Pollination and Fertilisation (5)

Question 1

What is pollination?

Answer 1

Pollination is the transfer of pollen from an anther to a stigma, thereby enabling fertilisation and reproduction.

Question 2

What happens when the anther is mature?

Answer 2

When the anther is mature it splits open and discharges the pollen. The pollen is then carried to the stigma by various natural means, the most common being wind and insects.

Question 3

In plant breeding, pollination is carefully controlled by ____.

Answer 3

humans

Question 4

What are the two kinds of pollination?

Answer 4

There are two kinds of pollen transfer – cross-pollination and self- pollination.

Question 5

What is cross-pollination?

Answer 5

In cross-pollination the pollen is transferred from the anther of a flower of one plant to the stigma of a flower of another plant, of the same species. This type of pollination will result in genetic variation in the offspring.

Question 6

what is self-pollination?

Answer 6

In self-pollination the pollen is transferred from the anther to the stigma of the same flower or to another flower on the same plant. This type of pollination will not result in genetic variation in the offspring.

Question 7

How can self-pollination be prevented in nature? (3)

Answer 7

− In bisexual flowers the anthers and stigmas ripen at different times. Most commonly the anthers ripen first. −Flowers are unisexual, they therefore cannot pollinate themselves.
− The stigma is positioned above the anthers.

Question 8

How can self-pollination be prevented by plant breeders?

Answer 8

Plant breeders will remove anthers to prevent self-pollination.

Question 9

What is fertilisation?

Answer 9

Fertilisation is the joining of two haploid cells, the male gamete and female gamete, to form a diploid zygote. The zygote develops by mitosis into the adult plant.

Question 10

When does fertilisation take place in flowering plants?

Answer 10

After pollination. After the pollen grain lands on the stigma it develops a pollen tube which grows along the style and into the ovule. The pollen tube carries the male gamete. Once the gamete enters the ovule fertilisation can occur. After fertilisation the development of the embryo and the seed can begin.

Question 11

How is a seed formed after fertilisation? (3)

Answer 11

• the zygote divides numerous times by mitosis and develops into an embryo consisting of: −cotyledons or seed leaves. The cotyledons often take food from the parent plant which they store for future use.
−a radical (embryonic root)
−a plumule (embryonic shoot).
• the rest of the ovule develops into endosperm tissue. This is the stored food, e.g. starch, protein or oil.
• the outer covering of the ovule thickens and hardens, forming the seed coat or testa. It saves the seed from being damaged as well as preventing the entry of bacteria and fungi.

Question 12

How is a fruit formed?

Answer 12

While a seed is being formed the ovary is also growing. It is now called a fruit. Fruit formation happens in different ways in different plants

Question 13

What are the functions of fruit?

Answer 13

1. They contain and protect the seeds.

2. Fruits help to disperse the seeds from the parent plant

Question 14

Of the approximate 75 000 species of edible plants 7 000 are used for food by humans. Humans have domesticated wild plants for their use for the last 9 000 to 11 000 years. Domestication lead to: (2)

Answer 14

• great phenotypic changes, (and altered genotypes) resulting in vastly improved food crops.
• new varieties developing.

Question 15

Today, all our principal food crops come from domesticated varieties. Most of the ____ involved cereals, i.e. wheat, maize and rice.

Answer 15

domestication

Question 16

Define wild plants.

Answer 16

plants that grow in nature without the aid of humans. Very few wild plants are now used as food sources.

Question 17

Domestication involved skilful breeding. The breeders used ____ that existed in plant species and also the variation that arose from sexual reproduction to asexually or sexually _____ the food crops further.

Answer 17

variation

improve

Question 18

What does asexual reproduction cover?

Answer 18

Asexual reproduction covers all those modes of the reproduction of plants where normal gamete formation and fertilisation does not take place.

Question 19

What are the asexual methods to improve crops? (4)

Answer 19

Techniques include:

• division,
• grafting, using
• storage organs (bulbs, corms, tubers and rhizomes)
• cuttings.

Question 20

Why is asexual reproduction good in crop production?

Answer 20

While the basic feature of asexual reproduction is genetic stability with no variation in the offspring a mutation could have produced a plant with a new superior trait. For example a crop plant could have produced bigger seeds, fruits or tubers. If these plants were then reproduced by asexual means more plants with the superior trait could have been grown. With repeated selection and elimination of plants without the superior trait the food crop would eventually have consisted entirely of plants with the superior trait. In this way the particular crop would have been improved by asexual means.

Question 21

What is grafting?

Answer 21

Grafting is a technique whereby tissues from one plant are inserted into those of another so that the two sets join together.

Question 22

Explain the process of grafting. (2)

Answer 22

• One plant is selected for its roots. This is called the rootstock. Rootstocks with good traits, e.g. resistance to certain pests and diseases and/or the ability to grow in difficult soil conditions would have been used.
• The other plant is chosen for its superior fruits (larger and improved yield) and is called the scion. As the scion contains the superior traits for food production the mature plant would be more productive. Further scions would be cut from this plant for further grafting resulting in an overall improved crop

Question 23

True or false

Grafting an outdated process.

Answer 23

False. Grafting has been practiced for thousands of years to improve crops, particularly fruit tree e.g. apples, pears. It is still today used in asexual propagation of certain commercially grown food crop plants, e.g. grapes and avocado pears.

Question 24

True or false

Plant breeders made use of sexual reproduction to improve crops as well.

Answer 24

True. Over time breeders also used sexual reproduction to improve their crops. The plants originating from sexual reproduction were often quite different from their parents and from each other. Some of these differences were beneficial traits that would improve the food crop. Such traits were larger yield, larger seed, tuber and fruit size, resistance to pests and/or disease and being able to grow in poorer soil.

Question 25

What did breeders select?

Answer 25

Breeders selected and planted seed from the superior plants, while eliminating seed from those plants with less desirable traits. With repeated selection an improved crop resulted.

Question 26

The ___- _______ of individuals of a species produced new crop varieties with improved traits. For example, a mildew-resistant pea may have been crossed with a high-yielding but mildew-susceptible pea. The purpose of the cross was to introduce mildew resistance without losing the high-yield traits. Eventually all seed produced from the favoured plants would have produced plants with the desirable traits. These plants became known as cultivars.

Answer 26

cross pollination

Question 27

What is a cultivar?

Answer 27

It is a plant or grouping of plants selected for desirable characteristics that can be maintained by propagation.

Question 28

A crop plant may have shown a new trait, e.g. a larger maize cob with more ‘pips’. To perpetuate this trait plants grown from this plants seeds were ____- _____. The next generation plants would have produced seed with this new trait. Repeated breeding by self-pollination eventually led to all maize having larger cobs – a highly desirable feature.

Answer 28

self-pollinated