Year 10 Syllabus Revision – Suggested Answers 45-51
GENETICS
45. Identify the role of cell division in growth, repair and reproduction in multicellular
organisms.
Recognise and name particular processes pertaining to the role of cell division in growth,
repair and reproduction in multicellular organisms.
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There are two basic types of cell division.
1. Mitosis
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Responsible for the growth and repair of the different body cells in multicellular organisms.
When an organism is growing or when cells die, new cells need to be produced.
Mitosis does this by a particular cell dividing to produce two identical cells to replace it.
The two daughter cells are identical to the parent cell in every aspect. They are the same shape
and size, have the same function and have the same number of chromosomes as the parent cell.
In this way all cells of a living organism can be replaced when needed.
The process is as shown in the diagram below.
2. Meiosis
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Responsible for the formation of sex cells (sperm and ovum) for reproduction in living
organisms.
In this type of cell division, four cells are produced from a parent cell (not two like mitosis).
The daughter cells also differ in that they each contain only half the number of chromosomes of
the parent cell.
This difference in chromosome number means that when a sperm fertilises an ovum the
resulting cell has the correct number of chromosomes (half from mother and half from father).
The process is shown in the diagram below.
46. Explain the advantages of DNA replicating exactly.
Describe the advantages of DNA replicating exactly.
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DNA (deoxyribonucleic acid) is the code that holds all the information needed to make and
control every cell within a living organism.
When DNA replicates it is possible that mistakes were made along the way. In other words a
base pair in one DNA molecule doesn’t match the corresponding pair in the other molecule. On
average, one mistake may exist in every billion base pairs. (That’s the same as typing out the
entire Encyclopaedia Britannica five times and typing in a wrong letter only once!)
Click on the link below to see an animation of DNA replication.
http://www.ncc.gmu.edu/dna/repanim.htm
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When the DNA in the nucleus of a person’s cells replicates it is essential that the new DNA
produced is an exact copy of the original.
Reasons for this exact copying include:
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Cells do not live forever thus they need to be replaced and carryout the same
functions.
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DNA controls cellular reactions, which need to continue in newly formed cells.
Preventing mutations that could be detrimental to the health of an organism. Eg. cancerous
cells.
The process by which cells replicate exactly is known as mitosis.
Mitosis involves one cell (parent cell) dividing to produce two identical cells (daughter cells).
47. Explain the advantages and disadvantages of DNA mutating.
Show the relationship between advantages and disadvantages of DNA mutating.
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A mutation is the incorrect copying of a piece of DNA during replication.
Many mutations would be classed as being detrimental to the survival of an organism, however,
some mutations do have beneficial effects.
The main advantages and disadvantages of mutations in DNA include:
Advantages
Variation in species (no two humans look
identical – except twins).
The main factor leading to evolution in
living organisms (natural selection).
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Disadvantages
Diseases and viruses quickly become
immune to antibiotics and other drugs.
Causes genetic diseases such as cancer,
cystic fibrosis, Down’s syndrome, etc.
48. Identify that information is transferred as DNA on chromosomes when cells reproduce
themselves.
Recognise and name the particular process of information transferred as DNA on chromosomes
when cells reproduce themselves.
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There are two basic cell division processes that are responsible for the transfer of DNA.
Click on the links below to view cell division animations (each near bottom of page)
http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html
http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3.html
3. MITOSIS – cell division whereby one parent cell divides once to produce two daughter cells with
the same number of chromosomes and exactly the same DNA. The basic process is outlined below:
Prophase: Each chromosome has duplicated and now consists of two sister chromatids.
Metaphase: The chromosomes align at the equator of the cell and are held in place by spindles attached to centromeres.
Anaphase: The centromeres divide. Sister chromatids separate and move toward the corresponding poles of the cell.
Telophase: Daughter chromosomes arrive at the poles. The spindles and centromeres disappear.
Cytokinesis: The cytoplasm divides; the cell membrane pinches inward ultimately producing two daughter cells.
