This is Kalanchoe daigremontiana, also known as Devil's Backbone or Mother of Thousands. Each of the tiny bumps on its leaves is a developing, new plant. When they are mature enough, they will separate from the parent plant, fall to the ground, and take root. This plant reproduces both asexually with its leaves, and sexually with its flowers. What is the advantage of sexual reproduction?

1. Sexual reproduction is faster.

   No. Asexual reproduction using its leaves is actually faster than sexual reproduction, and allows the plant to produce more offspring.

2. Sexual reproduction lets the plant produce more offspring.

   No. This plant produces more offspring by asexual reproduction than it does by seeds.

3. Sexual reproduction prevents the plant from passing on harmful mutations.

   No. Both sexual and asexual reproduction can pass a mutation on to the offspring.

4. Sexual reproduction gives the offspring genes from both parents.

   Yes! The main advantage of sexual reproduction is that the offspring gets half of its genetic material from each parent. This plant can reproduce asexually by producing the new, tiny plants on its leaves, but they are genetically the same as the parent. A disease or parasite which was fatal to one would be fatal to all. When it reproduces by flowers and seeds, half of the genetic material comes from the plant, and half comes from the pollen that fertilized seed. This produces offspring that have genetic variations, giving them a better chance of surviving. The survivors can then reproduce asexually to produce thousands of new plants with those traits.

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I wanted to test different amounts of fertilizer to see which was best for growing grass. I mixed water with different amounts of fertilizer, and then added sodium polyacrylate to change it into a gel. Then I sprinkled the grass seeds on top, and waited for them to grow.

I really need a control group for this experiment. What would I use for a control?

1. Water, fertilizer, and grass seed, without any sodium polyacrylate.

   No. For the control, we want to skip the thing we are testing for. We are not testing changes caused by the amount of sodium polyacrylate.

2. Water, sodium polyacrylate, and grass seed, without any fertilizer.

   Yes! We are testing to see how different amounts of fertilizer change the growth of the grass. The amount of fertilizer is the variable we are testing, so the control group should not have any fertilizer.

3. Water, sodium polyacrylate, and fertilizer, without any grass seed.

   No. For the control, we want to skip the thing we are testing for. We are not testing changes caused by the amount of grass seed, and we know that no grass will grow if we do not have any seeds.

4. Sodium polyacrylate, fertilizer, and grass seed, without any water.

   No. For the control, we want to skip the thing we are testing for. We are not testing changes caused by the amount of water.

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