cell reproduction

CELLS REPRODUCTION

1. What is the meaning of mitosis and meiosis?
Answer:
Mitosis is the process that facilitates the equal partitioning of replicated chromosomes into two identical groups. Before partitioning can occur, the chromosomes must become aligned so that the separation process can occur in an orderly fashion. The alignment of replicated chromosomes and their separation into two groups is a process that can be observed in virtually all eukaryotic cells.
Meiosis is a two-part cell division process in organisms that sexually reproduce. Meiosis produces gametes with one half the number of chromosomes as the parent cell.
2. Explain what did you know about The Stages of Mitosis
Answer:
The process of mitosis is divided into 6 stages. The Interphase, Prophase, Metaphase, Anaphase, Telophase, and cytokinasis. At Interphase, there is only one cell, but after cytokinasis there are two identical cells.
Before mitosis can take place, the cell need to store enough energy to drive the chemical processes during the cell division. During this period of time, there is intense cellular activity. The cell grows in size. The length of the grow phase varies between a few hours to a few months. We the cell has stored enough energy, it is ready to divide itself.
The following pictures shows a series of steps of how chromosomes divide. Note that for simplicity, only a few chromosomes are drawn.
Cytokinasis
This is the last stage of mitosis. It is the process of splitting the daughter cells apart. A furrow forms and the cell is pinched in two. Each daughter cell contains the same number and same quality of chromosomes.

