Chapter 16 - Cell Division Flashcards
Define growth.
Growth is a characteristic of all living things. It is a permanent increase in size. It is accompanied by cell division and differentiation to form tissues and organs.
What are 2 differences in growth for plants and animals?
1) growth of plants is restricted to growing points such as tips of shoots and roots, while in animals, growth occurs throughout body
2) growth occurs throughout the life of a plant while for animals, growth stops after a certain age, when the animal reaches maturity
What are 6 differences between mitosis and meiosis?
1) mitosis is involved in growth and development, while meiosis is involved in reproduction
2) mitosis produces 2 genetically identical cells, while meiosis produces 4 varied cells (gametes)
3) in mitosis, daughter cells contains same number of chromosomes as the parent cell. In meiosis, daughter cells contain half the number of chromosomes as the parent cell
4) in mitosis, pairing of homologous chromosomes does not occur. In meiosis, homologous chromosomes pair at prophase I
5) there is no crossing over in mitosis, but crossing over may occur in meiosis
6) mitosis involves only 1 nuclear division while meiosis involves 2 nuclear divisions.
Define mitosis.
Mitosis is a form of nuclear division that produces 2 daughter nuclei which have the same number of chromosomes as the parent nucleus, and is genetically identical to the parent.
How many chromosomes does humans have?
Every cell has 23 PAIRS of chromosomes.
Why is it important to produced genetically identical daughter cells during mitosis?
DNA replication copies all the information stored within the chromosomes. This ensures that daughter cells produced by mitosis contain all sections of DNA needed for subsequent cell division and differentiation.
What are the stages in a cell cycle during mitosis? (6)
1) interphase
2) mitosis: prophase
3) mitosis: metaphase
4) mitosis: anaphase
5) mitosis: telophase
6) cytokinesis
What happens during interphase? (5)
1) absorb nutrients
2) build up protoplasm
3) synthesis new organelles
4) chromosomes appears as long thin threads called chromatin. Just before the cell enters mitosis, the chromatin threads replicate, producing 2 identical chromatin threads joined at a point called centromere.
5) centrioles replicate and divide
Why must DNA replication and mitosis be precisely controlled?
It is to ensure all daughter cells are genetically stable. If an error occurs during replication, the new DNA strand formed would be different from original, which is known as gene mutation, and passes on to the daughter cell. Apart from that, some form of gene mutation may lead to uncontrolled division of cells(cancer: might be fatal)
What happens during early prophase of mitosis? (4)
1) The sister chromatids coil and shorten to form chromosomes, attached at the centromere.
2) in animal cells, asters form around centrioles.
3) The 2 pairs of centrioles move apart to opposite poles of the cell
4) nucleolus disappears
What happens during late prophase of mitosis? (2)
1) nuclear envelope disappears
2) a spindle forms with spindle fibres extending from one pole of the cell to the other
What happens during metaphase in mitosis?(2)
1) Chromosomes line up singly along the equatorial plane of the spindle.
2) the centromere of each chromosome is attached on both sides to a spindle fibre.
What happens during anaphase in mitosis?(3)
1) each centromere splits
2) the spindle fibres shorten and pull the sister chromatids apart to opposite poles of the cell.
3) once the sister chromatids are separated, they are called daughter chromosomes
What happens during telophase in mitosis? (4)
1) spindle fibres disintegrate
2) a nuclear envelope forms around the chromosomes at each pole of the cell
3) a nucleolus reforms in each nucleus
4) chromosomes uncoil and lengthen to become thin chromatin threads
What happens during cytokinesis in mitosis? (2)
1) division of cytoplasm
2) in animal cells, cleavage/furrows appear in the cytoplasm between two nuclei. Furrows deepen and split the cell into two identical daughter cells.
What are 2 differences between mitosis in plants and animal cells?
1) in plants, centrioles are absent while centrioles are present in animals
2) in plants, a cell plate forms between 2 daughter nuclei by the fusion of fluid filled vesicles made by the Golgi Apparatus, dividing the cell into 2. In animals, cleavage furrows appear during cytokinesis and divides the cell into 2.
Why is mitosis important?(3)
1) new cells are required for the growth of an organism
2) it repairs worn-out parts of tissue, heals wounds, replaces dead cells
3) asexual reproduction in plants such as the development of shoots and roots in storage organs like rhizomes and bulbs, allowing them to grow into new identical daughter plants.
