Life Sciences Grade 12: Reproductive Strategies and Fertilisation Study Notes
Reproductive strategies
Two main types of reproductive strategies:
r-strategy: organisms produce many offspring with little parental care; high juvenile mortality but enough survive to maintain the species.
K-strategy: organisms produce fewer offspring but invest heavily in parental care; offspring have a better chance of surviving to adulthood.
Examples: turtles (r-strategy with many offspring, little parental care); lions and elephants (K-strategy with substantial parental care).
Survivorship curves:
Illustrates the number of organisms that survive at different stages of their life span.
In functional terms, often linked to the two strategies: Type I (K-selected species) vs Type III (r-selected species).
Notation: let S(x) denote the number of individuals surviving to age x.
Overview of reproductive strategies:
Animals use various reproductive strategies to increase reproductive success.
These strategies are structural, functional and behavioural adaptations to increase the chances of fertilisation and survival of offspring.
Key strategies covered:
Courtship
External vs Internal Fertilisation
Ovipary, Ovovivipary and Vivipary
Amniotic Egg
Parental Care
Courtship
Courtship is the behavioural patterns of male and female animals that lead to mating and offspring.
Purpose:
Ensures both sexes are ready for mating.
Helps identify mating partners.
Helps to choose suitable mating partner.
Courtship takes place in various ways:
Visual stimuli
Sound stimuli
Chemical stimuli
Physical movements
Courtship examples:
Visual: male peacock using his colourful tail feathers to court the female.
Sound: male frogs make sounds to attract females.
Chemical: female lions secrete pheromones to signal sexual maturity and attract males.
Physical movements: scorpions perform a mating dance; male eagles perform aerobatics; male tortoises massage the females.
External vs Internal Fertilisation
Fertilisation is the fusion of the egg and sperm to form a diploid zygote:
The general idea: fertilisation produces a zygote with ploidy 2n.
Two types:
External fertilisation: fertilisation occurs outside the female body; water is required to keep gametes moist and as a medium for sperm to swim to the egg; no physical contact between parents necessary.
Internal fertilisation: fertilisation occurs inside the female body; male deposits sperm inside the female reproductive organs; no water is required; adaptations favor terrestrial life; fewer gametes produced due to higher fertilisation success.
Examples of organisms:
External fertilisation: frogs and fish.
Internal fertilisation: birds and mammals, including humans.
The importance of water in external fertilisation:
Keeps eggs moist to prevent desiccation.
Medium in which sperms swim to the egg.
Terminology summary (Key terms):
Fertilisation: process during which the sperm fuses with the egg to produce a diploid zygote. Use in sentence: Fertilisation results in the formation of a zygote.
External fertilisation: fertilisation outside the female’s body. Use: During external fertilisation all the sperms may not reach the egg.
Internal fertilisation: fertilisation inside the female’s reproductive organs. Use: Internal fertilisation is a more certain process.
Ovipary: eggs laid and development occurs outside the mother’s body. Use: Lizards and turtles are examples of animals that undergo ovipary.
Internal fertilisation details:
Fewer gametes are produced; fertilisation success is higher; adaptation for terrestrial life.
Examples: birds and mammals, including humans.
Ovipary, Ovovivipary and Vivipary
Ovipary (egg-bearing):
Eggs laid and development outside the mother’s body.
Eggs may be fertilised internally or fertilised outside after laying.
The egg hatches into a young animal.
Most invertebrates and many vertebrates reproduce this way.
Examples: pythons and hens.
Ovovivipary:
Eggs are produced, but they develop within the mother’s body and may hatch within the mother’s body.
Internal fertilisation has taken place.
The young get nutrition from the yolk, not the mother.
Examples: puffadder and reptiles.
Vivipary:
Young develop inside the mother’s uterus after internal fertilisation.
During development, the young receive nutrients from the mother’s blood via the placenta.
Parental care takes place.
Examples: hammerhead sharks and humans.
Terminology recap (definitions):
Ovovivipary: eggs develop within the mother’s body and hatch inside the mother’s body before being born.
Vivipary: young develop inside the mother’s uterus with placenta nourishment and parental care.
Ovipary: eggs laid with development outside the mother’s body.
Parental care: ways in which parents increase the chances of survival of their offspring.
Amniotic Egg
All amniotes form eggs with extra-embryonic membranes after fertilisation; membranes are filled with fluid; example – a chicken egg.
Importance of the amniotic egg:
The shells reduce dehydration (waterproof).
Enables terrestrial living across a wide range of habitats; no need to be near water.
Shell provides protection for the organism.
The egg nourishes the organism via the yolk sac.
Increases chance of survival.
Amniotic membranes (summary):
Extra-embryonic membranes support the developing embryo by providing protection, waste management, gas exchange, and nutrients (in the yolk or via placenta, depending on type).
Parental Care
Parental care refers to the ways in which parents increase the chances of survival of their offspring until they reach sexual maturity.
Examples of parental care:- Guarding eggs
Incubation of eggs
Keeping young warm
Feeding young
Protection from predators
Terminology (Key terms) – quick reference
Fertilisation: process during which the sperm fuses with the egg to produce a diploid zygote.
External fertilisation: fertilisation outside the female’s body.
Internal fertilisation: fertilisation inside the female’s reproductive organs.
Ovipary: eggs laid and development outside the mother’s body.
Ovovivipary: eggs develop inside the mother’s body and hatch inside the mother before birth.
Vivipary: young develop inside the mother’s uterus and are nourished via placenta; parental care.
Parental care: ways in which parents increase the chances of survival of their offspring.
Practice questions (with answers)
1) Method of reproduction in which the foetus is nourished through an umbilical cord is…
A: Ovipary
B: Vivipary
C: Both A and B
D: Neither A nor B
Answer: B
2) The method of reproduction in which the young hatch from eggs outside the mother’s body…
A. Vivipary
B. Ovipary
C. Ovovivipary
D. None of the above
Answer: B
3) The liquid that protects embryo against mechanical shock…
A. Chorion
B. Allantois
C. Amnion
D. Yolk sac
Answer: C
4) Allows for gaseous exchange only…
A. Chorion
B. Allantois
C. Amnion
D. Yolk sac
Answer: A
5) Stores waste substances produced by the embryo…
A. Chorion
B. Allantois
C. Amnion
D. Yolk sac
Answer: B
6) Serves as food for the embryo …
A. Chorion
B. Allantois
C. Amnion
D. Yolk sac
Answer: D
7) Reduces dehydration…
A. Chorion
B. Allantois
C. Egg shell
D. Yolk sac
Answer: C
8) Fertilisation that occurs within the female body…
A. Internal fertilisation
B. External fertilisation
C. Both A and B
D. None of the above
Answer: A
9) Fertilisation that occurs outside the female body…
A. Internal fertilisation
B. External fertilisation
C. Both A and B
D. None of the above
Answer: B
10) Method of reproduction in which the young develop from eggs that are internally fertilized and retained within the mother’s body and hatch after development…
A. Ovovivipary
B. Vivipary
C. Ovipary
D. None of the above
Answer: A
Notes on the answer key: The sequence corresponds to the solution provided in the transcript: B, B, C, A, B, D, C, A, B, A.