Grade 12 Reproduction in Flowering plants Part 3 - Seed, Fruit and Crops Flashcards
Explain in detail how a seed is formed:
**After fertilisation. **
1) ZYGOTE divides numerous times by MITOSIS and develops into an embryo consisting of:
-cotyledon or seed leaves - take food from parent plant for storage
-radical (embryonic root)
-Plumule (embryonic shoot)
2) The **rest of ovule develops into ENDOSPERM TISSUE **- stored food e.g. starch, protein, oil
3) The outer covering of the ovule thickens and hardens, forming the seed coat or TESTA. Why? saves the seed from damage and prevents entry of bacteria and fungi
Explain how a FRUIT is formed:
- While seed is being formed, the ovary is also growing.
- This is called FRUIT
- Happens in different ways in different plants
What are the functions of fruit?
1) They contain and protect the seeds.
2) Fruits help to disperse the seeds from the parent plant.
Discuss how asexual / sexual reproduction historically lead to improved food crops:
- 7000 / 75 000 species of edible plants used for food by humans
- Humans have domesticated wild plants for their use for last 9000 - 11000 years
- Domestication lead to = great phenotypical changes (and altered genotypes) resulting in improved food crops, and NEW varieties developing.
- Today all principal food crops come from domesticated varieties.
- Most domestication involve cereals - wheat, maize, rice etc.
- Wild plants - grow in nature without aid of humans. Very few used as food source.
- Domestication involves skilful breeding - using variation that existed in plant species and also arose in sexual reproduction, to asexually or sexually improve food crops.
How did asexual reproduction improve crops?
Techniques include **division, grafting, using storage organs (bulbs, corms, tubers, rhizomes) and cutting:
**
Basic feature of asexual reproduction = genetic stability with no variation, in offspring a MUTATION could have produced a plant with a new superior trait.
E.g. a crop plant could have produced a bigger seed, fruit or tubers
If these plants were reproduced by asexual means, more plants with superior trait could have been grown
Repeated selection and eliminaiton = food crop would in time consist entirely of plants with superior trait
Crop improvement
Grafting: Tissues from one plant are inserted into those of another so that the two sets join together
One plant selected for its roots - the rootstock (good traits e.g. pest resistant, ability to grow in difficult soil conditions)
PLUS other plant selected for SUPERIOR FRUITS - (larger / improved yield) - the SCION
Thus Rootstock + SCION = Mature plant would be more productive
Used for thousands of years already in apples, pears and still today e.g. grapes, avocado pears
In a nutshell, what is the benefit of asexual reproduction in the mass production of food?
1) The product is always PREDICTABLE - identical to the parent plant and contains the desired genes e.g. large quantities of nutritious maize
2) Once plants are genetically engineered and coded to develop into the desired food product, asexual reproduction ensures that many IDENTICAL plants can be produced form the one parent plant and cultivated.
3) RAPID, COST EFFECTIVE production of thousands of copies of nutritious crop plants may form part of the solution to food crises in various parts of the world. (Food security)
4) Micro-propagation (tissue culture) numerous identical plants (clones) are produced.
5) Grafting - Fruit trees will grow more quickly to maturity and thus fruit production e.g. avocado pears.
Why is micro-propagation (tissue culture) favoured over traditional crop breeding methods? (4)
1) Commercially imported crop plants can be mass propagated in a short period of time e.g. bananas, pineapples, potatoes, date, oil palms, papaya
2) Disease free plants can be produced - selecting disease free cells and cutting in sterile conditions
3) Propagation can take place all year
4) May be used together with genetic engineering to propagate transgenic plants form genetically modified cells
Define tissue culture:
A process whereby a small amount of plant tissue is cultured in a growing medium to produce a callus (a shapeless clump of cells) and then plantlets
How did sexual reproduction improve crops?
Breeders made use of beneficial traits that offspring sometimes had to improve food crops e.g. larger yield, larger seed, tuber and fruit size, pest resistance, ability to grow in poorer soils.
* Breeders selected plants and planted seed from the superior plants, while eliminating seed from plants with less desirable traits.
* With repeated selection an improved crop resulted.
**Examples: **
* Cross-pollination of individuals of a species = mildew-resistant pea crossed with a high-yielding but mildew-susceptible pea.
* Plants produced - cultivars.
Self-pollination:
* A crop plant may show a new trait e.g. larger maize cob with more pips. Plants grown from this plants seed were self-pollinated, so that next generation plants would have produced seed with this new trait. Repeated breeding led to maize with larger cobs. (See example in textbook!)
In a nutshell, what is the benefit of sexual reproduction in mass production of food crops?
-Led to **improved food crops **through centuries as farmers deliberately crossed plants with desired characteristics to breed crops with an ideal combination of characteristics.
-Also introduces the opportunity of breeding out undesirable or weak traits to cultivate HIGH quality crops.
-**Polyploidy **=
* Caused by abnormal cell division in sexually reproduction resulting in multiple sets of chromosomes. Instead of two sets of chromosomes (2n), there may be 3 (3n) or 4 sets (4n). the extra sets of chromosomes may result in larger fruit, more ears in corn, larger stores of food etc.
* Useful to provide large quantities of food in short time.
How does genetic engineering benefit crop production?
- GMO plants means the production of a new variety with a desired trait is achieved in much shorter time compared to traditional breeding
- No real interspecies barriers - all organisms use the same genetic code so genes from bacteria, for example, will produce the correct protein in maize plant.
- Proteins produced by transgenes are identical to those produced in original species, as genetic code is universal.
- BUT signals needed to express these genes are plant-specific are not universal.
- Some modification must be made to the signal that control gene expression, since these are more species specific.
Define genetic engineering:
- The process of taking a gene out of one organism and put it into the DNA of another organism. The resulting plants are known as genetically modified organisms (GMO’s, GM Crops or BIOTECH crops).
- The transplanted gene is a TRANSGENE
Discuss a few examples of GMOs - See textbook page 66
Bt Maize - Soil bacterium produces a protein that kills many insect pests, especially the maize ear worm. Most USA maize crops.
Roundup Ready soybeans - herbicide (chemical that kills weeds / herbs) called glyphosate. A bacterial gene that confers resistance to herbicide has been transplanted to many crops. Farmer can spray fields with glyphosate and kill weeds without harming crops
What are GMO crops mostly grown as?
- Soy, maize, rape seed (canola)
- USA, Canada, Brazil, Argentina, India, China
- Not more risk to humans than conventional crops
What traits are biotechnologist trying to incorporate into food crop plants?
1)Resistance against certain diseases and herbicides e.g. disease resistant rice grown in China and virus resistant sweet potato in Kenya
2) Increased tolerance to insect pests e.g. GM white maize in SA resistant to stalk borer. 60% Yield increase.
3) Nutrient-content enrichment e.g. golden rice enriched with beta-carotene, precursor of vitamine A.
4) Increased tolerance to environmental pressure e.g. DroughtGard maize - drought resistant maize crops planted in USA
5) Flood tolerance e.g. Swarna-Subi planted in by nearly four million famers in Asia (25% yield increase)
6) Longer storage life of harvested crops e.g. strawberries to extend shelf life.
