This isn't true. There are numerous factors as to when and why a cell divides; just a little bit of searching will return a great deal of information concerning the why and when.
This is true, but isn't the primary reason that a cell divides; I misinterpreted the question.
Growth and cell size does determine when cell division takes place. In short, the demands of the cell become to great for the DNA contained in the cell. Remember, the DNA contains the genetic code to produce the proteome that is needed to maintain the inter-workings of a cell. When the cell becomes to large, the proteome is not able to meet the requirements of the cell, which leads to division.
The link that I included in the source has a great deal of information concerning this.
The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.
DNA and RNA
Transcription. During the process of transcription, an enzyme called RNA polymerase binds to DNA at a gene's promoter, then begins unwinding the DNA and making a complementary strand of RNA from the exposed DNA template. Depending on the gene being transcribed, the result can be a molecule of mRNA (messenger RNA), tRNA (transfer RNA), or rRNA (ribosomal RNA). Each type of RNA performs a specific function later in translation.
rRNA
Ribosomal RNA (rRNA) along with ribosomal proteins make up ribosomes, the "workbenches" on which polypeptides (proteins) are synthesized. It turns out that it is actually rRNA, and not a protein, in the large subunit of the ribosome that performs the peptidyl transferase function of linking amino acids together via peptide bonds. In eukaryotes, the genes coding for rRNAs are located in the nucleolus of the nucleus. A ribosome has 3 binding sites: an A (aminoacyl) site, a P (peptidyl) site, and an E (exit) site.
mRNA
The message carrying the information needed to make a particular polypeptide exists in the mRNA molecule. It binds with a ribosome and the ribosome starts reading it one codon - 3 consecutive mRNA bases - at a time. Each of the possible 64 codons codes for a particular amino acid, or for a release factor (in which case it is a STOP codon). So the order of bases in the mRNA specifies the order in which amino acids are linked together to form a polypeptide.
tRNA
A tRNA molecule has 2 main sites. At one end it has an amino-acid attachment site and on the opposite end it has a 3-base anticodon. An enzyme (an aminoacyl-tRNA synthetase) recognizes the type of tRNA and attaches the appropriate amino acid to it, at which point the tRNA is said to be charged. Charged tRNA molecules "bump into" the empty ribosome A site, but only if there is a complementary match between the mRNA codon associated with that site and the anticodon on the tRNA does the charged tRNA dock.
Hopefully, that's enough...
Answer:
Hydrogen ion (H+) pumps work against their concentration gradient and therefore they need energy inputs from sources such as ATP
Explanation:
The hydrogen ion (H+) pumps are proteins that move protons across biological membranes. These pumps use energy in the form of ATP in order to generate a proton gradient on one side of the membrane. For example, in plants, H+ pump ATPases are able to generate an electrochemical gradient in the plasma membrane. In this case, the proton gradient is employed to drive secondary transport processes, thereby enabling the uptake of diferent metabolites such as nutrients, sugars, amino acids, etc., from the extracellular space.
True is the correct answer
