Chapter 17 - Reproduction In Plants

Question 1

Define asexual reproduction.

Answer 1

It is the process resulting in the production of genetically identical offspring from one parent by mitosis, without the fusion of nuclei of haploid gametes.

Question 2

Define sexual reproduction.

Answer 2

It is the process involving the fusion of nuclei of the haploid female gamete and haploid male gamete to form a diploid zygote which is genetically dissimilar from its parents through fertilization. The male and female gametes are produced by meiosis in the gonads.

Question 3

List 5 advantages of asexual reproduction.

Answer 3

1) only one parent required
2) fusion of gametes not required
3) all beneficial qualities are passed on to the offspring.
4) faster method as contrasted to sexual reproduction
5) since organisms are already in a suitable habitat, they can colonize the area rapidly

Question 4

What is a disadvantage of asexual reproduction?

Answer 4

There will be no genetic variation in the offspring, which might cause them to be not well adapted to changes in the environment.

Question 5

What are 2 advantages of sexual reproduction?

Answer 5

1) offspring may inherit beneficial qualities from both parents
2) greater genetic variation in offspring: leads to species that are better adapted to changes in the environment.

Question 6

What are 3 disadvantages of sexual reproduction?

Answer 6

1) 2 parents are required
2) fusion of nuclei of gametes is required
3) slower method of reproduction compared to asexual reproduction.

Question 7

What are 4 differences between asexual and sexual reproduction?

Answer 7

1) gametes: AR does not involve fusion of nuclei of gametes, while SR involves the fusion of haploid nucleus of male gamete with haploid nucleus of female gamete to form a diploid zygote.
2) parent: AR only requires 1 parent, while SR requires 2 parents (except plants with bisexual flowers)
3) offspring: AR produces offspring that are genetically identical, while SR produces offspring that are genetically dissimilar
4) time: AR is relatively quicker while SR is relatively slower

Question 8

What does a complete flower contain? (6)

Answer 8

1) pedicel
2) receptacle
3) sepals
4) petals
5) stamens (anther, filament)
6) carpels (stigma, style, ovary, ovule)

Question 9

What is a sepal?

Answer 9

It is a modified leaf that encloses and protects the flower in the bud stage. The collective of sepals is called the calyx. It usually forms the outermost layer of floral leaves, but some flowers like hibiscus had another layer of floral leaves outside the sepals, which are known as epicalyx.

Question 10

What are petals?

Answer 10

Petals are modified leaves forming the most obvious part of the flower. The collective term for petals is corolla.

Question 11

How are petals adapted for insect-pollinated flowers?(2)

Answer 11

1) bright coloured and conspicuous (obvious) to attract insects for pollination
2) provide a landing platform for insects

Question 12

What is the receptacle?

Answer 12

The enlarged end of flower stalk (pedicel) that bears parts of the flower

Question 13

What is the stamen?

Answer 13

It is the male part of the flower. The collective term for stamen is androecium. It consists of an anther and a filament.

Question 14

What are 2 functions of the anther?

Answer 14

1) it consists of 2 lobes, each containing 2 pollen sacs. Pollen sacs contain pollen grains which are produced by the anther. When the anther matures, it splits open to produce pollen grains.
2) it contains a vascular bundle, made up of a phloem and xylem.

Question 15

What is the function of the filament?

Answer 15

It is the stalk that holds the anther in a suitable position to disperse pollens.

Question 16

What are pollen grains?

Answer 16

They are haploid and produced by meiosis. Each pollen grain contains a male gamete, which is the nucleus. It has 2 nuclei, generative nucleus and the pollen tube/vegetative nucleus.

Question 17

What is a carpel?

Answer 17

The female part of the flower. Its collective term is pistil. It consists of ovary, style and one or more stigma.

Question 18

What is the stigma and what is its function?

Answer 18

It is a swollen structure that receives pollen grains.

A mature stigma secrete sugary fluid to stimulate the germination of pollen grains.

Question 19

What are 2 functions of a style?

Answer 19

1) It connects the stigma to the ovary

2) holds the stigma is suitable position to trap pollen grains.

Question 20

What is the ovary?

Answer 20

It is the structure that will develop into a seed after fertilization. It produces a female haploid gamete (ovum) by meiosis. The ovum is attached to the placenta by a stalk called the funicle.

Question 21

Define pollination.

Answer 21

Pollination is the transfer of pollen grains from the anther to the stigma.

Question 22

Why is pollination important?

Answer 22

It brings together male and female gametes to enable fertillization to take place.

Question 23

What are two types of pollination?

Answer 23

1) self pollination (not asexual)

2) cross pollination

Question 24

Define self pollination.

Answer 24

It is the transfer of pollen grains from the anther to the stigma of the same flower, or a different flower on the same plant.

Question 25

What are 3 features of self-pollinating plants?

Answer 25

1) flowers are bisexual with anthers and stigmas maturing at the same time
2) stigma situated directly below anthers
3) certain flowers in bisexual plants never open, thus only self pollination can occur in these flowers

Question 26

What are 5 advantages of self pollination?

Answer 26

1) only 1 parent plant is required
2) beneficial qualities more likely to pass down to offspring
3) not dependent on external factors for pollination
4) higher probability of pollination as anthers are close to stigmas of the same flower.
5) less pollen and energy wasted as compared to cross-pollination

Question 27

What are 3 disadvantages of self-pollination?

Answer 27

1) offspring produced are genetically similar to parents, causing fewer varieties of offspring
2) probability of harmful recessive alleles being expressed in offspring is higher as compared to cross-pollination
3) continued self pollination may lead to offspring becoming weaker, smaller, and less resistant to diseases.