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MEIOSIS – cell division whereby one parent cell divides twice to produce four daughter cells with
half the number of chromosomes and varied DNA. The basic process is outlined below:
 First division of meiosis
Prophase 1: Each chromosome duplicates and remains closely associated. Crossing-over can occur during the latter part of
this stage (swapping of DNA between chromosomes).
Metaphase 1: Homologous chromosomes align at the equator of the cell.
Anaphase 1: Homologous pairs separate with sister chromatids remaining together.
Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of homologous pair.
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Second division of meiosis: Gamete formation
Prophase 2: DNA does not replicate.
Metaphase 2: Chromosomes align at the equatorial plate.
Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.
Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.
NOTE: You do not have to know the names of the stages just the general process.
49. Identify that genes are part of DNA.
Recognise and name particular features of DNA in respect to genes.
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Chromosomes are structures within the nucleus of a cell that contain the genetic information that is
passed on from one generation to the next.
A gene is a section of a chromosome. A gene carries coded information within a sequence of
chemicals. When appropriate, a section of this information is decoded and used to provide the
recipe for protein synthesis within the cell. The proteins synthesised affect the way the cell interacts
with its environment. This, in turn, may affect the way the organism responds to its environment.
The term for the DNA bases in their groups of three is codons, and it is these codons, grouped
together as genes, which hold the information for the accurate production of all the cells’ proteins.
Put simply, chromosomes made up of strings of genes and genes are made up of the chemical
substance called DNA (Deoxyribonucleic Acid).
The whole structure is
made up of DNA.
50. Identify the role of genes and environmental factors in determining the features of an
organism.
Recognise and name particular events that show the role of genes and environmental factors
in determining the features of an organism.
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Phenotype – refers to an individual’s anatomical structure, physiology and behaviour (traits).
Phenotype refers to everything that can be easily observed and measured about an organism.
Genotype – refers to the pair of genes (or alleles) that are responsible for a particular characteristic.
Environment – all the external pressures placed on an organism in its struggle for survival.
Eg. nutrition, shelter, climate, etc.
Phenotype = Genotype + Environment
It is obvious that genes play an important role in determining the features of an organism since
genes carry the genetic code for making the organism.
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However, it is a fact that the phenotype of an organism is also determined by its environment.
Often it is assumed that the phenotype is the sum of the genotype and the environment. The
phenotype can also be seen as the interaction between genetics and environmental factors, some
genotypes are better in one environment and others are better in another environment.
If a genotype results in a good phenotype in one environment, the same genotype will not
necessarily result in a good phenotype in another environment, thus the environmental conditions
select those traits that are better suited.
51. Describe some benefits and problems of using biotechnology.
Provide an outline of some benefits and problems and some of the social and ethical issues of
using biotechnology.
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Biotechnology is the manipulation of a living organism (usually genetically) to change a particular
feature of that organism.
Examples of biotechnology include:
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The major benefits of biotechnology include:
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possible elimination of genetic diseases
improved medical treatments
increased plant and animal production
production of better vaccines or medicines
The major problems of biotechnology include:
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genetically modified (GM) foods – altering food crops to make them more pest resistant, grow
all year round or contain beneficial substances
growing new body parts – regrowing faulty organs outside the body (heart, lung, kidney)
gene splicing – taking a gene/s from one organism and placing it into the DNA of another
organism so that it obtains that characteristic
cloning – producing an exact copy of a living organism (Dolly the sheep)
embryonic stem cell research – using stem cells from embryos to try to cure certain cellular
diseases
long term effects of modifying genes not known
possibility of harmful mutations in organisms
the number of failures to get a success (especially in cloning)
expensive
Along with the benefits and problems associated with biotechnology, there are a number of social
and ethical issues that need to be addressed. These include:
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religious issues (playing god)
safety of experiments (possibility of causing epidemics)
who decides if the technique can be done or will be done
will it be available to everyone or only those who can PAY for it
people may want to use the technique for selfish reasons