Animal reproduction
7Ba(4)
1 In 1694, a Dutch scientist called Nicolas Hartsoeker discovered sperm cells in humans and other animals. He believed that he could see tiny people inside the sperm cells and that these then grew into babies inside women. This was called the homunculus theory. a What piece of apparatus do you think Hartsoeker used to make his discovery?
7 B a
b A good theory is able to explain many observations. Which of these observations can the homunculus theory not explain? X People look like their fathers and their mothers. Y Babies grow inside women. Z Sperm cells are needed to produce a new animal life. c Hartsoeker drew sperm cells to show that the homunculus theory was correct. He published these drawings. What would you do to show that Hartsoeker’s drawings were incorrect? 2 What are the advantages and disadvantages of internal and external fertilisation? You could think about: • the amount of energy needed to produce lots of egg cells • the numbers of egg cells and sperm cells that are wasted • how much time and effort it takes to find a mate (some animals will just release sperm and eggs into the water in roughly the same place). Present your ideas as a table. 3 A female bullfrog will produce about 20 000 egg cells. Suggest two reasons why only about 5000 young are produced. 4 Make key points to compare the ways in which two animals reproduce – one mammal and one bird. Use books, CD-ROMs or the internet to find your information. Limit your key points to four sentences about each animal, which should summarise the most important points. Keep a careful record of where you find your information.
I CAN... Exploring Science
Unit02.indd 48
• use information to make comparisons • make reasoned suggestions to test theories and explain observations • carry out research on my own. edition
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