Life Cycle - Plants (5B)
Pre Lab 

   
OBJECTIVES:
  • Exploring the diversity of plant reproduction.
  • Comparing and contrasting plant reproduction. 
VOCABULARY:
  • asexual
  • sexual
MATERIALS:
  • worksheet

Students look at how plants reproduce.

BACKGROUND:

Sexual reproduction in plants occurs when a detached reproductive cell unites with another reproductive cell. Unlike animals, plants do not have to have separate male and female sexes, in many plants both sexes are located on the same species. In asexual reproduction, the cell, tissue, or organ develops directly into a new organism. Sexual reproduction allows combinations of different genetic material to be introduced into a new individual (this is the method by which humans reproduce and provides for genetic rearrangement and assortment.) In asexual reproduction an exact copy is made from the mother cell, therefore, the genetic material remains the same. Vascular plants are more complicated than non-vascular plants. The development of complex tissues and organs in vascular plants to aid in the movement of water and food, created the need for different strategies to reproduce.

ASEXUAL REPRODUCTION OF NONVASCULAR PLANTS
Unicellular algae reproduce by the simplest type of reproduction which consists of cell division. In simple cell division, two daughter cells are produced from one mother cell. Some algae have asexual spores which produce specialized reproductive cells that are capable by themselves of producing new plants by cell division and growth.

ASEXUAL REPRODUCTION OF VASCULAR PLANTS.
Vegetative reproduction involves no special reproductive cells. One of the most common types of vegetative propagation occurs in plants with horizontal stems growing either above ground (runners or stolons) or underground (rhizomes). Several plants propagate vegetatively by tubers or the thickened, fleshy ends of rhizomes. Some plants have long slender stems that develop roots when they touch the ground. Bulbs such as those of onions form large buds that grow. Corms are the short, fleshy vertical underground stems have more stem tissue and smaller scale leaves than a bulb. Some plants reproduce by having horizontal roots while others have leaves that will start to ground. Some plants can propagate by cutting either stems or tubers into pieces that will grow. There are many different types of asexually reproducing vascular plants.

SEXUAL REPRODUCTION OF NONVASCULAR PLANTS.
Although not common, many small algae will reproduce sexually by forming specialized sex cells. This usually happens when the asexual cycle has terminated its cycle. (This is called alteration of generations.) Some spores are also formed by asexual means.

SEXUAL REPRODUCTION OF VASCULAR PLANTS.
Trees reproduce sexually through seeds (female) and pollen (male). Gymnosperms produce a naked seed whereas angiosperms (flowering plants) produce a true seed.

PROCEDURE:
  1. Plants provide an excellent means to review reproduction. Plants reproduce in so many ways that students will get a better understanding of the complexities needed to duplicate their own species. This will help students understand human reproduction.
      
  2. Review the different methods of plant reproduction. Make sure students remember the difference between vascular (more complex) and non-vascular (mainly bryophytes and algae) plants.
      
  3. On the students' worksheet have the students determine whether the organisms reproduce by sexual or asexual means

    Answers: Asexual: 1,3,5,6; Sexual 2,4,7,8

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