III: 1 - Reproduction (part 1)

Question 1

Define

asexual reproduction

Answer 1

The process resulting in the production of genetically identical offspring from one parent

Question 2

What are the advantages of sexual reproduction?

Answer 2

• faster method of reproduction
• only one organism is required
• good characteristics of parent will be passed down
• less energy required

Question 3

What are the disadvantages of asexual reproduction?

Answer 3

• no variation
• genetic mutations are passed on
• hereditary diseases are passed on
• species cannot adapt if the environment changes

Question 4

List four types of asexual reproduction

Answer 4

• vegetative propagation (natural or artificial)
• tissue culture
• binary fission (in bacteria)
• spore production (in fungi)

Question 5

Describe asexual reproduction in bacteria

Answer 5

Binary fission

• Bacterium divides into two
  
  • DNA replicates
  • Cell splits into two
  • Each cell grows bigger and is now identical to the parent
• The generation time is the time taken for a cell to divide into two

Question 6

Describe asexual reproduction in fungi

Answer 6

Spore production

• Spores land on a food source and produce a network of threads (the threads are hyphae, the network is the mycelium)
• Vertical hyphae grow up and form a tip called a sporangium/spore capsule
• This has many nuclei which become spores
• Each spore contains cytoplasm and one or more nuclei, depending on the species

Also: see classification - fungi

Question 7

Describe asexual reproduction in potatoes

Answer 7

Tuber formation

• A potato plant starts as a lateral bud (seed) under the soil.
• In favorable conditions, a shoot grows out from the bud vertically, which then becomes the stem of the plant above the soil. Roots also grow out of the bud downwards into the soil. The bud is now a plant.
• The stem then grows a part of it under the soil, which is called underground stem. Swellings start to grow from the underground stem; these swellings are called tubers which are the new potatoes. Glucose formed by photosynthesis in the leaves of the above ground stem is converted into sucrose and transported down the stem to the tubers to be stored there as starch.
• When the tubers are fully grown the mother plant dies and the new lateral buds form on the tubers. These buds then grow into new potato plants identical to the mother plant.

Question 8

Define

sexual reproduction

Answer 8

Sexual reproduction is a process where two haploid nuclei (gametes) fuse to make a diploid zygote of genetically dissimilar offspring.

Question 9

What are the advantages of sexual reproduction?

Answer 9

• variation is possible as each new organism receives a different set of genes from the two parent organisms
• offspring may not inherit harmful genes

Question 10

What are the disadvantages of sexual reproduction?

Answer 10

• slower method of reproduction
• requires two organisms/parents
• some combinations of genes may produce less successful individuals
• not always reliable

Question 11

What is the function of the petals?

Answer 11

Attracts pollinators, e.g. bees and animals, as they are colourful and scented.

Question 12

What is the stamen?

Answer 12

The male reproductive organ containing the anther and filament.

Question 13

What is the function of the anther?

Answer 13

Produces pollen grains.

Question 14

What is the function of the filament?

Answer 14

Holds the anther in a favourable position.

Question 15

What is the carpel?

Answer 15

The female reproductive organ containing the stigma, style and ovary.

Question 16

What is the function of the stigma?

Answer 16

Receives the pollen grain. It may be sticky or have hairs/spikes to hold the pollen in place.

Question 17

What is the function of the style?

Answer 17

Holds the stigma in a favourable position. It connects the stigma and ovary, providing a passage the the pollen tube can grow down.

Question 18

What is the function of the ovary?

Answer 18

Produces and contains ovules and egg cells.

Question 19

What is the function of the ovule?

Answer 19

Produces the egg cell.

Question 20

What is the function of the nectary?

Answer 20

Produces nectar to attract pollinators, e.g. bees.

Question 21

What is the function of the sepals?

Answer 21

Protect the flower when it is in the bud stage. It also undergoes photosynthesis.

Question 22

Define

pollination

Answer 22

The transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma).

Question 23

What is the difference between self-pollination and cross-pollination?

Answer 23

Self-pollination:

The pollen grain transfers from the anther to the stigma of the same flower.

Cross-pollination:

The pollen grain transfers from the anther to the stigma of a different flower of the same species.

Question 24

What is self-pollination preferable to cross-pollination?

