16 — reproduction in plants

Question 1

Sepal

Answer 1

Sepal — modified leaf that enclose and protects the flower in the bud stage

(All sepals make up calyx
Some flowers hv another layer of floral leaves outside the sepals known as the epicalyx)

Question 2

Petal

Answer 2

Petal — modified leaf that forms the most obvious part of a flower

Insect-pollinated flowers:
1. Petal brightly coloured with conspicuous modified leaves to attract insects for pollination
2. Prov a landing platform for insects

(All petals tgt make up the corolla)

Question 3

Stamen

Answer 3

Male part of the flower that consists of an anther and a filament. Anther has 2 lobes, each contains 2 pollen sacs which produce pollen grains. The pollen grain contains 2 male gametes.

(All of stamens tgt make up the androecium (plural: androecia))

Question 4

Filament

Answer 4

Holds anther in a suitable position to disperse pollen grains

(Pollen grains contains male gametes)

Question 5

Anther

Answer 5

Produces pollen grains. It is made up of 2 lobes, each containing 2 pollen sacs. It consists of a vascular bundle made up of a phloem and a xylem.

Question 6

Carpel

Answer 6

Female part of the flower. Consists of an ovary which contains ovules, a style through which pollen tube grows, and one or more stigmas which capture pollen grains.

All of the carpels tgt make up the pistil or gynoecium (plural: gynoecia)

Question 7

Pollen grains

Answer 7

Hv a haploid set of chromosomes. Each pollen grain has 2 nuclei, the generative nucleus and the pollen tube nucleus or vegetative nucleus.

Question 8

Stigma

Answer 8

Swollen structure that receives pollen grains. A mature stigma secretes sugary fluid to stimulate the germination of pollen grains.

The style connects the stigma to the ovary, and holds stigma in a suitable position to trap pollen grains

Question 9

Ovary

Answer 9

Contains 1 or more ovules. The ovule contains the ovum and the definitive nucleus. The ovum has a haploid set of chromosomes. The ovule is attached to the placenta by a stalk called called the funicle.

Question 10

Pollination

Answer 10

Pollination is the transfer of pollen grains from the anther of the male to the stigma of the female part of the flower

• Pollination is important to help
  bring together the male and female
  gametes to enable fertilisation to
  take place.
• Pollination can be brought about
  by insects or wind.
• There are two types of pollination:
  1) Self-pollination
  2) Cross-pollination

Question 11

Self-pollination

Answer 11

Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower or a different flower on the same plant.

• Flowers are bisexual with
  anthers and stigmas
  maturing at the same time.
• The stigma is situated
  directly below the anther. (Anther higher stigma lower)
• Certain flowers in bisexual
  plants never open
  (cleistogamous) and only self-
  pollination can happen.

Question 12

Advantages of self-pollination

Answer 12

1. Beneficial qualities are passed down from parent plant to offspring.
2. Not dependent on external factors for pollination.
3. More likely to take place since stigmas are closer to anthers.
4. Less pollen and energy is wasted.
5. Only one parent is required.

Question 13

Disadvantages of self-pollination

Answer 13

1. Offspring produced are genetically similar to parents causing fewer varieties of offspring, less adaptable to changes in the environment.
   Note: genetically similar not = genetically identical, not asexual.
2. Probability of harmful recessive alleles being expressed in offspring is higher as compared with cross-
   pollination.

Question 14

Cross-pollination

Answer 14

Cross-pollination involves the transfer of pollen grains to the flower of another plant of the same species.

• Dioecious plants bear either
  male or female flowers making
  self-fertilisation impossible.
• In bisexual plants, cross-pollination can happen when:
• anthers and stigmas mature at different times.
• Stigmas of plants are situated at a distance away from the anthers.
  (Anther may be below stigma in this case)

Question 15

Advantages of cross-pollination

Answer 15

1. More varieties of offspring are produced as they’re genetically dissimilar to parents, which leads to greater genetic variation, which can be less prone to diseases/probability of harmful recessive alleles being expressed in offspring is lower.
2. Increased probability of offspring being heterozygous.
3. Increased probability
   of offspring being heterozygous. (Alleles r diff)
4. Seeds produced are capable of surviving longer before germination
   (Seeds-> sexual reproduction)
5. Probability of harmful recessive
   alleles being expressed in offspring is lower as compared with self-pollination.
6. Offspring can inherit beneficial
   qualities from both parents.

Question 16

Disadvantages of cross-pollination

Answer 16

1. Two different plants of the same species are required. -> nd more energy
2. Dependant on external factors for pollination.
3. Less likely to occur as compared to self-pollination.
4. More energy and pollen are wasted.

Question 17

androecium

Answer 17

• The androecium consists of ten stamens with long filaments.
• The filaments of nine stamens are fused to form a trough that encloses the pistil.
• Nectar of the flower collects at the bottom of the stamen trough. Hence, they can be reached only by insects with long tubular mouth (proboscis).

Question 18

Insect pollination

Answer 18

• The insect lands on the standard petal.
• It follows the nectar guide into the flower.
• In order to collect nectar, the insect forces its way in between the two wing petals.
• The insect’s back forces the keel petal upwards to expose the anthers and stigma.
• Pollen grains from the anther stick onto the back of the insect and get transferred to a stigma and is deposited.
• When insect leaves flower, the keel petals spring back to its original position.

