Seconday 5 (MYE) - Essay (8)

8. (a) A trip to research institute MARDI is organised to study tissue culture techniques. Based on the short notes collected randomly from different officers at the institute, write a report of how tissue culture is carried out on a named plant with illustration.

Short notes:
· Growth hormones
· Callus
· Steriled culture media
· Subculture
· Explants
· Nursery [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]


(b) Knowledge on the concept of mitosis is applied to cloning of plants and animals in agriculture. What are the advantages and disadvantages of cloning to mankind? Support your answer using named examples. [6 marks]

· Advantages
· 1. Selection of quality & desired traits
· e.g. a disease resistance gene is extracted from tobacco and is then inserted into the cotton plant to be resistant against a particular pest
· 2. Large & fast production of desired traits
· e.g. a copy of the human insulin gene encoding for insulin synthesis is inserted into E. coli bacteria. The bacteria can now produce insulin for commercial use
· 3. Pollinating agents are not required (vegetative reproduction)
· e.g. reproduction with seeds takes a long time. Clones mature fast and produce seeds within a short time
· 4. Genetic manipulation can be carried out
· e.g. genetic engineering allows genetically modified bacteria to clean up oil spills in ocean / heavy metals in soil

· Disadvantages
· 1. No variation / Preventing natural selection
· e.g. clones are unable to adapt to drastic changes of the environment
· e.g. a new pathogen can wipe out the entire clones as they have the same level of resistance to the pathogen
· 2. Transfer of undesired genes
· e.g. clones might undergo mutation, and the mutated gene could be transferred to other plants by viruses
· e.g. herbicide-resistant gene is transferred from clones to weed, which makes them resistant to the herbicide applied (herbicide is no longer effective) – ‘super weed’
· 3. Short term or long term side effects
· unknown, could lead to development of bio-weapons
· 4. Playing God (ethical & religious issues)
· e.g. can vegetarians consume crops with insertion of bovine growth hormone gene?

(c) Contrast the division process that takes place in the apical meristem to that of the anther. [4 marks]

MITOSIS (Apical meristem)
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