Unit 2 Quiz – The variety of living organisms- Answers

1.      State three ways in genetic variation can be increased in sexually reproducing organisms? Mutations, meiosis, fusion of gametes

2.      How is genetic variation increased in asexually reproducing organisms? Only by mutation

3.      Give definitions for interspecific variation and intraspecific variation? Interspecific – species differ from one another, intraspecific – members of the same species differ

4.      Give two reasons why a sample may not be representative of the populations as a whole? Sampling bias and chance

5.      How may sampling bias be prevented? Random sampling (divide study area into a grid, random number generator and intersection of coordinates)

6.      Draw and label a nucleotide? Phosphate, deoxyribose and organic base

7.      In terms of the structure of the DNA molecule explain why the base pairings are not A with G and T with C? C/T are single ring bases and G/A are double ring bases. The base pairs are always made up of one of each

8.      If the base pairs on one strand of DNA are TGGAGACT what is the base sequence on the other strand? ACCTCTGA

9.      If 19.9% in human DNA are G what percentage of human DNA is T? 30.1%

10.  What is a gene? A section of DNA that contains the coded information for polypeptides.

11.  How many bases of DNA are required for a chain of 6 amino acids? (triplet code) 18 bp

12.  What is the function of the protein found in chromosomes? DNA is wound around protein molecules to keep it in place (histones)

13.  In which two ways does meiosis lead to an increase to a genetic diversity? Recombination by crossing over, independent segregation of chromosomes

14.  Describe the quaternary structure of haemoglobin? Four polypeptides, two alpha, two beta – each with a Haem group containing a ferrous ion.

15.  Why is the process of DNA replication described as semi conservative? Half of the original DNA is saved and built into the new DNA molecules (P165)

16.  What are the three main stages of the cell cycle? Cell division, interphase, nuclear division (mitosis)

17.  What is a tissue? Collection of similar cells that perform a specific function

18.  Name three factors which affect the rate of diffusion of a substance into cells? (Ficks law) SA, conc gradient, diffusion distance

19.  What is meant by counter current flow and why is it an efficient means for transporting gases across fish gills?  Blood and water travel in opposite directions, constant rate of diffusion across length of gill, 80% O2 abs into blood – parallel 50%

20.  Distinguish between horizontal and vertical gene transmission? Horizontal – DNA can be passed from one species to another, vertical – genes passed down from one generation to the next within the same species.