If a tree 50 meters (m) high has 30,000 leaves, the surface area of the leaves is 300 m2, and the amount of ground covered by the tree's canopy is 75 m2. The leaf area index (LAI) is
A) 4.
B) 6.
C) 100.
D) 400.
A
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Aldosterone is a hormone secreted by the adrenal cortex, and insulin is a peptide secreted by the pancreas
When aldosterone contacts a target cell, it binds to an intracellular receptor and migrates to the nucleus; insulin binds to extracellular receptors on the plasma membrane. What is the most likely reason for this difference? A. Aldosterone is hydrophilic and therefore must enter the aqueous environment of the cytoplasm to have an effect. B. Aldosterone is lipid-soluble and therefore easily crosses the phospholipid bilayer of the plasma membrane. C. Aldosterone is too small to bind extracellular receptors on the plasma membrane. D. Insulin is too large to interact with DNA.
The development of multicellular organisms likely originated
a. from colonies of unicellular organisms of the same species. b. from endocytosis of other cells followed by mitosis. c. from cooperation between different species of cells. d. from colonies of numerous species of cells. e. from endosymbiotic eukaryotes.
Viruses always lack which of the following?
A. organelles B. an envelope C. a protein coat D. genetic material E. None of the answer choices is correct.
Puberty in males marks the start of
a. sperm production. b. testosterone production. c. the emergence of secondary sexual traits. d. fertility. e. all of these.