Question 19

Differences betw insect-pollinated and wind-pollinated flowers

Answer 19

Petals:
I: large w brightly-coloured petals
W: small, dull-coloured n without petals

Nectar:
I: nectar is present
W: nectar is absent

Scent:
I: fragrant and sweet-smelling flowers
W: scent is absent in flowers

Stigmas
I: small, compact n do not protrude out of flowers
W: large, feathery n protrude out of flowers to provide large SA

Stamens:
I: Not pendulous and do not protrude out of flowers.
W: Long and pendulous filaments with protruding anthers.

Pollen:
I: Fairly abundant. Pollen grains are larger with rough surfaces.
W: More abundant. Pollen
grains are tiny with smooth surfaces.

Nectar guides:
I: Nectar guides are present.
W: Nectar guides are absent.

Question 20

Pollen allergy

Answer 20

A reaction by the immune system to fight against a specific pollen

Signs and symptoms:
Sneezing, stuffy nose, runny nose, watery eyes, wheezing, itchy
throat

Causes:
Breathing in pollen from some trees and wind-pollinated plants such as grass

Question 21

Fertilisation

Answer 21

1. After pollination, pollen grain
   germinates in response to
   sugary fluid secreted by mature
   stigma.
2. A pollen tube grows out from the
   pollen grain. Growth of pollen tube
   is controlled by the pollen tube
   nucleus.
3. The cytoplasm, the generative nucleus and the pollen tube nucleus
   pass into the pollen tube.
4. The pollen tube secretes enzymes to digest the surrounding tissue of stigma and style to allow the pollen tube to penetrate through the style as it grows.
5. Pollen tube enters the
   ovule through the micropyle.
6. The generative nucleus
   divides into two male gametes, while the pollen tube nucleus
   disintegrates.
7. When the pollen tube
   reaches the ovule, its tip absorbs sap and bursts, releasing the
   two male gametes.
8. Haploid nucleus of male
   gamete fuses with haploid
   nucleus of the ovum to form
   the diploid zygote
   (fertilisation). The other haploid
   nucleus of male gamete fuses
   with the definitive nucleus (in
   the ovule) to form the
   endosperm nucleus.
9. Zygote divides mitotically
   and develops into the embryo,
   and the endosperm nucleus
   will give rise to an endosperm.

Question 22

Discuss the differences in the process of fertilisation in a human and a flowering plant.

Answer 22

• Male and female nuclei are found in sperms and ova/eggs in
  humans while male and female nuclei are found in pollen grains
  and ovules in a flowering plant.
• Male gamete is delivered by pollen tube in a flowering plant while
  male gametes swims on their own/motile in humans.
• Fertilisation takes place in the oviduct/ fallopian tube in
  humans while it takes place in the ovule in the ovary in a
  flowering plant.
• Involves double fertilisation in a flowering plant but single
  fertilisation in humans.

Question 23

Describe the early development of the zygote after fertilisation has taken place. [4]

Answer 23

The fertilised egg, zygote continues to divide by mitosis to form a ball of cells called an embryo. [1]
The embryo travel / move down the oviduct into the uterus by the
contraction of the oviduct muscles via peristalsis [1] and with the help of the cilia. [1]
Implants itself into the uterine lining/uterus wall. [1]

Question 24

Compare and contrast between the adaptations of insect-pollinated and wind-pollinated flowers. [6]

Answer 24

Similarities:
Both Involve formation of flowers.[1]
Both need anther and stigma. [1]
Both involve production and transferring of pollen. [1]

Differences:

1. petals:
   I: Flowers are usually large with
   brightly-coloured petals.
   W: Flowers are usually small and
   dull-coloured, without petals
2. Stigmas:
   I: Stigmas are usually small and
   compact.
   W: Stigmas are large and feathery
   to provide a large surface area
   to trap pollen.
3. Stamens:
   I: Stamens are not pendulous.
   W:Stamens have long pendulous
   filaments and protruding
   anthers.
4. Pollen:
   I: Pollen is larger with rough
   surfaces to attach to insects.
   W: Pollen are smooth surfaces and
   are light and tiny to be carried
   by wind.
5. Nectar guides:
   I: Nectar guides may be present
   on the petals to guide insects.
   W: Nectar guides are absent.

Question 25

Compare and contrast between self-pollination and cross-pollination. [4]

Answer 25

Similarities (any 2)
1. Forms of sexual reproduction/Involve the production of male and female
Gametes/Involves formation of flowers/ Gives rise to genetic variation in offsprings

Differences (any 2)
1. Self-pollination involve only one plant whereas cross pollination involve 2 different plants
2. Self-pollination does not depend on external factors for pollination
whereas cross pollination needs
3. Self-pollination requires less energy and pollen wastage whereas cross pollination requires more energy and more pollen wastage.
4. Self-pollination gives rise to less genetic variation and less adaptability to environment whereas cross pollination gives rise to more genetic variation
and more adaptability to environment

Question 26

Ways to prevent self-pollination

Answer 26

1. Stamen and pistil mature at different times
2. Unisexual plant
3. Stigma of flower is above the anther
4. Stigma and anther are situated far apart from each other.

Question 27

Process of wind pollination

Answer 27

1. The pendulous filaments expose the anthers to the wind
2. When the wind blows, pollen grains are released and carried away by the wind
3. The pollen grains land on large feathery stigma, which increases surface area to trap the pollen grains.