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Diversity of Living Things - chapter 2

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Tracking Polar Bears. Polar bears are well adapted to life in the cold Arctic environment. Their thick fur and blubber keep them so well insulated that it is actually easy for them to overheat. They also have large paws that help them move around on the snow and sea ice, where they hunt, breed, and den. Similar to how snowshoes allow people to walk across snow without sinking, the large size of the paws helps distribute the bears' weight over a larger surface area.

Small bumps covering the pads of their feet and hair between the pads increase traction and help prevent polar bears from slipping on ice. They also have claws, which they use when running or climbing on ice and for gripping prey. In addition, they use their paws as paddles in the water. Polar bears primarily eat seals, although they may also hunt young walruses and beluga whales, and occasionally eat other foods such as reindeer, rodents, birds, vegetation, or garbage. Photosynthesis. It's not surprising that early scientists hypothesized that plants ate dirt. They didn't know, as we now do, how energy-rich sunlight is. Still, it seems remarkable that plants have evolved photosynthesis--the ability to harness the sun's energy to produce their own food. Photosynthesis is the process by which plants transform water and carbon dioxide (a gas that's plentiful in the air) into carbohydrates (sugars and starches), using the energy of sunlight.

While sunlight provides the energy needed to drive this reaction, a chemical in the leaves of plants makes the reaction possible. That chemical is a green pigment called chlorophyll. Chlorophyll is found inside the photosynthetic cells of plants, attached to the membranes of small, round structures called chloroplasts. As remarkable as photosynthesis is, the process is not very efficient. One of the most critical factors influencing the efficiency of photosynthesis is the amount (intensity and duration) of light that hits a leaf. The Mating Game. The most important thing an animal can do in its lifetime, at least in terms of evolution, is reproduce. An individual, regardless of how long it lives, contributes nothing to the evolution of its species unless it passes its genes on to the next generation.

Organisms reproduce in a wide variety of ways. Some reproduce asexually, producing offspring that are genetically identical to themselves. Many plants, including aspen trees and strawberry plants, reproduce this way at least some of the time. Other organisms, including humans and the creatures featured in this activity, produce offspring by a process called sexual reproduction. Scientists often refer to sex as a biological tradeoff. This genetic variation provides an important evolutionary advantage: It gives species (not individuals) the ability to evolve more quickly in response to challenging and constantly changing environmental conditions. Cell Division.