3. Explain the Process of meiosis.
Answer:
Because meiosis is a "one-way" process, it cannot be said to engage in a cell cycle as mitosis does. However, the preparatory steps that lead up to meiosis are identical in pattern and name to the interphase of the mitotic cell cycle.
Interphase is divided into three phases:
• Growth 1 (G1) phase: This is a very active period, where the cell synthesizes its vast array of proteins, including the enzymes and structural proteins it will need for growth. In G1 stage each of the chromosomes consists of a single (very long) molecule of DNA. In humans, at this point cells are 46 chromosomes, 2N, identical to somatic cells.
• Synthesis (S) phase: The genetic material is replicated: each of its chromosomes duplicates, producing 46 chromosomes each made up of two sister chromatids. The cell is still considered diploid because it still contains the same number of centromeres. The identical sister chromatids have not yet condensed into the densely packaged chromosomes visible with the light microscope. This will take place during prophase I in meiosis.
• Growth 2 (G2) phase: G2 phase is absent in Meiosis
Interphase is followed by meiosis I and then meiosis II. Meiosis I consists of separating the pairs of homologous chromosome, each made up of two sister chromatids, into two cells. One entire haploid content of chromosomes is contained in each of the resulting daughter cells; the first meiotic division therefore reduces the ploidy of the original cell by a factor of 2.
Meiosis II consists of decoupling each chromosome's sister strands (chromatids), and segregating the individual chromatids into haploid daughter cells. The two cells resulting from meiosis I divide during meiosis II, creating 4 haploid daughter cells. Meiosis I and II are each divided into prophase, metaphase, anaphase, and telophase stages, similar in purpose to their analogous subphases in the mitotic cell cycle. Therefore, meiosis includes the stages of meiosis I (prophase I, metaphase I, anaphase I, telophase I), and meiosis II (prophase II, metaphase II, anaphase II, telophase II).
Meiosis generates genetic diversity in two ways: (1) independent alignment and subsequent separation of homologous chromosome pairs during the first meiotic division allows a random and independent selection of each chromosome segregates into each gamete; and (2) physical exchange of homologous chromosomal regions by recombination during prophase I results in new combinations of DNA within chromosomes.
4. Explain the Meiosis-phases.
Answer:
Meiosis I
Meiosis I separates homologous chromosomes, producing two haploid cells (23 chromosomes, N in humans), so meiosis I is referred to as a reductional division. A regular diploid human cell contains 46 chromosomes and is considered 2N because it contains 23 pairs of homologous chromosomes. However, after meiosis I, although the cell contains 46 chromatids it is only considered as being N, with 23 chromosomes, because later in anaphase I the sister chromatids will remain together as the spindle pulls the pair toward the pole of the new cell. In meiosis II, an equational division similar to mitosis will occur whereby the sister chromatids are finally split, creating a total of 4 haploid cells (23 chromosomes, N) per daughter cell from the first division.
Prophase I
During prophase I, DNA is exchanged between homologous chromosomes in a process called homologous recombination. This often results in chromosomal crossover. The new combinations of DNA created during crossover are a significant source of genetic variation, and may result in beneficial new combinations of alleles. The paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. At this stage, non-sister chromatids may cross-over at points called chiasmata (plural; singular chiasma).
Leptotene
The first stage of prophase I is the leptotene stage, also known as leptonema, from Greek words meaning "thin threads".[1] During this stage, individual chromosomes begin to condense into long strands within the nucleus. However the two sister chromatids are still so tightly bound that they are indistinguishable from one another.
Zygotene
The zygotene stage, also known as zygonema, from Greek words meaning "paired threads",[1] occurs as the chromosomes approximately line up with each other into homologous chromosomes. This is called the bouquet stage because of the way the telomeres cluster at one end of the nucleus.
Pachytene
The pachytene stage, also known as pachynema, from Greek words meaning "thick threads",[1] contains the following chromosomal crossover. Nonsister chromatids of homologous chromosomes randomly exchange segments of genetic information over regions of homology. (Sex chromosomes, however, are not wholly identical, and only exchange information over a small region of homology.) Exchange takes place at sites where recombination nodules (the aforementioned chiasmata) have formed. The exchange of information between the non-sister chromatids results in a recombination of information; each chromosome has the complete set of information it had before, and there are no gaps formed as a result of the process. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope.
Diplotene
During the diplotene stage, also known as diplonema, from Greek words meaning "two threads",[1] the synaptonemal complex degrades and homologous chromosomes separate from one another a little. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. However, the homologous chromosomes of each bivalent remain tightly bound at chiasmata, the regions where crossing-over occurred. The chiasmata remain on the chromosomes until they are severed in Anaphase I.
In human fetal oogenesis all developing oocytes develop to this stage and stop before birth. This suspended state is referred to as the dictyotene stage and remains so until puberty. In males, only spermatogonia(Spermatogenesis) exist until meiosis begins at puberty.
Diakinesis
Chromosomes condense further during the diakinesis stage, from Greek words meaning "moving through".[1] This is the first point in meiosis where the four parts of the tetrads are actually visible. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. Other than this observation, the rest of the stage closely resembles prometaphase of mitosis; the nucleoli disappear, the nuclear membrane disintegrates into vesicles, and the meiotic spindle begins to form.
Synchronous processes
During these stages, two centrosomes, containing a pair of centrioles in animal cells, migrate to the two poles of the cell. These centrosomes, which were duplicated during S-phase, function as microtubule organizing centers nucleating microtubules, which are essentially cellular ropes and poles. The microtubules invade the nuclear region after the nuclear envelope disintegrates, attaching to the chromosomes at the kinetochore. The kinetochore functions as a motor, pulling the chromosome along the attached microtubule toward the originating centriole, like a train on a track. There are four kinetochores on each tetrad, but the pair of kinetochores on each sister chromatid fuses and functions as a unit during meiosis I. [2][3]
Microtubules that attach to the kinetochores are known as kinetochore microtubules. Other microtubules will interact with microtubules from the opposite centriole: these are called nonkinetochore microtubules or polar microtubules. A third type of microtubules, the aster microtubules, radiates from the centrosome into the cytoplasm or contacts components of the membrane skeleton.
Metaphase I
Homologous pairs move together along the metaphase plate: As kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align along an equatorial plane that bisects the spindle, due to continuous counterbalancing forces exerted on the bivalents by the microtubules emanating from the two kinetochores of homologous chromosomes. The physical basis of the independent assortment of chromosomes is the random orientation of each bivalent along the metaphase plate, with respect to the orientation of the other bivalents along the same equatorial line.
Anaphase I
Kinetochore microtubules shorten, severing the recombination nodules and pulling homologous chromosomes apart. Since each chromosome has only one functional unit of a pair of kinetochores[3], whole chromosomes are pulled toward opposing poles, forming two haploid sets. Each chromosome still contains a pair of sister chromatids. Nonkinetochore microtubules lengthen, pushing the centrioles farther apart. The cell elongates in preparation for division down the center.
Telophase I
The last meiotic division effectively ends when the chromosomes arrive at the poles. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids. The microtubules that make up the spindle network disappear, and a new nuclear membrane surrounds each haploid set. The chromosomes uncoil back into chromatin. Cytokinesis, the pinching of the cell membrane in animal cells or the formation of the cell wall in plant cells, occurs, completing the creation of two daughter cells. Sister chromatids remain attached during telophase I.
Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.
Meiosis II
Meiosis II is the second part of the meiotic process. Much of the process is similar to mitosis. The end result is production of four haploid cells (23 chromosomes, 1N in humans) from the two haploid cells (23 chromosomes, 1N * each of the chromosomes consisting of two sister chromatids) produced in meiosis I. The four main steps of Meiosis II are: Prophase II, Metaphase II, Anaphase II, and Telophase II.
Prophase II takes an inversely proportional time compared to telophase I. In this prophase we see the disappearance of the nucleoli and the nuclear envelope again as well as the shortening and thickening of the chromatids. Centrioles move to the polar regions and arrange spindle fibers for the second meiotic division.
In metaphase II, the centromeres contain two kinetochores that attach to spindle fibers from the centrosomes (centrioles) at each pole. The new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I, perpendicular to the previous plate.
This is followed by anaphase II, where the centromeres are cleaved, allowing microtubules attached to the kinetochores to pull the sister chromatids apart. The sister chromatids by convention are now called sister chromosomes as they move toward opposing poles.
The process ends with telophase II, which is similar to telophase I, and is marked by uncoiling and lengthening of the chromosomes and the disappearance of the spindle. Nuclear envelopes reform and cleavage or cell wall formation eventually produces a total of four daughter cells, each with a haploid set of chromosomes. Meiosis is now complete and ends up with four new daughter cells.


