Fourth graders who learn about the blood pumping action of the heart across the arteries of the human circulatory system will find the "measure your pulse with a straw" interesting. The children are given a basic overview of how the heart functions and how different activities affect heartbeat rate. They are made aware of the various easy-to-check pulse points, namely the inner wrist, under the jaw bone and side of the neck. The children are encouraged to measure their pulse at varied time points (after relaxing, to get a resting heat rate, and after exercising, to get a rapid heart rate) by sticking clay on to a pulse point and then inserting the straw into the clay. The timed number of straw movements is recorded as a direct indication of the heart rate.
"Drinking plants" demonstrates how roots work against gravity and pull up water. Children dip a carrot into a cup of blue-colored water (food colorant mixed to water) and record the time before cutting up the carrot's lower sections to look for blue dots. A variant of this experiment is "capillary celery," in which fourth graders dip two lower ends of a celery stalk in two cups of water with food colorants (one with blue and other with red) and observe the colored spots in the bottom sections of the celery. This effectively teaches the concept of capillary action in plants.
Growing molds as a life science experiment is a way of introducing fourth graders to the microbial world. Put three pieces of bread in a sealed bag with a little water. Label and place the bags in three different environmental conditions; namely, a dark area, the refrigerator and in the sun. Encourage children to come up with their hypothesis by contributing their ideas on what would be the natural mold environment, which foodstuffs develop mold and what conditions are most conducive for mold growth. The bags are checked for any mold growth and the observations recorded to verify the hypothesis. Children learn that omnipresent spores grow into mold when provided with the most conducive environment, and that different molds have different growing conditions. They also learn that molds produce antibiotics that stop other spores from growing, but any moldy bread, cheese or cake should not be eaten.
The blubber experiment is a practical explanation for how the warm-blooded or endothermic animals (blue whales, seals and sea lions) keep themselves warm (all mammals are endotherms that generate heat to maintain body temperature). To make your blubber, fill Vaseline in the space formed in between two Ziploc bags that are placed inside one another (the second inner bag is reversed or turned inside out and aligned in order to enable the zipping of its edge with that of the first bag). Zip the adjacent lined-up edges of the two bags together; the edges of outer first bag are zipped to the edges of the inner second bag, and the Vaseline filled in the space between the two bags serve as the fat layer. This forms a pouch, or a makeshift blubber glove, to insert the hand. This is kept in ice water along with "control" bags with no Vaseline (two zip lock bags placed one inside the other and the inner one reversed inside out before zipping adjacent edges to form a pouch). Children place one hand in the makeshift blubber pouch (one with Vaseline) and the other hand in the control pouch (bags with no Vaseline) and record the time that they can keep it before feeling the cold. The temperature difference between the blubber and the control is also measured using a thermometer. The children learn that the blubber acts as an insulator and slows down the transfer of heat from animal body to water to protect it from cold.