Unformatted text preview: e; still part of the same chromosome
as an extra chromatid.
B. Late prophase: Chromosomes condense (coil
and fold up) into visible form. Centrioles move to
opposite ends of the cell.
C. Metaphase: Spindle fibers form between the
centrioles. Chromosomes attach to the spindle
fibers at the cell ‘equator’.
D. Late anaphase: Chromatids from each
chromosome are pulled apart and move in
opposite directions, towards the centrioles.
E. Telophase: Chromosomes begin to unwind again.
Two new nuclei form. A cleavage furrow forms
across the midline of the parent cell, pinching it in
F. Cytokinesis: Cell cytoplasm divides to create two
distinct ‘daughter cells’ from the original cell. It is
in this form for most of its existence, and carries
out its designated role (normal function). Cancer: Cells out of Control (page 31)
1. 2. 3. Cancerous cells have lost control of the genetic
mechanisms regulating the cell cycle so that the cells
become immortal. They also lose their specialized
functions and are unable to perform their roles.
The cell cycle is normally controlled by two types of
gene: proto-oncogenes, which start cell division and
are required for normal cell development, and tumorsuppressor genes, which switch cell division off.
Tumor suppressor genes will also halt cell division if
the DNA is damaged and, if it cannot be repaired, will
bring about a programmed cell suicide (apoptosis).
Normal controls over the cell cycle can be lost if either
the proto-oncogenes or the tumor suppressor genes Tissues and Organs (page 33)
1. (a) Diffusion.
(b) Phagocytosis. 2. (a)
(d) 3. (a) Muscle tissue: Dense tissue comprising highly
specialized contractile cells called fibers held
together by connective tissues.
(b) Nervous tissue: Tissue comprising densely
packed nerve cells specialized for transmitting
electro-chemical impulses. Nerve cells may be
associated with supportive cells (e.g. Schwann
cells), connective tissue, and blood vessels.
(c) Connective tissues: Supporting tissue of...
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- Winter '13