Chapter 16: Reproduction in Plants

Question 1

Parts of a flower

Answer 1

1. Petal
2. Sepal
3. Flower Stalk
4. Receptacle
5. Filament
6. Anther
7. Stamen
8. Stigma
9. Style
10. Ovary
11. Ovule
12. Carpel

Question 2

Petal

Answer 2

• modified leaves, forming the most obvious part of the flower
• in insect-pollinated flowers, petals are brightly coloured to attract insects
• petals provide a platform for insects to land
• petals have lines that guide insects to the base of the petals to obtain nectar

Question 3

Sepal

Answer 3

• modified leaves that encloses and protect the other parts of the flower in the bud stage
• it usually form the outermost layer of teh floral leaves

Question 4

Flower Stalk

Answer 4

• it attaches to the stem
• some flowers do not have stalks and are attached to the plant directly at the base

Question 5

Receptacle

Answer 5

• it is the swollen end of the flower stalk

Question 6

Stamen

Answer 6

• the male part of the flower
• consists of the filament and the anther

Question 7

Filament

Answer 7

• the stalk that holds the anther in a suitable position to disperse the pollen

Question 8

Anther

Answer 8

• it produces pollen grains
• when an anther matures, it splits up to release the pollen grains

Question 9

Pollen Grains

Answer 9

• contains the male gamete
• the male gametes are produced by meiosis and and are haploid
• male gametes have half the number of chromosomes as a normal cell

Question 10

Carpel

Answer 10

• the female part of the flower
• consists of the ovary, style, and the stigma

Question 11

Stigma

Answer 11

• a swollen structure at the end of the style
• it receives the pollen grains
• the mature stigma secretes a sugary fluid that stimulates the pollen grain to germinate

Question 12

Style

Answer 12

• a stalk that connects the stigma to the ovary
• it holds the stigma in a suitable position to trap the pollen grains

Question 13

Ovary

Answer 13

• contains one or more ovules
• within each mature ovule is a female gamete or egg cell that is called ovum
• ovum is produced by meiosis, and hence is haploid

Question 14

Pollination

Answer 14

• the transfer of pollen grains from the anther to the stigma

Question 15

Self-pollination

Answer 15

• the transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant

Question 16

Features of flowers that favour self-pollination

Answer 16

• flowers are bisexual with anthers and stigmas maturing at the same time
• the stigma is situated directly below the anthers
• in certain plants with bisexual flowers, some flowers never open. Only self-pollination occurs in these flowers

Question 17

Advantages of self-pollination

Answer 17

• only one plant is required
• offspring inherits its genes from parent plant after fertilisation, hence all beneficial qualities are passed down
• it does not depend on external factors such as insects or wind for pollination
• since anthers are close to stigmas of same flower, there is higher probability of successful pollination
• less pollen and less energy is wasted in self-pollination as compared to cross-pollination

Question 18

Disadvantages of self-pollination

Answer 18

• there will be less genetic variation in offspring, making species less well-adapted to changes in envrionment
• continued self-pollination may lead to the offspring becoming weaker, smaller and less resistant to diseases

Question 19

Cross-pollination

Answer 19

• the transfer of pollen grains from one plant to the stigma of a flower in another plant of the same species

Question 20

Features of flowers that favour cross-pollination

Answer 20

• they bear either male/female flowers
• in plants with bisexual flowers, anthers and stigma mature at different times
• stigmas of plants with bisexual flowers may be situated some distance away from the anthers so that self-pollination is unlikely

Question 21

Advantages of cross-pollination

Answer 21

• offspring may have inherited beneficial qualities from both parents
• there will be greater genetic variation in the offspring as compared to self-pollination, increasing species changes of survival when there are changes in envrionment
• more viable seeds are produced, such seeds are capable of surviving longer before germination

Question 22

Disadvantages of cross-pollination

Answer 22

• 2 plants are required
• depends on external factors such as insects or wind from pollination
• since pollen grains have to be transferred from the anther of one plant to stigma of another plant, probability of pollination occurring is lower
• more energy and pollen are wasted as compared to self-pollination

Question 23

Structural adaptations of insect-pollinated flower

Answer 23

• flowers are usually large with brightly coloured petals to attract insects
• nectar is present
• flowers are fragrant or sweet-smelling
• stigmas are usually small, compact and do not protrude out of the flower
• stamens are not pendulous and usually do not protrude out of the flower
• pollen is abundant, pollen grains are usually larger with rough surfaces so that they can cling onto the body of insects
• nectar guide may be present on petals to guide insects towards the nectar

Question 24

Structural adaptations of wind-pollinated flowers

Answer 24

• flowers are usually small and dull-coloured, without petals
• nectar is absent
• flowers are odorless
• stigmas are large, feathery and usually protrude out of the flower to provide a large surface area to trap pollen
• stamens have long pendulous filaments and protruding anthers, pollen grains are hence easily shaken off from anther
• pollen is more abundant, pollen grains have smooth surfaces and are light and tiny so that they are easily blown about by wind
• nectar guide absent

Question 25

Pollination of insect-pollinated flowers

Answer 25

• when an insect visits the flower, it lands on petal
• it follows nectar guide into flower
• insect forces its way and moves in to collect nectar
• as insect moves in, stigma and anther brush hairy back of insect
• some pollen grains from the anther stick to the hairy back of insect
• at the same time, pollen grains on the insect’s back from an earlier visited flower, are transferred to the sticky stigma
• although the flower is well-adapted to insect-pollination, self-pollination can still occur

Question 26

Pollination of wind-pollinated flowers

Answer 26

• stamens have long filaments and protruding anthers
• when filaments sway in the wind, dust-like pollen is shaken free and dispersed by the wind
• stigmas are large, extended and feathery, thus they provide a large surface area to receive any pollen that is floating around in the wind

Question 27

Fertilisation process

Answer 27

1. after pollination, pollen grain germinated after coming into contact with stigma, in response to sugary fluid secreted by the mature stigma
2. pollen tube grows out from each pollen grain, male gamete enters pollen tube
3. as pollen tube grows, it secretes enzymes to digest surrounding tissue of stigma and style, thus pollen tube grows down the style into the ovary
4. pollen tube enters the ovule through an opening in the ovule wall called the micropyle
5. within ovule, tip of the pollen tube absorbs the sap and burst, releasing male gamete
6. nucleus of the male gamete fuses with nucleus of the ovum to form the zygote
7. after fertilisation, ovary develops into fruit and ovule develops into the seed

Question 28

Post-fertilisation changes

Answer 28

• ovary becomes fruit
• ovule becomes seed
• zygote becomes embryo, which consists of embryonic shoot, the embryonic root and cotyledons
• petals, style, stigma and anthers wither and drop off