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Biology Unit 2: (Development, Plants and the Environment)
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1 Describe the ultrastructure of a typical eukaryotic cell (nucleus, ribosomes, rough and
smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, nucleolus)

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2 Distinguish between the ultrastructures of prokaryotic and eukaryotic cells
The main differences between the eukaryotic and prokaryotic cells are:
The prokaryotic cell has chloroplasts
l The prokaryotic cell has a central vacuole
l The prokaryotic cell has a cell wall
l The prokaryotic cell has plasmodesmata
l The eukaryotic cell has membrane bound organelles
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3 Explain the role of the rough endoplasmic reticulum and the golgi apparatus in protein
trafficking within cells
The rough endoplasmic reticulum is responsible for transporting proteins made by ribosomes to
other parts of the cell
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As they move through the golgi apparatus, they are modified and
packed into vesicles
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There must be
enough information here in order to produce two new cells
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Microtubules from the cytoplasm form a three dimensional structure called the spindle
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The
chromosomes centromeres attach to the spindle fibres at the equator
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Cytoplasmic division- The cell surface membrane constricts around the centre of the cell, which
narrows until the cell is cleaved into two new cells
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5 Explain the significance of mitosis for growth and asexual production
Mitosis occurs in any organism as it develops from a single cell into a multicellular orgasnism
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Some organisms reproduce without producing gametes, they grow copies of themselves by mitosis,
producing offspring which are genetically indentical to themselves
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6 Explain how mammalian gametes are specialised for their functions including the
acrosome reaction

The cytoplasm in the ovum contains protein and lipid food reserves for the early development of the
embryo
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The sperm is much smaller than the ovum, and can move
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In order to penetrate the ovum, the
acrosome in the head of the sperm releases digestive enzymes which break down the jelly like
coating of the ovum
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Sexual reproduction is
important because it allows the zygote to have genetic information from both parents
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There are identical chromosomes pairs
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The homologous chromosomes line up on the equator of the cell and then separate
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During the process of meiosis, only one chromosome from each homologous pair ends up in each
gamete, which is a random process
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Furthermore, because the
gametes join with another gamete at fertilsation this pretty much ensures variation
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Pluripotent is a
cell which can only develop into many types of cells but not all, for example, embryonic stem cells
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As the embryo develops, the cells of which it is made from become increasingly differentiated, that
is they become specialised
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)
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10 Discuss the moral, ethical and and sprititual implications of stem cell research
Just about everyone agrees that there are no ethical objections to using multipotent stem cells
derived from adults
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Some people believe that the embyro
should be granteded full human status from the moment of it's creation
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11 Explain how genes can be switched on and off by DNA transcription factors and how
this gene switching gives rise to specialised cells
As the embryo develops, cells differentiate and become specialised for one function
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This is determined by which genes
in a cell are expressed (that is, the ones which are transcribed and translated to produce the proteins
they code for)
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Genes remained switched off by failure of the
transcription initiation complex to form and attach to the promoter region, which can be due to the
absence of protein transcription factors or the action of repressor molecules
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12 Explain how certain characteristics may be affected by both genotype and the
environment, including human height, skin colour, hair colour and cancers
Characteristics in an orgasnism, such as height, sex, blood group are known as phenotypes
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Human height is controlled by genetics but there are clearly some environmental factors involved,
for example, taller man are said to have more children, which would result in gradual change in the
genetic make up of the population
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Skin and hair colour are also an example of how the environment and our genotypes interact with
each other
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13 Explain that cancers arise from uncontrolled cell division, and describe genetic,
environmental and lifestyle causes of cancer
Cancer occurs when the rate of cell multiplication is greater than the rate of cell death
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If there is mutations in the genes,
it can stop tumour suppressor genes from breaking the cell cycle, so the cell cycle continues
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DNA can be damaged by lifestyle factors such as increased
exposure to UV light or diet
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It can also be damaged by chemicals,
such as carcinogens, which may be in the environment
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14 Discuss the principle outcomes of the Human Genome Project and the social, moral and
ethical issues which arise from it
A genome is all the DNA of an organism including the genes that carry out all the information for
making the variety of proteins required by the organism
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It has produced these outcomes:
l Detailed information about the genome
l Identification of new genes (breast cancer gene, colour blindness gene)
l Indentification of new drug targets
l Preventative medicine and improved drug treatment (side effects for patients may be
different when using the same drug, believed to be a slight alteration in the genome for each
person, so the human genome project aims to pinpoint these differences)
l Investigating evolution of the human genome (compares our genome with other animals, it
is possible to look at the evolution aspect of our genetics)
However, there are issues relating to the Human Genome Project:
l Who owns and controls genetic information?
l How does personal genetic information affect the individual and societies perceptions of the
individual?
l Do peoples genes make them behave a certain way?
l Where is the line between medical treatment and enhancement?

