2. How do natality, morality and migration affect population size?

Population Size = (Immigration + Natality) – (Mortality + Emigration)

Explanation:

The change in the size of a population over time is determined by four key factors:

•  Natality:  Increases to population size through reproduction (births)

•  Immigration:  Increases to population size from external populations

•  Mortality:  Decreases to population size as a result of death

•  Emigration:  Decreases to population size due to loss to external populations

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answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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