Cell Biology and Structure

Blood cells are spherical in shape, nerve cells are long and elongated, whereas muscle cells and cardiac cells are spindle-shaped.

Nucleolus is a spherical-shaped structure present in the nucleus of a cell.

Plastids are the organelles which are only present in plant cells. They are scattered in the cytoplasm of a leaf cell.

A plant cell is said to be eukaryotic and it possesses a well defined nuclear membrane around the nucleus and encloses the genetic material.

These cells do not contain mitochondria. Hence, these cannot respire.

The body in sponges are diploblastic having an intermediate lining of loose membrane. A circulatory system is absent in sponges.

Cytoplasm is the jelly-like substance that lies between the nucleus and the cell membrane. It mainly holds all the organelles.

These proteins transport specific substances from one part of body to the others. Most familiar is haemoglobin of red blood cells (erythrocytes or RBCs) of vertebrates. Serum albumin transports fatty acids in blood from fatty tissues to other tissues. Transferrin protein transports iron, and certain other proteins transport steroid hormones, drugs, toxins, etc. in blood. Transport proteins of plasma membrane transport materials across the membrane. For instance, glucose and amino acids enter into all cells through membrane transport proteins.

Passage cells are found in root endodermis. They are thin walled cells just opposite to protoxylem patches that help in passage of water from cortex to xylem.

A tylosis is a bladder-like distension of a parenchyma cells into the lumen of adjacent vessels in wood.

Centrosome is not present in the ovum as centrosome is required for cell division, which is not required in the ovum.

Most of the steps of pentose phosphate pathway take place in plastids in plants.

Nucleus is absent in mature sieve tubes. They use the nucleus of companion cells for metabolic regulation.

The tonoplast is the specialized cytoplasmic membrane that surrounds the vacuole in plant cells, regulating the movement of ions and molecules.

Leucoplasts are non-pigmented plastids found in plant cells that function primarily for the storage of starch, lipids, or proteins.