Grade 12 Reproduction in Flowering plants Part 1 - Types of Reproduction

Question 1

Define reproduction:

Answer 1

• The ability of organisms to produce a new generation of themselves.
• NB for the survival and evolution of species because through reproduction, an individual passes on its genes to the next generation.

Question 2

Name the two natural types of reproduction:

Answer 2

1. **Asexual **- production of a new generation of the same species by one parent.
2. Sexual - production of a new generation of the same species by bringing together the genetic material of two parents.

Question 3

What is the similarity between asexual and sexual reproduction?

Answer 3

• Both processes product the same kind of organism in order to prevent their species from dying out and becoming extinct.
• Both processes result in food being produced which is vital to feed the world’s population.

Question 4

What is the difference between asexual and sexual reproduction with regards to:
number of parents

Answer 4

One (asexual) v Two with two genders (sexual)

Question 5

What is the difference between asexual and sexual reproduction with regards to:
Processes

Answer 5

• Asexual: One stage (i.e. mitosis with no fusion of cells, therefore quicker) v
• Sexual: Two stages (i.e. meiosis and fertilisation with fusion of two cells, therefore slower)

Question 6

What is the difference between asexual and sexual reproduction with regards to:
Gamete formation

Answer 6

*Asexual: No gametes formed
* Sexual: Gametes formed

Question 7

What is the difference between asexual and sexual reproduction with regards to:
End result

Answer 7

Asexual: Offspring are genetically identical to parent - no variation because alleles are not shuffled

Sexual: Offspring genetically different - there is variation because alleles shuffled during:

meiosis - when gametes are formed
fertilisation - when alleles are joined in new combinations

Question 8

What is the difference between asexual and sexual reproduction with regards to:
Value

Answer 8

Asexual: In unchanging stable environment - well adapted individuals are preserved, reproduction is possible where there are no or few mates
Sexual: In changing environment individuals with variations can adapt to new conditions

Question 9

What is the difference between asexual and sexual reproduction with regards to:
Rate of reproduction

Answer 9

Asexual: Faster - all individuals can reproduce
Sexual: Slower - half population are males who do not produce offspring

Question 10

What is the difference between asexual and sexual reproduction with regards to:
Energy input

Answer 10

Asexual: More efficient, no energy input needed
Sexual: Less efficient - energy input is needed to produce gametes, and fin and court a mate

Question 11

What is the difference between asexual and sexual reproduction with regards to:
Outside agents

Answer 11

Asexual: None needed
Sexual: Pollinators often necessary for pollination

Question 12

What is the difference between asexual and sexual reproduction with regards to:
Ability to adapt to the environment

Answer 12

Asexual: no
Sexual: Yes

Question 13

What is the difference between asexual and sexual reproduction with regards to:
Possibility of evolution

Answer 13

Asexual: Low - usually no genotype variation
Sexual: Good - genotype variation

Question 14

List 4 advantages of asexual reproduction:

Answer 14

1) All individuals can produce
2) Process is simple and fast
3) Very useful in unchanging / stable environments
4) Favourable mutation can spread rapidly enabling population to adapt quickly to new environmental conditions e.g. resistance to antibiotics and insecticides.

Question 15

Name the disadvantages of asexual reproduction:

Answer 15

1) No variation in the offspring (unless mutation) - problematic when environment changes and population unable to adapt to new conditions and could die out. Thus difficult to evolve.
2) Overcrowding may occur - resources such as food in short supply

Question 16

List 4 advantages of sexual reproduction:

Answer 16

Results in variation which:
1) is the basis of evolution
2) gives better chance of survival in unstable environment as offspring may adapt to new conditions
3) May prevent spread of disease - as offspring may be more genetically resistant
4) May reduce chance of inheriting a disease form parent.

Question 17

List 4 disadvantages of sexual reproduction?

Answer 17

1) High expenditure of energy - special organs of reproduction need to be produced e.g. flowers.
2) Slower reproduction process - takes time for games production and meeting of gametes.
3) Unfavourable mutations and recessive genes might be expressed in offspring.
4) Outside agents may be needed in plants to carry pollen or seeds.

Question 18

Explain how sexual reproduction takes place:

Answer 18

-Diploid parent produces gametes (sex cells) in the gonads (sex organs) by MEIOSIS
-Gametes are HAPLOID as they contain ONE set or HALF the number of chromosomes.
-Male and female gametes are brought together by pollination (plants) or mating (animals).
-The gamete nuclei then fuse - FERTILISATION
-The new cell - ZYGOTE - is diploid (2nd) as it has two sets of chromosomes.
-The zygote grows by MITOTIC CELL DIVISION into new individual.

Question 19

Discuss gametes:

Answer 19

Female gamete is quite large
NOT motile

Male gamete is small
Motile in animals

In many plants male gamete is just a nucleus in a pollen grain while the female gamete is an egg cell (Ovum) in an embryo sac.

Question 20

What is angiosperm reproduction?

Answer 20

Plants with FLOWERS which produce their OVULES ENCLOSED IN AN OVARY.
Not naked in a cone scale, as in GYMNOSPERMS (e.g. pines)
Angiosperms grows in nearly every habitat (except ocean - where algae is found) - Unlike mosses and ferns which grows in damp habitat

Question 21

Explain what a flower is:

Answer 21

-An organ of sexual reproduction.
-Contains reproductive organs - often will attract pollinators.
-Many flowers make both male and female gametes - Hermaphrodite / bisexual.
-Male gamates - found inside the pollen grains produced by ANTHERS
-Female gamates - found inside the OVULES which are found enclosed by OVARY.

Question 22

Discuss how asexual / sexual reproduction historically lead to improved food crops:

Answer 22

• 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.

Question 23

How did asexual reproduction improve crops?

Answer 23

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

Question 24

In a nutshell, what is the benefit of asexual reproduction in the mass production of food?

Answer 24

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.

Question 25

How did sexual reproduction improve crops?

Answer 25

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!)

Question 26

In a nutshell, what is the benefit of sexual reproduction in mass production of food crops?

Answer 26

-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.

Question 27

How can sexual reproduction be used to produce new and improved varieties of food crops?

Answer 27

• Hybridsation of crops - hybrid crops are crops that are produced by cross-pollinating two inbred plants of dissimilar genotypes.
• Seeds from this cross-pollinated plant are hybrid seeds and thus produce a hybrid crop.
• The crossing results in genetic variation thus hybrid crop could exhibit new traits some of which could be desirable forming an improved crop or new variety.
• Hybrid plants are NOT GMO Modified.