Module 6 Cloning and Biotechnology

Question 1

Natural clones in plants

Answer 1

• Plants reproduce asexually at meristems in a process called vegetative propagation in roots/shoots and the vascular cambium. Miniature plants form at these locations which can detach and live independently and are clones of the parent plant, with the same phenotype.
• Horizontal runners ensure there is no competition between the parent plant and the clone. Roots from these runners are called adventitious roots. The runner will die once the daughter plant can survive on its own. Strawberry plants grow runners.
• Propagation does not require seeds as this is asexual reproduction. Modified stems generate meristematic tissue. Tubers from potatoes, rhizomes from ginger, bulbs from onions, suckers from roots of cherry trees and off sets of tulips are all examples.
• In horticulture desired characteristics can be propagated asexually at lower cost.
• Cuttings are taken by cutting a small length of plant stem. The base of the cutting in dipped in rooting powder containing the hormone auxin. When the new roots grow, the cutting is placed in the soil and allowed to grow.

Question 2

Artificial clones – plants

Answer 2

• Vegetative propagation is the basis of artificial cloning. Cultivars are the genetically identical plants produced.
• Micropropagation and tissue culture involve the use of a plant with actively dividing cells.
• A small section of the plant known as an explant is used. All surfaces are disinfected, and aseptic techniques are used to avoid contamination of fungi. The explant is soaked in sterilising solution and then placed on an agar growth medium for 3 weeks, resulting in the growth of a complete clone.
• Advantages – all plants have the same genotype and so phenotype, immunity can be increased, a large yield is produced, can recover endangered species.
• Disadvantages – the process is expensive, results in no genetic variation and can lead to microbial contamination.

Question 3

Natural clones – animals

Answer 3

• Asexual reproduction can sometimes result in parthenogenesis.
• Identical twins are much more common. A sperm cell will fuse with an egg cell to form a zygote. This zygote will divide to form an embryo, which will then split to form two embryos. Therefore identical twins are referred to as monozygotic and also why the embryos are identical, so the twins are clones.

Question 4

Artificial clones – animals

Answer 4

• Embryo twinning is a routine procedure involving the deliberate division of an embryo, which is then inserted into a surrogate mother. The offspring are identical twins and clones of each other, but not of their parents.
• Reproductive cloning, as seen with Dolly the Sheep, involves somatic cell nuclear transfer. 3 animals are involved – the one to be cloned, the one donating the egg cell and the surrogate mother. The animal to be cloned donates a somatic cell. An egg cell is extracted and enucleated. The nucleus of the somatic cell is injected into the enucleated cell. The cell is then injected into the surrogate mother for gestation.
• Therapeutic cloning replaces dead/damaged cells. Embryos are cloned and totipotent stem cells replace specialized cells.
• Uses- embryo twinning is non- controversial. It can maximise agricultural output, remove undesirable characteristics and preserve endangered species. SCNT is controversial. It is unreliable, may have unknown long-term risks and produce animals that are abnormally large. Therapeutic cloning involves the destruction of embryos and may prevent normal mechanisms.

Question 5

Uses of microorganisms

Answer 5

• The advantages of using microorganisms include that they have simple growth requirements, needing little space and food that is cheap and readily available. Microorganisms also have short life cycles, reproduce quickly and can be grown on an industrial scale.
• Processes using microorganisms include yeast being used for brewing and baking. Producing ethanol and a product for whiskey through anaerobic respiration and air bubbles of CO2 from aerobic and anaerobic respiration for rising bread. In the making of cheese and yoghurt bacteria in milk breaks down lactose into lactic acid, which lowers the pH and causes the milk to coagulate and form curds and whey. Penicillin can be produced from cultured mould in deep tank fertilisation and bacteria can produce human insulin through recombinant DNA technology.
• Bioremediation remediates land to remove pollutants through oxidative digestion. Aerobic digestion by microorganisms adds nutrients.

Question 6

Culturing microorganisms

Answer 6

• Aseptic techniques are used to stop microbes escaping and becoming contaminated. These include washing hands, having no food or drink in the lab, disinfecting surfaces, wearing gloves and goggles, working near a lit Bunsen burner to provide a convection current, sterilising using an autoclave.
• Process of culturing – pour hot sterilised agar onto a petri dish. Sterilise an inoculating loop. Flame the lip of the culture tube. Take a sample of culture using the inoculating loop. Flame the neck of the tube again. Wipe the loop on the agar then sterilise the loop. Tape the lid of dish and sterilise at 25 degrees for 24 hours. This prevents harmful pathogens from growing.
• Batch fermentation is when microorganisms are grown in batches in a closed culture. Between each cycle the product is removed, and the fermenter is cleaned.
• Continuous fermentation is when microorganisms are continually grown, and the products harvested. Waste is removed and nutrients are added.
• Conditions that are controlled include ensuring optimum pH and temperature, sufficient oxygen through supply of sterile air to maximise respiration, nutrients continuously added, paddles to ensure even distribution, contamination is prevented through steam cleaning and waste removal prevents toxic effects.

Question 7

Microorganisms and food consumption

Answer 7

• As the human population increases, microorganisms are a more productive form of food production.
• The advantages are that microorganisms are more efficient at converting energy to biomass than animals. They reproduce faster and can be grown on substrates that are waste products of other reactions. The input is cheap, and fermenters can be set up anywhere. The products are low fat and high protein.
• The disadvantages are that consumers may not want to buy products produced by microorganisms. It can lead to contamination and sterile technique is expensive. Microorganisms reproduce quickly and so can lead to a fast rise in mutations. Processing is required to lower the levels of nucleic acids. Food produced has little flavour or texture. Bacteria can become infected by viruses.

Question 8

Growth of microorganisms

Answer 8

• Populations of microorganisms can be measured using direct counting of individuals, viable counting of colonies or turbidity. Turbidity measures the absorbance using a colorimeter. As the suspension become more turbid, the absorbance can be measured at regular time intervals.
• The lag phase involves slow increase of population as the population adjusts to the new environment.
• Due to a high availability of nutrients the population increases exponentially during the log phase.
• When the population reaches the stationary phase, the rate of reproduction is equal to the death rate as population is limited by available resources.
• When the population reaches the decline phase, a lack of nutrients and build-up of toxic waste causes a decline in population as the death rate is greater than the rate of reproduction.
• Binary fission is when a bacteria cell replicates its DNA and then splits into two daughter cells. The final number of bacteria cells can be calculated using N=N0 x 2^n. N = final number of bacteria cells. N0 = initial number of bacteria cells. n = number of divisions.
• Logarithmic scales can be used to represent the large number of bacteria cells.
• Factors effecting growth of microorganisms – temperature, pH, nutrient availability. Use serial dilutions to decrease no. of bacteria cells and investigate effects.