What happens when atp binds to myosin heads during muscle contraction?
a. calcium ions are released from the sarcoplasmic reticulum.
b. calcium ions are taken up by the sarcoplasmic reticulum.
c. cross-bridges between myosin heads and actin filaments are broken.
d. myosin heads form cross-bridges with actin filaments.

Use this diagram of an animal cell to answer the question. where does the first stage of cellular respiration occur? w x y z

This is due ! matching pairs of chromosomes from parents are called a. homologous chromosomes b. heterozygous chromosomes c. herterogenes d. homologous bands

Aparent with freckles is crossed with a parent without freckles. the punnett square shows the possible genotypes and phenotypes of the offspring. which statement accurately describes the probability of phenotypes? a.the offspring are more likely to have freckles. b.the offspring are more likely to have no freckles. c.the likelihood of the offspring having freckles and not having freckles is the same. d.the likelihood of the offspring having freckles and not having freckles cannot be determined.