Seconday 4 (MYE) - Essay (8)

8. (a) Diagram 13 shows the process of cell division in the apical meristem of the root of a plant. Explain the process of cell division that takes place and contrast with the one that occurs in the anther of the plant. [6 marks]

Diagram 13 - Root meristem

· Mitotic cell division takes place actively in the meristematic tissues of the root tip and shoot tip of plants [1]
· Active cell division in meristematic tissues allows growth and elongation of a plant to take place at a faster rate [1]








MITOSIS (Meristematic tissue)

Synapsis / Cross over: No
Number of divisions: 1
Number of daughter cells produced: 2
Number of chromosomes in daughter cells: Diploid (2n), same as the mother cell
Genetic contents in daughter cells: Identical to the mother cell
Genetic variation : No

MEIOSIS (Anther)

Synapsis / Cross over: Yes
Number of divisions: 2
Number of daughter cells produced: 4
Number of chromosomes in daughter cells: Haploid (n), half of the mother cell
Genetic contents in daughter cells: Different from the mother cell
Genetic variation : Yes

ANY FOUR

(b) A trip to research institute MARDI is organised to study tissue culture techniques. Write a report of how tissue culture is carried out on a named plant with illustration. [10 marks]












· All apparatus and materials used in this technique must be sterilized and autoclaved. [1]
· The surface of a tobacco leaf is sterilized with ethanol, then is cut into small pieces. [1]
· The small pieces of plant tissues are called explants. [1]
· The explants are then placed inside a test tube/Petri dish containing steriled nutrient agar medium with glucose, amino acids, vitamins, mineral salts, growth hormones, etc. [1]
· The cultures are incubated at 37C and agitated, if necessary. [1]
· After three to four weeks, the explants develop into callus (a group of undifferentiated cells). [1]
· The callus can now be propagated indefinitely by sub-culturing onto new nutrient media. [1]
· The callus is finally transferred onto a fresh agar medium containing different concentrations of auxin and cytokinin for root and shoot generation. [1]
· The rooted plantlets (clones) are then transferred to soil and kept in a controlled environment. [1]
· From one original plant, thousands of genetically identical clones can be produced. [1]

(c) Breast cancer makes up more than 10% of cancer cases reported in Sabah. It is the second most common cause of death among Malaysian women after heart disease. Approximately one out of 20 women in Malaysia will get breast cancer. Explain how cancer is due to uncontrolled mitosis. [4 marks]

· When a cell divides by mitosis repeatedly, without control and regulation, it can produce cancer cells. [1]
· This is due to severe disruption to the mechanism that controls cell cycle, which eventually causing the cells to divide freely and uncontrollably without heeding the cell cycle control system. [1]
· Cancer cells compete with the surrounding normal cells to obtain sufficient nutrients and energy for their own growth. [1]
· They can also intrude on and spread to other tissues which then lead to the malfunction of the tissues and ultimately death. [1]