Asexual Asexual & &

Sexual Sexual ReproductionReproduction

Asexual Asexual ReproductionReproduction Type of reproduction in which Type of reproduction in which

a new organism is produced a new organism is produced from from ONEONE parent and the parent and the offspring is offspring is identicalidentical to the to the parent.parent.

Occurs in most plants, Occurs in most plants, bacteria, protists, and low bacteria, protists, and low invertebrates.invertebrates.

Asexual Asexual ReproductionReproduction One parentOne parent Offspring Offspring

are identical are identical to the parents.to the parents. One

Parent

Identical Offspring

Asexual Asexual ReproductionReproduction Types of Asexual ReproductionTypes of Asexual Reproduction

BinaryBinary FissionFission – used by – used by bacteria, an organism bacteria, an organism whose cells do not whose cells do not contain a nucleus contain a nucleus copycopy then then dividedivide into two into two identical organismsidentical organisms Example: bacteriaExample: bacteria

Asexual Asexual ReproductionReproduction Types of Asexual Types of Asexual

ReproductionReproduction BuddingBudding – organism that produces – organism that produces

a bud that a bud that breaksbreaks awayaway to live on to live on its own.its own. Example: hydraExample: hydra

Asexual Asexual ReproductionReproduction Types of Asexual Types of Asexual

ReproductionReproduction RegenerationRegeneration – organism uses – organism uses

cell division to cell division to re-growre-grow body body parts.parts. Example: starfish, salamanderExample: starfish, salamander

Asexual Asexual ReproductionReproduction Types of Asexual Types of Asexual

ReproductionReproduction VegetativeVegetative PropagationPropagation – results in – results in

a new plant that is genetically a new plant that is genetically identicalidentical to the parent plant (a to the parent plant (a clone).clone). Examples: strawberry plant, Examples: strawberry plant,

vegetables, and crops.vegetables, and crops.

Asexual Asexual ReproductionReproduction Advantages and Disadvantages of Advantages and Disadvantages of

Asexual ReproductionAsexual Reproduction Advantages – Identical to parent, Advantages – Identical to parent,

so will get all so will get all goodgood characteristicscharacteristics.. Disadvantages – Identical to Disadvantages – Identical to

parent, so will also get bad parent, so will also get bad characteristics and is less able to characteristics and is less able to adapadapt to the t to the environmentenvironment..

Sexual Sexual ReproductionReproduction TwoTwo parents parents Offspring are Offspring are

a a combinationcombination of of bothboth parents parents and are and are therefore therefore differentdifferent from each parent.from each parent.

unique / diverse offspring

Two Parents

External Fertilization External fertilization occurs outside the female - the

male releases sperm cells onto the egg cells as the female lays them

External fertilization occurs in fish and most water dwelling animals (e.g. amphibians). These organisms usually produce a large number of sex cells which are released into the water.

There are usually courtship rituals which make sure the male and female sex cells are released near each other.

However, the chances of fertilization are very low, so huge numbers of eggs and sperm are needed to ensure enough offspring are produced

External Fertilization Why is it that organisms which produce by external

fertilization produce so many more sex cells?

The chances of fertilization are much lower in externally fertilized organisms, as the sex cells are further apart from each other: -

This means the sex cells are more likely to be predated

They can also be separated from one another (due to currents in water)

In external fertilization there is also less parental care, so the offspring are more likely to be killed (hence producing lots of them)

Internal Internal ReproductionReproduction Types of Sexual ReproductionTypes of Sexual Reproduction

PlantsPlants – when the reproductive – when the reproductive cells of one plant fertilize cells of one plant fertilize (pollinate) the (pollinate) the reproductive cells reproductive cells of another plant. This produces of another plant. This produces seeds that can grow seeds that can grow into a new plant.into a new plant.

Internal Fertilization Internal fertilization occurs inside the female

Internal fertilization occurs in most land dwelling organisms (such as mammals) - this is necessary as sperm need fluid in order to be able to swim to the egg (the fluid comes from semen, ejaculated along with the sperm from the male).

These organisms produce far fewer sex cells, as the chances of successful fertilization are much higher (the sex cells are much closer together when they are released)

Sexual Sexual ReproductionReproduction Advantages and Disadvantages of Advantages and Disadvantages of

Asexual ReproductionAsexual Reproduction Advantages – variety and/or Advantages – variety and/or diversitydiversity of of

offspring (color, shape, size, offspring (color, shape, size, intelligence, ability, etc.), More able to intelligence, ability, etc.), More able to adaptadapt to environmental changes. to environmental changes.

Disadvantages – uniqueness, sometimes Disadvantages – uniqueness, sometimes traits needed for traits needed for survivalsurvival are not are not passedpassed on.on.

Internal Fertilization Why then are there so few sex cells produced in internal

fertilization?

As the likelihood of successful fertilization is higher in internally fertilised organisms, because the sex cells are so much closer together, producing a great many sex cells would cause problems because: -

There is only a limited amount of space within the female’s uterus to accommodate a growing fetus

In internal fertilization there is a greater deal of parental care, so the offspring are more likely to survive (hence there is no need to produce lots of them)