natural selection?

Question

most cactuses have spines, which are leaves modified to protect the plant. the spines cover juicy stem that stores water. explain how cactus leaves and stems might have changed through the process of natural selection.

Answer 1

the dominant plants, the ones with spines survived, where others did not. it's that simple. Spines help retain water because they don't breathe and the plants with regular leaves lost too much water The pollination of the cacti by insects helped spead the growth of
spines to more cacti. They over time were the survivors and they became the dominate plant

Answer 2

Well, the cactus grows in dry areas, and would be a juicy snack for thirsty animals. So I guess the spines tell the animals to find their own water.
Somewhere somehow a cactus grew with a mutation in it's DNA causing it to have spiny leaves. Those leaves certainly are poor in photosynthesis, and such a cactus would have died without reproducing (and passing the "bad" DNA along) if it weren't for the fact that that particular cactus actually was better protected against predators and actually outlived it's competitors.

Etcetera.

Answer 3

The simple idea is this: The cacti which have spines reproduce more readily since they are eaten less than their broad-leafed counterparts.

However, keep in mind that natural selection can't create something that's not there. It can only promote that which is already present. There has to be something in the cactus' genetics which prompt the spines' growth.

Answer 4

well, most cacti live in the desert, so there isn't the problem of sun. now that they can survive with the lack of water, using their waxy stem to reduce transpiration, other animals will take advantage of them. in order to survive, the plants need protection. since the leaves are not needed for photosynthesis, they transformed so the cacti wouldn't be eaten by herbivores, and wiped out.

all cacti were forced to change and survived, compared to other plants that didn't survive. it is also known as survival of the fittest.

Answer 5

the spines came about as a defense mechanism of the plant to prevent animals from chewing on its leaves.

Answer 6

I'm not sure about natural selection on this one. Could be natural protection

Answer 7

Google it!