: In the cultivation of potatoes.

Question 34

Why is parthenogenesis a form of asexual reproduction?

Answer 34

-A form of asexual reproduction in which an unfertilized egg develops into an adult

For example: The whiptail lizard is another animal that reproduces by parthenogenesis

Question 35

What are spores?

Answer 35

A spore is a structure that contains genetic material and cytoplasm surrounded by a protective sheath or wall. The wall protects the contents until conditions are favourable, at which point the spore wall opens and the organism begins to develop.

Spores may be haploid or diploid, and not all spores are the product of asexual reproduction. Some organisms produce spores by meiosis, resulting in an alternation of generations.