Answer:The four main divisions of gymnosperms are Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta. Gymnosperms are often found in temperate forest and boreal forest biomes. Common types of gymnosperms are conifers, cycads, ginkgoes, and gnetophytes.
Explanation:
The statement above is false. The blood levels of calcium is regulated by parathyroid hormone.When one is not getting adequate calcium in one's diet and the blood level of calcium is low, the parathyroid hormone will be released. The parathyroid hormone can increase the blood calcium in several ways:
1. by stimulating osteoclasts which break down bone and release calcium into the blood stream.
2. by increasing the amount of calcium re-absorbed by the kidney before it can be excreted in urine.
3. by triggering the formation of calcitriol which increases the absorption of dietary calcium at the intestines.
Oh sweetheart. Leave the person if you're clearly not in love with them as they are with you. You're only hurting yourself, and that other person. They deserve someone who loves them as much as they love. And so do you! Be with whom you love, and set that other person free. Yes its not going to be easy, but life isn't easy. That's just part of life and growing up.
Mammalian fertilization comprises sperm migration through the female reproductive tract, biochemical and morphological changes to sperm, and sperm-egg interaction in the oviduct. Recent gene knockout approaches in mice have revealed that many factors previously considered important for fertilization are largely dispensable, or if they are essential, they have an unexpected function. These results indicate that what has been observed in in vitro fertilization (IVF) differs significantly from what occurs during “physiological” fertilization. This Review focuses on the advantages of studying fertilization using gene-manipulated animals and highlights an emerging molecular mechanism of mammalian fertilization.
