Cell Biology and Structure

Within the cell, the site of respiration is mitochondrion. 

Endocardial membrane of the heart is made up of simple squamous epithelium. It performs the function of protection carried out by the endothelial wall.

Intercalated discs are responsible for syncytium formation. Cardiac syncytium is a network of cardiomyocytes connected to each other by intercalated discs that enable the rapid transmission of electrical impulses through the network, enabling the syncytium to act in a coordinated contraction of myocardium.

Cardiac cells are constantly undergoing contractions and require more energy to perform their functions. Thus, cardiac cells have more mitochondria. In fact, mitochondria occupy 25% of cell space.

Neurons are the longest cells in the human body, with axons extending from the spinal cord to the toes (up to 1 meter). Lymphocytes, osteocytes (bone cells), and leucocytes (white blood cells) are microscopic cells without such elongated processes. The neuron's length enables rapid signal transmission across distances.

Vacuoles are larger in size as compared to vesicles.

A prominent central vacuole is found in plant cells. It occupies 80-90% of cell volume. The main role of the central vacuole is to maintain turgor pressure against the cell wall.

Acrosome is derived from Golgi apparatus.

The largest organelle of a plant cell is vacuole. It covers 80-90% of the volume of a plant cell.

Tonoplast is the membrane of vacuole. It is the cytoplasmic membrane surrounding a vacuole, separating the vacuolar contents from the cell's cytoplasm.

When protons are transported from the cytosol to the vacuole, it stabilises cytoplasmic pH and makes the vacuolar interior more acidic.

Plastids, responsible for photosynthesis, possess numerous internal membrane layers called thylakoids. These are the sites of light absorption and ATP synthesis, and contain many proteins, including those involved in the electron transport chain. Photosynthetic pigments such as chlorophylls a, b and c, and some others like xanthophylls, carotenoids and phycobilins are also embedded within this membrane, thus plastids are responsible for photosynthesis containing numerous internal membranes.

Amyloplasts are the largest leucoplasts. They function in storage of starch.

Besides being selectively permeable, plasma membrane of eukaryotes also functions in synthesis of ATP through chemiosmosis.

Caveolae are the small invaginations of plasma membrane of many vertebrate cell types, especially in endothelial cells and adipocytes. These are rich in proteins and lipids.