Cell Biology Test - 3

Haustorium which enters in to the cells of host and absorbs food or water and minerals from the host.

• Matthias Schleiden and Theodore Schwann together formulated the cell theory which states that bodies of plants and animals are composed of cells and their products.
• This theory did not explain how new cells are formed.
• Rudolf Virchow first explained that cells divided and new cells are formed from pre-existing cells.
• Robert Hooke viewed a thin cutting of cork and discovered empty spaces contained by walls which he termed cells.
• The discovery in 1953 of the double helix, the twisted-ladder structure of deoxyribonucleic acid (DNA), by James Watson and Francis Crick marked a milestone in the history of science and gave rise to modern molecular biology.
• Thomas Hunt Morgan was awarded the Nobel Prize in Physiology or Medicine in 1933. The work for which the prize was awarded his discovery of the white-eyed mutation in the fruit fly, Drosophila.
• Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance.

In all living cells water forms 50‑80% of total cell contents.

J. David Robertson (1959) proposed the “Unit membrane model”. It has a thickness of about 7.5 nm with a central lipid layer of 3.5 nm thick and two peripheral protein layers of 2.0 nm each.

The membranes of archaebacteria are built with a monolayer of branched chain lipids. They lack peptidoglycan in their cell wall. Their cell wall contains non-cellulosic polysaccharides and proteins.

A typical prokaryotic cell contains the plasma membrane, cytoplasm, ribosomes and genetic material etc. It does not have well-defined nucleus, membrane-bound organelles, and centrioles etc.

The lampbrush chromosomes are found in oocytes of many vertebrates (Amphibian, reptiles and birds) and some invertebrates (insects). They also occur in the giant nucleus of the unicellular algae Acetabularia.

The nucleus is an organelle found in eukaryotic cells. Inside its fully-enclosed nuclear membrane, it contains the majority of the cell’s genetic material. It controls the functions of the entire cell by regulating gene expression. If it is removed then the cell will die because all the metabolic activities will be ceased.