ANSWERS: 1
  • Plants and animals are all different sizes because they have evolved to fill different niches. Size is based on environment and lifestyle, or how the species earns a living.

    Land Plants

    Land plants need to grow structural support and collect sunlight. Plants that use direct sunlight are usually taller, more slender and tougher than plants that use indirect sunlight, which are broader, closer to the ground and have softer tissues.

    Seaweeds and Algae

    Water plants are supported by water and do not need to grow structural support. Those deep underwater need to reach sunlight and tend to be tall and thin. Those near the surface often form mats only a few cells thick.

    Land vs. Water Animals

    Land animal sizes are constrained by physiology and gravity. Beyond a maximum size a land animal's organs would be crushed by its own weight. Water animals are supported by water, so their size is only limited by access to food.

    Warm Blooded Animals

    Birds and mammals must burn a great deal of fuel (food) in order to maintain their very high, steady body temperature. Warm blooded animals are constantly losing some of this heat through their skin.

    Cold Blooded Animals

    Cold blooded animals are not limited by the need to maintain body temperature and so can be any size or shape.

    Size Limits Within Species

    A species' size range is determined by genetics. The sizes of individuals are controlled by many factors, especially biological sex and early nutrition.

    Source:

    National Biological Information Infrastructure: Botany

    Animal Diversity; Cleveland P. Hickman, Jr., et al.; 2007

    Integrated Principles of Zoology; Cleveland P. Hickman, Jr., et al.; 2004

    More Information:

    Encyclopedia of Plants and Flowers

    All About Marine Biology

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