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The Circle of Life

It's all happening at the pond.

Daily Living

All life begins. Living things all have a moment at which they become "alive." That beginning of life marks the first point on the circle of life. Each family of living things has its own life cycle. Some organisms, like some fast plants, are born, mature, and die rapidly. Other organisms, like bristlecone pine trees, have life cycles lasting for thousands of years.
Definition of Life
Forest Life Cycle
Bristlecone Pine
Wisconsin Fast Plants
The Amazing Story of Kudzu
What is a healthy forest?

Another organism with a rapid life cycle is the fruit fly. However, the fruit fly's life cycle involves a process of metamorphosis. During its life cycle, the fruit fly changes from one form to a completely different form. Butterflies are also well-known for their metamorphosis. During the fruit fly's life cycle, it changes from egg to larva to pupa to adult. Each of the four distinct life phases is a natural part of the life cycle. The egg of an adult female is fertilized by a male and then placed "in a nest" (usually in fruit) by the female. The egg soon hatches into a larva which is an immature animal. The larva of the fruit fly looks completely different than the adult. The larva eats (from the fruit) and grows. Soon, the larva enters into the pupa stage by covering itself with a protective case known as a cocoon. During the pupa stage, change takes place. When ready, the fully developed fruit fly comes out of the pupa. The mature adult fruit fly is now ready to reproduce and continue its life cycle.
Mutant Fruit Flies
Drosophila
HANDS ON Fruit Flies
The birth, growth, reproduction, and death of a fruit fly is quite rapid. In just a week you should observe the entire life cycle.
Once an organism begins its life cycle, it immediately faces survival needs. In order for it to achieve its full, natural lifespan, the organism must overcome many obstacles. Most living things require food, water, sunlight, and oxygen to survive and grow. Many living things also need minerals for healthy living. They get these resources in many different ways however. For example, flowering plants have roots, yet the root systems can vary. Monocots have many small roots spread out beneath the entire plant. Dicots have a single large, deep root that produces smaller roots. Monocots are better at absorbing water because the many small roots are constantly drawing in water. Dicots are more sturdy, stable plants because the large root serves as an anchor.
Monocots versus Dicots
Plant Encyclopedia
Invasive Weeds
Florida Plants Online
The Ultimate Citrus Page
Rocks and Minerals
HANDS ON Examine Your Roots
Help some seeds grow roots and consider the function of a plant's root system.
If these natural survival resources are not available, some living things will, over time, adapt to their environment and find a way to survive anyway. The process of adaptation occurs in all living things. For example, some plants that live deep below the surface of the ocean never see sunlight, yet they are able to survive.
The Plant Tracker
Hydroponics
Turfgrass Information Center

Sometimes, plants and animals that share a habitat find a way to share the natural resources, allowing both to survive. Many organisms live together in relationships where one depends upon the other. This interdependent relationship is known as mutualism.
The Yucca Plant and Yucca Moth: Mutualism

Even more common, however, is the relationship between plants and animals and the supply of oxygen. Through respiration, many animals take in oxygen and produce carbon dioxide. For many plants, the respiration process uses carbon dioxide to produce oxygen through photosynthesis.
What is Photosynthesis?
Why Study Photosynthesis?
Contact Information:
Photosynthesis Center
Arizona State University
Box 871604
Tempe, AZ 85287-1604

Animals have strong survival instincts. An instinct is a behavior with which an animal is born. For example, from birth, a puppy instinctively knows to suck milk from its mother. Instincts help animals find food, mate, reproduce, and raise their young. Survival instincts also lead animals to migrate or move to a better habitat. Some animals migrate only short distances. Others, like the wildebeest on the African Serengeti, are continually migrating great distances. Why do they migrate? To find better living conditions.
Animal Migration
Wildebeest

Instead of migrating, some animals instinctively protect themselves from changes in living conditions through hibernation. In seasonal habitats, some animals survive the winter by going into deep sleep during which the animal lives off of its stored fat and uses very little energy. This way, the scarcity of sunlight, food, and warmth don't risk the animal's survival. Bears are certainly the best known hibernators, but not the only.
Bears
The Bear Den
Bear Photos

Living things continually face threats to their survival and life cycle. Sometimes, the threats are natural and uncontrollable, like sudden changes in climate. For example, plants can be threatened by an unexpected drop in temperature. Sometimes, however, the threats are unnatural, manmade, and controllable. Pesticides, for example, threaten the survival of insects that feed on plants. However, animals that also feed on the plants can be threatened by the pesticide too. Yet, the animals need to be able to eat the plants. So, how to control the insects, protect the plants, and feed the animals all at once? Nematodes are one possibility. The nematode is a parasite that feeds on the insect without hurting the plant. Information
DDT: An Introduction
Beneficial Nematodes
Nematodes as Biological Control Agents

Survival is a daily challenge for all living things. Meanwhile, other concerns also must be addressed. Plants and animals reproduce at different stages of their life cycle and in different ways. Flowers, for example, have both male and female reproductive organs. The male organ, called the stamen produces pollen which, through pollination, gets moved and attached to the sticky pistil. The pollen then grows down into the pistil until it reaches the ovary which houses and protects the ovule. Once the male pollen cells join with female cells, fertilization occurs. The fertilized embryo grows into a seed that can grow into a new plant.

Many flowers require cross-pollination. The pollen from the stamen of one blossom is intended to fertilize the ovule of another blossom. If two tulips are growing side by side, the pollen from the first tulip should attach to the pistil of the second tulip. How? Most often the wind or insects transport the pollen from flower to flower. The bee is the best equipped agent of fertilization for the flower. The attractive color, scent, and flavor of a flower draw the bee to the pistil where it "drinks" the flower's juices. As the bee flies away, it touches the stamen, picks up some pollen, and carries it to another flower's pistil. This mutually beneficial relationship is known as symbiosis.
Symbiosis
Symbiosis and Co-Evolution
HANDS ON Fruits and Flowers
Dissect a flower and a fruit and consider the difference. You may gain a whole new perspective on produce.
For plants, reproduction is often the final stage of maturity. Death is the end of the plant's life cycle. Some animals also die right after they reproduce. Other animals, however, have an extended period of aging following reproduction. Eventually, however, all living things conclude their natural life cycle.
Animal Lifespans

Questions?
If you didn't find the answers to your life cycles questions, try searching Ask A Scientist.
Keywords and Cross-References:
adaptation (anatomy), adaptation (eating), adaptation (climate), birth, bristlecone pine, cocoon, death, dicots, egg, embryo, fast plants, fertilization, food, fruit fly, growth, hibernation, hydroponics, instinct (behavior), larva, life cycles, lifespan, maturity, metamorphosis, migration, minerals (non-living world), monocots, mutualism, nematodes, ovary, ovule, oxygen, pesticides, photosynthesis, pistil, pollen, pollination, pupa, reproduction (classification), reproduction (earthworms), respiration, roots, stamen, sunlight, survival, symbiosis (shared habitats), water

Curriculum Connections:
Macmillan/McGraw-Hill:
Unit 10, Lessons 1, 2
Unit 17, Lessons 1, 2, 5, 7
National Science Education Standards:
K-4 Life Science Content Standard C
K-4 Life Science Content Standard F
5-8 Life Science Content Standard C
K-4 Science as Inquiry Content Standard A
5-8 Science as Inquiry Content Standard A
K-4 Science in Personal & Social Perspective Content Standard F
5-8 Science in Personal & Social Perspective Content Standard F
Photosynthesis

Living Things