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1 Recall the typical structure of a plant cell (presence of cell wall), chloroplasts,
amyloplasts, vacuole, tonoplast, plasmodesmata, pits and middle lamellae

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2 Compare the structure and function of the polysaccharides starch and cellulose
including the role of hydrogen bonds between beta glucose molecules in the formulation of
cellulose microfibrils
Woods strength comes from the thin cellulose walls of plant cells and the 'glue' that holds them
together
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Starch is made from alpha glucose, whereas cellulose is made from
beta glucose
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It is this which makes cellulose a long unbranched molecule
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Individually, the hydrogen bonds are relatively weak compared
with the glycosidic bonds, but together the large number of hydrogen bonds in the microfibril
produce a strong structure
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3 Describe the structure of sclerenchyma fibres and xylem vessels and where they are
found in the plant stem
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There are two specialised types of cells which allow this function to be carried out:
l Xylem vessels – these form tubes for transport, and their stiffened cell walls help support
the plant
l Sclerenchyma fibres – columns of these cells with their stiffened cell walls also provide
support
The xylem and the sclerenchyma fibres are found in the stem
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They can be used to make clothes, paper, and rope
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4 Explain the relationship between structure and function in sclerenchyma fibres
(support) and in xylem vessels (support and transport of water and mineral ions through the
stem)
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5 Explain the importance of water and inorganic ions (nitrate, calcium and magnesium) to
plants
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6 Explain the role of adhesion, cohesion, and the transpiration steam in the movement of
water through the stem
Xylem vessels for transport:
Xylem vessels are long thin lignified (waterproof) columns which are continuous from the roots to
the leaves
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Water vapour diffuses out through the stoma down a diffusion gradient
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Water moves across the leaf down a diffusion gradient
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Water moves up the xylem vessel due to the difference in hydrostatic pressure (low at the
top, high at the bottom)
The continuous column of water moving up the xylem vessel is known as the transpiration steam
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Adhesion in the
vessels occurs when water adheres to the walls of the vessels, helping to hold the column of water
within the vessel
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Cohesion occurs because there is strong cohesive
forces between water molecules, which keeps the water together as a continuous column
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The xylem vessels also help to transport inorganic ions
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If the inorganic ions
are not absorbed in sufficient amounts, then the plant will show deficiency symptoms
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7 Compare how William Withering developed his digitalis soup with drug developing and
testing nowadays
William Withering had a friend who was showing signs of Dropsy, and who had some of her
special tea containing some 20 herbs, one being Foxglove
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One of his patients was a brewer who
was suffering from swollen limbs and an irregular heartbeat
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But his next patient died so
Withering gave up
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Today, a potetial new drug must pass a series of tests before it is safe to use
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8 Relate the structure of seeds to their role in the dispersal and survival of the plant
(adaptations for dispersal, protection and nutrition of the embryo)
Seeds are vital to the survival of a plant, they:
l protect the embryo
l aid dispersal
l provide nutrition for the new plant
The embryo develops into three distinct parts- a radicle (young root), a plumule (young shoot) and
one or two cotyledons (seed leaves)
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The outer layers of the ovule become lignified forming a tough seed coat (testa) which
helps to protect the embryo
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Some ways which dormancy can be broken include:
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Intense heat
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This brings
about metabolic changes in the seed, and production of plant growth substances are switched on,
which cause the secretion of enzymes that break down the food reserves
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Seeds come in all shapes and sizes, which allow the seed to be widely dispersed
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They are useful because when the starch granules are heated in water, they
swell and absorb the water which thickens the liquid, and this process is the basis of custard and
wallpaper paste
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Furthermore, plants can be used as oils, for example vegetable oil in diesel engines
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However, if we use plant
based products, it can reduce this problem because we can plant new plants in replace of the ones
we use
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Today, a plant breeder will identify individual plants with desired characteristics,
and if the plant has both male and female parts, these then can be self pollinated
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If this process is repeated
several times the genetic variation is reduced and becomes more homozygous
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This is the process
whereby desired characteristics (genes) are inserted into the plants DNA
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So, if the new genes are inserted into
the plasmid, then they can be carried directly to the DNA of the plant
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l DNA gun
The scientists need a method of screening to find out which plant cells have the new gene
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The
plant cells are then incubated with the antibiotic, and the only cells which survive are those which
have taken the new gene and are resistant
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This micropropagation can multiply a single cell to form a mass of plant cells
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However, it has to be said
that the use of GM crops makes plants more widely available, and increases yield
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The religious aspect suggests that genes should not be altered
because god created us they way that we should be made
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14 Outline the causes of global warming – including the role of green house gases in the
green house effect
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Methane is an example of a greenhouse gas, it is produced by anaerobic decay of organic matter,
decay of domestic waste, and the decomposition of animal waste
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There is also evidence for
increase in carbon dioxide and increase in global temperature, however there is no proof that one
causes the other
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Methane can be lowered by better waste recycling and by using a biofuels (where one greenhouse
gas changes into two less serious ones)
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Also, by reafforestation
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This is because
each year the tree forms new xylem vessels
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Peat bogs can also be used to determine climate conditions ears ago
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Pollen grains are particularly well preserved
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17 Explain how climate change (rising temperature, changing rainfall patterns, and
change in seasonal cycles) can affaect plants and animals (distribution of species, development
and life cycles)
Animals are likely to be affected by changing climates
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Furthermore,
changing of the seasons is a natural indicator for some animals, for example for migration
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Also,
sometimes the hatching or birth of animals is synchronised with maximum food availability, so if
increase in temperature affects hatching of food sources, then there will not be enough food

available, leading to low survival rates
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This is
due to the rate of enzyme activity
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At
low temperatures the reaction is very slow, this is because the enzyme and substrate molecules
move slowly and don't collide very often
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However, this happens until an optimum temperature is reached where maximum rate of reaction
occurs
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The enzyme has become denatured

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