5. Explain about Meiosis in females.
Answer:
In females, meiosis occurs in cells known as oogonia (singular: oogonium). Each oogonium that initiates meiosis will divide twice to form a single oocyte and two polar bodies.[5] However, before these divisions occur, these cells stop at the diplotene stage of meiosis I and lay dormant within a protective shell of somatic cells called the follicle. Follicles begin growth at a steady pace in a process known as folliculogenesis, and a small number enter the menstrual cycle. Menstruated oocytes continue meiosis I and arrest at meiosis II until fertilization. The process of meiosis in females occurs during oogenesis, and differs from the typical meiosis in that it features a long period of meiotic arrest known as the Dictyate stage and lacks the assistance of centrosomes.
6. Explain about Meiosis in Male
Answer:
In males, meiosis occurs in precursor cells known as spermatogonia that divide twice to become sperm. These cells continuously divide without arrest in the seminiferous tubules of the testicles. Sperm is produced at a steady pace. The process of meiosis in males occurs during spermatogenesis.

REPRODUCTION ACCORDING TO VEGETATIVE (ANIMAL)

1. Explain, what did you know about asexual reproduction (vegetative).
Answer:
Asexual reproduction (vegetative) is to form new individual without does sex cell fusion.
2. Based your knowledge, write down the types of asexual reproduction (animals), and explain one of the types.
Answer:
The types of asexual reproduction is: establishment bud, Fragmentation, slit the self
Fragmentation:
One broken organism is two parts or more, then every part will grow to be new individual same likes the mother. Event fragmentation base on regeneration ability that is ability repairs tissue or organ that lost. Fragmentation happen among others in animal spons (porifera), flatworm, algae formed thread.

REPRODUCTION IN INDIVIDUALISM (ANIMALS)

1.Vertebrata that alive at the water, explain it reproduce
Answer:
In vertebrata alive at water does fertilization outside body (external fertilization).
example: fish and frog.
Alive at land does impregnation in body (internal fertilization).
in mammal male, the sex tool is called penis in reptile likes house lizard and lizard uses hemi penis (penis faked), in for example bird nation: duck, to canalize sperm uses end its kloaka.