What is reduction division?
During meiosis, it results in the production of four daughter nuclei, which contains half the number of chromosomes of the parent cells.
What are gametes?
Gametes are reproductive cells that contain half the number of chromosomes (haploid) as normal body cells. (Diploid)
Why are gametes produced for?
Sexual reproduction involves fusion of 2 gametes. The nucleus of the male gamete fuses with the nucleus of the female gamete to form a diploid zygote.
Define meiosis.
Meiosis is a form of nuclear division that produces 4 daughter nuclei containing haploid number of chromosomes as the parent nucleus.
What are the stages of meiosis? (3)
1) interphase
2) meiosis I - prophase, metaphase, anaphase, telophase, cytokinesis
3) meiosis II - prophase, metaphase, anaphase, telophase, cytokinesis
What happens during interphase of meiosis?(2)
1) Chromatid threads replicate, producing 2 identical sister chromatids (not visible under microscope)
2) centrioles divide
What happens during prophase I of meiosis?(6)
1) chromatin threads condense, coil and shorten into visible chromosomes
2) synapsis occurs: homologous chromosomes that each pair up, and each pair is known as a bivalent.
3) crossing over between chromatids of homologous chromosomes may occur at the chiasma. They cross and twist around each other, and the strength of coiling may cause them to break and exchange parts, producing a new combination of alleles along the chromosomes.
4) asters form around the centrioles which move apart to opposite poles of the cell
5) nuclear envelope and nucleolus disintegrates.
6) spindle fibres form
What are homologous chromosomes?
They are 2 chromosomes of the same shape, gene and length, each inherited from 1 parent.
What happens during metaphase I of meiosis? (2)
1) pairs of homologous chromosomes arrange themselves along the equatorial plane of the spindle.
2) two chromosomes of each pair face opposite poles of the cell, which each chrosomes attached to one spindle fibre.
What happens during Anaphase I of meiosis?
1) homologous chromosomes separate
2) the homologous chromosomes are pulled to opposite poles of the cell.
What happens during telophase I in meiosis? (3)
1) spindle fibres disintegrate
2) nuclear envelope reforms (for animal cells only)
3) most plant cells do not undergo telophase I and move straight to metaphase II
What happens during cytokinesis I of meiosis?
1) centrioles replicate(复制) into 2
2) cytoplasm cleaves into 2, producing 2 haploid daughter cells.
What happens during prophase II of meiosis?(3)
1) two pairs of centrioles move to opposite poles of the cell
2) nuclear envelope breaks down and disappears
3) spindle fibres appear
What happens during metaphase II? (1)
Chromosomes line up singly along the equatorial plane of the spindle. This differs from Metaphase I: homologous chromosomes do not lie next to each other
What happens during Anaphase II of meiosis?
1) centromeres divide and sister chromatids are separated, becoming daughter chromosomes
2) daughter chromosomes are pulled to opposite poles of the cell
What happens during telophase II of meiosis? (2)
1) spindle fibres disintegrate and disappear
2) nuclear envelopes form around 2 daughter chromosomes at each pole. Nucleolus also reforms.
What happens during cytokinesis II of meiosis?
Cleavage of cytoplasm results in four daughter cells being produced, each with a haploid number of chromosomes.
Why is meiosis important in sexual reproduction? (3)
1) it produces haploid gametes, which fuses together during fertillisation to form diploid cells (zygote)
2) it gives rise to genetic variation
3) increases chances of survival of species during changes in the environment
How does meiosis give rise to genetic variation?(3)
1) crossing over between homologous chromosomes at prophase I results in new combination of alleles
2) independent assortment of chromosomes: random arrangement of homologous pairs of chromosomes at the equator at metaphase I Ieads to random separation of homologous chromosomes at anaphase I, which produces different combinations of genetic material in gametes
3) since fertilisation is random, where any sperm fuses with any egg, such variations in gametes produce variations in the offspring.
How does variation increase chances of survival of species during changes in the environment?
When environmental conditions change, nature selects those with the most favourable characteristics to survive, while the others die, so that they can pass on favorable genes to their offspring, ensuring their species live on, and prevent the whole species to be wiped out if they had the same genes.
