Cell Biology and Structure

The acrosome is an organelle that develops over the anterior half of the head in the spermatozoa (sperm cell) of many animals. It is a cap-like structure derived from the Golgi apparatus. Acrosome formation is completed during testicular maturation.

Lysosomes are cellular organelles that contain acid hydrolase enzymes to break down waste materials and cellular debris. They are found in animal cells, while in yeast and plants the same roles are performed by lytic vacuoles.Lysosomes digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria.

A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen.

Ribosomes occur, both as free in the cytoplasm and as associated with endoplasmic reticulum. Ribosome are of 80 S kind. There are two subunits. Ribosomal RNA and proteins occur in the constitution of ribosomes.

 In plant cells, a large vacuole occurs which is surrounded by a semipermeable membrane called tonoplast. The membrane around vacuoles in animal cells is made up of lipoprotein. Normally, vacuoles do not occur in animal cells.

Within the cells of basidiomycete fungi are found microscopic structures called parenthesomes or septal pore caps. They are shaped like parentheses and found on either side of pores in the dolipore septum which separates cells within a hypha.

The part of the cell which occurs between the plasma membrane and nuclear envelope is called the cytoplasm. The cytoplasm is composed of the matrix, the organelles and non-living inclusions like vacuoles and granules.

Being a dynamic structure, it is quite flexible. Hence, it does not restrict growth, movements, and changes in the shape of a cell.

The cell membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively-permeable to ions and organic molecules and controls the movement of substances in and out of cells. It consists of the phospholipid bilayer with embedded proteins.

Guard cells have thin and elastic outer walls and thick inner walls. When turgid, the thin outer walls stretch and bulge outward, opening the stomatal pore. This asymmetric thickening is essential for stomatal opening and closing.

A fibrocyte is an inactive mesenchymal cell, that is, a cell showing minimal cytoplasm, limited amounts of rough endoplasmic reticulum and lacks biochemical evidence of protein synthesis.

Thin-walled hypodermal cells constitute the stomium or line of dehiscence.

Each stoma (stomatal pore) is surrounded by two specialized guard cells that change shape to open or close the pore. This regulates gas exchange and water loss.

Primary cells are non-rechargeable batteries that cannot be restored to their original chemical state once discharged. The Voltaic, Daniel, and Leclanche cells are all primary cells. Lead-acid cells are secondary cells that can be recharged multiple times by applying an external current to reverse the chemical reaction.

Lysosomes are single membrane-bound organelles containing digestive enzymes. The nucleus has a double membrane (nuclear envelope), mitochondria and chloroplasts also have double membranes, making lysosome the correct answer.