Please help me with these ecology questions! Thank you 21. Fertilizers provide plants with
a. nitrogen.
b. carbon.
c. water.
d. oxygen.
22. Which of the following convert(s) nitrogen from air into a form plants can use?
a. bacteria
b. lightning
c. sunlight
d. both a and b
23. Plants use nitrogen to make
a. carbohydrates.
b. nitrogen gas.
c. amino acids
d. both b and c.
24. An animal returns nitrogen to the environment when it
a. breathes.
b. decomposes.
c. urinates.
d. both b and c.
25. Animals get phosphorus from
a. the air.
b. eating plants.
c. water.
d. the soil.
26. Phosphorus in the soil comes from
a. rocks.
b. decaying organisms.
c. the air.
d. both a and b

One statements is an example of a scientific observation. another statement is an example of a scientific explanation. identify the correct statement for each category to illustrate how scientific explanations are inferred from scientific observations.

Mouse liver cells were homogenized and the homogenate subjected to equilibrium density-gradient centrifugation with sucrose gradients. fractions obtained from these gradients were assayed for marker molecules (i.e., molecules that are limited to specific organelles). the results of these assays are shown in the figure. the marker molecules have the following functions: cytochrome oxidase is an enzyme involved in the process by which atp is formed in the complete aerobic degradation of glucose or fatty acids; ribosomal rna forms part of the protein-synthesizing ribosomes; catalase catalyzes decomposition of hydrogen peroxide; acid phosphatase hydrolysis monophosphoric esters at acid ph; cytidylyltransferase is involved in phospholipid biosynthesis; and amino acid permease aids in transport of amino acids across membranes. a) name the marker molecule and give the number of the fraction that is most enriched for each of the following cell components: lysosomes; peroxisomes; mitochondria; plasma membrane; rough endoplasmic reticulum; smooth endoplasmic reticulum.

Astudent is looking through a microscope at some cells of an onion root tip. many of these cells are undergoing division since the root tip grows quickly and requires more cells. which cell most recently underwent metaphase? w x y z