Download Patterns In Nature Part 5 Maintenance of organisms requires growth

Patterns In Nature
Part 5
Maintenance of organisms requires growth and repair
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
identify mitosis as a process of nuclear division and explain its role
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Mitosis is the process by which a multicellular organism grows, repairs, maintains
and reproduces itself.
It is a type of cell division that results in the production of cells which are identical
to the original cell.
Mitosis itself is a process of division of the nucleus, and cytokinesis is the
division of the cytoplasm.
Young multicellular organisms grow rapidly due to mitosis, which increases the number
of cells.
Mitosis continues in adult organisms in certain areas. It provides a ‘repair and
maintenance’ service to old and damaged body cells.
 identify the sites of mitosis in plants, insects and mammals
Plants
- In mature plants, mitosis occurs in the tips of roots and stems, causing an increase in
length.
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Mitosis in special cells in the stem, (cambium), results in an increase in its width.
Plants continue to grow throughout their life from cells capable of mitosis known as
meristematic cells.
Primary growth occurs from apical meristems.
An apical meristem is the growing point where mitosis occurs at the tips of roots
and stems
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Insects
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Most insects have immature forms known as larvae. When larvae hatch from the
egg, they grow and increase in size, but this is a result of cell enlargement, not cell
division. Mitosis occurs when the insects changes (metamorphosis) from larvae
into adult. The stage is called the pupal stage.
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In pupal form, the larval cells break down, and adult cells (called imaginal
discs) undergo mitosis to create a massive transformation from larvae to adult.
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They grow in both size and number to form the adult insect or imago.
Mammals
- In young mammals, mitosis rates are high and growth is rapid in all areas of the body.
At maturity growth ceases but the repair and maintenance of cells continues.
- In adult mammals, mitosis occurs in the skin, replacing the cells that continually flake
off, and causing hair/fur and nails/claws to grow.
- New blood cells are made every day in the bone marrow.
- Cells lining the digestive system are constantly being replaced.

explain the need for cytokinesis in cell division
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Division of the cytoplasm usually occurs immediately after mitosis. This is
necessary to ensure that the chromosome number in each cell remains constant.
The chromosome number doubles in mitosis and one cell now contains two sets of
chromosomes.
Division of the cytoplasm (cytokinesis) results in two cells, each with a set of
chromosomes.
In animal cells, the cytoplasm constricts at the centre in a process called cleavage. A
ring of microfilaments forms in the centre of the cell. As they constrict, the cell
begins to ‘pinch’ or cleave into two. The cell surfaces show very active movement
or ‘bubbling’ as they separate.
In plant cells a dividing plate (the cell plate) forms across the centre of the cell,
separating the two new cells, called daughter cells. A new cell wall is built from this
plate.
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
identify that nuclei, mitochondria and chloroplasts contain DNA
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Nuclei contain DNA in the form of chromosomes
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These contain genetic information that determines heredity
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It also has information in producing proteins, which in turn determines our
characteristics
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Mitochondria have a set of DNA of their own
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It is a ring of DNA, like in a procaryotic cell.
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Chloroplasts also have a circular ring of DNA in their own structure
perform a first-hand investigation using a microscope to gather information from prepared
slides to describe the sequence of changes in the nucleus of plant or animal cells
undergoing mitosis
The stages of mitosis
- Prophase: Each chromosome is visible as two identical, joined strands, called
chromatids. The nuclear membrane breaks down and disappears by late prophase.
- Metaphase: A tapered system of microtubules stretches across the cell, forming a
spindle. The chromosomes line up at the centre of the cell, attached to the spindle
fibres at the point known as the centromere. The chromatids separate. (Note: in
animal cells, the centriole is involved in spindle formation. Centrioles are absent
in plants, the spindle attaches to the plant cell wall.)
- Anaphase: The chromatids, now referred to as single-stranded chromosomes, move
towards opposite poles, carried on the spindle fibres.
- Telophase: The spindle disappears. New nuclear membranes form around the two
sets of chromosomes.
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