1.3 - Growth Curves

Types of Plants Based on Life Cycles

Plants can be classified based on their life cycles.

• Annual plants
  • Plants that have only one life cycle for a season or a year.
  • Normally die after completing their biological cycle, from germination to flowering or production of seeds.
  • Examples of annual plants include paddy, pumpkin and watermelon.

• Biennial plants
  • Plants that need 2 years with 2 seasons of growth to complete their life cycle.
  • The first growth season is the vegetative growth where the roots, leaves and stems grow.
  • The second growth season is reproduction.
  • Most of these plants live in temperate regions.
  • After vegetative growth, the growth process stops during winter and resumes again during spring and summer for reproduction.
  • Plants produce flowers, fruits and seeds and eventually the plants die.
  • Examples of biennial plants are cabbage, carrot and silver cock's comb.

• Perennial plants
  • Plants that live more than 2 years.
  • Long lifespan (depends on the types of species and environmental conditions).
  • Can be categorized into woody perennial plants and herbaceous perennial plants.
  • Most of the plants can produce flowers and bear fruits many times throughout their lives.
  • Can adapt to the environment and changes in the surrounding temperature.
  • Examples of perennial plants are grass, hibiscus plant and mango plant.

Growth Curve in Plants

Can you recall the sigmoid curve for human and animal growth from Form 4 Chapter 15? The shape of the growth curve in plants is different based on a number of factors affecting it.

1. The growth curve of annual plants

   Figure 12 - The growth curve is a sigmoid curve. Stage A shows decreasing dry mass. The stored food in cotyledon is used for germination process. Stage B shows increasing dry mass. Here, the rate of growth increases rapidly. The plants carry out photosynthesis with the grown leaves. Stage C shows constant dry mass. The rate of growth is zero and the plants reach maturity stage. Stage D shows decreasing dry mass. The mass decreases slowly due to aging, low rate of photosynthesis, shedding of leaves and seed dispersal.

2. The growth curve of biennial plants

   Figure 13 - The growth curve has two sigmoid curves. During the first growth season , the plants produce leaves and carry out photosynthesis. The food produced is stored in tubers. During the second growth season , the food stored is used to produce flowers and seed.

3. The growth curve of perennial plants

   Figure 14 - The growth curve is a series of small sigmoid curves combined. The growth curve for every year is a sigmoid curve. Growth of plants happen throughout their lifetime. During spring and summer, the rate of growth is high. High light intensity maximizes the rate of photosynthesis. During winter, the rate of growth decreases.