The Fundamental Unit of Life

Practice flashcards based on lecture notes covering the fundamental unit of life, including the history of cell discovery, structural organization, specific organelles, and cell division processes.

Who first discovered cells and in what year?

Robert Hooke discovered cells in $1665$ while observing a thin slice of cork.

What is the Latin meaning of the word 'cell'?

'A little room'.

Which scientist discovered free-living cells in pond water for the first time in $1674$?

Leeuwenhoek.

Who discovered the nucleus in the cell in $1831$?

Robert Brown.

What term did Purkinje coin in $1839$ for the fluid substance of the cell?

Protoplasm.

Who presented the cell theory stating that all plants and animals are composed of cells?

Schleiden ($1838$) and Schwann ($1839$).

What was Virchow's ($1855$) expansion to the cell theory?

He suggested that all cells arise from pre-existing cells.

What are unicellular organisms?

Organisms consisting of a single cell that constitutes the whole organism, such as Amoeba, Chlamydomonas, Paramoecium, and bacteria.

What are the three main features observable in almost every cell under a microscope?

Plasma membrane, nucleus, and cytoplasm.

Why is the plasma membrane called a selectively permeable membrane?

Because it permits the entry and exit of some materials while preventing the movement of others.

What is diffusion in the context of cellular transport?

The spontaneous movement of a substance (like $CO_2$ or $O_2$) from a region of high concentration to a region of low concentration.

What is osmosis?

The passage of water from a region of high water concentration through a selectively permeable membrane to a region of low water concentration until equilibrium is reached.

What happens to a cell placed in a hypotonic solution?

The cell will gain water by osmosis and is likely to swell up because the surrounding medium has a higher water concentration than the cell.

What happens to a cell placed in a hypertonic solution?

The cell will lose water by osmosis and shrink because the surrounding medium has a lower concentration of water than the cell.

What organic molecules make up the plasma membrane?

Lipids and proteins.

What is endocytosis?

A process where the flexibility of the cell membrane enables the cell to engulf food and other material from its external environment, as seen in Amoeba.

What is the plant cell wall primarily composed of?

Cellulose, which provides structural strength to plants.

What is plasmolysis?

The phenomenon where a living plant cell loses water through osmosis, causing the contents of the cell to shrink or contract away from the cell wall.

What are chromosomes made of and when are they visible?

They are composed of DNA and protein, and are visible as rod-shaped structures only when the cell is about to divide.

What are genes?

Functional segments of DNA (Deoxyribo Nucleic Acid).

What is a nucleoid?

An undefined nuclear region containing only nucleic acids, found in prokaryotes due to the absence of a nuclear membrane.

What are the two types of Endoplasmic Reticulum (ER)?

Rough Endoplasmic Reticulum (RER), which has ribosomes for protein manufacture, and Smooth Endoplasmic Reticulum (SER), which helps manufacture fat molecules or lipids.

What is membrane biogenesis?

The process where some proteins and lipids manufactured by the ER help in building the cell membrane.

What are the functions of the Golgi apparatus?

Storage, modification, and packaging of products in vesicles, as well as the formation of lysosomes.

Why are lysosomes known as 'suicide bags'?

If the cell gets damaged, lysosomes may burst and their powerful digestive enzymes will digest their own cell.

Why are mitochondria called the 'powerhouses' of the cell?

They release the energy required for chemical activities in the form of ATP (Adenosine triphosphate) molecules.

Which two organelles contain their own DNA and ribosomes?

Mitochondria and plastids.

What are the two types of plastids found in plant cells?

Chromoplasts (coloured plastids, including chloroplasts for photosynthesis) and leucoplasts (white or colourless plastids for storage).

What is the difference between mitosis and meiosis?

Mitosis results in two identical daughter cells for growth and repair; Meiosis results in four new cells with half the number of chromosomes for gamete formation.

What is the size range of a typical prokaryotic cell?

$1-10\,\mu m$ ($1\,\mu m = 10^{-6}\,m$).