This is an extensive and detailed set of notes for each Year 12 Module (5, 6, 7, 8), complete with diagrams and explanations to guide and facilitate your understanding of the Year 12 Biology Syllabus. The notes are structured according to the syllabus so that each dot point is answered in depth.
Reproduction
Inquiry question: How does reproduction ensure the
continuity of a species?
● Explain the mechanisms of reproduction that ensure the continuity
of a species, by analysing sexual and asexual methods of
reproduction in a variety of organisms, including but not limited
to:
● Reproduction: evolutionary process of a chemical system making copies of itself
● Reproductive success: an organism’s ability to produce fertile offspring that can
survive, mature, and produce their own offspring
● Biological fitness: a measure of an individual’s reproductive success
○ Calculated as the average contribution to the gene pool made by a certain
genotype in a population, and the relative likelihood that those alleles will be
represented in the future
■ Alleles with higher fitness are more likely to be represented in future
generations
- Animals: advantages of external and internal fertilisation
● Requires two parents
● Produces offspring distinct in offspring
● Requires meiosis and production of haploid gametes (n)
● Common in vertebrates
,● Asexual reproduction - one parent which produces genetically identical offspring,
common in invertebrates, requires mitosis and produces 2n cells (diploid number of
chromosomes)
○ Advantages:
■ Passing on 100% of of genetic material to offspring (as opposed to 50%
in sexual reproduction) → favourable in stable environment
■ No competition/no need to expend energy and time to find a mate
■ Faster and more energy efficient → favourable in stable environments
○ Disadvantages:
■ Low genetic diversity - if there is a selection pressure they would not
survive as they will all respond to the selection pressure the same way
○ Parthenogenesis: the female produces eggs which develop into young without
ever being fertilised
■ Occurs in some fish, insects, amphibians
■ Produced from combination of two ova from the same parent, but
crossing over in meiosis creates variation
○ Fragmentation: adult animal spontaneously and purposefully breaks up itself to
produce exact copies of itself
■ Occurs in invertebrates like planarian flatworms
○ Regeneration: if a part of the animal is cut off and contains enough genetic
information, it can develop into a new individual
■ Occurs in sea stars
● Sexual reproduction - two parents produce offspring which have a mix of the
parents’ genes (and hence are different)
○ Advantages:
■ Greatest advantage - genetic diversity → some offspring may have
random variations that make them better adapted to the environment →
they will be able to gain selective advantage over other individuals
● When the environment changes, the adaptations may allow the
species to have a greater chance of survival
○ Disadvantage:
■ The process requires more time and energy → before producing young,
there are processes like finding a mate, courtship, gamete producing,
and mating → these processes may make organisms more vulnerable to
predators
● For successful fertilisation of ova by sperm, the gametes must meet without
dehydrating in the process; fertilisation is the fusion of two haploid gametes to form
a diploid zygote (the first cell of a new organism), which restores the normal number
of chromosomes (haploid has n - two haploid gametes = 2n = diploid)
, ○ Hence external fertilisation is better suited to organisms in an aquatic or
moist environment; internal fertilisation is better suited to organisms in a
terrestrial environment
● External fertilisation:
○ The egg is fertilised outside the female’s body - many male and female
gametes are released into the surroundings in which some fuse to form a
zygote
○ Occurs in amphibians, fish, coral, plants
○ Advantages:
■ Less time and energy are required from the parents as there is less
parental care
■ Wider dispersal of young
● Reduces food and spatial competition and allows the population to
establish in different areas
● Greater genetic variation can be achieved through mating
○ Disadvantages:
■ Gametes may be eaten by predators
■ In aquatic environments, although currents can disperse young, they can
also sweep away gametes and prevent fertilisation
● Internal fertilisation (usually in terrestrial organisms)
○ Practised by species that lay shelled eggs or have a period of internal
embryonic development (gestation)
○ The egg is fertilised inside the female’s body - female mammals (except
monotremes) develop an embryo inside the body
○ Reptiles and birds lay eggs after fertilisation which develops outside the
female’s body
■ Extra protection increases the chance of survival
○ Male and female must be in close proximity to each other
○ Reproductive cycles
■ There are times when they are fertile (oestrus)
■ Often timed so that the offspring will be born when temperatures are
warm and food supplies are plentiful (so chances of survival are
increased)
○ Advantages:
■ Protects gametes from dehydration
■ Protects gametes from loss to environment/external elements
■ Protects fertilised eggs and developing young from predation
■ Fewer eggs are required for the survival of a sufficient number of
offspring
■ High probability of fertilisation
, ○ Disadvantages:
■ Need to expend energy to find a mate and care/protect offspring
■ Cannot disperse offspring easily
■ Limited space in reproductive tract → fewer offspring produced
■ Potential spreading of STIs
● Types of development:
○ Oviparous - egg develops a shell and is laid externally
○ Viviparous - egg becomes an embryo, nurtured in the female’s body to obtain
nutrients, and is born alive (occurs in most mammals)
○ Ovo-viviparous - a combination where eggs are retained in the mother’s body
until they are ready to hatch, where they are born alive
- Plants: asexual and sexual reproduction
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