Question

1. Which of the following describes an endocytosis? There may be more than one answer.

Select one or more:

a. A cell engulfs a bacterium by pushing its cell membrane around the bacterium forming a phagosome that will pinched off from the cell membrane and enter the cytoplasm.

b. Specific solutes accumulate along an indented cell membrane that will form into an endosome and it will pinch off from the cell membrane and enter the cytoplasm.

c. A process that transports molecules outside the cell via fusion of a vesicle with the plasma membrane.

d. A pinocytosis is an uptake of a non-selective materials, like the extracellular fluid, into a cell via endosome that pinches off from the plasma membrane into the intracellular fluid.

e. The process is initiated when an influx of Ca²⁺ interacts with rabs and snares in the intracellular fluid.

2.

What are the characteristics of the red blood cells (RBCs)? There may be more than one answer.

Select one or more:

a. RBCs are circular, flattened, and biconcave cells which transport oxygen from the tissues to the lungs and carbon dioxide from the lungs to the tissues.

b. RBCs lacked nucleus and organelles but contained glycolytic enzymes, carbonic anhydrase, and hemoglobin.

c. RBCs, leukocytes, and platelets are derived from uncommitted pluripotent hematopoietic stem cells.

d. Erythropoiesis in adult occurs in the liver, spleen, and all red bone marrow.

e. RBCs live for about 9 days.

Answer 1

1) The following describes endocytosis :-

(a) A cell engulfs a bacterium by pushing its cell membrane around the bacterium forming a phagosome that will pinched off from the cell membrane and enter the cytoplasm.

(b) Specific solutes accumulate along an indented cell membrane that will form into an endosome and it will pinch off from the cell membrane and enter the cytoplasm.

(d) A pinocytosis is an uptake of a non-selective materials, like the extracellular fluid, into a cell via endosome that pinches off from the plasma membrane into the intracellular fluid.

Endocytosis is a cellular process in which molecules/substances are internalized by engulfing it with its membrane. It can be of two types :- Phagocytosis and pinocytosis.

In phagocytosis, a cell engulfs and internalize particulate matter and bacterium forming an phagosome that fuse with endosome and lysosome for degradation of bacteria.

In pinocytosis, there is uptake and internalization of of non-selective substances such as extracellular fluid via endosome that pinches off from the plasma membrane into the intracellular fluid.

The other options are incorrect since :-

• A process that transports molecules outside the cell via fusion of a vesicle with the plasma membrane is called Exocytosis.

• Exocytosis is initiated when an influx of Ca2+ interacts with rabs and snares in the intracellular fluid.

Thus the correct answers are (a), (b) & (d).

2) Characteristics of Red blood cells (RBCs) :-

(b) RBCs lacked nucleus and organelles but contained glycolytic enzymes, carbonic anhydrase, and hemoglobin.

(c) RBCs, leukocytes, and platelets are derived from uncommitted pluripotent hematopoietic stem cells.

RBCs have all other orgenelles except the nucleus. It containes other hemoglobin which helps in carrying oxygen to the tissues and have other glycolytic enzymes for glycolysis and have carbonic anhydrase.

RBCs, leukocytes, platelets are derived from uncommitted hematopoietic stem cells (the stem cells that give rise to blood cells).

The other options are incorrect since :-

• RBCs carry oxygen from lungs to tissues and carbon dioxide from tissues to lungs. So option (a) is incorrect.

• Erythropoiesis in adults mainly occurs in red bone marrow. The liver and spleen are site of erythropoiesis in fetus. But in certain disease extramedullary erythropoiesis takes place in liver and spleen. Since in normal conditions it is not produced so is incorrect.

• The life span of RBCs are 100-120 days. So Option (e) is incorrect.

Thus the correct answers are (b) & (c).