Direct Development
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Direct development is a type of life cycle in which the characteristics of the
offspring look very similar to those of the parents. Basically, the offspring are a
smaller version of the parents.
Organisms that undergo direct development will simply grow in size. They do
not drastically change form.
Examples of organisms that go through direct development include: dogs, cats,
horses, humans, alligators, birds, bats, monkeys, earthworms, spiders, and fish
(just to name a few).
Questions:
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What is direct development?
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How is direct development different than metamorphosis?
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Name 3 organisms that undergo direct development.
Metamorphosis
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Organisms that change form/shape at each stage of their life cycle are said to
undergo metamorphosis.
Metamorphosis can be broken down into two types: complete metamorphosis and
incomplete metamorphosis.
Complete metamorphosis has 4 stages: egg, larva, pupa and adult. During the
larval stage, the organism spends most of its time eating so it can store energy to
use during the pupa stage (when the organism does not appear to be moving
much).
Incomplete metamorphosis has 3 stages: egg, nymph, adult
In either type of metamorphosis, the adult stage is when the organism is
completely mature and able to reproduce.
Most insects undergo metamorphosis. Frogs also undergo metamorphosis.
Questions:
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What is metamorphosis?
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Which type of metamorphosis do butterflies undergo?
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How are complete and incomplete metamorphoses different?
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If your older brother said dogs go through metamorphosis, would he be correct?
Why or why not?
Life Cycle
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Plants and animals go through different stages during their lives. These stages of
growth and development are called a life cycle.
Organisms grow into mature adults which means they can reproduce and make
more organisms of the same kind.
Plants and animals have different stages as they develop into mature adults.
Life Cycles
Animal
s
Metamorphosis
Complete
Plants
Direct
Development
Incomplete
Seeds
Cones
Questions:
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What is a life cycle?
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Do all living things have life cycles?
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What two types of animal life cycles exist?
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What are the two types of plant life cycles?
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How are all life cycles similar?
Flowers
Spores
Plant:
Insect:
Seeds and Spores
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Most plants reproduce with seeds, however, ferns and mosses do not. They
reproduce with spores.
Seeds: Flowers and cones both contain seeds. Seeds are made up of three parts.
The seed coat surrounds the outside and protects the undeveloped plant inside.
Inside the seed are the embryo (undeveloped plant) and a supply of food for the
plant to use while it germinates. A seed will germinate (sprout) when the right
conditions for it to grow are present.
Spores: A spore is a single reproductive cell that grows into a new plant. Mosses
and ferns develop either a spore stalk or a spore case. The spore stalk/case has
hundreds of spores inside that they release. Each spore can develop into a new
plant.
Questions:
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What types of organisms begin their life cycle with a seed?
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What is a seed?
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What are the three main parts of a seed?
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What is a spore?
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How are spores and seeds different?
Fertilization / Pollination
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In order for organisms to produce offspring, fertilization must occur.
In fertilization, male reproductive cells unite with female reproductive cells.
In plants, the male reproductive cells are the pollen grains (yellow stuff) on the
stamen. The female reproductive cells (the pistil) are in the center of the flower.
For fertilization to occur in plants, the flower must first be pollinated.
Pollination is the transfer of pollen from the anther to the stamen to the pistil.
Wind, insects and animals aid in pollination by carrying pollen from one plant to
another.
Once pollination and fertilization have occurred, a seed forms inside the center of
the flower. This may develop into a fruit depending on they type of plant.
Questions:
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What is fertilization and why is it important?
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What is pollination and why is it important?
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How can plants be pollinated?
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Once pollination and fertilization occur, what happens?
Seed Dispersal
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Seed dispersal is the spreading of seeds away from the parent plant so they can
grow.
If seeds land right next to the parent plant, the seeds do not have a good chance of
growing.
Some plants produce seeds that are light or shaped like wings so that they can be
carried by the wind.
Many seeds are inside fruits. Fruits are often eaten by animals. Animals cannot
digest the seeds, so they are left in a new location to grow when release with the
animal waste.
Some seeds/fruits may fall in water. Water will carry these seeds to a new
location where they can grow.
Seeds may also be covered in a bur. The outside of the bur is rough and sticks to
the fur of passing animals. The bur will eventually fall off and grow in a new
location.
Questions:
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What does it mean for seeds to disperse?
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Why do seeds need to be dispersed from the parent plant?
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How do animals aid in the dispersal of seeds?
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How does the wind disperse seeds?