8/17/2019 CHAPTER 5 FORM 4 TISSUE CULTURE & CANCER.docx

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CHAPTER 5 : CELL DIVISION

Tissue Culture Technique

A small piece of a plant’s leaf, shoot, bud, stem or root tissues are

cut out. These cut out plants tissues are called explants. Alternatively,enzymes are used to digest the cell walls of tissues, for example, the

mesophyll tissue from a leaf. This result in naked cells without cell walls

called protoplasts. The explants or protoplasts are sterilised and then

placed in a glass container which contains a nutrient solution with a xed

chemical composition. A culture medium or growth medium normally

consists of a complex mixture of glucose, amino acids, minerals, and other

substances reuired for the growth of the tissues. The culture medium and

the apparatus used must be in a sterile condition and free from

microorganisms which can contaminate the tissue culture. The p! and thetemperature of the culture medium also need to be maintained at

optimum levels.

 The explants or protoplasts begin to divide by mitosis. "ell division

produces aggregates of cells. The aggregates of cells develop into a

callus, an undi#erentiated mass of tissue. The callus develops into a

somatic embryo. The embryo develops into a plantlet which can later be

transferred to the soil for growth into an adult plant. All the plantlets

produced this way are genetically identical. Therefore, all the adult plants

that develop from them share the same traits.

Cancer

$hen a cell divides by mitosis repeatedly without control and

regulation, it can produce cancer cells. "ancer is a disease caused by

uncontrolled mitosis due to severe disruption to the mechanism that

controls the cycle. "ancer cells divide freely and uncontrollably without

heeding the cell cycle control system. "ancer cells compete with thesurrounding normal cells to obtain su%cient nutrients and energy for their

own growth. A cancer cell that is not destroyed will divide uncontrollably

to form a tumour, an abnormal mass of cells. "ancer cells can intrude on

and spread to other tissues which then lead to the malfunction of the

tissues and ultimately death.

"ancer can be caused by many factors such as damage to the &'A,

changes in genes (mutation) that control cell division, ionising radiation,

for example, *+rays, ultraviolet rays and gamma rays, certain chemical

compounds like tar in tobacco smoke or carcinogenic (cancer+causing)compounds such as formaldehyde.

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