Answer 24

Cross-pollination increases variation as the genes of different plants are combined, which increases the chance of the species’ survival as some plants will be able to adapt to a changing environment.

Question 25

What methods may plants use to encourage cross-pollination?

Answer 25

• The stigma may grow taller than the stamens so pollen cannot fall onto it.
• The stigma and anthers can mature at different times.
• The plant can have different flowers for male and female parts.

Question 26

How are insect-pollinated plants adapted in terms of the following characteristics?

• Petals
• Scent and nectar
• Number of pollen grains
• Pollen grains
• Anthers
• Stigma

Answer 26

• Petals are large and brightly coloured to attract insects
• Usually scented and with nectar to attract insects
• Moderate number of pollen grains (insects transfer pollen grains efficiently)
• Sticky or spiky pollen grains (stick to insects well)
• Anthers are inside flower, stiff and firmly attached to brush against insects
• Stigma is inside flower and sticky, so pollen grains stick when an insect brushes past

Question 27

How are wind-pollinated plants adapted in terms of the following characteristics?

• Petals
• Scent and nectar
• Number of pollen grains
• Pollen grains
• Anthers
• Stigma

Answer 27

• Small petals, often dark green or brown (no need to attract insects)
• No scent or nectar
• Large amounts of pollen, as most are not tranferred to another flower
• Smooth and light pollen grains (easily carried by wind and won’t clump together)
• Anthers hang outside flower, loose on long filaments (more anthers than on insect-pollinated flowers)
• Hairy/feathery stigmas hang outside flower, forming a network to catch drifting pollen grains.

Question 28

What stimulates the pollen tube to grow when it is on the stigma?

Answer 28

Chemicals (lipids, sucrose) at the surface of the stigma stimulate the pollen grain to grow a pollen tube.

This attraction to chemicals is known as chemotaxis.

Question 29

How does the pollen tube grow down through the style?

Answer 29

This starts by the stigma secreting chemicals that start a pollen tube. At the tip of the pollen tube, enzymes are secreted that digest the tissue of the style digging the pollen tube further down till it opens on the other end in the ovule. The growth of the tube is controlled by a tube nucleus at the tip of the tube. The male gamete enters the pollen tube and starts its journey downwards to the micropyle of the ovule.

Question 30

Why do pollen grains only produce tubes in flowers of their own species?

Answer 30

This is because the pollen tube will only grow with the right chemicals on the stigma. If a pollen grain falls on the stigma of a flower of a different species, the stigma will not secrete the chemicals to start a pollen tube and fertilization fails.

Question 31

When does fertilisation occur?

Answer 31

After the pollen tube is grown and the nucleus of the male gamete fuses with the nucleus of the female gamete in the ovule.

Question 32

What type of division occurs to produce an embryo plant from the diploid zygote formed after fertilisation?

Answer 32

Mitosis

Question 33

Which parts of the plant wither away after fertilisation?

Answer 33

• petals
• sepals
• stamens
• stigma & style

Question 34

What happens to the parts of the plant that do not wither away after fertilisation?

Answer 34

• Egg cell becomes the zygote
• Ovule becomes the seed
• Ovary becomes the fruit

Question 35

How does a seed become dormant?

Answer 35

A seed becomes dormant when it is dry and the enzymes are deactivated. The seed is metabolically inactive and can survive for a long period of time.

Question 36

What are the four mechanisms of seed dispersal?

Answer 36

1. Wind (e.g. sycamore has wings and is light)
2. Water (e.g. coconut is hollow and has a waterproof case and fibres to make it buoyant)
3. Animals (e.g. blackberry gets eaten and egested, burdock has hooks to attach to fur)
4. Mechanical/Explosion (e..g. lupin dries unevenly and splits open)

Question 37

Why do seeds need to be dispersed away from the parent plant?

Answer 37

• reduce competition for water, sunlight and mineral salts
• reduce overcrowding
• colonise new areas

However, a seed may land in an area unsuitable for its growth, and there may not be other plants nearby to fertilise it when it is grown.

Question 38

Label parts A - E

Answer 38

• A: radicle - root
• B: micropyle - small hole through which pollen tube entered, important route for water and oxygen entry
• C: plumule - shoot
• D: cotyledon - food reserves with starch
• E: testa - tough seed coat, protective layer