2. Explain what did you know about animals internal fertilization.
Answer:
a. ovipar/lay eggs:
when does embryo bloom in egg.
for example: in bird kinds and fish.
b. ovovivipar/lay eggs and yean:
when does embryo bloom in egg incubation in body, with nutrition source comes from egg.
for example: in several shark fish kinds.
c. vivipar/yean:
when does embryo grow and bloom in uterus and get, nutrition from the mother passes plase.
for example: in several kinds mammal
in general mammal give birth to the child (vivipar) and then give suck the child until self-supporting the child. several exceptions, for example: in duck beak animal (platypus, lay eggs, after hatch breastfed new the child. in animals has pocket (marsupialia), example: kangaroo, the child borns young (very premature) then crawls to enter, the mother poke, look for putting milk, then breastfeed in poke until self-supporting.
3. Explain, what did you know about reproduction in reptile.
Answer:
Reproduction in reptile
Reptile group likes lizard, snake and turtle is animals fertilization happen in body (internal fertilization). Its usually has ovipar reptile, but there also reptile has ovovivipar, like snake garter and lizard. snake egg garter or lizard will hatch in the female mother body. But the food is got from existing food reservist in egg. female reptile produces ovum in ovary. ovum then move alongside oviduct aim kloaka. Male reptile produces sperm in testis. Sperm moves alongside direct channel relates to testis, that is epididimis. From epididimis sperm moves to aim vase deferens and end at hemi penis. Hemi penis be two penis that related by one testis that can spread like radius in rubber gauntlet. at the (time) of reptile animal group holds copulate, only one hemi penis that putted into into female sex channel.
ovum female reptile that impregnate sperm will pass oviduct and at the (time) of pass oviduct, ovum that impregnate be surrounded by eggshell that waterproof. this matter will overcome problem after egg will be put in wet environment. Majority reptile kind, egg is planted in warm place and left by the mother. Its egg found galore egg yolk provision.
Reptile animal likes lizard, iguana sea, several snakes and turtle with various crocodile kind lets a large part underwater the alive, but they will return to when put the egg
4. Explain, what did you know about reproduction in Pisces (fish).
Answer:
Fish is animal group ovipar, female fish and male fish doesn't has sex organ outside. female fish doesn't take outside egg squate, but will take ovum will not bloom when not impregnate by sperm. Ovum taked from ovary passes oviduct and taked to pass kloaka. moment will lay, female fish looks for dense place by growth at water or between underwater stoney.
at the same time, male fish also take outside sperm dar testis that canalized to pass channel urogenital (urine channel all at once sperm channel) and out pass kloaka, so that fertilization underwater (external fertilization). this event is then goes on until hundreds ovum impregnate cling in water plant or in stone gaps.
eggs that impregnate appear like white coloured little circles. These eggs will hatch during 24 - 40 clocks.
Bew fry will hatch will get the first food from the egg yellow remainder, appear like lump in the stomach that still clear. from in such a way fry quantity, only several that can survive alive

ANGIOSPERMAE REPRODUCTION

1. Write down the characteristic of angiospermae plant.
Answer:
• multiply with seed
• seed is protected fruit tissue
• reproduction structure found in flower
• alive cycle:
#. generation sporofit dominant, free alive
#. generation gametofit eduksi, alive not free

2. How does formation gamet in Angiospermae?
Answer:
Powder boutique formation happens in powder poke. In powder poke there are a lot of powder grain mother cell diploid. This powder boutique mother cell then will split according to meiosis will be 4 powder grain cells (microspora) haploid. Like in this draft:


powder grain mother cell (DIPLOID)
Meiosis
four powder grain cells (HAPLOID)
each powder grain nucleus splits to mitosis
One nucleus vegetative and one nucleus generative

3. Explain how does formation gamet female.
Answer:
Gamet female formed in future seed (ovule) or institution poke. In this part can found mother cell megaspora (mother cell pocket institution) diploid. It cells will split according to meiosis and from one institution poke mother cell forms 4 cells haploid. Three cells will reduce and gone to live one that bloom. Furthermore, this cell splits according to mitosis 3 times and formed 8 cells. From cell that number 8 this, 3 cells will move to aim adversative direction with mikropil, 2 another cells is to contain secondary copper, and 3 latest cells aims to near mikropil. From 3 cells (that aim near mikropil) this last two is sinergid and one cell again be egg cell. Under the circumstances contain institution ripe and ready for impregnate. It’s bud that ripe usually take outside sticky liquid in the end that functioneds as essence powder adherence place.