Module 5 Heredity.pdf - Inquiry Question: How does...

Inquiry Question: How does reproduction ensure the continuity of a
species?
● 1.1 - 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
1. 1.1a - animals: external and internal fertilisation
External Fertilisation Examples:
■ Stag horn coral: pheromones are released once coral spawns,
stimulating nearby individuals to spawn.
■ Palolo worm: shed their eggs and sperm within a two-hour period
annually, determined by the moon and tide, and a few hours after
complete darkness.
■ Fish: female lays eggs in the water and the male sheds sperm on top.
Some fish have special clasping structures to ensure egg fertilisation.
■ Amphibians: male frogs clamp onto the body of the female while she
lays eggs into the water, then the male sheds sperm directly onto
them.
Internal Fertilisation Examples:
■ Reptiles: have either a penis or a structure called a hemipenis. Both
deliver sperm into the females’ cloacae during mating. The egg then
leaves the females body through the cloaca. The shell, membranes
and other structures protect and nourish the embryo, keeping it moist
and safe during embryonic development.
■ Birds: fertilisation occurs internally, but the fertilised egg undergoes
most of its development externally, closely tended to by one or both
parents.
■ Mammals: three types of mammals: monotremes, placentals and
marsupials. Monotremes (platypus, echidna) are oviparous. Their eggs
are deposited outside the mother’s body after fertilisation to complete
their development. These eggs have more yolk than marsupials and
placentals, but less than reptiles. After hatching, the young feed on

milk from the mothers’ mammary glands. Marsupials don't lay eggs.
the young embryo is nourished by the yolk inside the uterus of the
mother, however there isn't enough yolk for full embryonic
development, therefore young are born at a very immature stage and
moved to the pouch of the mother. Here, they draw nourishment and
protection from the mother’s milk until fully developed. In placentals,
fertilisation occurs in the oviducts. The zygote then implants itself in
the uterine wall, where it begins development. The foetus receives all
nutrition and oxygenated blood from the female through the placenta,
which is attached to the fetus' abdomen via an umbilical cord.
2. 1.1b - plants: asexual and sexual reproduction
Asexual Reproduction Examples:
■ Bulbs: very short stems with closely packed leaves arranged in
concentric circles around the stem. A terminal bud will produce next
year’s flowering shoot and the lateral buds will produce new plants,
e.g., onions.
■ Rhizomes: stems which grow horizontally under the ground. The
terminal bud turns upwards to produce the flowering shoot and the
lateral buds may grow out to form new rhizomes, e.g., ginger.