Question 28

Define cross pollination.

Answer 28

It is transfer of pollen grains from anther of one plant to the stigma of a flower in another plant of the same species.

Question 29

What are 4 features favouring cross-pollination/preventing self-pollination?

Answer 29

1) stamen and pistil mature at different times
2) dioecious (unisexual) plants like papaya only has either male or female flowers
3) stigmas above anther
4) stigma and anther situated far apart from each other

Question 30

What are 5 advantages of cross-pollination?

Answer 30

1) more varieties of offspring are produced which leads to greater genetic variation
2) increased probability of offspring being heterozygous
3) seeds produced are capable of surviving longer before germination
4) probability of harmful recessive alleles being expressed in offspring is lower, as compared to self-pollination
5) offspring can inherit beneficial qualities from both parents

Question 31

What are 4 disadvantages of cross-pollination?

Answer 31

1) two different plants of the same species are required
2) dependent on external factors like insects or wind for pollination
3) more energy and pollen wasted as compared to self-pollination
4) pollen grain have to be transferred to anther of one plant to stigma of another plant: less likely to successfully pollinate as compared to self-pollination

Question 32

How is the Clitoria adapted for insect pollination? (7)

Answer 32

1) bisexual
2) corolla consists of 5 brightly-colored petals of different shapes and sizes, which helps attract insects
3) standard petals has lines (nectar guides) that guide insects to where the nectar is located
4) androecium consists of ten stamens with long filaments. The filaments of 9 stamens fused to form a trough that encloses the pistil. Nectar of the flower collects at the bottom of the stamen trough. Hence, it can only be reached by insects with long proboscis
5) the stigma is small and compact
6) style is long, curved and hairy
7) the ovary is long and narrow with a single row of ovules

Question 33

How does insect pollination take place? (On the clitoria,6)

Answer 33

1) an insect lands on the petals
2) insect follows nectar guide into flower
3) insect forces its way in between 2 wing petals and moves in to collect nectar
4) the insect’s back forces the keel petal upwards, exposing the anthers and stigma.
5) pollen grain from another flower, which the insect had visited earlier, are transferred from the insect’s body onto the stigma.
6) as the insect brushes the anther, it picks up pollen grains, which will be used to pollinate another flower

Question 34

How is the Ischaemum muticum adapted for wind-pollination?

Answer 34

1) upper bisexual flower consists of an ovary, two long feathery stigmas, three stamens, two Iodicules
2) lower flower is male

Question 35

How does wind pollination occur? (ischaemum muticum, 3)

Answer 35

1) mature, pendulous, long filaments hang downwards. It exposes anthers to the wind
2) when the wind blows, filaments sway and pollen grains are released and carried away by the wind
3) pollen grains land on large and feathery stigma. It provides large surface area to capture pollen floating in the air

Question 36

What are 6 parts of the plants that differ between insect and wind pollinated flowers?

Answer 36

1) petals
2) nectar&nectar guides
3) scent
4) stigmas
5) stamens
6) pollen

Question 37

How does petals differ between insect and wind pollinated flowers?

Answer 37

IPF have large and bright colored petals to attract insects, while WPF are small and dull-colored, without petals.

Question 38

How does nectar and nectar guides differ between insect and wind pollinated flowers?

Answer 38

IPF have nectar and nectar guides while they are absent is WPF.

Question 39

How does scent differ between insect and wind pollinated flowers?

Answer 39

IPF are fragrant, while WPF are odorless.

Question 40

How does stigma differ between insect and wind pollinated flowers?

Answer 40

IPF usually have small, compact stigmas that do not protrude out of flower, while WPF have large, feathery stigmas that protrude out of the flower, to provide a large surface area to trap pollen.

Question 41

How does stamen differ between insect and wind pollinated flowers?

Answer 41

In IPF, stamens are not pendulous and usually do not protrude out of flower. In WPF, stamens have long pendulous filaments and protruding anthers, so that pollen grains can be easily shaken out of anthers.

Question 42

How does pollen differ between insect and wind pollinated flowers?

Answer 42

IPF have fairly abundant pollens. Pollen grains are larger with rough surfaces so that they readily cling onto insects’ bodies. WPF have more abundant pollens. Pollen grains have smoother surfaces and are tiny and light so they are easily blown about by wind.

Question 43

How does fertillisation take place?(10)

Answer 43

1) after pollination, the pollen grains germinate in response to a sugary fluid secreted by the mature stigma
2) a pollen tube grows out of each pollen grain
3) the cytoplasm, generative nucleus and pollen tube nucleus of each pollen grain pass into the pollen tube
4) the pollen tube’s growth is controlled by the pollen tube nucleus. As it grows, enzymes are secreted to digest the surrounding tissues of stigma and style. It allows the pollen tube to penetrate through the style as it grows.
5) the pollen tube enters the ovule through an opening known as the micropyle.
6) along the way, the generative nucleus divides to form 2 male gametes, and the pollen tube nucleus disintegrates
7) within the ovule, the tip of the pollen tube absorbs sap and bursts to release the 2 male gametes
8) the nucleus of one male gamete fuses with the nucleus of the ovum to form the zygote, while the other male gamete fuses with the definitive nucleus to form the endosperm nucleus
9) the zygote divides and develops into the embryo in the seed, while the endosperm nucleus divides to give rise to food storage tissue known as the endosperm.
10) after fertilization, the ovary develops into the fruit and the ovule develops into the seed.