Easy-peasy Biology

MARCH 2020 P12 15 Which description of cell surface membrane permeability is correct? A An increase in the concentration of cholesterol molecules in the cell surface membrane can increase its permeability to hydrophilic substances.  B Cell surface membrane permeability to large hydrophilic molecules is high and can be increased by membrane transport proteins involved in facilitated diffusion.  C The permeability of the cell surface membrane to ions increases as the proportion of saturated fatty acid chains in the phospholipids increases.  D Without the presence of carrier and channel membrane proteins, the cell surface membrane has a low permeability to large polar molecules.  ANSWER D   In this question, we need to keep in mind that cell surface membrane has a low permeability to hydrophilic substances if transport proteins are not present since the phospholipid bilateral itself is hydrophobic in nature. Therefore, in A an increase in cholesterol molecules...

MARCH 2020 PAPER 12 : Which cell structures contain RNA?  1 centrioles  2 mitochondria  3 nucleus  4 ribosomes  A 1, 2, 3 and 4  B 1 and 2 only  C 2, 3 and 4 only  D 3 and 4 only ANSWER C The centrioles do not contain RNA. Mitochondria has a prokaryotic background thus it contains features similar to those of prokaryotes. Since prokaryotes contain RNA formed by transcription and translation( because prokaryotes also carry out the processes of protein synthesis), mitochondria which are evolved from prokaryotes, also contain RNA. The nucleus is basically the site of transcription where gene is transcribed to form mRNA. The mRNA is a form of RNA. Therefore, the nucleus contains RNA. Ribosome is basically a complex structure made up of rRNA and proteins. rRNA is a form of RNA. Thus, ribosome is also the correct option available. 5 It is possible for a bacterium to synthesise a eukaryotic protein.  This involves introducing a eukaryotic gene ...