Environmental Studies
FACT SHEET
www.curriculum-press.co.uk
Number 178
Do we still need vegetative propogation?
This Factsheet:
• Outlines the process of vegetative reproduction in potatoes
• Describes the advantages of vegetative reproduction
• Discusses the possible advantages and problems of GM potatoes
• Reviews recent exam questions on this topic
Vegetative reproduction is asexual reproduction i.e. it doesn’t involve fertilisation.
Most plants can carry out some form of vegetative reproduction and a few plants only use this technique.
Humans exploit vegetative reproduction in two main ways:
• By taking cuttings to grow e.g. houseplants, potatoes, bananas and oranges
• By taking cells or tissues from a plant and using them to grow genetically identical clones of the old plant
Advantages of vegetative reproduction
The plants that are produced are genetically identical to the parent and each other so useful characteristics e.g. size, shape, taste, disease resistance
are all the same.
The new, young plant gets its food from part of the parent plant so isn’t as reliant on nutrients in the soil. As a result, survival rates are high.
Case Study: Potatoes
The potato Solanum tuberosum originates from the Andes mountains in
South America, is the most important ‘root crop’ grown in the world and is
well adapted for survival in a cool climate like the UK.
Despite this, it is estimated that 30% of the worldwide potato crop is lost
each year to disease:
Fungi such as as late blight (Phytophthora infestans), attack the foliage;
fungal and bacterial diseases cause wilting and early death of plants; Many
viruses attack systemically i.e. travel through the xylem and phloem of the
plant
Source: USDA
For these reasons genetic engineers have been trying to develop genetically modified varieties for decades. There have been success stories
but in Europe many environmentalists remain strongly opposed to any GM trials, including those using GM potatoes.
Why are potatoes so important?
After wheat and rice, they are the 3rd most widely grown species on Earth
They are high in complex carbohydrates, fibre, protein, vitamins and minerals and contain virtually no fat
The tuber-bearing genus Solanum is a huge genetic resource – there are 230 wild and primitive species within
the genus so finding genes that control useful characteristics is relatively easy
Vegetative reproduction of potatoes
Although potatoes can reproduce sexually using seeds, humans grow them vegetatively i.e. asexually.
Potatoes are propagated vegetatively using small “seed” potatoes that possess at least one axillary bud. This bud will grow into a new potato
plant using the energy contained in the seed poato. Follow the numbers around Fig.1 (p2).
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Environmental Studies
Factsheet 178 - Do we still need vegetative propagation?
Fig. 1 Vegetative propagation of potatoes
Seed potato planted in soil
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Aerial parts die in first autumn frost and
gardener digs their potatoes up
One potato has turned into 8!
2
8
Bud develops into shoot that emerges from soil
Aerial parts photosynthesise i.e.
turn CO2 from the air and water
from the soil and potato into new
tissue
3
4
7
5
Gardener piles soil against
the newly emerged stem
(“earthing up”)
Tuber shrinks as the new
plant digests its starch store
for energy to grow
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New tubers (potatoes) develop using energy
from photosynthesis of aerial parts
Normally, each “seed” potato will have several buds, each of which
may develop into a new plant, so productivity is high.
Genetically engineered potatoes
So, if vegetative reproduction is so great, why would we want
genetically engineered potatoes?
Typical Exam Question
(a) Potatoes are usually propagated vegetatively.
What are the advantages of this approach? (3)
(b) The diagram shows the energy ratio for a variety of crops.
Because we can cut genes that control desired characteristics out of
other plants and insert them into potatoes which then have the new,
desired characteristic. Such characteristics include:
• Improved protein content – important for populations suffering
protein deficiency
• Herbicide resistance – so that weeds that reduce yields can be killed
without harming the potatoes
• Increased resistance to disease – which reduce yield or kill the
potatoes and might mean we could grow potatoes with less
pesticide use
• Increased tolerance of salt water – important in areas that are likely
to be flooded by seawater
• Increased drought tolerance – allowing potatoes to be grown where
they otherwise couldn’t be grown
• Genes that control the production of vaccines could be inserted into
potatoes thus resulting in edible vaccines – much more attractive
than needles!
• A gene that produces a specific type of starch now can be used to
make paper pulp, glue or animal feed – this GM potato has just
been banned from sale in the EU
These “improved” potatoes could then be reproduced by vegetative
propagation.
The energy ratio is given by:
energy output
energy input
Suggest a reason for the energy ratio for potatoes (1)
100
60 tropical crops - subsistence
10.0
5.0 tropical crops
4.20 sugar beet UK
1.0
1.75 potatoes UK
0.90 peas UK
0.38 milk production UK
0.1
0.14 battery eggs UK
The desired genes are cut out of the plants using enzymes and then a
harmless virus is used to carry the desired gene into the potato.
0.04 fishing fleet UK
Potatoes, as with all of our other staple crops have been improved
over centuries by artificial selection – crossing plants with useful
characteristics in the hope that they will be combined in the offspring
– but GM is faster and more accurate.
0.01
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Environmental Studies
Factsheet 178 - Do we still need vegetative propagation?
Possible dangers of GM potatoes
Many environmentalists are concerned that genes inserted into potatoes may mutate resulting in unforeseen problems. There is also the
possibility that these foreign genes might “jump” across other species, again with unforeseen consequences. For example, some are worried
that a potato that has had a gene inserted that offers resistance to a particular disease may cross with a weed species – making the weed species
disease resistant and reducing crop yields.
Others are worried that introducing foreign genes – from other plant species or even animals or microorganisms – could lead to an increase in
their allerginicity – their potential to cause allergic reactions.
Scientists are carrying out trials across the world, including in the UK, to test whether these problems are real but campaigners have threatened
to destroy the trial crops.
Activity
Using the info above and your own research, draw a spider diagram showing all the possible advantages and possible dangers of growing
GM potatoes.
Sources of info:
Supporting GM – www.monsanto.com
Against GM – www.greenpeace.org
There are loads more!
Mark scheme for Typical Exam Questions
(a)Growing from seeds would produce more variation/ All potatoes are genetically identical / possess same useful characteristics as the
parent;
No sexual reproduction involved/no meiosis so only one parent needed;
Ref to mitosis;
Large numbers can be produced quickly;
Asexual reproduction enables organisms to survive harsh conditions e.g. as spores or bulbs that can survive dormant in soil;
(b)Energy obtained from “seed” potato/tuber as well as photosynthesis/ energy efficient variety chosen as “seed”;
Practice Questions
Potato plants originate from the Andes mountains in South America. They are adapted for survival in a cool climate.
The potatoes we eat are food storage organs, called tubers, and are produced on underground stems.
The graph shows the rates of photosynthesis and respiration of one common variety of potato plant.
photosynthesis
Rate
respiration
0
5
10
15
20
25
30
Temperature/ oC
Mark scheme
(a) 7/8– 24°C;
(b)Photosynthesis rate only just above/ equal to respiration rate;
So little gain in biomass / net loss of biomass;
Ref to energy being lost at night (via) respiration;
Due to (night-time) respiration;
No excess production for storage in tubers;
(a) Between which temperatures is there a net gain of energy by the
potato plant? (1)
(b) When this variety was grown in a region with a mean daytime
temperature of 24.0 °C, it failed to produce tubers. Suggest why (2)
Acknowledgments: This Factsheet was researched and written by Kevin Byrne.
Curriculum Press, Bank House, 105 King Street, Wellington, Shropshire, TF1 1NU
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