Cell Biology

Step 1: Understanding blood circulation.
Arteries usually carry oxygenated blood, except pulmonary artery.

Step 2: Identifying the vessel.
The coronary artery supplies oxygen-rich blood to the heart muscles.
Coronary sinus and coronary vein carry deoxygenated blood.

Step 3: Conclusion.
Hence, the correct answer is coronary artery.

Step 1: Structure of a nerve.
A nerve is composed of many nerve fibres grouped together into bundles, and each structural level is protected by a connective tissue sheath.
Step 2: Coverings of nerve fibres.
A bundle of nerve fibres (fascicle) is covered by the perineurium. Several such bundles together are enclosed by the epineurium to form a nerve.
Step 3: Analysis of options.
(A) Incorrect — endoneurium surrounds individual nerve fibres.
(B) Correct — perineurium covers bundles and epineurium covers the entire nerve.
(C) Incorrect — endoneurium does not cover bundles.
(D) Incorrect — epineurium is the outermost covering.
Step 4: Conclusion.
The correct sequence is A – Perineurium and B – Epineurium.

Step 1: Understanding mesosome.
Mesosomes are infoldings of the plasma membrane in prokaryotic cells.
Step 2: Functional role.
They are believed to help in DNA replication, respiration, and distribution of chromosomes during cell division.
Step 3: Conclusion.
Thus, the correct statement is that mesosomes are involved in replication of DNA.

Step 1: Understanding membrane permeability.
A semi-permeable membrane allows solvent molecules like water to pass through while restricting solute molecules.
Step 2: Eliminating incorrect options.
Freely permeable membranes allow both solute and solvent, while impermeable membranes allow neither.
Step 3: Conclusion.
Hence, the correct term is semi-permeable membrane.

Step 1: Understanding polysomes.
A polysome or polyribosome consists of multiple ribosomes attached to a single mRNA molecule.
Step 2: Functional significance.
Polysomes increase the efficiency of protein synthesis by allowing simultaneous translation of the same mRNA.
Step 3: Conclusion.
Therefore, a polysome is a group of ribosomes.

Step 1: Understanding lysosomes.
Lysosomes are membrane-bound organelles that contain enzymes responsible for digesting cellular waste and debris. They are single membrane-bound and originate from the Golgi apparatus.
Step 2: Analyzing the options.
(A) single membrane bound, Golgi apparatus: Correct — Lysosomes are single membrane-bound organelles that originate from the Golgi apparatus, where they are formed and then sent to their destination.
(B) double membrane bound, Golgi apparatus: Incorrect — Lysosomes are single membrane-bound, not double membrane-bound.
(C) double membrane bound, endoplasmic reticulum: Incorrect — Lysosomes are not double membrane-bound and do not originate from the endoplasmic reticulum.
(D) single membrane bound, nucleus: Incorrect — Lysosomes do not originate from the nucleus, but from the Golgi apparatus.
Step 3: Conclusion.
The correct answer is (A) single membrane bound, Golgi apparatus, as lysosomes are single membrane-bound and originate from the Golgi apparatus.

Step 1: Understanding 70S ribosomes.
70S ribosomes are found in prokaryotic cells like bacteria and in certain organelles in eukaryotic cells, such as mitochondria and chloroplasts. These ribosomes are smaller than the 80S ribosomes found in the cytoplasm of eukaryotic cells.
Step 2: Analyzing the options.
(A) Bacterial cells, endoplasmic reticulum and mesosome: The endoplasmic reticulum does not contain 70S ribosomes, and the mesosome is a structure in bacterial cells, but not a consistent location for ribosomes.
(B) Bacterial cells, mitochondria and chloroplasts: Correct — 70S ribosomes are found in bacteria, mitochondria, and chloroplasts, as these organelles have evolved from ancestral prokaryotes.
(C) Nucleus, mesosome and mitochondrion: The nucleus does not contain 70S ribosomes.
(D) Chloroplasts, Golgi complex and mitochondria: The Golgi complex does not contain 70S ribosomes, so this option is incorrect.
Step 3: Conclusion.
The correct answer is (B) Bacterial cells, mitochondria and chloroplasts. These are the places where 70S ribosomes are located.

Step 1: Definition of polyribosomes.
Polyribosomes (polysomes) consist of multiple ribosomes attached to a single mRNA molecule.
Step 2: Functional significance.
They allow simultaneous translation of the same mRNA, increasing the rate of protein synthesis.
Step 3: Rejecting incorrect statements.
Polyribosomes contain rRNA and are actively involved in polypeptide synthesis.