Basic features of cells
All cells are bounded by a plasma membrane. The semifluid substance within the membrane is the cytosol, containing the organelles. All cells contain chromosomes which carry genes in the form of DNA. All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes. A major difference between prokaryotic and eukaryotic cells is the location of chromosomes. Eukaryotic cell- chromosomes are contained in a membrane-enclosed organelle, the nucleus. Prokaryotic cell- the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell.
Fig.1 Bacteria Problems with Cell Size
In general, eukaryotic cells are much bigger than prokaryotic cells: Most bacteria are 1-10 microns in diameter. Eukaryotic cells are typically 10-100 microns in diameter. A large cell requires "much more" in terms of the cellular components. Uptake from the environment is also a problem for large cells: there is less surface area compared to the volume. Distribution of nutrients from one portion of a large cell to another is also a problem, simply because of the distance required for the nutrients to travel.
Fig 2
Thus most cells are small: sufficient surface area to accommodate the volume. Larger organisms do not generally have larger cells than smaller organisms, - just simply more cells.
Question 1.What will be the size range of bacteria in millimeter? (1 micron= 10-3 mm)
103mm-102mm
10-3mm-10-2mm
102mm-103mm
10-2mm-10-3mm
Question 2 .(a)The cells can be Prokaryotic or Eukaryotic .Fig. 1 explains the structure of which type?
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Question 3 Why cells are preferred to be of small size? Write two reasons.
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Question 4 The DNA present in the cell signifies chemical nature of--
Genes
Chromosomes
Ribosomes
Prokaryotes
Choose the correct option-
a and c
b and d
a and b
c and d
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