Plant Reproduction

Question 1

What is an angiosperm?

Answer 1

A flowering plant.

Question 2

Describe asexual reproduction and what types of plants are involved.

Answer 2

No sex, no seed, results in clones

E.g tubers (potatoes), suckers, runners, budding, fragmentation/shedding (cacti)

Question 3

Describe the angiosperm life cycle in steps.

Answer 3

• alternating generations between the haploid (n) stage and diploid (2n) stage.
  1. Meiosis produces haploid microspores in pollen sac (male) and megaspores in the ovary (female).
  2. The male pollen sac microspores then undergo mitosis to produce microgametophytes in the form of pollen grains (male). Meanwhile, the female ovary megaspores undergo mitosis to produce megagametophytes in embryo sacs.
  3. POLLINATION then occurs with male pollen grains entering pollen tube and female embryo sacs entering ovary.
  4. FERTILISATION then occurs with sperm fusing with embryo sac, producing zygote within parent ovary.
  5. Mitosis then produces embryo within seed, which then produces independent sporophyte.
  6. Independent sporophyte then produces flower.

Question 4

What is the dominant generation in flowering plants?

Answer 4

The diploid stage

Question 5

Describe the general structure of a flower.

Answer 5

• flower grows in 4 whorls around the tip of the flower stalk (receptacle)
• whorl 1 contains the sepal which is a leaf like structure on top of the stem
• whorl 2 contains the petal, some of which may contain honey guides that guide pollinators to the nectary glands
• nectary glands are not part of any whorl
• whorl 3 is the stamen which is the male reproductive organs and contains anthers on top of filaments
• whorl 4 is the carpel which is the female reproductive organs and contains the ovary, ovule, style and stigma

Question 6

Where do ovules develop?

Answer 6

In the ovary

Question 7

What is an embryo sac and what does it contain?

Answer 7

It is the female gametophyte and contains an egg cell

Question 8

What gender are stamens and what do they consist of?

Answer 8

Stamens are male and consist of anther on top of filaments.

Question 9

What is produced in the anther?

Answer 9

Male gametophytes which are pollen grain

Question 10

What gender are carpels and what do they consist of?

Answer 10

Carpels are female and consist of an ovary containing ovules, and a style stemming from the ovary with a stigma on top of the style.

Question 11

What is a gynoecium?

Answer 11

Several carpels fused together.

Question 12

What is the stigma covered in? Why is this substance important?

Answer 12

Covered in papillae. It increases surface area.

Question 13

What is the function of the stigma?

Answer 13

Captures pollen grains

Question 14

Why is pollen size important?

Answer 14

Must be the right size in order to stick between papillae

Question 15

How do the sperm reach egg cells?

Answer 15

• pollen must be transported from the anther to the female stigma by air, water or animal vectors.
• pollen that arrives on a stigma germinates to produce a pollen tube that grows down the style to the ovary.
• in this way, male gametes are transferred to the egg cell in the embryo sac, lying within the ovule
• fertilisation takes place and an embryo is formed, the new diploid generation

Question 16

What is a seed?

Answer 16

An embryo, together with some food reserved and an outer coat. Also known as the unit of dispersal.

Question 17

What is the product of fertilisation?

Answer 17

A seed containing an embryo

Question 18

Describe what happens as a pollen tube approaches an ovule involving synergid cells.

Answer 18

• one synergid cell degenerates
• once the pollen tube reaches the embryo sac, it enters the degenerated synergid
• tube tip ruptures and releases pair of sperm cells and tube nucleus

Question 19

What does double fertilisation involve? Explain the steps.

Answer 19

It involves true fertilisation (fusion of sperm and egg) and an accessory fusion (between sperm and central cell).

One sperm cell released form the pollen tube fuses with the egg cell to form the diploid zygote, the first cell of the new sporophyte generation.

The other sperm cell fuses with a central cell containing two nuclei to produce a triple fusion nucleus. This nucleus divides mitotically to produce a nutritive triploid tissue called endosperm that supports growth of the embryo and the young seedling.

Question 20

What is formed in the first fertilisation event?

What is formed in the second fertilisation event?

Answer 20

1. Embryo

2. Endosperm

Question 21

What is apomixis?

Answer 21

Meiosis does not occur and embryos develop asexually.

Question 22

What do ovules develop into?

What does carpel wall develop into?

Answer 22

1. Seeds

2. Fruit

Question 23

What do flowering plants use to select appropriate mates?

Answer 23

This selection takes place on the stigma or in the style.

Question 24

What are abiotic methods of seed dispersal?

Answer 24

• wind e.g dandelion, sycamore seed
• gravity
• water (buoyancy) e.g coconut floating

Question 25

What are biotic methods of seed dispersal?

Answer 25

• fleshy fruits to attract frugivores
• sticky seeds to catch on animals
• cap on seed as reward for ants that provides them with nutrients

Question 26

Why do plants control mate choice?

Answer 26

To avoid mating with relatives.

Question 27

What is inbreeding?

Answer 27

Mating within a single individual (can still be between different flowers on the same plant)

Question 28

What are the advantages and disadvantages of inbreeding?

Answer 28

Advantages:

• preserves well-adapted genotypes
• ensures seed set in absence of pollinators
• single colonising individual possible

Disadvantages:

• decreases genetic variability
• offspring with deleterious (harmful) mutations

Question 29

What is outbreeding?

Answer 29

Mating between two different individuals.

Question 30

What are the advantages and disadvantages of outbreeding?

Answer 30

Advantages:

• increased genetic variability
• strong evolutionary potential
• adaptation to changing conditions

Disadvantages:

• can destroy well-adapted genotypes
• relies on effective pollination vectors

Question 31

What is cross-pollination?

Answer 31

The transfer of pollen from one plant to the stigma of a different plant of the same species.

Question 32

What is self-pollination?

Answer 32

Transfer of pollen to a stigma of a flower on the same plant.

Question 33

What are the ways in which self-pollination is prevented?

Answer 33

Dioecy: unisexual flowers on different plants (separate plants have male or female organs)

Protandry: male organs mature first.
Protygyny: female organs mature first
(Therefore temporal separation of male and female function)

Self-incompatibility: genetic control of pollen compatibility. Plant will possess same genotypes alleles in all flowers, therefore cannot be pollinated (self incompatible alleles)

Question 34

What are the ways in which self-pollination is encouraged?

Answer 34

Cleistogamy: flowers that don’t open and therefore self-pollinate

Apomixis: egg cells form mitotically and develop into clone embryos without fertilisation

Question 35

What is generalist pollination?

Answer 35

Many kinds of flower visitors that act as couriers to transport pollen = anyone

Question 36

What is specialist pollination?

Answer 36

Exclusive set of flower visitors that act as couriers to transport pollen, often one species.

Question 37

Why is specialist pollination advantageous?

Answer 37

Bc pollen is less likely to be wasted on a different species of flower.

Question 38

How has evolutionary feedback worked with pollination?

Answer 38

Flower adapts to sensory system of the pollinator.

Question 39

Describe examples of co-evolution between pollinators and flowers.

Answer 39

Bird pollination: bird pollinated flowers are almost always red because birds are visually driven.

Moth pollination: pale nocturnal flowers with deep nectar tubes. Emit aromatic hydrocarbons

Carrion fly pollination: flower emits rotting smell which is irresistable to carrion flies

Buzz pollination: “poricidal anthers” only release pollen when vibrated at a fundamental frequency. Pollen is therefore only accessible to the bee who can produce that frequency. E.g tomato