2.4 Reproductive Strategies

Key Themes

• 2 Types of reproduction (sexual & asexual)• Both internal and external fertilisation• Adaptations to life on land– Eggs (birds and reptiles)– Internal gestation (mammals)– Insects

• Flowering plants

Asexual reproduction

• Individuals are genetically identical (clones)• Cells with diploid number are produced by

mitosis• Advantages:

• Disadvantages:

Sexual reproduction

• Produces offspring that are genetically different

• Haploid cells or gametes are produced by meiosis

• Advantages:

• Disadvantages:

• Males and females produce different sized gametes

• Fertilisation involves the fusion of a haploid sperm and a haploid egg

diploid zygote

• Most aquatic beasties undergo

External Fertilisation– will lay eggs (sometimes in a nest)– then spread sperm over those eggs

Internal fertilisation

• Advantages:

• In many animals the fertilised egg / zygote actually develops outside of the body– Examples?

• When this is the case, a large number are produced to increase survival

Adaptations to life on land

• Amphibians• Reptiles• Birds• Mammals

All these _____ show increasing adaptations for colonising the land

Reptiles and Birds

• Evolution of the amniotic egg• Anatomy of the egg:– Fluid filled cavity– Membrane– Protective shell– Encloses embryo

inside the yolk sac • Birds incubate eggs, the embryo completing

development outside the mothers body

Mammals

• Young are retained in uterus / womb without a shell

• Embryo is nourished there from mother’s blood supply via a placenta

• Means that young can be born fairly well advanced in terms of development

discussion point: Different species have diff strategies on this

Parental care

• What animals exhibit parental care?• What are the advantages?• How many offspring do your examples have?• Name something that has no parental care…• How many offspring does that have?

*As degree of parental care increases, number* of offspring decreases

Insects

• Abundant, Diverse & Widespread

Insects lives and lifestyles affect almost all other terrestrial organisms

• Insect zygotes develop into an intermediate form (nymph or larva) before becoming an adult

NymphsNymphs resemble the adults

They go through several moults (instar)

Incomplete metamorphosis

LarvaeDifferent from the adult form

Larval stage followed by pupa

Then complete metamorphosis into the adult

Flowering Pants

• Flowering Plants are well adapted for life on land in terms of their morphology and reproduction

• They have similar reproductive strategies to animals for colonisation.… what are they?

http://www.videopediaworld.com/video/22961/11-30-the-private-life-of-plants--03--

flowering

Plant relationships

• Key to plant success is their relationship with animals:– Pollination– Seed Dispersal

The Seed

• Food store enables embryo to develop until leaves are produced

• Resilient coat allows it to withstand adverse conditions