chapter 16: cell division Flashcards
how does growth take place in plants and animals?
in plants:
- growth is restricted to the tips of shoots and roots
> known as growing points
> the shoot and root tips can continue to grow throughout the life of the plant
in animals:
- growth occurs throughout the body
- for multicellular organisms to grow normally
> cells must divide
- cell division that takes place during growth is called mitosis
what is mitosis?
- it is a form of nuclear division that produces daughter nuclei containing the same number of chromosomes as the parent nucleus
> the daughter nuclei are genetically identical
what are chromosomes made of?
- chromosomes are made of deoxyribonucleic acid (DNA)
> DNA stores all the information that a cell needs in order to grow and to carry out vital activities
> this information is stored as sections of DNA or genes - the daughter cells produced by mitosis are genetically identical to the parent cell
why is it important to produce genetically identical daughter cells?
- DNA replication copies all the information stored within the chromosomes
> this ensures that daughter cells produced by mitosis contain all the sections of DNA (genes) needed for subsequent cell division and differentiation
> resulting daughter cells are genetically identical - a zygote (cell) divides to form an embryo
> the cells formed as the zygote divides must be genetically identical for the embryo to develop normally - if an error occurs during DNA replication or mitosis
> it will be transmitted tot he daughter cells which may lead to harmful changes to the genes and affect how the cells function
> embryo may not develop normally - changes in the genes during DNA replication can also cause abnormal proteins to be produced
- cells (containing abnormal proteins) may be rejected or destroyed by the body’s immune system
- in adults, mistakes made in DNA replication/ mitosis can result in an uncontrolled division of cells (cancer)
> cancer can be fatal
> as cells lose the ability to control the way they divide and cannot perform their normal functions
what are the three stages of the cell cycle?
- interphase or ‘resting stage’
- mitosis, nuclear division
- cell division, which is division of the cytoplasm, cytokinesis
what happens during interphase?
- called ‘resting stage’ but cells do not actually rest
- they carry out activities such as absorbing nutrients and building up protoplasm
- at interphase, chromosomes appear as long thin threads called chromatin
> chromatin threads cannot be distinguished individually - during interphase, centrioles divide in an animal cell
- just before the cells divide, each chromatin thread (contains 1 DNA molecule) REPLICATES
> producing two IDENTICAL chromatin threads ( two identical DNA molecule)
> joined at a point called the CENTROMERE - the two chromatids attached to the same centromere are called sister chromatids
what are the four stages of mitosis?
prophase, metaphase, anaphase and telophase
what happens during prophase?
(stages of mitosis)
-chromatin threads condense, coil and shorten to become chromosomes
> each chromosomes consists of two sister chromatids attached to the centromere
> chromosomes now visible under the microscope as x-shaped structures
- in an animal cell, ASTERS form around the centrioles
> ASTERS are made of MICROTUBULES - the two pairs of centrioles move to opposite poles of the cell
- the nucleolus and nuclear envelope disappear
- a spindle forms with the spindle fibres extending from one pole of the cell to the other
what happens during metaphase?
(stages of mitosis)
- chromosomes line up along the equatorial plane of the spindle
- the centromere of each chromosome is attached on both sides to a spindle fibre
what happens during anaphase?
(stages of mitosis)
- each centromere divides
- the spindle fibres shorten and pull the chromatids apart to opposite poles of the cell
> once the chromatids are separated, they are called daughter chromosomes
what happens during telophase?
(stages of mitosis)
- spindle fibres break down
- a nuclear envelope forms around the chromosomes at each pole of the cell
- a nucleolus reforms in each nucleus and the chromosomes uncoil and lengthen to become thin chromatin threads
what happens during cytokinesis?
- the division of the cytoplasm
- in animal cells, FURROWS appear in the cytoplasm between the two nuclei
- furrows deepen and two identical daughter cells are finally produced
what happens during mitosis in plant cells?
it is similar to animal cell except that:
- centrioles are absent in a plant cell
- cleavage of the cytoplasm does not occur during cytokinesis
> instead, a cell plate is formed between the two daughter nuclei, dividing the cell into two
> the cell plate is formed by the fusion of small fluid-filled vesicles by the Golgi apparatus
why is mitosis important?
- it enables the growth of an organism
> for multicellular organisms to grow, new cells must be produced by mitosis - it is needed for the repair of worn-out parts of the body
- it allows asexual reproduction to occur
what are some examples of mitosis being needed for the repair of worn out parts of the body?
- each time you bruh your teeth, hundreds of dead and worn-out cheek cells are being shed into your saliva
> mitosis constantly replaces dead cells - mitosis helps heal wounds
> if you cut, skin produces new cells to help seal the cut - cells in malpighian layer of the skin divide constantly by mitosis
> replace worn out cells from upper layers of the skin
