UNIT 4:
Animal REPRODUCTION
Types of animal reproduction
Reproduction is the biological process by which living beings (progenitors) produce new organisms (offspring).
There are two main types of reproduction:
•Asexual reproduction: It requires just one parent. The offspring is genetically identical to the progenitor. It only
occurs in simple animals and plants. There are two types:
- Gemmation: The new organism grows on the parent’s body. Later it separates to live as a free individual
(ex. fresh water hydra) or remains attached to the parent to form a colony (ex. coral).
- Fragmentation: The new organism grows from a fragment of the parent. Fragmentation occurs in Planaria
worm, starfish and fungi.
•Sexual reproduction: It usually requires two parents, male and a female. They have different reproductive organs
called gonads which produce different reproductive cells. The offspring get a combination of the genetic material
from both parents. The individuals that carry out this type of reproduction can be:
- Unisexual: Each individual have only one type of reproductive organs.
- Hermaphrodites: Each individual has both male and female gonads.
But some animals can reproduce both sexually and asexually. This is the case of jellyfish. Most jellyfish pass through
two life phases during their life cycle: the polyp phase (with asexual reproduction) and the medusa phase (with
sexual reproduction).The polyp lives attached to the bottom whereas the jellyfish has an umbrella shaped body with
tentacles hanging from the border and lives free in the water.
1.- Make a diagram to summarize the text.
2.- Which of the following statements correspond to sexual reproduction? Which to asexual?
a)
b)
c)
d)
e)
f)
Descendants are identical to progenitors.
Requires two organisms.
Fertilization must occur.
The descendant’s characteristics are a mix of both progenitors.
Progenitors generate many descendants.
Progenitors can be hermaphrodite.
3.- Read the text and then complete the diagram naming the stages in jellyfish life cycle:
Jellyfish reproduction (www.jellyfishart.com/kb/jellyfish-biology/jellyfish-reproduction)
Male and female jellyfishes release sperm and eggs into the water, which join to make a microscopic
swimming larva called a planula. The planula swims until it finds a hard surface to attach to, such as a
rock or an oyster shell. Then it transforms into a small polyp that looks like a tiny sea anemone. After
several months, this polyp elongates and segment, which is also called strobilation. Each segment
separates as a free-swimming larva called an ephyra, which grows in size to become an adult jellyfish.
Planula
Strobiolating polip
Adult medusa
Ephyra
Polyp
Fertilized egg
4.- Put in order the steps of jellyfish life cycle:
a) The polyp feeds on passing, floating food.
b) Ephyra undergoes a series of morphological changings, such as the tentacle development and size increase
and within few weeks they become one centimeter wide jellyfish.
c) The fertilized egg (zygote) turns into a free-swimming larva called planula which floats in the current.
d) Within few months the jellyfish is able to reproduce: there are male and female jellyfish that respectively
produce sperm and eggs.
e) Polyp’s body divides into a pile of disc-shaped structures resembling a stack of coins.
1
f) Male medusa releases sperm and female medusa produces eggs so fertilization takes place.
g) The tiny planula finds a place to attach itself and turns into a polyp.
h) Each of these discs detaches from the pile. These structures are called ephyrae and float away in the sea.
5.- Use some of the sentences in exercise 4 to describe what is happening in this animation:
https://www.youtube.com/watch?v=oHiVA9J_YIM