MEKANISME SEL DAN SIKLUS HIDUP TANAMAN

MITOSIS

- Istilah mitosis : proses yg menghasilkan dua sel anak yg identik.

- Mitosis memegang peranan dalam pertumbuhan dan perkembangan organisme.

- Pada tanaman mitosis terjadi pd sel-sel meristematis, misalnya ujung-ujung akar, dan ujung batang, kambium.

MitosisMitosis

Prophase• In prophase, the cell begins the process of

division. • 1. The chromosomes condense. The

proteins attached to the DNA cause the chromosomes to go from long thin structures to short fat one, which makes them easier to pull apart.

• 2. The nuclear envelope disappears. The double membrane that surround the nucleus dissolves into a collection of small vesicles, freeing the chromosomes to use the whole cell for division

• 3. The centrosomes move to opposite poles. During interphase, the pair of centrosomes were together just outside the nucleus. In prophase they separate and move to opposite ends of the cell.

• 4. The spindle starts to form, growing out of the centrosomes towards the chromosomes.

Metaphase

• Metaphase is a short resting period where the chromosomes are lined up on the equator of the cell, with the centrosomes at opposite ends and the spindle fibers attached to the centromeres. Everything is aligned for the rest of the division process to occur.

Anaphase

• In anaphase, the centromeres divide. At this point, each individual chromosome goes from:– 1 chromosome with 2

chromatids – to:– 2 chromosomes with one

chromatid each.

• Then the spindle fibers contract, and the chromosomes are pulled to opposite poles, towards the centrosomes.

Telophase

• In telophase the cell actually divides.

• The chromosomes are at the poles of the spindle.

• The spindle disintegrates• The nuclear envelope re-

forms around the two sets of chromosomes.

• The cytoplasm is divided into 2 separate cells, the process of cytokinesis.

Cytokinesis• The organelles (other than the

chromosomes) get divided up into the 2 daughter cells passively: they go with whichever cell they find themselves in.

• Plant and animal cells divide the cytoplasm in different ways.

• In plant cells, a new cell wall made of cellulose forms between the 2 new nuclei, about where the chromosomes lined up in metaphase. Cell membranes form along the surfaces of this wall. When the new wall joins with the existing side wall, the 2 cells have become separate.

• In animal cells, a ring of actin fibers (microfilaments are composed of actin) forms around the cell equator and contacts, pinching the cell in half.

Meiosis

• Reduces the number of chromosomes in new cells to half the number in the original cell

• Produces gametes (sperm and egg cells)

Terjadi 4 kejadian penting pada meiosis

• Perpasangan kromosom yg homolog (synapsis)

• Pertukaran bagian kromosom (crossing over)• Distribusi kembali kromosom• Susunan materi genetik mungkin berbeda dg

tetua akibat crossing over

Gamete Formation

• Gametes are sex cells (sperm, eggs)• Arise from germ cells

testes

ovaries

anther ovary

Stages of Meiosis

Meiosis I

• Prophase I• Metaphase I• Anaphase I• Telophase I

Meiosis II

• Prophase II• Metaphase II• Anaphase II• Telophase II

DNA Replication

Meiosis

Meiosis

Meiosis I

Each homologue in the cell pairs with its partner,

then the partners separate

Meiosis I - Stages

Prophase I Metaphase I Anaphase I Telophase I

Prophase I

• Each duplicated, condensed chromosome pairs with its homologue (synapsis)

• Homologues swap segments (crossing over)

Homologous Chromosomes

Homologous Chromosomes

Synapsis

Crossing Over

Effect of Crossing Over

• After crossing over, each chromosome

contains both maternal and parental

segments

• Creates new allele combinations in offspring

Metaphase I

• Chromosomes are pushed and pulled into the middle of cell

• Sister chromatids of one homologue orient toward one pole, and those of other homologue toward opposite pole

Anaphase I

• Homologous chromosomes segregate from

each other randomly (independent

assortment)

• Independent assortment results in genetic

variation

Independent Assortment

Telophase I and Cytokinesis

• The chromosomes arrive at opposite poles

• The cytoplasm divides

• There are now two haploid cells

• This completes Meiosis I

Meiosis II

• The two sister chromatids of each duplicated chromosome are separated from each other

one chromosome (duplicated)

two chromosomes (unduplicated)

Meiosis II - Stages

Prophase II Metaphase II Anaphase II Telophase II

Prophase II

• Microtubules attach to the kinetochores of the duplicated chromosomes

• Chromosomes move toward the spindle’s equator

Metaphase II

• All of the duplicated chromosomes are lined up at the spindle equator, midway between the poles

Anaphase II

• Sister chromatids separate to become independent chromosomes and move to opposite poles

Telophase II and Cytokinesis

• The chromosomes arrive at opposite ends of the cell

• A nuclear envelope forms around each set of chromosomes

• The cytoplasm divides• There are now four haploid cells

Meiosis Animation II Meiosis Animation I

Results of Mitosis and Meiosis

• Mitosis

– Two diploid cells produced

– Each identical to parent

• Meiosis

– Four haploid cells produced

– Differ from parent and one another

* Buatlah Uraian tentang Mitosis dan Miosis

SIKLUS HIDUP TANAMAN

MAIZE LIFE CYCLE

A. TasselB. MicrosporocyteC. Megasporocyte (2n)D. MeiosisE. Microspore (n)F. Germinated pollen grainG. Sperm nuclei (n)H. FertilizationI. Ear shootJ. Mature spotophyte (2n)K. Endosperm (3n)L. Embryo (2n)M. Mature kernel (2n)N. 4 megaspores (n)O. Degenerating megasporesP. Surviving megasporesQ. Mature embryo sacR. Polar nuclei (n)

Gametogenesis Tumbuhan

• Mikrosporogenesis (pada anther)• Megasporogenesis (pada bunga

betina/ovarium)

Canna Hibiscus

Microsporogenesis

Megasporogenesis

Megasporogenesis & Megagametogenesis

Megasporogenesis & Megagametogenesis

Megasporogenesis & Megagametogenesis