chapter 9: reproductive strategies

Question 1

compare sexual and asexual reproduction in terms of the number of parents and genetic makeup of offspring

Answer 1

• sexual reproduction usually involves two parents (sometimes more than two - sneaker) and the genetic makeup of offspring is different
• asexual reproduction involves one parent and the genetic makeup of offspring are all identical

Question 2

two methods of asexual reproduction in animals

Answer 2

budding and parthenogenesis

Question 3

describe the process of fragmentation

Answer 3

• occurs when an organism splits into fragments and each fragment can develop into a mature organism
• daughter organisms are smaller than the parent
• occurs in sea stars as well as plants with tubers (potato plants)

Question 4

describe the process of parthenogenesis

Answer 4

• reproduction without fertilisation and mostly involves the development of an unfertilised egg
• Offspring are produced from unfertilised eggs — no sperm is necessary
• These eggs are produced by mitosis and develop into offspring identical to the female parent.
• occurs in komodo dragons when necessary
• with no access to a mate, the female komodo dragon duplicates the DNA of the eggs to create a viable embryo

Question 5

two methods of asexual reproduction in plants

Answer 5

fragmentation and vegetative propagation

Question 6

describe the process of budding
(not sure if animal or plant - ask teacher)

Answer 6

• a new organism develops, through cell division, from an outgrowth of the parent
• occurs in sponges and hydra
• Sponges are able to reproduce from small groups of cells formed by mitosis that bud or break away from the main organism
• these are carried by currents to other locations where they settle and develop into new sponges

Question 7

describe the process of vegetative propagation

Answer 7

• cuttings:
  
  • some plants can be cloned by taking pieces of shoots, roots or leaves and planting them
• runners:
  
  • stem-like growths from the parent plant that run along the ground
  • New buds develop into roots, leaves, flowers and fruit
• rhizomes:
  
  • underground stems that grow horizontally
  • buds and roots sprout along a rhizome and produce new daughter plants.
    
    • can be distinguished from plant roots by the presence of buds, nodes and often tiny, scale-like leaves
    • Typically thick in structure because they have food reserve (starch)

Question 8

compare binary fission to mitosis

Answer 8

binary fission:

• prokaryotic organisms
• faster
• circular DNA
• no checkpoint - higher rates of mutation
• no spindle fibres
• used for reproduction

mitosis

• eukaryotic organisms
• slower
• linear DNA
• checkpoints
• spindle fibres attach to chromosomes
• used for growth, repair and replacement of old cells

similarities

• cytokinesis
• genetically identical daughter cells

Question 9

3 advantages of asexual reproduction

Answer 9

• can reproduce quickly
• no energy expended finding a mate
• do not have to rely on other organisms/means to spread pollen/seeds
• well-suited to the environment
• able to colonise cleared areas rapidly

Question 10

2 disadvantages of asexual reproduction

Answer 10

• Lack of genetic variation reduces the chance of a population adapting to new environmental conditions
• if conditions change, entire populations can be lost
• Pressure on availability of resources - reproduce rapidly so there will be competition for resources

Question 11

internal fertilisation

Answer 11

• occurs when males deliver sperm directly into the reproductive tract of females
• fertilisation of eggs occurs inside the body of females.

Question 12

features of internal fertilisation

Answer 12

• It has an energy cost of finding, attracting and securing a female mate.
• It has the benefit of increasing the chances of the gametes meeting, and therefore increases the chances of fertilisation.
• It occurs in some aquatic organisms as well as in terrestrial organisms.
• All terrestrial animals use internal fertilisation, except for amphibians, such as frogs that mate in the water.

Question 13

external fertilisation

Answer 13

• occurs when animals release their gametes into the external environment
• fertilisation occurs outside the body of females.

Question 14

features of external fertilisation

Answer 14

• Very large numbers of gametesare produced.
• Large numbers of gametes increase the chance of fertilisation but also mean there is gamete wastage.
• limited to animals that either live in aquatic environments or reproduce in a watery environment, as sperm need a watery environment to swim to an egg
• It occurs in aquatic invertebrates (such as coral polyps), bony fish and amphibians
• There are various strategies to increase the chances of fertilisation.

Question 15

3 advantages of sexual reproduction

Answer 15

• Genetic diversity within the species
• Variation increases survival chances if conditions change (as crossing over and independent assortment occur during meiosis)
• More traits to select for when choosing a mate (can pick the most desirable trait)— enabling natural selection to occur

Question 16

2 disadvantages of sexual reproduction

Answer 16

• Energy expended to find a mate
• Some organisms can be injured (or killed) in competition for a mate

Question 17

importance of variation

Answer 17

• variation is important in a changing environment because it enables features (adaptations) to arise that are suited to the new environment
  
  • adaptations: structural, behavioural or physiological feature that enhances the survival of an organism in particular environmental conditions.
• this means that they are better equipped to survive and reproduce in new environmental conditions (like natural disasters, bacterial diseases etc.)

Question 18

define ‘clone’

Answer 18

clones are genetically identical copies

Question 19

describe one method of cloning plants

Answer 19

tissue culture cloning

• begins with a small piece of leaf, bud or stem.
  
  • this tissue comes from a plant with specific desirable traits (flower colour, disease resistance)
  • they must contain meristematic tissue (only tissue capable of cell division)
• tissue is sterilised and placed in a sterile test tube with a culture medium (nutritive substance)
• treated with cytokinin → stimulates shoot formation by mitosis
• the sample is then incubated (controlled temp)
• subculturing occurs - new shoots are cut and placed in fresh culture tubes and are treated with cytokinin (repeated several times)
• hormone auxin is added to stimulate root production
• small plants with roots, stems and leaves develop
• plants are removed from culture and placed in sterile compost

Question 20

two methods of producing animal clones

Answer 20

embryo splitting and somatic cell nuclear transfer

Question 21

describe embryo splitting

Answer 21

• parents are chosen because of desirable characteristics such as high milk yield in dairy cattle, or muscle formation in beef cattle.
• typically, the embryos to be split are produced throughin-vitrofertilisation (IVF)
• using a very fine glass needle, an embryo at an early stage of development is divided into two smaller embryos
• the small embryos are identical, as well as the adults that develop from them.
• each small embryo is then implanted into the uterus of a surrogate female parent, where embryonic development continues

Question 22

describe somatic cell nuclear tranfer

Answer 22

1. the nucleus of a donor egg cell is removed, creating anenucleated cell (cell with the nucleus removed)
2. the nucleus of the individual to clone is added
3. an enucleated cell can be fused with a somatic cell using a short electrical pulse
4. the egg develops into an embryo

Question 23

what are the benefits of cloning for farmers

Answer 23

• Slow-growing plants can be produced in large numbers.
• Rather than relying on seasonal growth, plants can be cultured all year round in controlled conditions
• Virus-free tissue can be used to produce a large number of plants that do not carry the virus. (Viruses are responsible for many plant diseases)
• Cultured plants can be transported from country to country.
  
  • the sterile conditions where they are cultured ensure the plants are pest-free so that lengthy quarantine periods are avoided.

Question 24

why is human cloning illegal

Answer 24

• there is a very high level of opposition to the reproductive cloning of human beings
• Over 30 countries,including Australia, have banned experiments directed to producing human clones
• has a variety of ethical issues such as
  
  • the safety of the procedure
  • commodification of human life