Life Cycle - Plants (3A)
Pre Lab 

  • Investigating the requirements for plant growth.
  • Comparing different stages of germination.


  • germination
  • photosynthesis
  • transpiration
  • worksheet

Students use a worksheet to compare how different seeds grow.



The life cycle of a plant varies depending on the individual species. There are, however, certain requirements for life that most plants need. The growth of a plant is dependent upon light, water, oxygen, carbon dioxide, minerals in the soil, temperature and microbes in the soil. Light, water, and carbon dioxide are needed for photosynthesis which produces food for the plant. Oxygen is needed when it is dark, because the plant then needs oxygen to maintain itself. The correct temperature, soil, and minerals are all needed when the plant first germinates and subsequently grows. Soil helps bind the roots so the plant can anchor itself. Microbes in the soil include a number that are beneficial to plants. Microbial activity helps bring about the decay of organic material (dead plant material and animals) necessary for the production of soil. Temperature or light intensity varies for each type of plant, and this helps explain global plant distribution; light intensity or temperature also effects the rate of photosynthesis in plants; the time at which a plant flowers and the rate at which water loss occurs in a plant (transpiration.)

When these requirements are static for a seed, it will begin to grow or germinate. Sufficient food and minerals are stored in almost all seeds, so that these factors do not limit germination. As water is absorbed by a seed, the inner tissue swells more rapidly than the seed coat. The penetration of water allows the tissues to become hydrated and enzyme activity increases. The food that is stored in the cotyledons or the endosperms are now digested and used.


  1.  Instruct students to list some uses of plants: food, drink (cola, wine), lumber, clothes (cotton), medicine (aspirin) and paper (trees). Plants also release oxygen into our atmosphere which is then used by animals for respiration.
  2. Ask students to name some plants. There are hundreds of thousands of species of plants throughout the world. There are small plants and large plants; plants that live in water or land; and even plants that can survive and live in environments without soil.
  3.  Plants utilize seeds for reproduction. The seed is dormant until the right conditions allow it to grow. Review the diagram of the seed on the preceding page and discuss once more the requirements for plant growth.
  4. On the worksheet, have the students examine the different germinating seeds, including the squash, garden bean, pea seed, and corn grain. Instruct students to compare the 4 seeds and write down the differences and similarities that they observe.  

 In the squash, the cotyledons are lifted out of the ground and function as green leaves for a brief period. Garden beans have cotyledons which are lifted out of the soil, but they are bulky storage organs and do not function as leaves. In pea seeds the cotyledons remain in the soil. A germinating corn grain is really a fruit in which the seed coat is fused with the ovary wall.

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