There is external and internal so I'll list th external. The most important is skin then mucus, sweat or secretion, hair, nails and tears which are all part of the integumentary. Some internal defenses are white blood cells and T cells.
It depends on your teacher, it should be A. It could be B if that’s what your teacher wants but I would go with A.
Answer:
DIFFUSION
Explanation:
Water, carbon dioxide, and oxygen are among the few simple molecules that can cross the cell membrane by diffusion (or a type of diffusion known as osmosis ). Diffusion is one principle method of movement of substances within cells, as well as the method for essential small molecules to cross the cell membrane.
This is called Homeostasis
They separate during meiosis I is true of tetrads.
Explanation:
In Prophase 1, tetrads are formed. Each chromosome has two sister chromatids. When two homologous chromosomes align for crossing over they have four parts and these are termed tetrads.
When homologous chromosome separate tetrads get broken. Tetrads are not present in mitosis because no crossing over takes place in mitosis.
In Anaphase 1 homologous chromosome separate by getting pulled by spindle fibres forming two haploid cells and tetrads get separate.